Vital Alert, through its wholly-owned subsidiary, Waldo Technologies, has developed a positioning and navigation system for autonomous vehicle underground parking.
The system uses VLF (very low frequency) signal beacons and a miniaturized vehicle receiver to navigate a driverless vehicle within radio-frequency-denied environments such as tunnels and multi-story underground parking garages. The system provides position accuracy of less than 7 inches, and is not affected by objects such as other vehicles.
See the video. https://youtu.be/FJQVCsfT9C0