The US Department of Commerce's telecommunications division has released an assessment of problems that the LightSquared 4G service might create for commercial and government Global Positioning System services (GPS), and the conclusion isn't pretty. LightSquared's deployment of wholesale LTE "poses a significant potential for harmful interference" to commercial and government GPS, the National Telecommunications and Information Agency's Lawrence Strickling wrote in his introduction to the report.

The NTIA assessment contains testing results overseen cheap software by the National Executive Committee for Space-Based Positioning, Navigation, and Timing (EXCOM). "The LightSquared Network initial deployment would cause severe operational impact over significant regions of the United States," EXCOM's testing team advises.

The report's main conclusion: "LightSquared should not commence commercial services per its planned deployment for terrestrial operations in the 1525 - 1559 MHz Mobile-Satellite Service (MSS) Band due to harmful interference to GPS operations."

We contacted LightSquared about the document. The company reiterated that it has a new proposal that will address "99 percent of interference with GPS devices." Strickling's letter  acknowledges that the fix has been offered.

"I note that LightSquared has now proposed a modification to its planned deployment. . . . " he writes. "Therefore, NTIA supports the EXCOM's recommendation that additional tests be performed and recommends that the FCC continue to withhold authorization for LightSquared to commence commercial operations until all the available test data can be analyzed and all valid concerns have been resolved."
A disruptive force?

LightSquared's business plan is to convert its two Mobile Satellite Service (MSS) space vessels into broadband dispensers, streaming 4G Internet to thousands of ground level mobile stations ("Ancillary Terrestrial Component" [ATC] in government geekspeak) which would relay the signal to consumer devices across the nation.

The company wouldn't sell broadband on a retail basis, but would market it wholesale to all buyers. A big LightSquared talking point was that this approach would allow vendors an easy way to roll out broadband in underserved areas. LightSquared will function as "a disruptive force" in US wireless "by democratizing wireless broadband services," the firm's Chair and CEO Sanjiv Ahuja proclaimed almost a year ago.
(NTIA)

But GPS-dependent industries have been loudly protesting that  buy cheap software signal interference will cripple their products long before anything gets "democratized." (The LightSquared band sits right next to GPS signals.)

The NTIA report says that this isn't just industry FUD. The EXCOM interference study was run by the National Space-Based Positioning, Navigation, and Timing Systems Engineering Forum (NPEF). It includes a photograph which depicts two contour areas where NPEF thinks that GPS receivers subjected to early phase LightSquared spectrum deployment would be "unusable" for air vehicles flying at 500 feet above the ground.

"A common airborne receiver used on transport-category aircraft would be unable to track any GPS satellites in the orange region, while both this receiver and a very popular general aviation airborne receiver would be unable to track any GPS satellites in the red region," the report says. "Both receivers would be significantly degraded over much larger regions than depicted on the map."

"Results in these Tables demonstrate that for all GPS applications assessed during this NPEF effort, the LightSquared signal caused degradation at distances of approximately one kilometer to several hundred kilometers for LightSquared Phase 0, 1, and 2 configurations," the test assessment explains. "These distances are in excess of the planned spacing between base stations for all but the most rural areas."

The report has plenty of discussion about the significance of these interference distances, and about current and potential mitigations of the problem. But the bottom line is bad news:

    At the conclusion of this NPEF effort, significant technical concerns remain that operation of an ATC service can successfully coexist with GPS. Rigorous analysis of potential interference had been impossible prior to now due to non-availability of relevant commercial ATC equipment. This recommendation suggests there is a need for additional analysis to determine if ATC architectures can be accommodated in the MSS L-band without impacting GPS.

Thus flows the recommendation that LightSquared deployment be put on indefinite hold.
Middle ground

LightSquared engineers say they have a fix for all this. The satellite company's updated plan proposes a "middle ground" that will allow it to stream in the lower 10MHz portion of its allotted spectrum. This zone "poses no risk to the users of over 99 percent of GPS devices," the company says. The industry would "coordinate and share the cost of underwriting a workable solution for the small number of precision measurement and other devices that may be at risk."

    "What happens? There's now going to be a U2 concert an inch past your lot line 24/7."

The long term goal is to deploy a "full complement of more terrestrial frequencies operating at appropriate power levels," LightSquared says, but the firm will delay accessing the upper 10MHz of its spectrum "in which transmissions may jeopardize legacy GPS usage."

    This solution already has cost LightSquared over a hundred million dollars to shift the timing of its access to portions of the frequency bands it shares with Inmarsat that serve as a critical component of the LightSquared network. It will cost LightSquared even more in disruption to its operations and uncertainty regarding the timing and composition of its full complement of terrestrial frequencies operating at appropriate power levels. LightSquared is willing to bear that expense and disruption in order to move forward with its network.

But any debate over expense sharing will doubtless be accompanied by a feud over the appropriateness of the LightSquared authorization in the first place. The original LightSquared spectrum licenses contemplated only a satellite service without ground base stations; by the time such signals reach the ground, they are faint. Ground-based towers can blast out huge amounts of power compared to the relatively fragile GPS signal in the next band.

One engineer involved in the debate (he takes the GPS side) provided us with an analogy:

    What the FCC did was say, "While this was supposed to be a suburban neighborhood, we are changing the rules after 40 years. Company X has bought all the houses to the left of your house, and we are changing the zoning from your lot line left." As they bulldoze the houses (LSQ pays off Inmarsat to scoot over), you find out that they are going to allow them to build a concert stadium next to your two-post fence to the end of the block (put in GROUND stations broadcasting 3 billion times more powerfully than originally intended).

    What happens? There's now going to be a U2 concert an inch past your lot line 24/7. There will be people fighting in the parking lot and the sirens of cops and ambulances going on all day and night forever.

    Now—are they in your yard? Not at all. They are on their side of the lot line.

But LightSquared's company report partially blames GPS device cheap software makers for the problem, saying that GPS receivers "do not adequately" block transmissions from adjacent bands because they have been "deliberately or, sometimes, inadvertently, designed or manufactured with the assumption that there would be no adjacent-band terrestrial transmissions—ignoring regulations first adopted in 2003 that permit such transmissions."

This perspective is not shared by James A. Kirkland, Vice President and General Counsel of GPS company Trimble Navigation Limited.

"Whatever the history, or debatable assertions about it, the  buy cheap software responsibility for eliminating interference to GPS, or bearing the costs of eliminating it, rests squarely with LightSquared," Kirkand told the Commission in June. "When the FCC authorized ATC, it made it clear that in the event that services in bands adjacent to ATC operations, like GPS, suffered harmful interference, it would be the responsibility of the ATC operator, not the GPS provider, to cure that interference."

No predictions from us as to where this grudgematch is headed. The FCC did not respond to requests for comment, but its original game plan did make clear that "addressing the interference concerns regarding GPS must be completed to the Commission's satisfaction before LightSquared commences offering commercial service" on its MSS frequencies.

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