Multi-user / Multi-relay Collaborative Wireless Communications Technology

As one of the key technologies of next generation wireless communication, Multiple Input Multiple Output (MIMO) can effectively overcome the inherent multi-path fading of wireless channel. However, since the mobile station size, power consumption constraints, it is difficult to realize MIMO in the uplink. Based on this consideration, a new concept called Cooperative Communications has been proposed recently. It is also called"virtul MIMO". The technology allows multiple users to share a single antenna gain between the antenna spatial diversity gain, thereby increasing system capacity and transmission performance. In this paper, we take diversity and cooperative technology into consideration to analyze the system performace.First, the single-user single-relay collaborative communication systems which use the DCF method are discussed. In order to find a trade off between performance and complexity of traditional protocols Amplify-and-Forward (AF) and Decode-and-Forward (DF), Decouple-and-Forward (DCF) has been proposed recently. Based on DCF protocol, we analyze the outage probability of space-time coded decouple-and-forward relay network in Nakagami-m fading channels. Both accurate expressions and closed-form bounds are derived for computing the outage probability. The Nakagami-m model represents a wide variety of realistic fading channels encountered in practice. Therefore our solution can be used to evaluate the outage probability performance under different fading severity conditions. By setting m = 1, our results are applicable for Rayleigh fading. Numerical and computer simulations confirm our mathematical analysis.Following that, we study the Network Coding (NC) based collaborative multi-user single-relay communication systems. By comparing the traditional multi-access relay channel (Multiple Access Relay Channel, MARC), point to point systems, and network-based collaborative communications system (NCBC), we come to the conclusion that NCBC is a promising candidate to solve the efficiency problem in multi-user-single-relay setup. Not only we derive the user-level outageprobability of the NCBC system, but also we obtain a system-level result. Besides, we try to find the effect of nodes'location to the performance.Finally, the relay selection proble in single-user-multi-hop system has been analyzed. In this situation, multiple relay candidates do exist. Therefore, no matter which cooperative protocol will be chosen, the first step is to decide which relays to choose. In this paper, two different selection algorithms are compared. The location-based mehed, which requires each player in the system to know its onw location exactly, is much suitable for a static network. By contrast, the instantaneous channel information based way is better for a network in which the nodes change their position frequently.