Despite some mature indoor navigation techniques, innovative solutions for indoor and underground environments are still appearing. The project INSIDE, performed by Astri Polska (Poland), aims to “define the most appropriate localisation technique, which could enable better accuracy and positioning in all possible conditions, especially indoor and underground.

The proposed solution makes use of 3 or 4 transmitters located outdoors broadcasting signals in the VLF frequency band (3-30 kHz). Using such frequencies, signals are able to cross walls and be sensed deep indoor and underground.

The positioning technique is based on the angle of arrival method which requires a minimum of 3 three transmitters with a good spatial distribution for an optimum accuracy.

Claimed advantages are a good positioning accuracy, the absence of multipath, diffraction and reflections, and cost-effective transmitters. On the opposite, admitted disadvantages are the large transmitter and receiver antennas.

The size of the required receiver antenna limits the use of such technique in standard portable devices, meaning that it is actually not a technology that may compete directly with pseudolites.