  In this paper, an efficient beam and channel acquisition scheme together with
joint angle-delay power profile (JADPP) construction are proposed for
single-carrier mm-wave wideband sparse massive multiple-input multiple-output
(MIMO) channels when hybrid beamforming architecture is utilized. We consider
two different modes of operation, namely slow-time beam acquisition and
fast-time instantaneous channel estimation, for training stage of time division
duplex based systems. In the first mode, where pre-structured hybrid beams are
formed to scan intended angular sectors, the joint angle-delay sparsity map
together with power intensities of each user channels are obtained by using a
novel constant false alarm rate thresholding algorithm inspired from adaptive
radar detection theory. The proposed thresholding algorithm employs a
spatio-temporal adaptive matched filter type estimator, taking the strong
interference due to simultaneously active multipath components of different
user channels into account, in order to estimate JADPP of each user. After
applying the proposed thresholding algorithm on the estimated power profile,
the angle-delay sparsity map of the massive MIMO channel is constructed, based
on which the channel covariance matrices (CCMs) are formed with significantly
reduced amount of training snapshots. Then, by using the estimated CCMs, the
analog beamformer is reconstructed by means of a virtual sectorization while
taking the inter-group and inter-symbol interference into account. Finally, for
the second mode of operation, two novel reduced-rank instantaneous channel
estimators, operating in a proper beamspace formed by the hybrid structure, are
proposed. The proposed beam and channel acquisition techniques attain the
channel estimation accuracy of minimum mean square error filter with true
knowledge of CCMs.
