WCG Publications

Articles dans des revues avec comité de lecture

2024

Joint metrics for EMF exposure and coverage in real-world homogeneous and inhomogeneous cellular networks

This paper evaluates the downlink performance of cellular networks in terms of coverage and electromagnetic field exposure (EMFE), in the framework of stochastic geometry. The model is constructed based on datasets for sub-6 GHz macro cellular networks but it is general enough to be applicable to millimeter-wave networks as well. On the one hand, performance metrics are calculated for β-Ginibre point processes which are shown to faithfully model a large number of motion-invariant networks. On the other hand, performance metrics are derived for inhomogeneous Poisson point processes with a radial intensity measure, which are shown to be a good approximation for motion-variant networks. For both cases, joint and marginal distributions of the EMFE and the coverage, and the first moments of the EMFE are provided and validated by Monte Carlo simulations using realistic sets of parameters from two sub-6 GHz macro urban cellular networks, i.e., 5G NR 2100 (Paris, France) and LTE 1800 (Brussels, Belgium) datasets. In addition, this paper includes the analysis of the impact of the network parameters and discusses the achievable trade-off between coverage and EMFE.

A spatial data focusing and generalized time-invariant frequency diverse array approach for high precision range-angle-based geocasting

A novel unified frequency diverse array (FDA) and spatial data focusing (SDF) approach is proposed to simultaneously overcome time-variance and precision constraints of conventional FDA in geocasting, i.e., spatially confined broadcasting, scenarios. This paper describes a free space FDA-based SDF (FDA-SDF) system model for 2-dimensional range-angle-based focusing, including a generalized multi-purpose baseband approach for time-invariant FDA, complemented by SDF processing for improved spatial focusing precision and reduced array size. Comprehensive analytical derivations - general for any frequency offset configuration - describe the geographical FDA-SDF properties and design rules, such as geocast delivery zone steering, location, uniqueness, and size. Simulations of the proposed scheme validate theoretical derivations and demonstrate FDA-SDF's superior spatial precision and minimal design complexity. In particular, using novel alternating logarithmic frequency offsets, a 3-antenna FDA-SDF setup is shown to match the radial and azimuthal precision of its beamforming-based FDA counterpart using, respectively, 64 and 24 antennas.

2023

Comparing crowding perception and sensor counts at the Ghent festivities

Little is known about crowding perception on events and the link with objective visitor counts and visitor's behavior. This research aims to fill this gap by collecting WiFi sensor counts and comparing them with perception ratings of visitors and police and first aid data of Europe's largest outdoor urban festival: the Ghent festivities. During 48 h visitors were asked to rate the human crowding, spatial crowding and pleasure on two event plazas and one passageway within the festivities zone. The results show that spatial crowding ratings are a better indicator for visitor counts than human crowding ratings. On two locations a pleasure drop occurred each night, which cannot be linked to the visitor counts, but it can be linked to people's ratings of crowding as follows: pleasure dropped when the human crowding ratings exceeded 3 and if the spatial crowding ratings increased above 3 on a five-point rating scale during the pleasure drop. In a last step, two datasets on visitor behavior were included in the analysis, i.e., number of police interventions and first aid visits. The analysis of these datasets shows that behavior, crowding and emotional response are linked at the Ghent festivities (e.g., at Vlasmarkt most police interventions and almost exactly 50% of the first aid happened during the pleasure drop), but we cannot say anything about the causality. This research demonstrates both the need for and potential of sensing what lives within a crowd in addition to the use of visitor counting sensors.

Direct tracking of a wireless transmitter based on rao-blackwellized point mass filter

In this article, we address the problem of direct tracking of a wireless transmitter. That is, the inputs given to the Bayesian filter are the received baseband signals instead of pre-computed ranges or angles. We first propose to use the Rao-Blackwellized Point Mass Filter (RBPMF) to solve such a tracking problem. As such, the resulting tracking solution is still computationally expensive. Therefore, we propose an approach for reducing the computational cost of the RBPMF. More precisely, we replace the prediction step by the one of the Linear Kalman Filter (LKF). This combination helps to avoid expensive operations such as the weight convolution in the prediction step. In addition, it also allows complexity reductions in the correction step. As a result, the complexity is reduced by one order of magnitude compared to the original RBPMF. We compare our approach to representative direct-tracking methods, based on Iterative Extended Kalman Filter (IEKF) and Particle Filter (PF). The proposed solution has lower and comparable localization error compared to IEKF and PF, respectively. In addition, the proposed solution is of slightly less complexity than PF. However, the complexity reduction is significant compared to the conventional RBPMF.

Adv-Bot: Realistic Adversarial Botnet Attacks against Network Intrusion Detection Systems

Due to the numerous advantages of machine learning (ML) algorithms, many applications now incorporate them. However, many studies in the field of image classification have shown that MLs can be fooled by a variety of adversarial attacks. These attacks take advantage of ML algorithms' inherent vulnerability. This raises many questions in the cybersecurity field, where a growing number of researchers are recently investigating the feasibility of such attacks against machine learning-based security systems, such as intrusion detection systems. The majority of this research demonstrates that it is possible to fool a model using features extracted from a raw data source, but it does not take into account the real implementation of such attacks, i.e., the reverse transformation from theory to practice. The real implementation of these adversarial attacks would be influenced by various constraints that would make their execution more difficult. As a result, the purpose of this study was to investigate the actual feasibility of adversarial attacks, specifically evasion attacks, against network-based intrusion detection systems (NIDS), demonstrating that it is entirely possible to fool these ML-based IDSs using our proposed adversarial algorithm while assuming as many constraints as possible in a black-box setting. In addition, since it is critical to design defense mechanisms to protect ML-based IDSs against such attacks, a defensive scheme is presented. Realistic botnet traffic traces are used to assess this work. Our goal is to create adversarial botnet traffic that can avoid detection while still performing all of its intended malicious functionality.

2022

TAD: Transfer learning-based multi-adversarial detection of evasion attacks against network intrusion detection systems

Nowadays, intrusion detection systems based on deep learning deliver state-of-the-art performance. However, recent research has shown that specially crafted perturbations, called adversarial examples, are capable of significantly reducing the performance of these intrusion detection systems. The objective of this paper is to design an efficient transfer learning-based adversarial detector and then to assess the effectiveness of using multiple strategically placed adversarial detectors compared to a single adversarial detector for intrusion detection systems. In our experiments, we implement existing state-of-the-art models for intrusion detection. We then attack those models with a set of chosen evasion attacks. In an attempt to detect those adversarial attacks, we design and implement multiple transfer learning-based adversarial detectors, each receiving a subset of the information passed through the IDS. By combining their respective decisions, we illustrate that combining multiple detectors can further improve the detectability of adversarial traffic compared to a single detector in the case of a parallel IDS design.

A multi-antenna super-resolution passive Wi-Fi radar algorithm

In recent years, Wi-Fi has become the main gateway that connects users to the internet. Considering the availability ofWi-Fi signals, and their suitability for channel estimation, IEEE established the Wi-Fi Sensing (WS) Task Group whose purposeis to study the feasibility of Wi-Fi-based environment sensing. However, Wi-Fi signals are transmitted over limited bandwidthswith a relatively small number of antennas in bursts, fundamentally limiting the range, Angle-of-Arrival and speed resolutions.This paper presents a super-resolution algorithm to perform the parameter estimation in a quasi-monostatic WS scenario. Theproposed algorithm, RIVES, estimates the range, Angle-of-Arrival and speed parameters with Vandermonde decomposition ofHankel matrices. To estimate the size of the signal subspace, RIVES uses a novel Model Order Selection method which eliminatesspurious noise targets based on their distance to the noise and signal subspaces. Various scenarios with multiple targets aresimulated to show the robustness of RIVES. In order to prove its accuracy, real-life indoor experiments are conducted with humantargets by using Software Defined Radios.

MAC address anonymization for crowd counting

Research has shown that counting WiFi packets called probe requests (PRs) implicitly provides a proxy for the number of people in an area. In this paper, we discuss a crowd counting system involving WiFi sensors detecting PRs over the air, then extracting and anonymizing their media access control (MAC) addresses using a hash-based approach. This paper discusses an anonymization procedure and shows time-synchronization inaccuracies among sensors and hashing collision rates to be low enough to prevent anonymization from interfering with counting algorithms. In particular, we derive an approximation of the collision rate of uniformly distributed identifiers, with analytical error bounds.

Physical layer security in an OFDM time reversal SISO communication with imperfect channel state information

A frequency domain time-reversal (TR) precoder is proposed to perform physical layer security in single-input single-output (SISO) systems using orthogonal frequency-division multiplexing (OFDM) and artificial noise (AN) injection. This scheme guarantees the secrecy of a communication towards a legitimate user, Bob, by exploiting the frequency diversity selective behaviour in multipath channels. The transmitter, Alice, has imperfect channel state information (CSI) of the legitimate link thanks to the channel reciprocity in time division duplex systems and does not know the instantaneous CSI of a potential eavesdropper, Eve. Three optimal decoding structures at Eve are considered in a block fading environment depending on the handshake procedure between Alice and Bob. Closed-form approximations of the signal-to-noise ratio required at Bob and the maximal CSI error that can be made at Alice, in order to guarantee a communication ergodic secrecy rate (ESR), are derived. Furthermore, the optimal amount of AN energy to inject, considering imperfect CSI, is also given as a closed-form expression. A trade-off on the choice of the spreading factor of the TR precoder is established between maximizing the ESR and decreasing the ϵ-achievable secrecy rate. Finally, thanks to these results, Alice can be a priori aware of the ESR over which she can establish a secure communication.

Self-synchronization based localization of a time-misaligned transmitter in cellular networks

Geo-localization services are an important functionality in cellular networks. Besides,the use of Ultra Dense Networks and small cells, in current and future cellular networks, greatly increases the complexity of centralized localization approaches. Consequently, we propose a self-synchronization Positioning Estimation (SSPE) algorithm that estimates the transmitter position in a distributed fashion.The proposed SSPE algorithm reaches consensus for the posterior distribution of the transmitter position rather than on the final estimates. Such consensus ensures that the proposed SSPE algorithm converges to the centralized Direct Positioning Estimation (DPE) approach, which has the best performance of all localization approaches. We show that the proposed algorithm is related to the Iterative Positioning Estimation (IPE) algorithm, since both exploit the self-synchronization mechanism. As a result, the improvements and extensions for IPE, previously studied in other works, can be directly applied to the proposed SSPE algorithm. In addition, the proposed algorithm is able to localize the transmitter even when it is not time synchronized with the network as it is usually the case. The performance of the algorithms is numerically assessed through Monte-Carlo simulations by the mean distance error and mean range offset error. Finally, we not only show that our approach gets close to the DPE performance after a few iterations, but also that it converges for different logical network configurations.

Monitoring large crowds with WiFi: a privacy-preserving approach

This paper presents a crowd monitoring systembased on the passive detection of probe requests. The systemmeets strict privacy requirements and is suited to monitoringevents or buildings with a least a few hundreds of attendees. Wepresent our counting process and an associated mathematicalmodel. From this model, we derive a concentration inequalitythat highlights the accuracy of our crowd count estimator. Then,we describe our system. We present and discuss our sensorhardware, our computing system architecture, and an efficientimplementation of our counting algorithm—as well as its spaceand time complexity. We also show how our system ensures theprivacy of people in the monitored area. Finally, we validateour system using nine weeks of data from a public libraryendowed with a camera-based counting system, which generatescounts against which we compare those of our counting system.This comparison empirically quantifies the accuracy of ourcounting system, thereby showing it to be suitable for monitoringpublic areas. Similarly, the concentration inequality provides atheoretical validation of the system.

Near-field exposure in FM frequencies: new methodology and estimation formulas

Workers inside transmission pylons with FM antenna arrays are likely to be exposed to near‐field radiation exceeding reference levels for occupational exposure. In this study, the near-field behavior of 64 FM pylons was studied using a new methodology. Near‐field characterization was done using field metrics without taking into account field sources' size or distance from field source. The specific absorption rate (SAR) was assessed in five hundred different near‐field cases using a human phantom. Estimation formulas for both local and whole‐body SAR are provided and validated numerically. Local and whole‐body SAR are linked to electric field strength. © 2022 Bioelectromagnetics Society

Privacy-Enhanced MQTT Protocol for Massive IoT

The growing expectations for ubiquitous sensing have led to the integration of countless embedded sensors, actuators, and RFIDs in our surroundings. Combined with rapid developments in high-speed wireless networks, these resource-constrained devices are paving the road for the Internet-of-Things paradigm, a computing model aiming to bring together millions of heterogeneous and pervasive elements. However, it is commonly accepted that the Privacy consideration remains one of its main challenges, a notion that does not only encompasses malicious individuals but can also be extended to honest-but-curious third-parties. In this paper, we study the design of a privacy-enhanced communication protocol for lightweight IoT devices. Applying the proposed approach to MQTT, a highly popular lightweight publish/subscribe communication protocol prevents no valuable information from being extracted from the messages flowing through the broker. In addition, it also prevents partners re-identification. Starting from a privacy-ideal, but unpractical, exact transposition of the Oblivious Transfer (OT) technology to MQTT, this paper follows an iterative process where each previous model's drawbacks are appropriately mitigated all the while trying to preserve acceptable privacy levels. Our work provides resistance to statistical analysis attacks and dynamically supports new client participation. Additionally the whole proposal is based on the existence of a non-communicating 3rd party during pre-development. This particular contribution reaches a proof-of-concept stage through implementation, and achieves its goals thanks to OT's indistinguishability property as well as hash-based topic obfuscations.

2021

OFDM-based spatial data focusing for wireless physical layer geocasting in multipath channels

OFDM-based spatial data focusing (OFDM-SDF) is proposed as a novel means of performing wireless physical layer geocasting, i.e. spatially confined broadcasting. It is shown that this approach overcomes beamforming and directional modulation (DM) limitations by exhibiting higher spatial precision with a reduced number of antennas and offering uncoupled range-angle-dependent focusing. This paper describes the OFDM-SDF system model for multipath channels, including multipath robust equalization, design rules for steering phases and sidelobe mitigation, analytical geocast delivery zone derivation, and optimized symbol mapping. Using density-based clustering of the spatial bit error rate distribution, a procedure for identifying a practical geocast delivery zone and evaluating its precision and connectivity is proposed. OFDM-SDF's performance and multipath robustness are evaluated through Rice channel simulations as a function of the Rice factor. In particular, it is shown that a 2-antenna OFDM-SDF array matches the radial and angular precision of, respectively, a 6 and 12-antenna DM array in recent literature, while robustness is ensured for 5G small cell channels.

Anonymous Sealed-Bid Auction on Ethereum

In a competitive market, online auction systems enable optimal trading of digital products and services. Bidders can participate in existing blockchain-based auctions while protecting the confidentiality of their bids in a decentralized, transparent, secure, and auditable manner. However, in a competitive market, parties would prefer not to disclose their interests to competitors, and to remain anonymous during auctions. In this paper, we firstly analyze the specific requirements for blockchain-based anonymous fair auctions. We present a formal model tailored to study auction systems that facilitate anonymity, as well as a generic protocol for achieving bid confidentiality and bidder anonymity using existing cryptographic primitives such as designated verifier ring signature. We demonstrate that it is secure using the security model we presented. Towards the end, we demonstrate through extensive simulation results on Ethereum blockchain that the proposed protocol is practical and has minimal associated overhead. Furthermore, we discuss the complexity and vulnerabilities that a blockchain environment might introduce during implementation.

Indoor tracking of multiple individuals with an 802.11ax Wi-Fi-based multi-antenna passive radar

We investigate indoor human multi-target tracking in cartesian coordinates based on range, Doppler and Angle-of-Arrival measurements obtained with a four-antenna passive bistatic radar capturing 802.11ax Wi-Fi signals. A reference antenna selection method is described to perform angle processing correctly when dealing with target detection diversity among antennas. The tracking is performed by an Unscented Kalman Filter (UKF) to handle the non-linear relation between the measurement space and the state space. A Joint Probabilistic Data Association Filter is coupled to the UKF to handle the data association between tracks and measurements when dealing with multiple targets. Simulations are performed to determine the tracking parameters under heavy constraints and identify key scenarios. An experimental setup is built using Universal Software Radio Peripherals, featuring an over-the-air phase calibration for angle processing with an anchor antenna. It is used to validate the proposed single and multi-target tracking scheme.

A stochastic geometry approach to EMF exposure modeling

Downlink exposure to electromagnetic fields due to cellular base stations in urban environmentsis studied using the stochastic geometry framework. A two-dimensional Poisson Point Process is assumedfor the base station distribution. Mathematical expressions of statistics of exposure are derived from a simplepropagation model taking into account the height of the base stations. The error on exposure made by takinga limited number of base stations, instead of the whole set, is quantified. The relative impact of the modelparameters on the statistics of exposure is highlighted. The method is then applied and the model parametersare calibrated using experimental data obtained by drive-tests in two Brussels municipalities, in Belgium,for the 2100 MHz and 2600 MHz frequency bands. It is shown that the proposed model fits experimentalvalues, paving the way to a new methodology to assess general public exposure to electromagnetic fields,for any frequency band. An insight is given on how to apply the methodology to a real case without accessto experimental data.

Super resolution passive radars based on 802.11 ax Wi-Fi signals for human movement detection

Passive Radars based on Wi-Fi signals provide an excellent opportunity for human sensing without violating the privacy of individuals. Due to the limited integration time of Wi-Fi bursts and relatively low bandwidths, Fourier Transform-based methods do not provide the required accuracy. Herein, a Wi-Fi-based passive radar algorithm is proposed for indoor human movement detection with super resolution which relies on the ESPRIT algorithm to estimate range/speed parameters from limited number of measurements. To determine the number of targets in the environment, a new Model Order Selection (MOS) method is proposed which exploits the orthogonality between the basis vectors of signal and noise subspaces obtained from the sample covariance matrix of the measurements. The new MOS method along with the proposed algorithm are numerically analysed and compared with other existing methods. Finally, the performance of the algorithm is experimentally validated in indoor conditions.

Exploring the security landscape: NoC-based MPSoC to Cloud-of-Chips

In this paper, we present a detailed and systematic overview of communication security aspects of Multi-Processor Systems-on-Chip (MPSoC) and the emerging potential threats on the novel Cloud-of-Chips (CoC) paradigm. The CoC concept refers to highly scalable and composable systems, assembled not only at system design-time using RTL, like traditional SoC, but also at integrated circuit (IC) packaging time thanks to 3D-IC integration technology. Practical implementation of CoC systems needs to solve the problem of scalable, configurable and secure communication not only between different functional blocks in a single ICs, but also between different ICs in a single package, and between different packages on the same or different PCBs and even between different systems. To boost such extremely flexible communication infrastructure CoC system relies on Software-Defined Network-on-Chip (SDNoC) paradigm that combines design-time configurability of on-chip systems (NoC) and highly configurable communication of macroscopic systems (SDN). This study first explores security threats and existing solutions for traditional MPSoC platforms. Afterwards, we propose SDNoC as an alternative to MPSoC communication security, and we further extend our discussion to CoC systems to identify additional security concerns. Moreover, we present a comparison of SDNoC based approach over existing approaches and discuss its potential advantages.

2020

Focusing gain analysis of time-reversal precoding in MISO OFDM communication systems

Emerging communication systems can benefit from time-reversal (TR) technology thanks to its goodspatio-temporal signal focusing effect. The recent advances in low-cost wideband devices fabricationfurther leverage the use of TR wideband communication systems. The TR is generally carried out inthe time domain and the focusing effect of TR comes from the use of a high transmit rate back-offfactor (BOF), which is the signal up-sampling rate. In spite of the widely-used orthogonal frequencydivisionmultiplexing (OFDM) modulation, few works have investigated the frequency-domain (FD) TRprecoding in combination with OFDM communication systems. Furthermore, most existing works onFD/TR precoding rely on multiple-antenna technology at the transmitter to create the focusing effect. Inthis paper, we investigate the focusing gain provided by TR precoding in multiple-input single-output(MISO) OFDM systems. In particular, we compare the communication performance of such system atthe intended position and that at the unintended position. Based on the analysis, we demonstrate thatincreasing the BOF and/or the number of transmit antennas significantly improves the focusing effectat the intended position. In contrast, the unintended positions receive less useful power. We deriveapproximated mean-square-error (MSE) expressions of equalized received signals at both intendedand unintended positions. The subsequent focusing gain is presented as a function of the BOF andthe number of antennas, enabling us to gain insights in the contributions of each parameter to thesystem performance. Numerical simulations with multi-path Rayleigh fading channels are carried outto validate the MSE expressions.

