  In orthogonal time frequency space (OTFS) modulation, information-carrying
symbols reside in the delay-Doppler (DD) domain. By operating in the DD domain,
an appealing property for communication arises: time-frequency (TF) dispersive
channels encountered in high mobility environments become time-invariant. The
time-invariance of the channel in the DD domain enables efficient equalizers
for time-frequency dispersive channels. In this paper, we propose an OTFS
system based on the discrete Zak transform. The presented formulation not only
allows an efficient implementation of OTFS but also simplifies the derivation
and analysis of the input-output relation of TF dispersive channel in the DD
domain.
