Recently, non-orthogonal multiple access (NOMA) has attracted considerableinterest as one of the 5G-defining techniques. However, as NOMA isintrinsically in favour of the transmission of strong users who are capable ofcarrying out successive decoding, judicious designs are required to guaranteeuser fairness. In this paper, a two-user downlink NOMA system over fadingchannels is considered. For delay-tolerant transmission, the average sum-rateis maximized subject to both average and peak power constraints as well as aminimum average user rate constraint. The optimal resource allocation isobtained using Lagrangian dual decomposition under full channel stateinformation at the transmitter (CSIT), while an effective power allocationpolicy under partial CSIT is also developed based on analytical results. Inparallel, for delay-limited transmission, the sum of delay-limited throughput(DLT) is maximized subject to a maximum allowable user outage constraint underfull CSIT, and the analysis for the sum of DLT is performed under partial CSIT.Furthermore, a sophisticated orthogonal multiple access (OMA) scheme is alsostudied as a benchmark to prove the superiority of NOMA over OMA with fullCSIT. Finally, the theoretical analysis is verified via simulations by means ofvarious trade-offs for the average sum-rate (sum-DLT) versus the minimum(maximum) user rate (outage) requirement.
展开▼
