Joint user pairing and power control for C-NOMA with full-duplex device-to-device relaying

This paper investigates the performance of coop- erative non-orthogonal multiple access (C-NOMA) in cellulardownlink systems. The system model consists of a base station(BS) that needs to serve multiple users within a region of service.A subset of the users, especially those located close to thecell edge, undergo severe fading and suffer from poor channelquality and low achievable rates. To overcome this problem, C-NOMA is proposed as the system design methodology, in whichusers that have the capability of full-duplex (FD) communicationcan assist the transmissions between the BS and users withpoor channel quality through device-to-device (D2D) communi-cations. To harness both the multiplexing gain from NOMA andthe diversity gain from FD-D2D communications, we formulateand solve a novel optimization problem that jointly deter-mines D2D user pairing and power allocation. The formulatedproblem is a mixed-integer non-linear program (MINLP) withprohibitively high complexity. To overcome this issue, a two-steppolicy is proposed to solve the problem in polynomial time. Oursimulation results show that with reasonable assumptions, theproposed scheme always outperforms some existing schemesin the literature, and that, under undesirable conditions, e.g.,poor D2D channel conditions or imperfect self-interference (SI)cancellation, the proposed scheme is reduced to conventionalNOMA.