Joint Waveform Design and Sub-Carrier Allocation for Multiuser MIMO ISAC

We consider a multicarrier integrated sensing and communications (ISAC) system that operates as a monostatic MIMO radar while simultaneously providing downlink communication services to multiple single-antenna users. We investigate the joint optimization of transmit waveform design, radar receiver filtering, and subcarrier allocation. Two subcarrier allocation strategies are examined, namely, non-overlapping, where a subset of subcarriers is dedicated to sensing and the remainder to communications, and overlapping, where a subset is allocated for radar sensing while the entire bandwidth is used for communications. Our focus is on maximizing an objective function that balances the minimum radar signal-to-interference-plus-noise ratio (SINR) and communications SINR under power constraints. To address the resulting mixed-integer non-convex problem, we employ alternating optimization combined with the successive convex approximation (SCA) algorithm to find effective solutions. Numerical results assess the performance of the proposed methods and demonstrate the tradeoff between radar and communications performance. The results indicate that the overlapping strategy provides better communications performance, while the non-overlapping strategy enhances sensing performance.