Covert Communication in Backscatter Radio

Covert communication in backscatter radio systems is considered, where the transmitter controls its transmit power to keep the transponder's response hidden, while a warden tries to detect this covert communication. To achieve covertness, we propose a non-conventional transmission scheme where the transmitter emits noise-like signal with transmit power varying across different communication slots. Under the assumption of a radiometer as the detector at the warden, we first derive the optimal detection threshold for this detector. Next, building upon the detection performance of warden, we analyze the condition on the transmit power to achieve a target level of covertness. Our numerical results illustrate the price a backscatter system has to pay, in terms of bit error rate, for achieving covert communication.