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Ergodic Secrecy Rate Analysis for RSMA Among Untrusted Users over Rician Fading Channels

Pradosh Kumar Hota, Deepak Mishra, Ravikant Saini, Ankit Dubey

Published Dec 8, 2024• 3 citations

Abstract

Rate-splitting multiple access (RSMA) is a technique that is widely used in next-generation wireless systems to efficiently manage multiple users. RSMA splits the transmission into two parts using rate splitting, which increases spectral efficiency. However, this technique also makes a portion of the transmission vulnerable to eavesdropping, which can compromise information security. This vulnerability is not limited to external eavesdroppers but also includes internal eavesdropping among users who share the same transmission. Therefore, there is an increasing need to develop secure RSMA systems to address these critical security issues among untrusted users. This paper focuses on a single-antenna RSMA downlink system with multiple untrusted users undergoing Rician channel fading. In this novel system framework considered for performance analysis, each user interprets its own common and private streams while attempting to eavesdrop on the private streams of other users. We evaluate the system-level performance in practical settings involving line-of-sight (LoS) paths using the Rician channel model and derive a tight closed-form approximate expression of the ergodic secrecy rate. Finally, we conduct numerical simulations to validate the theoretical analysis and provide valuable insights into the critical system parameters that impact the achievable ergodic secrecy performance of the RSMA system with untrusted users.

DOI: 10.1109/globecom52923.2024.10901268

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Rate-splitting multiple access (RSMA) is a technique that is widely used in next-generation wireless systems to efficiently manage multiple users. RSMA splits the transmission into two parts using rate splitting, which increases spectral efficiency. However, this technique also makes a portion of the transmission vulnerable to eavesdropping, which can compromise information security. This vulnerability is not limited to external eavesdroppers but also includes internal eavesdropping among users who share the same transmission. Therefore, there is an increasing need to develop secure RSMA systems to address these critical security issues among untrusted users. This paper focuses on a single-antenna RSMA downlink system with multiple untrusted users undergoing Rician channel fading. In this novel system framework considered for performance analysis, each user interprets its own common and private streams while attempting to eavesdrop on the private streams of other users. We evaluate the system-level performance in practical settings involving line-of-sight (LoS) paths using the Rician channel model and derive a tight closed-form approximate expression of the ergodic secrecy rate. Finally, we conduct numerical simulations to validate the theoretical analysis and provide valuable insights into the critical system parameters that impact the achievable ergodic secrecy performance of the RSMA system with untrusted users.

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Rate-splitting multiple access (RSMA) is an emerging multiple access strategy, with non-orthogonal multiple access (NOMA) and space division multiple access (SDMA) as its two special cases. RSMA divides the messages required by users into the private and common parts, and the private streams are naturally suitable for the secure transmission. In this paper, we establish a unified rate-splitting framework to ensure the secure transmission for the three multiple access systems mentioned above. The precoders at the multi-antenna transmitter are conjointly optimized to improve the transmission rate of common message. Successive interference cancellation (SIC) is utilized, and the private message for the downlink broadcasting RSMA network can be effectively hidden in the high-power common message. Simulation results demonstrate that the proposed rate-splitting framework can effectively guarantee the secure transmission of the secrecy information.

Rate-splitting multiple access (RSMA) is a promising technology for future wireless networks. In the present paper, a two-user RSMA-aided multiple access channel (MAC) in the presence and the absence of one eavesdropper with correlated Rayleigh fading coefficients is considered. The correlation between random variables is modeled by the aid of copula theorem. (I) The ergodic capacity of RSMA-aided MAC, (II) the individual ergodic secrecy rate (ESR) of RSMA-aided multiple access wiretap channel (MAC-WT), and (III) the positive secrecy capacity probability (PSCP) are obtained by the aid of Farlie-Gumble-Morgenstren (FGM) copula. The results are extended to NOMA-aided MAC and NOMA-aided MAC-WT. The theoretical results are evaluated by numerical results.

This paper investigates the secrecy performance of a hardware-impaired secure rate-splitting multiple access (HIS-RSMA) network in multi-user multiple-input single-output (MISO) Internet of Things (IoT) scenarios over Nakagami-mfading channels. Closed-form expressions for the secrecy capacity (SC) and secrecy outage probability (SOP) are derived and validated through Monte-Carlo simulations. The proposed analytical framework explicitly accounts for the joint effects of non-ideal hardware (NIH), imperfect successive interference cancellation (SIC), and imperfect channel state information (CSI), thereby providing a realistic evaluation of secrecy in IoT networks. Numerical results reveal that NIH has a negligible impact on the secrecy of the common message but significantly degrades the secrecy of private messages at high transmit powers. Moreover, both NIH and imperfect SIC introduce non-vanishing SOP error floors, while imperfect CSI at the eavesdropper can substantially enhance secrecy. The number of transmit antennas and the operating frequency are also shown to critically influence secrecy performance. Overall, the findings highlight that HIS-RSMA is a promising solution for secure and efficient transmission in IoT networks, underscoring the need for joint optimization of transceiver design, antenna configuration, and physical-layer security strategies in beyond fifth-generation (B5G) wireless systems.

In this paper, we consider a sum secrecy spectral efficiency (SE) maximization problem in a downlink rate-splitting multiple access (RSMA) system with multiple antennas. We also assume two types of users: secret users whose private streams require information security and normal users whose private streams do not require security. Due to its max and min operations in the wiretap SE and the SE of the common stream, respectively, which makes the non-convex problem even non-smooth, solving the problem is highly challenging. To deal with the difficulties, we reformulate the optimization problem into an approximated smooth problem using a LogSumExp approach. Then, we identify the first-order optimality condition and develop formulas into a generalized eigenvalue problem. We use a power iteration based algorithm to find the best local optimal solution. Simulations validate the proposed secure RSMA precoding method.