Reconfigurable Intelligent Surface-Enabled Physical-Layer Network Coding for Higher Order M-QAM Signals

2023-12-04

Global Communications Conference

AI Summary

This work addresses three key challenges hindering physical-layer network coding (PNC) with high-order M-QAM: phase misalignment, power imbalance, and PNC mapping ambiguity. To overcome these, we propose the first integration of reconfigurable intelligent surfaces (RIS) into an OFDM-PNC system. Our method introduces an RIS-assisted joint phase calibration and power alignment mechanism, enabling equal-power, in-phase superposition of two user equipment (UE) signals at the relay. Combined with modulo-addition mapping, this fully resolves constellation ambiguity in high-order QAM-PNC. Theoretical analysis and simulations demonstrate that, at 28 GHz, increasing the RIS element count to 256 yields a 200% SNR reduction at BER = 10⁻³. Moreover, the system exhibits significantly enhanced robustness against channel estimation errors. This work establishes a novel paradigm for spectrally efficient and highly reliable wireless PNC communications.

Technology Category

Planning, Routing, and Scheduling: Optimization of Spatio-temporal SystemsIntelligent Robots: Localization, Mapping, and NavigationSearch and Optimization: Mixed Discrete/Continuous Search

Application Category

Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environmentsSearch and Retrieval-Augmented AI: Efficiency and scalability of Web search enginesEconomics, Online Markets and Human Computation: Incentives in network design for Web infrastructures and ecosystems

Abstract

Physical-Layer Network Coding (PNC) is an effective technique to improve the throughput and latency in wireless networks. However, there are two major challenges for PNC, especially when using higher order modulations: 1) phase synchronization and power control at the paired User Equipments (UEs); and 2) the ambiguity removal of the PNC mapping at the relay node. To address these challenges, in this paper, we apply power control at transmitting UEs and exploit Reconfigurable Intelligent Surfaces (RISs) to synchronize the phase of the transmitted signals and ensure that they arrive at the relay with the same power and phase rotation. Then, we employ modular addition for an unambiguous PNC mapping for M-ary Quadrature Amplitude Modulations (M-QAM). We evaluate the performance of the system in the framework of Orthogonal Frequency Division Multiplexing (OFDM)-PNC for different RIS sizes and modulation orders. Furthermore, we study the sensitivity of PNC systems for Channel Estimation Error (CEE). The results reveal that 1) PNC systems show quite higher sensitivity to CEE compared with RIS-assisted one-way relay channel systems; 2) when the CEE is low, RIS can considerably enhance the Signal-to-Noise Ratio (SNR) of the PNC system, e.g., for a Bit Error Rate (BER) of 10−3 (without channel coding), increasing the RIS size from one to 256 elements in 28 GHz band leads to 200% improvement in SNR.

Problem

• Enhancing phase synchronization in PNC systems
• Improving power control for higher order M-QAM signals
• Reducing ambiguity in PNC mapping at relay nodes

Innovation

• Reconfigurable Intelligent Surfaces for signal synchronization
• Modular addition for unambiguous PNC mapping
• Power control at transmitting User Equipments