  The orthogonal time frequency space (OTFS) modulation as a promising signal
representation attracts growingcinterest for integrated sensing and
communication (ISAC), yet its merits over orthogonal frequency division
multiplexing (OFDM) remain controversial. This paper devotes to a comprehensive
comparison of OTFS and OFDM for sensing from the perspective of Cramer-Rao
lower bounds (CRLB) analysis. To this end, we develop the cyclic prefix
(CP)-Free and CP-added model for OFDM, while for OTFS, we consider the Zak
transform based and the Two-Step conversion based models, respectively. Then we
rephrase these four models into a unified matrix format to derive the CRLB of
the delays and doppler shifts for multipath scenario. Numerical results
demonstrate the superiority of OTFS modulation for sensing, and the effect of
physical parameters for performance achievement.
