  Quantifying the performance bound of an integrated localization and
communication (ILAC) system and the trade-off between communication and
localization performance is critical. In this letter, we consider an ILAC
system that can perform communication and localization via time-domain or
frequency-domain resource allocation. We develop an analytical framework to
derive the closed-form expression of the capacity loss versus localization
Cramer-Rao lower bound (CRB) loss via time-domain and frequency-domain resource
allocation. Simulation results validate the analytical model and demonstrate
that frequency-domain resource allocation is preferable in scenarios with a
smaller number of antennas at the next generation nodeB (gNB) and a larger
distance between user equipment (UE) and gNB, while time-domain resource
allocation is preferable in scenarios with a larger number of antennas and
smaller distance between UE and the gNB.
