Integrated Sensing and Communication (ISAC)

Integrated Sensing and Communication (ISAC) enables communication base stations to not only transmit and receive data but also "see" the surrounding environment like a radar. It is regarded as one of the most revolutionary technologies of 5G-Advanced and 6G. By sharing spectrum and hardware, ISAC allows a network to possess both communication and sensing capabilities simultaneously, achieving "one network, dual use."

Core Principle: Deep Integration of Two Capabilities

 1. How Does It Work?

Traditionally, communication and sensing (radar) are two independent systems. The breakthrough of ISAC lies in: using the reflection characteristics of communication signals to sense the environment.

- Communication Function: The base station transmits electromagnetic waves carrying data, and terminal devices receive the signals to complete information exchange.

- Sensing Function: When the same base station's electromagnetic waves encounter objects like drones, vehicles, or pedestrians, they generate reflected echoes. The base station receives these echoes and analyzes them to calculate the target's distance, speed, and angle.

This is similar to a bat's echolocation — it emits a sound and listens for the echo to determine what lies ahead and how far away it is. The difference is that the ISAC base station emits communication signals, not sound, achieving "seamless sensing during ongoing communication."

2. Why is ISAC Necessary?

Spectrum Efficiency：Communication and sensing share the same spectrum, avoiding duplicate occupation of valuable frequency resources.

Hardware Simplification：A single base station performs both tasks, reducing deployment costs.

Seamless Coverage：Leverages the existing wide-area coverage of cellular networks to enable ubiquitous sensing across cities.

Real-Time Capability：Sensing and communication are instantaneous and integrated, with no additional transmission delay.

 Two Key Enabling Technologies

1. Massive MIMO Antenna Arrays

The physical foundation of ISAC is massive Multiple-Input Multiple-Output (MIMO) antenna arrays.

- Communication Mode: Uses beamforming to precisely focus electromagnetic energy on target users, improving data rates.

- Sensing Mode: The same array transmits sensing waveforms and receives environmental reflections, using phase differences between array elements to calculate target positions.

With their large physical apertures and numerous independently controllable channels, antenna arrays enable flexible manipulation of electromagnetic waves in the spatial dimension — a core technical foundation of ISAC.

2. Reconfigurable Intelligent Surfaces (RIS)

RIS is a programmable "intelligent reflective surface" that actively reshapes the propagation environment by controlling the phase of numerous tiny elements. In ISAC, RIS can:

- Assist Communication: Bounce signals around obstacles to reach coverage holes and expand communication range.

- Enhance Sensing: Steer sensing beams toward specific directions to improve radar detection accuracy and distance.

RIS is considered one of the key enabling technologies for 6G ISAC, providing the technological underpinning for deep integration of communication and radar systems.

 Core Application Scenarios

The most significant application scenario for ISAC is the low-altitude economy. Drone flight regulation has been included in the Chinese government's work report, and traditional radar solutions face high costs, significant urban obstruction, and deployment difficulty. ISAC is considered the optimal solution to this challenge.

 Latest Technological Breakthroughs

 1. ISAC in the Optical Domain (Reverse Breakthrough)

Traditional ISAC operates in the radio frequency (RF) domain. Optical ISAC extends sensing capabilities into optical fiber communication networks. A research team from Shenzhen University proposed a forward-transmission distributed optical fiber vibration sensing scheme that deeply integrates with existing optical communication systems, achieving over 200 km single-span sensing without interfering with normal communication. This can be applied to ocean monitoring, earthquake early warning, and more.

The core value of this approach lies in utilizing the vast existing optical fiber infrastructure and evolving it from a simple transmission link into "communication + sensing + intelligent processing" comprehensive infrastructure.

 2. Multi-Modal Fusion Sensing

China Telecom, in collaboration with BUPT, completed the world's first "RF + Optical" multi-modal ISAC field trial in Hangzhou. By fusing the advantages of base station RF sensing and optical camera sensing:

- Successfully identified whether targets were balloons or drones, with recognition accuracy >95%

- Dual-target ranging error <1.5 meters, trajectory integrity >95%

The trial, conducted on China Telecom's cloud-network convergence platform, completed multi-target sensing tests under various weather conditions, including strong light, low light, and rain/fog.

 3. Artificial Intelligence Enabling ISAC

Research by experts such as Professor Zhao Nan from Dalian University of Technology and Academician Yang Xiaoniu indicates that AI is driving ISAC from "model-driven" toward "data-driven" :

- Deep Learning: Used for parameter estimation, waveform design, and beam prediction

- Reinforcement Learning: Optimizes resource allocation and interference management

- Federated Learning: Enables distributed sensing information fusion

AI effectively eliminates the dependence of traditional sensing systems on precise mathematical models, reduces computational complexity, and improves system adaptability in dynamic environments.

4. Retro-Reflective Optical ISAC (RO-ISAC)

A research team from Chongqing University systematically studied retro-reflective optical ISAC systems. By equipping targets (e.g., drones) with corner cube reflector (CCR) modules, optical signals emitted from the base station return along the original path, significantly enhancing echo strength.

This solution enables high-precision sensing and large-capacity communication in indoor, drone-based, and underwater scenarios, opening a new technological pathway for optical-domain ISAC.

Industry Progress and Timeline

Additionally, China has taken a leading position in standardization: spearheading the IMT2020 ISAC Group, leading two CCSA ISAC projects, filing 24 patents, and applying relevant achievements in pilots across 10+ provinces.

Conclusion

ISAC is reshaping the boundaries of mobile communication networks — upgrading them from simple information transmission pipelines into intelligent platforms capable of "seeing" the physical world. It is both a core innovation of 5G-Advanced and a key capability of 6G, with a clearly visible development path:

- Short to Medium Term (2025-2027) : Large-scale deployment of 5G-Advanced ISAC, focusing on critical scenarios such as low-altitude drone regulation and waterway monitoring, achieving "see and manage".

- Medium to Long Term (2028-2030) : Deep integration of sensing and communication in the 6G era, combined with AI and RIS, achieving integrated "Communication, Sensing, Computing, and Intelligence" to empower autonomous driving, smart manufacturing, and other intelligent connectivity scenarios.

For the optical communication industry, ISAC opens up two entirely new tracks: firstly, RF ISAC driving demand for high-speed front-haul/backhaul optical modules at base stations; and secondly, optical fiber ISAC upgrading existing cable infrastructure into "sensing networks," creating incremental markets for ocean monitoring, earthquake early warning, pipeline anti-digging, and more.