Crowd forecasting based on WiFi sensors and LSTM neural networks

To ensure effective management and security in largescale public events, it is imperative for the event organizers to beaware of potentially critical crowd densities. This paper, therefore,presents a solution to the above problem in terms of WiFi basedcrowd counting and LSTM neural network based forecasting.Monitoring of an actual event organized in Brussels has beendescribed, wherein crowd counts are obtained using WiFi sensorsin a privacy-preserved manner. The time-stamped crowd countsare used to develop univariate time-series, which are in-turnutilized for forecasting. Five different LSTM models are utilizedfor crowd time-series forecasting and analyzed for theirsuitability. A random walk model is used as reference forperformance assessment. Among different LSTM models,Convolutional LSTM delivered the best performance. Overallresults and analysis show that the developed system is suitable forcrowd monitoring.

Secrecy capacity of FBMC-OQAM modulation over frequency selective channel

This letter studies the Information-theoretic secrecy capacity of an Offset-QAM-based filterbank multicarrier (FBMC-OQAM) communication over a wiretap frequency selective channel. The secrecy capacity Is formulated as an optimization problem which has a closed-form solution In the high signal-to-noise ratio (SNR) regime. Two of the most common equalization strategies In FBMC-OQAM are considered, namely, single-tap and multi-tap equalization. For the sake of comparison, we also consider the secrecy capacity of a generic modulation and a cyclic prefix-orthogonal frequency division multiplexing (CP-OFDM) modulation. As a result, we find that FBMC-OQAM Is particularly competitive for medium-to-long burst transmissions.

Crowd monitoring

With the growing concerns over public safety, the importance of crowd monitoring is being realized by varioussecurity and event management agencies worldwide. Estimation of crowd dynamics can help such agencies in prevention ofany unanticipated accidents or issues. Research on crowd monitoring has been underway since the past few decades. Conventionalcrowd monitoring systems mainly rely on computer vision approach. Due to predominant use of videos/ imagesequences, the existing techniques may raise data privacy concerns. This has led to development of new crowd monitoringtechniques which are privacy preserving and require minimum public participation. This paper aims to serve as a single andsufficient source of information to the concerned researchers on various aspects of crowd monitoring and also provide futuredirections which can be helpful in developing advanced crowd monitoring techniques.

Design of an integrated platform for mapping residential exposure to Rf-Emf sources

Nowadays, information and communication technologies (mobile phones, connectedobjects) strongly occupy our daily life. The increasing use of these technologies and the complexity ofnetwork infrastructures raise issues about radiofrequency electromagnetic fields (Rf-Emf) exposure.Most previous studies have assessed individual exposure to Rf-Emf, and the next level is to assesspopulational exposure. In our study, we designed a statistical tool for Rf-Emf populational exposureassessment and mapping. This tool integrates geographic databases and surrogate models tocharacterize spatiotemporal exposure from outdoor sources, indoor sources, and mobile phones.A case study was conducted on a 100 x 100 m grid covering the 14th district of Paris to illustratethe functionalities of the tool. Whole-body specific absorption rate (SAR) values are 2.7 times higherthan those for the whole brain. The mapping of whole-body and whole-brain SAR values showsa dichotomy between built-up and non-built-up areas, with the former displaying higher values.Maximum SAR values do not exceed 3.5 and 3.9 mW/kg for the whole body and the whole brain,respectively, thus they are significantly below International Commission on Non-Ionizing RadiationProtection (ICNIRP) recommendations. Indoor sources are the main contributor to populationalexposure, followed by outdoor sources and mobile phones, which generally represents less than 1%of total exposure.

Iterative NDA Positioning Using Angle-of-Arrival Measurements for IoT Sensor Networks

Various positioning techniques have been developed to localize Internet of Things (IoT) devices accurately. Because IoT communications are often narrowband, efficient localization can be achieved by deducing the device position from the estimated signal Angle of Arrival (AOA) at multiple arrays of antennas. It has recently been shown that significant accuracy gains can further be obtained by iterating between the AOA estimation and multi-lateration steps. However, the existing method relies on the knowledge of the transmitted signal (Data-Aided (DA) estimation) which makes it impractical for narrowband communications where the preamble is short. Non-Data-Aided (NDA) estimation is recommended to improve the positioning accuracy for low capacity IoT sensors. This paper proposes an NDA iterative (NDA-It) algorithm using AOA measurements to determine the position of an IoT sensor. Simulation results show that the proposed algorithm significantly outperforms the DA-It in a Bluetooth Low Energy (BLE) context because it can use a much higher number of samples (snapshots); however, it needs more iterations to converge. The computational complexity analysis proves the competitiveness of the proposed NDA-It. The performance of the algorithms is further investigated in multipath and Non-Line-of-Sight (NLOS) propagation environments. Finally, an experimental setup is built to validate the performance of the proposed algorithms.

Forecasting Crowd Counts With Wi-Fi Systems: Univariate, Non-Seasonal Models

Recently, event organizers and researchers have advocated the development of novel technologies supporting crowd control, notably for public events. This paper presents a crowd monitoring system based on probe requests (PRs), which are Wi-Fi packets smartphones send periodically. By estimating the global rate at which nearby smartphones send PRs, Wi-Fi sensors can estimate crowd counts. The core contribution of this paper is a computationally tractable method that forecasts crowd counts up to thirty minutes in the future, with forecasts becoming available as soon as two hours of data are available. The forecasting method relies on autoregressive integrated moving average (ARIMA) models. Contributions also include two methods that compute prediction intervals associated with the forecasts, one of which is based upon generalized autoregressive conditional heteroskedasticity (GARCH) models. Recent real-world data from Winter Wonders 2018/2019 (an event that took place in Brussels, Belgium) notably demonstrate that the proposed forecasting method outperforms its immediate variations as well as baseline models (i.e., random walk models).

UAV Mobility Model for Dynamic UAV-to-Car Communications in 3D Environments

In scenarios where there is a lack of reliable infrastructures to support car-to-car communications, Unmanned Aerial Vehicles (UAVs) can be deployed as mobile infrastructures. However, the UAVs should be deployed at adequate location and heights to maintain the coverage throughout time as the irregularities of the terrain may have a significant impact on the radio signals sent to distribute information. So, flight altitude and location should be constantly adjusted in order to avoid hilly or mountainous terrains that might hinder the Line-of-Sight (LOS). In this paper, we propose a three-dimensional mobility model to define the movement of the UAV so as to maintain good coverage levels in terms of communications with moving ground vehicles by taking into account the elevation information of the Earth's surface and the signal power towards the different vehicles. The results showed that our proposed model is able to extend the times with connectivity between the UAV and the cars compared to a simpler two-dimensional model, which never considers the altitude, and a static model, which maintains the same UAV position from the beginning to the end of the experiment.

CSI-based versus RSS-based Secret-Key Generation under Correlated Eavesdropping

Physical-layer security (PLS) has the potential to strongly enhance the overall system security as an alternative to or in combination with conventional cryptographic primitives usually implemented at higher network layers. Secret-key generation relying on wireless channel reciprocity is an interesting solution as it can be efficiently implemented at the physical layer of emerging wireless communication networks, while providing information-theoretic security guarantees. In this paper, we investigate and compare the secret-key capacity based on the sampling of the entire complex channel state information (CSI) or only its envelope, the received signal strength (RSS). Moreover, as opposed to previous works, we take into account the fact that the eavesdropper’s observations might be correlated and we consider the high signal-to-noise ratio (SNR) regime where we can find simple analytical expressions for the secret-key capacity. As already found in previous works, we find that RSS-based secret-key generation is heavily penalized as compared to CSI-based systems. At high SNR, we are able to precisely and simply quantify this penalty: a halved pre-log factor and a constant penalty of about 0.69 bit, which disappears as Eve’s channel gets highly correlated.

2019

Analysis of residual CFO impact on downlink massive MISO systems

Massive antenna technologies provide a good power focusing gain for emerging communication systems. They can easily be integrated into an orthogonal frequency-division multiplexing (OFDM) system. However, OFDM is known to be prone to carrier frequency offset (CFO) due to the loss of the orthogonality among OFDM subcarriers. In this Letter, the authors investigate the impact of residual CFO (RCFO) on the downlink performance of massive multiple-input single-output (MISO) OFDM systems using matched-filter (MF) and maximum-ratio-transmission (MRT) precoders. Particularly, the exact mean-square-error (MSE) expressions of the equalised received signal of both MF and MRT systems are derived. Numerical simulations with Rayleigh fading channels are carried out to validate the analysis. The results show that the RCFO causes a MSE plateau compared to the ideal case of no CFO.

A twofold group key agreement protocol for NoC-based MPSoCs

A symmetric group key agreement protocol enables the group members to derive a shared session key for secure communication among them, whereas an asymmetric one facilitates security to any communication from outside, without adding outsiders into the group. In order to combine both the functionalities, a hybrid key agreement protocol is needed, which can output a shared symmetric key for inside communication and an asymmetric key pair for any unrestricted sender. The application mentioned in this paper pushes the need of secure on-chip communication for intersecure and intrasecure zones simultaneously. In particular, we look forward for a solution to ensure communication security among multiple processing clusters actively running on an integrated circuit. The proposed protocol offers a lightweight symmetric encryption for intrazone communication and a public key encryption for interzone communication taking most advanced security issues into account.

La révolution des communications électroniques, ce n'est pas (que) la 5G

SSPSoC: A Secure SDN-Based Protocol over MPSoC

In recent years, Multi-Processor System-on-Chips (MPSoCs) are widely deployed in safety-critical embedded systems. The Cloud-of-Chips (CoC) is a scalable MPSoC architecture comprised of a large number of interconnected Integrated Circuits (IC) and Processing Clusters (PC) destined for critical systems. While many researches have focused on addressing the hardware issues of MPSoCs, the communication over them has not been very well explored. Following the SDN concept, we propose a new protocol in order to secure the communication and efficiently manage the routing within the CoC. The SSPSoC includes a private key derivation phase, a group key agreement (GKA) phase, and a data exchange phase in order to ensure that basic security primitives are preserved and provide secure communication. Furthermore, a network of 1-30 nodes is set in order to validate the proposed protocol and measure the network performance and memory consumption of the proposed protocol.

Performance analysis of frequency domain precoding time-reversal MISO OFDM systems

Time reversal (TR) recently emerged as an interestingcommunication technology capable of providing a goodspatio-temporal signal focusing effect. New generations of largebandwidthdevices with reduced cost leverage the use of TRwideband communication systems. TR can easily be integratedinto an orthogonal frequency-division multiplexing (OFDM) systemby precoding the signal in the frequency domain. In thispaper, we first extend the frequency-domain TR precoding to rateback-off factors (BOFs) different than one. We secondly derive aclosed-form mean-square-error (MSE) expression of the receivedequalized symbols as a function of the BOFs and the numberof antennas. The derived MSE formula is validated numericallywith Rayleigh fading channels.

2018

Low complexity iterative localization of time-misaligned terminals in cellular networks

Recently, iterative localization has arisen as a promising approach to localize a Mobile Station (MS) in a cellular system. The conventional geo-location is obtained in a two-step approach: propagation delays are estimated and then the multi-lateration is responsible for the determination of the user position, based on the estimated delays. Iterative localization iterates between the two conventional steps to progressively refine delay estimates based on the position estimate available from the previous iterations. This localization scheme was seen to provide appealing performances compared to the two-step approach. It also seems to be computationally attractive with respect to direct localization that estimates the position using the digitized received signals directly. However, the iterative localization solution developed in literature relies on a strict time synchronization between MS and Base Stations (BSs). Moreover,the computational complexity of the iterative approach is not thoroughly compared to two-step and optimal solutions. This paper therefore proposes a new iterative localization method able to operate in a cellular system with time-misaligned terminals.We show by means of a detailed complexity analysis that the iterative positioning algorithm is one order of magnitude less complex than direct localization. Simulation results prove that the achievable performance after a few iterations approaches the performance of the direct localization solution.

Iterative RToF-based localization and time synchronization in WLAN-like systems

Iterative localization is currently arising as a solution to localize a Mobile Station (MS) in a cellular network. We recently showed that iterating between the conventional delay estimation and multi-lateration steps allows one to approach the performance of direct localization algorithms. Until now, the method has only been applied to the case of networks where the access points are perfectly synchronized with each other. In this letter, we present a localization and time synchronization iterative algorithm suitable for networks where access points are not synchronized. We show numerically that iterating between the two conventional steps brings a significant performance gain.

Secure communication on NoC based MPSOC

Virtual multi-antenna array for estimating the direction of a transmitter: system, bounds and experimental results

A method is proposed to estimate the direction of a radio-frequency transmitter with a mobile single-antenna receiver. By considering the received signal at several points along its trajectory, the receiver implicitly creates a virtual multiantenna array, which can be used to estimate the direction of the transmitter. Virtual arrays differ from conventional multiantenna arrays in two ways: 1) the position and orientation of each antenna in the virtual array depend on the movement of the receiver and are not known a priori; and 2) the local oscillator (LO) frequency offset between the transmitter and the receiver adds a phase offset to the signal received by each antenna of the virtual array, which must be estimated and compensated. The first problem is solved by using an inertial measurement unit, which can provide the relative position of the receiver for short time durations. The second problem is solved by estimating the LO frequency offset jointly with the direction of the transmitter by extending the MUSIC algorithm for multidimensional estimation. We investigate the Cramér-Rao lower bound of the proposed estimator, which provides some insights in the design of our system. We implement our system on a software-defined radio testbed and present some measurement results obtained in a controlled environment.

2017

Wideband off-body measurements and channel modeling at 60 GHz

A wideband indoor channel model between an external base station and a worn receiver on the user body at 60 GHz has been developed based on indoor measurements. The results are presented for three different receiver locations: head, wrist, and belt. A Saleh-Valenzuela impulse response is proposed as numerical model for this scenario. Also path loss and delay spread results are driven out in order to discuss the node location for assessing an off-body communication.

Performance of emerging multi-carrier waveforms for 5G asynchronous communications

This paper presents an extensive and fair comparison among the most promising waveform contenders for the 5G air interface. The considered waveform contenders, namely filter-bank multi-carrier (FBMC), universal-filtered multi-carrier (UFMC), generalized frequency-division multiplexing (GFDM) and resource-block filtered orthogonal frequency-division multiplexing (RB-F-OFDM) are compared to OFDM used in 4G in terms of spectral efficiency, numerical complexity, robustness towards multi-user interference (MUI) and resilience to power amplifier non-linearity. FBMC shows the best spectral containment and reveals to be almost insensitive to multi-user interference. It however suffers from its bad spectral efficiency for short bursts and from its poor multiple input multiple output (MIMO) compatibility. GFDM reveals to be the most promising contender, with the best spectral efficiency and the smallest complexity overhead compared to OFDM. It is also the most resilient to multi-user interference after FBMC and is MIMO compatible as soon as the interference can be managed. UFMC and RB-F-OFDM are finally the closest to OFDM and benefit therefore from a better compatibility with existing systems, even if their performance is generally lower than FBMC and GFDM.

Experimental comparison of radio duty cycling protocols for wireless sensor networks

The performances of three different asynchronous radio duty cycling protocols available in the Contiki lightweight operating system have been compared experimentally in view of their adoption in medium sized wireless sensor networks integrated in the Internet of Things. This study unveils some of the subtleties of those protocols, allowing an improved tuning of their parameters, as well as the identification of overlooked shortcomings and implementation flaws. To ensure fair comparisons default options have been unified and small implementation and design problems have been tackled. Besides the previously mentioned interventions, default values for parameters were kept. The results of the comparison can help designers of wireless sensor networks with their choices and guide designers of protocols to overcome some critical issues.

Assessment of on-body skin-confined propagation for body area network

This letter assesses the potential of using surface waves to implement secure on-body communications. The propagation medium being the human skin, a transverse resonance method is used to analyze existing modes within the multilayered structure that composes the human tissues. Confinement capabilities as well as propagation losses are investigated for frequency up to 60 GHz. It is shown in particular that the 3-10 GHz band could allow us secure communications up to few tens of centimeters. This frequency band is furthermore considered as ultrawideband channels in the IEEE 802.15.6 standard dedicated to body area networks.

Input impedance of an aperture over a lossy half-space: application to on-body antenna performance at 60GHz

This paper presents a theoretical approach to compare the performance of a directive and a quasi-omnidirectional on-body antennas. Two canonical antennas, namely, a dipole and a rectangular aperture, are considered in the 60 GHz band. We first demonstrate that for this on-body configuration, the classically-defined far-field antenna gain depends on the observation distance. Consequently, we derive results in terms of radiation efficiency and link budget. To do so, the antenna input impedance computation is a preliminary step to normalize the input power to allow a fair comparison between the two antennas. The impedance over a lossy half-plane of an aperture illuminated by a TE10 mode normally polarized is therefore derived into a convenient easy-to-compute formulation, which to authors' best knowledge, is not available in the literature. In terms of link budget, it is obtained that the received power due to an aperture is generally higher than the one due to the dipole in the main lobe direction. A constant difference is observed along the distance, and this difference increases with the aperture width for antennas touching the body. Besides, it is shown that the standard aperture waveguide WR15 exhibits a slightly higher efficiency than a vertical dipole with the same vertical size when being placed at a distance less than 3mm (i.e., 0:6λ) from the body phantom surface. Above this distance, the dipole and the aperture exhibit similar efficiency in the order of 60%.

2016

Variographic analysis of public exposure to electromagnetic radiation due to cellular base stations

The spatial structure of the vertical component of the electric field emitted by base stations in the Brussels region (Belgium) is measured, and studied using the variogram. A relationship between the variogram shape and base station antenna density in each measurement area is found; the variogram range and sill level are shown to depend on cellular base stations' antenna density, following exponential laws. Bioelectromagnetics. © 2016 Wiley Periodicals, Inc.

Performance assessment of IR-UWB body area network (BAN) based on IEEE 802.15.6 standard

Performance of impulse radio-based ultra-wideband (IR-UWB) communications in wireless body area networks are investigated using the dedicated IEEE 802.15.6 standard. An IR-UWB transceiver system is implemented for both on-off keying and differential binary phase-shift keying modulations. Bit error rates are determined from measurements for different on-body links with different data rates. It is shown that that using a 25 dB-gain LNA at the receiver, reaching an uncoded BER of 10-3 was not possible for some links operating at higher data rates. Power and energy consumption issues are then addressed and results in terms of required pJ/bit to achieve a certain quality of communication are given and discussed.

Millington effect and propagation enhancement in 60 GHz body area networks

Millington effect for on-body propagation enhancement is presented in the 60-GHz band. Millington's equations are developed to describe propagation above a flat inhomogeneous surface. This study focuses on mixed paths (human skin-metallic) for on-body scenarios. It is shown that adding metallic paths on the human skin can improve the power link budget between two nodes placed on the body. Two different schemes are studied experimentally to assess the analytical model using a flat phantom with electric properties of human skin and different lengths of metallic inserts. The first scheme considers a metallic plate between the transmitting and receiving antennas, while the second scheme proposes locating the metallic plates under the antennas. It is shown that the second scheme yields a better link budget than the first one for the same length of metal. Moreover, a numerical study is performed to assess the impact of the following different parameters: the location of the metal plate, size of the plate, and the height of the antennas. Excellent agreement between numerical and experimental results has been shown. In the best cases, the presented techniques allow to improve the path loss of 10-20 dB.

Demonstrating the versatility of a low cost measurement testbed for wireless sensor networks with a case study on radio duty cycling protocols

Today, Wireless Sensor Networks (WSNs) with open source operating systems still need many efforts to guarantee that the protocol stack succeeds in delivering its expected performance. This is due to subtle implementation problems and unexpected interactions between protocol layers. The subtleties are often related to the judicious choice of parameters, in particular those related to timing issues. As these issues are often not visible in simulation studies, this paper proposes a low-cost versatile measurement testbed and demonstrates its usefulness in measuring the performance of RDC protocols. We demonstrate how the testbed helped to identify bugs in the implementation of an RDC protocol.

