Minimizing AoI under Covertness Constraints in Internet of Things Networks

Covertly collecting the latest status information is great crucial for the controller to make decision in Internet of Things (IoT) networks. In this paper, age of information (AoI) is leveraged to evaluate the information freshness. To improve the information freshness, packet re-transmission is exploited at the transmitter, while the re-transmission increases the probability that the transmission behavior is being detected by the adversaries. Hence, we propose a time constrained re-transmission strategy to make a trade-off between the AoI and transmission covertness. Specifically, the maximum allowable re-transmission times have different effects on the AoI and transmission covertness. We formulate an optimization problem to minimize AoI under the constraint of system covertness. The closed-form expression of the average AoI and the expected probability of error detection are derived. Then, the number of maximum re-transmission time slots is optimized to minimize the average AoI. Finally, numerical results demonstrate that the optimal choice of the re-transmission times is the upper bound value of the consecutive transmission time slots that satisfies the covertness constraint. Proposed retransmission strategy can guarantee the information freshness under a given covertness constraint.