Blockage-Resilient Covert Beamforming in mmWave Networks with Multi-BS Collaboration

Given the vulnerability of millimeter-wave (mmWave) bands to dynamic blockages, multi-base station (BS) collaboration serves as an efficient solution in ensuring reliable connectivity via offering alternative transmission paths. However, these additional transmission paths inevitably increases the risk of detection by potential eavesdroppers in the network. In this paper, we study a blockage-resilient multi-BS collaborative covert beamforming design for multi-user mmWave systems, which can simultaneously ensure covertness and blockage resilience. Given that the power of jamming signals transmitted by the collaborating BSs are randomized to degrade the eavesdropper's detection capability, we derive the joint probability distribution of the aggregated jamming signals and then obtain the eavesdropper's detection error probability (DEP). The blockage-resilient covert beamforming design is formulated as a max-min fairness optimization under covertness constraints accommodated to all potential blockage combinations. The nonconvex problem is solved via a successive convex approximation (SCA)-based iterative algorithm. Simulation results show that the proposed beamforming design significantly outperforms non-blockage-aware beamforming, achieving improvements in transmission rate while ensuring covertness requirements.