Transmission strategies and resource allocation for wireless cooperative networks

Abstract

In a wireless ad hoc network, a wireless node not only acts as a source or a destination, but also works as a relay to help forward messages for other sourcedestination pairs. In general, cooperative transmission methods can be classified as transmitter cooperation and receiver cooperation, depending on whether cooperation is among transmitters or among receivers. One of the most fundamental concerns in cooperative communication is to comprehend the performance limits in the networks with cooperation. That leads to a growing demand on the area of network information theory and especially the topic of relay networks. Based on the considerations above, we analyze two kinds of networks respectively. One is wireless networks with receiver cooperation, and the other one is wireless networks with full cooperation in which both transmitter cooperation and receiver cooperation exist. In order to demonstrate the problem in a simple and direct way, we assume that there are two source-destination pairs in both networks we concern, and that the channel state is fixed and perfectly known at all nodes. In the wireless network with receiver cooperation, we assume that there is a direct link between the source and the destination of a pair. Besides there is also a cross link between a non-paired source node and a destination node. Furthermore, the two destination nodes have cooperative links between them for the cooperation. For the frequency-flat model, a cut-set outer bound and a cooperative coding strategy are derived. We use Matlab to see the performance of the proposed strategy, and compare it with the outer bound and two other strategies in the scenario of high signal to noise ratio (SNR) and low SNR, respectively. Moreover, we found that our proposed strategy achieves the outer bound in a special case. Then, we extend the model to a frequency-selective one, in which each node can take several subcarriers to transmit messages. We develop two resource allocation methods to maximize the sum rate, and compare them with two counterparts in the regimes of high SNR and low SNR.We also compare them in terms of computational complexity, and realize the tradeoff between the sum rate and computational complexity. In order to present the problem in a more general way, we add cooperative links between the two source nodes in the model of wireless networks with full cooperation. In this model, each source node can also work as a relay to help forward messages of the other source-destination pair. Therefore, there exist three relay paths for either source-destination pair. The first one is a two-hop path by the other destination node as relay. The second one is a two-hop path by the other source node as relay. The last one is a three-hop path by the other two nodes as relay. Likewise, an outer bound in the scenario of frequency-flat channel is given for comparison and a forwarding strategy is proposed. We evaluate the performance of the strategy under different channel conditions. It is shown that there is a gap between the proposed strategy and the outer bound in every case we have for full cooperation. Besides, its performance in high SNR regime and low SNR regime are also studied. For the scenario of frequency-selective channel, we utilize similar resource allocation methods used in the networks with receiver cooperation, and compare them with two other schemes in terms of sum rate and computational complexity.

Date of Award	4 Oct 2010
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Chi Wan SUNG (Supervisor)