Hybrid beamforming for two-user SDMA in millimeter wave radio

An effective joint radio-frequency (RF) and baseband (BB) hybrid beamforming (HBF) scheme is presented for two-user spatial division multiple access (SDMA) in 60GHz radio using planar antenna arrays (PAA). Taking into account the physical constraints of the phase shifters of PAA, we study the design of downlink HBF from two perspectives of conic optimization: transmit power minimization subject to a lower limit on the signal-to-interference plus noise ratio (SINR), and the maximization of the minimum SINR subject to an upper limit on the transmit power. For the power minimization problem, we obtain closed-form expressions for the BB beamforming (BF) weights. And for the SINR maximization, a simple iterative scheme is obtained based on the closed-form expressions for the first problem. Simulation results show that the bit error rates with HBF can significantly outperform the ones with RF BF only when the desired user´s signal is severely jammed by the interfering user´s signal.