Conference Paper

# Space Diversity for Multi-antenna Multi-relay Channels

Institute for Digital Communications, School of Engineering and Electronics, University of Edinburgh, EH9 3JL, UK

Conference: Wireless Conference 2006 - Enabling Technologies for Wireless Multimedia Communications (European Wireless), 12th European Source: IEEE Xplore

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**ABSTRACT:**In this paper we analyze the performance of multiple relay channels when multiple antennas are deployed only at relays. Specifically, we investigate the simple repetition-coded decode-and-forward protocol and apply two antenna combining techniques at relays, namely maximum ratio combining (MRC) on receive and transmit beamforming (TB). We assume that the total number of antennas at all relays is fixed to N. With a reasonable power constraint at the relays, we show that the antenna combining techniques can exploit the full spatial diversity of the relay channels and can achieve the same diversity multiplexing tradeoff as achieved by more complex space-time distributed coding techniques, such as those proposed by Laneman and Womell (2003).Communications, 2007. ICC '07. IEEE International Conference on; 07/2007 - [Show abstract] [Hide abstract]

**ABSTRACT:**This paper investigates the optimal beamforming weight matrix for Multiple-Antenna Multiple-Relay (MAMR) Networks. It is assumed that each relay makes use of the Amplify and Forward (AF) strategy, i.e., it multiplies the received signal vector by a matrix, dubbed the relay weight matrix, and forwards the resulting vector to the destination. The relay weight matrices have to be concurrently designed to optimize a desired criterion at the destination, assuming each relay node is subject to a power constraint. In this work, the Mean Square Error (MSE) metric is assumed to be the corresponding cost function. In this regard, it is demonstrated that the aforementioned problem can be cast as a convex optimization problem in which the individual power constraints are tackled by employing the method of Lagrange multipliers. Then, it is demonstrated that the optimal solution can be tackled in two-fold. First, an elegant analytical method for the corresponding dual problem is devised; rendering the current complex vector optimization problem can be translated to a scalar optimization problem. Then, these scalar variables are computed numerically. Numerical results are provided, showing the Bit Error Rate (BER) achieved through using the proposed method outperforms that of MMSE-MMSE method introduced by Oyman et.al., which is regarded as the best known method for such problem.EURASIP Journal on Wireless Communications and Networking 01/2010; 2012(1). · 0.54 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**The optimal beamforming weight matrix for amplify and forward multiple-antenna multiple-relay network is investigated. It is assumed that the partial first and second hop channel state information (CSI) is available at relays. In order to minimize the mean square error (MSE) at destination, all relay weight matrices must be designed simultaneously under individual relay power constraints. Using the Lagrange dual variables, it is shown that this general vector optimization problem can be converted into a scalar optimization problem whose scalar Lagrange multipliers can be obtained numerically. This is the generalized version of the scheme suggested for complete CSI. The proposed scheme is evaluated through computer simulation with various numbers of relays and antennas to obtain MSE and bit error rate (BER) metrics. It is also shown that the resulting MSE and BER are less than those of the schemes available in the literature by a good margin depending upon the amount of the utilized relay and antennas as well as the estimation error.Wireless Personal Communications 68(4). · 0.43 Impact Factor

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