6,954 research outputs found
Récepteur itératif pour les systÚmes 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 lâaccroissement de dĂ©bit et de robustesse dans les futurs systĂšmes de communication sans fil, les processus itĂ©ratifs sont de plus considĂ©rĂ©s dans les rĂ©cepteurs. Cependant, lâadoption dâun traitement itĂ©ratif pose des dĂ©fis importants dans la conception du rĂ©cepteur. Dans cette thĂšse, un rĂ©cepteur itĂ©ratif combinant les techniques de dĂ©tection multi-antennes avec le dĂ©codage de canal est Ă©tudiĂ©. Trois aspects sont considĂ©rĂ©s dans un contexte MIMOOFDM: la convergence, la performance et la complexitĂ© du rĂ©cepteur. Dans un premier temps, nous Ă©tudions les diffĂ©rents algorithmes de dĂ©tection MIMO Ă dĂ©cision dure et souple basĂ©s sur lâĂ©galisation, le dĂ©codage sphĂ©rique, le dĂ©codage K-Best et lâannulation dâinterfĂ©rence. Un dĂ©codeur K-best de faible complexitĂ© (LC-K-Best) est proposĂ© pour rĂ©duire la complexitĂ© sans dĂ©gradation significative des performances. Nous analysons ensuite la convergence de la combinaison de ces algorithmes de dĂ©tection avec diffĂ©rentes techniques de codage de canal, notamment le dĂ©codeur turbo et le dĂ©codeur LDPC en utilisant le diagramme EXIT. En se basant sur cette analyse, un nouvel ordonnancement des itĂ©rations internes et externes nĂ©cessaires est proposĂ©. Les performances du rĂ©cepteur ainsi proposĂ© sont Ă©valuĂ©es dans diffĂ©rents modĂšles de canal LTE, et comparĂ©es avec diffĂ©rentes techniques de dĂ©tection MIMO. Ensuite, la complexitĂ© des rĂ©cepteurs itĂ©ratifs avec diffĂ©rentes techniques de codage de canal est Ă©tudiĂ©e et comparĂ©e pour diffĂ©rents modulations et rendement de code. Les rĂ©sultats de simulation montrent que les approches proposĂ©es offrent un bon compromis entre performance et complexitĂ©. Dâun point de vue implĂ©mentation, la reprĂ©sentation en virgule fixe est gĂ©nĂ©ralement utilisĂ©e afin de rĂ©duire les coĂ»ts en termes de surface, de consommation dâĂ©nergie et de temps dâexĂ©cution. Nous prĂ©sentons ainsi une reprĂ©sentation en virgule fixe du rĂ©cepteur itĂ©ratif proposĂ© basĂ© sur le dĂ©codeur LC K-Best. En outre, nous Ă©tudions lâimpact de lâestimation de canal sur la performance du systĂšme. Finalement, le rĂ©cepteur MIMOOFDM itĂ©ratif est testĂ© sur la plateforme matĂ©rielle WARP, validant le schĂ©ma proposĂ©
Implementable Wireless Access for B3G Networks - III: Complexity Reducing Transceiver Structures
This article presents a comprehensive overview of some of the research conducted within Mobile VCEâs Core Wireless Access Research Programme,1 a key focus of which has naturally been on MIMO transceivers. The series of articles offers a coherent view of how the work was structured and comprises a compilation of material that has been presented in detail elsewhere (see references within the article). In this article MIMO channel measurements, analysis, and modeling, which were presented previously in the first article in this series of four, are utilized to develop compact and distributed antenna arrays. Parallel activities led to research into low-complexity MIMO single-user spacetime coding techniques, as well as SISO and MIMO multi-user CDMA-based transceivers for B3G systems. As well as feeding into the industryâs in-house research program, significant extensions of this work are now in hand, within Mobile VCEâs own core activity, aiming toward securing major improvements in delivery efficiency in future wireless systems through crosslayer operation
Channel coded iterative center-shifting K-best sphere detection for rank-deficient systems
Based on an EXtrinsic Information Transfer (EXIT) chart assisted receiver design, a low-complexity near-Maximum A Posteriori (MAP) detector is constructed for high-throughput MIMO systems. A high throughput is achieved by invoking high-order modulation schemes and/or multiple transmit antennas, while employing a novel sphere detector (SD) termed as a center-shifting SD scheme, which updates the SDâs search center during its consecutive iterations with the aid of channel decoder. Two low-complexity iterative center-shifting SD aided receiver architectures are investigated, namely the direct-hard-decision centershifting (DHDC) and the direct-soft-decision center-shifting (DSDC) schemes. Both of them are capable of attaining a considerable memory and complexity reduction over the conventional SD-aided iterative benchmark receiver. For example, the DSDC scheme reduces the candidate-list-generation-related and extrinsic-LLR-calculation related complexity by a factor of 3.5 and 16, respectively. As a further benefit, the associated memory requirements were also reduced by a factor of 16
MIMO-aided near-capacity turbo transceivers: taxonomy and performance versus complexity
In this treatise, we firstly review the associated Multiple-Input Multiple-Output (MIMO) system theory and review the family of hard-decision and soft-decision based detection algorithms in the context of Spatial Division Multiplexing (SDM) systems. Our discussions culminate in the introduction of a range of powerful novel MIMO detectors, such as for example Markov Chain assisted Minimum Bit-Error Rate (MC-MBER) detectors, which are capable of reliably operating in the challenging high-importance rank-deficient scenarios, where there are more transmitters than receivers and hence the resultant channel-matrix becomes non-invertible. As a result, conventional detectors would exhibit a high residual error floor. We then invoke the Soft-Input Soft-Output (SISO) MIMO detectors for creating turbo-detected two- or three-stage concatenated SDM schemes and investigate their attainable performance in the light of their computational complexity. Finally, we introduce the powerful design tools of EXtrinsic Information Transfer (EXIT)-charts and characterize the achievable performance of the diverse near- capacity SISO detectors with the aid of EXIT charts
Adaptive and Iterative Multi-Branch MMSE Decision Feedback Detection Algorithms for MIMO Systems
In this work, decision feedback (DF) detection algorithms based on multiple
processing branches for multi-input multi-output (MIMO) spatial multiplexing
systems are proposed. The proposed detector employs multiple cancellation
branches with receive filters that are obtained from a common matrix inverse
and achieves a performance close to the maximum likelihood detector (MLD).
Constrained minimum mean-squared error (MMSE) receive filters designed with
constraints on the shape and magnitude of the feedback filters for the
multi-branch MMSE DF (MB-MMSE-DF) receivers are presented. An adaptive
implementation of the proposed MB-MMSE-DF detector is developed along with a
recursive least squares-type algorithm for estimating the parameters of the
receive filters when the channel is time-varying. A soft-output version of the
MB-MMSE-DF detector is also proposed as a component of an iterative detection
and decoding receiver structure. A computational complexity analysis shows that
the MB-MMSE-DF detector does not require a significant additional complexity
over the conventional MMSE-DF detector, whereas a diversity analysis discusses
the diversity order achieved by the MB-MMSE-DF detector. Simulation results
show that the MB-MMSE-DF detector achieves a performance superior to existing
suboptimal detectors and close to the MLD, while requiring significantly lower
complexity.Comment: 10 figures, 3 tables; IEEE Transactions on Wireless Communications,
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