Space Diversity for Multi-antenna Multi-relay Channels
ABSTRACT In this paper we analyze the performance of multiple relay channels when multiple antennas are deployed only at relays. We apply two antenna diversity techniques at relays, namely maximum ratio combining (MRC) on receive and transmit beamforming (TB). We show that with K relays the network can be decomposed into K diversity channels each with a different channel gain, and that the signals can be effectively combined at the destination. We assume that the total number of antennas at all relays is fixed at N. If the total transmit power for all relays are the same as for the source and equally distributed among all the relays, the network capacity will be lower bounded by that of N relay channels each with single antenna, and upper bounded by that of single relay channels with N antennas.
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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). DOI:10.1109/ISABEL.2010.5702868 · 0.81 Impact Factor
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ABSTRACT: In this paper, we design and analyze a new 802.11- based cooperative MAC protocol. Since the wireless fading interval sometimes is comparable to the time of multiple-frame transmission, the traditional retransmission schemes may not be optimal. We consider designing a multi-relay system where neighbor nodes can assist the retransmission in order to achieve transmission diversity and combat channel fading. Since the cooperative capacity varies from relay to relay, the key point lies in how to assign different priorities to relays. This paper proposes a priority-based contention mechanism in cooperation, and tries to derive the optimal cooperation contention window size to maximize the network throughput. We present the results both from simulation and from theoretical analysis, which jointly verify the excellent performance of our new protocol.01/2011; DOI:10.1109/wicom.2011.6040212
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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 02/2012; 68(4). DOI:10.1007/s11277-012-0542-5 · 0.98 Impact Factor