On Relay Cooperative Techniques For Wireless Cooperative Communication Systems

In recent years, owing to their abilities to increase the system capacity and transmission reliability, cooperative diversity technologies have attracted lots of attention from the academic and industrial circles. Cooperative diversity technologies allow nodes scattered in the network to share their single antenna to form a distributed multiple antenna system. Such a multiple antenna system is the so called virtual multiple-input multiple-output (MIMO) system, which, however unlike conventional MIMO technologies, has no need for equipping multiple antennas at each terminal, hence promising a vast application prospect in wireless networks. Specially, relay-based cooperative diversity technologies can also increase the network coverage and data rate of cell-edge users, and cover dark area, which have been extensively studied in the research community. Focused on a multiple-relay cooperative communication system, this dissertation mainly investigates the relay cooperative schemes:relay selection and distributed beamforming. The major contributions are outlined as follows:The first part analyzes the performance of conventional three-nodes cooperative communication systems. The probability density function (PDF), cumulative distribution function (CDF) and moment generating function (MGF) of the harmonic mean of two independent exponential variates. Applying these results, the exact outage probability and average bit error rate (BER) expressions are derived.The second part study joint power allocation and relay selection schemes for multiple-relay cooperative communication systems. Tow power allocation optimization problem are proposed:maximizing received signal to noise ratio (SNR), minimizing total energy consumption. According to the obtained closed-form optimal solutions, two joint power allocation and relay selection schemes are presented. Simulation results show that the proposed schemes can effectively improve the system performance.The third part investigates distributed beamforming schemes for for multiple-relay cooperative communication systems. All the relays take part into the cooperation and generate a virtual multiple-antenna system. For such a network, based on the second-order statistics of the channel coefficients, we study two different beamforming design approaches. As the first approach, we the beamformer is determined through minimizing the total transmit power consumption while satisfying the receiver SNR requirements. In the second approach, we design the beamforming weights by maximization of the receiver SNR subject to two different types of power constraints, namely the total transmit power constraint and individual relay power constraints.