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International audience; Recently, dual-polarized antenna has attracted strong attention in Millimeter wave (mmWave) systems. It provides an additional degree-of-freedom in wireless communication, yielding higher throughput. Nowadays, with the development of antenna technology, dual-polarized large scale antenna arrays can be realized inexpensively. However, several challenges must be addressed when using dual-polarized antennas in practical transmission such as mobile phone rotation and non-ideal polarization isolation. We address these challenges in the frame of dual-polarized hybrid beamformers. In this paper, we analyze the performance of dual-polarized beamforming based on two popular techniques: Beam steering and Orthogonal Matching Pursuit. Three categories of dual-polarized beam steering are analyzed : (1) same ray : the two polarizations are sent on the same ray, (2) different ray-same polarization : the two polarizations are sent on different pathes, and the receiver uses the same polarization as the emitter, (3) different ray-different polarization : the receiver uses the orthogonal polarization w.r.t. the emitter. An algorithm to choose the rays and polarizations to use, taking the mobile rotation into account, is also developed. Moreover, we develop a hybrid beamforming algorithm inspired by Orthogonal Matching Pursuit that approaches the fully digital beamforming data-rate and outperforms beam steering. Its developed version-Orthogonal based Matching Pursuit-is also introduced to reduce the computational complexity and overcome the unavailability of the Angle of Arrival.

Orthogonal Frequency Division Multiplexing (OFDM) schemes provide high data rates and good robustness against frequency selective fading for communication systems. Space-Time Block Coding (STBC) is an efficient way to introduce space-time diversity in Multiple-Input Multiple-Output (MIMO) systems. Using non-linear modulations such as Continuous Phase Modulation (CPM) with its constant envelope property may be a way to construct MIMO OFDM systems that alleviates the typical Peak to Average Power Ratio (PAPR) issue of OFDM. However, CPM based systems are usually plagued by decoding complexity issues. In this paper, we introduce space-time-frequency diversity techniques based on L2-orthogonal multi-h CPM Space-Time codes designed for OFDM transmission. We benchmark these codes under frequency selective Rayleigh channels and show how they achieve full spatial diversity at full rate for any number of antennas, good spectral compactness, low PAPR and robustness to frequency fading. Furthermore, L2-orthogonality allows fast decoding with complexity growing only linearly in the number of Tx antennas.

International audience; Recently, Phase Difference of Arrival (PDoA) has been tremendously used to detect Direction-of-Arrival (DoA) of RFID UHF Tags because of its accuracy and robustness in difference environments. However, most of the methods just use RFID Reader with phase range from 0 degree to 360 degree instead of 0 degree to 180 degree which is the case in most of the Commercial off-the-shelf (COTS) RFID Readers. In this paper, some problems of DoA estimation will be introduced when using RFID Reader with range of 180 degree: first, coupling when placing antennas too close; second, phase ambiguity. Real experiments will also be introduced to prove the results.

One of the biggest challenges in operating massive multiple-input multiple-output systems is the acquisition of accurate channel state information at the transmitter. To take up this challenge, time division duplex is more favorable thanks to its channel reciprocity between downlink and uplink. However, while the propagation channel over the air is reciprocal, the radio-frequency front-ends in the transceivers are not. Therefore, calibration is required to compensate the RF hardware asymmetry. Although various over-the-air calibration methods exist to address the above problem, this paper offers a unified representation of these algorithms, providing a higher level view on the calibration problem, and introduces innovations on calibration methods. We present a novel family of calibration methods, based on antenna grouping, which improve accuracy and speed up the calibration process compared to existing methods. We then provide the Cram\'er-Rao bound as the performance evaluation benchmark and compare maximum likelihood and least squares estimators. We also differentiate between coherent and non-coherent accumulation of calibration measurements, and point out that enabling non-coherent accumulation allows the training to be spread in time, minimizing impact to the data service. Overall, these results have special value in allowing to design reciprocity calibration techniques that are both accurate and resource-effective., Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible

International audience; In this work, we propose a beam selection scheme that exploits the geometric sparsity of the multi-user (MU) massive multiple input and multiple output (MIMO) channel, using its beamspace representation. Assuming knowledge of the beamspace channel, the beamspace precoder consists in selecting and weighting the beams steered to the users, in order to maximize the signal-to-interference-and-noise ratio (SINR) at the user equipment (UE). Low complexity solutions are proposed through three simple heuristics. In a first step, the heuristics use the maximal ratio transmission (MRT) principle to determine the beam gains. In a second step, the beams are selected to enhance the SINRs. For all heuristics, we solve this problem in two steps i) selection of beams ii) power allocation. We show that using MRT as base, adding and/or removing some beams improve the system performance. Simulation results show that, compared to the linear MRT precoder, the proposed heuristics can improve the performance under a scenario with channel sparsity.

