Relay Selection Strategy And Performance For Decode-and-Forward Cooperative Communication System

In the domain of wireless cooperative communication,pre-existing researches have proved that utilizing excessive relays to participate in a single cooperative transmission is not an advisable method.As how to accurately select optimal one or more relays from numerous relays decides the reliability and energy efficiency of cooperative communication system,relay selection becomes one of the critical technologies for the practical application of cooperative communication.Considering that Decode-and-Forward is in the ascendant in terms of simple implementation and flexible application,this dissertation addresses the relay selection performance in different scenarios,and in the mean time investigates a practical cooperative scheme based on the Decode-and-Forward cooperative relay system.The main research contributions of this dissertation are summarized as follows:1).Based on FDF-OFDM cooperative system,an opportunistic relay selection with maximal-ratio-combine strategy which is carried by destination node in terms of equivalent channel capacity is proposed.First of all,the performance of our strategy that combines signals from the opportunistic relay and the direct link is investigated.Then,the system outage probability with maximal-ratio-combine is derived.Ultimately,the results show that when a direct link exists,the system performance will be further improved via the combination of relay selection and maximal-ratio-combine,which outperforms the opportunistic relay selection scheme without direct link.2).For a SDF single carrier cooperative system,we analyze the performance of the relaying network which utilizes maximal-ratio-combine(MRC)method to combine signals from the direct link and the selected relay.Firstly,three SDF relay selection strategies are investigated.Secondly,the system outage probability is analyzed and diversity gain is obtained by using Squeeze Theorem.Finally,the theoretical analysis and simulation results confirm that for a SDF relay selection system,the aforementioned method outperforms much better than FDF relaying system and its performance can be further improved via MRC strategy.3).Based on a FDF-OFDM cooperative system,the performance of relay selection with imperfect CSI is analyzed.At the first step,channel estimation error model is established and system signal-to-noise ratio with imperfect CSI is obtained.In the following step,the outage performance of Bit Loading and Equal Bit Allocation,two general kinds of OFDM relaying system strategies,is respectively investigated using mathematical induction.In the end,Monte-Carlo simulations are consistent with numerical results,which demonstrate that the accuracy and reliability of CSI has a substantial impact on the performance of relay selection system.4).In allusion to a typical 1-N-1 distributed SDF cooperative relaying system,a practical relay selection scheme based on CSI is proposed.Initially,we analyze the factors that affect the accurate acquisition of CSI,which indicates that designing a relay selection scheme by reasonably utilizing CSI is of great importance.After that,through the measured CSI data,we find it an advisable method to make the relay selection at destination node.Moreover,on the basis of analysis in our paper,we propose a practical relay selection scheme which is mainly based on transmitting the number of selected relay and secondarily on transmitting the CSI.As decreasing the information interaction among different nodes,the scheme is conducive to the practical application of relay selection in distributed cooperative networks.Eventually,we simulate the scheme with different parameters,and the results indicate that the system performance is improved prominently while increasing the number of relay nodes and the time of relay retransmission.