  This paper analyzes the performance of a multiuser integrated sensing and
communications (ISAC) system, where nonorthogonal multiple access (NOMA) is
exploited to mitigate inter-user interference. Closed-form expressions are
derived to evaluate the outage probability, ergodic communication rate, and
sensing rate. Furthermore, asymptotic analyses are carried out to unveil
diversity orders and high signal-to-noise ratio (SNR) slopes of the considered
NOMA-ISAC system. As the further advance, the achievable sensing-communication
rate region of ISAC is characterized. It is proved that ISAC system is capable
of achieving a larger rate region than the conventional frequency-division
sensing and communications (FDSAC) system.
