Distributed Modulation Exploiting IRS for Secure Communications

Abstract

Due to the broadcast nature of wireless communications, users’ data transmitted wirelessly is susceptible to security/privacy threats. The conventional modulation scheme “loads” all of the user’s transmitted information onto a physical signal. Then, as long as an adversary overhears and processes the signal, s/he may access the user’s information, hence breaching communication privacy. To counter this threat, we propose IRS-DMSC, a Distributed Modulation based Secure Communication (DMSC) scheme by exploiting Intelligent Reflecting Surface (IRS). Under IRS-DMSC, two sub-signals are employed to realize legitimate data transmission. Of these two signals, one is directly generated by the legitimate transmitter (Tx), while the other is obtained by modulating the phase of the direct signal and then reflecting it at the IRS in an indirect way. Both the direct and indirect signal components superimpose on each other at the legitimate receiver (Rx) to produce a waveform identical to that obtained under traditional centralized modulation (CM), so that the legitimate Rx can employ the conventional demodulation method to recover the desired data from the received signal. IRS-DMSC incorporates the characteristics of wireless channels into the modulation process, and hence can fully exploit the randomness of wireless channels to enhance transmission secrecy. However, due to the distribution and randomization of legitimate transmission, it becomes difficult or even impossible for an eavesdropper to wiretap the legitimate user’s information. Furthermore, in order to address the problem of decoding error incurred by the difference of two physical channels’ fading, we develop Relative Phase Calibration (RPC) and Constellation Point Calibration (CPC), to improve decoding correctness at the legitimate Rx. Our method design, experiment, and simulation have shown the proposed IRS-DMSC to prevent eavesdroppers from intercepting legitimate information while maintaining good performance of the legitimate transmission.