Poster: Contikimac, some critical issues with the cc2420 radio

During experimental evaluations of RPL on a network with some 20 Zolertia Z1 motes running Contiki version 2.6, inconsistent Packet Delivery Ratios (PDR) and message la-tencies were frequently observed. Replacing ContikiMAC by NullRDC brought consistency, proving that the problem had to be found in the Radio Duty Cyling (RDC) protocol. Two implementation issues of ContikiMAC were found guilty. The first is the timing of the inter-packet interval related to the interval between two successive Clear Channel Assessment (CCA) probes. The second is the choice of the value of the CCA threshold. These issues will be analyzed in this poster, a satisfactory work-around has been implemented and some to be tested alternatives are proposed.

2015

TDOA estimation method using 60 GHz OFDM spectrum

In the field of high data rate wireless communications, localization issues play a key role in achieving energy-efficient communication and geographic routing. time-difference of arrival (TDOA)-based localization methods present numerous advantages. In this paper, a new method of TDOA estimation is proposed. With this method, unlike conventional TDOA measurements, it is possible to perform communication and localization at the same time by using a multi-input single-output system. By transmitting ultra-wide-band orthogonal frequency-division multiplexing signals using spatial diversity, it is possible to extract TDOA from interference patterns in spectral domain. In addition, increasing the precision of localization is also studied using a multi-band approach. This whole study is made within the framework of the WiGig alliance specifications; however, it is compatible with other standards.

Sensitivity of whole body dosimetry to channel model parameters

Impact of channel model parameters on the whole-body specific absorption rate (SAR) is studied. Closed-form expressions are derived for the mean value and the standard deviation of the SAR, taking into account the random nature of the channel parameters. Total sensitivity indices of the SAR with respect to the channel parameters are derived. They are estimated using a Monte-Carlo approach. Noninfluential channel parameters are identified. They are then suppressed from channel models for dosimetry purpose.

Near-body shadowing analysis at 60GHz

A numerical model of the fading of a receiver (Rx) located near the user body at 60 GHz in an indoor environment is presented. The model is based on the indoor channel model IEEE 802.11ad. The results are presented for a-Rx located in a zone from 5 to 30 cm away from the body. With the shadowing depending on the region (front or back) with respect to the base station, the mean attenuation of the channel over the bandwidth is analyzed and modeled thanks to a two-wave diffuse power distribution model.

UWB interferometry TDOA estimation for 60GHz OFDM communication systems

A simple technique to estimate the time difference of arrival (TDOA) that necessitates only one reference device to perform 1-D positioning of a mobile device is presented. Using a multiple-input-single-output (MISO) system, this interferometric technique uses ultrawideband signals and is particularly well suited for 60-GHz orthogonal frequency-division multiplexing (OFDM) communications. The accuracy of the technique is assessed by simulation, using the IEEE 802.11ad channel, as well as by measurement.

2014

V-band velocity estimation of creeping waves around the human body

This letter investigates the phase velocity of an electromagnetic wave propagating between two sensors located on the human body surface by using the formulation of a creeping wave around a circular cylinder. The study is performed for both horizontal and vertical polarizations. The velocity is studied over the V-band. It is theoretically shown that the variation of the phase velocity is negligible over the bandwidth. Measurements are conducted on a metallic circular cylinder to assess the validity of these formulations. Then, an experimental validation of the circular cylinder assumption for the human body is performed. Deviation between the measurements and the theoretical circular model is between 2% and 3.5%.

Information spatial focusing scheme for UWB wireless communications in smart environments

This letter presents an information spatial focusing method for future smart environments using ultrawideband (UWB) wireless communications. This method allows to send high-data-rate information at predetermined specific spatial positions without localizing users, thereby protecting their privacy. The proposed approach is a combination of simplified UWB beamforming and signal processing. Compared to classical UWB beamforming, the proposed method exhibits greater information focusing capabilities by increasing greatly the peak-to-floor ratio between main and side beams.

Statistical on-body measurement results at 60 GHz

This communication studies the path loss and shadowing between two body mounted devices at 60 GHz. The temporal fading is experimentally investigated and the Doppler spectrum is characterized and modeled. Measurements have been conducted in an anechoic chamber for both horizontal and vertical polarizations.

Analytical creeping wave model and measurements for 60 GHz body area networks

The propagation of 60 GHz electromagnetic waves around a human body is studied analytically and experimentally. The body is treated here as a circular lossy cylinder, which is an approximation of the human torso. Analytical formulations based on creeping wave theory are given and discussed for both vertical and horizontal polarizations. An exact path gain expression is derived from analytical formulations and a simpler first order approximation is given. Path gain coefficients are shown for frequencies spanning the world available 60 GHz unlicensed band and for several sizes of the torso. Finally, the results of an experimental campaign conducted in an anechoic chamber to isolate the contribution of on-body propagation are reported. The measurement of the distance dependence of the received power on a brass cylinder and on a human body for both vertical and horizontal polarizations confirmed theoretical predictions. © 2014 IEEE.

Creeping wave model of diffraction of an obliquely incident plane wave by a circular cylinder at 60 GHz

Study of human exposure using kriging method

This paper develops the kriging method to calculate the whole body Specific Absorption Rate (SAR) for any angle of incidence of a plane wave on any body model using a minimum number of Finite Difference Time Domain (FDTD) simulations. Practical application of this method is to study people's exposure. Thanks to kriging method, it will enable to answer to the challenge of studying the exposure in a realistic environment. This approach develops a new tool in order to improve the field of stochastic dosimetry. The kriging method is applied to a girl body model in order to determine the variogram model, then this model is validated on a boy body model. Thanks to only 40 numerical SAR values, kriging method enables to estimate any SAR value with a mean relative error under 3%.

Poster abstract: Outdoors range measurements with Zolertia Z1 Motes and Contiki

Practically useful outdoor transmission ranges have been determined experimentally for Zolertia Z1 motes running Contiki. Both internal and external antennas were tested. The analog and digital quality of the received signal as well as the packet delivery rate have been measured. The influence of transmission power, bushes and weather conditions have been explored. Internal antennas were excessively sensitive to orientation, while external antennas allowed reliable and rather stable communications over distances between motes of up to 150 m. Radio duty cycling was responsible for some, still partially unexplained, packet losses. © Springer International Publishing Switzerland 2014.

2013

A formally verified protocol for secure vertical handovers in 4G heterogeneous networks

In this paper, we propose a formally verified protocol to securely manage vertical handovers heterogeneous networks (HetNets), even when different cryptographic algorithms are used in the infrastructure. The protocol presentation goes with a review of the current propositions of security mechanisms and procedures dedicated to manage vertical handovers. From a critical analysis, the HetNets are positioned in the context of wireless security to describe the possible attacks that afflict this new kind of infrastructure. From this analysis, it is revealed that the different entities involved in the management of handovers are surrounded by new security challenges. This challenges and the positioning of HetNets helps to deliver a new suited protection. Securing vertical handovers means to deal with the different cryptographic algorithms from the security architecture of the different technologies that protect the sessions of communications. © 2013 SERSC.

Theoretical and experimental investigation of a 60 GHz off-body propagation model

A fast computation and accurate analytical model for off-body propagation is derived in this paper. The paper discusses the off-body model propagation from an external source to a receiver located on the body. The model is developed for normal incident plane wave by describing the human body with a circular cylinder. We show that the total received electric field around the human body can be written as a creeping wave in the shadow region and as a geometrical optics result for the lit region. It is also shown that at 60 GHz, the shadow boundary width is negligible. The model shows perfect agreement with the experimental results conducted on a perfectly conducting cylinder. Measurements of the creeping wave path gain have been also conducted on a real body to assess the validity of the cylinder assumption. The results have shown a path gain of about 5 dB/cm for the TM case and 3 dB/cm for the TE case. The standard deviation between the measurements and the cylindrical model is about 3.5 dB for both TM and TE cases. © 2013 IEEE.

Food collection and response to pheromones in an ant species exposed to electromagnetic radiation

We used the ant species Myrmica sabuleti as a model to study the impact of electromagnetic waves on social insects' response to their pheromones and their food collection. We quantified M. sabuleti workers' response to their trail, area marking and alarm pheromone under normal conditions. Then, we quantified the same responses while under the influence of electromagnetic waves. Under such an influence, ants followed trails for only short distances, no longer arrived at marked areas and no longer orientated themselves to a source of alarm pheromone. Also when exposed to electromagnetic waves, ants became unable to return to their nest and recruit congeners; therefore, the number of ants collecting food increases only slightly and slowly. After 180 h of exposure, their colonies deteriorated. Electromagnetic radiation obviously affects social insects' behavior and physiology. © Informa UK Ltd.

Dynamic resource allocation for MIMO cognitive radio networks with low control traffic and low computational complexity

Radio spectrum scarcity hampers the development of new wireless technologies and services. Cognitive radios have been proposed to enable unlicensed (or secondary) users to borrow locally idle bands of the spectrum provided that no significant interference is created for the licensed (or primary) users. Fast adaptation to the changing spectrum availability is naturally a major requirement in such systems. This adaptation consists of detecting the spectrum occupied by the primary users, computing a new resource allocation for the secondary network, and communicating this allocation through the network. In that context, we develop a resource allocation scheme for multi-input-multi-output wireless mesh networks. The proposed algorithm combines low computational complexity and light control traffic thanks to a combination of relevant approximations in the general nonpolynomial-hard allocation problem. The allocation consists of two steps. First, a centralized carrier allocation is performed at a coordinator node based on partial knowledge of the network parameters. Then, each node locally computes its power allocation through simple water-filling algorithms. Numerical results show that compared to state-of-the-art techniques, 10% of the total throughput of the network is sacrificed to reduce the computation time and the control traffic by two orders of magnitude.

Dynamic channel modeling for multi-sensor body area networks

A channel model for time-variant multi-link wireless body area networks (WBANs) is proposed in this paper, based on an extensive measurement campaign using a multi-port channel sounder. A total of 12 nodes were placed on the body to measure the multi-link channel within the created WBAN. The resulting empirical model takes into account the received power, the link fading statistics, and the link auto- and cross-correlations. The distance dependence of the received power is investigated, and the link fading is modeled by a log-normal distribution. The link autocorrelation function is divided into a decaying component and a sinusoidal component to account for the periodical movement of the limbs caused by walking. The cross-correlation between different links is also shown to be high for a number of specific on-body links. Finally, the model is validated by considering several extraction-independent validation metrics: multi-hop link capacity, level crossing rate (LCR) and average fade duration (AFD). The capacity aims at validating the path-loss and fading model, while the LCR and AFD aim at validating the temporal behavior. For all validation metrics, the model is shown to satisfactorily reproduce the measurements, whereas its limits are pointed out.

Statistical characterization and modeling of doppler spectrum in dynamic on-body channels

The time variation, i.e., time-selective fading, of on-body channels in body area networks is dominated by the body dynamics, which not only contribute to dynamic scattering, but also modify the geometry of links over time. In this letter, we experimentally investigate the Doppler spectra of narrowband on-body channels in anechoic (at 2.45 GHz) and indoor (at 4.2 GHz) environments for people walking. The body dynamics resulting from people walking are shown to directly affect the Doppler spectrum, and empirical models are proposed to describe the global and/or local Doppler spreads. © 2013 IEEE.

2012

Tri-polarized MIMO systems in real-world channels

Polarized multi-antenna systems are an effective solution for reducing inter-antenna spacing while still maintaining low inter-antenna correlation. Traditionally, only dual-polarized antenna systems are used for polarized transceivers. In this paper, tri-polarized antenna systems are investigated. Starting from the polarization mechanisms in the wireless propagation channel, it is shown that dual-polarized MIMO systems show high sensitivity to the transmitter and receiver orientation, which may be very critical in practical applications. Tri-polarized MIMO systems are introduced as a solution to obtain a robust MIMO performances, which are independent of the transmitter and receiver orientation. The performances of dual- and tri-polarized MIMO systems are evaluated on real-world measured channels, and the limits of each of these systems is highlighted.

Tri-polarized spectrum sensing based on an experimental outdoor-to-indoor cognitive-radio scenario

Compared to classical spatially separated multiple antenna system, cross-polarized co-located antenna systems are an interesting way to reduce equipment size while reducing the inter-antenna correlation. In this paper the spectrum sensing of a Cognitive Radio (CR) system taking advantage of polarization diversity under Rayleigh fading is investigated and compared to an equivalent system using spatial diversity. This analysis is based on a theoretical formulation applied to a real-world scenario. For this purpose, an outdoor-to-indoor measurement campaign at a frequency of 3.5 GHz is realized, where an indoor secondary user senses the signals received from an outdoor primary base station. The signals received at each antenna are first combined and then applied to an energy detector. The theoretical expressions are simulated in the measurement context. The detection probability behavior as a function of distance between the Primary Transmitter (PTx) and the Secondary Terminal (STE) and the inter-antenna correlation effect on the sensing performance are studied. © 2012 Elsevier B.V.

Vertical handover security in 4G heterogeneous networks

In this paper, we propose a review of the mechanisms and procedures to securely manage vertical handovers in heterogeneous networks. The purpose of the paper is to position the heterogeneous networks in the context of wireless security and to describe the possible attacks that come along with this new kind of infrastructure. From a critical analysis of the literature, this paper focuses on the new security challenges that surround the different entities involved in the handover management.

Model parametrization and validation for specular-diffuse clustered channel models

A model parameterization and validation is proposed for specular-diffuse clustered channel models. The double-directional model parameters, based on an experimental measurement campaign, are presented. The specular-diffuse model is validated with regard to the following validation metrics: mutual information, singular values, Demmel condition number and ellipticity. A good agreement is observed when comparing the model with experimental measurements. Finally, the influence of the diffuse multipath component on the performance of the model validation is evaluated. © 1963-2012 IEEE.

GSM 900 MHz radiation inhibits ants' association between food sites and encountered cues

The kinetics of the acquisition and loss of the use of olfactory and visual cues were previously obtained in six experimental colonies of the ant Myrmica sabuleti meinert 1861, under normal conditions. In the present work, the same experiments were conducted on six other naive identical colonies of M. sabuleti, under electromagnetic radiation similar to those surrounding GSM and communication masts. In this situation, no association between food and either olfactory or visual cues occurred. After a recovery period, the ants were able to make such an association but never reached the expected score. Such ants having acquired a weaker olfactory or visual score and still undergoing olfactory or visual training were again submitted to electromagnetic waves. Not only did they lose all that they had memorized, but also they lost it in a few hours instead of in a few days (as under normal conditions when no longer trained). They kept no visual memory at all (instead of keeping 10% of it as they normally do). The impact of GSM 900 MHz radiation was greater on the visual memory than on the olfactory one. These communication waves may have such a disastrous impact on a wide range of insects using olfactory and/or visual memory, i.e., on bees. © Informa Healthcare USA, Inc.

A human body model exposed to a cluster of waves

The impact of wireless channel modeling on exposure to electromagnetic radiation is studied. Two methods are developed in order to assess the statistical properties of whole body Specific Absorption Rate for exposure estimation in indoor environment. The body model is exposed to a bundle of waves, named cluster, following the wireless channel modeling approach. The first method is analytical and based on the Uncorrelated Scattering Assumption of the incident waves. The second method is a classical stochastic method. The point is to identify the parameters of Wireless Channel which led to significant SAR's variation.

Sensing time and power allocation for cognitive radios using distributed Q-learning

In cognitive radios systems, the sparse assigned frequency bands are opened to secondary users, provided that the aggregated interferences induced by the secondary transmitters on the primary receivers are negligible. Cognitive radios are established in two steps: the radios firstly sense the available frequency bands and secondly communicate using these bands. In this article, we propose two decentralized resource allocation Q-learning algorithms: the first one is used to share the sensing time among the cognitive radios in a way that maximize the throughputs of the radios. The second one is used to allocate the cognitive radio powers in a way that maximizes the signal on interference-plus-noise ratio (SINR) at the secondary receivers while meeting the primary protection constraint. Numerical results show the convergence of the proposed algorithms and allow the discussion of the exploration strategy, the choice of the cost function and the frequency of execution of each algorithm.

Correlation for multi-frequency propagation in urban environments

The multi-frequency propagation in urban environment is investigated in this letter. An experimental measurement campaign is conducted to simultaneously measure the GSM-900, GSM-1800 and UMTS band of a cellular system in a suburban environment. The shadowing and small-scale fading parameters are extracted, and the correlation of these parameters across the different frequency bands is measured. It is shown that shadowing coeffcients are highly correlated, while small-scale fading is completely uncorrelated between different frequency bands.

Uncertainty propagation and sensitivity analysis in ray-tracing simulations

Up to now, ray-tracing simulations are commonly used with a deterministic approach. Given the input parameters, the ray-tracing algorithm computes a value for the electric field. In this paper, we present a method that aims at computing the mean and standard deviation of the electric field. More precisely, we aim to obtain the probabilistic content of the electric field value and direction. We assume that this uncertainty results from input random variables which we consider uniformly distributed. Since ray-tracing computations have a high computational cost, we use spectral methods in order to optimize the number of simulations. We consider 2D electromagnetic propagation for the multi-path components, which can interact with the environment through four processes: transmission, single reflection, double reflection and diffraction. These are modelled using adequate coeffcients. In order to calculate the polynomial chaos expansion coeffcients, we use the projection method and Gauss-Legendre quadratures. These coeffcients can then be used to determine the Sobol indices of input parameters. This is done in order to neglect variables in practical computation of the uncertainties.

2011

Special issue on "Towards the connected body: advances in body communications"

Impact of the environment and the topology on the performance of hierarchical body area networks

Personal area networks and, more specifically, body area networks (BANs) are key building blocks of future generation networks and of the Internet of Things as well. In this article, we present a novel analytical framework for network performance analysis of body sensor networks with hierarchical (tree) topologies. This framework takes into account the specificities of the on-body channel modeling and the impact of the surrounding environment. The obtained results clearly highlight the differences between indoor and outdoor scenarios, and provide several insights on BAN design and analysis. In particular, it will be shown that the BAN topology should be selected according to the foreseen medical application and the deployment environment.

Link-level performance of indoor body area networks with centralized topologies

sensors networks and, more specifically, body area networks (BANs) are key building blocks of the future generation networks and the Internet of Things as well. In the last years, research has focused on channel modeling and on the design of efficient medium access control (MAC) mechanisms. Less attention has been paid to network-level performance analysis. Thereby, this paper presents a novel analytical framework for network performance analysis with star (i.e., centralized) topologies. This framework takes into account realistic channel statistics and provides several insights on BAN design and analysis. © Dricot et al.

A wideband channel model for intravehicular nomadic systems

The increase in electronic entertainment equipments within vehicles has rendered the idea of replacing the wired links with intra-vehicle personal area networks. Ultra-wideband (UWB) seems an appropriate candidate technology to meet the required data rates for interconnecting such devices. In particular, the multiband OFDM (MB-OFDM) is able to provide very high transfer rates (up to 480 MBps) over relatively short distances and low transmit power. In order to evaluate the performances of UWB systems within vehicles, a reliable channel model is needed. In this paper, a nomadic system where a base station placed in the center of the dashboard wants to communicate with fixed devices placed at the rear seat is investigated. A single-input single-output (SISO) channel model for intra-vehicular communication (IVC) systems is proposed, based on reverberation chamber theory. The model is based on measurements conducted in real traffic conditions, with a varying number of passengers in the car. Temporal variations of the wireless channels are also characterized and parametrized. The proposed model is validated by comparing model-independent statistics with the measurements.

An analytical modeling of polarized time-variant on-body propagation channels with dynamic body scattering

On-body propagation is one of the dominant propagation mechanisms in wireless body area networks (WBANs). It is characterized by near-field body-coupling and strong body-scattering effects. The temporal and spatial properties of on-body channels are jointly affected by the antenna polarization, the body posture, and the body motion. Analysis on the time variant properties of on-body channels relies on a good understanding of the dynamic body scattering, which is highly dependent on specific scenarios. In this paper, we develop an analytical model to provide a canonical description of on-body channels in both time and space domains to investigate the on-body propagation over the trunk surface of a walking human. The scattering from the arms and the trunk in different dimensions is considered with a simplified geometrical description of the body and of the body movements during the walk. A general full-wave solution of a polarized point source with multiple cylinder scattering is derived and extended by considering time evolution. The model is finally validated by deterministic and statistical comparisons to different measurements in anechoic environments. © 2011 Lingfeng Liu et al.

