Drones proved their worth in the aftermath of hurricanes Harvey and Maria this year, by serving as eyes in the sky for first responders and by inspecting critical infrastructure for damage. Recently AT&T added another important job: helping storm-ravaged Puerto Rico get its cell phone service back.
The island was struck by back-to-back disasters, and when Hurricane Maria passed directly overhead in September, Puerto Rico’s telecommunications network suffered a near-total breakdown. The few remaining operational cell towers were quickly overwhelmed, as residents desperately tried to contact the outside world. At the end of October, with 25 percent of Puerto Rico’s population still without service, AT&T came up with a stopgap solution: a Flying COW.
Originally, COW stood for Cell On Wheels. These were essentially deconstructed cell towers placed on the back of trucks, where they could provide additional network coverage in the wake of tornadoes, hurricanes, and other disasters, including the September 11, 2001 terrorist attacks on New York. Since then, the company has found that deploying antenna-carrying drones is far easier and adds more coverage than putting towers on trucks. So COW became Cell on Wings. Using drone helicopters with 7.5-foot rotor spans—the company declines to name its manufacturer—AT&T has essentially created flying cell towers.
“I’m speaking to you through the flying COW right now,” says Art Pregler, who heads AT&T’s drone program, during a phone call from San Juan. The COW is stationed on the edge of existing cell service near the Puerto Rican capital, in order to extend service to as many people as possible. Current models can connect up to 8,000 users at once. “Flexibility is key to our program,” says Pregler. The COW connects to the AT&T network through fiber optic and Ethernet cables, or via satellite if necessary.
About two years ago, the company began experimenting with multi-rotor drones, the most common type in use today. But a single-rotor platform was chosen for Puerto Rico, says Pregler, because “helicopters are very efficient aeronautical platforms.” He says his helicopter “weighs 25 pounds but can carry 30 pounds of payload, which is more than most multi-rotors can do.”
According to Pregler, the helicopter can fly nonstop for up to 14 hours because it’s connected to the ground by a tether that supplies electrical power and communications, while ensuring that the drone doesn’t fly away unexpectedly. The line is long enough that the COW can fly up to 550 feet above the ground (higher altitude means better coverage). The helicopter also is attached to two fiber optic cables, one of which connects COW users to the LTE cellphone network, while the other provides flight control from the ground and telemetry from the aircraft.
Tethered drones are relatively rare, but it means Pregler’s helicopter can fly without heavy batteries, using the weight savings for more antennas instead. Some of the required network hardware also stays on the ground, in a support trailer. In case the tether breaks, or in the event of a ground power failure, a small flight battery allows the helicopter to land safely.
Using drones for emergency communications is not a new idea, but AT&T’s COW is in the first wave of such devices. Google’s Loon, an unguided balloon with antenna attached, has also been used over Puerto Rico, and the military has for years used large drones for communications relay. Sprint has experimented with smaller drones as well.
The Flying COW is not about to become a permanent fixture in Puerto Rico, or anywhere else, for that matter. Even though they are more capable than other temporary solutions, it’s better to build permanent towers than keep drones aloft. And, Pregler stresses, “it’s still considered experimental.” He’s already convinced, though, that drones will become a permanent part of AT&T’s future emergency response efforts.