  In this paper, we analyze the performance of orthogonal time frequency space
(OTFS) modulation with antenna selection at the receiver, where $n_s$ out of
$n_r$ receive antennas with maximum channel Frobenius norms in the
delay-Doppler (DD) domain are selected. Single-input multiple-output OTFS
(SIMO-OTFS), multiple-input multiple-output OTFS (MIMO-OTFS), and space-time
coded OTFS (STC-OTFS) systems with receive antenna selection (RAS) are
considered. We consider these systems without and with phase rotation. Our
diversity analysis results show that, with no phase rotation, SIMO-OTFS and
MIMO-OTFS systems with RAS are rank deficient, and therefore they do not
extract the full receive diversity as well as the diversity present in the DD
domain. Also, Alamouti coded STC-OTFS system with RAS and no phase rotation
extracts the full transmit diversity, but it fails to extract the DD diversity.
On the other hand, SIMO-OTFS and STC-OTFS systems with RAS become full-ranked
when phase rotation is used, because of which they extract the full spatial as
well as the DD diversity present in the system. Also, when phase rotation is
used, MIMO-OTFS systems with RAS extract the full DD diversity, but they do not
extract the full receive diversity because of rank deficiency. Simulation
results are shown to validate the analytically predicted diversity performance.
