The Connection in One Sentence
ISAC makes the network sense and communicate; RIS makes the propagation environment controllable.
The combination is powerful because sensing and communication both depend on radio propagation. If the propagation path is blocked or weak, both functions degrade. RIS can create additional controllable paths.
The figure shows the central coupling. A RIS phase pattern that maximizes user rate may not maximize target echo strength. A pattern that focuses on the target may reduce user SINR. RIS-assisted ISAC research is therefore about balancing these goals with a single physical surface and a shared waveform.
What ISAC Provides
ISAC provides shared communication and sensing functionality:
- Data transmission to users.
- Radar-like detection.
- Range, angle, and Doppler estimation.
- Tracking and environment awareness.
What RIS Provides
RIS provides propagation control:
- NLoS path creation.
- Signal focusing.
- Interference shaping.
- Virtual anchors for localization.
- Alternative sensing viewpoints.
Why the Combination is Needed
High-resolution ISAC often uses mmWave/sub-THz bands. These bands provide wide bandwidth and narrow beams, but they are vulnerable to blockage. If the line-of-sight path is blocked, the base station may lose both communication and sensing visibility.
RIS can restore visibility by redirecting the waveform.
Correcting a Common Misunderstanding
RIS-assisted ISAC is not simply "bouncing radar from a mirror." The RIS phase pattern changes the effective channel and must be optimized jointly with:
- BS transmit beamforming.
- Communication user quality of service.
- Target illumination.
- Echo reception.
- Interference and clutter.
- RIS hardware constraints.
Main System Types
| System | Description |
|---|---|
| Passive RIS-aided ISAC | Low-power surface shapes ISAC beams |
| Active RIS-aided ISAC | RIS amplifies reflected signals to reduce multiplicative loss |
| STAR-RIS ISAC | Surface serves/senses both sides |
| Multifunctional RIS ISAC | RIS includes sensors or receiving elements |
Takeaway
RIS and ISAC are connected because both are about using radio waves more intelligently. ISAC extracts information from the environment; RIS reshapes the environment so extraction and communication become easier.
References and Further Reading
- M. A. Haider and Y. D. Zhang, "RIS-Aided Integrated Sensing and Communication: A Mini-Review", Frontiers in Signal Processing, 2023.
- M. Rihan, A. Zappone, S. Buzzi, and G. Fodor, "Passive vs. Active Reconfigurable Intelligent Surfaces for Integrated Sensing and Communication", IEEE Network, 2023.
- A. Tishchenko et al., "The Emergence of Multi-Functional and Hybrid Reconfigurable Intelligent Surfaces for Integrated Sensing and Communications", IEEE Communications Surveys & Tutorials, early access, 2025.