  In millimeter-wave communications (MMWC), in order to compensate for high
propagation attenuation, phased arrays are favored to achieve array gain by
beamforming, where transmitting and receiving antenna arrays need to be jointly
trained to obtain appropriate antenna weight vectors (AWVs). Since the
amplitude of each element of the AWV is usually constraint constant to simplify
the design of phased arrays in MMWC, the existing singular vector based
beamforming training scheme cannot be used for such devices. Thus, in this
letter, a steering vector based iterative beamforming training scheme, which
exploits the directional feature of MMWC channels, is proposed for devices with
constant-amplitude phased arrays. Performance evaluations show that the
proposed scheme achieves a fast convergence rate as well as a near optimal
array gain.
