Esquemas distribuídos para seleção de múltiplas antenas em redes com retransmissores do tipo amplifica-e-encaminha

Orientador: José Cândido Silveira Santos FilhoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: A seleção de antena na transmissão tem sido apresentada como uma estratégia promissora para explorar os benefícios do uso de múltiplas antenas em sistemas de comunicações com retransmissores. No entanto, essa abordagem pode exigir um montante considerável de estimações de canal, transmissões de realimentação e atraso, dado que a sua implementação ótima e centralizada requer o monitoramento do estado do canal de todos os enlaces. Para aliviar essas deficiências, este trabalho propõe e analisa um conjunto de esquemas subótimos de seleção de antena na transmissão para sistemas com retransmissores do tipo amplifica-e-encaminha, os quais podem ser implementados de uma forma distribuída. Nos esquemas propostos, a antena é selecionada com base na informação local do estado de canal que está disponível na fonte, requerendo, portanto, um atraso e uma carga de realimentação pequenos e constantes. Tal abordagem é considerada em uso conjunto com diferentes técnicas, incluindo métodos de combinação de diversidade (combinação por máxima razão e combinação por seleção) no destino, protocolos de ganho fixo ou variável no relay, e transceptores com múltiplas antenas no relay. Além disso, para o caso particular em que o retransmissor tem ganho fixo e uma única antena, considera-se também o uso de um mecanismo de seleção de enlace na fonte. Para cada caso, o desempenho do sistema é avaliado em termos de probabilidade de outage, eficiência espectral e/ou vazão. O foco principal é direcionado à probabilidade de outage, para a qual são deduzidas expressões exatas e limitantes de desempenho. Uma análise assintótica é também efetuada para enriquecer a compreensão do comportamento do sistema quando operando sob alta relação sinal-ruído. Finalmente, como contribuição isolada, uma estratégia subótima e simples de alocação de potência é elaborada para um sistema com múltiplos retransmissores do tipo decodifica-e-encaminha, considerando-se enlaces com erros e codificação de fonte distribuídaAbstract: Transmit-antenna selection has been presented as a promising strategy for exploiting the benefits of multiple antennas in relaying communication systems. However, this approach may demand a considerable amount of channel estimations, feedback transmissions, and delay, since its optimal centralized implementation requires monitoring the channel state of all links. To alleviate those impairments, this work proposes and analyzes a set of suboptimal transmit-antenna selection schemes for amplify-and-forward relaying systems, which can be implemented in a distributed manner. In the proposed schemes, the antenna is selected based on the local channel-state information that is available at the source, thus requiring a low and constant delay/feedback overhead. Such an approach is considered along with different techniques, including diversity combining methods (maximal-ratio combining and selection combining) at the destination, fixed- and variable-gain protocols at the relay, and multi-antenna transceivers at the relay. A link-selection mechanism at the source is also considered for the special case of a single-antenna fixed-gain relay. For each case, the system performance is assessed in terms of outage probability, spectral efficiency, and/or throughput. The main focus is placed on the outage probability, for which exact or bound expressions are derived. An asymptotic analysis is also performed to provide further insights into the system behavior at high signal-to-noise ratio. Finally, as an isolated contribution, a simple suboptimal power allocation strategy is designed for a decode-and-forward multi-relay system with lossy intra-links and distributed source codingDoutoradoTelecomunicações e TelemáticaDoutora em Engenharia ElétricaCAPE

Joint Source and Relay Precoding Designs for MIMO Two-Way Relaying Based on MSE Criterion

Properly designed precoders can significantly improve the spectral efficiency of multiple-input multiple-output (MIMO) relay systems. In this paper, we investigate joint source and relay precoding design based on the mean-square-error (MSE) criterion in MIMO two-way relay systems, where two multi-antenna source nodes exchange information via a multi-antenna amplify-and-forward relay node. This problem is non-convex and its optimal solution remains unsolved. Aiming to find an efficient way to solve the problem, we first decouple the primal problem into three tractable sub-problems, and then propose an iterative precoding design algorithm based on alternating optimization. The solution to each sub-problem is optimal and unique, thus the convergence of the iterative algorithm is guaranteed. Secondly, we propose a structured precoding design to lower the computational complexity. The proposed precoding structure is able to parallelize the channels in the multiple access (MAC) phase and broadcast (BC) phase. It thus reduces the precoding design to a simple power allocation problem. Lastly, for the special case where only a single data stream is transmitted from each source node, we present a source-antenna-selection (SAS) based precoding design algorithm. This algorithm selects only one antenna for transmission from each source and thus requires lower signalling overhead. Comprehensive simulation is conducted to evaluate the effectiveness of all the proposed precoding designs.Comment: 32 pages, 10 figure

