Récepteur itératif pour les systèmes MIMO-OFDM basé sur le décodage sphérique : convergence, performance et complexité

Recently, iterative processing has been widely considered to achieve near-capacity performance and reliable high data rate transmission, for future wireless communication systems. However, such an iterative processing poses significant challenges for efficient receiver design. In this thesis, iterative receiver combining multiple-input multiple-output (MIMO) detection with channel decoding is investigated for high data rate transmission. The convergence, the performance and the computational complexity of the iterative receiver for MIMO-OFDM system are considered. First, we review the most relevant hard-output and soft-output MIMO detection algorithms based on sphere decoding, K-Best decoding, and interference cancellation. Consequently, a low-complexity K-best (LCK- Best) based decoder is proposed in order to substantially reduce the computational complexity without significant performance degradation. We then analyze the convergence behaviors of combining these detection algorithms with various forward error correction codes, namely LTE turbo decoder and LDPC decoder with the help of Extrinsic Information Transfer (EXIT) charts. Based on this analysis, a new scheduling order of the required inner and outer iterations is suggested. The performance of the proposed receiver is evaluated in various LTE channel environments, and compared with other MIMO detection schemes. Secondly, the computational complexity of the iterative receiver with different channel coding techniques is evaluated and compared for different modulation orders and coding rates. Simulation results show that our proposed approaches achieve near optimal performance but more importantly it can substantially reduce the computational complexity of the system. From a practical point of view, fixed-point representation is usually used in order to reduce the hardware costs in terms of area, power consumption and execution time. Therefore, we present efficient fixed point arithmetic of the proposed iterative receiver based on LC-KBest decoder. Additionally, the impact of the channel estimation on the system performance is studied. The proposed iterative receiver is tested in a real-time environment using the MIMO WARP platform.Pour permettre l’accroissement de débit et de robustesse dans les futurs systèmes de communication sans fil, les processus itératifs sont de plus considérés dans les récepteurs. Cependant, l’adoption d’un traitement itératif pose des défis importants dans la conception du récepteur. Dans cette thèse, un récepteur itératif combinant les techniques de détection multi-antennes avec le décodage de canal est étudié. Trois aspects sont considérés dans un contexte MIMOOFDM: la convergence, la performance et la complexité du récepteur. Dans un premier temps, nous étudions les différents algorithmes de détection MIMO à décision dure et souple basés sur l’égalisation, le décodage sphérique, le décodage K-Best et l’annulation d’interférence. Un décodeur K-best de faible complexité (LC-K-Best) est proposé pour réduire la complexité sans dégradation significative des performances. Nous analysons ensuite la convergence de la combinaison de ces algorithmes de détection avec différentes techniques de codage de canal, notamment le décodeur turbo et le décodeur LDPC en utilisant le diagramme EXIT. En se basant sur cette analyse, un nouvel ordonnancement des itérations internes et externes nécessaires est proposé. Les performances du récepteur ainsi proposé sont évaluées dans différents modèles de canal LTE, et comparées avec différentes techniques de détection MIMO. Ensuite, la complexité des récepteurs itératifs avec différentes techniques de codage de canal est étudiée et comparée pour différents modulations et rendement de code. Les résultats de simulation montrent que les approches proposées offrent un bon compromis entre performance et complexité. D’un point de vue implémentation, la représentation en virgule fixe est généralement utilisée afin de réduire les coûts en termes de surface, de consommation d’énergie et de temps d’exécution. Nous présentons ainsi une représentation en virgule fixe du récepteur itératif proposé basé sur le décodeur LC K-Best. En outre, nous étudions l’impact de l’estimation de canal sur la performance du système. Finalement, le récepteur MIMOOFDM itératif est testé sur la plateforme matérielle WARP, validant le schéma proposé

Iterative receiver for MIMO-OFDM systems based on sphere decoding : convergence, performance and complexity tradeoffs

