Minimum Distance Optimization on Signature Code for Uplink Non-orthogonal Multiple Access

Abstract

This paper studies the design of signature code multiple access (SIGMA) to support code domain non-orthogonal multiple access (NoMA). In a NoMA system, the users apply the spreading codes for multiple access that shares the same time-frequency resource element simultaneously. Consequently, multiple access interference (MAI) occurs which degrades the error performance and limits the number of connectivities. In SIGMA, each user is assigned the codewords from the signature codebook to generate the complex spreading code. In this work, the SIGMA scheme constructs the signature codebook with minimum distance maximization to improve the error performance. Numerical simulation has been conducted to evaluate the error performance. The simulation results show that the codebook minimum distance affects the error performance. The error performances of prior arts such as the multi-user shared access (MUSA) and the sparse code multiple access (SCMA) are compared with the SIGMA by using the maximum likelihood (ML) detection.