Abstract: Physical layer security encryption technology is an effective physical layer security method to ensure the safe transmission of information.The signal constellation is designed by means of phase rotation,modulation constellation diversity,symbol obfuscation,amplitude adjustment and symbol sequence change to protect modulation mode and modulation symbol information.The existing physical layer security encryption technology has some disadvantages,such as unclassified key sharing and insufficient constellation ambiguity.The MIO scheme adoptes the encryption method of superposition of artificial noise symbol key andmo-dulated symbol vector to solve the problem of insufficient constellation ambiguity.Inspired by MIO scheme,this paper proposed a new physical layer security encryption scheme based on constellation obfuscation design (COD) by superimposing channel coefficient and modulated symbol vector.Under the condition of TDD mode and channel reciprocity,the channel coefficient of the legitimate channel is used as the key to solve the problem of unclassified key pre-sharing.This paper introduced the complete transmission process of sending-end encryption and legal-end decryption,and analyzed the reception process of high-order cumulant modulation re-cognition and intelligent attack eavesdropper.The theoretical SER (symbol error rate) equation of legitimate receiver in Rayleigh fading channel was derived.Simulation of SER performance of legitimate receiver,high order cumulant modulation re-cognition eavesdropper and intelligent attack eavesdropper were conducted.The performance of the legitimate receiver and eavesdropper of MIO scheme and COD scheme are compared.Simulation results show that when the SER of legitimate receiver is 1×10^－4,the SNR(signal-to-noise ratio) of COD scheme is 6dB lower than that of MIO scheme.After the COD scheme is encrypted,when SNR is 0,the success rate of modulation identification is 11.8%,and the highest success rate of modulation identification is 25%,which remains stable after the SNR is greater than 40dB.In the first three data packets,the SER of the COD scheme’s intelligent attack eavesdropping terminal is always 0.284,while that of the MIO scheme’s eavesdropper who knowns the starting key is lower.With the SNR between 0 and 54dB,the SER performance of the legitimate receiver is always better than that of the modulation recognition eavesdropping terminal and the intelligent attack eavesdropping terminal.Therefore,the proposed COD scheme can guarantee the secure communication and resist the attack of modulation recognition and intelligent attack eavesdropper,and the effectiveness and reliability of COD scheme are better than MIO scheme.

Key words: Constellation mapping, Constellation obfuscation, Modulation, Physical layer security, Physical layer security encryption