Precoder Design And Performance Analysis In Wireless Multi-antenna Cooperative Networks

Multiple-input multiple-output(MIMO) technique has been seen as one of the major achievements in wireless communications during the past decades. By implementing multiple antennas at the transmitting end or the receiving end, the capacity and the transmission reliability of the system can be significantly improved. As for the study of the MIMO, precoder design is an important direction. Through exploiting channel state information(CSI) at the transmitter, we can properly design precoding vectors to increase the receiver’s signal-to-noise ratio(SNR) and suppress the interference. On the other hand, cooperative communication has also been a hot topic in the research of wireless communications. By introducing cooperation among the base stations and users, we can further improve the spectrum efficiency and reduce the power consumption. In this thesis, we focus on the precoder design and performance analysis for the wireless multi-antenna cooperative networks. We deeply study the precoder algorithm design and try to exploit the gain brought by the MIMO technique and cooperative communications. The main contributions of this thesis are as follows:Firstly, we consider the multicell multicast network and investigate two coordinated beamformer designs: the quality-of-service(Qo S) beamforming and the max-min signal-to-interference-plus-noise ratio(SINR) beamforming. For the Qo S beamformer design, the feasibility of the optimization problem is analyzed. Then, based on the primal decomposition method in the convex optimization theory, we propose a novel decentralized beamforming algorithm. This algorithm only requires limited information sharing among base stations and each base station only needs local CSI. For the max-min SINR beamforming, we try to maximize the minimum SINR among the users while satisfying the individual power constraint for each base station. By deriving the relationship between the max-min SINR problem and the weighted peak-power minimization problem, we propose an iterative algorithm which can obtain the near-optimal solution.Secondly, we study physical layer multicasting in the multicell network where each base station is equipped with a very large number of antennas. Based on the asymptotic orthogonality of the users’ channel vectors, we derive the asymptotically optimal beamformer when the perfect CSI is available at the base station end. Then,we consider the imperfect CSI scenario and derive the asymptotic SINR for each user when the pilot contamination exists. As for the pilot contamination issue, which is quite important and challenging in the massive MIMO system, based on the derived asymptotically optimal structure of the beamformer, we propose a new pilot scheme to eliminate the pilot contamination without increasing the complexity of the beamformer design at the base station end. Further, we consider the pilot power control among the users and derive the closed-form optimal solution.Thirdly, we study the robust beamformer design problem for the multi-antenna wireless multicasting system with simultaneous information and power transmission,under the assumption of imperfect CSI at the transmitter end. Following the worst-case deterministic model of the CSI, our objective is to maximize the worst-case harvested energy for the energy receiver while guaranteeing that the rate for the information receiver is above a threshold for all possible channel realizations. Through exploiting the special structure of the optimization problem, we simplify its objective function and constraints. Then, based on the semidefinite relaxation method, we propose an efficient beamforming algorithm。More over, we show that the proposed algorithm can always obtain the optimal solution of the original problem.Fourthly, we consider the performance analysis of the MIMO two-way X relay channel. We first derive an upper bound of the degrees of freedom(Do F) for the considered system. Then, by applying signal alignment for network coding and joint transceiver design for interference cancellation, we propose a novel transmission scheme and derive the necessary and sufficient condition for the scheme to achieve the Do F upper bound. Further, we consider the generalized MIMO two-way X relay channel and analyze its diversity order. Based on the signal alignment, we propose an efficient transmission scheme and analyze the diversity order of the considered channel. Then, by exploiting the available dimension of the null space for the users’ channel matrices, we further propose an enhanced signal alignment scheme and show that the diversity order of the system can be increased under such scheme.