High-Speed User-Centric Beampattern Synthesis via Frequency Diverse Array

In this paper, we study how to maintain the communication quality for high-speed users by utilizing array processing techniques. In conventional phase-array approaches, the phase lags among array antennas need to be updated frequently to tune the array transmission direction, thereby rendering considerable operational costs. To alleviate this, we develop a novel frequency diverse array (FDA) approach. The key point is introducing small frequency offsets across array antennas to generate a time-variant beampattern, making it possible that the FDA beampattern peak automatically accompanies the quickly-moving user without the need of refreshing the frequency offsets, which is referred to as a user-centric beampattern. In this work, we consider two cases of interests: 1) one base station (BS) equipped with an FDA serves a user moving quickly along a relatively short track; 2) multiple BSs cooperatively serve the user along a much longer track. In the single-BS case, we optimize the frequency offsets such that the beampattern peak maximally accompanies the user. In the multi-BS case, we further incorporate BS activation to well balance the service quality and the BS maintenance cost. Two low-complexity algorithms are designed to iteratively solve the two problems with stationary convergence guarantee. Simulations confirm that with the same implementation complexity, the FDA approach serves the high-speed user better than the phase-array approach.