Physical Layer Security for Practical RSMA-Based Hybrid Satellite-Terrestrial Relay Networks

This paper investigates the physical layer security for a rate-splitting multiple access (RSMA)-based hybrid satellite-terrestrial relay network (HSTRN) under the joint impact of hardware impairments (HIs) and channel estimation errors (CEEs). In the proposed RSMA-based HSTRN, a satellite communicates with multiple users via terrestrial relays in the presence of an eavesdropper. In order to improve the secrecy performance, we propose two relay selection schemes, namely, partial relay selection (PRS) and two-stage relay selection (TSRS). We derive exact closed-form expressions of outage probability (OP), intercept probability (IP), and effective secrecy throughput (EST) for the PRS and TSRS schemes. To further enhance the secrecy performance of proposed system, the relay selection schemes are extended to jammer-assisted HSTRN, and we propose the jammer aided PRS (JPRS) and jammer aided TSRS (JTSRS) schemes. The exact closed-form OP, IP, and EST expressions for the JPRS and JTSRS schemes are also obtained. Numerical results show that in the high signal-to-noise ratio (SNR) region, the TSRS scheme outperforms the PRS scheme in terms of EST, while in the low SNR region, the result is opposite. Additionally, in the high SNR region, the secrecy performance of jammer-aided relay selection schemes, i.e., JPRS and JTSRS schemes, outperform relay selection schemes without the support of a jammer, i.e., PRS and TSRS schemes. Moreover, it shows that the RSMA-based HSTRN achieves better secrecy performance than the non-orthogonal multiple access (NOMA)-based HSTRN in high SNR region.