| In cooperative networks, terminals cooperate and form a distributed multi-antenna system to provide spatial diversity. In order to improve the diversity order, we consider the use of multiuser diversity in cooperative networks. Two cooperative strategies, the amplify-and-forward protocol and the decode-and-forward protocol, are combined with multiuser diversity.; In the amplify-and-forward protocol with multiuser diversity, the signals are relayed only by the relay terminal with the highest instantaneous signal-to-noise ratio (SNR). An asymptotic expression of the average symbol error rate (SER) is derived and it is shown that the diversity order is improved substantially. Based on the result of the asymptotic average SER, an optimal power allocation algorithm is proposed.; For cooperative networks with the decode-and-forward protocol, we first develop a hard decision detector in order to simplify the analysis of the diversity order and the derivation of the average SER. Compared to the optimal maximum likelihood (ML) detector, the proposed hard decision detector has much lower complexity while achieving almost the same diversity order. Next, the decode-and-forward protocol is combined with multiuser diversity, in which the signals are relayed by the relay terminal with the smallest conditional SER. The diversity order of this protocol is obtained and an approximate expression of the average SER is derived. Numerical results demonstrate that the proposed scheme considerably outperforms the previous schemes. |
