Papers published in national and international conferences or symposium proceedings

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Communications publiées lors de congrès ou colloques nationaux et internationaux

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High-precision geocasting for LEO satellites using combined spatial data focusing and beamforming

Hybrid beamforming for satellite ground stations in the mmWave band

Leaky-wave antenna-based crowd monitoring in Integrate Sensing and Communications

Radar systems utilize electromagnetic signals to detect and track multiple human targets. This study focuses on multi-target tracking using range, Doppler, and Angle-of-Arrival (AoA) measurements from a monostatic radar system. Human crowds are modeled as dielectric cylindrical shells interacting with an incident electromagnetic field. The scattered field generated by the targets is processed to extract channel transfer function coefficients, enabling the derivation of range and Doppler profiles. A key novelty of this work is the use of a leaky-wave antenna at the receiver, which enables AoA estimation with a single-port antenna, therefore reducing system complexity, cost and eliminating the potential phase shift discrepancies inherent to multi-receiver configurations.

2024

Meta distribution of passive electromagnetic field exposure in cellular networks

This paper focuses on the meta distribution of electromagnetic field exposure (EMFE) experienced by a passive user in a cellular network implementing dynamic beamforming. The meta distribution serves as a valuable tool for extracting fine-grained insights into statistics of individual passive user EMFE across the network. A comprehensive stochastic geometry framework is established for this analysis. Given the pivotal role of accurately modeling the main and side lobes of antennas in this context, a multi-cosine gain model is introduced. The meta distribution is closely approximated by a beta distribution derived from its first- and second-order moments, which is demonstrated to be mathematically tractable. Theimpact of the number of antennas in the ULA on the meta distribution is explored, shedding light on its sensitivity to this parameter.

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.

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.

TDoA and Monostatic Radar Data Fusion for Single Object Localization and Tracking

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

La diffusion géolocalisée de données sans fil requière des capacités de focalisation au niveau des stations de base. La focalisation spatiale de données permet d'outrepasser les limites physiques rencontrées dans les réseaux d'antennes afin d'obtenir des précisions angulaires supérieures. Ce papier présente l'implémentation d'un tel schéma permettant une focalisation angulaire et radiale, tout en étant robuste aux multitrajets.

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.

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.

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

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.

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.

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

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.

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.

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

2015

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

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.

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.

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.

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.

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.

2011

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.

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

2008

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

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

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

see more DI-fusion

Communications publiées lors de congrès ou colloques nationaux et internationaux

A paraître

Maximum likelihood alternating summation for multistatic angle-based multitarget localization

Recent advancements in Wi-Fi sensing have sparkedinterest in exploiting OFDM modulated communication signalsfor target detection and tracking. In this study, we address theangle-based localization of multiple targets using a multistaticOFDM radar. While the maximum likelihood approach optimallymerges data from each radar pair comprised by the system,it entails a complex multi-dimensional search process. Leveraging pre-estimation of the targets' parameters obtained via theMUSIC algorithm, our method decouples this multi-dimensionalsearch into a single two-dimensional estimator per target. Theproposed alternating summation method allows the computationof a combined likelihood map aggregating contributions fromeach radar pair, enabling target detection via peak selection. Besides reducing computational complexity, the method effectivelycaptures target interactions and accommodates varying radarpair localization abilities. Also, it requires transmitting only theestimated channel covariance matrices of each radar pair to thecentral processor. Numerical simulations demonstrate superiorperformance over existing approaches.

Hybrid fusion for 802.11ax Wi-Fi-based passive radars exploiting beamforming feedbacks

Passive Wi-Fi-based radars (PWRs) are devices thatenable the localization of targets using Wi-Fi signals of opportunity transmitted by an access point. Unlike active radars thatoptimize their transmitted waveform for localization, PWRs alignwith the 802.11 amendments. Specifically, during the channelsounding session preceding a multi-user multiple-input multipleoutput downlink transmission, an access point isotropically transmits a null data packet (NDP) with a known preamble. Fromthese known symbols, client user equipments derive their channelstate information and transmit an unencrypted beamformingfeedback (BFF) back to the access point. The BFF comprisesthe right singular matrix of the channel and the correspondingstream gain for each subcarrier, which allows the computationof a beamforming matrix at the access point. In a classicalPWR processing, only the preamble symbols from the NDP areexploited during the channel sounding session. In this study,we investigate multiple target localization by a PWR exploitinghybrid information sources. On one hand, the joint angle-of departure and angle-of-arrival evaluated from the NDP. Onanother hand, the line-of-sight angle-of-departures inferred fromthe BFFs. The processing steps at the PWR are defined and anoptimal hybrid fusion rule is derived in the maximum likelihoodframework. Monte-Carlo simulations assess the enhanced accuracy of the proposed combination method compared to classicalPWR processing based solely on the NDP, and compare thelocalisation performance between client and non-client targets.

2024

Meta distribution of passive electromagnetic field exposure in cellular networks

This paper focuses on the meta distribution of electromagnetic field exposure (EMFE) experienced by a passive user in a cellular network implementing dynamic beamforming. The meta distribution serves as a valuable tool for extracting fine-grained insights into statistics of individual passive user EMFE across the network. A comprehensive stochastic geometry framework is established for this analysis. Given the pivotal role of accurately modeling the main and side lobes of antennas in this context, a multi-cosine gain model is introduced. The meta distribution is closely approximated by a beta distribution derived from its first- and second-order moments, which is demonstrated to be mathematically tractable. Theimpact of the number of antennas in the ULA on the meta distribution is explored, shedding light on its sensitivity to this parameter.

