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

TL;DR

This paper proposes using Reconfigurable Intelligent Surfaces (RIS) to enhance phase synchronization and unambiguous decoding in higher order M-QAM Physical-Layer Network Coding systems, significantly improving performance under low channel estimation errors.

Contribution

It introduces RIS-assisted phase synchronization and modular addition-based PNC mapping for M-QAM, addressing key challenges in high-order modulation PNC systems.

Findings

RIS improves SNR significantly with larger array size.

PNC systems are highly sensitive to channel estimation errors.

RIS can triple the SNR at low CEE levels for 28 GHz band.

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.