Pour permettre l’accroissement de débit et de robustesse dans les futurs systèmes de communication sans fil, les processus itératifs sont de plus considérés dans les récepteurs. Cependant, l’adoption d’un traitement itératif pose des défis importants dans la conception du récepteur. Dans cette thèse, un récepteur itératif combinant les techniques de détection multi-antennes avec le décodage de canal est étudié. Trois aspects sont considérés dans un contexte MIMOOFDM: la convergence, la performance et la complexité du récepteur. Dans un premier temps, nous étudions les différents algorithmes de détection MIMO à décision dure et souple basés sur l’égalisation, le décodage sphérique, le décodage K-Best et l’annulation d’interférence. Un décodeur K-best de faible complexité (LC-K-Best) est proposé pour réduire la complexité sans dégradation significative des performances. Nous analysons ensuite la convergence de la combinaison de ces algorithmes de détection avec différentes techniques de codage de canal, notamment le décodeur turbo et le décodeur LDPC en utilisant le diagramme EXIT. En se basant sur cette analyse, un nouvel ordonnancement des itérations internes et externes nécessaires est proposé. Les performances du récepteur ainsi proposé sont évaluées dans différents modèles de canal LTE, et comparées avec différentes techniques de détection MIMO. Ensuite, la complexité des récepteurs itératifs avec différentes techniques de codage de canal est étudiée et comparée pour différents modulations et rendement de code. Les résultats de simulation montrent que les approches proposées offrent un bon compromis entre performance et complexité. D’un point de vue implémentation, la représentation en virgule fixe est généralement utilisée afin de réduire les coûts en termes de surface, de consommation d’énergie et de temps d’exécution. Nous présentons ainsi une représentation en virgule fixe du récepteur itératif proposé basé sur le décodeur LC K-Best. En outre, nous étudions l’impact de l’estimation de canal sur la performance du système. Finalement, le récepteur MIMOOFDM itératif est testé sur la plateforme matérielle WARP, validant le schéma proposé.Recently, iterative processing has been widely considered to achieve near-capacity performance and reliable high data rate transmission, for future wireless communication systems. However, such an iterative processing poses significant challenges for efficient receiver design. In this thesis, iterative receiver combining multiple-input multiple-output (MIMO) detection with channel decoding is investigated for high data rate transmission. The convergence, the performance and the computational complexity of the iterative receiver for MIMO-OFDM system are considered. First, we review the most relevant hard-output and soft-output MIMO detection algorithms based on sphere decoding, K-Best decoding, and interference cancellation. Consequently, a low-complexity K-best (LCK- Best) based decoder is proposed in order to substantially reduce the computational complexity without significant performance degradation. We then analyze the convergence behaviors of combining these detection algorithms with various forward error correction codes, namely LTE turbo decoder and LDPC decoder with the help of Extrinsic Information Transfer (EXIT) charts. Based on this analysis, a new scheduling order of the required inner and outer iterations is suggested. The performance of the proposed receiver is evaluated in various LTE channel environments, and compared with other MIMO detection schemes. Secondly, the computational complexity of the iterative receiver with different channel coding techniques is evaluated and compared for different modulation orders and coding rates. Simulation results show that our proposed approaches achieve near optimal performance but more importantly it can substantially reduce the computational complexity of the system. From a practical point of view, fixed-point representation is usually used in order to reduce the hardware costs in terms of area, power consumption and execution time. Therefore, we present efficient fixed point arithmetic of the proposed iterative receiver based on LC-KBest decoder. Additionally, the impact of the channel estimation on the system performance is studied. The proposed iterative receiver is tested in a real-time environment using the MIMO WARP platform

UNII-MAC protocol: Design and evaluation for 5G ultra-dense small cell networks operating in 5 GHz unlicensed spectrum

International audienceUltra-densification and efficient spectrum utilization are key features for the next 5G wireless networks to address the well-known challenges of high capacity demands and mobile data traffic explosion. In this article, a physical layer and a medium access control (MAC) sublayer are presented for small cells to operate in the 5 GHz unlicensed national information infrastructure (UNII) band. The physical layer is based on filter bank multi-carrier modulation able to achieve better spectral efficiency and access flexibility. The MAC protocol is based on beacon-enabled superframe consisting of scheduled and contention access schemes. The proposed UNII-MAC design relies on a listen-before-talk (LBT) procedure in order to comply with ETSI regulations and to fairly coexist with neighboring systems sharing the same band. The performance of the UNII-MAC is then evaluated in dense indoor/outdoor deployment scenarios under various parameters and traffic patterns. Moreover, the coexistence between UNII-MAC and WiFi systems is reported. Based on the obtained results, we provide recommendations for 5G small cell deployment in dense environments