Enabling MIMO Radars in WLAN Sensing: From Spatial Multiplexing to Beamsteering

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.

Deceptive jamming in WLAN sensing

Joint Communication and Sensing (JCAS) is taking its first shape in WLAN sensing under IEEE 802.11bf, where standardized WLAN signals and protocols are exploited to enable radar-like sensing. However, an overlooked problem in JCAS, and specifically in WLAN Sensing, is the sensitivity of the system to a deceptive jammer, which introduces phantom targets to mislead the victim radar receiver. Standardized waveforms and sensing parameters make the system vulnerable to physical layer attacks. Moreover, orthogonal frequency-division multiplexing (OFDM) makes deceptive jamming even easier as it allows digitally generated artificial range/Doppler maps. This paper studies deceptive jamming in J CAS, with a special focus on WLAN Sensing. The provided mathematical models give insights into how to design jamming signals and their impact on the sensing system. Numerical analyses illustrate various distortions caused by deceptive jamming, while the experimental results validate the need for meticulous J CAS design to protect the system against physical layer attacks in the form of deceptive Jamming.

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.

Multistatic OFDM radar fusion of MUSIC-based angle estimation

This study investigates the problem of angle-based localization of multiple targets using a multistatic OFDM radar. Although the maximum likelihood (ML) approach can be employed to merge data from different radar pairs, this method requires a high complexity multidimensional search process. The multiple signal classification (MUSIC) algorithm simplifies the complexity to a two-dimensional search, but no framework is derived for combining MUSIC pseudo-spectrums in a multistatic configuration. This paper exploits the relationship between MU-SIC and ML estimators to approximate the multidimensional ML parameter estimation with a weighted combination of MUSIC pseudo-spectrum. This enables the computation of a likelihood map on which a peak selection is applied for target detection. In addition to reducing the computational complexity, the proposed method relies only on transmitting the estimated channel covariance matrices of each radar pair to the central processor. A numerical analysis is conducted to assess the benefits of the proposed fusion.

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.

TDoA and Monostatic Radar Data Fusion for Single Object Localization and Tracking

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.

A geometry-based algorithm for TDoA-based localization in the presence of outliers

Localization of non-cooperative radio frequency transmitters in wireless networks can be performed by using Time Difference of Arrival (TDoA). However, TDoA measurements are often degraded by limited signal-to-noise ratio, multipath components, non-line-of-sight (NLOS) visibility, etc. This causes the TDoA measurements to have strong outliers, which cannot easily be modelled mathematically. This paper investigates algorithms to perform TDoA-based localization in the presence of outlier measurements. Our algorithm is based on a geometric interpretation, rather than a mathematical, noise model-based approach. We show that our algorithm outperforms existing algorithms when applied to real-world data in a vehicular scenario.

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

La diffusion géolocalisée de données sans fil requière des capacités de focalisation au niveau des stations de base. La focalisation spatiale de données permet d'outrepasser les limites physiques rencontrées dans les réseaux d'antennes afin d'obtenir des précisions angulaires supérieures. Ce papier présente l'implémentation d'un tel schéma permettant une focalisation angulaire et radiale, tout en étant robuste aux multitrajets.

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.

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.

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.

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.

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.

Adaptive filter design for simultaneous in-band full-duplex communication and radar

The in-band full-duplex (IBFD) wirelesscommunication can achieve not only appreciable throughputgain but also is a key technology to enable concurrent radar andcommunication by one hardware. In such a system, an analogself-interference (SI) canceller is essential so that the receivedsignal can be processed digitally to achieve sufficient SNRfor IBFD communication. Unlike the previous similar workswhich rely on a classical matched filter, this paper derives therange-Doppler profile from the state of an adaptive filter, whichprimarily is applied to cancel the residual SI. Using standardIEEE 802.11ac signal, the proposed waveform-independenttechnique in this paper is simulated in a multi-target IBFDscenario. Furthermore, we employed a proof of concept setup tovalidate the proposed approach. The simulation and experimentalresults confirm that our method can render accurate rangeand velocity detection, and potentially satisfies a wide spectrumof opportunistic wireless sensing applications, ranging fromhand/body gesture detection to tracking and localization.

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

An over-the-air CFO-assisted synchronization algorithm for TDOA-based localization systems

Time-difference-of-arrival (TDOA) localization systemsestimate the difference in propagation delay between atarget transmitter and pairs of receivers in order to locatethe target. One important requirement is that the receivernodes should be accurately time-synchronized, which is hard toachieve in practice without relying on cable-connected receivers.Over-the-air synchronization algorithms often rely on periodicmessages from a master node, but due to clock drift, the rateof these messages needs to be high. In this paper, we proposea new synchronization algorithm that additionally exploits thecarrier frequency offset (CFO) between the target node andthe receiver nodes to reduce the rate of messages from themaster node while maintaining good synchronization accuracy.Simulation results show the good performance of the proposedmethod, and preliminary experimental results show its feasibilityon a hardware platform.

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.

Radar fusion for multipath mitigation in indoor environments

One of the main challenges of radar-based localization applications in indoor environments is the presence of strong multipath. When the radar bandwidth is large enough, multipath components can be resolved in range but they result in unwanted ghost targets. We propose a novel multipath mitigation approach that exploits the fact that multipaths are highly dependent on the scene geometry. The multipath mitigation approach discards the ghost targets based on the fused information of multiple radars located at different positions in the scene. For such radar fusion, the output of the radar signal processing chain is translated into the world coordinate system that is common for all the radars. We propose a radar alignment approach to estimate the translation and rotation parameters from radar to world coordinate system and vice versa. Our multipath mitigation method is combined with an unscented Kalman filter to improve the localization accuracy. We demonstrate the effectiveness of our complete approach with a real experiment using two radars to detect and track a target in a room with severe multipath.