2010

A polarized clustered channel model for indoor multiantenna systems at 3.6 GHz

Multiple-input-multiple-output (MIMO) technologies allow high data rates to be obtained, but they suffer from interantenna correlation caused by the limits in interantenna spacing. Polarized MIMO systems resolve this problem by using colocated perpendicularly polarized antennas that have low interantenna correlation. In this paper, a polarized single-directional channel model for 2 × N MIMO systems at 3.6 GHz in an indoor environment is presented. The wireless channel is modeled as a sum of clusters, where each cluster has specular and diffuse components. The polarization of the specular component of the clusters is included by considering a per-path polarization. The diffuse component of the clusters is modeled with a FisherBingham (FB5) spectrum in the azimuthcoelevation domain and with an exponential power delay profile. Polarization is analyzed by introducing the cross-polar discrimination of the exponential power delay profile parameters. All of the parameters in the model are extracted from an experimental measurement campaign performed in an indoor environment at 3.6 GHz. Individual paths are extracted from the measurements with the space-alternating generalized expectation-maximization (SAGE) algorithm. These paths are grouped in clusters within the azimuth of arrivalelevation of arrivaldelay domains at the receiver side using automatic clustering algorithms. The specular component properties of the clusters are then determined. Finally, the diffuse components of the clusters are investigated and parameterized by applying a beamforming algorithm on the diffuse part of the impulse response. © 2006 IEEE.

Higher-order cyclostationarity detection for spectrum sensing

Recent years have shown a growing interest in the concept of Cognitive Radios (CRs), able to access portions of the electromagnetic spectrum in an opportunistic operating way. Such systems require efficient detectors able to work in low Signal-to-Noise Ratio (SNR) environments, with little or no information about the signals they are trying to detect. Energy detectors are widely used to perform such blind detection tasks, but quickly reach the so-called SNR wall below which detection becomes impossible Tandra (2005). Cyclostationarity detectors are an interesting alternative to energy detectors, as they exploit hidden periodicities present in man-made signals, but absent in noise. Such detectors use quadratic transformations of the signals to extract the hidden sine-waves. While most of the literature focuses on the second-order transformations of the signals, we investigate the potential of higher-order transformations of the signals. Using the theory of Higher-Order Cyclostationarity (HOCS), we derive a fourth-order detector that performs similarly to the second-order ones to detect linearly modulated signals, at SNR around 0 dB, which may be used if the signals of interest do not exhibit second-order cyclostationarity. More generally this paper reviews the relevant aspects of the cyclostationary and HOCS theory, and shows their potential for spectrum sensing. Copyright © 2010 Julien Renard et al.

Probabilistic co-existence and throughput of cognitive dual-polarized networks

Diversity techniques for cognitive radio networks are important since they enable the primary and secondary terminals to efficiently share the spectral resources in the same location simultaneously. In this paper, we investigate a simple, yet powerful, diversity scheme by exploiting the polarimetric dimension. More precisely, we evaluate a scenario where the cognitive terminals use cross-polarized communications with respect to the primary users. Our approach is network-centric, i.e., performance of the proposed dual-polarized system is investigated in terms of link throughput in the primary and the secondary networks. In order to carry out this analysis, we impose a probabilistic co-existence constraint derived from an information-theoretic approach, i.e., we enforce a guaranteed capacity for a primary terminal for a high fraction of time. Improvements brought about by the use of our scheme are demonstrated analytically and through simulations. In particular, the main simulation parameters are extracted from a measurement campaign dedicated to characterization of indoor-to-indoor and outdoor-to-indoor polarization behaviors. Our results suggest that the polarimetric dimension represents a remarkable opportunity, yet easily implementable, in the context of cognitive radio networks.

A comprehensive channel model for UWB multi-sensor multi-antenna body area networks

Body area networks consist of a number of biological sensors communicating over the air with a central sink placed in close proximity of the human body. A promising solution is to use multisensor multiantenna ultrawideband architecture; each sensor carries one antenna, while the central sink supports an antenna array. In this paper, a complete analytical channel model has been developed for the on-body diffracted waves mechanism. It builds on the existing IEEE 802.15.4a standard channel model and offers an innovative space-time correlation model.

Cross-layering between physical layer, medium access control, and routing in wireless ad-hoc networks

Routing is a key issue in wireless ad-hoc networks. The goal of an efficient routing strategy is to set up routes so that the overall quality of communications will be the best possible. While the Open Systems Interconnection (OSI) reference model advocates for a clear separation of routing, access, and physical layers, in this paper we show that in scenarios with strongly faded communications, cross-layer interactions have to be carefully considered. More precisely, we compare the performance of the Ad-hoc On-demand Distance Vector (AODV) routing algorithm with that of one of its physical layer-oriented variants, denoted as AODVφ. It will be clearly shown that no single routing strategy is always optimal and that an intelligent information fusion at the Medium Access Control (MAC) level can be very beneficial. Copyright © 2012 Inderscience Enterprises Ltd.

Coupled reverberation chambers for emulating MIMO channels

This article describes a new experimental set up for emulating MIMO channels, based on two mode stirred reverberation chambers (MSRC), coupled together with a waveguide. This guide allows one to control the order of the channel diversity, the chambers generating a Rayleigh environment. This set up could thus be used to perform tests of MIMO communication systems in perfectly defined environments and thus under reproducible conditions. After a brief recall of the advantages and drawbacks of using a single reverberation chamber, we describe the theoretical approach and the experimental results for the analysis of two coupled chambers. © 2009 Académie des sciences.

Polarization measurements and modeling in indoor NLOS environments

Cross-polarized antenna systems are an attractive way to reduce equipment size while maintaining low interantenna correlation. In this paper, the polarization behaviour of indoor channels is investigated. A measurement campaign has been conducted at 3.6 GHz for a dual-polarized transmitter and a tri-polarized receiver in a non-Line-of-Sight (NLOS) scenario. The spatial and delay characteristics are extracted using a pertap beamforming algorithm. Distinct paths are isolated and the polarization of each wave is expressed in terms of its spherical components. The cross-polarization discrimination (XPD) of the wave is investigated as a function of its physical propagation parameters. The XPD of the wave is shown to be sensitive to spatial characteristics, while being insensitive to delay.

Multi-polarized channel statistics for outdoorto- indoor and indoor-to-indoor channels

Compared to classical spatial MIMO wireless systems, cross-polarized MIMO systems are an interesting way to reduce equipment size while reducing the inter-antenna correlation. Cross-Polar Discrimination (XPD) and Co-Polar Ratio (CPR) are two important parameters describing multi-polarized channels. In this paper, the behavior of these parameters is investigated for different observation scales. A measurement campaign has been performed in both Outdoor-to-Indoor and Indoor-to-Indoor scenarios, at a frequency of 3.5GHz. Small-scale variations of XPD and CPR are analyzed in different spatial positions. The distance-related and large-scale variations of XPD and CPR are also investigated and a model is deduced.

2009

Multipolarized MIMO channel characteristics

MIMO technologies enable high communication data rates, but suffer from the large antenna spacing that is required to achieve sufficiently low inter-antenna correlation. Cross-polarized antenna systems resolve this problem by using perpendicular antennas. Correlation is reduced while keeping antennas co-located. Inter-antenna correlation and cross-polar discrimination (XPD) are two fundamental parameters of these polarized antenna systems. This paper proposes an analytical channel model, from which closed-form solutions for the correlation coefficient and the XPD are deduced. The environment is supposed to have a truncated Laplacian power azimuth spectrum that is widely used in standardization bodies. The receiving di- or tri-pole antenna can have random orientation. The correlation and the XPD show to be highly sensitive to receiver orientation, azimuth spread and environment depolarization behavior. Measurements have been conducted at 3.5 GHz to validate the solution obtained. Good agreement is achieved when comparing theoretical curves and experimental results for different receiver orientations, both for the correlation coefficient and the XPD. © 2009 IEEE.

Small-scale variations of cross polar discrimination in ricean fading channels

Analytical angular correlation function in a mode-stirred reverberation chamber

Cross-layering between physical layer and routing in wireless ad-hoc networks

Routing is a key issue in wireless ad-hoc networks. The goal of an efficient routing strategy is to set up routes so that the overall quality of communications will be the best possible. While the Open Systems Interconnection (OSI) reference model advocates for a clear separation of routing, access, and physical layers, in this paper we show that in scenarios with faded communications, cross-layer interactions have to be carefully considered. More precisely, we compare the performance of the Ad-hoc On-demand Distance Vector (AODV) routing algorithm with that of one of its physical layer-oriented variants, denoted as AODVφ . It will be clearly shown that no single routing strategy is always optimal and that an intelligent adaptation should be performed. © 2009 Springer-Verlag Berlin Heidelberg.

2008

Delay spread and coherence bandwidth in a reverberation chamber

2007

On-body propagation velocity estimation using ultra-wideband frequency-domain spatial correlation analyses

2006

Statistical study of NLOS-mutlipath in urban canyons

Ultra wideband channel model for communication around the human body

Using ultra-wideband (UWB) wireless sensors placed on a person to continuously monitor health information is a promising new application. However, there are currently no detailed models describing the UWB radio channel around the human body making it difficult to design a suitable communication system. To address this problem, we have measured radio propagation around the body in a typical indoor environment and incorporated these results into a simple model. We then implemented this model on a computer and compared experimental data with the simulation results. This paper proposes a simple statistical channel model and a practical implementation useful for evaluating UWB body area communication systems. © 2006 IEEE.

An ultra wideband body area propagation channel model

Body worn wireless sensors for monitoring health information is a promising new application. In developing these sensors, a communication channel model is essential. However, there are currently few measurements or models describing propagation around the body. To address this problem, we have measured electromagnetic waves near the torso and derived relevant statistics. We find that components diffracting around the body are well modeled using correlated log normal variables, and a Nakagami-m distribution can be used to incorporate the influence of arm motions. We have implement this model and evaluated it in terms of important communication metrics. This paper describes body area propagation statistics and proposes a suitable computer model implementation. © 2006 IEEE.

Electromagnetic fields estimation using spatial statistics

The spatial statistics formalism is applied to electromagnetic fields analysis. Fields are considered as realizations of a random function. Their spatial structure is studied by a method known as variographic analysis. To infer unknown values of the fields, an interpolation method called kriging is then used. It is shown how kriging can be performed on experimental or numerical data to speed up the fields estimation process.

Statistical study of NLOS-multipath in urban canyons

2005

Modeling of NLOS-multipath in urban canyons for GNSS applications

WLAN deployment strategy for best indoor performance

2004

Statistical response of antennas under uncorrelated plane wave spectrum illumination

Electromagnetic wave propagation and coupling

Channel model for wireless communication around the human body

Electromagnetic coupling to transmission lines under complex illumination

A wavelet-based approach for disturbance line identification in printed circuit boards

Disturbance lines identification in printed circuit boards by means of wavelets

Etude des performances des réseaux WLAN en milieu indoor

2003

A volume/surface potential formulation of the method of moments applied to electromagnetic scattering

Spatial correlation functions for fields in three-dimensional rayleigh channels

Starting from a continuous plane-wave representation of the electric and magnetic fields, spatial auto- and cross-correlation functions for field components and their modulus are derived in the three-dimensional Rayleigh channel case. It is shown that existing results, generally relying on two-dimensional or isotropic models, can significantly differ from those obtained thanks to a three-dimensional approach.

Spatial correlation functions for fields in three-dimensional rayleigh channels -abstract

Starting from a continuous plane-wave representation of the electric and magnetic fields, spatial auto- and cross-correlation functions for field components and their modulus are derived in the three-dimensional Rayleigh channel case. It is shown that existing results, generally relying on two-dimensional or isotropic models, can significantly difffer from those obtained thanks to a three-dimensional approach. © Journal of electromagnetic waves and applications. All Rights reserved.

2002

Indoor propagation analysis for broadband personal area networks

2001

A potential integral equation method for electromagnetic scattering by penetrable bodies

A method for computing the electromagnetic scattering by general inhomogeneous penetrable bodies is presented. The method is based on the volume equivalence principle and it uses the electromagnetic potentials as unknowns. The resulting coupled integral equations system is solved by the method of moments in combination with cubical and curvilinear meshes in the special case of purely dielectric scatterers. To show the accuracy of the method, numerical results of the transmitted and of the scattered fields are compared with existing analytical and experimental results.

2000

An extrapolated version of the Gordon's interpolation applied to the method of moments

The use of the transfinite interpolation in the method of moments applied to electromagnetic scattering by dielectric cylinders

The method of moments (MoM) solution of electromagnetic scattering presents two major numerical difficulties: the number of unknowns and the computation time necessary to calculate the matrix elements. To circumvent these problems, a MoM using the transfinite interpolation and a reduced integration scheme is presented here. The so-called h and p versions of the new method are applied to the scattering of an electromagnetic wave by an infinite dielectric cylinder (TM case) in the Richmond's formulation. The transfinite and classical methods are compared in terms of the convergence rates of the radar cross section and of the total electric field inside the dielectric. The results confirm the superiority of the new schemes as predicted by the theory.

The use of transfinite elements in the method of moments applied to electromagnetic scattering by dielectrics cylinders

Simulating Mimo systems in reverberation chambers

The use of tansfinite elements in the methods of moments applied to electromagnetic scattering by dielectric cylinders

1999

Use of transfinite elements in the methods of moments applied to electromagnetic scattering by dielectric cylinders

Many electomagnetic applications involve the analysis of the scattering of an electromagnetic wave by a dielectric body. This kind of problem is often carried out using the method of Moments (MoM) applied to volume or surface integral equations. Unfortunately, this method seems unreliable in certain cases. In this paper, to evaluate this problem, we developed a two-dimensional MoM based on the volume-surface integral equation and employing the transfinite elements theory which provides a powerful tool to study separately the effects of the geometrical modeling and those of the interpolation schemes for all the methods (cell shapes and interpolation schemes) encountered in the conventional MoM.

1998

Why are some patients with onychomycosis still not responding to the newer antifungal agents ?

Communications publiées lors de congrès ou colloques nationaux et internationaux

A paraître

Outdoor group counting based on micro-Doppler signatures obtained with a 77GHz FMCW radar

In numerous mass gathering settings along withdaily commutes, maintaining an accurate count of individualsis imperative. Radar systems, known for their cost-effectivenessand low energy consumption, facilitate discreet monitoring acrossvarious applications. In this work, data was collected via a77GHz frequency-modulated continuous wave radar (FMCW)in an outdoor pedestrian street. We leverage the unique gaitmodel of each individual, which results in a distinct instantaneousvelocity pattern as a function of time to be able to countpeople. Therefore, we analyze and process our data in thetime-frequency domain to generate the so called micro-Dopplersignatures (MDS). Then, these MDS are fed to a ConvolutionalNeural Network (CNN) to classify groups of different sizes.Furthermore, due to the lack of significant amount of data,the CNN was firstly trained with synthetic data and later onwith the measurement data, to increase the system performance.The proposed system overcomes the limitations of existingcamera-based people counting techniques such as being affectedby lighting conditions and distinctly from other radar relatedwork, targets an outdoor scenario.

An Improved PUF-Based Privacy-Preserving IoT Protocol for Cloud Storage

The IoT technology allows many types of personal data to be measured by many kinds of devices and sensors, and to be sent over the Internet for various applications. However, this data transmission has to be secure and the privacy of the users should ideally be preserved. In this work, we propose a SRAM PUF-based privacy-preserving IoT protocol for cloud storage based on an existing protocol from the literature. Proposals are made to increase the supply chain security of the PUF construction used by a device, to extend the secure lifetime of this device by increasing the number of keys it may generate and avoiding reboot-based attacks, and to allow a PUF construction to be used for different applications. These proposals only require changes on the device enrollment and on the master key generation procedure, leaving the PUF construction, the fuzzy extractor construction and the cryptographic key derivation unchanged. Benefits and limitations of this new protocol are evaluated and security objectives achieved with these proposals are analyzed.

2024

People flow estimation with a Wi-Fi-based passive radar

We investigate crowd monitoring with a Wi-Fi-based passive radar in the context of large events with multiple areas connected by alleys or streets, such as events in city centres. We derive an average people flow expression in people per second, away from a radar and towards it, and propose aprocessing scheme to estimate this flow with a Wi-Fi-based passive radar. It relies on splitting the range-Doppler map (RDM) in its negative and positive Doppler speeds parts, corresponding to the flow away from the radar and towards it respectively, and combining people counting and average people's speed estimation on each RDM part. A flow estimation error metric is introduced, and our proposed flow estimation framework isexperimentally validated with a Wi-Fi-based passive radar setup using High-Efficiency Long Training Fields from the 802.11ax standard and built with Universal Software Radio Peripherals. A successful flow estimation is achieved, by obtaining a flow estimation error significantly lower than the true flow averaged on all measurements.

2023

Frequency diverse array spatial data focusing

This paper presents the first-ever experimental validation of both spatial data focusing (SDF) and time-invariant frequency diverse array (FDA) range-angle-based focusing, in both free space and multipath environments. In particular, a hybrid FDA-based SDF (FDA-SDF) approach is considered for spatially confined broadcasting, i.e. geocasting. First, the base FDA-SDF free space system model is reviewed. Next, a novel OFDM-based FDA-SDF system model is introduced to ensure robust operation in multipath channels. The schemes are validated, respectively, in an anechoic chamber and outdoor measurement setup using software defined radios. Results confirm FDA-SDF's anticipated supreme spatial precision: a 0.9 m × 4.0° range-azimuth geocast delivery zone is generated by a 4-antenna array in free space. Additionally, they illustrate that OFDM-based FDA-SDF provides all necessary performance improvements for practical operation in outdoor multipath environments. Most notably, FDA-SDF is shown to overcome the time-variance flaw of conventional FDA.

Group counting using micro-doppler signatures from a 77GHz FMCW radar

People counting and detection technologies have shown great versatility in various scenarios and have become an important tool for event organizers and city planners to optimize their operations. This paper presents a novel approach for people counting using Micro-Doppler Signatures (MDS) extracted from a Frequency-Modulated Continuous-Wave (FMCW) radar operating at 77GHz. The system utilizes the unique gait model of each individual, which results in a distinct instantaneous velocity over time, to generate the MDS that are later used to classify groups of different sizes with a Convolutional Neural Network (CNN). Those results are compared with using existing CNNs for image classification, in a transferred learning approach. The proposed system overcomes the limitations of existing camera-based people counting techniques such as the need for a clear line of sight and being affected by lighting conditions.

Decentralized group authentication with membership verification in islanded smart grids

Smart grids have a growing role in today's society. Therefore, it is crucial to ensure their proper functioning at all time. While research already investigated the islanding of the electrical side of the smart grids, we look at this problem from a network security perspective, this network being very decentralized and highly communicant. To prevent the loss communication and a possible blackout of the sub-grid through islanding, we used a combination of the group authentication protocol and the lightweight verifiable secret sharing to propose an alternative authentication method. This method allows the different nodes to build trust as well as to identify and exclude malicious nodes trying to either join or prevent the group authentication. We also discuss the main security properties of our protocol and its limitations.

Group counting using micro-doppler signatures from a 77GHz FMCW radar

People counting and detection technologies haveshown great versatility in various scnearios and have become animportant tool for event organizers and city planners to optimizetheir operations. This paper presents a novel approach for people counting using Micro-Doppler Signatures (MDS) extractedfrom a Frequency-Modulated Continuous-Wave (FMCW) radaroperating at 77GHz. The system utilizes the unique gait modelof each individual, which results in a distinct MDS, to classifygroups of different sizes using a Convolutional Neural Network(CNN). The proposed system overcomes the limitations of existingpeople counting techniques such as the need for a clear line ofsight and being affected by lighting conditions.

