Research On Beamforming For Wireless Relay Communication System

To support users’ demand for high data rate in a reliable manner, one effective solution is to use multi-antenna-based spatial diversity technology, and another one is cooperative diversity using relays between the transmitter and receiver. Therefore, this thesis studied the beamforming techniques based on the combination of spatial diversity and cooperative diversity for wireless MIMO relay communication systems. The main contributions can be summarized as follows:First of all, some basic principles, such as network coding, beamforming and two-way relaying(TWR), are briefly introduced. Then, a simple three-node model is formulated for one-way and two-way relay system, respectively.Next, the beamforming algorithms based on three criteria in multi-pair MIMO TWR system are presented separately. That is, maximizing sum rate subject to sum power constraint on the relay, maximizing the minimum user rate subject to sum power constraint on relay with max-min fairness, and minimizing the relay transmit power subject to individual signal-to-interference-plus-noise ratio(SINR) constraints. Among them, the Min-POTDC algorithm to maximize the minimum rate is the essence of this work. Since asymmetral channel is more common in actual multi-user communication systems, the optimization object needs to consider not only the system sum rate, but also ensuring the reliability and reflecting the user fairness to guarantee that the user with poor channel can communicate effectively. Numerical results show that, the proposed method enjoys the merits of both max-min fairness and sum-rate when compared with existing relay beamforming methods. In addition, this thesis also optimizes the beamforming matrix via Dinkelbach-Type algorithm, named improved Dinkelbach-Type algorithm. It is verified that this improved Dinkelbach-Type algorithm is better than the original one in terms of convergence speed theoreticallyn.With respect to physical security, this thesis proposed secure beamforming optimization algorithms based on two principles for MIMO TWR system in presence of eavesdropper. First, a secure beamforming approach is proposed to maximize the secrecy rate under total relay power constraint, and then the successive convex algorithm(SCA) is adopted to solve it. Numerical results show that, while compared with the one-way relaying, the two-way relaying has obvious performance advantage. Then, under the constraints of both relay power and achievable rate at the eavesdropper, this thesis also gives a beamforming design to maximize the sum rate of legitimate users. The proposed methods are verified by the simulation results under different threshold values and relay antenna number, respectively.