Joint Time and Beam Domain Non-Orthogonal Multiple Access

In this paper, an uplink joint time and beam domain non-orthogonal multiple access (JTBMA) scheme for the massive multiple-input multiple-output (MIMO) networks is proposed to enhance the access connectivity and decoding performance. This scheme mainly includes two processes: joint time and beam domain sparse access matrix design and beamforming matrix design, which are coordinated by the base station (BS). An optimization problem is formulated to seek an optimal transmission policy with the goal of improving decoding performance. To simplify the non-convex problem, we solve it with two steps. Firstly, different access patterns are allocated to users to obtain a sparse access matrix based on a fixed beamforming matrix; then, the prime optimization is transformed as a beamforming matrix design problem. Because of the sparsity of the access matrix, message passing algorithm (MPA) is performed to recover the users’ transmitted messages. Simulation results show that the JTBMA scheme exhibits significant performance gain in terms of BER performance and user connectivity.