MAC design for 5G dense networks based on FBMC modulation

International audienceThe fifth generation (5G) of wireless networks is currently under investigation in order to address the well-known challenges of the high capacity demands and traffic volume. The promising solutions to meet these targets can be achieved through ultra-densification, efficient use of spectrum and advanced filtered modulation techniques. In this paper, we present an enhanced MAC protocol for 5G small cells operating at 5 GHz and assuming an FBMC physical layer. The proposed MAC design consists of scheduled-based and contention-based access schemes and involves a listen before talk (LBT) procedure to comply with ETSI regulations. The performance of the proposed FBMC-MAC design is then evaluated in dense deployment scenarios under different PHY/MAC parameter settings. Moreover, we study the performance of FBMC-MAC systems in the context of coexistence with WiFi systems

Low Complexity K-Best based Iterative Receiver for MIMO Systems

International audienceIterative receiver combining multiple-input multiple-output (MIMO) detection with channel decoding is an attractive solution to greatly improve the error rate performance of wireless communication systems. However, such iterative process poses significant challenges for efficient receiver design. In this paper, a modification of soft-input soft-output K-Best decoder is proposed to provide high throughput with low complexity. Moreover, the convergence of combining sphere decoder based detection algorithms with LTE turbo decoder is analyzed with the help of EXtrinsic Information Transfer (EXIT) charts. An optimized scheduling of the number of iterations is therefore proposed. Simulation results show that the proposed decoder and the new schedule achieve almost the same performance compared to the conventional schedule with a large saving in computational complexity

Performance and Complexity Evaluation of Iterative Receiver for Coded MIMO-OFDM Systems

Multiple-input multiple-output (MIMO) technology in combination with channel coding technique is a promising solution for reliable high data rate transmission in future wireless communication systems. However, these technologies pose significant challenges for the design of an iterative receiver. In this paper, an efficient receiver combining soft-input soft-output (SISO) detection based on low-complexity K-Best (LC-K-Best) decoder with various forward error correction codes, namely, LTE turbo decoder and LDPC decoder, is investigated. We first investigate the convergence behaviors of the iterative MIMO receivers to determine the required inner and outer iterations. Consequently, the performance of LC-K-Best based receiver is evaluated in various LTE channel environments and compared with other MIMO detection schemes. Moreover, the computational complexity of the iterative receiver with different channel coding techniques is evaluated and compared with different modulation orders and coding rates. Simulation results show that LC-K-Best based receiver achieves satisfactory performance-complexity trade-offs

Détecteur Itératif pour les récepteurs MIMO : compromis compelxité/performance

International audienceRecently, iterative receiver combining multiple-input multiple-output (MIMO) detection withchannel decoding has been widely considered to achieve near-capacity performance and reliable highdata rate transmission, for future wireless communication systems. However, such iterativeprocessing increases the computational complexity at the receiver. In this paper, the computationalcomplexity of MIMO detection algorithms combined with turbo decoding is investigated. We firstpresent an overview of the family of MIMO detection algorithms based on sphere decoding, K-Bestdecoding, and interference cancellation. A recently proposed low-complexity K-Best decoder(LC-K-Best) is also presented. Moreover, we analyze the convergence of combining these detectionalgorithms with the turbo decoder using the extrinsic information transfer (EXIT) chart.Consequently, a new scheduling order of the number of iterations for the iterative process isproposed. Several system configurations are developed and compared in terms of performance andcomplexity. Simulations and analytical results show that the new scheduling provides goodperformance with a large saving in the complexity. Additionally, the LC-K-Best decoder shows agood performance-complexity tradeoff, and it is therefore suitable for parallel and pipelinearchitectures that can meet high throughput requirement