Part 01 Principles of Wi-Fi Perception  

Wi-Fi awareness 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 reflections and attenuation of Wi-Fi signals, Wi-Fi sensing algorithms can determine the location, presence and movement of objects and people, even through walls and other obstacles. To understand the principle of Wi-Fi perception, you must first understand what CSI is.

When the wireless signal propagates between the transmitter and the receiver, it will be blocked and reflected by objects on the line of sight path, causing changes in the signal, including amplitude attenuation and phase deviation. The communication system needs to adjust the system parameters according to this change, so as to ensure effective and reliable data transmission, so there is CSI.

CSI (Channel State Information), 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 first path of wireless signal transmission (due to the multipath effect of wireless signal transmission, there are more than one transmission path), and represents the signal attenuation and delay on the first path at any time, and represents the carrier frequency . The magnitude and phase of CSI are affected by the displacement of wireless transmitters and receivers, the placement of objects in the environment, and human activity. So when we measure the CSI data, we can use wireless system modeling or machine learning methods to infer environmental changes and human activities, including personnel activity intensity, type, personnel location and other information.

Part 02 Application of Wi-Fi Awareness  

Wi-Fi awareness 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 location-based real-time information and directions, which can help them navigate the environment more easily and efficiently.

② Smart home automation: Wi-Fi awareness can make the home smarter and more efficient. For example, Wi-Fi sensing can be used to automatically turn off lights when a room is unoccupied, or to 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 behaviors (such as falls) in time and call the police.

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

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

In 2022, the China Mobile Smart Home Center will launch broadband services for the elderly based on Wi-Fi sensing capabilities. Using the integration of Wi-Fi smart sensing products and China Mobile broadband networking products, a complete set of home security broadband network solutions will be formed. The program can effectively detect the activity status of the elderly at home, continuously monitor the long-term inactivity and abnormal living habits of the elderly, and can notify the family in time to ensure the safety of the elderly living alone.

Part 03 Advantages of Wi-Fi Awareness  

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

• Privacy protection: Different from optical sensors such as cameras that use images and videos to detect human activities, Wi-Fi sensing uses channel state information between Wi-Fi devices for sensing, without collecting images, and there is no risk of privacy violations. Therefore, It can be used in some sensitive scenes, such as bathrooms, bedrooms, etc.
• Low cost: For human activity detection methods such as millimeter-wave radar and infrared thermal imaging that also have privacy protection features, special detection devices need to be integrated, and the equipment is expensive, generally around 1,000 yuan; Using the channel state between two Wi-Fi devices (usually STA and AP) for sensing, no special detection equipment is required, the cost is lower, and it is more conducive to large-scale deployment.

Part 04 Challenges of Wi-Fi Perception  

Despite the many benefits of Wi-Fi awareness, to realize its full potential, several challenges need to be addressed, mainly including:

• Interference: The Wi-Fi Sense signal is subject to interference from other Wi-Fi networks as well as other sources of electromagnetic interference. This may affect the accuracy and reliability of Wi-Fi perception;
• Scenario complexity: Whether it is a family or a public area, it is a very complex scene, and its environment layout, type and intensity of personnel activities may change greatly, so how to make Wi-Fi perception applicable to most scenarios , is also the direction that needs to be worked hard.

Part 05 Conclusion   

In general, although Wi-Fi perception needs to overcome some challenges, such as interference, complexity, etc., we can see that more and more research teams in academia have begun to conduct research in the field of Wi-Fi perception. Manufacturers have also begun to lay out for Wi-Fi perception, and IEEE will release new standards for Wi-Fi perception in 2024. So we can still believe that Wi-Fi sensing is a promising technology that has the potential to change the way people interact with their environment.