Secrecy Fairness Aware NOMA for Untrusted Users

Abstract

Spectrally-efficient secure non-orthogonal multiple access (NOMA) has recently attained a substantial research interest for fifth generation development. This work explores crucial security issue in NOMA which is stemmed from utilizing the decoding concept of successive interference cancellation. Considering untrusted users, we design a novel secure NOMA transmission protocol to maximize secrecy fairness among users. A new decoding order for two users' NOMA is proposed that provides positive secrecy rate to both users. Observing the objective of maximizing secrecy fairness between users under given power budget constraint, the problem is formulated as minimizing the maximum secrecy outage probability (SOP) between users. In particular, closed-form expressions of SOP for both users are derived to analyze secrecy performance. SOP minimization problems are solved using pseudoconvexity concept, and optimized power allocation (PA) for each user is obtained. Asymptotic expressions of SOPs, and optimal PAs minimizing these approximations are obtained to get deeper insights. Further, globally-optimized power control solution from secrecy fairness perspective is obtained at a low computational complexity and, asymptotic approximation is obtained to gain analytical insights. Numerical results validate the correctness of analysis, and present insights on optimal solutions. Finally, we present insights on global-optimal PA by which fairness is ensured and gains of about 55.12%, 69.30%, and 19.11%, respectively are achieved, compared to fixed PA and individual users' optimal PAs.

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

“…Taking this challenge into account, a decoding order has been proposed for a two-user untrusted NOMA scenario in the preliminary version [1] of this work that is feasible in providing positive secrecy rate for both near and far NOMA users. As an extension of [1], in this work, we study all possible decoding orders for a two user NOMA system including conventional one and investigate the best decoding order under secrecy constraint for both users. Besides, in [1], we have considered ideal SIC receivers in which interference from the decoded user is completely removed while decoding the later user.…”

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

“…As noted, [9]- [10] have assumed only far user as untrusted, however, there exists a serious security risk for the far user also in case the near user is untrusted. Taking this into account, [11] has considered a twouser NOMA system assuming both the users as untrusted and proposed a new decoding order that is efficient in providing positive secrecy rate at both the users.…”

“…Also, keep this in mind that the number of users should not be too large in NOMA due to the practical limitations such as high interference and implementation complexity at receivers with more users [12]. Besides, [11] assumes perfect SIC that cancels the interference from the decoded users entirely which is a strong assumption due to practical implementation issues [2]. Therefore, imperfect SIC model is highly realistic to explore secure NOMA which has been considered in [13] for two-user NOMA case.…”

“…In [9]- [10], the secrecy performance of trusted near user is analyzed against untrusted far user in NOMA. Further, [11] investigated a new decoding order for untrusted NOMA that is efficient in providing secure data transmission at all users. Note that the work in [11] for NOMA security is limited to the study of two users.…”

“…Further, [11] investigated a new decoding order for untrusted NOMA that is efficient in providing secure data transmission at all users. Note that the work in [11] for NOMA security is limited to the study of two users. As inferred, the decoding order selection problem for more users becomes rather complicated because the problem is of combinatorial nature.…”