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.

Clutter removal for WiFi-based passive bistatic radar

We address the problem of static clutter removalin Wi-Fi-based passive bistatic radars. Our goal is to detectslowly moving targets in highly cluttered indoor environments,using Orthogonal Frequency-Division Multiplexing signals fromthe 802.11n and 802.11ac Wi-Fi standards as sources of opportunity.We propose alternatives to the commonly used ExtendedCancellation Algorithm (ECA) clutter removal method. Thosealternatives are compared to ECA with simulations using aninnovative metric based on CA-CFAR detection, and validatedwith experimental measurements using two Universal SoftwareRadio Peripherals, along with a fan and an electric train asradar targets. The conclusion of that analysis is that, thanks tothe decoupled range and Doppler radar processing, simple novelmethods such as Average Removal are efficient alternatives tothe computationally intensive ECA which is currently the stateof-the-art in CR.

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.

Impact of phase noise on mutual interference of FMCW and PMCW automotive radars

During the last decade, the demand of smart sensors for advanced driving assistance systems (ADAS) has increased in order to keep the road safety at a sufficient level. For ADAS, one of the most widely considered sensors are radars. In the next few years, it is expected that each new car model will be equipped with many radars providing a 360view of the scene. Due to the significant increase of number of radars in heavy traffic conditions, it is expected that the interferences among those radars will significantly reduce their reliability.Unfortunately, analog front-end imperfections such as phase noise are known to aggravate the interference problem. Since there is no standardisation of the radar waveforms, the radardesigners are free to choose the best waveforms to minimise the impact of the interferences on the radar performance. Our aim is to compare the robustness of frequency-modulated continuous wave (FMCW) and phase-modulated continuous wave (PMCW) waveforms to mutual interference when the radars are subject to phase noise. A mathematical model of the radar is built to formalise the problem and numerical results are provided in order to assess the degradations on range-Doppler Maps.

Passive radar based on 802.11ac signals for indoor object detection

Passive radars opportunistically capture communications signals to detect and track targets in the environment. Since Wi-Fi signals are widely available today and have a limited coverage, interestingly they can be used by passive radars in local areas. Until now, passive radars based on Wi-Fi signals have only been designed for 11a/b/n signals, which makes the radar range accuracy insufficient for object detection because of the limited signal bandwidth (20-40 MHz). This paper investigates the use of the recent 11ac signals of much wider bandwidth (80-160 MHz) to significantly improve the range accuracy. The radar works by observing the 11ac preamble transmitted at the beginning of each data burst by the Wi-Fi access point and applies either a two-dimensional cross-correlation or a frequency/time domain channel estimation to build range/Doppler maps of the radar scene. It is shown by simulations that radar processing based on time-domain channel estimation is the only viable solution due to the frequency guard bands introduced in the signal that cause significant sidelobes in the range/Doppler map. Experimental results held in our research lab confirm that the radar is capable of separating objects of small size in an indoor environment (a fan and an electric train in our experiments).

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.

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

Passive radar based on 802.11ac signals for indoor object detection

Passive radars opportunistically capture communications signals to detect and track targets in the environment. Since Wi-Fi signals are widely available today and have a limited coverage, interestingly they can be used by passive radars in local areas. Until now, passive radars based on Wi-Fi signals have only been designed for 11a/b/n signals, which makes the radar range accuracy insufficient for object detection because of the limited signal bandwidth (20-40 MHz). This paper investigates the use of the recent 11ac signals of much wider bandwidth (80-160 MHz) to significantly improve the range accuracy. The radar works by observing the 11ac preamble transmitted at the beginning of each data burst by the Wi-Fi access point and applies either a two-dimensional cross-correlation or a frequency/time domain channel estimation to build range/Doppler maps of the radar scene. It is shown by simulations that radar processing based on time-domain channel estimation is the only viable solution due to the frequency guard bands introduced in the signal that cause significant sidelobes in the range/Doppler map. Experimental results held in our research lab confirm that the radar is capable of separating objects of small size in an indoor environment (a fan and an electric train in our experiments).

Focalisation spatiale de donnée via une approche temporelle

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.

Uncertainty estimation in AoA based localization using PCE

2017

On the feasibility of DVB-T based passive radar with a single receiver channel

The DVB-T signals are an attractive illumination source for thepassive radars due to their wide bandwidth and signal structure.The DVB-T standard permits the reconstruction of the receivedsignal to enhance its signal-to-noise ratio (SNR). The signalreconstruction possibility allows the use of a simplified configurationof the radar by employing a single receiver. In thispaper, we propose an optimized processing scheme for the singlereceiver DVB-T passive radar. We carry out Monte-Carlosimulations to assess the performances of the single receiverconfiguration, and we present real-data results to validate theproposed scheme.

On the static clutter suppression for DVB-T based passive radars

Passive coherent location (PCL) radars employ noncooperativetransmitters for target detection. The major issuesfor the PCL radars are the noise presence in the referencesignal and the static clutter contribution in the surveillancesignal. This paper examines the static clutter suppressionmethods for the DVB-T based PCL radars. Precisely,it evaluates the impact of the reference signal noiseon the existing static clutter suppression methods and it proposesan improved method. Real-data results are employedto demonstrate the proposed method and its efficiency.

