From Reliability to Security: How RIS-Assisted Adaptive SM and SSK Enhances Wireless Systems

TL;DR

The paper tackles spectral efficiency and physical layer security in RIS-assisted wireless systems by introducing two received-impaired, RIS-enhanced index modulation schemes: RASM and RASSK. Both schemes dynamically map information to receive-antenna combinations using RIS-based passive beamforming to raise SNR at selected antennas while reducing transmitter RF-chain costs. The authors provide analytical expressions and bounds for spectral efficiency, bit-error rate, and secrecy rate, and validate them through extensive Monte Carlo simulations, including imperfect CSI and eavesdropper scenarios. The results show superior SE and PLS performance of the proposed schemes compared with traditional RIS-assisted IM variants, with the generalized AC selection further reducing detector complexity and maintaining robustness.

Abstract

This paper proposes two novel wireless transmission schemes, namely reconfigurable intelligent surface (RIS)-assisted received adaptive spatial modulation (RASM) scheme and RIS-assisted received adaptive space shift keying (RASSK) scheme, designed to enhance spectral efficiency (SE) and physical layer security (PLS).In both proposed schemes, transmitting bits are dynamically mapped at receive antennas by leveraging the characteristics of the RIS in each time slot, which enables the enhancement of signal-to-noise ratio (SNR) at specific selected antennas with near few power, thus leading a reliable and green wireless communication. This adaptive approach facilitates the conveyance of extra bits to the receiver, which means it needs less cost of radio-frequency chains at transmitter while improving SE. Besides, the proposed schemes offer an inherent PLS security advantage, as the eavesdropper is unable to completely detect signals reflected from the RIS. To comprehensively evaluate the performance of the proposed RASM and RASSK schemes, this paper presents a detailed analytical performance of their spectral efficiency, detection complexity, bit error rate, and secrecy rate, which are accompanied by insightful findings and conclusions. Simulation and analytical results demonstrate the superiority of the proposed schemes, showcasing their improved error performance and robustness against wiretapping, while also highlighting the potential of the RASM and RASSK schemes for future wireless applications.

Figures (8)

• Figure 1: System models for the RASM and RASSK schemes.
• Figure 2: System model of the RASM and RASSK schemes eavesdropper.
• Figure 3: Analytical and simulation BER results of the RASM in (a) and (b), and RASSK schemes in (c).
• Figure 4: (a) BER performance and (b) spectral efficiency represented by bpcu of various IM schemes with different $N_d$, $N_r=16$, $M=2$, and $N=8$.
• Figure 5: BER performance of the RASM, RASSK, and RASM schemes with imperfect CSI estimation.