  This paper investigates the bit error rate (BER) minimum pre-coder design for
an orthogonal time frequency space (OTFS)-based integrated sensing and
communications (ISAC) system, which is considered as a promising technique for
enabling future wireless networks. In particular, the BER minimum problem takes
into account the maximized available transmission power and the required
sensing performance. We devise the precoder from the perspective of
delay-Doppler (DD) domain by exploiting the equivalent DD channel. To address
the non-convex design problem, we resort to minimizing the lower bound of the
derived average BER. Afterwards, we propose a computationally iterative method
to solve the dual problem at low cost. Simulation results verify the
effectiveness of our proposed precoder and reveal the interplay between sensing
and communication for dual-functional precoder design.
