Satellite links are often the only option for BVLOS and remote operations, so I’ve been investigating the reliability of the Iridium Certus satellite service for ArduPilot (MAVLink) telemetry.
There’s a few manufacturers that produce modems for the Certus service (in particular GroundControl, who supplied a modem for testing), that are quite small and lightweight (<1kg typically), making them ideal for unmanned vehicles.
The Certus service has a number of different datarate tiers, from 100-700kbps. The higher tiers require larger modems and antennas though. For the purpose of these tests, a Certus 100 service was used, giving 88Kbps downlink and 22Kbps uplink. Note that the uplink (Vehicle to GCS) is the critical datarate, as most telemetry data flows in that direction.
I tested ArduPilot telemetry over an Iridium Certus 100 connection using a RockREMOTE UAV OEM modem, measuring latency, packet loss, and overall reliability under a range of configurations, using the mavlinklinktester software.
What I found was:
- A streamrate of 2Hz telemetry is needed (instead of the default 4Hz) to avoid flooding the link
- Using a “direct” connection (not using a VPN) gave 7-8% packet loss over UDP and 0% loss over TCP. Latency was 800ms for UDP and 1.2sec for TCP.
- VPN services (such as Wireguard or Zerotier) were not practical to use. Packet loss and outages were a minimum of 50%.
- For a stable service, the antenna should be place at or above the treeline/roofline. Any sustained ground testing should ensure the antenna is elevated to this height to give representative results.
In terms of airtime costs, running at a 2Hz streamrate will typically cost around $30/hour.
The full report is attached below.
Writeup.pdf (370.2 KB)