Joint Precoding And Power Allocation For Multi-User Mimo-Relay Systems

Multi-user MIMO relay system with the multi-antenna at the base station and relay, can pro-vide the additional space gains (including the multiplexing gain and diversity gain), can expandthe coverage of the wireless network and reduce the access cost. However, the benefits possessedof the multi-user MIMO relay system are depend on the techniques of the precoding and powerallocation. Hence, this dissertation studies the precoding and power allocation schemes for themulti-access MIMO-relay channel, the MIMO-relay broadcast channel and the multi-user MIMOtwo-way relay channel under the context of the relay model (Type-II) in the next generation ofcellular wireless communications system.The following content are the main work of this dissertation:1. For the precoding design and power allocation problem in the multi-access MIMO relaychannel with the source-destination direct links, we propose an optimal source precodingmatrix structure based on the point-to-point MIMO channel techniques, and a new relay pro-cessing matrix structure under the modified power constraint at relay node, based on which,a nested iterative algorithm of jointly optimizing sources precoding and relay processing isestablished. We also show that the capacity based optimal source precoding matrices sharethe same structure with the MSE based ones, so does the optimal relay processing matrix,but with different power allocation policy. Simulation results demonstrate that the proposedalgorithm outperforms the existing results.2. For the precoding design and power allocation problems based on sum-rate maximization orthe minimum achievable rate among all users maximization in the MIMO relay broadcastchannel with the source-destination direct links. Both problems are nonlinear non-convexand the optimal solutions remain unsolved. To solve the sum-rate maximization problem,we first set up an equivalent problem, and then solve it by decomposing it into two convexsubproblems. Finally, we propose a general linear iterative design algorithm based on al-ternative optimization to joint design the source precoding matrix, relay processing matrix.Furthermore, the solution to each convex subproblem is optimal and unique, thus the pro-posed algorithm is convergent. To the max-min problem, we propose a modified iterative design algorithm based on the aforementioned algorithm and it is also convergent. Simula-tion results demonstrate that the proposed algorithms outperform the existing results.3. To further improve the spectrum efficiency, we further consider the precoding design andpower allocation problem based on sum-rate maximization in the multi-user MIMO two-way relay channel. This problem is also nonlinear non-convex and its optimal solution alsoremain unsolved. Inspired by the work in the MIMO relay broadcast channel, we found thatthe idea for solving the sum-rate maximization problem in the MIMO relay broadcast chan-nel can be generalized to this considering problem. Thus, we similarly set up an equivalentproblem firstly, and then solve it by decomposing it into three convex subproblems. Finally,we propose a modified iterative algorithm to joint design the sources and relay matrices. Fur-thermore, we also propose a low complexity precoding design method for the case that theantennas equipped with relay is only equal to the antennas equipped with base station or allusers. In this low complexity precoding design method, the relay processing matrix design isonly based on the users’ channel matrices to deal with the multi-user interference signal fromusers, the base station precoding matrix can be designed by blockwise-RZF algorithm justlike the general multi-user MIMO broadcast channel after relay matrix design, and the users’precoding matrices can be designed by unitary matrix algorithm just like the point-to-pointMIMO channel.In addition, it is worth noting that this dissertation is only considering the precoding designand power allocation problems in multi-user MIMO relay channel for a single cellular wirelesscommunications system，and assumed that all channel state information is fully known at thebase station. However, multi-cell MIMO cooperative network is the direction of the cellular com-munications networks development. In the future work, it is therefore a good idea to considerthat how to generalize the ideas of this dissertation to the problems of the multi-user MIMO chan-nel including direct links with limited-feedback and user-selection techniques in multi-cell MIMOcooperative networks.