Non-Reciprocal RIS-Assisted Wireless Communications: Channel Modeling

Non-reciprocal reconfigurable intelligent surface (NR-RIS) has emerged as a promising technology for enhancing the performance of wireless communication systems. Unlike conventional RIS, NR-RIS can support asymmetric signal transmission, which enables different signal paths between the transmitter and receiver. In this paper, we investigate the potential of NR-RIS-assisted wireless communication systems and analyze the impact of various system parameters on performance metrics, including the signal-to-noise ratio (SNR) and the bit error rate (BER). Specifically, we first develop a path loss model for a simple RIS-aided system, and we study the effect of different parameters, such as the number of RIS elements, and the distance between the base station, RIS, and user. We then derive a channel model for nonreciprocal RISs, and we study the effects of non-reciprocity on the channel coefficients and phase shift matrix at RIS in both uplink and downlink channels. Simulation results show that nonreciprocity can significantly affect the performance of RIS-aided systems and that a careful design of the RIS is necessary to achieve optimal performance.