Abstract
The widely used embedded impulse pilot for channel estimation of
orthogonal time frequency space modulation (OTFS) has a prohibitively
large peak to average power ratio (PAPR). Hence, in this paper, we
propose a novel embedded pilot with cyclic prefix (PCP) that has a
significantly reduced PAPR compared to the impulse pilot. This is
achieved by spreading the pilot power along the delay dimension using a
constant amplitude Zadoff-Chu (ZC) sequence with a cyclic prefix (CP).
We analytically derive upper bound PAPR expressions for the impulse
pilot and the proposed PCP. Together with our numerical results, these
upper bounds attest the significant PAPR improvement that is achieved by
PCP. We also develop a twostage channel estimation technique with a
superior performance to the threshold-based channel estimation for the
impulse pilot. At the first stage, the channel is estimated by a linear
estimator under the assumption of the channel being locally linear time
invariant over each time-slot within the OTFS block. Taking advantage of
the benefits that are offered by the CP in our proposed pilot structure,
we develop a low complexity least squares based estimator for
implementation of the first stage. At the second stage, we use the
channel estimate from the first stage and the generalized complex
exponential basis expansion model (GCE-BEM) to accurately estimate the
full channel. Finally, we numerically anayze and show the superior
estimation performance of our proposed channel estimator for PCP to the
threshold-based estimator for the impulse pilot.