In this paper, we consider a non-orthogonal multiple access cognitive radionetwork, where a full-duplex multi-antenna relay assists transmission from abase station (BS) to a cognitive far user, whereas, at the same time, the BStransmits to a cognitive near user. Our objective is to enlarge the far-nearuser rate region by maximizing the rate of the near user under a constraintthat the rate of the far user is above a certain threshold. To this end, anon-convex joint optimization problem of relay beamforming and the transmitpowers at the BS and cognitive relay is solved as a semi-definite relaxationproblem, in conjunction with an efficiently solvable line-search approach. Forcomparisons, we also consider low complexity fixed beamformer design, where theoptimum power allocation between the BS and cognitive relay is solved. Ourresults demonstrate that the proposed joint optimization can significantlyreduce the impact of the residual self-interference at the FD relay andinter-user interference in the near user case.
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