Signal Detective In Multi-user Cooperative Diversity

Space cooperative diversity has recently emerged as an effective way to achieve high capacity of the channel. As one of diversity technologies, MIMO (multiple-input multiple-output) communication technology is widely studied by researchers. It is very difficult to equip multiple antennas in mobile terminal taking into consideration the limitation of cost, battery consumption and terminal's volume. Cooperative diversity can solve this problem. As there are many users in the wireless system, cooperative diversity allows sharing the resources (e.g., time, frequency) among cooperative users and each user can serve as a relay for the transmissions of other users'information, and then each user can obtain diversity gain. The cooperative diversity brings a set of new tools that improve communication capacity, speed and performance, reduce the battery consumption and extend network coverage area. Although this technology is not mature now, it has been one hotspot in future wireless communication systems.In order to improve the performance of the communication system, different modes of cooperative diversity, different combining methods were analyzed and simulated in this paper. This is very important to enhance cooperative diversity system's development. Firstly, the mathematical model of amplify-and-forward protocol and decode-and-forward protocol were built based on analyzing different forward principles in cooperative diversity communication. The capability and outage probability were discussed and simulated both in direct transmission and AF relaying, from the simulations we can see the performance of AF cooperative diversity is better than that of direct transmission. Secondly, the performance of receiver under different combining methods in wireless cooperative diversity systems is studied and simulated by Matlab software. From the simulation we can see that the impact to the system is greatly different when adopting different reception combining methods. Compared with EGC, FRC and SNRC, the enhanced SNR combining which was proposed has shown a very good performance, and it has greatly reduced the complexity of the receiver. Thirdly, convolutional coding was firstly used in differential DF modulation, at the same time many communication blocks were designed, such as Viterbi decoding, convolutional coding, BPSK modulation and different combining methods. Various results show that the performances of systems can obtain two order's diversity gain without knowing the channel state information (CSI). Performance comparison of reception combining methods in differential DF system when rates of coded are 3/4,2/3,/1/2 is studied. From the results we know that the lower coding rate is, the better performance system can gain. In this model, the instance CSI that needed in SNRC is replaced by average CSI, so the performance of SNRC is worse than that of EGC, FRC combining, and EGC is the best combining among EGC, FRC and SNRC.