"Early analysis from Russian military bloggers on Telegram indicates that the drones communicated back to their Ukrainian handlers via Russian mobile networks using a simple modem that’s connected to a Raspberry Pi-style board."
The Ardupilot software has a few advantages for this use:
"The software can connect to a DIY drone, pull up a map of the area they’re in that’s connected to GPS, and tell the drone to take off, fly around, and land. A drone pilot can use ArduFlight to create a series of waypoints that a drone will fly along, charting its path as best it can. But even when it is not flying on autopilot (which requires GPS; Russia jams GPS and runs its own proprietary system called GLONASS), it has assistive features that are useful.
ArduPilot can handle tasks like stabilizing a drone in the air while the pilot focuses on moving to their next objective. Pilots can switch them into loitering mode, for example, if they need to step away or perform another task, and it has failsafe modes that keep a drone aloft if signal is lost. "