Research On The Cooperative Relay Transmission In Wireless Communication Systems

With the rapid increasing of the smart devices and mobile internet service, wireless communication faces great challenges:higher speed, lower cost and power consumption, and wider coverage. Spectral efficiency (SE) and energy efficiency (EE) are becoming the most important metrics for the future wireless networks. Wireless cooperative relay communication, is considered as a promising technique to meet the SE and EE challenges for its advantage on coverage extension, transmission rate improvement and potential for energy saving, and has drawn considerable attention from both the academia and industry.This dissertation focus on the key physical layer techniques related to the cooperative relay systems to improve the SE and EE, including precoding techniques of the multiuser MIMO relay networks, the energy efficient resource allocation techniques in two-way relay networks and the energy efficient transmission scheme for simultaneous information and power transfer systems. The major work and contributions of this dissertation are summarized as follows:Firstly, for the single relay aided multiuser MIMO relay network, we propose low complexity joint transceiver design. The proposed method is based on the minimum mean square error criterion. By decomposing the error covariance matrix into two individual error matrices, the original optimization problem is transformed to the simple point to point MIMO optimization problem and the traditional multiuser optimization problem. The closed-form precoding matrix of the base station is derived. The proposed scheme greatly degrades the complexity of the joint transceiver design and mitigates the feedback overhead. Further, considering the scenario with the direct link transmission, a joint BS precoding and relay precoding are proposed taking both the direct link and the relay link into consideration to maximize the weighted sum rate. Simulation results demonstrate that the proposed algorithm offers significant performance gain over existing methods. In addition, we also propose a modified robust joint transceiver design which is robust to the imperfect channel state information (CSI).Secondly, we propose decentralized joint BS and relay precoding algorithms and the corresponding CSI signaling concepts for weighted sum rate maximization in multi-relay aided multiuser MIMO network. Three iterative decentralized algorithms are developed with the local CSI requirements at the base station and the relay nodes and few feedback information. Moreover, CSI signaling and decentralized processing in TDD system are analyzed. Simulation results show the effectiveness of the decentralized transmission schemes compared to the existing algorithms. The proposed decentralized algorithm are quite suitable for LTE/LTE-A systems since it can provide favorable performance with only few feedback overhead.Thirdly, focusing on the EE metric, we propose the optimal energy efficient power allocation shceme for single carrier two-way relay system. Furthermore, we extend the work into OFDM based two-way relay network and propose the energy efficient bit and power loading scheme. For the sinlge carrier case, we decompose the non-convex EE optimization problem into to two convex subproblems. The optimal power allocation among the transceiver and relay node is derived by solving the equivalent subproblems. As for the OFDM case, since the energy efficient bit and power loading problem is a mixed integer problem and non-convex, we transform it to an equivalent quasi-concave one-dimension problem and therotically find the increasing and decreasing conditions of EE. Based on the therotical analysis, the optimal energy efficient bit and power loading algorithm and its simplified low complexity version are proposed. It is worth mentioning that the proposed energy efficient bit and power laoding algorithm is not only dedicated to the two-way networks but also suitable for the general OFDM networks. Similuation results show that the proposed EE optimization scheme can improve the system energy efficiency remarkably.Finally, to further enhance the EE, we study the EE opitmizaiton for the simultaneous information and power transfer (SWIPT) network, in which the idle nodes can act as an energy relay, harvest the ambient raido from the transmitter and store it in the battery for further transmission. In this way, the transmit power is recycled and reused in a more energy efficient manner. Considering that the feedback overhead is usually limited in pratical scenarios, we propose the energy efficient precoding and both the optimal and suboptimal power allocation based on the statistical CSI feedback. Simulation results show that the proposed scheme significantly outperform the traditional rate maximization scheme in terms of EE. In addition, compared with the EE performance of the traditional network without the energy harvesting relay, the proposed EE optimization for the SWIPT system also offers better performance.