Cooperative Transmission for Wireless Relay Networks Using Limited Feedback

To achieve the available performance gains in half-duplex wireless relay networks, several cooperative schemes have been earlier proposed using either distributed space-time coding or distributed beamforming for the transmitter without and with channel state information (CSI), respectively. However, these schemes typically have rather high implementation and/or decoding complexities, especially when the number of relays is high. In this paper, we propose a simple low-rate feedback-based approach to achieve maximum diversity with a low decoding and implementation complexity. To further improve the performance of the proposed scheme, the knowledge of the second-order channel statistics is exploited to design long-term power loading through maximizing the receiver signal-to-noise ratio (SNR) with appropriate constraints. This maximization problem is approximated by a convex feasibility problem whose solution is shown to be close to the optimal one in terms of the error probability. Subsequently, to provide robustness against feedback errors and further decrease the feedback rate, an extended version of the distributed Alamouti code is proposed. It is also shown that our scheme can be generalized to the differential transmission case, where it can be applied to wireless relay networks with no CSI available at the receiver.Comment: V1: 27 pages, 1 column, 6 figures. Submitted to IEEE Transactions on Signal Processing, February 2, 2009. V2: 30 pages, 1 column, 8 figures. Revised version submitted to IEEE Transactions on Signal Processing, July 23, 200

Distributed quasi-orthogonal space-time coding for two-way wireless relay networks

Abstract—The contribution in this paper is to consider distributed quasi orthogonal space-time block coding (D-QO-STBC) for two-way (TW) wireless relay networks. In particular we exploit a two time slot protocol and both open-loop and closedloop D-QO-STBC with full cooperative diversity. In the openloop approach constellation rotation is exploited to improve performance, whereas two feedback terms are used in the closedloop schemes. Our end-to-end bit error rate simulations show that TW closed-loop D-QO-STBC and rotated open-loop D-QO-STBC are approximately 8 dB and 7.5 dB better than the distributed Alamouti TW approach at 10−4 bit error rate (BER), which confirms the advantage of four relay schemes in relay network

Cooperative strategies for imperfect CSI scenarios based on distributed Alamouti

Les comunicacions cooperatives estan guanyant un gran interès en les comunicacions modernes degut a que permeten millorar la transmissió dʼinformació entre un emissor i un receptor utilitzant una sèrie de terminals situats entre ells. Aquest projecte és un estudi complet del sistemes cooperatius, analitzant el seu rendiment i comparant lʼús dʼun sol dʼaquests terminals amb lʼús del codi Alamouti, que utilitza dos terminals. Primer hi ha una introducció als sistemes cooperatius i a la teoria de la informació. Després hem estudiat un sistema cooperatiu amb la teoria de la informació com a base, en termes de probabilitat de fallada del sistema, i posteriorment lʼhem adaptat a un sistema cooperatiu real utilitzant una modulació QPSK, estudiant la seva probabilitat dʼerror de paquet. Finalment es proposen diversos protocols que permeten millorar el rendiment del sistema cooperatiu estudiat.Las comunicaciones cooperativas están ganando mucho interés en las comunicaciones modernas debido a que permiten mejorar la transmisión de información entre un emisor y un receptor usando una serie de terminales intermedios. Este proyecto es un estudio completo de los sistemas cooperativos, analizando su rendimiento y comparando el uso de uno solo de estos terminales con el uso del código Alamouti, el cual usa dos terminales. Primero hay una introducción a los sistemas cooperativos y a la teoría de la información. Después hemos estudiado un sistema cooperativo con la teoría de la información como base, en términos de probabilidad de fallo del sistema, y posteriormente lo hemos adaptado a un sistema cooperativo real usando una modulación QPSK, estudiando su probabilidad de error de paquete. Finalmente se proponen varios protocolos que permiten mejorar el rendimiento del sistema cooperativo estudiado.Cooperative communications are gaining much interest in modern communications because they allow to improve the information transmission between a source and a destination using various intermediate terminals. This project is a complete study of cooperative systems, analyzing its performance and comparing the use of a single terminal with the use of the Alamouti code, which uses two terminals. First, there is an introduction to cooperative systems and to information theory. Then we have studied a cooperative system using the information theory, in terms of outage probability, and subsequently we have adapted it to a real cooperative system using a QPSK modulation, studying its packet error probability. Finally several protocols are proposed to improve the performance of the studied cooperative system

