  Hybrid beamforming is considered a key enabler to realize millimeter wave
(mmWave) multiple-input multiple-output (MIMO) communications due to its
capability of considerably reducing the number of costly and power-hungry radio
frequency chains in the transceiver. However, in mmWave MIMO orthogonal
frequency-division multiplexing (MIMO-OFDM) systems, hybrid beamforming design
is challenging because the analog precoder and combiner are required to be
shared across the whole employed bandwidth. In this paper, we propose
closed-form solutions to the problem of designing the analog precoder/combiner
in a mmWave MIMO-OFDM system by maximizing the upper bound of the spectral
efficiency. The closed-form solutions facilitate the design of analog
beamformers while guaranteeing state-of-art performance. Numerical results show
that the proposed algorithm attains a slightly improved performance with much
lower computational complexity compared to the considered benchmarks.
