  Integrated sensing and communication (ISAC) is a promising paradigm to
provide both sensing and communication (S&C) services in vehicular networks.
However, the power of echo signals reflected from vehicles may be too weak to
be used for future precise positioning, due to the practically small radar
cross section of vehicles with random reflection/scattering coefficient. To
tackle this issue, we propose a novel mutual assistance scheme for intelligent
surface-mounted vehicles, where S&C are innovatively designed to assist each
other for achieving an efficient win-win integration, i.e., sensing-assisted
phase shift design and communication-assisted high-precision sensing.
Specifically, we first derive closed-form expressions of the echo power and
achievable rate under uncertain angle information. Then, the communication rate
is maximized while satisfying sensing requirements, which is proved to be a
monotonic optimization problem on time allocation. Furthermore, we unveil the
feasible condition of the problem and propose a polyblock-based optimal
algorithm. Simulation results validate that the performance trade-off bound of
S&C is significantly enlarged by the novel design exploiting mutual assistance
in intelligent surface-aided vehicular networks.
