Stacked-Intelligent-Surface-Assisted MIMO Integrated Sensing and Communication

This paper investigates the application of Stacked Intelligent Surfaces (SIS) in Integrated Sensing and Communication (ISAC) systems. Unlike conventional multiple-input multiple-output (MIMO) systems, SIS offer unique advantages in terms of complexity and energy efficiency by performing signal processing directly on radio waves, potentially reducing the need for extensive RF chains and antennas. We explore two SIS-assisted ISAC schemes: a hybrid digital-analog beamforming scheme and an analog-only beamforming scheme. To evaluate these schemes, we consider two case studies: integrated data transmission with channel estimation for the hybrid scheme, and data transmission integrated with target detection for the analog-only scheme. In the first scenario, we demonstrate that SIS can provide better rates and channel estimation accuracy compared with hybrid beamforming in multiple-input single-output (MISO) systems. In the second scenario, we show that SIS enable data transmission with target detection and radar beamforming that closely match binary-beam MIMO. Finally, we outline several future extensions to further enhance the capabilities and applicability of SIS-assisted ISAC systems.