New spectrum configuration for LightSquared might be easiest fix for GPS interference problem

Lynnette LunaSpeaking at an event sponsored by the National Space-Based PNT Advisory Board, Trimble Vice President and General Counsel Jim Kirkland called on the FCC to focus its efforts on moving LightSquared to new spectrum. A new spectrum configuration may very well have to be the solution that gets LightSquared up and running the fastest.

Kirkland, under the "Coalition to Save Our GPS" banner, declared that test data shows "substantial interference to GPS if LightSquared turns on high-powered terrestrial facilities in the spectrum next door to GPS. The data confirm what the industry told the FCC before it granted the waiver, and also confirms that there is no viable technical fix.  It's time for the FCC to stop squandering resources trying to find a solution to an unfixable problem.  Instead, it should focus its efforts on finding spectrum that LightSquared can operate in--where LightSquared won't interfere with GPS."

In January, the FCC granted LightSquared a conditional waiver to operate using terrestrial-only equipment on an accelerated timetable. LightSquared plans to operate in the L-band satellite spectrum, which sits next to GPS spectrum, but first it has to satisfy any interference concerns. The GPS has become vocal in its opposition to LightSquared being allowed to operate in the band.

The PNT Advisory Board, a government entity that advises and coordinates federal departments and agencies on GPS matters, conducted its own tests in May. The PNT tests showed that some GPS receivers lost signal strength while others were completely disabled by LightSquared's signal. In particular, it found interference in the higher portion of LightSquared's spectrum bands and minimal GPS interference in the lower portions of the spectrum.  

Separate tests commissioned by the Federal Aviation Administration, and conducted by RTCA, an organization that writes GPS avionics specifications for the FAA, found that "GPS operations below elevations of 2,000 feet would be unavailable over a large radius of metro" areas for aircraft. The RTCA tests found that there was more interference with the upper portion of the 1525-1559 MHz L-band than the lower portion. 

Deane Bunce, the co-chair of the National PNT Engineering Forum, called out a number of possible mitigation steps, such as moving LightSquared's service to a different frequency band, limiting the service to the lower part of the L-band spectrum it owns and installing filters on GPS receivers. However, Bunce said that the filters could taken between seven to eight years to put in place at a significant cost, and that even with the filters, receivers might still face interference.

Jeff Carlisle, LightSquared's executive vice president of regulatory affairs, told the Wall Street Journal that the company is committed to finding a solution. "I think we do need to talk about the possibility of accommodations on our side in order to figure out if there is a way forward," he said. Carlisle added that LightSquared believes a variety of solutions exist, including adjusting the base station transmitting power and reviewing the frequencies LightSquared is using to launch its network as opposed spectrum it might use to expand its network.  

Carlisle and the FCC have consistently brought of up the fact that when the FCC removed the limit on the number of base stations that could be deployed using the L-band and okayed the power limit LightSquared plans to use in 2005, that the GPS community made no issue of the move. However, several members of the PNT Advisory Board said that the wider GPS community and GPS users in general had not been properly informed of the changes by the FCC, which is why the arguments over potential GPS interference only began to surface late last year.

LightSquared will be using part of the L-band downlink frequencies in the 1525-1559 MHz band, while GPS (and GLONASS) operates in the 1559-1610 MHz band. LightSquared already plans to outfit its base stations with filters that cut off the signal at the top of the L-band to keep its signals from leaking into the GPS band. The issue, however, is that most GPS devices don't have strict filtering at the bottom of the GPS band and therefore could be overwhelmed by the high-power transmissions coming from LightSquared's terrestrial transmissions.

While LightSquared has access to a total of 59 MHz of spectrum, it only has current access to the 1525-1559 MHz band, which is the band next to the GPS bands. The company is paying Inmarsat to transition parts of its spectrum so LightSquared has a contiguous block of spectrum, and it is expected to get access to two more 5 MHz channels no later than November 2012, depending on how fast Inmarsat can get out of the band. Two more 10 MHz channels are expected to become available for LightSquared's use by the end of 2013.

LightSquared may very well be forced to use just the lower portion of its spectrum--up to 1545 MHz--for terrestrial base stations to avoid interference, which would give the operator more time to find a fix interference. Carlisle, in a conference call with reporters, recently indicated that this type of solution is on the table. But such a move would have a big impact on the network's capacity, and its ability to host a number of wholesale operators.

In that context, it doesn't sound so ludicrous that LightSquared is in discussions with AT&T to rent capacity from the operator, according to a Bloomberg report that surfaced earlier this month. Under an arrangement with AT&T (NYSE:T), LightSquared would reportedly pay to use AT&T's LTE network when it needs extra capacity.

We'll have a more complete interference picture on Wednesday, when LightSquared and the GPS Coalition release their final report to the FCC.--Lynnette

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