The Complete Pareto Points for In-Band Full Duplex Integrated Sensing and Communication Systems

Abstract

In this article, we investigate beamforming and transmit power optimization for in-band full-duplex integrated sensing and communications (FD-ISAC) systems. Our focus is on an FD-ISAC base station (BS) that simultaneously communicates with both downlink (DL) and uplink (UL) communication users (CUs) while detecting a target. Existing FD-ISAC studies typically: 1) consider either DL or UL users, not both, leading to additional interference; 2) neglect radar signal-to-interference-plus-noise ratio (SINR) as a performance metric; or 3) address single-objective optimization, focusing on either communication or radar performance. We formulate the problem as a weighted multiobjective optimization, balancing the achievable sum rate for CUs and the received radar SINR–two inherently conflicting objectives. To solve this nonconvex problem, we propose two solutions: A complexity-oriented design (COD) utilizing convex transformations and relaxations. And a performance-oriented design (POD) leveraging single-objective solutions to address the multiobjective formulation. Numerical evaluations demonstrate that both methods achieve comparable performance for CUs and radar. However, COD performs better for radar, while POD is superior for CUs, especially with a higher number of BS antennas. COD also has lower computational complexity. Our proposed FD-ISAC schemes outperform existing half-duplex (HD) ISAC schemes by approximately 6 dB for radar SINR and 8 bits/s/Hz for CU rate.