SCMA for Downlink Multiple Access of 5G Wireless Networks

TL;DR

This paper explores SCMA, a non-orthogonal multiple access technique for 5G, enhancing spectral efficiency through layered codeword multiplexing and iterative detection, with developed algorithms for multi-user downlink scenarios.

Contribution

It introduces a multi-user SCMA technique for downlink 5G, including user pairing, power sharing, and scheduling algorithms to improve network throughput under heavy load.

Findings

Enhanced downlink throughput with multi-user SCMA

Effective overloading and link adaptation mechanisms

Improved performance in lightly loaded networks

Abstract

Sparse code multiple access (SCMA) is a new frequency domain non-orthogonal multiple-access technique which can improve spectral efficiency of wireless radio access. With SCMA, different incoming data streams are directly mapped to codewords of different multi-dimensional cookbooks, where each codeword represents a spread transmission layer. Multiple SCMA layers share the same time-frequency resources of OFDMA. The sparsity of codewords makes the near-optimal detection feasible through iterative message passing algorithm (MPA). Such low complexity of multi-layer detection allows excessive codeword overloading in which the dimension of multiplexed layers exceeds the dimension of codewords. Optimization of overloading factor along with modulation-coding levels of layers provides a more flexible and efficient link-adaptation mechanism. On the other hand, the signal spreading feature of SCMA can improve link-adaptation as a result of less colored interference. In this paper a technique is developed to enable multi-user SCMA (MU-SCMA) for downlink wireless access. User pairing, power sharing, rate adjustment, and scheduling algorithms are designed to improve the downlink throughput of a heavily loaded network. The advantage of SCMA spreading for lightly loaded networks is also evaluated.