  In this paper, we develop two high-resolution channel estimation schemes
based on the estimating signal parameters via the rotational invariance
techniques (ESPRIT) method for frequency-selective millimeter wave (mmWave)
massive MIMO systems. The first scheme is based on two-dimensional ESPRIT
(TDE), which includes three stages of pilot transmission. This scheme first
estimates the angles of arrival (AoA) and angles of departure (AoD) and then
pairs the AoA and AoD. The other scheme reduces the pilot transmission from
three stages to two stages and therefore reduces the pilot overhead. It is
based on one-dimensional ESPRIT and minimum searching (EMS). It first estimates
the AoD of each channel path and then searches the minimum from the identified
mainlobe. To guarantee the robust channel estimation performance, we also
develop a hybrid precoding and combining matrices design method so that the
received signal power keeps almost the same for any AoA and AoD. Finally, we
demonstrate that the proposed two schemes outperform the existing channel
estimation schemes in terms of computational complexity and performance.