Crowd counting model training with the method of moments in electromagnetics

Passive Wi-Fi-based radars with 802.11ax MU-MIMO signals

2022

Frequency diverse array spatial data focusing for high precision range-angle-based geocasting

A unified frequency diverse array (FDA) and spatialdata focusing (SDF) system, or FDA-SDF, is proposed as a novelapproach to perform spatially confined broadcasting of information, i.e. geocasting. It is shown that SDF processing exploitsFDA range-angle-dependency more effectively than conventionalpower focusing implementations, resulting in improved spatialfocusing precision and reduced array size. Additionally, thetime-variance flaw in conventional FDAs is addressed and mitigated by introducing a generalized baseband FDA model. Thispaper describes the FDA-SDF system model in free space, including dedicated SDF precoding, beamsteering, and equalization,exploiting FDA multi-frequency transmission for 2-dimensionalrange-angle-based time-invariant geocasting. Simulations of theFDA-SDF system illustrate compatibility with conventional FDAfrequency offset schemes and highlight degrees of freedom forgeocast delivery zone manipulation. Finally, FDA-SDF's superiorspatial precision is demonstrated: a 3-antenna FDA-SDF setupmatches the radial and angular precision of a conventional FDAusing, respectively, 13 and 23 antennas.

Geocasting sans fil basé sur la focalisation spatiale de données en OFDM

Impact of inter-body scattering on people counting with Wi-Fi sensing

We investigate the interactions between human bodies exposed to an incident electric field from a sensing-enabled Wi-Fi access point, to assess how it could affect people counting in the framework of Wi-Fi sensing. We model people with dieletric cylindrical shells with a thickness slightly higher than the electromagnetic skin depth. The electric field scattered by people is computed using the two-dimensional method of moments for electromagnetic scattering, accelerated using an iterative GMRES solver with Adaptive Cross Approximation and a block-Jacobi preconditionner. That scattered field is used to derive channel transfer functions that are combined to obtain a range-Doppler map. The presence of several ghost targets even in simple cases is highlighted, and could hinder people counting. When two people are aligned in front of the sensing-enabled Wi-Fi access point, the first blocking the line-of-sight of the second, it is shown that the field passing through the first person and reflected on the second person is sufficiently strong to detect it. We quantify the corresponding attenuation.

Impact of MU-MIMO on passive Wi-Fi radars: threat or opportunity?

Passive Radars are devices that make use of existingcommunication signals for wireless channel sensing. On the otherhand, Wi-Fi has become the main gateway that connects devicesto the internet. Recently, IEEE established the WLAN SensingTask Group whose purpose is to study the feasibility of Wi-Fi-based environment sensing, where some of the technologiesshare similarities with Passive Radars. In the meantime, Multi-User Multiple-Input Multiple-Output (MU-MIMO) technologyis introduced to the Wi-Fi standard. It is designed to improvethe spatial efficiency of the wireless channel by simultaneouslytransmitting directive Wi-Fi signals to users. This paper aimsat quantifying the impact of MU-MIMO signals on Passive Wi-Fi-based Radar-like sensing. First, based on the position of theclient devices and the channel geometry, the radiation pattern ofthe AP is derived. While the wireless channel is illuminated bydirective radio waves, the magnitude of the Poynting vector isobtained at a local point target, which then reflects the incidentradio waves. Finally, the signal power seen by a sensing deviceis computed under the influence of a multipath channel. Ournumerical analyses focus on an urban street, and we show thatMU-MIMO can be seen as; i) an opportunity, since the vicinityof client devices are better illuminated, or ii) a threat, since theremaining parts of the street do not receive sufficient amount ofpower for channel sensing applications.

Joint rate and power density analysis in Manhattan environments: (a comparison of) stochastic geometry and ray-tracing approaches

The proposed work tries to quantify how relevant it is to use a deterministic channel model likeray tracing at a network deployment level in a Manhattan-like environment. More precisely, the goal isto compare it with simplier and more computationally efficient models to see if similar results can beobtained at a lower cost. In the framework of the analysis, ray tracing is thus compared to a stochasticgeometry-based model in terms of coverage probability and exposure at a centric user for which we wereable to derive semi-closed form expressions. In addition, a good lower bound for the joint coverage exposure distibution was found. In order to easily mimic the propagation mechanisms implementedin the UCLouvain RT software and enable fair comparison, the Berg recursive model was consideredas channel model. Finally, the analytical expressions were further enhanced to take into account theantenna height as well as the line-of-sight probability in the typical street and to distinguish a typicaluser located at a crossroad from a typical user located inside a street.

Environment mapping with 28 GHz beamsteering transceivers: hardware architecture and preliminary results

The evolution of radio communication systemstowards millimeter-wave (mm-wave) frequencies allows fornew opportunities in terms of localization and environmentmapping. The increase in bandwidth and size of antennaarrays creates great similarities between 28 GHz communication systems and radar systems. There are severalchallenges to use 28 GHz communication systems forenvironment mapping: 1) it is unclear whether multipathcomponents can be identified with arrays that rely onbeamsteering, 2) the local oscillator (LO) is not sharedbetween the transmitter and the receiver, causing considerable LO frequency offsets, and 3) the high power of theline-of-sight component tends to “blind” the receiver toall other multipath. In this paper, we realize (relatively)low-cost 28 GHz software-defined radio-based transceiversthat use 4×4 antenna arrays. The transceiver architectureis presented, and the setup is used to perform somepreliminary measurements. These first results indicate thatsome amount of multipath components can be recovered,even with limited angular resolution of a 4×4 beamsteeringarray.

Modeling the spatial distributions of macro base stations with homogeneous density: theory and application to real networks

Stochastic geometry is a highly studied fieldin telecommunications as in many other scientific fields.In the last ten years in particular, theoretical knowledgehas evolved a lot, whether for the calculation of metricsto characterize interference, coverage, energy or spectralefficiency, or exposure to electromagnetic fields. Manyspatial point process models have been developed but areoften left aside because of their unfamiliarity, their lackof tractability in favor of the Poisson point process orthe regular lattice, easier to use. This article is intendedto be a short guide presenting a complete and simplemethodology to follow to infer a real stationary macroantenna network using tractable spatial models. The focusis mainly on repulsive point processes and in particular ondeterminantal point processes which are among the mosttractable repulsive point processes. This methodology isapplied on Belgian and French cell towers. The resultsshow that for all stationary distributions in France andBelgium, the best inference model is the β-Ginibre pointprocess.

Detect & Reject for Transferability of Black-box Adversarial Attacks Against Network Intrusion Detection Systems

In the last decade, the use of Machine Learning techniques in anomaly-based intrusion detection systems has seen much success. However, recent studies have shown that Machine learning in general and deep learning specifically are vulnerable to adversarial attacks where the attacker attempts to fool models by supplying deceptive input. Research in computer vision, where this vulnerability was first discovered, has shown that adversarial images designed to fool a specific model can deceive other machine learning models. In this paper, we investigate the transferability of adversarial network traffic against multiple machine learning-based intrusion detection systems. Furthermore, we analyze the robustness of the ensemble intrusion detection system, which is notorious for its better accuracy compared to a single model, against the transferability of adversarial attacks. Finally, we examine Detect & Reject as a defensive mechanism to limit the effect of the transferability property of adversarial network traffic against machine learning-based intrusion detection systems.

Impact of the reliability of ICT systems on power systems with system integrity protection schemes

2021

Self-synchronization based distributed localization of wireless transmitters

In this paper, we introduce a fully distributedlocalization algorithm based on self-synchronization mechanism.The proposed algorithm reaches consensus for the posteriordistribution of the transmitter position at each base station. Toreduce the communication overhead at each iteration, we proposeto represent the state variable matrices of the self-synchronizationmechanism with only four parameters (radial and angularmeans and variances). The performance of the algorithmsis numerically assessed by the mean distance error andmean Kullback-Leibler divergence. Finally, we show throughMonte-Carlo simulations that our approach gets very close to thedirect-centralized-localization performance after a few iterations.

A statistical estimation of 5G massive MIMO's exposure using stochastic geometry

This paper aims to estimate the exposure in 5G massiveMIMO networks using a stochastic geometric approach.The paper investigates the effect of beamforming, and theeffect of multi-user massive MIMO on the exposure of a5G network. The massive MIMO antenna patterndistribution is obtained by fitting the radiation patternobtained by running a large amount of channel simulationson NYUSIM. The distribution is then implemented into ananalytical framework based on stochastic geometry, so wecan obtain a close form expression of the downlinkexposure.

Near-field occupational exposure in FM transmission pylons

This paper provides a new method to generalizeelectromagnetic field exposure via surrogate modeling.The study focuses on linking maximum local specificabsorption rate and field intensity in FM transmissiontowers.

Semi-empirical model of global exposure using stochastic geometry

Exposure to electromagnetic fields due to cellularnetworks in an urban environment is studied using stochasticgeometry. We describe a simple but functional and realisticsemi-empirical model based on the modeling of base stationpatterns as Poisson Point Processes and applied to two Brusselsmunicipalities. Using this model, a study of the impact of basestation densification is performed according to two theoreticalscenarios. From simple assumptions, it is concluded that globalexposure is expected to remain approximately constant in thecase of intelligent network evolution involving the densificationof macro cells and the addition of a network of low-power smallcells.

Anonymous Fair Auction on Blockchain

Adversarial Training for Deep Learning-based Intrusion Detection Systems

Nowadays, Deep Neural Networks (DNNs) report state-of-the-art results in many machine learning areas, including intrusion detection. Nevertheless, recent studies in computer vision have shown that DNNs can be vulnerable to adversarial attacks that are capable of deceiving them into misclassification by injecting specially crafted data. In security-critical areas, such attacks can cause serious damage; therefore, in this paper, we examine the effect of adversarial attacks on deep learning-based intrusion detection. In addition, we investigate the effectiveness of adversarial training as a defense against such attacks. Experimental results show that with sufficient distortion, adversarial examples are able to mislead the detector and that the use of adversarial training can improve the robustness of intrusion detection.

Iterative ToA-based localization of wireless transmitters using Dirichlet-Kernel-based range representation

Iterative localization is currently seen as an attractive solution to localize a transmitter in a cellular network. It has been shown that, by iterating between a range estimation step and a multi-lateration step, it is possible to refine the estimation in the first step, where only local information is used at iteration one. The iterative approach gets close to the performance of direct localization; nevertheless, it does not seem to converge to the direct localization performance for medium and low signal-to-noise-ratio values, due to the fact that it still suffers from loss of information due to projections and data representation. In this work, we propose to approximate the range log-likelihood at the base station with a Dirichlet kernel and to perform all the processing in a common xy-domain so that projections are no longer needed. We numerically show that our approach brings significant performance gains as compared to the time-of-arrival based iterative position estimation algorithm, getting really close to the performance of direct localization.

A stochastic geometry approach to EMF exposure modeling

Downlink exposuretoelectromagneticfields(EMF)inurbanenvironmentsisstudiedusingthestochastic geometry(SG)framework.A2DPoissonpointprocess(PPP)isassumedforthebasestation (BS)distributionandtheheightofthebasestationsistakenintoaccountinthepropagationmodel. Fromsimpleassumptions,mathematicalexpressionsofstatisticsofexposurearederivedfromthemodel.Theerrormadebytakingareducednumberofbasestations,insteadofthewholeset ofbasestations,isquantified.Asensitivityanalysisisproposedinordertoevaluatetheimpactof themodelparametersonthestatisticsofexposure.ThemethodisthenappliedtotwoBrusselsmunicipalities, inBelgium,fortheUMTS2100andLTE2600frequencybands.Itisshownthattheproposedmodelfitsexperimentalvalues,pavingthewaytoanewmethodologytoassessgeneralpublic exposuretoelectromagneticfields.

High resolution 802.11ax-based passive radar for human movement monitoring

Passive Radars, based on the emerging 802.11ax Wi-Fi standard, are considered for indoor human movement detection. Since the Wi-Fi access points transmit multiple frames in bursts, the FFT-based Doppler estimation techniques fail due to the limited duration of the bursts. Therefore, super resolution techniques are examined for low Doppler frequency estimation based on a small number of frames. An algorithm is proposed which uses ESPRIT in an iterative fashion. The performance of the algorithm is numerically analysed, compared to theoretical bounds, and validated experimentally.

2020

A novel Network-on-Chip security algorithm for tolerating Byzantine faults

Efficient Intrusion Detection Using Evidence Theory

Intrusion Detection Systems (IDS) are now an essential element when it comes to securing computers and networks. Despite the huge research efforts done in the field, handling sources' reliability remains an open issue. To address this problem, this paper proposes a novel contextual discounting method based on sources' reliability and their distinguishing ability between normal and abnormal behavior. Dempster-Shafer theory, a general framework for reasoning under uncertainty, is used to construct an evidential classifier. The NSL-KDD dataset, a significantly revised and improved version of the existing KDDCUP'99 dataset, provides the basis for assessing the performance of our new detection approach. While giving comparable results on the KDDTest+ dataset, our approach outperformed some other state-of-the-art methods on the KDDTest-21 dataset which is more challenging.

Towards NoC Protection of HT-Greyhole Attack

OFDM-based spatial data focusing in multipath channels: evaluation and improvements

Wireless geocasting, i.e. wirelessly broadcasting information towards confined spatial locations, requires spatial focusing capabilities from base stations. By focusing both in the angular and radial domains, OFDM-based Spatial Data Focusing (OFDM-SDF) allows for 2-dimensional geocasting, providing a great increase in flexibility for geocasting compared to T-SDF and beamforming, both limited to angular focusing only. However, just as T-SDF, OFDM-SDF suffers from a strong sensitivity to mulipaths, harshly decreasing its performance in scenarios other than free space. This TD re-evaluates the free space OFDM-SDF system model by exploring the additional challenges when applying SDF in multipath channels and proposes improvements to the OFDM-SDF scheme to increase its robustness in non free space environments.

Experimental implementation of a multi-antenna 802.11ax-based passive bistatic radar for human target detection

We investigate and experimentally demonstrate amulti-antenna Wi-Fi-based passive bistatic radar (PBR) to performindoor range-Doppler-angle detection of human targets.The latest Wi-Fi standard, 802.11ax, is considered as signalof opportunity, enabling a high range resolution suited forindoor detection. We build a Uniform-Linear-Array (ULA) usingUniversal Software Radio Peripherals (USRPs) as PBR receiver(RX), and present a novel calibration method to compensate thehardware-induced phase shift difference between the signals fromthe different antennas of the ULA. To avoid data associationproblems and limitations on the number of detectable targetsfor the Direction-of-Arrival (DoA) estimation, we demonstratetheoretically the possibility to use only the cell of the target inthe radar range-Doppler maps (RDMs) across antennas as inputto the Multiple Signal Classification (MUSIC) algorithm, ratherthan using the raw received signals. We validate the experimentalsetup and the processing by detecting the range, speed and DoAof two human targets moving in a room.

Stochastic geometry modeling of EMF exposure due to cellular networks in urban environments

Stochastic geometry is used to model global exposureto Electro-Magnetic Fields (EMF) in urban environments. Themethod is applied to two distinct urban environments: the historiccity center of Brussels, Belgium, and the 14th district of Paris,France. It is shown that the proposed model fits experimentalvalues, paving the way to a new methodology to assess generalpublic exposure to EMF.

OFDM-based spatial data focusing for high resolution 2-dimensional wireless geocasting

An OFDM-based Spatial Data Focusing (OFDM-SDF) approach is proposed as an improvement over standard Time-based Spatial Data Focusing (T-SDF) as a means of wirelessly broadcasting information towards confined spatial locations, i.e. wireless geocasting. It is shown that this approach allows for 2-dimensional focusing, hence leading to far greater flexibility in terms of geocasting scenarios compared to T-SDF and beamforming, both limited to angular focusing only. This increased flexibility does not come at any trade-off costs in terms of spatial selectivity, and hence, just as T-SDF, OFDM-SDF is shown to establish a considerable increase in attainable geocasting accuracy when compared to traditional power focusing methods. This paper describes the free space OFDM-SDF system model for uniform linear antenna arrays, including beamsteering and sidelobe mitigation techniques. Based on simulations, the performance of OFDM-SDF is compared to both T-SDF, as well as classical beamforming.

Impact of realistic propagation conditions on reciprocity-based secret-key capacity

Secret-key generation exploiting the channel reciprocitybetween two legitimate parties is an interesting alternativesolution to cryptographic primitives for key distribution inwireless systems as it does not rely on an access infrastructureand provides information-theoretic security. Many works in theliterature assume that the eavesdropper gets no side informationabout the key from her observations provided that: (i) it is spacedmore than a wavelength away from a legitimate party and (ii) thechannel is rich enough in scattering. In this paper, we show thatthis condition is not always verified under realistic propagationconditions and we study the resulting secret-key capacity.

Outage probability analysis of the relay network with correlated relaying channels

A relay network can provide the extended linkcapacity and coverage thanks to its good spatial diversity.In order to analyze the relay network performance, mostof the works in literature assume the independent relayingchannels. In practice, the received signals experience thecommon scatterers, hence the correlated relaying channelsshould be considered. In this paper, we first derive anovel and accurate probability density function (PDF)of a modulus of the sum of products of two correlatedzero-mean complex Gaussian random variables (RVs),which is useful for the statistical analysis of the cascadedrelaying fading channels. Based on this result, we secondlyinvestigate the received signal-to-noise ratio (SNR) outageprobability of a relay network in the presence of correlatedrelaying channels. It is found that the correlation magnitudeis more important than the correlation phase for theanalysis of power-based signal-detection of relay networks.Numerical simulations have been carried out to confirmthe correctness of the derivation.

Performance analysis of matched-filter precoded MISO-OFDM systems in the presence of imperfect CSI

Multiple-antenna technologies provide a goodspatial diversity gain for emerging communication systems.In combination to the orthogonal frequency division multiplexing(OFDM) modulation, a precoding system can beeasily implemented and efficient to combat the effect offading channels. However, the precoding system requiresa perfect knowledge of the channel, which is not usuallyhold in practical cases. In this paper, we investigate theimpact of the imperfect channel state information (CSI)on the downlink performance of multiple-input singleoutput(MISO) OFDM systems using a matched-filter (MF)precoder. Particularly, the exact mean-square-error (MSE)expression of the equalized received signal of the MFprecoding system is derived. Numerical simulations withRayleigh fading channels are carried out to validate theanalysis. The results show that the imperfect CSI-basedprecoder causes a MSE plateau compared to the ideal caseof using the perfect CSI.

Anchor selection in angle-of-arrival estimation-based localization using polynomial chaos expansions

Angle-of-arrival (AoA) estimation-based localizationsystems are a promising technology in the context of Internetof-Things. The system considered is a densely deployed set ofanchors equipped with arrays of antennas able to measure theAoA of the signal emitted by the device to be located. Naturally,the AoA measurements are prone to uncertainties due to noise,channel conditions and uncertainties on the anchors placementand orientations. In this work, a method based on PolynomialChaos Expansions is proposed to perform anchor selection inorder to enhance the precision of the positioning. An experimentalsetup with six anchors is implemented to evaluate theperformance of the proposed method. The experimental resultsdemonstrate that by applying our anchor selection method, theperformance of the localization system improves.

Experimental demonstration of AoA estimation uncertainty for IoT sensor networks

In practice, the subspace-based algorithmssuch as Multiple Signal Classification (MUSIC) suffer fromsensitivity to antenna-array response errors and thereforethey require the assessment of the calibration gain andphase perturbations. This paper evaluates experimentallythe accuracy of Angle-of-Arrival (AoA) estimation based onthe MUSIC algorithm only coming from these perturbationsin the context of Internet-of-Thing (IoT) applications.First of all, a new Over-the-Air (OTA) calibration method isproposed and gain and phase uncertainties are investigated.The impact of these uncertainties on the accuracy ofAoA estimation is then studied and compared with thetheoretical analysis. The experimental results show that thecalibration errors coming from hardware imperfections cancause some degrees of uncertainty in AoA estimation.

Impact of interference on OFDM based radars

The goal of this work is to identify the possibledegradations on a Wi-Fi based Passive Radar in the presence ofan interferer. We assume that the signal-of-opportunity and theinterference are 802.11ax compliant. The mathematical modelderived for the interference shows that in a synchronized case,the interference may yield ghost targets. When a more occasionalinterference scenario is considered, the range/Doppler Map accuracydecreases significantly. Furthermore, numerical results areprovided to quantify certain effects of OFDM radar interferenceon range/Doppler Maps.

