Multi-User Downlink Precoding and Radiation Pattern Design for Reconfigurable MIMO

Reconfigurable antennas (RAs) can actively adjust their radiation patterns to meet the demands of the communication network. In this paper, we investigate precoding and radiation pattern design in a multi-user multi-input single-output (MUMISO) downlink system. To fully exploit RAs, we introduce pattern sample vectors corresponding to each user's sub channel to assess the impact of pattern reconfiguration across all scattering paths. Based on this, we formulate the design problem by adopting closed-form precoding to optimize the radiation patterns for maximizing the sum rate. Specifically, we propose two methods: a heuristic approach using singular value optimization (SVO) and a successive convex approximation (SCA)-based minimization strategy to achieve desired patterns. These methods effectively address the non-convexity in the objective function. Numerical results demonstrate that the reconfigurable radiation pattern can strategically manipulate the wireless channel, leading to significant enhancements in system performance.