Abstract

The increasing demand of mobile Internet and the IoTs poses exacting requisites for 5G wireless communications,\nlike high spectral efficiency. Hence, a promising technology, non-orthogonal multiple access (NOMA), is discussed. Unlike\nstandard orthogonal multiple access technologies, NOMA can serve much more users via non-orthogonal resource allocation.\nThe most striking attribute of NOMA is to serve multiple users at the same time/frequency/code, but with different power\nlevels, which produces a remarkable spectral efficiency gain. There are mainly two types of NOMA techniques, powerdomain\nand code-domain. This paper primarily focuses on power-domain NOMA that utilizes superposition coding (SC) at\nthe transmitter and successive interference cancellation (SIC) at the receiver. Also, this paper discusses how NOMA performs\nwhen it is combined with other wireless communication techniques, for example cooperative communications, multiple-input\nmultiple-output (MIMO). Furthermore, this paper discusses several important issues on NOMA implementation and provides\nsome avenues for future research.