Ligado Networks, formerly known as LightSquared, has demonstrated it can provide persistent command, control and data connectivity to a small unmanned aircraft in a beyond-visual-line-of-sight (BVLOS) power-line inspection role over a fused space and terrestrial communications network.
As part of a three-day test with Dominion Virginia Power and the Virginia Tech Mid-Atlantic Aviation Partnership in rural central Virginia from April 11-13, the telecommunications company used three different links—its SkyTerra 1 L-band geostationary satellite (operating in the 1.6-GHz band), its FCC-licensed 1,670-1,675-MHz terrestrial band, and the unlicensed 2.4-GHz wireless spectrum—to funnel commands and data to and from anfixed-wing unmanned aircraft system (UAS) performing power-line inspections under the watchful eye of a Robinson R44 chase helicopter.
“We are showcasing the power, availability, reliability and security when you combine terrestrial and satellite links,” says Tamara Casey, chief technology officer for Ligado. “Our goal is to have both networks available and connected as much as possible.”
Casey says that during the testing along high-voltage power lines near Dillwyn, Virginia, Ligado was able to use the unlicensed Wi-Fi link to track and communicate with the Puma out to 5.4 nm (10 km) using a high-gain directional antenna, and the 1,670-1,675 MHz band to maintain connection with the Puma as far as 12.4 nm, the full length of the airspace corridor themade available for the demonstration (see graphic). Satellite connectivity can be maintained continuously using a small transceiver mounted to the top of the Puma fuselage (see photo).
The satellite link is meant for command and control and “critical telemetry,” while the terrestrial links can support both command and control as well as the high-bandwidth sensor data flowing from the Mantis i45 electro-optical and infrared articulated camera payloads on the Puma, Casey says.
Command-and-control data rates of 200 kbps for the downlink and 10 kbps for the uplink were “far more than required,” says Casey. Regarding the much higher payload data rates, which vary based on which cameras and sensors are being used, she says “that’s where the terrestrial augmentation comes in.”
Dominion Virginia Power is interested in BVLOS for power-line inspections, particular after storms. The company largely uses contracted helicopter services to perform two types of surveys—comprehensive structure-to-structure inspections, where a lineman onboard spends approximately 5 min. per tower checking for defects through an articulated camera, and routine line inspections between substations that are approximately 50 mi. apart.
Steve Eisenrauch, manager of transmission line services for Dominion, says the company inspects all 6,500 mi. of its high-power transmission lines—those carrying 68,000-500,000 volts—at least once per year, searching for leaning trees or broken components. “With UAS, we would potentially fly more often,” he says. “There’s a big potential for cost reduction once BVLOS is possible.”
The FAA currently allows only visual-line-of-sight (VLOS) operations for commercial UAS through its Part 107 regulations, rules that Dominion uses for niche inspections with UAS services provided by Hazon Solutions. “There are some things the helo does well and there are some things the UAV does very well,” says Eisenrauch, adding that the company will use UAVs in “highly congested areas” and for horse farms—helicopters “spook” the horses while drones do not.
Dominion hopes to be able to use UAS for post-storm damage assessments or when power is out. “If a crew can dispatch a BVLOS UAV from a site nearby—fly out, hover and get real-time video—[then] they can figure out how many workers they’ll need, the access and the materials required, before the work crews get to the office.”
Ligado is planning to support commercial BVLOS operations pending FCC approval of a petition to modify portions of 40 MHz of spectrum it owns in the L-band for base stations and mobile-use terminals. The company’s 1,670-1,675-MHz band is already approved for terrestrial uses, but required a “special temporary authority” from the FCC for the Dillwyn testing, says Casey.
Ligado predecessor LightSquared’s plans to operate a mobile network in the 1,526-1,555-MHz band fell through in 2012 due to proven concerns that out-of-band emissions would corrupt GPS units that operate in the nearby 1,563-1,587-MHz band. The company declared bankruptcy in 2012, emerged with new owners in 2015 and rebranded as Ligado in 2016. Some companies, including Iridium, have expressed concerns to the FCC about the plan to reallocate portions of the spectrum for mobile use. However, Casey says, “All the technical obstacles have been cleared and [the FCC] is dotting the i’s and crossing the t’s.”
Ligado had earlier agreed not to use the 10-MHz block of its spectrum that is closest to the GPS band. “When we gave up a block of spectrum and said we would only use that for satellite, never for terrestrial, that is what allowed our satellite and terrestrial networks to coexist,” says Casey.
Other broader issues could still impact rollout of BVLOS services that Dominion and many others would like to use. U.S. Sen. Mark Warner (D-Va.), speaking at the April 12 power-line inspection demonstration, said that while he expects the UAS boom to have the same or greater potential as the wireless revolution, he has concerns about security.
Says Warner, the ranking Democrat on the Senate Intelligence Committee: “One of the things I want to do is start engaging with Virginia law enforcement immediately so that we don’t get through all these other hurdles—safety issues, FAA approvals, spectrum issues and community acceptance—and then say, ‘Oops, we haven’t thought through the possibility of one of these devices being taken over and potentially having explosive devices on board. . . . If we can sort through some of the security concerns at the beginning of this industry, it will be a lot better.”