In this paper, we investigate the physical layer security of a multiuser satellite communication system in the presence of multiple eavesdroppers. Particularly, we propose a threshold-based scheduling scheme among the multiple legitimate users, where the geographically clustered eavesdroppers with both the colluded and collaborated eavesdropping scenarios are assumed. Specifically, the closed-form expression for the secrecy outage probability (SOP) is derived for the passive eavesdropping scenario when the channel state information (CSI) of the eavesdroppers is unavailable. In order to get insights of the proposed scheduling scheme at high signal-to-noise ratios (SNRs), the asymptotic analysis for the SOP is also obtained. Moreover, the reduced percentage with respect to number of user examination is also given, which validates the simplicity and efficiency of our proposed scheme compared to the traditional approaches. Numerical results suggest that with the proposed scheme, a comparable system performance with regard to the maximal selection (MS) scheme can be achieved.

In this paper, we investigate the performance of two-way multiple relay non-orthogonal multiple access (NOMA) based networks with hardware impairments (HIs). Especially, opportunistic relay selection scheme is applied to enhance the spectral efficiency along with the spatial diversity. With the increasing of relay's processing capacity, decode-and-forward (DF) protocol is considered in the networks. Based on the proposed relay selection scheme and NOMA protocol, the closed-form expressions for the outage probability (OP) of the system are derived. In order to study the energy efficiency (EE) of the system, simulation results for EE are also obtained. Furthermore, for the purpose of observing the impacts of HIs' level, NOMA protocol and the number of relays on the system performance at high signal-to-noise ratios (SNRs), the asymptotic expressions of the OP are also derived. Finally, Monte Carlo (MC) simulation results are presented to verify the correctness of the analytical results.INDEX TERMS Two-way multiple relay networks, non-orthogonal multiple access (NOMA), opportunistic relay selection scheme, hardware impairments (HIs), outage probability (OP), energy efficiency (EE).

In this article, we investigate the impact of hardware impairments (HIs) on the performance of non-orthogonal multiple access (NOMA) based integrated satellite-terrestrial relay networks (ISTRNs). Particularly, we obtain the novel closed-form expression for the outage probability (OP) of the considered NOMA-based ISTRNs with HIs. Furthermore, to get further insights of the effect of HIs on the considered system in high signal-to-noise ratios (SNRs) scenario, the asymptotic expression for the OP is also obtained, which provides an efficient way to evaluate the system performance, and effective quantification of different parameters on the system performance. Furthermore, we study the energy efficiency (EE) of the considered system and obtain interesting findings when NOMA scheme is applied. At last, numerical Monte Carlo (MC) results are given to verify the correctness of the theoretical results.INDEX TERMS Non-orthogonal multiple access (NOMA), integrated satellite-terrestrial relay networks (ISTRNs), hardware impairments (HIs), outage probability (OP), energy efficiency (EE).

No abstract