Massive multiple-input multiple-output (MIMO) is considered as one of the key technologies that will enable the next generation of wireless communications. In order to perform downlink (DL) beamforming algorithms with large antenna arrays, the biggest challenge is the acquisition of accurate channel state information at the transmitter (CSIT). To take up this challenge, time division duplex (TDD) is favorable to massive MIMO systems thanks to its channel reciprocity in DL and uplink (UL). However, while the physical channel in the air is reciprocal, the radio-frequency (RF) front-ends in transceivers are not; therefore, calibration should be used in practical systems to compensate the RF hardware asymmetry. In this thesis, we focus on turning massive MIMO concept into reality based on TDD reciprocity calibration. The contributions can be summarized as follows. First, we propose a unified framework for reciprocity calibration, which generalizes various calibration methods existing in literature, providing a higher level view on the calibration problem as well as opening up possibilities of numerous innovations on calibration methods. Second, based on this general representation, we propose three new calibration schemes: a fast calibration method based on antenna grouping, a calibration scheme for hybrid beamforming architecture, as well as a calibration parameter tracking and system health monitoring mechanism which allows fast detection of parameter change. Third, we carried out measurements of calibration parameters on a real platform in order to reveal the hardware properties. Fourth, we study, from a system point of view, how accurately a TDD massive MIMO system should be calibrated. Last but not least, enabled by TDD reciprocity calibration, we build up an open source long term evolution (LTE) compatible massive MIMO testbed based on the OpenAirInterface platform, which can directly provide Internet service to a commercial device. The testbed demonstrates the feasibility of integrating massive MIMO into current 3rd Generation Partnership Project (3GPP) standards and its usage in 5G can be a smooth evolution from current 4G systems., Entrées multiples, sorties multiples (MIMO) massif est considéré comme l'une des technologies clés de la prochaine génération de communications sans fil. Afin d'effectuer des algorithmes de formation de faisceau en liaison descendante (DL) avec un grand réseau d'antennes, le plus grand défi est l'acquisition d'informations précises d'état de canal à l'émetteur (CSIT). Pour relever ce défi, le duplex à division temporelle (TDD) est favorable aux systèmes MIMO massif grâce à sa réciprocité de canal de la DL et la liaison montante (UL). Cependant, alors que le canal physique dans l'air est réciproque, les front-ends de radiofréquence (RF) dans les émetteurs-récepteurs ne le sont pas ; par conséquent, la calibration devrait être utilisée dans des systèmes pratiques pour compenser l'asymétrie matérielle RF. Dans cette thèse, nous nous efforçons de transformer le concept MIMO massif en réalité en utilisant la calibration de la réciprocité TDD. Les contributions peuvent être résumées comme suit. Tout d'abord, nous proposons un cadre unifié pour la calibration de la réciprocité, qui généralise diverses méthodes de calibration existant dans la littérature, offrant une vue supérieure sur le problème de calibration ainsi que l'ouverture de nombreuses innovations sur les méthodes de calibration. Deuxièmement, sur la base de cette représentation générale, nous proposons trois nouveaux schémas de calibration : une méthode de calibration rapide basée sur le groupement d'antennes, un schéma de calibration pour l'architecture hybride de formation de faisceau, ainsi qu'un mécanisme de suivi des paramètres de calibration et de surveillance de la santé du système qui permet une détection rapide du changement de paramètre. Troisièmement, nous avons effectué des mesures des paramètres de calibration sur une plate-forme réelle afin de révéler les propriétés matérielles. Quatrièmement, nous étudions, du point de vue du système, avec quelle précision un système MIMO massif TDD devrait être calibré. Enfin, grâce à la calibration de réciprocité TDD, nous avons construit un banc d’essai pour MIMO massif, qui est compatible avec l'évolution à long terme (LTE) basé sur la plate-forme « open source » OpenAirInterface, et peut directement fournir un service Internet à un appareil commercial. Le banc d'essai démontre la faisabilité d'intégrer le MIMO massif dans les normes actuelles du projet de partenariat de troisième génération (3GPP) et son utilisation dans le 5G peut être une évolution à partir des systèmes 4G actuels.