  The high directionality and intense Doppler effects of millimeter wave
(mmWave) and sub-terahertz (subTHz) channels demand accurate localization of
the users and a new paradigm of channel estimation. For orthogonal frequency
division multiplexing (OFDM) waveforms, estimating the geometric parameters of
the radio channel can make these systems more Doppler-resistant and also
enhance sensing and positioning performance. In this paper, we derive a
multiuser, multiple-input multiple-output (MIMO), maximum likelihood,
parametric channel estimation algorithm for uplink sensing, which is capable of
accurately estimating the parameters of each multipath that composes each
user's channel under severe Doppler shift conditions. The presented method is
one of the only Doppler-robust currently available algorithms that does not
rely on line search.
