Research On Relay Selection And Power Allocation In Cooperative Communication Systems

The performance of wireless communication will be seriously affected due to the fading characteristic of the wireless channel. In order to effectively combat the fading characteristics of wireless channel, Multi-Input Multi-Output (MIMO) technology has been proposed by researchers. However, the realization of MIMO need to configurate multi-antenna on terminals. In particular, due to the restrictions such as size, power etc, the terminals can not configure multiple antennas, which have limited the application of MIMO technology. To overcome this drawback, the concept of cooperative communications has recently been proposed and gained large interest in the research community. The main idea of cooperative communications is to form a virtual MIMO system by utilizing neighbor nodes mutually transfer information on each other. With this approach, the benefits of MIMO systems can be attained in a distributed fashion, thereby improving the system performance.This thesis focus on relay node selection and power allocation in cooperative communications systems carried out researching. The thesis is divided into six chapters, the main contents are listed as follows:Firstly, the research status of cooperative communications has been illustrated generally. With the contents of this sthesis, the research progress of relay as well as the relay selection and power allocation in cooperative communications have been introduced in a brief way.Secondly, a brief introduction has given to the related technologies of cooperative communications, which including the common diversity and combing methods as well as cooperative diversity and relaying procotols. The performance of Amplify-and-Forward (AF) and Decoded-and-Forward (DF) have simply simulated and compared.Next, combed with best relay selection, a threshold relay selection method has been analyzed in AF system. The symbol error rate as well as bandwidth efficiency have been analyzed for this method under M-PSK and M-QAM modulation schemes. Simulation results illustrate that the performance of the threshold method approaches to the best selection method in a low threshold condition. What's more, in different SNR region and relay nodes, better SER performance or bandwidth efficiency can be obtained by adjust the threshold to an appropriate value.Finally, the power allocation issue has been analyzed in AF and DF systems under the conditon that the total system power is constant. The performance of different power allocation schemes have simulated. For AF system, the allocation schemes based on minimize the symbol error rate and maximize the system capacity have been analyzed, and then a joint allocation scheme has been analyzed. For DF system, the power allocation schemes for the purpose of maximize the system capacity and minimize the symbol error rate have been analyzed. Combined with the power allocation issue, this thesis analyzed the location of the relay nodes impact on the system performance both for AF and DF system.