Channel Estimation Techniques for CP-Aided OTFS Systems Relying on Practical Pulse Shapes

This paper develops delay-Doppler domain CSI estimation techniques for cyclic prefix (CP)-aided OTFS systems that employ arbitrary pulse shapes at the transmitter/receiver. In this context, the vectorized model and an equivalent 2D-circular convolution relationship is derived between the input and output symbols for a CP-aided OTFS system. Initially, a pilot impulsebased CSI estimation technique is derived that exploits only the 2D-circular convolution relationship between the input and output symbols. Subsequently, an enhanced data-embedded pilot frame is proposed, where the data symbols are appropriately placed in the pilot frame, while being separated by delay-Doppler domain guard intervals from the pilot impulse, which eliminates the interference between the resulting data and pilot outputs. The proposed data-embedded channel estimation scheme exploits the pilot impulse for channel estimation. Subsequently, a vectorized input-output relationship is determined for data detection, followed by a linear MMSE (LMMSE) receiver that employs the estimated channel state information (CSI). Finally, simulation results are presented to demonstrate the performance of the proposed CSI estimation techniques in various settings and also to benchmark their performance with respect to an ideal system with perfect CSI.