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.

Optimum reference signal reconstruction for DVB-T based passive radars

The present work investigates the optimum reconstructionof the reference signal in passive coherent location(PCL) radars exploiting Digital Video Broadcasting-Terrestrial(DVB-T) signals. Reference signal reconstruction is widely usedto improve the signal-to-noise ratio (SNR) in the reference signalfor DVB-T based PCL radars. Reference signal reconstructionis limited since for low SNR values, the signal demodulationis not sufficiently accurate which leads to a mismatch betweenthe reconstructed signal and the transmitted one. In this work,we propose an optimum reconstruction strategy that includesan optimum estimation of the detected QAM symbols, specificfor radar applications. To verify the proposed detection strategy,we calculated analytic models for the optimum filter and thedetection statistics. The analytic models are validated throughMonte-Carlo simulations. The results showed that the proposedmethod outperforms the conventional reference signal reconstructionscheme in terms of detection probability performance.

ML and MAP phase noise estimators for optical fiber FBMC-OQAM systems

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.

Extended kalman filter for carrier phase recovery in optical filter bank multicarrier offset QAM systems

Human body communication channel modeling using vector network analyzer measurement

On the exact recovery condition of simultaneous orthogonal matching pursuit

Improving the correlation lower bound for simultaneous orthogonal matching pursuit

2016

Generalized optimal pilot allocation for channel estimation in multicarrier systems

This paper addresses the design of MSE-optimal preambles for multicarrier channel estimation under a maximum likelihood or minimum mean squared error criterion. The derived optimality condition gives insight on how to allocate the pilots that compose the preamble. While many papers show that equispaced and equipowered allocation is optimal, the generalized condition demonstrates that there exist many different configurations that offer the same optimal performance. Furthermore, the condition applies not only to maximum likelihood but also to minimum mean squared error channel estimation. An application of the generalized condition in the presence of inactive subcarriers (virtual subcarriers problem) is shown such that a non equispaced allocation can achieve the same optimal performance as if an equispaced one could be used.

Low-complexity blind phase search for filter bank multicarrier offset-QAM optical fiber systems

A low-complexity blind phase search (BPS) for the carrier phase estimation in optical FBMC- OQAM systems is proposed. Compared to the BPS algorithm, the proposed method is of lower complexity while still delivering a similar performance.

High performance bio-inspired analog equalizer for DVB-S2 non-linear communication channel

To ensure a high signal-to-noise power ratio at the terrestrial receiver, the power amplifier aboard the satellite often works close to its saturation point. Unfortunately, this operating point also adds non-linear distortions in the communication channel. The literature proposes several digital equalizers to compensate for this channel. But their complexity makes their digital implementation difficult in particular for high bandwidth communications. Analog equalizers are an interesting solution to reduce the equalizer complexity. Here we numerically demonstrate that a dedicated analog optoelectronic implementation based on the Echo State Network paradigm can reach state-of-the-art performance of digital equalizers, while reducing the required resolution of the analog-to-digital converters.

Target detection for DVB-T based passive radars using pilot subcarrier signal

Passive coherent location (PCL) radars employ non-cooperative transmitters fortarget detection. The cross-correlation (CC) detector, as an approximation ofthe optimum detector, is widely applied in PCL radars: it cross-correlates thereference signal and the surveillance signal. The CC detector is sensitive tosignal-to-noise ratio (SNR) in the reference signal and thus a pre-processing ofthe reference signal is required. DVB-T based PCL radars can benefit from thepossibility of reference signal reconstruction for SNR enhancement. The recon-struction process requires an SNR level that allows accurate signal demodulation.Hence, for low SNR values, signal reconstruction performance is limited. In thispaper, we present a new approach that employs the subcarrier pilot signal forCC detection in DVB-T based PCL radars. We demonstrate the effectiveness ofreplacing the noisy reference signal with the a locally generated subcarrier pilotsignal for CC detection.

Receiver design for non-linear satellite channels

Because of the small energy available aboard a satellite, the power amplifier must work with a restricted power supply which limits its maximum output power. To ensure a sufficient signal-to-noise power ratio (SNR) at the receiving side, the amplifier must work close to the saturation point. This is power efficient but, unfortunately, adds non-linear distortions in the communication channel.Several algorithms have been proposed to equalize this non-linear channel. The most widely used in the literature is the baseband Volterra filter. Recently, the Echo State Network (ESN), coming from the artificial neural network field, has been shown to perform equally well.To compensate for this channel, both equalizers adapt their coefficients with the help of a training sequence in order to recover the transmitted constellation points. We will show that, the usual detection, based on Euclidean distances, is no longer optimal. The aim of this paper is to first propose a new detection criterion which meets with the Maximum Likelihood (ML) criterion. Secondly, we will propose a modification of the training reference points to improve the performances of these equalizers and make the detection based on Euclidean distances optimal again. This last solution can offer a significant reduction of the Bit Error Rate (BER) without increasing the equalizers complexity. Only the new training reference points must be evaluated.

