What Is CSI Sensing?

How Does CSI Sensing Work?

CSI sensing works based on the multipath effect of radio signal propagation and changes to CSI.

Due to the propagation characteristics of radio signals, the electromagnetic wave signals radiated by a transmit antenna can reach a receive antenna either through a direct path or by reflection off the surrounding environment (such as walls, human bodies, and furniture). Finally, the electromagnetic wave signals reaching the receive antenna are the superposition of direct-path signals and multiple reflection-path signals. This phenomenon is known as the multipath effect of radio signal propagation.

Multipath effect of radio signal propagation

Environmental changes can result in changes in the reflection paths as well as in CSI data. CSI is an important concept in wireless communications. It provides detailed data of the end-to-end signal transmission process. CSI data, including amplitude attenuation and phase offset during propagation, is carried in subcarriers, which are formed by dividing a channel using Wi-Fi OFDM technology. When no object moves in an environment, the paths of multipath signals are relatively stable, and there are only slight changes to CSI data. When a person or object moves in the space, the signal reflection paths change (for example, a path is blocked or a reflection path is added). As a result, the amplitude and phase of multipath signals change after being superimposed, causing fluctuations in CSI data.

By collecting and analyzing the variation pattern of CSI data, CSI sensing technology can detect human presence, identify behaviors, and even measure weak fluctuations due to breathing and heartbeats. For example, when a person is sleeping, the only movements are regular changes in the chest position due to breathing. By extracting the regular changes of CSI, the chest movements can be detected, making it possible to identify whether a person is present.

Depending on the location relationship between the transmitter and receiver, CSI sensing can be classified as bi-static or mono-static sensing.

• Bi-static sensing: Two devices participate in sensing — one sends Wi-Fi signals and one receives Wi-Fi signals.
• Mono-static sensing: The same device is used to receive and send Wi-Fi signals. For example, the CSI sensing function provided by Huawei APs innovatively uses the antenna-algorithm co-design to minimize non-ideal factors and strong self-interference between the transmitter and receiver. A single AP can sense centimeter-level movements in the environment using the sonar-like capability, without the need of other devices. This greatly reduces deployment and maintenance costs.

Bi-static sensing and mono-static sensing

Application Scenarios of CSI Sensing

CSI sensing technology demonstrates great potential in smart campuses. By accurately sensing human activities in physical spaces, it supports intelligent device energy consumption management and security protection, enabling efficient campus operations.

Smart Lighting for Saving Energy in Conference Rooms

In conference rooms of smart campuses, device usage exhibits a clear tidal characteristic: surging when a meeting starts and dropping sharply after the meeting ends. With CSI sensing technology, the system can monitor the activity of people in conference rooms in real time and intelligently control the device status. When detecting that someone enters the meeting room, the system wakes up and starts the meeting room devices, such as the smart screen, air conditioner, lighting, and curtain rail, to provide an appropriate working environment. If no one is detected for a long time (for example, more than 10 minutes), the system automatically shuts down devices or reduces their power, saving energy and reducing the carbon footprint.

Intelligent Energy Saving and Guest Room Fraud Detection in Hotels

In hotels, energy saving is achieved through a key card switch. However, guests may leave the key card in the slot when going out. This increases energy consumption. To address this issue, some hotels use infrared sensors in guest rooms to replace the key card switch. However, infrared sensors can cover only a limited area and cannot accurately detect the sleep state of the guests. Additionally, some employees may commit fraud by not recording guests' actual check-in information in the hotel management system or concealing guests' check-in information to embezzle room fees or for other improper benefits. CSI sensing technology can accurately monitor guests' entering, leaving, and sleeping in guest rooms by detecting the fluctuation of electromagnetic wave reflection signals, ensuring guests' privacy, and helping hotels achieve energy saving and room fraud detection.

Saving Energy in Indoor Open Areas

In indoor open areas of office buildings, such as lobbies and corridors, device usage also exhibits tidal characteristics. In such areas, there are no obvious boundaries or area divisions, and so the CSI sensing result of a single AP is usually insufficient to accurately determine the human activity of the entire area. Additionally, the system integrates CSI sensing data of multiple APs to comprehensively determine the human activity in the area. By setting a long period (longer than 15 minutes is recommended) for determining the unattended state, the system can reduce unnecessary device power-on and power-off operations, improving user experience and consistently saving energy.

Intrusion Detection

In warehouses or R&D sites with high security requirements, CSI sensing technology provides an innovative non-contact intrusion detection method. The system can quickly identify typical intrusion behaviors (such as personnel entering and leaving the room, and doors and windows being opened and closed) and immediately trigger alarms to protect core assets and R&D sites. Compared with traditional monitoring devices, CSI sensing technology can better ensure privacy and security.

CSI Sensing Solution Architecture

Only some Wi-Fi 7 APs support the CSI sensing function. For details, search for the specifications on Info-Finder (Enterprise Network or Carrier).

CSI sensing is supported in both WAC + Fit AP and cloud AP networking scenarios. After collecting and calculating CSI data, APs report the data to Huawei's intelligent network analysis platform iMaster NCE-CampusInsight (CampusInsight for short) or a third-party server. You can select one or more of the following data reporting modes based on the network requirements:

• Reporting data to CampusInsight

  The CSI sensing function is controlled by the AP power-saving license on CampusInsight.

  After CSI data is reported to CampusInsight, it displays the physical and digital map and provides the intrusion detection alarm, among other functions. In addition, CampusInsight provides interfaces for interconnecting with third-party application systems to implement more applications such as intelligent shutdown of electrical appliances.

  
  CampusInsight-based CSI sensing solution architecture
• Reporting data to a third-party server

  APs can directly report the CSI sensing results to a third-party server. The server triggers the nearby IoT devices to complete operations such as energy saving and shutdown based on the received data.

For more information about Wi-Fi 7 APs, see Huawei Wi-Fi 7 APs.