Energy-Focusing Window Based Power Leakage Elimination for Wideband mmWave Massive MIMO -OFDM Systems

In a massive multiple-input multiple-output (MI-MO) system, the large antenna array and the large bandwidth will induce the spatial-wideband effect and the related beam squint effect, which make the energy of each multipath component distributed mainly within a square region in angle-delay domain rather than distributed like an impulse (or basically a Dirichlet kernel). With finite numbers of antennas and subcarriers in practical massive MIMO-OFDM systems, the power leakage of each multipath component outside the corresponding square area is non-negligible. In this paper, we design an optimal energy-focusing window, which shapes the channel in spatial-frequency domain to maximally concentrate the energy of each path inside the corresponding square area in angle-delay domain. With the help of this window, the power (a) leakage can be significantly reduced. Accordingly, the sparsity of millimeter-wave channels can be primely preserved and the inter-user interference can be significantly alleviated for the angle- and delay-based channel estimation and precoding. Simulation results are provided to demonstrate the effectiveness of the proposed window design.