Coalition formed to protect GPS


The Federal Communications Commission (FCC) in January 2010 gave LightSquared, a communications company in Reston, Va., that has been assigned frequencies in the mobile satellite services (MSS) band, a conditional approval to operate as a wholesaler of terrestrial-only, high-speed wireless services. Although the controversial waiver which allowed this to happen was the culmination of almost a decade of advocacy within the FCC, the final step appears to have been rushed through, according to the global positioning system (GPS) view.

The potential problem for aviation is huge. LightSquared wants to provide fourth generation (4G) wireless services, using the 1525-1559-megahertz MSS band for their satellite downlink. The trouble is the company is authorized to use its downlink frequencies to broadcast high-power terrestrial signals from ultimately as many as 40,000 transmitters. In the past the MSS band was reserved for space-to-Earth transmissions, so that power levels in that area were low. The GPS L1 signal used by civil aviation is not far away, centered at 1575.42 megahertz.

The company plans to launch its network at the end of this year, pending FCC satisfaction with a June 15 report by a government/industry technical working group (TWG) on interference issues. Whether comprehensive testing and analysis can be completed by then remains to be seen.

Although LightSquared has given the U.S. GPS Industry Council (USGIC), the co-chair of the TWG, verbal assurance that the company will not exceed 1.5 kilowatts (32 dBW) in the 1545-1555-MHz band, LightSquared is authorized to transmit at as much as 15.5 kilowatts (42 dBW) in its allotted frequency bands.

The TWG is looking at GPS overload and desensitization issues for both levels of LightSquared transmit power.

Experts say civil aviation receivers may have a hard time hearing the billiontimes-weaker GPS received signal in the neighboring, protected 1559 -1610- megahertz, aeronautical radio navigation service (ARNS) band if the company’s 1.5-kilowatt, high-speed wireless transmitters are turned on as currently designed.

There are several ways to address the problem. LightSquared could be moved to frequencies further away from GPS, the company could broadcast at lower power levels or filters could be applied to GPS as well as LightSquared. If GPS users end up having to modify the installed base, however, it will be a costly and lengthy process.

If the aviation users of GPS have to modify their receivers because of interference, it could be a five- to six-year process. That includes two years to design, develop, and test new products, two years for the technical standard order (TSO) process and two years for certification.

Furthermore, a new filter would change the housing and size of the system, making it difficult to fit back into the aircraft.

Representatives of a wide variety of industries and companies have joined the Coalition to Save Our GPS to resolve a serious threat to the reliability and viability of the Global Positioning System.

If you are concerned about the proposed LightSquared network spilling over into the Canadian border areas and interfering with GPS receivers on Canadian aircraft, vessels, vehicles, utility networks or other uses, then please consider the following actions and include a reference to the US Federal

Communications Commission file number “FCC SAT-MOD-20101118-00239” in your correspondence:

COPA is a member of the Coalition to Save Our GPS. For more information visit: