Decoding Orders and Power Allocation for Untrusted NOMA: A Secrecy Perspective

Abstract

The amalgamation of non-orthogonal multiple access (NOMA) and physical layer security is a significant research interest for providing spectrally-efficient secure fifth-generation networks. Observing the secrecy issue among multiplexed NOMA users, which is stemmed from successive interference cancellation based decoding at receivers, we focus on safeguarding untrusted NOMA. Considering the problem of each user's privacy from each other, the appropriate secure decoding order and power allocation (PA) for users are investigated. Specifically, a decoding order strategy is proposed which is efficient in providing positive secrecy at all NOMA users. An algorithm is also provided through which all the feasible secure decoding orders in accordance with the proposed decoding order strategy can be obtained. Further, in order to maximize the sum secrecy rate of the system, the joint solution of decoding order and PA is obtained numerically. Also, a sub-optimal decoding order solution is proposed. Lastly, numerical results present useful insights on the impact of key system parameters and demonstrate that average secrecy rate performance gain of about 27 dB is obtained by the jointly optimized solution over different relevant schemes.

Novel Outage-Aware NOMA Protocol for Secrecy Fairness Maximization Among Untrusted Users

“…Note that the SIC can be performed by all users in a system because SIC on the receivers' side is actually a physical layer capability enabling the receiver to decode packets that arrive collectively. Thus, far user may also decode the information signal of near user using SIC which has been extensively studied in literature also [12], [13], [25], [26]. In this work, we consider imperfect SIC model, where decoding error may occur at both users, resulting in residual interference from the incompletely decoded user after SIC.…”

“…In decoding order (2,1), the order of decoding is different only for the far user in comparison to conventional decoding order. Note that the far user can even first decode the signal of near user, and then decodes its own signal after applying SIC [25], [26]. As a result, we obtain…”