Low-complexity laser phase noise compensation for filter bank multicarrier offset-QAM optical fiber systems

We report on a low-complexity modified blind phase search (BPS) for the carrierphase estimation in optical filter bank multicarrier o↵set quadrature modulationformat (FBMC-OQAM) systems. More particularly, the distance calculationsin the complex plane in state-of-the-art BPS method are replaced by simplemultiplication-free operations in the real plane. Moreover, a modified phasesearching strategy is also applied, leading to further reduction of the computationalcomplexity. The proposed methods are numerically validated in a 5-subcarriers FBMC-16OQAM system. Similar to conventional BPS method, thetolerated normalized linewidth (the product of laser linewidth and symbol duration)of the proposed BPS method is 10

Noise stabilization with simultaneous orthogonal matching pursuit

This paper addresses the problem of recovering several sparse signals acquiredby means of a noisy linear measurement process returning fewer observationsthan the dimension of the sparse signals of interest. The proposed signal modelassumes that the noise is additive and Gaussian. Within the aforementionedframework, theoretical developments making use of the theory of compressivesensing show that sparse signals with similar supports can be jointly and reliablyrecovered by means of the greedy algorithm entitled simultaneous orthogonalmatching pursuit (SOMP) provided that the linear measurements are appropriatelydesigned. A variant of SOMP weighting each measurement vector accordingto its noise level is then presented. Finally, simulations confirm the benefits ofweighting the measurement vectors in SOMP and show that the optimal weightspredicted by the theory match the empirical ones under proper conditions.

Generalized optimal pilot allocation for channel estimation in multicarrier systems

This paper⇤ addresses the design of MSE-optimal preambles for multicarrier channelestimation under a maximum likelihood or minimum mean squared error criterion.The derived optimality condition gives insight on how to allocate the powerof the pilots that compose the preamble. While many papers show that equispacedand equipowered allocation is optimal, the generalized condition demonstratesthat there exist many different configurations that offer the same optimalperformance. Furthermore, the condition applies not only to maximum likelihoodbut also to minimum mean squared error channel estimation. An application ofthe generalized condition in the presence of inactive subcarriers (virtual subcarriersproblem) is shown such that a non equispaced allocation can achieve thesame optimal performance as if an equispaced one could be used.

Non-linear satellite channel equalization based on a low complexity echo state network

Satellite communications systems designers are continuously struggling to improve the link capacity. A critical challenge comes from the limited power available aboard the satellite. To ensure a sufficient signal-to-noise power ratio (SNR) at the terrestrial receiving side, the amplifier aboard the satellite is usually operated close to the amplifier saturation point which adds non-linear distortions to the communication channel. Several algorithms have been proposed to equalize the non-linear satellite channel. The Echo State Network (ESN) algorithm, coming from the field of artificial neural networks, has been shown to perform well in this task: it can achieve a similar bit error rate (BER) as the state-of-the-art Volterra equalizer. In the present paper we show that with an appropriate design, the complexity of the ESN can be significantly lower than that of the Volterra equalizer, while conserving the low BER.

2015

Multiband spectrum sensing for cognitive radios based on distributed compressed measurements

A wideband spectrum sensing method for cognitive radios is presented which is based on compressed measurements. The proposed detector does not require signal reconstruction from the compressed measurements. A fusion centre collects the measurements from different sensing nodes and then makes a sensing decision based on a simplified maximum likelihood criterion which does not require prior signal information. This results in an efficient and low complexity spectrum detector especially for dynamic spectrum occupancy scenarios. The performance of the proposed detector is exhibited by means of numerical simulations for probability of erroneous detection and receiver operating characteristic curves.

Equalization of the non-linear satellite communication channel with an echo state network

Because of the small energy available aboard a satellite, the power amplifier must achieve a very high power efficiency which suggest to work close to the saturation point. This would be power efficient, but unfortunately would add non-linear distortions to the communication channel. Several equalization algorithms have been proposed to compensate for this non-linear behaviour. The Echo State Network (ESN), an algorithm coming from the field of artificial neural networks, has also been proposed for this task but has never been compared to state-of-the-art equalizers for non-linear channel. The aim of this paper is to adapt the ESN to the satellite communication channel and to compare it to the baseband Volterra equalizer. We show that the ESN is able to reach the same performances as the Volterra equalizer, evaluated in terms of bit error rate, and has similar complexity. In addition, we propose a new training strategy for the ESN and the Volterra equalizer to improve their performance.

Consensus algorithms for distributed spectrum sensing based on goodness of fit test in cognitive radio networks

In this paper, we study a consensus algorithm for distributed spectrum sensing (DSS) in cognitive radio networks (CRN) integrating a Goodness of Fit based spectrum sensing scheme. Existing work in this area often applies energy detector as a local spectrum sensing method for DSS, however in this case one needs to make the assumption that the noise level is the same at every node in the network, otherwise the threshold can not be set properly. In GoF based spectrum sensing, the threshold for the binary test depends only on the desired false alarm probability and not on the local noise powers. Motivated by this nice feature of GoF based spectrum sensing, we consider the goodness of fit (GoF) test statistic to be exchanged among cognitive radio (CR) users (consensus variable) instead of the energy. Moreover, a weighted consensus based DSS scheme is proposed and compared to the conventional consensus based on DSS. Simulations are conducted to show the effectiveness of the consensus algorithm based on GoF test.

Implementation of a distributed compressed sensing algorithm on USRP2 platforms

Pilots allocation for sparse channel estimation in multicarrier systems

2014

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.

