Study On Resource Allocation For Cooperative Diversity In Wireless Networks

In wireless networks, multipath fading severely degrades the system performance. As we all know, MIMO system is an efficient way to combat multipath fading by exploiting space diversity, and doesn't loss spectral efficiency. However, many mobile terminals, e.g., mobile phones and sensor nodes, can not practically adopt multiple-antenna techniques, due to their size, power, cost limitations. Therefore, cooperative diversity has been proposed, which enables single-antenna users to exploit space diversity in a distributed way by sharing their antenna and creating the virtual antenna array (VAA) for relayed transmission.Relayed transmission is completed by the cooperation between source and relay. As a result, resource allocation becomes an important issue in wireless cooperative diversity networks. In this paper, we investigate two aspects of resource allocation: optimal power allocation and partner selection.In cooperative communication, both source and relay consume power while transmitting the signal. So diversity gains are obtained at the expense of the total power of source and relay. On the assumption of constant total transmit power, an optimal power allocation scheme between source and relay is proposed in the amplify-and-forward (AF) protocol and the decode-and-forward protocol, using the lower bound or upper bound of bit error rate (BER) in high SNR as objective function. Simulation results show that the proposed scheme promises to reduce BER and enhances the system performance by decreasing the outage probability, compared to uniform power allocation between source and relay.Until now, the research of cooperative diversity mainly concentrates on two users models. When extended to multi-user cooperative communication, partner selection plays an important role in the performance of the whole networks. After generalizing the closed approximate expression of outage probability in high SNR, we present a new selecting scheme in the coded cooperation (CC) protocol using Hungarianalgorithm. Simulation results show that, although an approximate outage probability, Hungarian algorithm produces global optimal solution. Thus it improves the outage probability performance in high SNR or low rate, compared to greedy algorithm.In partner selection, if we only aim at minimizing the average outage probability of the whole networks, not all users can benefit from the cooperation. The outage probability performance of some users may be even worse than those in direct transmission, due to the improper selecting partners. On the other hand, the fair improvement of outage probability is reasonable among users, because of their similarities. In this paper, we use Nash Bargaining Solution (NBS) strategy to select partners. Simulation results show NBS strategy not only minimizes the average outage probability of the whole networks, but also makes sure that the outage probability performance of each user in cooperation outperforms that in direct transmission and the improvement is relatively fair among users. In this way, a tradeoff between efficiency and fairness is obtained.