Against Half-Colluding Wardens: Covert Communication Performance Analysis and Transmit Power Optimization

In this paper, we analyze the performance of covert communication using a half-colluding detection strategy for a pair of communicating users who face multiple Wardens aided by artificial noise. Introducing multiple Wardens increases the diversity of detecting strategy and makes the detection process more flexible. In our scenario, Wardens employ a half-colluding strategy where each detector performs the detection independently and uploads its respective detection results to the fusion center (FC) in the form of 1-bit messages. The FC combines these results and makes decisions based on the K-out-of-N rule. First, we analyze the detection performance of Wardens, solve the optimal threshold of the fusion rule, and derive an expression for the covertness constraint under the half-colluding strategy. Next, we analyze the covert rate under the covertness constraint and construct an optimization problem based on this analysis to maximize the covert rate of the communicating users by optimizing the transmit power. Finally, we validate our theoretical findings through numerical results.