Intermittent Artificial Noise Assisted Covert Cooperative Backscatter Communication With Residual Hardware Impairments

Existing works on artificial noise (AN) assisted covert backscatter communication (BC) assumed a jammer continuously transmitting AN, leading to the reduction of the reliability of the legitimate link. Additionally, the unavoidable residual hardware impairments (RHIs) in transceivers have been largely ignored particularly for AN assisted covert BC. Motivated by the above two observations, in this paper, we investigate an intermittent AN assisted covert cooperative backscatter communication (CoBC) system under RHIs. To assess its covertness and reliability, we derive approximate expressions for the detection error probability (DEP) of an eavesdropper and the system outage probability (SOP) under a high transmit signal-to-noise ratio (SNR) region, respectively. To obtain a satisfactory covertness of system, we devise a problem to jointly optimize the AN transmission power and the eavesdropping detection threshold to maximize the minimum DEP while meeting a maximum tolerance system outage probability, and propose an iterative algorithm based on block coordinated descent (BCD) to solve it. Numerical simulations confirm the accuracy of derived results and the valid of the proposed algorithm, and reveal that the intermittent AN achieves a better system reliability than the continuous one when the system requirement for covertness is below a certain value, and that the proposed iterative algorithm outperforms the benchmark scheme in covertness under the same SOP constraint.