Hybrid beamforming design for mmWave OFDM distributed antenna systems

This paper presents a hybrid beamforming design for millimeter-wave (mmWave) orthogonal frequency division multiplexing (OFDM) distributed antenna systems (DASs). First, we derive a downlink signal transmission model that considers the delay spread differences (DSDs) caused by the distributed nature of the network. We then propose a cooperative wideband hybrid beamforming method under the transmitting power constraints of each remote access unit. In a simulation study, the proposed method performed comparably to fully-digital beamforming, even when operated with practical finite-resolution phase shifters. We further confirm that the DSDs are the dominant cause of performance degradation in mmWave OFDM DASs.