  From the industrial standpoint on integrated sensing and communication
(ISAC), the preference lies in augmenting existing infrastructure with sensing
services while minimizing network changes and leveraging available resources.
This paper investigates the potential of utilizing the existing infrastructure
of fifth-generation (5G) new radio (NR) signals as defined by the 3rd
generation partnership project (3GPP), particularly focusing on pilot signals
for sensing within the ISAC framework. We propose to take advantage of the
existing positioning reference signal (PRS) for sensing and the physical
downlink shared channel (PDSCH) for communication, both readily available in 5G
NR. However, the use of PRS for sensing poses challenges, leading to the
appearance of ghost targets.
  To overcome this obstacle, we propose two innovative approaches for different
PRS comb sizes within the ISAC framework, leveraging the demodulation reference
signal (DMRS) within PDSCH to eliminate ghost targets. Subsequently, we
formulate a resource allocation problem between PRS and PDSCH and determine the
Pareto optimal point between communication and sensing without ghost targets.
Through comprehensive simulation and analysis, we demonstrate that the joint
exploitation of DMRS and PRS offers a promising solution for ghost target
removal, while effective time and frequency resource allocation enables the
achievement of Pareto optimality in ISAC.
