  In this paper we consider Orthogonal Time Frequency Space (OTFS) modulation
based multiple-access (MA). We specifically consider Orthogonal MA methods
(OMA) where the user terminals (UTs) are allocated non-overlapping physical
resource in the delay-Doppler (DD) and/or time-frequency (TF) domain. To the
best of our knowledge, in prior literature, the performance of OMA methods have
been reported only for ideal transmit and receive pulses. In [20] and [21], OMA
methods were proposed which were shown to achieve multi-user interference (MUI)
free communication with ideal pulses. Since ideal pulses are not realizable, in
this paper we study the spectral efficiency (SE) performance of these OMA
methods with practical rectangular pulses. For these OMA methods, we derive the
expression for the received DD domain symbols at the base station (BS) receiver
and the effective DD domain channel matrix when rectangular pulses are used. We
then derive the expression for the achievable sum SE. These expressions are
also derived for another well known OMA method where guard bands (GB) are used
to reduce MUI (called as the GB based MA methods) [19]. Through simulations, we
observe that with rectangular pulses the sum SE achieved by the method in [21]
is almost invariant of the Doppler shift and is higher than that achieved by
the methods in [19], [20] at practical values of the received signal-to-noise
ratio.
