Noncoherent Reflecting Modulation for Reconfigurable Intelligent Surface-Based Communications

Reconfigurable intelligent surface (RIS)-based communication has emerged as a novel concept that can transform signal in a cost-effective and energy-efficient manner. However, the RIS system is confronted with the following several problems. First, the substantial number of reflecting elements complicates the estimating of channel state information (CSI). Second, passive RIS systems merely reflect signals to the receiver. The enhancements in bit error rate (BER) performance are insufficient. Third, the existing RIS systems only consider the influence of noise at the receiver. Nevertheless, in reality, the signal is affected by noise on both RIS and receiver. To address these limitations, a noncoherent reflecting modulation (NRM) system is designed in this paper. In the NRM system, the active RIS is adopted. It modifies not only the phase but also the amplitude, which significantly enhances the BER performance. Energy signals and differential techniques are employed, allowing the system to function without any CSI at the transmitter, RIS, or receiver. The simulation results demonstrate that NRM exhibits a 9 dB improvement in BER performance and exhibits superior noise resistance compared to the existing differential RIS system. The upper bound of the average symbol error probability is derived. Extensive simulations validate the superiority of the NRM scheme in scenarios such as 6G.