RIS/IRS-assisted physical layer security enhancement scheme and its application to SCMA systems

This study explores the performance of a reconfigurable intelligent surface (RIS)-assisted communication system combined with Sparse Code Multiple Access (SCMA) under different channel conditions, attack models, and user distribution patterns. SCMA, as an advanced multiple access scheme for 5G/6G, provides high spectrum efficiency and supports large-scale connectivity, but its shared-resource nature exposes it to potential security threats. By integrating RIS with SCMA, our study evaluates how physical layer security can be significantly enhanced in complex environments. This study aims to explore the performance of reconfigurable intelligent surface (RIS)-assisted communication system under different channel conditions, attack models and user distribution patterns. With the continuous advancement of wireless communication technology, RIS, as a new communication optimization technology, has shown great potential in improving system throughput and enhancing network security. This study evaluates the application effect of RIS in complex environments through experimental design, focusing on its performance in improving communication throughput, anti-interference ability and anti-eavesdropping ability. The study constructs an experimental model including RIS-assisted and traditional communication schemes, and uses the Rayleigh and Rician channel model for simulation. The experimental results show that under the condition of SNR of 20 dB, the average throughput of legitimate users of the RIS-assisted scheme is 500 bps, while that of the traditional scheme is only 300 bps, an increase of 67 %. When the SNR is reduced to 10 dB, the throughput of the RIS-assisted scheme remains at 450 bps, while that of the traditional scheme drops to 250 bps, an increase of 80 %. Under poor channel conditions (SNR of 5 dB), the throughput of RIS remains stable at 480 bps, while the traditional solution is only 280 bps, showing the significant advantages of RIS under low channel quality. In terms of security assessment, the study conducted a detailed analysis of two attack modes: direct eavesdropping and relay eavesdropping. Taking the eavesdropper distance of 50-100 meters as an example, without the assistance of RIS, the eavesdropper's received signal rate is 100 bps, while with the assistance of RIS it is only 50 bps, a reduction of 50 %. As the eavesdropper distance increases to 100-200 meters and more than 200 meters, the anti-eavesdropping effect of RIS is still significant, reducing the eavesdropping signal rate from 200 bps to 100 bps, and from 300 bps to 150 bps, respectively, with a reduction of 50 %. Finally, this study evaluated the impact of different RIS configurations on system performance in a multi-user scenario. The experimental results show that as the number of reflection units increases from 64 to 128, the total throughput of the system increases from 1000 bps to 1200 bps, an increase of 20 %. In addition, as the number of eavesdroppers increases, the security gain (ΔR) of the RIS system always remains positive, indicating that RIS can still effectively protect the communication security of legitimate users in an environment with multiple eavesdroppers. Under an SNR of 20 dB, the RIS assisted scheme attains an average legitimate-user throughput of 500 bps versus 300 bps for the traditional baseline. When the SNR is 10 dB, the measured throughput of the RIS assisted scheme is 450 bps, while at 5 dB it is 480 bps. Note that these two points correspond to different operating conditions: the 10 dB case uses a distributed-user, medium-interference setting with the dynamic RIS adjustment disabled (stress-testing interference), whereas the 5 dB case uses a centralized-user layout with the dynamic adjustment enabled and favorable RIS alignment. Therefore, the 5 dB and 10 dB figures are not intended for a monotonic SNR comparison but to illustrate performance under distinct operating modes.