Research On Low-Complexity Transmission Schemes For MIMO Two-Way Relay Systems

In recent years,with the rapid development of multimedia service,the transmission requirements of wireless communication systems continually increase.Although wireless communication breaks the limitations of traditional wired networks,its channel fading hinders reliable and efficient signal transmission.The relay technique is considered as an effective method to improve the performance of wireless communication systems,which can enhance system capacity and extend system coverage with low cost and flexible deployment.Compared to traditional one-way relay,analog network coding(ANC)based two-way relay takes less time slots to realize the transmission,and thus makes more efficient use of spectrum resources.Meanwhile,multiple-input multiple-output(MIMO)technique can obtain additional spatial freedom to combat channel fading without extra energy consumption and time-frequency resources.Therefore,integrating MIMO technique into two-way relay systems can significantly improve the system performance.In this thesis,we focus on ANC based MIMO two-way relay networks and propose low complexity transmission schemes for some pratical transmission scenarios.Following the analysis and discussion of the proposed schemes,numerical simulation is given to verify the theoretical results.The main contributions of this thesis are summarized as follows:1.Two opportunistic transmission schemes are proposed and analyzed for multi-user multirelay MIMO two-way relay networks with the rate asymmetry,using beamforming and antenna selection respectively to achieve the multi-antenna diversity.The main idea is to implement joint user-relay selection in a distributed manner.Then we derive the upper and lower bounds on the outage probability of the two proposed transmission schemes under Nakagami-m fading environment,and present the analysis of the diversity gain and coding gain,followed by some discussions on special relay deployments.At last,simulation results verify these analytical results and show the effectiveness of the proposed schemes.2.A simplified scheme is proposed and analyzed for MIMO two-way relay networks,in which the source adopts beamforming while the relay employs antenna selection.The relay does not perform channel estimation to determine the optimal relay antenna,but simply compares the minimum pilot signaling powers received by each antenna.The theoretical analysis of system outage probability and average symbol error rate(SER)indicates that the simplified scheme can achieve full diversity gain.After that,we discuss the effect of antenna correlation on the outage probability.It can be concluded that antenna correlation merely damages the system coding gain,and the full diversity gain can still be obtained.Numerical simulation results confirm the correctness of the previous theoretical analysis.Moreover,the outage performance of the proposed scheme with imperfect channel state information(CSI)is presented through simulation.