Delay-wise Superimposed Pilot based Compressed Sensing Channel Estimation for OTFS Systems

In the OTFS channel estimation scheme, the spectral efficiency loss can be mitigated by a superimposed pilot (SP) scheme, yet it compromises the peak-to-average power ratio (PAPR) performance. This paper introduces a delay-wise super-imposed pilot placement scheme, termed the SP-DW scheme, based on Zadoff-Chu (ZC) sequences. This scheme is designed to enhance the PAPR performance of the system. Specifically, the ZC sequences can maintain good mutual incoherence between the column vectors of the dictionary matrix in compressed sensing-based channel estimation, thereby averting estimation failure. Additionally, a two-step channel estimator and iterative scheme based on the multipath matching pursuit (MMP) algorithm are developed to search for fractional delays and Doppler shifts. The MMP algorithm optimally combines multiple paths in the fractional dictionary matrix to identify sparse candidates, subsequently improving the accuracy of channel estimation. Simulation results indicate that the proposed scheme outperforms the existing SP scheme in terms of PAPR, channel estimation, and bit error rate (BER) performance.