Robust Design of Integrated Sensing and Communication in LEO Satellite Systems

Low Earth Orbit (LEO) satellites are increasingly utilized for both communication and remote sensing. Traditionally, these functions operate in separate systems, leading to inefficient use of spectrum and hardware. Integrated Sensing and Communication (ISAC) aims to combine these functions into a single satellite platform. However, LEO satellites face unique challenges, including high mobility, significant Doppler shifts, and limited onboard energy. A critical hurdle is the acquisition of accurate Channel State Information (CSI), as phase errors—caused by noise, quantization, and acquisition delays—can severely degrade both sensing accuracy and communication quality.

The authors establish a mathematical framework for an ISAC LEO satellite system that simultaneously serves multiple communication users and senses multiple targets. They model the system's performance using Mean Squared Error (MSE) for sensing and Signal-to-Interference-plus-Noise Ratio (SINR) for communication. To address the practical reality of imperfect CSI, the researchers explicitly incorporate channel phase uncertainty into the design. They formulate a robust optimization problem with the objective of minimizing total transmit power while satisfying strict quality-of-service (QoS) constraints for both functions. To solve this, they develop an iterative algorithm that alternates between optimizing the satellite's transmit beamforming vectors and the sensing receiver's beamforming vectors.

The theoretical analysis and simulation results demonstrate that the proposed robust beamforming algorithm effectively mitigates the cross-functional interference exacerbated by phase errors. By explicitly accounting for phase uncertainty, the system maintains stable performance levels that outperform non-robust baseline methods. This work is significant for the development of 6G wireless networks, as it provides a scalable and energy-efficient strategy for deploying multi-functional LEO satellites that can support both high-speed data transmission and real-time environmental monitoring.