Communication Security of Microwave QR Code

This letter studies communication security of intelligent reflecting surface (IRS)-based microwave quick response (QR) code. Specifically, the confidential information at a low-cost low-power Internet-of-Things device (Alice) is encoded as a microwave QR code on its associated IRS. To acquire the microwave QR code, a radio frequency signal is transmitted by an authorized user (Bob) and then received by itself through the reflection at the IRS. Meanwhile, a passive eavesdropper (Eve) attempts to intercept the reflected signal from the IRS and decode the carried confidential information. To enhance security, the transmitted signal and the receiving beamforming at Bob are jointly designed while the receiving beamforming vector at Eve is also optimized to capture the worse case of eavesdropping. Based on this, the average bit error probabilities at Bob and Eve are derived for phase shift keying (PSK). The simulation results demonstrate the secrecy performance of the considered system.