Ligado's Proposed LTE Plans Sees Calls for More Changes

Ligado continues to talk with the aviation community and is committed to working with the Federal Aviation Administration (FAA) "to establish operating parameters that will satisfy [its] safety standards," the company said in a statement. Noting CEO Doug Smith's blog Monday (see 1605230031), the company said it's "committed to working with industry stakeholders to identify and address their concerns. We are in problem-solving mode and look forward to engaging in those types of discussions over the coming months."

The modifications were crafted to meet GPS industry concerns (see 1602040015 and 1512180020). Trimble said in its filing Monday in the docket that "the Agreed Licensing Conditions represent a compromise which balances the competing public policy interests raised by Ligado’s ... proposed use of their licensed spectrum." It said it supports the technical parameters and licensing conditions for Ligado's use of 1627.5-1637.5 and 1646.5-1656.5 MHz and the proposed limits on its use of 1545-1555 MHz, but it remains in disagreement with Ligado about use of 1526-1536 MHz, though the two continue to discuss licensing conditions.

The Aerospace Industries Association has "substantial concerns regarding the adequacy of the voluntary conditions Ligado offers" to protect avionics and GPS aviation safety equipment, AIA said in its filing. Any FCC authorization before Ligado comes to consensus with the FAA on maximum power levels "could lead to additional future complexity in achieving agreement" on power levels for different aviation safety-of-life systems, AIA said. It said potential interference to other global navigation satellite systems used in aviation, such as Galileo, GLONASS and BeiDou, and to satellite-based augmentation systems, needs study and potential addressing. AIA urged the FCC to merge to the parallel Ligado proceedings into one "as the resolution of the issues are inextricably linked to the overall technical regulatory viability of Ligado's proposal."

A collection of aviation filers said the FCC should delay any action on the license modification application until after the FAA studies the effects of introducing downlink commercial broadband operations in the 1526-1536 MHz band. The FAA should have oversight of Ligado's emissions profile in all bands to ensure aviation safety, said the Aircraft Owners and Pilots Association, Airlines for America, Helicopter Association International, the International Air Transport Association, Aviation Spectrum Resources, Bristow U.S., the Cargo Airline Association, Delta Air Lines, the National Air Transportation Association, Rockwell Collins, Southwest Airlines and United Parcel Service.

Boeing said Ligado "appears committed to ... a comprehensive solution to the challenging coordination problems posed by its ambitious proposal." Its comments suggested that before any grant of the proposal, details need to be worked out on replacement of affected transceivers; there needs to be some effective regulatory oversight for license conditions that protect aviation GPS; and flight test spectrum needs protection.

Iridium pushed for further unspecified license modification changes or else Ligado would cause "significant harmful interference" to Iridium's mobile satellite service network. In a filing Monday, Iridium said it's in discussions with Ligado about different operational parameters, but Ligado's currently proposed parameters "would result in significant harmful interference to Iridium's current and future MSS network."

Public Knowledge, New America's Open Technology Institute and Common Cause said the GPS agreements "satisfactorily address any lingering interference concerns." The groups said in a joint filing that the FCC should impose license conditions that permit opportunistic access to unused Ligado spectrum "on a use-or-share basis to the extent technically feasible" and that require Ligado and its wholesale customers to follow any privacy or network security rules already established by the agency or that it establishes for similarly situated services. Ligado "has aptly demonstrated the significant benefits that would flow from the availability of hybrid satellite-terrestrial technologies in the L band," ViaSat said in a filing. The Competitive Carriers Association also backed the Ligado plan.

Ligado's proposed modifications offer "a new view" on future terrestrial compatibility in the L-band," Greenwood Telecommunications Consultants said in a filing Tuesday. To tackle the remaining compatibility issues -- such as helicopters fitted with terrain avoidance -- it said the FCC should issue orders creating a multistakeholder forum to look into L-band compatibility issues and solutions.

The power level reductions in the license modification request "will cause [its] network to be invisible, inaudible, and non-existent to consumer GPS devices such as smartphones and general navigation devices," Ligado said in its own comments. The company also said some industrial GPS devices already co-exist with the proposed Ligado network, while others "will not be used near any network facility or can be replaced or retrofitted cost effectively well before Ligado's network would begin operation." Ligado said any more-restrictive limits on power or out-of-band-emissions "would cause unnecessary harm and would needlessly reduce the benefits to society that this L-band spectrum has to offer."

The company argued against using a 1 dB rise in carrier-to-noise ratio as the standard for tolerance of interference. It called that standard "technically flawed" since GPS devices in the ordinary course of their operations see changes in the noise floor of more than 1 dB "and yet still function smoothly" and since GPS devices see errors "due to the inherent limitations of the natural world" -- something a 1 dB limit can't predict. Ligado got some criticism for rejecting the interference limit (see 1605200064), and the standard is shaping up to be a battleground in the proceeding.

The standard "appears to have no connection to the levels of interference that will actually cause harm to GPS operations," Public Knowledge et al. said. They added that the FCC should determine the appropriate standard for measuring interference and that metric should be interference that actually causes harm to GPS receiver performance.

Garman called Ligado's license modifications for aviation devices and FAA concerns "a positive step," but cautioned against abandoning the 1 dB standard, saying relying on "user-perception or user-experience would produce results as numerous and varied as the domestic and worldwide uses of GNSS." Garmin said that not having a universal, quantifiable metric for gauging GNSS "would quickly halt technological innovation and render design and development of future equipment impossible." Trimble backed the 1 dB standard, as did the Aircraft Owners and Pilots Association et al. They called it "well-accepted and objective" and recommended the FCC not take any action on Ligado's application until after Transportation Department testing using the 1 dB standard.