Frequency-Time Resource Allocation for Multiuser Uplink ISAC Systems

Integrated sensing and communications (ISAC) is a promising technique for next-generation mobile networks, offering reduced device size, power consumption, cost, and improved spectrum efficiency. Full realization of such benefits relies on waveform design and resource allocation. This paper focuses on frequency-time (FT) resource allocation of multi-user uplink ISAC systems by minimizing the Cramér-Rao bound (CRB) of 5G new-radio signals. We first derive two types of CRBs for communications with respect to channel coefficients and parameters, respectively, and derive one CRB with respect to parameters for radar by removing the line-of-sight path and exploiting the shared parameters among different users' channels. Closed-form solutions to the FT resources are obtained under certain conditions for both radar and communication CRB minimizations, revealing the relationship and differences between the optimal radar and communication FT-resource allocations. Then, to balance the radar and communication CRB performance, we formulate two ISAC FT-resource optimization problems based on the two different communication CRBs and optimize FT resources accordingly. Finally, simulation results validate the effectiveness of the CRB optimization scheme.