  As the latest member of the multiple access family, non-orthogonal multiple
access (NOMA) has been recently proposed for 3GPP Long Term Evolution (LTE) and
envisioned to be an essential component of 5th generation (5G) mobile networks.
The key feature of NOMA is to serve multiple users at the same
time/frequency/code, but with different power levels, which yields a
significant spectral efficiency gain over conventional orthogonal MA. This
article provides a systematic treatment of this newly emerging technology, from
its combination with multiple-input multiple-output (MIMO) technologies, to
cooperative NOMA, as well as the interplay between NOMA and cognitive radio.
This article also reviews the state of the art in the standardization
activities concerning the implementation of NOMA in LTE and 5G networks.
