Age of information for short-packet covert communication with time modulated retrodirective array

In this paper, the covert age of information (CAoI), which characterizes the timeliness and covertness performance of communication, is first investigated in the short-packet covert communication with time modulated retrodirective array (TMRDA). Specifically, the TMRDA is designed to maximize the antenna gain in the target direction while the side lobe is sufficiently suppressed. On this basis, the covertness constraint and CAoI are derived in closed form. To facilitate the covert transmission design, the transmit power and block-length are jointly optimized to minimize the CAoI, which demonstrates the trade-off between covertness and timelessness. Our results illustrate that there exists an optimal block-length that yields the minimum CAoI, and the presented optimization results can achieve enhanced performance compared with the fixed block-length case. Additionally, we observe that smaller beam pointing error at Bob leads to improvements in CAoI.