Radiation Pattern Design for SINR Maximization in Multi-User Reconfigurable MISO Communications

Reconfigurable antennas (RAs) are capable of actively adjusting their radiation patterns to fulfill different needs of the wireless communication network. In this paper, we investigate the performance of RAs for a multi-user multiple-input single-output (MU-MISO) downlink system, where we propose an active beamforming scheme that exploits the effect of RAs to further improve the system performance. The joint design problem of beamforming and radiation pattern to maximize the minimum received signal-to-interference-plus-noise-ratio (SINR) is firstly formulated. Since the optimization variables are softly-coupled, we adopt an alternating optimization (AO) framework to decompose the joint design problem into the beamforming design sub-problem and the pattern design sub-problem, where we obtain the optimal beamformer and the radiation pattern of RAs that can achieve a desired communication performance. We further show that existing closed-form beamforming schemes can also benefit from RAs by designing proper radiation patterns, where the singular value optimization (SVO) approach and the successive convex approximation (SCA) method are proposed to obtain the desired radiation pattern. Both of them effectively address the optimization problem by dealing with the non-convexity in the objective function. Numerical results demonstrate that the proposed reconfigurable pattern design can further enhance the performance by manipulating the wireless channels in a judicious way.