Performance of SWIPT for AF MIMO Relay Systems With Direct Link

A simultaneous wireless information and power transfer scheme for amplify-and-forward relay systems with a direct source–receiver link is investigated. According to the minimum-mean-square-error criterion, we formulate a joint beamforming problem under an energy harvesting constraint at the receiver plus transmitting power constraints at source and relay. Using an iterative algorithm, the non-convex problem is decoupled into two subproblems. A successive convex approximation method with iterative algorithm is designed for obtaining the local optimum. Assuming that $\mathbf {M}_{s}\leq {\mathbf {min}(\mathbf {N}, \mathbf {M}_{d})}$ , we propose a simplified measure using singular value decomposition and generalized singular value decomposition techniques. Numerical results for the number of iterations and bit error rate are carried out to evaluate the performance of the three different schemes.