Filtered orthogonal matching pursuit

Low complexity block pre-distortion of a multi-carrier non-linear satellite channel

In a multi-carrier non-linear satellite communication channel, inter-symbol interference (ISI) and adjacent channel interference (ACI) occur due to the non-linear power amplifier aboard the satellite. In order to prevent a too high performance degradation, large input back-offs (IBO) are generally considered. However, if all carriers are issued from the same ground station, pre-distortion of the whole transmitted signal can be a better solution to achieve higher power efficiency aboard the satellite and/or spectral efficiency. The relation between the symbols transmitted on the channel and the received symbols is tricky for a multi-carrier system, as it involves several symbol flows. Few approaches have been proposed yet to provide an efficient algorithm with reasonable complexity in such context. In this paper, we will derive a sub-optimum algorithm for the pre-distortion of a multi-carrier non-linear satellite channel which offers a good trade-off between performance and complexity.

Turbo-equalization of the remaining interference in a pre-distorted non-linear satellite channel

In satellite broadcast and broadband communication systems, it is desirable to relax as much as possible the complexity of terminals for feeder-to-user links. Pre-distortion algorithms are therefore considered at the transmitter side to compensate for the non-linear interference induced by the channel. In case of large channel lengths and multi-level constellations, remaining interference after pre-distortion may however still be significant. In this paper, we show that the system performance can be improved by combining a pre-distortion algorithm with a low-complexity turbo-equalization structure at the receiver side. This structure relies on the observation that the interference before pre-distortion and the remaining interference after pre-distortion are correlated.

Multicarrier offset-QAM modulations for coherent optical communication systems

We study the performance of multicarrier offset modulation and root-raised-cosine shaped multicarrier modulation with aggregate 32.5 GBd symbol rate and show that offset modulation is preferable for non-zero rolloff factors.

2013

Per block pre-distortion of a multi-carrier non-linear satellite communication channel

In this paper, we propose a pre-distortion algorithm for a two carriers non-linear satellite communication channel. In the considered scenario, two linearly modulated carriers are amplified by the same non-linear power amplifier aboard the satellite. Due to the presence of the shaping filter at the transmitter side and the receiver filter (and possibly interference with filters aboard the satellite), the received signal is affected by non-linear intersymbol interference (ISI) but also non-linear adjacent channel interference (ACI). We consider the case where the two signals are transmitted from the same gateway, so that joint pre-distortion of the two signals is possible. Simulations for the 8PSK modulation show that the algorithm is able to greatly reduce the impact of the non-linear interference.

Decision feedback equalization for bandwidth-constrained 28Gbaud nyquist-WDM PDM-8QAM over 37.5 GHz grid

Low feedback downlink MIMO channel estimation for distributed FBMC systems using SNR measurements

In this paper, we present a new method to estimate the MIMO channel in a distributed MIMO system using FBMC modulation (Filter Bank based Multicarrier). As opposed to previously presented methods, it is not based on the existence of pilots and therefore avoids the necessity of auxiliary pilots or similar methods. Besides, it requires a very low amount of feedback. Only the SNR observed by the different users need to be fed back periodically. It is intended for the estimation of the downlink MIMO channel in a distributed beamforming system where the basestations can cooperate to some extent. It is based on the concept of adding small, controlled, perturbations to the transmitted signals and observing the related changes to the SNR at the receivers. It is shown in this paper that, based on a limited amount of SNR measurements from the receivers, it is possible to accurately estimate the MIMO channels, both in amplitude and phase. It is also shown that the proposed method exhibits the best performance in a tracking mode.

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.

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.

Design rules for pulse shaping in PDM-QPSK and PDM- 16QAM nyquist-WDM coherent optical transmission systems

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.

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

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.

2011

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.

Impact of carrier frequency offset in cooperative phase shift beamforming

We study the effects of residual carrier frequency offset (CFO) on the performance of cooperative phase shift (PSB) beamforming schemes. Cooperative beamforming may provide the diversity and the power gains of multi-antenna systems and is therefore seen as a promising technology for the next generation wireless communication systems. Considering the distributed nature of cooperative communications, the carrier frequency of each transmitter deviates from the desired one. In this paper, we present the derivations of the signal-to-noise ratio and diversity gains in the cooperative PSB scheme in presence of residual CFOs. It is shown that even with frequency synchronization prior to transmission, residual CFOs may still significantly degrade the performance due to the in-phase misalignment of the incoming streams at the destination. Furthermore, we show that because of the residual CFOs the collaborative beamforming scheme may perform worse than its non-collaborative counter-part. The results and the accuracy are illustrated through simulations.

Performance analysis of the distributed ZF beamformer in the presence of carrier frequency offset

We study the impact of residual carrier frequency offset (CFO) on the performance of the distributed zero-forcing (ZF) beamformer in the interference channel, i.e., where multiple nodes simultaneously transmit the same data towards multiple receivers. Distributed transmissions have been proposed to mitigate the co-channel interference inherent to such scenarios and provide the gains of multi-antenna systems. However, frequency synchronization among the cooperating transmitters is required. Even when the transmitters perform frequency synchronization before transmission, a residual CFO is to be expected that degrades the performance of the system due to the in-phase misalignment of the incoming streams. This paper presents the signal-to-noise ratio analytically and the diversity semi-numerically of the distributed ZF beamformer for the ideal case and in presence of a residual CFO. We illustrate our results and their accuracy through simulations.

