Differential Reflecting Frequency Modulation with QAM for RIS-Based Communications

Area of Science:

• Wireless Communications
• Signal Processing

Background:

• Reconfigurable intelligent surface (RIS)-aided index modulation (IM) offers potential for next-generation wireless networks.
• Acquiring channel state information (CSI) for RIS-based IM systems, especially multi-domain IM, leads to significant pilot overhead.

Purpose of the Study:

• To introduce a novel Differential Reflecting Frequency Modulation (DRFM) system integrating orthogonal frequency division multiplexing (OFDM) with RIS-aided differential reflecting modulation (DRM).
• To develop a CSI-free DRFM system that reduces pilot overhead and enhances communication efficiency.
• To design and evaluate a high-rate Quadrature Amplitude Modulation (QAM) scheme for DRFM to improve throughput and performance.

Main Methods:

• The DRFM system jointly encodes information bits through activation permutations of reflecting patterns, grouped carriers, and constellation symbols.
• The transmitter utilizes the Kronecker product to combine differentially coded reflecting-time and time-frequency blocks.
• A novel high-rate QAM scheme is designed for DRFM, offering improved data rates and error performance compared to traditional modulations.

Main Results:

• The proposed DRFM system operates effectively without requiring CSI at the transmitter, RIS, or receiver, thereby eliminating pilot overhead.
• The novel QAM scheme enhances DRFM's throughput and performance compared to PSK-based DRFM.
• Simulation results demonstrate that QAM-aided DRFM outperforms traditional PSK, APSK, and star-QAM modulations at similar spectral efficiencies, with a minor SNR penalty.

Conclusions:

• DRFM offers a promising CSI-free communication paradigm for RIS-aided systems, significantly reducing overhead.
• The integration of OFDM and a novel QAM scheme advances DRFM capabilities, providing superior performance and spectral efficiency.
• DRFM represents a viable and efficient solution for future wireless communication systems, particularly those employing RIS technology.