On The Performance Analysis Of Cooperative ARQ Protocols With Code Combining In Relay Communications

In order to counteract the fading of wireless channel, a variety of diversity techniques have received great attention in recent years. Cooperative diversity improves the reliability of data transmission by the way of relay node's assisting data tranmission of source node. On above basis, the system gets extra extra time diversity gain with code combining at the destination. Therefore, it has great theoretic and research value to research on cooperative ARQ with code combining in relay communication mode.Firstly, the Ampllified-and-Forward and Decode-and-Forward relay model is analyzed. With the fundamental principle discussion of cooperative ARQ and code combining, we obtain the code combining techniques for different ARQ protocols. Then, the performance of typeⅠcooperative ARQ with code combining in DF and AF relay communications and typeⅢcooperative ARQ in DF relay communications are analyzed. The results of the study show that the introduction of code combining brings an increase in diversity order and increased coefficient is relevant to code cluster number. With study of relay location's influence to ARQ system performance, we obtain below principles, the middle relay should be choosen in DF relay communicaitions with low SNR and the relay closer to destination node should be choosen; Cooperative ARQ system with AF relay can obtain better performance by choosing relay closer to source node. At last, the performance of cooperative ARQ system with code combining in multi-relay cooperative communication is analyzed. In DF relay communications, system performance with one more relay is equivalent to system performance with one more retransmission in single-relay. While in AF relay communicaitions the system performance will be decreased at low SNR and improved at high SNR with relay number increasing. Therefore, we can select transmission relay number according to the specific channel conditions.