Cooperative multi-antenna transmission is considered in relay networks, in which a source transmits its information to destination with the help of multi-antenna relay. In the first phase, source transmits its signal to the multi-antenna relay. Then the relay manipulates the received signal with the generalrank complex beamforming matrix and retransmits it. Assuming second-order statistics of channel state information, general-rank complex beamforming matrix is determined to minimize the power that dissipated in the multi-antenna relay. We show that this approach yields a closed-form solution and dependency of the forward and backward channels can help us to improve the performance of the network up to 7 dB compared to independent channels.

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We consider a two-way cooperative network consists of two transceivers and a set of relays. Assuming poor direct link between the two transceivers, they can exchange their data only with help of a set of distributed relays. This paper assumes that second-order statistics (SOS) of channel state information (CSI) is available. In this paper we obtain the complex beamforming weights to achieving signal-to-interference-plus-noise ratio (SINR) balancing in transceivers with total transmit power constraint at the relays. For solving the optimization problem, the complex beamforming weights are optimized with using a bisection search method. Simulation results show that increase in certainty about the channel coefficients helps in achieving a better performance in the two-way cooperative network.Index Terms-two-way networks, distributed beamforming, second-order statistics of CSI, SINR balancing, bisection search method.