  Using millimeter-wave (mmWave) bands is expected to provide high data rates
through large licensed and unlicensed spectrum. Due to large path loss and
sparse scattering propagation properties, proper beam alignment is important in
mmWave systems. Small carrier wavelengths at mmWave bands let wireless
communication systems use large antenna arrays to provide sufficient
beamforming gain with highly directional beams. Hence, high resolution channel
angle-of-departure (AoD) and angle-of-arrival (AoA) estimation is crucial for
beam alignment to get the advantages of large beamforming gain. Using large
antenna arrays, however, can lead to high system complexity and channel
estimation overhead. This paper proposes a channel AoD/AoA estimation technique
using widebeams to lower estimation overhead and auxiliary-beam-pair (ABP) to
get high resolution channel AoD/AoA estimates considering hybrid transceiver
structures. To fully use the hybrid transceiver structures, the linear
combination of discrete Fourier transform (DFT) vectors is considered to
construct widebeams. Numerical results show that the proposed estimator can get
high resolution channel AoD/AoA estimates with lower overhead compared to
previous estimators.
