When to Realign the Receive Beam in High Mobility V2X Communications?

Abstract

This paper studies a receive directional beam control method in vehicle-to-everything (V2X) wireless communication system. First, we reveal that for a given receive beam, the channel coherence time of fast varying vehicle channels decreases as time goes by. Then, we propose a novel adaptive receive beam control method termed dynamic beam management (DBM), tailored to this channel characteristic, which adaptively selects one of two predefined actions, i.e., channel estimation and beam alignment. The channel estimation is a process of reacquiring channel state information using known pilot signals for coherent detection toward a given receive beam direction. The beam alignment is a kind of analog beam selection method, which steers the direction of the receive beam to attain higher communication performance. Since the beam alignment must search through large dimension, it costs more time compared to the channel estimation. Therefore, given different time overheads of channel estimation and beam alignment, new design criteria are required to decide when each action should be conducted in V2X communications. The proposed DBM figures out the time point when to re-estimate the channel and to realign the receive beam, taking into account their gains and overheads. Furthermore, we show that although a narrow beam has a merit of high power gain, too narrow beam is vulnerable to the pointing error, and reduces channel coherence time, and thus we numerically find the optimal receive beamwidth. The effectiveness and feasibility of the proposed DBM are underpinned by both analytic and simulation results.