When warfighters on the ground think about UAVs, their needs are simple. They want lots of data, and they want it now. That shines the spotlight on the links that relay data to ground stations.
While many UAVs send data directly to terrestrial sites, these links often go upward to satellites. That’s putting far higher demands on satellites that in past years often carried voice messages.
“There’s an increase in the amounts of data with the growing use of UAVs,” said J.J. Shaw, Director of Naval Programs for Government Services at Inmarsat.
He noted that satellites are often used to pull data from UAVs and send it to earth stations. Video rates range from 128 kbits/s to 274 Mbits/s, varying widely depending on resolution and whether the UAV is streaming real-time video or simply sending photos.
Sometimes data is sent to satellites because there aren’t earth stations close enough to receive transmissions. When a UAV is lower than 50,000 ft, the station must be within 100 mi to receive line-of-sight transmissions. Other times, links go to satellites so data can be sent to many locations around the globe.
“Satellites are more important to UAVs than most people realize. When bigger UAVs have satellite capabilities, we can go directly to them and receive data anywhere on Earth,” said Gene Fraser, Aerospace Engineering Sector Vice President at Northrop Grumman.
It’s expensive and time-consuming to increase bandwidth by launching more satellites, so military planners are devising ways to trim bandwidth requirements. Electronics on the aircraft are processing sensor inputs rather than sending raw data.
“There is just not enough satellite bandwidth, and line-of-sight communications sometimes requires people to be in places they don’t want to be,” Fraser said. “Rather than pipelining all data directly to the satellite, we do onboard processing and send metadata instead of full real-time images.”
Though that reduces transmission requirements, bandwidth can still be an issue when many sensors on a UAV are all gathering information. That can be true regardless of whether data is being sent to satellites or earth stations. That means there must be buffers on the aircraft.
“Data link bandwidths and outages cannot keep up with massive amounts of sensor data being gathered to be transmitted real time to operators,” said Curtis Reichenfeld, CTO of Curtiss-Wright Controls Electronic Systems. “More onboard storage capability is needed to either buffer data for later transmission or stored for later offload and analysis. Multiple terabytes of onboard storage is no longer uncommon in modern UAVs with advanced payloads.”