Performance Evaluation of Dual RIS-Assisted Received Space Shift Keying Modulation

TL;DR

This work tackles indoor wireless coverage by proposing a dual-RIS architecture where RIS$_1$ near the transmitter passively reflects the signal and RIS$_2$ near the receiver dynamically steers beams to one of $N_r$ antennas based on source data bits, enabling data-driven spatial routing via space-shift keying. It develops an end-to-end multi-hop channel model with RIS phase optimization under perfect CSI, derives a semi-closed outage probability using a CLT-based Gaussian approximation that leads to a noncentral chi-square representation for the end-to-end SNR, and provides a large-$N$ deterministic-equivalent capacity bound $C_{avg} \approx \log_2(1 + \bar{\gamma}_m)$ with $\bar{\gamma}_m = \zeta^2 E_s \mu_Z^2 / N_0$. Simulation results indicate that increasing $N$ improves reliability and rate, while the 3 GHz band yields better outage performance; surprisingly, single-RIS configurations can outperform dual-RIS setups in outage under certain conditions, underscoring trade-offs between routing flexibility and coordination complexity. Overall, the dual-RIS framework offers flexible, energy-efficient indoor coverage and motivates further optimization and real-world deployment studies for multi-RIS networks in future wireless systems, including 5G/6G contexts.

Abstract

Reconfigurable intelligent surfaces (RISs) are gaining traction for their ability to reshape wireless environments with low energy consumption. However, prior studies primarily explore single-RIS deployments with static or semi-static reflection control. In this paper, we propose a novel dual-RIS-assisted architecture for smart indoor wireless signal routing, wherein the second RIS (RIS$_2$) is dynamically configured based on source data bits to steer signals toward specific receivers or indoor zones. The first RIS (RIS$_1$), positioned near a fed antenna or access point, passively reflects the incident signal. RIS$_2$, equipped with a lightweight controller, performs bit-driven spatial modulation to enable data-dependent direction selection at the physical layer. We develop a complete end-to-end system model, including multi-hop channel representation, RIS phase configuration mapping, and signal detection based on space shift keying (SSK). Performance analysis is evaluated in terms of achievable capacity and outage probability under varying inter-RIS distances and carrier frequencies.

Figures (4)

• Figure 1: Dual-RIS-assisted indoor communication system.
• Figure 2: Outage performance of the Dual-RIS assisted RSSK schemes: (a) with different $N$, (b) with different $f_c$ ($N_r=2$, $f_c= 3$GHz, $K=2$, $d=10$, and $\gamma_{\text{out}} = 10$ dB).
• Figure 3: Ergodic capacity of the Dual-RIS assisted RSSK schemes : (a) with different number of reflecting elements $N$, (b) with different distances $d$. ($N=128$, $N_r=2$, $f_c=3$GHz.
• Figure 4: Outage performance of the RIS assisted RSSK systems: (a) Dual-RIS with different $K$, (b) Single-RIS with different $K$ ($N=128$, $N_r=2$, $d=10$ m, $f_c=3$ GHz and $\gamma_{\text{out}} = 10$ dB).