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