Wi-Fi Sense: Your home's next sensor may not be a sensor

Part 01   How Wi-Fi Sensing Works  

Wi-Fi sensing is a technology that uses Wi-Fi signals to detect the presence, location, and movement of objects and people in a given environment. By analyzing the reflection and attenuation of Wi-Fi signals, Wi-Fi sensing algorithms can determine the location, presence, and movement of objects and people, and can even penetrate walls and other obstacles. To understand the principles of Wi-Fi sensing, you must first understand what CSI is.

When wireless signals propagate between the transmitter and the receiver, they are blocked and reflected by objects in the line of sight, causing changes in the signal, including amplitude attenuation and phase deviation. The communication system needs to adjust the system parameters according to this change to ensure effective and reliable data transmission, so CSI is born.

CSI (Channel State Information) is a parameter that characterizes channel changes. It represents the amplitude and phase information of the channel by sampling the frequency response of each subcarrier channel, which can generally be expressed as:

Among them, represents the th path of wireless signal transmission (due to the multipath effect of wireless signal transmission, there is more than one transmission path), and represents the signal attenuation and delay at the th path at the moment, and represents the carrier frequency . The amplitude and phase of CSI are affected by the displacement of the wireless transmitter and receiver, the placement of objects in the environment, and the activities of people. Therefore, when we measure the CSI data, we can use the wireless system modeling or machine learning methods to infer the changes in the environment and the activities of the human body, including the intensity, type, and location of human activities.

Part 02   Wi-Fi Aware Applications  

Wi-Fi sensing can detect the movement and behavior of people and has a wide range of potential applications, including:

① Indoor navigation: In large buildings, airports, shopping malls and other public spaces, through Wi-Fi awareness, users can receive real-time location-based information and directions, which can help them navigate the environment more easily and efficiently.

② Smart Home Automation: Wi-Fi sensing can make homes smarter and more efficient. For example, Wi-Fi sensing can be used to automatically turn off lights when no one is in a room, or adjust the temperature based on the presence of people.

③ Health monitoring: Wi-Fi sensing can be used to monitor the health and safety of the elderly and disabled. For example, Wi-Fi sensing can be used to track the activity status of the elderly, detect abnormal behavior (such as falls) in time, and issue an alarm.

④ Security: Wi-Fi sensing can be used for security protection in homes and public spaces. For example, when no one is at home, Wi-Fi sensing can be used to detect the home area and an alarm can be sounded when an intrusion is detected.

⑤ Retail Analytics: Wi-Fi sensors can provide stores with data about consumer behavior and preferences. For example, Wi-Fi sensing can be used to track shoppers’ movements and activities and determine which areas of the store are most popular, which can help retailers optimize operations and improve customers’ shopping experience.

In 2022, China Mobile Smart Home Center launched a broadband service for the elderly based on Wi-Fi sensing capabilities. By integrating Wi-Fi intelligent sensing products and China Mobile's broadband networking products, it has formed a complete set of home security broadband network solutions that can effectively detect the activity status of the elderly at home, and continuously monitor the elderly's long-term inactivity, abnormal living habits, etc., and can inform family members in time to ensure the safety of elderly people living alone.

Part 03   Advantages of Wi-Fi Aware  

There are many sensing methods at present, and Wi-Fi sensing has its unique advantages. Taking the above-mentioned elderly broadband service as an example, its advantages are mainly reflected in the following two points:

• Privacy protection: Unlike optical sensors such as cameras that use images and videos to detect human activities, Wi-Fi sensing uses channel status information between Wi-Fi devices for perception. It does not collect images and does not pose a risk of privacy violation. Therefore, it can be used in some sensitive scenarios, such as bathrooms and bedrooms.
• Lower cost: Millimeter-wave radar, infrared thermal imaging and other human activity detection methods that also have privacy protection features require the integration of dedicated detection devices, which are expensive, generally around RMB 1,000. However, Wi-Fi sensing devices use the channel status between two Wi-Fi devices (generally STA and AP) for perception, do not require dedicated detection equipment, are lower in cost, and are more conducive to large-scale deployment.

Part 04   Challenges of Wi-Fi Awareness  

Although Wi-Fi Aware has many benefits, there are still some challenges that need to be addressed to realize its full potential. These include:

• Interference: Wi-Fi sensing signals can be interfered with by other Wi-Fi networks and other electromagnetic interference sources. This may affect the accuracy and reliability of Wi-Fi sensing;
• Scenario complexity: Both home and public areas are very complex scenarios, and their environmental layout, types and intensity of human activities may vary greatly. Therefore, how to make Wi-Fi sensing applicable to most scenarios is also an area that needs to be worked on.

Part 05    Conclusion  

In general, although Wi-Fi sensing currently needs to overcome some challenges, such as interference and complexity, we can see that more and more research teams in academia have begun to conduct research in the field of Wi-Fi sensing, and various manufacturers in the industry have also begun to lay out plans for Wi-Fi sensing. IEEE will also release a new standard for Wi-Fi sensing in 2024. So we can still believe that Wi-Fi sensing is a very promising technology, which is likely to change the way people interact with the environment.

👇 References

[1] Tan S, Ren Y, Yang J, etal. Commodity WiFi Sensing in 10 Years: Status, Challenges, and Opportunities[J]. IEEE INTERNET OF THINGS JOURNAL, 2022(3164569).

[2] Ma, Yongsen, Gang Zhou, and Shuangquan Wang. "WiFi sensing with channel state information: A survey." ACM Computing Surveys (CSUR) 52.3 (2019): 1-36.