After months of sending drones into the airspace above its campus in San Diego, Qualcomm is sharing the results of what’s believed to be the first comprehensive, systematic study of cellular system performance in networks serving low-altitude drones.
Engineers tested key performance indicators including coverage, signal strength, throughput, latency and mobility under various scenarios on commercial LTE networks. The trial used AT&T’s commercially available spectrum and was made possible thanks to a certificate of authorization (COA) from the FAA because the area is located within highly restricted Class B airspace.
Qualcomm found that existing cellular networks can provide coverage to drones at low altitudes up to 400 feet, and the test drones also showed seamless handovers between different base stations during flights, noted VP of engineering Paul Guckian in a blog post. The trial supported the viability of LTE networks for drones operating beyond visual line of sight (BVLOS), but all of Qualcomm’s test flights were performed under VLOS per their FAA authorization.
One of Qualcomm’s buildings has an inactive helipad that makes it a great spot to do take-offs and landings. For this trial, flights were conducted at ground level and at 30, 60, 90 and 120 meters above ground and were focused on the PCS, AWS and 700 MHz bands.
“What we learned is that the signal is strong at these altitudes and that the mobility algorithms are doing a good job of maintaining connectivity throughout the flight at all times at all the altitudes,” said Harris Teague, lead engineer for the trial.
The ability to maintain a connection was similar at all the altitudes that were studied. “We found some interesting things about how the free space propagation environment at altitude changes some of the characteristics relative to ground use,” he told FierceWirelessTech.
Engineers conducted about 1,000 flights, and while that might sound like a fun day at the office, it requires adhering to a lot of safety procedures and protocols. “I have to say that when we’re doing these kinds of operations, it’s all business,” Teague said when quizzed about the fun factor.
There’s more study to be done. A 3GPP study item was accepted in March to enhance LTE support for aerial vehicles, and Qualcomm said it will share what it learned from the trial with the cellular community to help shape future standard optimizations.
“Long term, our goal is to introduce techniques into next generation cellular standards that will provide simultaneous services to ground and airborne UEs optimized to meet the performance requirement of each class of device,” the study said.
The report noted limitations of the study, saying it was important to construct a consistent flight path that could be executed repeatedly at different altitudes to enable apples-to-apples comparisons of results. However, the flight path does not exhaustively cover all conditions.
“For example, the path was chosen to give us diversity of serving cells so we could study handover events and interference at cell edges. Thus, we did not fly directly over any cells where the signal strengths would be expected to be even higher than those reported here,” the report said. “Also, the environment was a suburban residential/commercial area with good cellular network coverage in the bands studied and these results may not directly extend to urban or rural environments with different coverage and propagation characteristics.”