US government officials are proposing to develop a buffer around the spectrum allotted to GPS signals, an L-band zone that is highly sought after by the broadband community.
"We propose to work with [the National Telecommunications and Information Administration] to draft new GPS spectrum interference standards," said Deputy Secretary of Transportation John Porcari during a House aviation subcommittee hearing on 8 February. "We want to let operators know in advance which uses would and would not be compatible with GPS before anyone puts capital at risk."
L-band allotments have taken centre stage in an ongoing battle between upstart broadband wholesaler, LightSquared, and the aviation community over a conditional approval the company received from the Federal Communications Commission (FCC) in January 2011 to operate in an adjacent band.
After an initial round of government and industry testing last spring for compatibility between the two systems showed drastic interference, LightSquared modified its proposal, leading to a second round of testing in the fall.
During the hearing Porcari, who along with Deputy Secretary of Defence Ashton Carter, represents nine federal departments and agencies in the National space-based positioning, navigation and timing executive committee, repeated to lawmakers the government's assertion that the second phase of testing also showed incompatibility.
Porcari said the final report on the US Air Force-conducted testing of general purpose GPS units, including aviation receivers, is being readied for transmittal to the FCC, but that two laboratories - the Idaho national engineering lab and MIT's Lincoln lab - have independently verified the conclusions.
He said a separate analysis by FAA, which diverted more than $2 million from other programmes, revealed that critical safety of flight devices like terrain awareness and warning systems (TAWS) would also be jeopardised.
LightSquared contends the second round of testing was not impartial, and in December petitioned the FCC to decide whether GPS manufacturers should be allowed to design and sell GPS receivers that take input from a frequency range broader than that allocated for GPS, a typical operating mode for the units. Based on the request, the FCC opened a public comment period that will close in mid-March.
Porcari agreed that the more precise the GPS receiver, "the more they are likely to have a wideband receiver that needs to listen beyond the GPS frequency band", but that the "national investment in GPS", the benefits derived from the system and the international ramifications of an impaired GPS infrastructure favoured additional protection.
"ICAO and the global community are completely reliant on US policy on this," said ICAO air navigation bureau deputy director Vincent Galotti at the hearing. "[GPS] is the most fundamental and important piece of infrastructure for global navigation system."