A WiFi fingerprint is essentially a unique radio map or signature of a specific physical location, created by recording the received signal strength (RSS) values from all detectable WiFi access points in that area.
This concept is the foundation of WiFi Fingerprinting, a method used primarily for determining the location of a device or "asset." As the reference states, WiFi Fingerprinting "uses historical RSS information as well as known locations to determine the position of an asset given its current RSS values."
How the WiFi Fingerprinting Process Works
The process relies on building a database of these location-specific "fingerprints" and then matching current readings against that database. It typically involves two main stages:
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The Training Phase (Offline Phase):
- This involves surveying the area where positioning is needed.
- At numerous points with known geographic coordinates (the "known locations"), a device records the RSS values from all visible WiFi access points.
- This data – the RSS values paired with their corresponding known locations – forms the "historical RSS information" database, effectively mapping RSS patterns to physical space.
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The Localization Phase (Online Phase):
- When a device's position needs to be determined, it measures the current RSS values from the WiFi access points it detects.
- This "current RSS values" set is then compared to the historical fingerprints stored in the database.
- Algorithms analyze the current fingerprint and find the best match or interpolate among the closest matches in the database to estimate the asset's current position.
| Phase | Goal | Inputs Used | Output |
|---|---|---|---|
| Training | Create the fingerprint database | RSS from APs at known locations | Database of Location-Specific Fingerprints |
| Localization | Determine current position | Current RSS from APs, Fingerprint Database | Estimated Position of the Asset |
Key Elements
Understanding WiFi fingerprinting involves recognizing its core components:
- Received Signal Strength (RSS): A numerical measure indicating the power level of the WiFi signal received from an access point. Weaker signals typically mean greater distance, but the pattern across multiple access points is the key.
- Known Locations: Specific points where initial RSS data is collected during the setup phase, providing the geographic reference for the fingerprints.
- Historical RSS Information (Fingerprint Database): The collected dataset mapping specific RSS patterns to known physical locations.
- Current RSS Values: The real-time signal strength measurements taken by the device needing localization.
This technique is particularly valuable for indoor positioning systems (IPS) or in urban canyons where traditional GPS signals may be weak or unavailable, providing a software-based approach to determining location based on existing WiFi infrastructure.
