Exploiting Opportunistic Scheduling for Physical-Layer Security in Multitwo User NOMA Networks

Kyusung Shim,Beongku An

doi:10.1155/2018/2797824

Abstract

In this paper, we address the opportunistic scheduling in multitwo user NOMA system consisting of one base station, multinear user, multifar user, and one eavesdropper. To improve the secrecy performance, we propose the users selection scheme, called best-secure-near-user best-secure-far-user (BSNBSF) scheme. The BSNBSF scheme aims to select the best near-far user pair, whose data transmission is the most robust against the overhearing of an eavesdropper. In order to facilitate the performance analysis of the BSNBSF scheme in terms of secrecy outage performance, we derive the exact closed-form expression for secrecy outage probability (SOP) of the selected near user and the tight approximated closed-form expression for SOP of the selected far user, respectively. Additionally, we propose the descent-based search method to find the optimal values of the power allocation coefficients that can minimize the total secrecy outage probability (TSOP). The developed analyses are corroborated through Monte Carlo simulation. Comparisons with the random-near-user random-far-user (RNRF) scheme are performed and show that the proposed scheme significantly improves the secrecy performance.

Highlights

To support the 5G-and-beyond-5G communication networks, called future communication networks, nonorthogonal multiple access (NOMA) has been considered as a solution to increase the spectral efficiency by superposing multiple users in resource domain [1,2,3]
Using the Taylor’s series approximation of the term, that is, exp(−a/x) ≈ 1 − a/x, and after some algebraic manipulations, the asymptotic secrecy outage probability (SOP) of the selected near user can be obtained as
We investigate the effect on power allocation mechanism on the secrecy performance of the proposed scheduling scheme as shown in Figure 7, where the total secrecy outage probability of the selected user pair is plotted as a function of the transmit power and power allocation coefficient of the near user, θN

Summary

Introduction

To support the 5G-and-beyond-5G communication networks, called future communication networks, nonorthogonal multiple access (NOMA) has been considered as a solution to increase the spectral efficiency by superposing multiple users in resource domain (e.g., time and frequency) [1,2,3]. The downlink scenario of the multitwo user NOMA networks consisting of one base station, a near user (that has strong channel state information (CSI)), and a far user (that has low CSI) is actively considered. In [22], the authors proposed the transmit antenna selection (TAS) scheme to improve the secrecy performance for downlink multiple-input-single-output (MISO) NOMA system. In this paper, we propose a new users selection scheme to improve the PLS performance in downlink multitwo user NOMA system using the opportunistic scheduling in the presence of one eavesdropper. (ii) We drive novel expressions for the selected user pairs, respectively, to estimate the secrecy performance achieved by the proposed scheme. (iii) We present other results, called the asymptotic SOP, for the proposed scheme These expressions provide the insight into the behavior of the average far user channel power gain (λSF)

FM Fj directly decode xF Selected user Fb decode xF then subtract decode xN

System Model

Secrecy Outage Performance Analysis

Optimal Analysis of the Power Allocation Coefficients θN

Numerical Results

Conclusion