  Integrated sensing and communication (ISAC) is viewed as a key technology in
future wireless networks. One of the main challenges in realizing ISAC is
developing dual-functional waveforms that can communicate with communication
receivers and perform radar sensing simultaneously. In this paper, we consider
the joint design of a dual-functional orthogonal time-frequency space (OTFS)
signal and a receiving filter for the ISAC system. The problem of ISAC waveform
design is formulated as the minimization of the weighted integrated sidelobe
level (WISL) of the ambiguity function and the interference term from ISAC
waveform, with constraints on signal-to-noise ratio loss. The
majorization-minimization algorithm combined with alternating iterative
minimization is implemented to solve the optimization problem. Simulation
results show that the WISL and the interference term can be significantly
decreased to guarantee achievable data rates and detection performance.
