Secret Communication in IRS-Assisted MP-WFRFT Systems: Design, Analysis, and Optimization

In this paper, we propose a secret communication method with multiple legitimate receivers and multiple eavesdroppers that integrates an Intelligent Reflecting Surface (IRS) with the multiple parameters weighted fractional Fourier transform (MP-WFRFT). We send the MP-WFRFT to the legitimate receiver, and then reconstruct the legitimate channel and eavesdropping channel to maximize the minimum-secrecy-rate by optimizing the IRS phase. However, the signals of direct link and IRS reflection link superpose with each other at the receiver, which seriously deteriorates the camouflage effect of constellation diagram. To address these issues, we propose an optimization model for camouflage constellation diagram of the IRS-assisted MP-WFRFT system, aiming to optimize the ambiguity error and rotation error of constellation diagram detected at the eavesdropper. As MP-WFRFT can camouflage the PSK signal as the square QAM signal, we can perceive the characteristics of square QAM signal in the environment to flexibly change the signal camouflage type. By jointly the control parameters of MP-WFRFT and IRS, we can minimize the error between the camouflage constellation diagram of MP-WFRFT at the eavesdropper and the existing signal constellation diagram in the environment, achieving the best camouflage effect. The experimental results showed that compared with the situation without using IRS, the proposed method can significantly improve the secret rate of the communication system, and it can also enhance the bit error rate (BER) performance at the legitimate receiver and deteriorate the BER performance at the malicious eavesdropper. Besides, the best camouflage effect of the constellation diagram was achieved.