  This letter analyzes the performance of uplink integrated sensing and
communications (ISAC) systems where communication users (CUs) and radar targets
(RTs) share the same frequency band. A non-orthogonal multiple access (NOMA)
protocol is adopted in the communication procedure of the ISAC system. Novel
expressions are derived to characterize the outage probability, ergodic
communication rate, and sensing rate. Besides, the diversity order and high
signal-to-noise ratio (SNR) slope are unveiled to gain further insights. It is
found that when achieving the same communication rate, the ISAC system enjoys a
higher sensing rate than the conventional frequency-division sensing and
communications (FDSAC) system where CUs and RTs share isolated bands. All the
results are validated by numerical simulations and are in excellent agreement.