Residual energy-aware collaborative transmission beamforming in wireless sensor networks

Energy-Efficient transmission techniques are very important for extending the lifetime of a wireless sensor network (WSN) given that recharging batteries of a large number of WSN nodes is a very difficult and expensive operation. Collaborative transmission beamforming (CTB) saves energy consumed by each node by distributing between different WSN nodes the required total power transmission to get a desired bit error rate (BER) at the receiver. Moreover, by coherently combining the different signals transmitted by the WSN nodes, CTB increases the signal strength in the direction of the receiver, therefore decreases the total power transmission of the WSN. In this paper, we propose a new CTB technique that minimizes the total power transmission of the WSN while balancing the residual energy in different nodes. By solving this multi-objective optimization problem, we show that the WSN lifetime can be improved up to 30 % compared to the basic CTB algorithm, which aims at minimizing the total power transmission without taking into account the residual energy.

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.

Performance analysis of the distributed ZF beamformer in the presence of carrier frequency offset

We study the impact of residual carrier frequency offset (CFO) on the performance of the distributed zero-forcing (ZF) beamformer in the interference channel, i.e., where multiple nodes simultaneously transmit the same data towards multiple receivers. Distributed transmissions have been proposed to mitigate the co-channel interference inherent to such scenarios and provide the gains of multi-antenna systems. However, frequency synchronization among the cooperating transmitters is required. Even when the transmitters perform frequency synchronization before transmission, a residual CFO is to be expected that degrades the performance of the system due to the in-phase misalignment of the incoming streams. This paper presents the signal-to-noise ratio analytically and the diversity semi-numerically of the distributed ZF beamformer for the ideal case and in presence of a residual CFO. We illustrate our results and their accuracy through simulations.

Joint TX/RX analog linear transformation for maximizing the capacity at 60 GHz

The large bandwidth available at 60 GHz together with the resulting wavelength of only 5 mm allow the design of multi-Gbps wireless devices equipped with large arrays of tiny antennas. This enables wireless communication of large contents multimedia such as high-definition video. However, due to the high cost and power consumption of analog frond-end (AFE) chains at 60 GHz, it is practically infeasible to allocate a dedicated AFE to each antenna. Thus, it is highly desirable to design low complexity multi-antenna architectures in which an analog linear transformation (ALT) is carried out in order to reduce the required number of AFE chains for digital spatial processing, while minimizing the capacity loss. In this paper, we propose a non-iterative algorithm for joint transmit/receive (TX/RX) ALT. The proposed algorithm is designed with the aim of maximizing the capacity of the resulting reduced dimension MIMO system, assuming a frequency selective propagation channel.

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

2010

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.

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.

Frequency domain equalization for dispersive birefringent nonlinear optical fibers

Mixed analog/digital beamforming for 60 GHz MIMO frequency selective channels

Multi-antenna architectures, where beamforming processing is shared between analog and digital, are of great interest for future multi-Gbps wireless systems operating at 60 GHz. In this spectrum band, wireless systems can integrate large antenna arrays in a very small volume thanks to a wavelength of about 5 mm and thus provide the required gain to meet the severe link budget. However, the cost and power consumption of an analog front-end (AFE) chain, that carries out translation between radio frequency (RF) and digital baseband, are too high at 60 GHz to afford one AFE for each antenna. In this paper, we consider low cost multi-antenna architectures with a lower number of AFE chains than antenna elements. We propose a joint design of transmit-receive mixed analog/digital beamformers that aim at maximizing the received average signal-to-noise-ratio (SNR). The proposed scheme shows better performance than state-of-art solutions, which combine antenna selection techniques and digital beamforming.

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.

2009

Training sequence versus cyclic prefix for CPM with frequency domain equalization

Frequency domain equalization (FDE) of continuous phase modulations (CPM) has been thoroughly investigated lately. To enable this low-complexity FDE, all known techniques use a cyclic prefix (CP). However, using a training sequence (TS) of known symbols instead of a CP offers some advantages: the additional known symbols can be used to improve synchronization and channel estimation, with the same performance of a CP. Nevertheless, using a TS for CPM-FDE is not trivial because the memory in a CPM waveform has to be taken into account to guarantee cyclicity and phase continuity after insertion of the TS into a block of input symbols. In this paper, we therefore propose a technique for constructing a TS for CPMFDE. Simulation results in a 60 GHz environment show that the proposed technique satisfies all requirements. The 60 GHz case is chosen because CPM with FDE has recently been proposed for communications at 60 GHz and the latest IEEE and ECMA standards for these frequencies mandate the use of a TS rather than a CP.

Imperfect exchange of control information between cooperative cognitive radios

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.

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.

Tap and transmit antenna correlation based precoding for MIMO-OFDM systems

Maximum SINR-based beamforming for the MISO interference channel

Multi-antenna wireless mesh networks are a promising means to achieve high data rate in next generation of wireless networks. However, because co-channel interference (CCI) is a major source of performance degradation in such networks, cooperative techniques have been proposed to cope with CCI. Nevertheless, these techniques require the exchange of information between the transmit nodes (e.g. channel knowledge acquisition, synchronization, etc...) and are thus very complex to implement. Conversely, non-cooperative techniques have limited complexity and are therefore an interesting alternative. Two non-cooperative methods have been proposed in the literature: the zero-forcing and the maximal signal-to-noise ratio beamformers. However, those two schemes do not maximize the aggregate capacity of the network nor minimize the bit error rate (BER) of each communication channel. In this paper, we consider a different optimization metric based on maximizing the SINR at the transmitters. We show that the proposed scheme achieves maximal capacity and outperforms the two existing non-cooperative schemes in terms of BER.

