Beamforming And Power Allocation For Two Way Relay MIMO System

Relay-assisted cooperative transmission can offer significant benefits includingthroughput enhancement, coverage extension and power reduction in wirelesscommunications. It is therefore considered as a promising technique for the nextgeneration wireless communication systems. When employing multiple antennas at therelay, one can significantly improve the performance of a relay system. By resorting tothe idea of analog network coding，two users exchange their information through anassisting relay node. The information exchange can be completed in two time slots. Inthe first time slot, both users concurrently transmit signals to the relay node. In thesecond time slot, the relay node broadcasts the signals received at the first time slot toboth users. Since each node knows its own transmitted signals, the self-interferencecan be easily cancelled. In this work, we focus on two-way MIMO relay system. Themain tasks are as follows:First, for one-way MIMO relay system, we have learned that the proven optimalprecoding structure is to first parallelize the channels between the source and the relay,as well as between the relay and the destination using singular value decomposition(SVD) and then match the eigenchannels in the two hops. Even a unified frameworkhas been established to jointly optimize the source and relay precoding matrices for abroad class of frequently used objective functions in MIMO communications. Then,numerical simulations are carried out to compare the performance between thepreviously described the diagonal structure algorithm and an algorithm calledEnd-to-End Antenna Selection (EEAS), both are aimed at maximizing MutualInformation to show the optimality of the diagonal structure.Then the optimal problem need solved involves multiple matrix variables in atwo-way relay communication system. As it is not convex, the optimal solution is veryhard to be done. This paper proposes two suboptimal channel parallelization methodsto balance the performance and complexity, based on Interference alignment (IA) andJoint Unitary Triangularization (JUT), respectively. Comprehensive simulations are conducted to evaluate the effectiveness of the proposed precoding design.For practical systems, a relay must support multiple users. However, there is nosingle figure of merit to measure the overall performance of the multiuser bidirectionaltransmission. For example, in the system the sum-rate can be maximized while poweris allocated to the users with good channel condition and some with poor channelcondition are closed. The user’s fairness can’t be guaranteed. In this paper, we chooseto ensure the quality-of-service (QoS) for each user while minimizing the total systempower consumption. Block diagonalization relaying precoding scheme with powerallocation is proposed. Monte Carlo simulations illustrate the performance of theproposed scheme.The end of this paper concludes this dissertation and discusses the future work.