Beam Shape Optimization Method for Low Outage Beamforming Training with Limited Number of Beams

This paper considers beamforming training methods for mobile access network systems in high frequency bands such as millimeter wave bands. A two-stage beamforming training method is an attractive one to find the desired beam quickly, where the initial training stage is performed roughly, with a limited number of beams. The set of beams for the initial training should be designed carefully to reduce outage probability, because a base station cannot communicate with a mobile terminal if the terminal cannot receive any beams during the initial training. Therefore, we propose a beam shape optimization method for the initial beamforming training that maximizes the minimum received power in the coverage area with a limited number of beams. In the proposed method, the beam direction and beam width of each of the beams are optimized in the optimization process based on an envelope pattern of all the beams. The results of computer simulations where the free space propagation loss is assumed demonstrate that better outage performance can be achieved by beams optimized by the proposed method when compared with a method to optimize each beam separately based on a given beam width.