  Recently, orthogonal time-frequency-space (OTFS) modulation is used as a
promising candidate waveform for high mobility communication scenarios. In
practical transmission, OTFS with rectangular pulse shaping is implemented
using different prefix/suffix configurations including reduced-cyclic prefix
(RCP), full-CP (FCP), full-zero suffix (FZS), and reduced-zero padded (RZP).
However, for each prefix/suffix type, different effective channel are seen at
the receiver side resulting in dissimilar performance of the various OTFS
configurations given a specific communication scenario. To fulfill this gap, in
this paper, we study and model the effective channel in OTFS systems using
various prefix/suffix configurations. Then, from the input-output relation
analysis of the received signal, we show that the OTFS has a simple sparse
structure for all prefix/suffix types, where the only difference is the phase
term introduced when extending quasi-periodically in the delay-Doppler grid. We
provide a comprehensive comparison between all OTFS types in terms of channel
estimation/equalization complexity, symbol detection performance, power and
spectral efficiencies, which helps in deciding the optimal prefix/suffix
configuration for a specific scenario. Finally, we propose a novel OTFS
structure namely reduced-FCP (RFCP) where the information of the CP block is
decodable.
