Research On Relay Selection Scheme And Optimization In Cooperative Communication System

Cooperative communication technology is a research hotspot in the field of wireless communications because it can combat fading and achieve spatial diversity.In order to improve system performance and reduce resource consumption,the problems about selection of cooperative relays,cooperation method of relays and the opportunity of introducing relays have become the important content to research.So the research of this paper is mainly focused on the relay selection and optimization in cooperative communication system.Firstly,the background,current research situation and practical application of cooperative communication are introduced.Then the advantages and disadvantages about typical relaying methods and relay selection schemes are analyzed and summarized Briefly.Finally the relay selection and optimization is carried out to research.So the main research work and creative contents are as follows:(1)In order to improve the flexibility of relay selection scheme and reduce system overhead,by introducing Automatic Repeat Request technology and combined with Hybrid Decode-and-Amplify Forward(HDAF)relaying strategy,an improved relay selection scheme based on maximizing the received Signal-to-Noise-Ratio(SNR)is proposed.According to the feedback information from the destination node,the proposed scheme can choose the information transmission method of non-cooperative transmission,the source node retransmission and transmission by relay node,respectively.Simulation results show that the the proposed scheme not only achieves much better outage performance,but improve the spectrum efficiency greatly.So the proposed scheme can improve the reliability and flexibility of information transmission.When the outage probability is 10-2,compared with the scheme based on HDAF,it obtains about 1dB performance gain,and more candidate relays the performance improving more obviously.(2)To reduce energy consumption and computational complexity of the scheme,the fast optimal relay set selection scheme based on minimizing Symbol Error Rate(SER)using HDAF is proposed.Firstly,the approximate expression of SER about the system based on Amplify-and-Forward(AF),Decode-and-Forward(DF)and HDAF respectively is derived using by Moment Generating Function and then based on it,the HDAF equivalent channel gain is defined cleverly to use for fast selection of the optimal relay set.Secondly,under the condition of selecting single relay,the optimal power allocation which aims to get the SER actual demand value is researched.The numerical simulations show that,firstly,the proposed scheme,compared with the other relay selection scheme,achieves much better performance in SER effectively;secondly,the SER of the proposed relay selection scheme performs similarly to that of the optimal full-searchscheme,but consumes less complexity;thirdly,the scheme can reduce system total power consumption.under the same conditions,compared with the scheme based on AF and DF,the total power can reduce about 1-1.5dB.Morever,compared with the equal power allocation,the total power can reduce 0.2dB.So the proposed relay selection scheme can reach a compromise between lowing SER and total power consumption.It makes relay selection more practical.