  Orthogonal time frequency space (OTFS) technique is a two-dimensional
modulation method that multiplexes information symbols in the delay-Doppler
(DD) domain. OTFS combats high Doppler shift existing in high speed wireless
communication. However, conventional channel estimation in OTFS suffers from
high pilot overhead because guard symbols occupy a significant part of the DD
domain grids. In this paper, a superimposed channel estimation is proposed
which can completely estimate channel parameters without considering pilot
overhead and performance degradation. As the channel state information (CSI) in
the DD domain is sparse, a sparse recovery algorithm orthogonal matching
pursuit (OMP) is used. Besides, our proposed method does not suffer from high
peak to average power ratio (PAPR). To detect information symbols, a message
passing (MP) detector, which exploits the sparsity of DD channel
representation, is employed.