A virtual MIMO dual-hop architecture based on hybrid spatial modulation

International audienceIn this paper, we propose a novel Virtual Multiple-Input-Multiple-Output (VMIMO) architecture based on the concept of Spatial Modulation (SM). Using a dual-hop and Decode-and-Forward protocol, we form a distributed system, called Dual-Hop Hybrid SM (DH-HSM). DH-HSM conveys information from a Source Node (SN) to a Destination Node (DN) via multiple Relay Nodes (RNs). The spatial position of the RNs is exploited for transferring information in addition to, or even without, a conventional symbol. In order to increase the performance of our architecture, while keeping the complexity of the RNs and DN low, we employ linear precoding using Channel State Information (CSI) at the SN. In this way, we form a Receive-Spatial Modulation (R-SM) pattern from the SN to the RNs, which is able to employ a centralized coordinated or a distributed uncoordinated detection algorithm at the RNs. In addition, we focus on the SN and propose two regularized linear precoding methods that employ realistic Imperfect Channel State Information at the Transmitter. The power of each precoder is analyzed theoretically. Using the Bit Error Rate (BER) metric, we evaluate our architecture against the following benchmark systems: 1) single relay; 2) best relay selection; 3) distributed Space Time Block Coding (STBC) VMIMO scheme; and 4) the direct communication link. We show that DH-HSM is able to achieve significant Signal-to-Noise Ratio (SNR) gains, which can be as high as 10.5 dB for a very large scale system setup. In order to verify our simulation results, we provide an analytical framework for the evaluation of the Average Bit Error Probability (ABEP)

Distributed Coding and Modulation for 2-hop Communication via Relays

The past few decades have seen tremendous growth in the field of wireless communication systems. At this juncture, just before the advent of the 4th Generation of mobile standards, the question asked is how to improve the system in terms of coverage, capacity and reliability for the cell-edge users in a cellular network. Providing answers to this question could result in a significant improvement in the average throughput of the cell. The main purpose of the thesis work is therefore to implement Cooperative Communication via Distributed System of Relays. This concept is derived from the combination of relaying technology and multiple antenna techniques used in MIMO systems. During this thesis work, two transmit diversity schemes: the Delay Diversity Scheme and the Distributed Alamouti Scheme are developed on a 3GPP LTE compliant platform described as the OpenAir Interface. The ultimate objective is basically to improve the system performance by exploiting macro-diversity gains obtained as a result of these schemes. In the process of this development, numerous challenging tasks are provided with efficient solutions and have been implemented. Moreover, the last but the most crucial task of the thesis is to develop an entirely new HARQ protocol for a distributed system of relays. The work has been carried out at Eurecom, France as an initial step to implement the aforementioned schemes on a real-time network

Iterative detection for frequency-asynchronous distributed Alamouti-coded (FADAC) OFDM

We propose a near intercarrier interference (ICI)-free and very low complexity iterative detector for frequency-asynchronous distributed Alamouti-coded (FADAC) orthogonal frequency division multiplexing (OFDM). In the previous cancelation schemes, the entire subcarrier signals from one transmit (TX) antenna are estimated and canceled in the received signal from the other TX antenna and vice versa. However, the reliability of the estimated symbols are revealed to significantly vary across the subcarriers and thus, the poorly estimated symbols lead to the incorrect cancelation. Motivated from this, we first propose a scheme which does not cancel the interfering subcarrier(s) at the half band edges which undergo very high interference in FADAC-OFDM. For further improvement, we propose a so-called selective scheme which instantly measures the reliability of the detected symbols at each iteration and then exclude the unreliable symbols in the estimated interference generation. Moreover, the proposed scheme has a drastically reduced complexity by converting the cancelation process from the subcarrier domain to the time domain. In accordance with the analysis on the considered reliability measures, the numerical results show that the proposed scheme achieves the near ICI-free level only within three or four iterations for wide ranges of SNR, frequency offset, and delay spread.1

Novel precoded relay-assisted algorithm for cellular systems

Cooperative schemes are promising solutions for cellular wireless systems to improve system fairness, extend coverage and increase capacity. The use of relays is of significant interest to allow radio access in situations where a direct path is not available or has poor quality. A data precoded relay-assisted scheme is proposed for a system cooperating with 2 relays, each equipped with either a single antenna or 2-antenna array. However, because of the half-duplex constraint at the relays, relaying-assisted transmission would require the use of a higher order constellation than in the case when a continuous link is available from the BS to the UT. This would imply a penalty in the power efficiency. The simple precoding scheme proposed exploits the relation between QPSK and 16-QAM, by alternately transmitting through the 2 relays, achieving full diversity, while significantly reducing power penalty. Analysis of the pairwise error probability of the proposed algorithm with a single antenna in each relay is derived and confirmed with numerical results. We show the performance improvements of the precoded scheme, relatively to equivalent distributed SFBC scheme employing 16-QAM, for several channel quality scenarios. Copyright © 2010 Sara Teodoro, et al.European project CODIVPortuguese project CADWINPortuguese project AGILEFC