A Study On Relay Selection Strategy In Multi-user Collaborative Communication System

Wireless communications have encounted with many of obstacles, one of whichis due to the difficult to configure with multiple antennas in the moblile terminal sothat the ending-users can not get MIMO gain, For this reason, Sendonaris proposesthe concept of user cooperation diversity, and implements cooperative communication,that is a collaborative technology through virtual antenna array to obtain spatialdiversity. Since the concept of collaborative communication has been proposed , relaynode selection and power allocation have been the two hot spots for collaborativecommunication, and both often affect each other. This paper focus on relay nodeselection and power allocation for multi-user collaborative communication system.The completed tasks are as follows.Firstly, the paper introduces several common relay forward protocols,andemphasis on Amplify and Forward(AF) and Decode and Forward (DF) protocols.Thenintroduces the forward process for AF and DF and gets respective instantaneousmutual information、outage probability and symbol error ratio(SER). At the same time,the paper introduces an optimal power allocation scheme based on the criteria ofmaximizing the instantaneous channel capacity for AF protocol. Finally, simulates theperformance of channel capacity and symbol error ratio for AF and DF protocols, andsimulation results demonstrates that AF and DF protocols greatly improve theperformance of system compared with no-cooperation.Secondly, the paper studies the relay selection algorithms in multi-usercooperative system model. At first, introduces the network model of multi-relayamplify-and-forward protocol, then derives the channel capacity and outageprobability expressinon in the case of multi-relay. At the same time, the paperintroduceds a relay selection scheme based on instantaneous channel statusinformation, also calls opportunistic relay(OR) scheme; Finally, due to theimplementation complexity for OR is too high, the paper proposes a random selectiverelays(RSR) algorithm based on channel statistical information, that is, according tochannel statistical information , selecting randomly the number of cooperative relaynodes, in addition, proposes an optimal power allocation scheme based on RSRalgorithm. Simulation results demonstrate that RSR algorithm outperforms AAF andSAF algorithms on outage probability. In the high SNR,when the outage probability is 10 3，RSR obtains about 3dB SNR gain compared with SAF. The optimal powerallocation scheme furtherly enhances the system performance compared with equalpower allocation scheme.Thirdly, because the spectrum utilization for One-way relay mode is low, thepaper studies relay node selection algorithm and power allocation scheme forTwo-way relay mode. At first, the paper derives the system capacity for AF and DFprotocols, then introduces simply the concept of Physical Network Coding (PNC) andMax-Min relay selection scheme. Furthermore, based on the above two aspects andthe criterion of maximizing sum rate of system , then establishes a power optimizationproblem and proposes a second-best power allocation scheme.In order to futherimprove the system performance, the paper proposes a bidirectinal relay selection(BRS) scheme, then derives an optimal power allocation scheme based on BRSalgorithm. Simulation results demonstrates that BRS algorithm improves greatlysystem performance compared with traditional RRS algorithm and Max-Minalgorithm. Moreover, the proposed OPA algorithm outperforms with EPA algorithm.Fourthly, combining with the development of future wireless communication, thepaper probes some problems to be resolved for cooperative communication in thefuture.