Millimeter Wave Hybrid Beamforming with DFT-MUB Aided Precoder Codebook Design

The millimeter wave (mmWave) frequency band offers substantial hitherto unused spectral resources for future wireless communication systems in order to meet the increasing capacity demand. However, mmWave frequencies suffer from high propagation losses, which may be mitigated by directional beamforming in addition to baseband precoding. This is usually referred to as hybrid beamforming. In this paper, we investigate the so-called discrete Fourier transform- mutually unbiased bases (DFT-MUB) aided codebook design conceived for limited-feedback mmWave systems, where the MUB aided codebook is applied in the baseband, while the DFT codebook is invoked for RF analog phase shifters. We demonstrate that our DFT- MUB codebook design performs similarly to the optimal digital precoding matrix, where the precoder is selected as the right singular matrix of the channel. However, our solution significantly reduces the search complexity in the baseband, while performing within 2.5 dB from the optimal digital precoder.