RIS-Assisted Generalized Receive Quadrature Spatial Modulation with Extension to Multicast Communications

TL;DR

RIS-GRQSM integrates RIS with generalized receive quadrature spatial modulation to boost spectral efficiency by independently activating K receive antennas for both real and imaginary components. The authors formulate a max-min RIS phase-shift optimization, derive a closed-form suboptimal solution via Lagrange duality, and implement a low-complexity non-coherent energy-based greedy detector. They also extend to multicast scenarios with equal-SNR across users and provide ABEP analyses under both optimal and suboptimal designs, supported by numerical results showing SE and BER gains over benchmarks and substantial complexity reductions in multicast. Overall, the work presents a practical, energy-efficient transceiver design capable of high-capacity operation in beyond-5G networks.

Abstract

This paper proposes a novel reconfigurable intelligent surface (RIS)-assisted generalized receive quadrature spatial modulation (RIS-GRQSM) scheme to enhance the spectral efficiency (SE) of RIS-aided \textit{quadrature} spatial modulation (QSM) systems. By leveraging the principle of \textit{generalized} spatial modulation (GSM), multiple receive antennas are independently activated for \textit{both} the in-phase and quadrature components of spatial symbols. To fully exploit the potential of RIS, we formulate a max-min optimization problem to adjust the phase shifts of all RIS elements, thereby maximizing the effective signal-to-noise ratios (SNRs) at the activated antennas. Using Lagrange duality, the original high-dimensional non-convex problem is reduced to a tractable problem with a smaller number of real variables, and a closed-form suboptimal solution is also proposed, which achieves near-optimal performance with a sufficiently large RIS. At the receiver, a low-complexity non-coherent energy-based greedy detector (GD) is introduced for efficient symbol detection. We further extend the RIS-GRQSM framework to a multicast communication system, where all users receive identical information with equal SNR levels, and provide a detailed performance analysis of both systems. In particular, we derive the average bit error probability (ABEP) for the proposed RIS-GRQSM and multicast systems under optimal and suboptimal optimization strategies. Numerical results show that RIS-GRQSM significantly improves the SE and error rate performance compared with benchmark schemes, while the multicast extension achieves performance close to benchmark methods at substantially lower complexity.

Figures (6)

• Figure 1: A diagrammatic illustration of the RIS-assisted generalized receive quadrature spatial modulation (RIS-GRQSM) system.
• Figure 2: A diagrammatic illustration of RIS-assisted multicast communications.
• Figure 3: BER performance of the proposed RIS-GRQSM system; $N_{r}=8$, and (a) $R=12$ bpcu ($K=2$), (b) $R=16$ bpcu ($K=3$).
• Figure 4: Comparison of the BER performance of the proposed RIS-GRQSM system with that of RIS-RQSM and generalized RIS-RQSSK systems, for $N=256$, $N_{r}=8$, and (a) $R=12$ bpcu ($K=2$), (b) $R=16$ bpcu ($K=3$).
• Figure 5: Comparison of the BER performance of the proposed multicast system with that of the physical-layer broadcast scheme proposed in han2020broadcast, where 4-QAM is used, $N_{r}=2$, $N_{t}=1$ and (a) $N=128$, (b) $N=256$.

Theorems & Definitions (2)

• Theorem 1
• proof