Estimation of network densification impact on EMF exposure using stochastic geometry

EMF exposure in Brussels, Belgium, is studied in the framework of stochastic geometry. Poisson point processes withrealistic intensity are randomly generated to model base stations. Electric field level at random location is deduced froma simple path loss law. Statistical results are compared to experimental data's in order to optimize the model. Theimpact of network densification is analyzed and probabilities of exceeding exposure thresholds are derived.

Sécurité à la couche physique pour une communication SISO MROF dans le domaine fréquentiel avec renversement temporel

Ce papier présente une technique permettant de sécuriser une communication à la couche physique. Un précodage en renversement temporel implémenté dans le domaine fréquentiel utilisant un multiplexage par répartition orthogonale de la fréquence est considéré. Pour maximiser le taux de sécurité, le design d'un ajout de bruit artificiel est proposé. Ce nouveau schéma de communication assure une sécurité de communication vers un récepteur légitime tout en dégradant les performances de réception de la donnée vers un nœud espion. Le nœud espion est supposé passif à l'émetteur. L'effet du canal de propagation est également investigué.

Physical layer security in frequency-domain time-reversal SISO OFDM communication

A frequency domain (FD) time-reversal (TR) pre-coder is proposed to perform physical layer security (PLS) in single-input single-output (SISO) system using orthogonal frequency-division multiplexing (OFDM). To maximize the secrecy of the communication, the design of an artificial noise (AN) signal well-suited to the proposed FD TR-based OFDM SISO system is derived. This new scheme guarantees the secrecy of a communication toward a legitimate user when the channel state information (CSI) of a potential eavesdropper is not known. In particular, we derive an AN signal that does not corrupt the data transmission to the legitimate receiver but degrades the decoding performance of the eavesdropper. A closed-form approximation of the AN energy to inject is defined in order to maximize the secrecy rate (SR) of the communication. Simulation results are presented to demonstrate the security performance of the proposed secure FD TR SISO OFDM system.

EMF exposure modelling using stochastic geometry

2019

Spatial data focusing using time and IQ resources for wireless geocasting

Spatial Data Focusing (SDF) is introduced as a novel technique that allows wireless broadcasting of information towards specific spatial locations only. It is shown that this approach allows one to target geographic areas more accurately than traditional power focusing methods, using limited equipment at the transmitter. This paper describes the SDF system model for linear arrays, based on simple modulation techniques and transmitter architectures, both in pure line-of-sight and multipath environments. In particular, the robustness of the scheme is proven for over-the-ground propagation environments. Theoretic results are illustrated by simulations, confirming the increased spatial selectivity of SDF and showing the influence of various design parameters of the scheme on the resulting beam.

UAV mobility model for dynamic UAV-to-car communications

Performance analysis and mitigation method for I/Q imbalance-impaired time reversal-based indoor positioning systems

Time reversal-based indoor positioning system(TRIPS) is a promising technology for the centimeteraccuracyindoor positioning, since it exploits the richmultipath propagation in indoor environments as a specificsignature for each location. In TRIPS, a database is firstconstructed via channel probing. Well-calibrated devicesare usually assumed in this process, i.e., no hardwareimpairments. However, a low cost terminal to be located,whose typical impairment is the I/Q imbalance (IQI) at thefront-end transmitter, can significantly influence the TRIPSperformance. More specifically, IQI creates an interferenceimage of the signal that reduces the metric value used inTRIPS and hence decreases the localization accuracy. Inthis paper, we analytically investigate the impact of the IQIon the metric of TRIPS. A closed-form approximation ofthe localization metric inherent to the IQI is derived. Inorder to improve the TRIPS performance, an effective IQImitigation method is proposed. Numerical simulations arecarried out to validate the derived analytical expressionunder the IQI impact and the proposed compensationmethod.

Near-field relationship between maximum local SAR and maximum field intensity in FM frequencies

Iterative localization method using AoA for IoT sensor networks

Internet of Things (IoT) integrates numerous technologies to obtain the location information of the sensors in various ways. The most common localization methods are based on measuring a location dependent parameter such as Received Signal Strength (RSS) or Angle of Arrival (AoA). Then the measured parameters are used to estimate the sensor location by using a multilateration algorithm. AoA estimation can provide good localization accuracy for narrowband array-based systems. The research has drawn considerable attention in the literature and numerous methods have been proposed to improve the localization accuracy. The two-step method suffers from information loss from the received signals when the estimation of the parameters is communicated to the multilateration step. In this paper, we propose a new localization algorithm which iterates between AoA estimation and multilateration steps to refine the position estimate. We develop a localization scenario for the assessment and validation of the algorithm in Bluetooth Low Energy (BLE) sensor networks. Simulation results show that the proposed solution achieves a better localization accuracy when compared to the common two-step and achieving this after only a few iterations. Additionally, our method comes very close to the performance of the position estimation relying directly on the received signal, known as Direct Position Estimation (DPE), while reducing its complexity.

Spatial data focusing, implementation using spread spectrum modulation techniques

Focalisation spatiale de donnée via une approche temporelle

Identity-based TLS for cloud of chips

Spatial data focusing using time resources

2018

ToA-based iterative localization in rich multipath channels

Iterative localization is arising as a promising solution to determine the position of a mobile station in a cellular network. We recently showed that in a perfect line-of-sight environment, iterating between the conventional delay estimation and multi-lateration steps allows to approach the performance of the direct localization based on the observation of the received signals. In this paper we extend our iterative localization method to operate in rich multipath environments. Simulation results prove that given some prior knowledge on the power delay profile of the channel, the proposed iterative algorithm is robust to harsh propagation environments and performs very close to the direct localization approach

Impact of I/Q imbalance on time reversal-based indoor positioning systems

Time reversal has been shown as a promisingtechnology for the indoor positioning. Instead of mitigatingthe multipath channel, the time reversal based indoorpositioning system (TRIPS) exploits the rich multipathpropagation in indoor environments as a specific signaturefor each location. In order to do this, a database shouldbe first constructed by channel probing. The devicesused in this process are assumed to have no hardwareimpairments or be well calibrated. However, the low costterminal to be located can exhibit impairments, such asI/Q imbalance at the front end transmitter known to createan interference image of the signal that can particularlyimpact the performance of time reversal. In this paper, weinvestigate the impact of the I/Q imbalance on the TRIPS.We analytically show that the I/Q imbalance modifies themetric used for the localization and hence reduces thespatial focusing gain of TRIPS. Numerical simulationsare carried out to evaluate this observation. The resultsfurther show that the I/Q imbalance creates errors in thepositioning estimation. More specifically, at the gain andphase imbalances of respectively 1.1 and 10°, the focusinggain reduction is about 0.5 dB while the estimation errorrate is increased by about 5% in the specified scenario.

Experimental demonstration of BLE transmitter positioning based on AOA estimation

The introduction of the Bluetooth Low Energy (BLE) standard significantly streamlines the development of the Internet of Things (IoT) applications. These applications often require the sensor positioning to link the measurements with its location. Therefore, it is essential to conduct studies on BLE transmitter positioning methods. Power fingerprinting transmitter positioning approaches are commonly used in BLE network. However, these methods have their own limitations in terms of practical use and ease of implementation. The purpose is to develop a simple BLE transmitter positioning of high accuracy. In this paper, a BLE transmitter positioning method is proposed based on Angle of Arrival (AOA) estimation. Multiple Signal Classification (MUSIC) algorithm is used for angle estimation due to the high angular resolution and sensitivity. Several experiments have been conducted in an indoor environment and the results compared with simulation results. Experimental results show that our proposed BLE transmitter positioning method achieves a promising positioning accuracy.

Spatial data focusing

An alternative scenario is introduced in order to overcome antenna array's beamwidth limitations due to finite aperture size. The proposed approach aims to focus the transmitted data rather than the transmitted power. This scheme enables wireless broadcast of information to specific spatial locations, using fewer antenna elements compared to classical beamforming techniques. It is shown indeed with numerical examples that focusing the data is spatially more selective than focusing the power. In particular, we show that a linear 2-antenna array using spatial data focusing can exhibit similar beamwidths to a linear 7-antenna array using power focusing.

Experimental demonstration of BLE transmitter positioning based on AOA estimation

The introduction of the Bluetooth Low Energy(BLE) standard significantly streamlines the developmentof the Internet of Things (IoT) applications. These applicationsoften require the sensor positioning to link themeasurements with its location. Therefore, it is essential toconduct studies on BLE transmitter positioning methods.Power fingerprinting transmitter positioning approachesare commonly used in BLE network. However, thesemethods have their own limitations in terms of practicaluse and ease of implementation. The purpose is to developa simple BLE transmitter positioning of high accuracy.In this paper, a BLE transmitter positioning method isproposed based on Angle of Arrival (AOA) estimation.Multiple Signal Classification (MUSIC) algorithm is usedfor angle estimation due to the high angular resolutionand sensitivity. Several experiments have been conductedin an indoor environment and the results compared withsimulation results. Experimental results show that ourproposed BLE transmitter positioning method achieves apromising positioning accuracy.

A SDN solution for system-on-chip world

Uncertainty estimation in AoA based localization using PCE

2017

60 GHZ SIW horn antenna

A 6.6 dBi-gain Substrate Integrated Waveguide (SIW) horn antenna is used for off-body channel measurement at 60 GHz. Statistical scenario-based measurements are more suitable to assess Body Area Network (BAN) communication since they include both the environment and the antenna behaviors. Measurements are performed for four scenarios and two antenna positions. Results are discussed and compared with measurements at 4 GHz using a SkyCross monopole antenna in terms of link outage probability using receiver performance from the literature. In particular, it is shown that in all considered scenarios, results at 4 GHz and at 60 GHz led to outage of less than 15% and less than 8% respectively.

Iterative ToA-based terminal positioning in emerging cellular systems

Emerging cellular networks integrate the user terminal geo-localization function besides the communication function. The conventional positioning approach is to estimate the terminal location in two-steps: first the distance to all connected base stations is assessed based on signal time-of-flight measurements, then the location is deduced from the distances by multilateration. The two-step approach incurs a performance degradation because information is lost from the received signal when the multi-lateration is performed. In this paper, we propose to iterate between the two conventional steps to progressively refine the distance estimates based on the knowledge of the position estimate obtained from the previous iterations. The information exchanged between the two-steps not only consists in the mean of the estimates (distance or position) but also of their variance that convey information about the reliability of the estimates. Simulation results show that the achievable performance after a few iterations is close to the performance of the optimal approach that directly estimates the position based on the observation of the received signal.

Analyse de propagation confinée dans la peau pour les réseaux corporels BAN (Body Area Network)

Approche super-résolutive pour la mesure de la différence de temps d'arrivée (TDOA) à partir de trames OFDM

On-body skin confined propagation for body area networks (BAN)

Propagation of uncertainty in the MUSIC algorithm using polynomial chaos expansions

Polynomial chaos expansions are used to analyze the propagation of uncertainties on array parameters in Angleof-Arrival estimation performed by the MUSIC algorithm.

Human body communication channel modeling using vector network analyzer measurement

2016

Antenna radiation efficiency considerations in body area networks

Antenna radiation efficiency considerations in body area networks

In this paper, we present a theoretical investigation on the radiation efficiency of small on-body antennas in the context of Body Area Networks. In particular, we show that operation at frequencies above 20 GHz experiences less human-tissue losses than below 6 GHz, and could therefore be a suitable candidate for more efficient off-body wireless communications.

Dynamic QoS on SIP sessions using OpenFlow

FFT-OpenFlow, on the way towards real-time SDN

Influence of the urban characteristics on the spatial structure of electric field radiated by BTS antennas

Software-defined networking for low-latency 5G core network

Mobile communications have grown exponentially these last few years leading to an increasing demand. Software-Defined Networking appears to be a promising technology in order to provide flexible Quality of Service and very low latency. By modifying the 4G LTE architecture and integrating OpenFlow (SDN protocol) towards the 5G architecture, this new architecture promises to fulfill the requirements and to achieve better performances while participating to the network functions virtualization.

2015

Demonstrating the versatility of a low cost measurement testbed for wireless sensor networks with a case study on radio duty cycling protocols

Today, Wireless Sensor Networks (WSNs) with open source operating systems still need many efforts to guarantee that the protocol stack succeeds in delivering its expected performance. This is due to subtle implementation problems and unexpected interactions between protocol layers. The subtleties are often related to the judicious choice of parameters, in particular those related to timing issues. As these issues are often not visible in simulation studies, this paper proposes a low-cost versatile measurement testbed and demonstrates its usefulness in measuring the performance of RDC protocols. We demonstrate how the testbed helped to identify bugs in the implementation of an RDC protocol.

Demonstrating the versatility of a low cost measurement testbed for Wireless Sensor Networks with a case study on radio duty cycling protocols

On-body propagation characterization with an H-plane substrate intagrated waveguide

Faisabilité des réseaux définis par logiciel (SDN) pour les applications critiques et temps réel

Les réseaux définis par logiciel proposent un nouveau paradigme au niveau du fonctionnement des réseaux informatiques. Là où les routeurs et commutateurs exécutent des protocoles distribués prédéfinis, OpenFlow propose de les remplacer par des plates-formes où la logique déterminant le flux des paquets est librement programmable. Appliquée au domaine des réseaux temps réel, cette liberté permettrait de concevoir des réseaux en s'affranchissant des normes existantes et rendrait l'expérimentation aisée. L'article analyse cette possibilité en étudiant la définition via OpenFlow d'un réseau aux propriétés similaires au CAN, un bus temps réel éprouvé issu de l'industrie automobile.

Porcine skin as human body phantom at 60GHz

This communication presents the results of an experimental campaign carried out at 60 GHz to demonstrate that porcine skin can be used at 60 GHz as a phantom for the human body. Norton formulations above a flat human body are verified using porcine skin.

Indoor channels around a human subject at 2.45GHz and 60GHz

The increasing interest for the millimeter wave spectrum (30 GHz to 300 GHz) is due to the large bandwidth available for wireless, high throughput technologies. One of the key applications will be the cooperation with existent wireless technologies at lower frequencies in indoor environments. The propagation channel should be studied along with a human body in the closeness of the mobile device, since the presence of the user can greatly affect the propagation channel at millimeter range. This communication deals with the comparison between 2.4 GHZ et 60 GHz indoor channels around a user, in a zone that can be reached by the arm extension, which represent the region where a user often uses a wireless device like a smartphone or tablet.

3-D simulations for pharmaceutical materials exposure in reverberation chamber

Antenne cornet SIW pour réseaux de capteurs corporels à 60GHz

Antenna radiation characterization for on-body communication channel using creeping wave theory

Creeping wave theory is re-visited for BAN (Body Area Network) channel modeling. The formulation takes the characteristics of both antenna and human tissues into account. The field density at a certain distance from the radiating antenna can be directly determined by input power and on-body antenna gain. It is observed that the complicated on-body antenna gain measurement can be replaced by measuring antenna gain above infinitely large PEC (perfect electric conductor) plane to determine field density. Using time gating technique, the antenna gain above infinitely large PEC can be obtained by measuring continuous field on finitely large PEC, which is much easier to use in practice. The whole concept is validated through CST Microwave Studio. A very good agreement between the analytical model and full-wave simulation results is achieved.

2014

Sensitivity analysis of the specular and diffuse parts of clusters multipath on the exposure of a child body model

This paper studies the sensitivity of whole body Specific Absorption Rate (SAR) to indoor propagation channel parameters. Channel parameters are presented. SAR expectation over complex amplitude is analytically expressed. Then, total sensitivity index to channel parameters are estimated by a Monte Carlo approach and most influential parameters are extracted from this study.

Exposure homogeneity of pharmaceutical materials in reverberation chamber

The growing interest of using RFID technology in the pharmaceutical domain leads to questions about the EMF exposure of drugs. In this sense, different types of exposure systems have been studied and in particular the exposure in reverberation chamber. In order to expose multiple drug samples simultaneously, this study evaluate the difference in exposure homogeneity between one or multiple samples exposition. Simulations give condition on both the size and the distance between the samples to reach homogeneity.

Authenticated mobile groups to secure the backhaul

In this paper, it is proposed to use group communication cryptographic protocols as a new security paradigm. This new paradigm aims at redesigning the security of small cell communications over an insecure mobile backhaul. The Heterogeneous Networks are posi- tioned and a review of the current security mechanisms and their flaws is provided. A security and performance comparison between the current mechanisms and our proposition is developed, and this comparison leads to new development opportunities to increase the security of the overall backhauling.

Estimation du DAS corps entier avec la méthode du krigeage ordinaire

Horn antenna design for BAN millimeter wave on-body communication

The 60-GHz band is attractive for Body Area Networks (BANs) application for its high atmospheric attenuation, low interference with other networks, component compactness, large available bandwidth and low human body skin penetration [1] [2]. However, as far as we know, there is no accurate propagation model characterizing on-body communication at 60 GHz. To establish such a model, we need realistic measurement which requires low profile antenna.

Implementation and study of a numerical 60 GHz indoor off-body channel

In the field of 60 GHz high data rate wireless and Body Area Networks communications, fast computation and accurate analytic models are required to predict the budget link. In this paper, an indoor off-body channel model restricted to TE polarization transmitters and receivers is studied numerically. Some channel properties are extracted and compared to the indoor channel to study the impact of the human body on the 60 GHz propagation.

Experimental evaluation of message latency and power usage in WSNs

Different techniques for measuring packet delivery ratio, packet latency and power usage on single hop radio links have been developed. These techniques were tested with Zolertia Z1 motes running Contiki by measuring the performances of different radio duty cycling protocols using a range of radio wake-up rates and various levels of global radio traffic. Advantages and disadvantages of the different techniques are discussed and the feasibility of enhancing them for multihop networks is explored.

2013

NLOS influence on 60 GHz indoor localization based on a new TDOA extraction approach

In the field of 60 GHz high data rate wireless communications a new method for indoor localization at 60 GHz is proposed. This method is based on the extraction of the TDOA (Time Difference of Arrival), using a MISO system. With this method, unlike conventional TDOA measurements, it is possible to perform communication and localization at the same time by transmitting two identical UWB OFDM signals using two antennas at the TX and extracting TDOA from the interference spectrum of these two signals at the RX. TDOA. In addition, The NLOS (Non line of sight) influence on the TDOA and the localization precision is investigated for different cases. This whole study is made within the framework of the WiGig alliance specifications.

A 60 GHz off-body channel implementation

In the field of smart environments, high data rate wireless wireless communication can be reached with the unlicensed 60 GHz RF Band. In this spectrum, Body Area Networks channel modeling is required. In this paper, a 60 GHz Off-Body channel modeling is presented using a simplified and fast computation result of the scattering of plane waves by a human body at 60 GHz and the IEEE 802.11ad indoor channel model.

Propagation for on-body wireless links at 60 GHz

A creeping wave model of the propagation of electromagnetic waves around human torso at 60 GHz is presented. The theoretical model should be of interest for Wireless Body Area Networks design at 60 GHz, if the nodes are located on different side of the torso. Both vertical and horizontal polarizations are investigated. Results of a measurement campaign confirm theoretical predictions.

Simultaneous communication and localization for 60 GHz UWB OFDM systems

A new method for indoor localization at 60 GHz is proposed. This method is based on the extraction of the TDOA (Time Difference of Arrival), using a MISO system. With this method, unlike conventional TDOA measurements, it is possible to perform communication and localization at the same time by transmitting two identical UWB OFDM signals using two antennas at the TX and extracting TDOA from the interference spectrum of these two signals at the RX. The improvement of the localization precision is also studied via a multi-band approach to use the whole spectrum assigned to 60 GHz communications. This whole study is made within the framework of the WiGig alliance specifications. The simulations performed with commercial software, confirm the theoretical results while experimental measurements are implemented at lower frequencies to prove this approach.

