Abstract: In order to ensure the anti-eavesdropping security of signal transmission, a mapping-varied strategy based on multiple reconfigurable intelligent surfaces ( RIS ) is proposed. First, based on instantaneous channel quality between RIS and transmitter, the transmitter selects different mapping modes of spatial modulation and constellation modulation to improve the difficulty of eavesdropping. In order to ensure the security rate and bit error rate of legitimate receivers, the position and phase shift of RIS are optimized to maximize the signal-to-noise ratio of legitimate receivers. Meanwhile, the gradient projection method is used to solve the non-convex constant mode constraint problem of RIS phase shift. Simulation results show that the proposed secure transmission strategy can guarantee the performance of the legitimate receiver at a lower signal-to-noise ratio. Meanwhile, in instantaneous mapping mode, the eavesdropper cannot decode the eavesdropping information correctly, which greatly ensures the anti-eavesdropping security of the system.

Key words: spatial modulation, mapping pattern, reconfigurable intelligent surface, secrecy rate