  Fifth generation (5G) wireless networks face various challenges in order to
support large-scale heterogeneous traffic and users, therefore new modulation
and multiple access (MA) schemes are being developed to meet the changing
demands. As this research space is ever increasing, it becomes more important
to analyze the various approaches, therefore in this article we present a
comprehensive overview of the most promising modulation and MA schemes for 5G
networks. We first introduce the different types of modulation that indicate
their potential for orthogonal multiple access (OMA) schemes and compare their
performance in terms of spectral efficiency, out-of-band leakage, and bit-error
rate. We then pay close attention to various types of non-orthogonal multiple
access (NOMA) candidates, including power-domain NOMA, code-domain NOMA, and
NOMA multiplexing in multiple domains. From this exploration we can identify
the opportunities and challenges that will have significant impact on the
design of modulation and MA for 5G networks.