Estimation of specific absorption rate with kriging method

Summary form only given. The development of wireless technologies sets off new issues regarding exposure of the people to electromagnetic radiation. The non-ionizing dosimetry is focused on the calculation of the dose that can be absorbed by users of a wireless technology. The integration of the variability in the dosimetry is a major issue, especially the one led by the environment. Electromagnetic environment are described by wireless channel model. The model indicates that the exposure of people is random; the channel parameters follow known probability distributions. This model shows that the electromagnetic waves do not arrive separately but in cluster form. The angles of incidence and amplitudes of the electromagnetic waves follow specific probability distribution. In the framework of the study of people's exposure to complex environment, it is necessary to expose an anatomical body model to all possible angle of incidence. The computation time in dosimetry is especially long so it is essential to pitch for an efficient estimation method in order to obtain the SAR values for all possible angle of incidence. In this study, we look into estimation of SAR in function of azimuthal angle of arrival of the electromagnetic wave. Kriging method which proves its efficiency in many domains will be used to respond to this problem. The kriging method is a stochastic spatial interpolation method which estimates a value of a phenomenon at locations where no calculation or measure has been done and also estimation variance (called kriging variance). In the full paper an estimation method of whole body SAR based on kriging approach will be presented in order to decrease the number of FDTD calculation. In the full detailed results will be presented, showing the impact of the number of SAR values taken in kriging estimation.

Distributed compressed sampling architecture for maximum likelihood signal detection

Cognitive radios are a new technology introduced to resolve the spectrum scarcity problemby superimposing new services in the already allocated bands under a non-interference constraint.It has been recently demonstrated that the challenging implementation of the signal detectors canbe facilitated by using the theory of compressive sampling. In this paper, we consider a distributednetwork of secondary nodes that cooperate to detect the primary signals. Each secondary nodesamples the signal periodically at a rate much smaller than the Nyquist rate. The delays inherentto the propagation channel are used to implement a periodic non-uniform sampling detector whenthe secondary nodes combine their observations. We demonstrate that the proposed detector canefficiently detect the primary user signal, even under fading channels.

Equalization of the non-linear 60 GHz channel

The non linearities in a communication channel can severely affect the communicationquality. These problems are encountered in many communication systems. Because of the highcomplexity of their power amplifiers, which have a severe non-linear behaviour, combined withan important pathloss, which imposes an important output power, the 60 GHz communicationsare strongly affected by these non-linearities. Taking these non-linearities into account in channelequalization can increase the communication performances and enable us to work near the saturationpoint of the amplifier. This paper presents the reservoir computer as a new approach for theequalization of a non-linear communication channels in the case of the 60 GHz communications.We compare the performances and the complexity of the reservoir computer algorithm with aniterative maximum likelihood (ML) equalizer. We find that the reservoir computer is an interestinglow complexity solution for this task.

Analytical creeping waves model At 60 GHz for off-body communications

In the field of 60 GHz high data rate wireless and Body Area Networks communications a fast computation and accurate analytical model for creeping waves is described in this paper. The scattering of a plane wave by a perfectly conducting cylinder (PEC) is presented. It is shown that at 60 GHz higher creeping waves modes can be neglected. The model is then compared with experimental results.

Analytical creeping waves model at 60 GHz for on-body communications

The propagation of 60 GHz electromagnetic waves around a human body is studied. The body is treated as a circular cylinder. Analytic formulations based on creeping wave theory for both vertical and horizontal polarizations are given. Measurements conducted on a brass cylinder confirmed theoretical results.

On the security of WLAN access points integrated in 4G/LTE architectures

In this paper, an investigation of the security of the WLAN access points is conducted with a special focus on their integration into 4G LTE-Advanced networks. Indeed, the points of access will be physically accessible to the customers or the workers from enterprises and, thus, corruption is possible and will affect or compromise the underlying LAN architecture. For that reason, the paper will focus, through a threat analysis, on the possible attacks and manipulation that a corrupted base station could execute. The paper presents the foundation to counteract these threats.

Passenger influence on the performance of time reversal in intra-vehicular environment

In this paper, the performances of a time reversal (TR) system inside an intra-vehicular environment are experimentally investigated. Analysis of the spatial and temporal properties of Multiple-Input-Single-Output (MISO) TR systems over ultra-wideband channels are presented. In order to study the performances of the MISO-TR within an occupied car, measurements were made by varying the number of passengers and by studying different configurations of antennas. Results indicate that the TR technique works fine in this special environment even with the presence of the passengers. As TR can achieve good robustness against changes in the channel, an analysis about the robustness in the case of any change in the number of passengers is presented.

2012

Multiband maximum likelihood signal detection based on compressive measurements

Cognitive radios impose challenges on the design of efficient signal detectors, including wide bandwidth sensing and large dynamic range support. The recently considered compressed sensing theory helps in relaxing the constraints on the design of the analog front-end. The maximum likelihood method introduced here is computationally simple since it does not require a signal reconstruction, unlike most methods introduced in the current literature. Moreover, the metric is optimum, works for any modulation scheme and is independent of the emitted signal knowledge and the number of occupied bands. The results are supported with Matlab simulations, a statistical study is performed and the probabilities of misdetection and false alarm are plotted for different scenarios, proving the efficiency of the estimator in a range of plausible SNRs and subsampling factors.

Performance and improvement of the finite order compensation in a non-linear DVB-S2 communication channel

High order modulations defined in the DVB-S2 standard are very sensitive to the non-linear interference induced by the power amplifier combined with the filters present in the channel. Several methods have been proposed to mitigate this interference. The finite order compensation, or order p compensation, is an analytical method to remove non-linear interference. However, it shows poor performance in case of high interference channel. We propose therefore a modification of the finite order compensation in order to minimize the mean square error between the initial input symbols and the received symbols.

Study of the temporal dynamics of the polarization of received electromagnetic waves based on an indoor-to-indoor measurement campaign

Compared to classical spatial MIMO wireless systems, cross-polarized MIMO systems are an interesting way to reduce equipment size while still maintaining low inter-antenna correlation. In this paper, the time-variation of the polarization of the received waves is investigated. In this scenario, a theoretical formulation is proposed in order to obtain the parameters of the elliptical polarization, based on the signals received on three perpendicularly polarized antennas. A measurement campaign has been performed in an indoor-to-indoor scenario and at a frequency of 3.6 GHz. Different measurement positions are considered in a Line-Of-Sight (LOS) and a Non-Line-of-Sight (NLOS) scenario. Based on these measurements and the proposed theoretical formulation, the time-variation of the parameters describing the polarization ellipse is analyzed and a time-variant statistical model is proposed.

New combination scheme for cooperative spectrum sensing under imperfect control channels

We consider the sensing of the frequency spectrum for cognitive radios, based on energy detection. It has been shown that the sensing reliability can be improved by using several cooperating cognitive radios that exchange their individual sensing information to a coordinator node through specific control channels. The coordinator node then combines the received information in order to make a decision about the primary network presence. In this paper, we compute analytically the probability density functions of the noise coming from the two-bits non-uniform quantization of the energy measure at each node and from the non-uniform bit flipping on the control channel. The quantization step and the bit flipping probabilities are selected to reduce the impact of the error. A new optimal fusion rule is proposed that takes into account the control channel noise distribution. Numerical simulations show that this new scheme outperforms the Maximum Ratio Combining scheme when different false alarm probabilities are used by the nodes.

Power allocation in cognitive radio networks using distributed machine learning

In cognitive radios systems, the sparse assigned frequency bands are opened to secondary users, provided that the aggregated interferences induced by the secondary transmitters on the primary receivers are negligible. In this paper, a decentralized Q-learning power allocation algorithm is proposed to maximize the Signal on Interference-plus-Noise Ratio (SINR) at the secondary receivers while meeting the primary protection constraint. Numerical simulations allow to compare the performance of the proposed algorithm with the performance of the optimal centralized power allocation scheme in the scenario of multiple independent secondary cells located on the border of a primary network protection contour. The impact of the definition of the learning algorithm cost function on the secondary user fairness and the system performance is discussed. The optimal execution frequency of the algorithm is obtained and different strategies for the exploration of new solutions are compared.

Design hints for didactic simulators

The authors have observed that interactive simulators can be very efficient tools for clarifying the underlying principles of computer architecture and network routing provided that the effort students have to make to use the simulator is small compared to the learning benefits expected from the it. A series of simulators have been designed specifically for didactic purposes. Learning how to use them should not require more than 15 minutes. The functionality and operating principles of a set of simulators for routing algorithms in wireless sensor networks are described, with emphasis on how, through repeated interactions with the student-users, the design goals could be mostly fulfilled.

Statistical study of SAR under wireless channel exposure in indoor environment

Characterization of the polarization of received electromagnetic waves in indoor communication channels

Distributed allocation of the spectrum sensing durations for cooperative cognitive radios

Analytical and experimental study of spatial Focusing by UWB time-reversal in indoor environment

The Time Reversal (TR) technique enables to concentrate the transmitted power on a certain area, where the receiver is located. In this paper, a closed-form analytical solution for the spatial distribution of the energy of a time-reversed system is proposed. This model is based on a plane wave expansion in a local area. Theoretical results are compared with experimental measurements to assess the validity of the Ultra-wideband TR method.

Impact of wireless channel modeling on SAR estimation in indoor environment

The development of wireless technologies led to the birth of numerical dosimetry for non-ionizing radiation. In another hand, the studies of communication channel improve the knowledge of the electromagnetic environment. This paper studies the impact of wireless channel modeling spatial parameters on the exposure of a simple body model. The whole body Specific Absorption Rate (SAR) is evaluated with different conditions of exposure in order to do a statistical study of SAR. The point is to identify the parameters of Wireless Channel which led to significant SAR's variation.

Wideband compressed sensing for cognitive radios using optimum detector with no reconstruction

Cognitive radios need devices capable of sensing a large range of frequencies in order to detect the presence of primary networks and reuse their bands when they are not occupied. Due to the large spectrum to be sensed and the high power signal dynamics, low-cost implementation of the analog front-ends leads to imperfections. In this paper, we solve this problem with compressed sensing. The introduced maximum likelihood method is computationally simple since it does not require any signal reconstruction, unlike most methods in the current literature. Moreover, the metric is optimum, works for any modulation scheme and is independent of the emitted signal knowledge. The results are supported with Matlab simulations, a statistical study is performed and the probability of error is plotted for different cases, proving the efficiency of the estimator in a range of plausible SNRs and subsampling factors.

A time-variant statistical model for the polarization of received electromagnetic waves in indoor communication channels

Compared to classical spatial MIMO wireless systems, cross-polarized MIMO systems are an interesting way to reduce equipment size while still maintaining low inter-antenna correlation. In this paper, the time-variation of the polarization of the received waves is investigated. In this scenario, a theoretical formulation is proposed in order to obtain the parameters of the elliptical polarization, based on the signals received on three perpendicularly polarized antennas. A measurement campaign has been performed in an indoor-to-indoor scenario and at a frequency of 3.6 GHz. Based on these measurements and the proposed theoretical formulation, the time-variation of the parameters describing the polarization ellipse is analyzed and a time-variant statistical model is proposed.

Distributed allocation of the sensing times for cooperative spectrum sensing

In cognitive radio systems, the sparse assigned frequency bands are opened to secondary users. We consider the sensing of the frequency spectrum for cognitive radios, based on energy detection. It has been shown that the sensing reliability can be improved by using several cooperating cognitive radios that exchange their individual sensing information to a coordinator node. The coordinator node combines the received information in order to make a decision about the primary network presence. In this paper, we propose a decentralized Q-learning algorithm to share the sensing time among the cognitive radios in a way that maximizes the throughputs of the radios. Numerical results show the convergence of the proposed algorithm and allow to discuss the exploration strategy, the frequency of execution of the algorithm and its computational complexity.

2011

Didactic simulators for understanding routing protocols in wireless sensor networks

Wireless sensor networks consist of autonomous intelligent sensor nodes, usually powered by battery, that can measure certain characteristics of their environment, such as temperature, pressure, moisture, acceleration, etc. These sensor nodes communicate by radio with their neighbours to forward data to a central collection points from where it is sent to some analysis centre via the Internet. The use of batteries and radio communications minimizes the cost, but requires specific routing protocols. Wireless Sensor Networks fit in the broader category of “smart object networks” that are gaining attention as the large range of IPv6 addresses will make possible “the Internet of Things”. In this perspective the Internet Engineering Task Force (IETF) has created a working group in charge of the design of a new routing protocol for low power and lossy networks called RPL. The authors are regularly faced with masters students interested in wireless sensor networks as a research topic for their thesis, but not knowing enough about it to make a rational choice. For that reason, a very simple, user friendly, interactive simulator that exposes the underlying principles of the Distance Vector (DV), the Ad-hoc, On Demand Distance Vector (AODV) and the RPL protocols has been developed and is being evaluated with master's students. It does not replace in any sense the more sophisticated simulation environments that are available to researchers. On the contrary, it is used to clarify basics of routing before confronting the students with the fully fledged tools. This simulator is now used as a support for lectures on routing and as a self-teaching tool for students considering a master's thesis in two universities, one in Europe and one in Africa. Its didactic value is being quantitatively evaluated with the participants of an international summer school for engineering students. In this paper, the decision to build a didactic tool rather than adapting existing tools is motivated and the design issues are discussed, with emphasis on RPL. The results of the evaluation of the didactic qualities by various groups of students in different educational contexts will also be presented.

Finite order compensation of non linearities in DVB-52 communications

To improve the performance of a DVB-S2 communication channel, it is necessary to remove the non-linear interferences induced by the power amplifier. Due to the presence of filters in the channel, this non-linear interference is also interference with memory. One of the most used techniques to cancel out the interferences in this case is the order p compensation. The order p compensation can be mathematically described as a recursive algorithm. The non- linear interference is supposed to be smaller after each step of the algorithm. However this is not always the case and it is necessary to define upper bounds on the system to ensure convergence of the algorithm. Upper bounds were already defined for general nonlinear systems, but are however very inaccurate for the case of a DVB-S2 communication channel. In this paper, we will present two new methods to refine these upper bounds.

Cooperative spectrum sensing for cognitive radios using distributed Q-learning

In cognitive radios systems, the sparse assigned frequency bands are opened to secondary users. We consider the sensing of the frequency spectrum for cognitive radios, based on energy detection. It has been shown that the sensing reliability can be improved by using several cooperating cognitive radios that exchange their individual sensing information to a coordinator node. The coordinator node combines the received information in order to make a decision about the primary network presence. In this paper, we propose a decentralized Q-learning algorithm to share the sensing time among the cognitive radios in a way that maximize the throughputs of the radios. Numerical results show the convergence of the proposed algorithm and allow to discuss the exploration strategy, the choice of the cost function and the frequency of execution of the algorithm.

Extracting specular-diffuse clusters from MIMO channel measurements

In previous work, it has been observed that the specular and the diffuse component are linked in the angular domain. The idea of adding a diffuse component to each specular cluster has been proposed to model the specular-diffuse channel. In this paper, an approach is proposed to treat the specular and the diffuse measurement data simultaneously, with a clustering algorithm that is applied jointly on the specular and the diffuse component. The output of the clustering algorithm gives clusters that are characterized by their specular and their diffuse component. Measurement results are presented based on double-directional measurements, and parameter values are extracted using the proposed methodology.

Dynamic carrier allocation for cognitive radio networks

Cognitive radios have been introduced as a dynamic way to share the frequency spectrum within wireless networks. After sensing its environment to discover the available frequency resources, a cognitive network allocates the locally available carriers among its nodes, under the constraint of negligible interference on licensed operators. The allocation, based on partial knowledge of the network parameters, must be optimized in order to provide maximum rates in the cognitive network. In addition, having a stable allocation reduces the control traffic inherent in dynamic networks. This paper presents a new and fast iterative way to allocate the available carriers, that reduces the control traffic and provides fairness at the same time. Using the properties of a proportionally fair objective function, we fasten the optimum search in the space of possible allocations, and reach that optimum with no approximation. Numerical results show that the proposed iterative algorithm is less complex than an analytical solution in usual dynamic carrier allocation scenarios.

Convergence of order p compensation in DVB-S2 satellite communication

Spatial focusing of electromagnetic waves using the UWB time reversal method

Performance evaluation of time reversal in intra-vehicular environment

In this paper a time reversal (TR) system combined with multiple-input single output (MISO) antennas over ultra-wideband (UWB) channels are experimentally investigated. An analysis on the spatial and temporal properties of the MISO-TR is presented in the special case of an in-car environment. As the TR can benefit from rich scattering environment, the application of the TR in the in-car environment can achieve very high performances. For some medical reasons, it is not only the peak signal that it is supposed to be focused but also the total energy over the bandwidth, an analysis about the total energy of the equivalent channel impulse responses is presented.

Statistical study of SAR in clustered wireless channels

The development of wireless technologies led to the birth of numerical dosimetry for non-ionizing radiation. This paper validates two statistical methods to evaluate SAR for cylindrical body models. The first method is Monte Carlo method in a stochastic physical model of propagation, the second method is an analytical method based on Uncorrelated Scattering assumption. These methods allow a statistical study of averaged SAR. The second point is to study SAR's behaviour in a random clustered wireless channels. Variation of SAR is analyzed in function of cluster parameters changing, in order to examine different exposure conditions.

The COST 2100 MIMO channel model

The COST 2100 channel model is a geometry- based stochastic channel model (GSCM) that can reproduce the stochastic properties of MIMO channels over time, frequency, and space. In contrast to other popular GSCMs, the COST 2100 approach is generic and flexible, making it suitable to model multi-user or distributed MIMO scenarios. In this article a concise overview of the COST 2100 channel model is presented. Main concepts are described, together with useful implementation guidelines. Recent developments, including dense multipath components, polarization, and multi-link aspects, are also discussed.

2010

Cross-layering between physical layer and routing in wireless ad-hoc networks

On the link layer performance of narrowband body area networks

A time-variant statistical channel model for tri-polarized antenna systems

Polarized MIMO systems are an efficient solution for reducing inter-antenna correlation while maintaining compact terminal size. In this paper, a time-variant statistical channel model is proposed for tri-polarized antenna systems. The model is based on a coherent and a scattered component, where each component includes inter-channel correlation and cross-polar discriminations. The temporal variations of the channel are separated in slow and fast channel variations. A measurement campaign has been performed at 3.6 GHz to parameterize the model, in both static and mobile cases. A variant of the variogram technique has been adopted for extracting the slow-varying channel parameters. Experimental results are investigated and presented. The Doppler spectrum of the fast channel variations show fundamental differences between the static case and the mobile case. Finally, it is explained how the proposed model can be generated.

Primary exclusive region and optimality of the link-level throughput of cognitive terminals

A cognitive network consists of primary nodes, which have priority access to the spectrum, and cognitive (also referred to as secondary) nodes, which access the spectrum provided that the interference they generate in the primary system remains limited. In practice, it means that the cognitive terminals must remain outside of a region surrounding the primary receiver: the primary exclusive region. The focus of this paper is on the definition of this region and the analysis of the achievable throughput of cognitive terminals under the constraints imposed by the primary network. More precisely, we establish the fundamental limits of the terminal probability of transmission and under what conditions this throughput can still be optimal (in a network throughput sense) for the secondary network.

3-D body scattering interference to vertically polarized on-body propagation

In this paper, we developed an analytical model of vertically polarized on-body propagation to describe the body scattering interference to the on-body channels. The 3-D dimension scattering from the trunk and arms by a point source are considered. Measurements results in an anechoic chamber at 2.45 GHz are also presented to validate the model.

Polarization orthogonality for the co-existence of wideband fading cognitive networks

Orthogonality techniques for cognitive radio networks are important since they enable the primary and secondary terminals to efficiently share the spectral resources in the same location simultaneously. In this paper, we investigate a simple, yet powerful, orthogonality scheme by exploiting the polarimetric dimension. More precisely, we evaluate a scenario where the cognitive terminals use cross-polarized communications in a communication channel subject to wideband (or narrowband) Rayleigh fading. A primary exclusive region in which cognitive terminals are not allowed to transmit is defined and its radius is computed. Finally, the overall performance of the proposed solution is evaluated in terms of network throughput.

Primary exclusive region and throughput of cognitive dual-polarized networks

Diversity techniques are of importance in the context of cognitive radio networks since they enable the primary and secondary terminals to simultaneously and efficiently share the spectral resources in the same location. In this paper, we investigate a simple, yet powerful, diversity scheme based on the exploitation of the polarimetric dimension. More precisely, we consider a scenario where the cognitive terminals use cross- polarized communications with respect to the primary users. Our approach is network-centric, i.e., the performance of the proposed dual- polarized system is investigated in terms of link throughput in the primary and the secondary networks. Our results suggest that the polarimetric dimension represents a remarkable (and simple to implement) opportunity in the context of cognitive radio networks.

