1. NLoS Sensing
A normal base-station radar cannot sense a target hidden behind a building. A RIS can redirect the ISAC waveform around the obstacle and create an indirect sensing path.
This is useful for:
- Street corners.
- Indoor corridors.
- Factory shelves.
- Blocked vehicles or pedestrians.
The important point is that the RIS path is not just another random multipath component. Its position and phase program are known to the network, so the reflected echo can be interpreted geometrically. This makes RIS-assisted NLoS sensing more useful than relying on uncontrolled wall reflections.
References for this section3
- M. Rihan et al., "Passive vs. Active Reconfigurable Intelligent Surfaces for Integrated Sensing and Communication", IEEE Network, 2023.
- M. Rihan et al., "Active RIS-Aided ISAC Systems", IEEE Transactions on Communications, 2024.
- A. Tishchenko et al., "Multi-Functional and Hybrid RIS for ISAC: A Survey", IEEE Communications Surveys & Tutorials, 2025.
2. Better Sensing Geometry
Sensing accuracy depends on geometry. If all observations come from one direction, localization may be poor. RIS can add a new viewpoint and improve angular diversity.
References for this section3
- M. Rihan et al., "Passive vs. Active Reconfigurable Intelligent Surfaces for Integrated Sensing and Communication", IEEE Network, 2023.
- M. Rihan et al., "Active RIS-Aided ISAC Systems", IEEE Transactions on Communications, 2024.
- A. Tishchenko et al., "Multi-Functional and Hybrid RIS for ISAC: A Survey", IEEE Communications Surveys & Tutorials, 2025.
3. Virtual Anchors for Localization
A known RIS location can serve as a virtual anchor. When an ISAC system estimates a RIS-reflected path, it can use the known RIS geometry to improve localization and tracking.
References for this section3
- M. Rihan et al., "Passive vs. Active Reconfigurable Intelligent Surfaces for Integrated Sensing and Communication", IEEE Network, 2023.
- M. Rihan et al., "Active RIS-Aided ISAC Systems", IEEE Transactions on Communications, 2024.
- A. Tishchenko et al., "Multi-Functional and Hybrid RIS for ISAC: A Survey", IEEE Communications Surveys & Tutorials, 2025.
4. Beampattern Shaping
RIS can help shape the sensing beampattern:
- Focus energy at a target.
- Reduce leakage toward clutter.
- Create nulls toward interference.
- Split energy between users and targets.
References for this section3
- M. Rihan et al., "Passive vs. Active Reconfigurable Intelligent Surfaces for Integrated Sensing and Communication", IEEE Network, 2023.
- M. Rihan et al., "Active RIS-Aided ISAC Systems", IEEE Transactions on Communications, 2024.
- A. Tishchenko et al., "Multi-Functional and Hybrid RIS for ISAC: A Survey", IEEE Communications Surveys & Tutorials, 2025.
5. Communication-Sensing Feedback
Sensing can help communication by estimating user position and motion. Communication can help sensing by providing synchronization, waveform structure, and network coordination. RIS strengthens this loop by improving the controllability of paths.
References for this section3
- M. Rihan et al., "Passive vs. Active Reconfigurable Intelligent Surfaces for Integrated Sensing and Communication", IEEE Network, 2023.
- M. Rihan et al., "Active RIS-Aided ISAC Systems", IEEE Transactions on Communications, 2024.
- A. Tishchenko et al., "Multi-Functional and Hybrid RIS for ISAC: A Survey", IEEE Communications Surveys & Tutorials, 2025.
6. Active RIS Assistance
Passive RIS may be too weak for long multi-hop sensing paths. Active RIS can amplify reflected signals. This may improve sensing SINR, but it also introduces amplifier noise and power constraints.
References for this section3
- M. Rihan et al., "Passive vs. Active Reconfigurable Intelligent Surfaces for Integrated Sensing and Communication", IEEE Network, 2023.
- M. Rihan et al., "Active RIS-Aided ISAC Systems", IEEE Transactions on Communications, 2024.
- A. Tishchenko et al., "Multi-Functional and Hybrid RIS for ISAC: A Survey", IEEE Communications Surveys & Tutorials, 2025.
7. Multifunctional RIS
Multifunctional RIS may include sensors or receiving elements. This can reduce channel-estimation overhead and enable local sensing at the surface.
References for this section3
- M. Rihan et al., "Passive vs. Active Reconfigurable Intelligent Surfaces for Integrated Sensing and Communication", IEEE Network, 2023.
- M. Rihan et al., "Active RIS-Aided ISAC Systems", IEEE Transactions on Communications, 2024.
- A. Tishchenko et al., "Multi-Functional and Hybrid RIS for ISAC: A Survey", IEEE Communications Surveys & Tutorials, 2025.
Takeaway
RIS assists ISAC by adding controllable geometry. It can create paths, strengthen echoes, improve localization, and help balance communication and sensing objectives.
References for this section3
- M. Rihan et al., "Passive vs. Active Reconfigurable Intelligent Surfaces for Integrated Sensing and Communication", IEEE Network, 2023.
- M. Rihan et al., "Active RIS-Aided ISAC Systems", IEEE Transactions on Communications, 2024.
- A. Tishchenko et al., "Multi-Functional and Hybrid RIS for ISAC: A Survey", IEEE Communications Surveys & Tutorials, 2025.
Complete references and further reading
- M. Rihan et al., "Passive vs. Active Reconfigurable Intelligent Surfaces for Integrated Sensing and Communication", IEEE Network, 2023.
- M. Rihan et al., "Active RIS-Aided ISAC Systems", IEEE Transactions on Communications, 2024.
- A. Tishchenko et al., "Multi-Functional and Hybrid RIS for ISAC: A Survey", IEEE Communications Surveys & Tutorials, 2025.