Reliable and Secure Constellation Shifting Aided Differential Radio Frequency Watermark Design for NB-IoT Systems

Narrow band Internet of Things (NB-IoT) systems suffer from malicious attacks or eavesdropping due to the broadcasting properties of wireless channels. In this letter, we propose a differential constellation shifting (DCS) radio frequency (RF) watermark scheme to combat the security threats with high reliability. In our design, RF watermarking is utilized to hide the signals, while the characteristics of NB-IoT systems, which allow repetitive transmissions of host signals, are exploited to enhance reliability performances. Then with the aid of a specific watermarking strength, we construct the differential watermarked symbol pairs which consist of host and watermark symbols. At the receiver, by calculating the difference and the summation of the watermarked symbol pairs, both host and watermark symbols can be reliably recovered. Simulation results demonstrate that our proposed schemes can effectively improve the bit error rate (BER) performances while the covertness and the security performances outperform the benchmark watermark systems.