A flexible antenna selection scheme for 60 GHz multi-antenna systems using interleaved ADCs

We present a new scheme for maximizing the signal-to-noise ratio (SNR) in wideband multi-antenna receivers that employ time-interleaved analog-to-digital converters (ADCs). Current wideband receivers interleave a fixed number of slower ADCs into one fast ADC and assign this latter to one antenna according to an antenna selection algorithm. However, this does not always guarantee an optimal trade-off between thermal noise and quantization noise. This results in an overall SNR that is lower than what could be obtained with the same number of ADCs, assigned in a more optimal way. Therefore, we propose to adjust the number of slower ADCs assigned to a certain fast, interleaved ADC dynamically, according to the SNR of every individual antenna. Our proposed algorithm can be implemented at the expense of a very limited hardware complexity increase. The SNR gain of our new scheme can exceed 7 dB, depending on channel conditions and ADC specifications.

Joint transmit and receive analog beamforming in 60 GHz MIMO multipath channels

Analog beamforming (ABF) with one scalar weight per antenna is an attractive technique for low-cost, low-power 60 GHz multi-antenna wireless communication systems. However, the design of the corresponding joint transmit and receive (Tx/Rx) ABF optimization algorithms is still challenging in the case of multipath channels due to the constraint of having only one scalar weight per antenna. In this paper, we aim at maximizing the average signal to noise ratio (SNR) at the input of the equalizer and analytically derive close-to-optimal Tx/Rx scalar weights. We show that the required channel state information (CSI) for joint Tx/Rx ABF weights computation is the inner product between all Tx/Rx channel impulse response pairs. Taking the channel length into account, a training-based estimation strategy of this CSI is proposed. Simulation results carried out in a typical 60 GHz multipath environment show that the proposed scheme outperforms the existing ABF schemes in term of BER performances.

Beamforming at 60GHz: challenges and solutions

2008

Spectrum sensing over SIMO multi-path fading channels based on energy detection

High performance, low complexity frequency domain equalization for CPM

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.

System level aspects, air interface and standardization of 60 GHz wireless communication

A new symbol block construction for CPM with frequency domain equalization

We present a new symbol block construction which yields a cyclic continuous phase modulated (CPM) signal to enable frequency domain equalization. It is known that in addition to a cyclic prefix, a subblock of data-dependent symbols has to be inserted in each block to cope with the memory in the CPM signal. We propose a new subblock, called intrafix, valid for any CPM scheme. Our intrafix is shorter than what is currently known in the literature, reducing the overhead. Moreover, it can be calculated on a per-block basis, without knowledge of previous blocks. We also prove that there are constraints on the length of both the intrafix and the total block by studying the influence of the modulation index. Simulation results in a 60 GHz environment show that our new block construction satisfies all requirements.

Influence of 60GHz front-end nonidealities on CPM with frequency domain equalization

2007

Low-complexity frequency domain equalization for continuous phase modulation

Impact of phase noise on OFDM and SC-CP

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.

SC-FDMA versus CP-CDMA

Low-complexity EM-based joint CFO and IQ imbalance acquisition

Joint transmit/ receive IQ compensation for OFDM-based communication systems

Efficient QRD for SRI-RLS based chip level HSDPA equalizer in SDR

Front-end ADC requirements for uniform bandpass sampling in SDR

Comparison of OQPSK and CPM for communications at 60GHz with a non-ideal front-end

Laurent approximation for multi-level CPM

2006

Software defined radios for mobile terminals: enable and exploit scalability for low power operation

Quality-cost scalable chip level equalization in HSDPA receiver

Joint carrier and clock offset compensation in a mobile 802.16e OFDMA communication system

Performance analysis of the IEEE 802.16e mesh extension

Air interface and physical layer techniques for 60 GHz WPANs

Practical channel estimation for OFDM in time-varying channels

Front-end impact on candidate air interfaces in a 60GHz wireless communication channel

Optimal training sequences for joint channel and frequency-dependent IQ imbalance estimation in OFDM-based receivers

Joint compensation of CFO and IQ imbalance for 4G wireless systems

Offset-QPSK with FDE for 60 GHZ wireless communication systems

2005

Broadband WLAN

Acquisition specifications and solutions for a 4G flexible air interface

MC-CDMA performance in the presence of carrier frequency offset, sample clock offset and IQ imbalance

Impact and compensation of sample clock offset on uplink SC-CDMA systems

STBC for uplink single-carrier CDMA with equalization in the frequency domain

Impact and compensation of sample clock offset on uplink CP-CDMA systems

Impact of frequency offsets and IQ imbalance on MC-CDMA reception based on channel tracking

Space-time block coding for uplink cyclic-prefix CDMA

2004

Optimal training sequences for low complexity ML multi-channel estimation in multi-user MIMO OFDM-based communications

A generic transmission scheme for fourth generation wireless systems

A single-carrier - OFDM comparison for broadband wireless communications

OFDM versus single-carrier

A generic transmission scheme for fourth generation wireless systems

2002

MIMO communications for single carrier using decision feedback equalization

2001

Channel adapted precoding for interference-free uplink burst transmission

Channel adapted CDMA for MAI/ISI-free power optimized burst transmission with space diversity at the base station

CDMA code optimization for MAI/ISI-free burst transmission and space diversity at the base station

CA-CDMA

Linear and DF joint detectors for DS-CDMA communications using periodic long codes

FSLE and FDSF joint detectors for long code DS-CDMA codes

2000

CA-CDMA

Multiple access techniques for wideband upstream powerline communications

DMT-FDMA as a multiple access technique for wideband upstream powerline communications

1999

Multiple access techniques for wideband upstream powerline communications

A comparison between chip fractional and non fractional joint detectors