In non?orthogonal multiple access (NMA) system, signal transmitter and receiver are jointly optimized, so that multiple layers of data from more than one user can be simultaneously delivered in the same resource. To meet the 5G requirements on the number of connections and spectral efficiency, uplink NMA is becoming an important candidate technology and has been extensively studied in 3GPP. A number of uplink NMA schemes from different industrial companies have been proposed in recent 3GPP meetings. In terms of their basic technique principles, this paper classifies these NMA schemes into three categories, namely: scrambling based NMA schemes, interleaving based NMA schemes, and spreading based NMA schemes. Moreover, the key characteristics of these schemes are summarized, and the detailed introduction of each scheme is provided according to the comprehensive survey of the latest progress in 3GPP 5G standardization work.
5G; non?orthogonal multiple access; scrambling; interleaving; spreading