🤖 AI Summary
This study addresses interference suppression and bit error rate (BER) optimization in full-duplex reconfigurable intelligent surface (RIS)-assisted multi-user communications. A QPSK-based multi-user system is established, and a successive interference cancellation (SIC) optimization framework tailored for variable-amplitude RISs is proposed. By jointly designing three SIC ordering strategies with phase-shift optimization algorithms for amplitude-variable reflecting elements, the system performance is validated through Monte Carlo simulations. The results demonstrate that mean square error (MSE)-based ordering achieves optimal performance in small-scale RIS configurations, whereas the proposed optimization method excels in large-scale scenarios. This work reveals the optimal matching relationship between RIS scale and SIC ordering mechanisms, significantly reducing the system BER.
📝 Abstract
This work considers reconfigurable intelligent surface (RIS) aided multi-way communication systems employing QPSK. The objectives of such system is to allow multiple users to exchange information, exploiting the full-duplex capabilities of RIS. The system under consideration comprises $K$ user terminals and an RIS with $N$ reflective elements. Each user terminal is equipped with one transmit and $M$ receive antennas. To mitigate inter-user interference caused by the full-duplex operation of the RIS, three successive interference cancellation (SIC) techniques are considered. We investigate three SIC ordering methods: $1)$ descending channel variances, $2)$ increasing mean square error, $3)$ optimization approach which maximizes the combined channel gain within the system. The bit error rate (BER) performance of these three SIC methods are evaluated using extensive Monte-Carlo simulations for different numbers of RIS elements, ranging from 4 to 64, and a varying number of transmitting users, ranging from 1 to 5. Additionally, an RIS phase shift optimization method for RIS with reflection elements of varying amplitudes is considered. In this case the previous SIC optimization technique is adapted to address phase-dependent amplitudes in RIS reflection elements. Simulation results indicate that in both ideal and varying amplitude scenarios, when the number of RIS elements is small, SIC with ordering based on increasing mean square error achieves the best BER performance. However, as the number of RIS elements increases, SIC ordering based on the optimization method achieves the best BER performance.