User Scheduling Design for Covert Communication in Cooperative Cognitive Radio System

In this article, we investigate the covert communication for a cooperative cognitive radio (CCR) system, where the secondary transmitters (STs) help the primary transmitter (PT) to transmit information while covertly transmitting their own information to the secondary receiver (SR) against the warden of PT. In particular, the different ST scheduling schemes are proposed for covert communications, namely, covert rate maximization (CRM), best channel gain (BCG), and fairness oriented (FO). The closed-form expression is derived for the expected detection error probability at the warden PT. Based on that, we, respectively, analyze the covert rate and covert outage probability (COP) of the proposed ST scheduling schemes. The simulation results show that, under the both effects of channel uncertainty and noise uncertainty, the CRM scheme achieves the best covert rate performance, and the BCG and FO schemes ensure the quality of service (QoS) and the STs' fairness as the cost of covert performance degraded.