Achievable Rate Regions And Outage Performance Of Wireless Relay Communication Systems

With the development of wireless communication technique, mobile communication systems require high data transmission and broad area coverage. Multi-input multi-output (MIMO) transmission is one of the key techniques to solve above problems. By providing spatial diversity gain and multiplexing gain simultaneously, MIMO transmission can significantly improve the reliability and efficiency of wireless communication. On the other hand, in order to extend the coverage of wireless communication and make up the disadvantage that MIMO technique is difficult to realize at the mobile terminal, relay technique is proposed. By cooperative communications with destination nodes or user nodes, relay systems obtain spatial diversity gain, increase system capacity and improve the coverage of cell edge. In this dissertation, achievable rate regions and outage performance of wireless relay communication systems are investigated in detail.Firstly, the MIMO multi-way relay channel (MWRC) without direct links is considered, and the optimal diversity-multiplexing tradeoff (DMT) and power allocation optimization scheme are analyzed. Specifically, for the K-user MIMO MWRC where each user transmits a multicast message, the fundamental DMT is derived under Rayleigh fading, and we show that a compress-and-forward (CF) relay protocol can achieve the optimal DMT. For a three-user MIMO Y channel where each user transmits a unicast message, a signal space alignment (SSA) scheme under amplify-and-forward (AF) relaying is proposed and is shown to achieve the maximal degrees of freedom of the system. Based on the proposed scheme, the power allocation strategy at user terminals is discussed. Simulation results show that the proposed power allocation scheme has significant improvement in the sum-rate performance compared to the average power allocation case.Secondly, rate regions of a K-user discrete memoryless MWRC with direct links (MWRC-DL) are studied. Under the assumption that a restricted encoder is employed at each user, the cut-set outer bound on the capacity region is derived, and achievable rate regions under decode-and-forward (DF) and CF relaying are characterized. Meanwhile, the explicit expressions of the outer bound and achievable rate regions for the Gaussian MWRC-DL are also derived. It is shown that rate regions of DF and CF strategies for the two-way relay channel and the multiple-access relay channel can be obtained from those of the MWRC-DL. To further analyze the performance of the two strategies of the MWRC-DL system, the symmetric rates of a symmetric Gaussian network are analyzed. It is shown that the CF strategy achieves symmetric rates within 0.5/(K-1) bits of the capacity when the relay’s power is at least (K-1) times as large as the user power. When the relay link is stronger than the direct link and the relay power is relatively small, the symmetric rate of DF strategy approaches optimal with the increase of the number of users. Numerical results are provided to verify the above theoretical analysis.Next, the outage performance of an interference-limited AF two-hop multiple access channel (MAC) is studied in the presence of multiple interferers nearby the destination. Assuming that all the interferers are independent distinct-power Rayleigh fading, the exact integral-form expression of the common outage probability is derived. To decrease the computation complexity, an approximation of the common outage probability is derived in analytical form. Based on the approximation expression, the asymptotic analysis is performed. It is shown that the common outage probability converges when only the user power or the relay power becomes infinite. Based on the approximation, the common outage rate region is investigated. Besides, by assuming the relay power approaches infinity, the individual outage rate region is also derived. Numerical results demonstrate that the integral form of the common outage probability, the corresponding approximation, and the asymptotic results match well with the Monte Carlo simulations, and that the individual outage rate region is usually significant larger than the common outage rate region.Finally, outage rate regions of a DF two-hop MAC are studied with interference-limited destination. Based on the definitions of common outage and individual outage for the DF two-hop MAC, the decoding process at the relay and the destination are discussed, and closed-form expressions of two outage probabilities are derived. Further, the explicit common and individual outage rate regions are characterized. It is shown that the difference between the individual outage rate region and the common outage rate region becomes larger when the corresponding user-relay link becomes weaker or the relay-destination link becomes stronger. Numerical results show that the exact expressions of the common outage probability and the individual outage probability match well with the corresponding Monte Carlo results, and it also verifies the influence of each link on the difference between two kinds of outage rate regions.