Wi-Fi "GPS" (more accurately called Wi-Fi positioning) works by using the unique identifiers of nearby Wi-Fi access points (APs) to estimate a device's location. Instead of using satellites like traditional GPS, it leverages the already existing infrastructure of Wi-Fi networks.
Here's a breakdown:
- Scanning for Wi-Fi Networks: Your device (smartphone, tablet, etc.) constantly scans for available Wi-Fi networks, even if you're not actively connected to one.
- Identifying Access Points: Each Wi-Fi access point broadcasts a unique identifier called a BSSID (Basic Service Set Identifier), which is essentially its MAC address.
- Location Database: Large databases, like those maintained by Google, Skyhook, and Apple, correlate these BSSIDs with geographic locations. These databases are built by mapping the physical locations of Wi-Fi routers. This is often done using GPS-equipped vehicles that drive around and record the BSSIDs they encounter along with their corresponding GPS coordinates. Even mobile devices using Wi-Fi can contribute to these databases, anonymizing location data and BSSIDs.
- Location Estimation: When your device detects multiple Wi-Fi networks, it sends the BSSIDs of those networks to a location service provider (e.g., Google Location Services). The provider then looks up the corresponding locations of those access points in its database.
- Triangulation (or Multilateration): Using the known locations of the detected Wi-Fi access points, the service estimates your device's location. More sophisticated algorithms consider the signal strength of each detected Wi-Fi network. Stronger signals suggest closer proximity. This allows for a more accurate position estimate through a process similar to triangulation (actually multilateration, since it uses signal strength along with known positions).
- Location Provided to Applications: The estimated location is then provided to applications on your device that require location information (e.g., maps, weather apps, location-based games).
Key Advantages of Wi-Fi Positioning:
- Indoor Positioning: Wi-Fi positioning works indoors, where GPS signals are often weak or unavailable.
- Faster Location Fix: It often provides a faster initial location fix than GPS, as Wi-Fi signals are readily available in many areas.
- Lower Power Consumption (Potentially): Depending on the implementation, it may consume less power than continuously searching for GPS satellite signals.
Limitations:
- Accuracy Varies: Accuracy depends on the density of Wi-Fi access points and the completeness of the location database. Rural areas with fewer Wi-Fi networks will have less accurate Wi-Fi positioning.
- Database Dependence: The accuracy relies heavily on the accuracy and completeness of the Wi-Fi location database. If a Wi-Fi access point has been moved and the database hasn't been updated, the location estimate will be inaccurate.
- Privacy Concerns: Sending Wi-Fi BSSIDs to location service providers raises privacy concerns, as your device's location can be tracked. However, most modern systems use anonymization techniques to mitigate these risks.
In summary, Wi-Fi positioning provides an alternative or supplementary location method to GPS, particularly useful indoors and in urban environments, by leveraging the ubiquity of Wi-Fi networks and comprehensive location databases.
