Study Of The Performances In Wireless Relay Systems

With the increasing demands of wireless communication service, people needs wireless transmission with higher speed and better quality. Signal fading arising from multi-path propagation is the main problem to improve speed and quality of wireless transmission, so many methods are introduced to mitigate the impairment of multi-path fading among which diversity technique is one of most useful ways to conquer multi-path fading. Diversity, sorted by ways of multiplex, includes time diversity, frequency diversity and space diversity, among which space diversity is particularly attractive for its dramatic Performance without sacrificing delay and bandwidth. As a consequence, cooperative relay techniques will have been developing in the future wireless systems due to the requirements of users and network revolutions. Through the use of the multiple antennas and the cooperation between users, the wireless system will make use of space diversity and multiplexing gains to countermine multi-path fading, thus improving its performances.Cooperative relay transmission has been widely accepted and regarded as an effective way to combat multi-path fading. In this paper, we mainly study the relay node selection scheme and the power allocation in virtual MIMO relay system. Firstly, we investigate the relay selection from a lot of nodes randomly distributed between source and destination. Define a threshold, and generate a feasible set including the nodes which meet the selection condition. Then the source node choose the best one from the feasible set to be the relay. Also, we extend the selection scheme to that with multiple destination nodes. Secondly, we investigate power allocation algorithm of multi-relay system. This system model here we consider includes a base station with multiple antennas, multiple relay stations with only single antenna each and a mobile station with one antenna. For simplicity, path-loss and shadow fading are not taken into account here, and also the direct paths are ignored. Taking constraint of the total transmission power into account, we employ a power allocation algorithm between the antennas of BS and the RSs in order to maximize the capacity of this system. Compare with the traditional uniform power allocation scheme, numerical results indicate that the proposed scheme which distributes resource appropriately to each hop can provide better performance.