Comparative Study of Overloaded and Underloaded NOMA Schemes with Two Multiuser Detectors

Abstract

Different novel non-orthogonal multiple access (NOMA) schemes have been put forward in order to enable support for massive connectivity of devices and ensure optimum utilization of scarce radio resources. This paper compares three prominent NOMA schemes, multi-user shared access (MUSA), pattern division multiple access (PDMA), and sparse code multiple access (SCMA) schemes, when combined with two different types of receivers, ordered successive interference (OSIC)-based multiuser detector (MUD) and message passing algorithm (MPA)- based MUD. The three NOMA schemes in combination with the two MUDs are compared during overloading, fully loaded, and under-loading scenarios. Simulation results suggest that all the schemes when combined with the two MUDs, perform better during the under-loading scenario (apparently due to low interference occurrence) in comparison with their performances during fully loaded and overloading scenarios. The results also suggest that SCMA scheme does not work with OSIC. Also, PDMA using MPA and OSIC MUDs and SCMA using MPA perform equally well and better than the other combinations, especially at higher signal to noise ratio (SNR). This is apparently, due to similarity in the designs of both SCMA and PDMA schemes in code domain.