How to Understand LMMSE Transceiver Design for MIMO Systems From Quadratic Matrix Programming

In this paper, a unified linear minimum mean-square-error (LMMSE) transceiver design framework is investigated, which is suitable for a wide range of wireless systems. The unified design is based on an elegant and powerful mathematical programming technology termed as quadratic matrix programming (QMP). Based on QMP it can be observed that for different wireless systems, there are certain common characteristics which can be exploited to design LMMSE transceivers e.g., the quadratic forms. It is also discovered that evolving from a point-to-point MIMO system to various advanced wireless systems such as multi-cell coordinated systems, multi-user MIMO systems, MIMO cognitive radio systems, amplify-and-forward MIMO relaying systems and so on, the quadratic nature is always kept and the LMMSE transceiver designs can always be carried out via iteratively solving a number of QMP problems. A comprehensive framework on how to solve QMP problems is also given. The work presented in this paper is likely to be the first shoot for the transceiver design for the future ever-changing wireless systems.Comment: 31 pages, 4 figures, Accepted by IET Communication

Multi-Antenna Cooperative Wireless Systems: A Diversity-Multiplexing Tradeoff Perspective

We consider a general multiple antenna network with multiple sources, multiple destinations and multiple relays in terms of the diversity-multiplexing tradeoff (DMT). We examine several subcases of this most general problem taking into account the processing capability of the relays (half-duplex or full-duplex), and the network geometry (clustered or non-clustered). We first study the multiple antenna relay channel with a full-duplex relay to understand the effect of increased degrees of freedom in the direct link. We find DMT upper bounds and investigate the achievable performance of decode-and-forward (DF), and compress-and-forward (CF) protocols. Our results suggest that while DF is DMT optimal when all terminals have one antenna each, it may not maintain its good performance when the degrees of freedom in the direct link is increased, whereas CF continues to perform optimally. We also study the multiple antenna relay channel with a half-duplex relay. We show that the half-duplex DMT behavior can significantly be different from the full-duplex case. We find that CF is DMT optimal for half-duplex relaying as well, and is the first protocol known to achieve the half-duplex relay DMT. We next study the multiple-access relay channel (MARC) DMT. Finally, we investigate a system with a single source-destination pair and multiple relays, each node with a single antenna, and show that even under the idealistic assumption of full-duplex relays and a clustered network, this virtual multi-input multi-output (MIMO) system can never fully mimic a real MIMO DMT. For cooperative systems with multiple sources and multiple destinations the same limitation remains to be in effect.Comment: version 1: 58 pages, 15 figures, Submitted to IEEE Transactions on Information Theory, version 2: Final version, to appear IEEE IT, title changed, extra figures adde

Linear Precoding Designs for Amplify-and-Forward Multiuser Two-Way Relay Systems

Two-way relaying can improve spectral efficiency in two-user cooperative communications. It also has great potential in multiuser systems. A major problem of designing a multiuser two-way relay system (MU-TWRS) is transceiver or precoding design to suppress co-channel interference. This paper aims to study linear precoding designs for a cellular MU-TWRS where a multi-antenna base station (BS) conducts bi-directional communications with multiple mobile stations (MSs) via a multi-antenna relay station (RS) with amplify-and-forward relay strategy. The design goal is to optimize uplink performance, including total mean-square error (Total-MSE) and sum rate, while maintaining individual signal-to-interference-plus-noise ratio (SINR) requirement for downlink signals. We show that the BS precoding design with the RS precoder fixed can be converted to a standard second order cone programming (SOCP) and the optimal solution is obtained efficiently. The RS precoding design with the BS precoder fixed, on the other hand, is non-convex and we present an iterative algorithm to find a local optimal solution. Then, the joint BS-RS precoding is obtained by solving the BS precoding and the RS precoding alternately. Comprehensive simulation is conducted to demonstrate the effectiveness of the proposed precoding designs.Comment: 13 pages, 12 figures, Accepted by IEEE TW