Analyses of orthogonal and non-orthogonal steering vectors at millimeter wave systems

Abstract

Beamforming is one of the most challenging problems for millimeter wave communication. With limited codebook size, how to design the steering angles to compensate angles of arrival and departure (AoAs/AoDs) is essential to beamforming performance. Typically, two categories of steering vector sets are commonly used. One is orthogonal steering vector set where the spatial frequency indices of the steering angles are uniformly distributed in spatial frequency domain. The other one is non-orthogonal steering vector set where the steering angles are uniformly distributed in angle domain. In this paper, analyses of these two designs are presented. Due to the fact that beamwidth are constant with respect to different spatial frequency indices in spatial frequency domain, if the spatial frequency indices are uniformly distributed, one has the smallest deviation of the beamforming gain. Since the orthogonal steering vectors satisfy this condition that spatial frequency indices are uniformly distributed, they can achieve higher data rates than the non-orthogonal ones when the AoAs are uniformly distributed over (-π/2, π/2).