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Joint user scheduling and power allocation for massive MIMO downlink with two-stage precoding

Large-scale multiple-input multiple-output (MIMO) system with tens to hundreds of antennas is getting increasing attention for its very high spectral efficiency and energy efficiency. However, for frequency division duplexing (FDD) system, the cost of CSIT feedback becomes a bottleneck with the BS antennas increasing. To reduce the cost of the downlink training and the CSIT uplink feedback, joint spatial division and multiplexing (JSDM) scheme is proposed by Ansuman Adhikary, et al., which divides users into different groups according to their channel covariance eigenvectors and adopts the two-stage precoding. This paper proposes a joint user selection and power allocation (JUSPA) algorithm for JSDM scheme in massive MIMO downlink systems, which schedules users and allocates power iteratively with the MAX user scheduling and the Lagrange power optimization method. For user scheduling, it is noticed that the intra-group interference is so large that would disturb the user selection. Then the signal-to-interference noise ratio (SINR) of each beam is computed, neglecting the intra-group interference. The simulation results show that the proposed JUSPA algorithm performs better than the average power allocation method in the original JSDM scheme.