On resource allocation in covert wireless communication with channel estimation

This work, for the first time, tackles channel estimation design with pilots in the context of covert wireless communication. We consider Rayleigh fading for the communication channel from a transmitter to a receiver, both additive white Gaussian noise (AWGN) and Rayleigh fading for the detection channel from the transmitter to a warden. Before transmitting information signals, the transmitter has to send pilots to enable channel estimation at the receiver. For the case with AWGN detection channel, we first analytically prove that transmitting pilot and information signals with equal power minimizes the warden's detection performance. This motivates us to consider the equal transmit power and then optimize channel use allocation between pilot and information signals under this case. Our analysis shows that the optimal number of the channel uses allocated to pilots increases as the covertness constraint becomes tighter. For the case with Rayleigh fading detection channel, we present a general framework to optimally allocate transmit power and channel uses between pilot and information signals. Our examination shows that the covert communication performance gain achieved by this general framework is not remarkable relative to the scheme with equal transmit power and this gain diminishes as the covertness constraint becomes stricter.