A Simple NOMA Scheme with Optimum Detection

Abstract

Non-Orthogonal Multiple Access (NOMA) has been a hot research topic over the past few years, particularly because it is widely recognized that this technique represents a promising technology for massive Machine-Type Communications (mMTC) in future 5G cellular networks. The NOMA literature today is heavily focused on the so- called Power-Domain NOMA, which requires a strong power imbalance at the receiver between user signals. In some recent papers ([1] and [2]), the present authors revived a NOMA concept introduced back in the year 2000 and completely overlooked in the recent NOMA literature. This NOMA concept, which uses two sets of orthogonal signal waveforms and iterative interference cancellation at the receiver, fully avoids the power imbalance requirements of power-domain NOMA and makes it possible to grant the same data rates and performance levels to different users. In this paper, we first shed further light on the limitations of today's power-domain NOMA and we give insight on the potential of superposing the signals of two user groups with different characteristics instead of superposing two user signals. Next, we propose a new variant of the NOMA technique proposed in [1] and [2], which avoids the use of a complex interference canceler. This scheme achieves a 25% channel overloading factor at a negligible degradation of the signal-to-noise ratio (SNR) using a very simple maximumlikelihood (ML) receiver.