GPS Repeater for Indoor Coverage

ANAFI USA / ANAFI Thermal / ANAFI 4K
1

Hello,

We are looking at potentially using ANAFI drones in large, open indoor environments. Has anyone used a GPS repeater to achieve this? (for example, these offerings from Faltech GPS repeater systems for any indoor space; bring the outdoor signal inside) Does the ANAFI/ANAFI USA require particular GPS (L1/L2/GLONASS/Beidou/Galileo)? Do such solutions account for the offset of the drone with respect to the location of the receiver and the transmitter?

Regards,
Tom

2

Hi, I am also interested in this opportunity. Is it possible for us to work on this together?

3

Hello Tom,

The GPS works by triangulation from travel time differences of each satellite signal.
However after the repeater reception antenna, and up to the drone, all the gps satellite signals will suffer the exact same delay. So the triangulation no longer works, and the drone’s gps will actually measure the position of the repeater’s reception antenna.

The drone will know its location on Earth, however the drone will make a horizontal fly-away because its gps will tell it it is immobile at the location of the repeater’s reception antenna.

The ANAFI uses a Ublox M8N gps chip.

Another way to use the ANAFI in a large indoor environment is :

  • to let the drone use its vision system (vertical camera), by flying within range of the ultrasonic sensor, and with well textured floors (without shiny reflexions, …). However gps functionnalities, like FlighPlan will not work
  • if you wish to do indoor FlightPlan, maybe it can be done through the API by sending low-level (joystick like) commands to the drone and reading its position estimation, and writing a custom code to follow waypoints
  • to replace the ANAFI GPS receiver (antenna + ublox chip) with a custom indoor positioning system (like POZYX) which sends its measures on the gps uart link to the processor and emulates GPS measures (NMEA format + spying what over messages are exchanged on the uart with the ublox). But this is difficult and voids the warranty.
  • maybe some companies already do similar uses and can assist you, like Planck (https://anafiusa.planckaero.com/), or like Dronisos which make indoor shows with heavy tinkering on the drones (https://www.dronisos.com/)

Best regards,
Aurelien

4

Thanks for all the information @Aurelien. Are there any solutions that account for this by storing the drone offset with respect to the repeater? Or perhaps by having multiple repeaters positioned around the indoor space (i.e. reintroducing triangulation)?

5

Unfortunately it would not work.

I do not think it would work, as the drone’s ublox gps would just sense N possible fix locations (for N repeaters-antennas), and may just return the location with the strongest signal. But the chosen strongest signal would still be for a fix position with 0 doppler shift in the gps signals, so the ublox gps would not be able to make its velocity measurements.
However I am not fully confident on this answer.

6

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