Relay Research In The Cooperative Diversity

Transmission over wireless channels suffers from multi-path fading,which is the biggest problem that affects the data rate and quality of service.Diversity is a powerful technique to mitigate fading,such as time diversity,frequency diversity,spatial diversity, and so on.Spatial diversity is particillarly attractive since it provides diversity gain without incurring all expenditure of transmission time or bandwidth,and also can be combined with other diversity techniques.However,in practice,because of the size,weight,and energy,it's hard to equip multiple antennas at the mobile terminals.Thus a new diversity is proposed,which is called cooperative diversity.It means that mobile terminals share antennas of each other,which can be form a virtual antenna array to get the same gain as conventional MIMO technique does.A large number of research results show that cooperative diversity can enhance system capacity, increase data transfer rate, effectively combat multipath fading and reduce system outage probability and improve the quality of service and reliability.This paper firstly introduced various types of diversity technology and combination diversity technology currently existing, as well as the protocal of cooperative diversity and the methord of relay selection. Also analysis the performance of cooperate diversity based on two users cooperative diversity, simulation result show that about the up to rate areas ,as well as the investigation about the condition of cooperate diversity under different diversity protocol between two users who based on the duplication codes. The simulations about the different relay protocol's outage probabilities and diversity modulus show that AF protocol based duplication codes can get the full diversity gain,and DF protocol's diversity modulus equals 1.After discussion about the situation of two users,this paper do some theories researches about the AF protocol's error rate under multi-user.Finally,Proved the AF protocol's superiority under huge SNR through simulation,this paper also comes up with the solution of distributed power on relay node and the selection of relay which turns out to get the minimum outage probability under high signal to noise ratio.