A New Multiple Access Technique for 5G: Power Domain Sparse Code Multiple Access (PSMA)

In this paper, a new approach for multiple access in the fifth generation (5G) of cellular networks called power domain sparse code multiple access (PSMA) is proposed. In PSMA, we adopt both the power domain and the code domain to transmit multiple users’ signals over a subcarrier simultaneously. In such a model, the same sparse code multiple-access (SCMA) codebook can be used by multiple users, where, for these users, the power domain non-orthogonal multiple access (PD-NOMA) technique is used to send signals non-orthogonally. Although the signal of different SCMA codebooks can be detected orthogonally, the same codebook used by multiple users produces interference over these users. With PSMA, a codebook can be reused in the coverage area of each base station more than one time, which can improve the spectral efficiency. We investigate the signal model as well as the receiver and transmitter of the PSMA method. In the receiver side, we propose a message passing algorithm-based successive interference cancellation detector to detect the signal of each user. To evaluate the performance of PSMA, we consider a heterogeneous cellular network. In this case, our design objective is to maximize the system sum rate of the network subject to some system level and QoS constraints such as transmit power constraints. We formulate the proposed resource allocation problem as an optimization problem and solve it by successive convex approximation techniques. Moreover, we compare PSMA with SCMA and PD-NOMA from the performance and computational complexity perspective. Finally, the effectiveness of the proposed approach is investigated using numerical results. We show that by a reasonable increase in complexity, PSMA can improve the spectral efficiency about 50% compared with SCMA and PD-NOMA.