Adaptive Hybrid Beamforming for UAV mmWave Communications against Asymmetric Jitter

Jittering effect is a critical issue in the unmanned aerial vehicle (UAV) millimeter wave (mmWave) communications. In this paper, we identify and characterize the asymmetric impact of jitter on the angular domain information in the UAV mmWave channels, showing how it can lead to significant performance degradation if not properly handled. To address this issue, we propose an adaptive hybrid beamforming for the UAV mmWave communications to maximize the average transmission rate against the asymmetric jitter. The proposed adaptive hybrid beamforming consists of an optimal beam angular range design and an adaptive beamforming vector design. Specifically, we first analytically derive a compact expression of the average transmission rate of our systems. Based on the derived expression, we optimize the beam angular range to maximize the average transmission rate under arbitrary asymmetric jitter. Moreover, we derive the asymptotic expression of the optimal beam angular range in the high signal-to-noise ratio regime. We further develop a simple-yet-efficient algorithm to obtain an adaptive beamforming vector that delivers the optimal beam angular range. Through numerical results, we verify the destructive impacts of the asymmetric jitter, and demonstrate how our proposed scheme can be robust to it, compared to the existing methods without considering the asymmetric jitter.