Covert MIMO Communication in Two-hop Relay Systems

Covert communication can be traced back to secret information transmission technology. It aims to ensure that the transmitters and receivers establish reliable communication with a low probability detection by the warden in wireless communications. The scenario of this paper assumes a covert multiple-input-multiple-output (MIMO) communication in a two-hop relay system, in which a transmitter with multi-antenna sends covert messages to a multi-antenna receiver via a single-antenna half-duplex relay against the detection of a single-antenna warden. We first propose an antenna selection scheme to ensure the covertness of communications, where the transmitter and receiver use an optimally selected subset of antennas to transmit or receive the covert messages and the remaining antennas to generate artificial noise (AN). To depict the performance of covert transmission of the system, we analyze the average detection error probability and derive a closed-form expression. We further conduct theoretical covert throughput with a covertness constraint, and analysis to maximize it in the worst case of the system. Finally, the simulation results illustrate the impact of AN, the number of antennas as well as the transmission rate on the performance of this two-hop covert MIMO communication system.