WiFi RTT (802.11mc)
The Time-of-Flight Paradigm
Standard WiFi positioning uses RSSI (Received Signal Strength Indication). It is notoriously susceptible to multipath fading and shadowing—a person standing in front of a router interprets as "distancing" the device.
WiFi RTT (Round Trip Time), defined in the 802.11mc standard, utilizes the Fine Timing Measurement (FTM) protocol. It ignores signal power and instead measures the precise nanosecond duration it takes for a radio packet to bounce between an Initiator (Smartphone) and a Responder (Access Point).
Bandwidth and Resolution
The accuracy of the ranging result is physically limited by the bandwidth of the WiFi channel:
- 20 MHz (2.4GHz): Coarse resolution, errors of several meters.
- 80/160 MHz (5GHz/6GHz): Sharper correlation peaks, allowing sub-meter resolution and the ability to distinguish the "first arriving path" from late reflections.
Enterprise Logic: Open Locate
For stadium-scale deployments, enterprise hardware offers a critical software advantage:
- Self-Location: APs like the Aruba 500 Series can self-locate via built-in GPS and broadcast their precise Latitude/Longitude/Altitude coordinates directly in the FTM frames.
- Dynamic Trilateration: This allows the drone to enter a venue and begin positioning immediately without needing a pre-loaded database of anchor locations.
Validated Hardware
Consumer / Reference
- Google Wifi / Nest Wifi: The primary reference hardware for Android. Guaranteed to work as Google uses them for internal testing.
- Linksys Velop: Confirmed 802.11mc support in most modern firmware versions.
Enterprise (Recommended)
- Aruba 505 / 515: Supports the "Open Locate" protocol.
- Cisco Catalyst 91xx: High sensitivity, but requires a controller-based config to enable Responder mode.
Source Code Reference
- Android RTT Manager:
android/net/wifi/rtt/WifiRttManager.java- The API for initiating ranging requests and handling theonRangingResults()callback.