  In this letter, we investigate time-domain channel estimation for wideband
millimeter wave (mmWave) MIMO OFDM system. By transmitting frequency-domain
pilot symbols as well as different beamforming vectors, we observe that the
time-domain mmWave MIMO channels exhibit channel delay sparsity and especially
block sparsity among different spatial directions. Then we propose a
time-domain channel estimation exploiting block sparsity (TDCEBS) scheme, which
always aims at finding the best nonzero block achieving the largest projection
of the residue at each iterations. In particular, we evaluate the system
performance using the QuaDRiGa which is recommended by 5G New Radio to generate
wideband mmWave MIMO channels. The effectiveness of the proposed TDCEBS scheme
is verified by the simulation results, as the proposed scheme outperforms the
existing schemes.