Spectrum sensing based on the detection of fourth-order cyclic features

Sensitivity of spectrum sensing techniques to RF impairments

Cognitive radios are devices capable of sensing a large range of frequencies in order to detect the presence of primary networks and reuse their bands when they are not occupied. Due to the large spectrum to be sensed and the high power signal dynamics, low-cost implementations of the analog front-ends leads to imperfections. Two of them are studied in this paper: IQ imbalance and sampling clock offset (SCO). Based on a mathematical system model, we study analytically the impact of the two imperfections on the sensing performance of the energy detector and of the cyclostationarity detector. We show that the IQ imbalance does not impact the performance of the two detectors, and that the SCO only impacts significantly the performance of the cyclostationarity detector. © 2010 IEEE.

Quantization and transmission of the energy measures for cooperative spectrum sensing

We consider the sensing of the frequency spectrum based on energy detection for cognitive radios. It has been shown that the reliability of the sensing can be improved by using several cooperating cognitive radios. In such a network, the cognitive nodes exchange their individual sensing information to a coordinator node through specific control channels. The coordinator node then combines the received sensing informations in order to make a decision about the primary network presence. In this paper, we assess the impact of the noise coming from the quantization of the energy measure at each node and from the imperfect communication on the control channels. We also propose two complementary approaches to compensate for the noise: the system designer can firstly reduce the noise impact by using an energy coding technique that smartly shares out the bit error probabilities and secondly compensate for the remaining noise by designing a new soft metric fusion rule at the coordinator node. Numerical simulations show that this new scheme significantly improves the performance compared to the MRC scheme in the presence of control transmission noise.

Multi-polarized channel statistics for outdoor-to-indoor and indoor-to-indoor channels

Compared to classical spatial MIMO wireless systems, cross-polarized MIMO systems are an interesting way to reduce equipment size while reducing the inter-antenna correlation. Cross-Polar Discrimination (XPD) and Co-Polar Ratio (CPR) are two important parameters describing multi-polarized channels. In this paper, the behavior of these parameters is investigated for different observation scales. A measurement campaign has been performed in both Outdoor-to-Indoor and Indoor-to-Indoor scenarios, at a frequency of 3.5GHz. Small-scale variations of XPD and CPR are analyzed in different spatial positions. The distance-related and large-scale variations of XPD and CPR are also investigated and a model is deduced.

Dynamic and fair resource allocation in cognitive radio networks

Orientation-free XPD and CPR model in outdoor-to-indoor and indoor-to-indoor channels

Compared to classical spatial MIMO wireless systems, cross-polarized MIMO systems are an interesting way to reduce equipment size while reducing the inter-antenna correlation. Cross-Polar Discrimination (XPD) and Co-Polar Ratio (CPR) are two important parameters describing multi-polarized channels. In this paper, the behavior of these parameters is investigated for different observation scales. In order to overcome the ambiguity of the orientation of the receive antenna, the overall horizontal polarization is considered. A measurement campaign has been performed in both Outdoor-to-Indoor and Indoor-to-Indoor scenarios, at a frequency of 3.5GHz. Small-scale variations of XPD and CPR are analyzed in different spatial positions. The distance-related and large-scale variations of XPD and CPR are also investigated and an orientation-free model is deduced.

Diffuse multipath component characterization for indoor MIMO channels

Stochastic geometry-based models have been widely adopted for modeling wireless channels. These models are parametrized based on extensive measurement campaigns, where individual propagation paths are extracted with algorithms like SAGE or RiMax. It has been observed that when extracting individual propagation paths, part of the power is not captured. This residual power is referred to as the diffuse multipath component (DMC). In this paper, the spatio-temporal characteristics of the DMC are extracted from an extensive measurement campaign. It is observed that the angular power spectrum of the DMC is not angular-white, and that the angular properties of the DMC are significantly correlated with the angular properties of the specular part of the channel. A scheme is proposed to model the diffuse part of the channel by adding diffuse properties to each cluster corresponding to the specular part of the channel. The angular properties of the diffuse part of the clusters are modeled with Von-Mises distributions, whereas the delay properties of the clusters are modeled with an exponential decaying power profiles. Finally, the polarization properties of the diffuse part of the clusters are investigated.

2009

Imperfect exchange of control information between cooperative cognitive radios

MIMO channel emulator based on reverberation chambers

Multiple Input Multiple Output (MIMO), based on channel diversity, is a promising technique for increasing the performances of a communication. Nevertheless, the improvement will be strongly dependent on the propagation characteristics. If, for example, a ground to train communication is established in a tunnel, experiments described in the first part of the paper, show that at large distance, MIMO only slightly increases the capacity, contrary to what happens at short distance from the transmitter. This is due to a degeneracy of the transfer matrix H related to the propagation in a guiding structure. It is thus interesting to test communication equipments with laboratory setups, able to reproduce not only urban and rural environment but also environments like a tunnel leading to a degenerated H matrix. In this work, a new experimental setup for emulating MIMO channels is thus proposed. The system is composed of two mode stirred reverberation chambers, each one generating Rayleigh environments, which are coupled together with a rectangular waveguide. The transmitting antenna array is placed in one chamber whereas the receiving antenna array is placed in the other one. Depending on the dimension of the guide (i.e. its cut-off frequency), it is shown that one can control the order of the channel diversity. Hence, this setup could not only be used to perform tests of MIMO communication systems in perfectly defined environments but also under reproducible conditions.

UWB channel analysis within a moving car

Ultra-wideband communications inside a car are investigates in this paper. Measurements have been carried out in a typical sedan family car in two different environments. One of those was a one-way narrow street and measurement were taken while moving in the street. All the measurements were taken while varying the numbers of passengers. Based on those measurements, a channel model using reverberation chamber theory is proposed. Measurements results and channel model parameters are presented in this paper.

An ultra-wideband SAGE algorihtm for body area netwroks

Body area networks (BANs) consist of a set of bio-sensors placed on the human body and measuring some physiological or contextual information. The data are collected by some central devices located on the body or in the surrounding environment of the body via single or multi-hop transmissions. Typical applications include the real-time monitoring of heart activity blood pressure, breathing rate, or skin temperature, for the purpose of diagnostics or generating automatic calls for emergency.

Azimuth radiation pattern characterization of omnidirectional antenna near a human body

In this paper, measurements of radiation patterns for an antenna close to the human body at different frequencies are presented. An analytical channel model based on multiple cylinder scattering is proposed. Measurement results and simulations are compared and highlight the impact of body shadowing and arm scattering on the modification of the antenna azimuth radiation pattern.

Channel measurements and MB-OFDM performance inside a driving car

This paper investigates ultra-wideband intra-vehicular communications. Measurements have been carried out in a typical family car in two different environments. All the measurements were taken with different numbers of passengers. Based on those measurements, a channel model using reverberation chamber theory is proposed. Measurements results and performance of multi-band OFDM simulations are presented.

Clustered channel characterization for indoor polarized MIMO systems

A cluster-based channel model is presented that includes polarization characteristics. Measurements have been carried out in an indoor environment at 3.6 GHz using a dual-polarized transmitter and a tri-polarized receiver. Individual propagation paths are extracted using the SAGE algorithm, and a cross-polar discrimination (XPD) per ray is defined. Clusters are identified in the co-elevation-azimuth-delay domain, with an automatic clustering algorithm. The cluster properties are investigated and polarization characteristics are identified on a per-cluster basis. Finally, the obtained model is simulated and extraction-independent parameters are compared with experimental parameters for validation.

Integrated ad-hoc and cellular networking in indoor or faded environments

We consider real-time video packet transmission over a wireless channel. In our model, optimal rate allocation strategies are determined by the cross-layer perspective that minimize the average power consumed by the transmitter under the average delay constraints. We present simple packet scheduling policies which are influenced by both the queue and the channel state and those can be utilized to tradeoff characteristic between queueing delay and transmission power. The near-optimal scheduler adopts a low-complexity modified-linear-rule (MLR) which tends to make the queue evolve as a stable feed-back linear system. The parameter is chosen so as to reach the desired compromise between delay and power consumption. Throughout the extensive simulations, we generalize the scheme of MLR scheduler even in the multiuser wireless fading environments, compare it with the performance of the optimal scheduler and the log-linear scheduler and derive the optimal rate adaptation for video sources under the average delay and power constraints.

On the co-existence of dual-polarized CDMA networks

This paper investigates the use of the polarization as a diversity technique to allow the joint operation of co-located CDMA networks. We propose a closed-form expression for the link probability of success with respect to the topology of the deployment and the channel characteristics (code orthogonality and degree of polarization). Next, we derive the equivalence between the degree of polarization and the orthogonality in a scenario of two dual-polarized co-existent networks. A numerical analysis of the per-node throughput is presented to evaluate the gain achieved when a dual-polarized approach is used.

Interference and throughput analyses in dual-polarized wireless networks subject to rayleigh fading

Impact of noisy control channels on cooperative spectrum sensing

Polarimetric measurements for spatial wideband MIMO channels

This paper investigates the polarization behaviour of indoor multi-polarized MIMO channels at 3.6 GHz. Measurements have been carried out in non-line-of-sight (NLOS) and line-of-sight (LOS) using a dual-polarized transmitter and a tri-polarized receiver. The spatial and delay characteristics are extracted using a per-tap beamforming algorithm. Distinct waves are isolated and the polarization of each wave is expressed in terms of its spherical components. The evolution of the waves polarization is investigated as function of its physical propagation parameters. The polarization of the waves is shown to be sensitive to spatial characteristics, while being insensitive to delay. Direct line-of-sight rays show to have higher XPD than in the NLOS case, while the reflected rays have a similar XPD than in a NLOS case.

Polarization diversity for overlapping cellular networks

Coupled reverberation chambers for emulating MIMO channels

Fading correlation measurement and modeling on the front side of a human body

In this paper, measurement results for narrowband channel fading along the front side of human body at 2.45 GHz are presented. A simple propagation model corresponding to the investigated scenario is also introduced. The comparison between simulation and experimental results shows a reasonable similarity.

Un modèle de canal indoor par cluster pour systèmes MIMO polarisés

Small-scale variations of cross-polar discrimination in polarized MIMO systems

Cross-polarized MIMO systems are an attractive way to reduce equipment size while maintaining low inter-antenna correlation. The amount of leakage from one polarization to another is usually represented by the cross-polarization discrimination (XPD), making it a fundamental parameter of cross-polarized antenna systems. Starting from the definition of Rayleigh and Rice fading channels, we show that the small-scale variations of the XPD follow an F-distribution and a doubly non-central F-distribution respectively in Rayleigh and Ricean fading channels. This distribution is compared with the log-normal distribution that is usually reported in literature for the variations of the XPD. Consequences of this distribution are investigated, and it is shown that the variations of the XPD and the Ricean K-factors are linked by a non-trivial relationship. Measurements have been carried out in an indoor environment at 3.6 GHz to validate the theoretical F-model. The theoretical model and the experimental data are compared visually, by means of the mean square error and by means of the Kolmogorov-Smirnov test. The theoretical F-model shows excellent agreement with the measured XPD variations.

2008

A modular framework for user localization and tracking using machine learning techniques in wireless sensor networks

Reverberation chamber environment for testing communication systems

The impulse response in a reverberation chamber is investigated from an experimental and theoretical point of view. A full description is thus proposed based on measurements and confirmed by means of theoretical insights. In particular, the K factor of each tap is emphasized. BER simulations for OFDM and single carrier frequency domain equalization (SC-FDE) systems are applied on this channel model and compared to the 802.11n channel model showing some differences mainly for the OFDM transmission.

A spatially-correlated tapped delay line model for body area networks

Using wireless sensors worn on the body for pervasive monitoring is expected to become more and more common in the next years. The achievement of this application requires solving some challenges, especially in the power saving domain. In order to develop efficient power radio communications, an interesting investigation field is the multi-sensor MIMO (MS-MIMO) ultra-wideband (UWB) network. It is realistic to assume that each sensor carries one antenna, while the central device uses an antenna array. In this paper, a new analytical channel model for the diffracted waves mechanism is proposed. It is derived from the existing IEEE 802.15.4a standard channel model and innovates with space-time considerations.

Analytical model and experimental validation of cross-polar ratio in polarized MIMO channels

Cross-polarized antenna systems are used to reduce equipment size in MIMO systems while still achieving low inter-antenna correlation. One fundamental parameter of cross-polarized MIMO systems is the cross-polar discrimination (XPD). This paper proposes a model to determine the XPD as a function of channel condition and under different antenna configurations. The environment is supposed to have a truncated Laplacian Power Angular Spectrum (PAS) that is widely used in standardization bodies. Antenna XPD is shown to be sensitive to different channel conditions, as well as to different receiver orientations. Measurements were conducted at 3.5 GHz to validate the theoretical model. Good agreement is obtained between theoretical XPD and experimental results.

Channel correlation and cross-polar ratio in multi-polarized MIMO channels

This paper proposes a closed-form expression for the correlation coefficient and the cross-polarization discrimination (XPD) of a randomly oriented dual- or tri-polarized MIMO system. The environment is supposed to have a truncated Laplacian power azimuth spectrum that is widely used in standardization bodies. correlation and XPD are shown to be highly sensitive to receiver orientation, azimuth spread and environment depolarization behavior. Measurements were conducted at 3.5 GHz to validate the theoretical model. Good agreement is obtained between theoretical curves and experimental results for correlation and XPD when comparing at different receiver orientations.

Propagation modeling for UWB body area networks

Body area networks are now accepted as an important part of 4th generation mobile technology. These networks operating at very low consumption, efficient power radio communications have to be developed. A promising solution is using multi-sensor MIMO (MS-MIMO) ultra-wideband (UWB) systems : each sensor carries one antenna, while the central device uses an antenna array. Thereby, this paper proposes a new analytical channel model for the diffracted waves mechanism. This is derived from the existing IEEE 802.15.4 a standard channel model and innovates with space-time considerations.

A new precoding scheme for compact cross-polarized multi-antenna systems

Performance evaluation of machine learning techniques for the localization of users in wireless sensor networks

2007

Characterization of a confined environment based on acoustic and reverberation chamber theory

Ultra-wideband spatial channel characterization for body area networks

In this paper, spatial correlations are studied for the development of a UWB multi-sensors MIMO Body Area Network system, where the sensors communicate with a multi-antenna central device. The correlation in the frequency and delay domains has been extracted from channel measurements on the human body.

Modeling in-vehicle wideband wireless channels using reverberation chamber theory

In this paper, the wideband channel is studied inside a vehicle. Propagation inside a recent car (model bought in 2006) is investigated and the power delay profile is measured for three different scenarios. Two kinds of transmission bandwidths are studied, 200MHz around 5 Ghz and an ultra-wideband bandwidth of 3 Ghz around 4.5 GHz. The ultra-wideband measurements allow to clearly identify the propagation mechanism in this kind of environment. For each scenario, an exponential model for the power delay profile is shown to be in good agreement. A theoretical model based on reverberation chamber theory is proposed. It allows to predict the rms delay spread inside the car. A Comparison with measurements inside a reverberation chamber is presented. © 2007 IEEE.

Ultra-wideband spatial correlation study for multi-sensor multi-antenna body area networks

This paper is a first step towards the development of UWB multi-sensors MIMO body area networks, where the sensors communicate with a multi-antenna central device. The spatial correlation in the frequency and delay domains has been extracted from channel measurements on the human torso. We highlight two behaviours depending on the propagation mechanisms: diffraction around the body and environment reflections.

2006

NLOS-multipath effects on pseudo-Range estimation in urban canyons for GNSS applications

Pseudo-range (PR) errors due to NLOS-Multipath (non-line-of-sight-multipath) are studied in an urban canyon model. In order to determine the different reflected and diffracted rays which compose the NLOS-multipath, a dedicated ray tracing algorithm is applied. Two different methods are used in order to compute the PR error. The first one uses the error due to the maximum power ray and the second one uses an early minus late (E-L) receiver model. Simulations in different urban canyon configurations are carried out in order to obtain PR error distributions and associated probabilities due to NLOS-multipath rays above a given power threshold.

Testing MIMO systems with coupled reverberation chambers

In this paper, a new testbed composed of two reverberation chambers coupled through a waveguide is presented. A new wideband channel model for this testbed is emphasized. The theory about the waveguide coupling the two chambers is first reminded leading to a full description of the channel model. This model includes all the characteristics of the environment like the possibility to reproduce the number of degrees of freedom in the channel and the correlation between antennas. Some simulation results are presented showing a good agreement with theoretical and measurements results.

Statistical determination of the PR error due to NLOS-multipath in urban canyons

Wideband analysis of coupled reverberation chambers for testing MIMO systems

Adaptable measurement testbed for wireless systems applied to MIMO channel modeling

2005

Characterization of the ultra wideband body area propagation channel

Study of pseudo-range error due to non-line-of-sight-multipath in urban canyons

Statistical study of NLOS-multipath in urban canyons

Ultra wide-band body area channel model

Using wireless sensors placed on a person to continuously monitor health information is a promising new application. However, there are currently no models describing the radio channel around the human body making it difficult to design a suitable communication system. To address this problem, we have simulated electromagnetic wave propagation around the body and incorporated these results into a simple model. We then compared this model with measurements taken around the human torso and with previous studies in the literature. This paper proposes a simple statistical channel model useful for evaluating both UWB and (after resampling) narrow-band body area communication systems. © 2005 IEEE.

Multivariate analysis of the cross-layer interaction in wireless network simulations

2004

Modeling of NLOS-multipath in urban canyons for GNSS applications

WLAN deployment strategy for best indoor performance

Simulating Mimo systems in reverberation chambers

High-accuracy physical layer model for wireless network simulations in NS-2

Design of a new NS-2 extension for realistic in-building wireless simulations

Statistical response of devices immersed in electromagnetic chaos

Effect of 3D antenna parameters on MIMO systems with experimental validation in a reverberating chamber

2003

Disturbance lines identification in printed circuit boards by means of wavelets

Etude des performances des réseaux WLAN en milieu indoor

Impact of the physical layer on the performance of indoor wireless networks

A wavelet-based approach for cross-talk frequency estimation in printed circuit boards

A wavelet-based approach for frequency estimation of interference signals in printed circuit boards

Kriging the fields

A new statistical method for radiowave propagation analysis is presented based on spatial statistics tools known as kriging and variographic analysis. In the proposed method, fields are consid- ered as random variables of position. Using a few samples of those variables obtained by numerical or experimental means, unknown field values with confidence intervals are inferred. Validation of the new approach is carried out on measurements in indoor environment.

Electromagnetic wave propagation and coupling

Crosstalk analysis on printed circuit boards by means of wavelets

2002

Ad-hoc networks routing algorithms optimization for indoor environments

Electromagnetic wave propagation prediction using spatial statistics

Statistical analysis of broadband personal area networks disturbances on a transmission line in indoor environment

Statistical indoor propagation analysis for broadband Personal Area Networks

Random illumination by a dipole of a transmission line placed in a room, a probabilistic and statistical approach

Analyse statistique du couplage entre une ligne de transmission et un dipôle

2001

A nodal volume-surface integral equations method for electromagnetic scattering by dielectric bodies

Jini as a solution to develop distributed instrumentation networks in engineering

Statistical analysis of the end voltage of a transmission line illuminated by an elementary current source at random orientation and position

The deterministic analysis of coupling between wireless communication systems and sensitive electronic devices connected by means of cables is intricate because of the variability of geometry. A statistical approach appears to be more appropriate. Application of such an approach is illustrated by the study of a simple transmission line illuminated by a short length dipole located above a ground plane or inside a typical room. The aim is to analyze the end current in the line by means of the quantile in terms of various factors.

Development of distributed self-adaptive instrumentation networks using JINI technology

This paper describes a client-server architecture for the creation of dynamic and self-adaptive instrumentation over the network, either local or the Internet. The proposed solution allows multiuser, multi-instrument sessions by the means of a new cooperative concept known as Jini. Client applications take advantage of this system-independent technology by using the Java programming language.

A potential integral equation method for electromagnetic scattering by penetrable bodies

The use of high-order non-uniform grids in the method of moments applied to electromagnetic scattering

2000

EM Workshop, an interactive tool to build web-based electromagnetics courses

1999

The use of transfinite elements in the method of moments applied to electromagnetic scattering by dielectric cylinders