Delay-Doppler Parameter Estimation for DFRC-OTFS Using 2D Root-MUSIC

Orthogonal time frequency space (OTFS) is a modulation scheme based on transmitting information symbols over ideal pulse-Doppler radar signals. As a result, the pilot component of an OTFS transmitted signal can be designed to take the form of a desired pulse-Doppler radar signal. This property results in dual-function capabilities for OTFS, where in addition to the transmitted communications symbols, the pilot signal serves as a sensing radar waveform. In this paper, a two-dimensional (2D) root-MUSIC approach is presented to estimate the delays and Doppler shifts corresponding to multiple targets using such an OTFS waveform. Particularly, the application of the 2D root-MUSIC method for an arbitrary pilot pulse is presented. A heuristic argument is presented that suggests that the widely-used linear frequency modulated (LFM) chirp provides a higher effective signal-to-noise ratio (SNR) as compared to the single-pilot case. Numerical results for the proposed method demonstrate that the LFM pulse, owing to its pulse compression properties, achieves a better estimation performance as compared to a single pilot for a given peak transmitted pilot power.