LightSquared interferes with GPS, so now what?

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LightSquared CEO Sanjiv Ahuja

Edit Note: This is an excerpted and updated version of a blog written by Harold Feld on the Wetmachine blog. The original post can be found here.

LightSquared filed a report on Thursday that showsits planned wholesale LTE wireless network would interfere with existing GPS equipment, and suggested a three-part plan to resolve the issue. The report, filed with the FCC, could throw the operation of LightSquared’s network into some doubt. But Feld argues in this post that the bigger issue here isn’t so much the fight between LightSquared and the GPS industry, but how the FCC will handle it and continue to make more spectrum available for wireless broadband.

For some time now, I’ve been rooting for LightSquared, the planned wholesale 4G network using both terrestrial and satellite networks. Despite the fact that it faces tough odds trying to build out an expensive wireless network, a wireless network built from ground up for wholesale only could totally change the wireless market. I just love the fight between LightSquared and the GPS industry because it manages to contain everything that makes spectrum policy in this country like running a marathon with concrete blocks on your feet: bad neighbors operating critical systems so they can get away with being prima donnas, hostility from other federal agencies, unanticipated interference issues that crop up on deployment, and efforts to politicize the FCC’s technical process.

For a spectrum wonk such as myself, it simply does not get better than this.

Today, the FCC received a report (PDF) that confirms that, yes, when LightSquared operates it system, it creates interference for existing, deployed GPS systems. As a result, only the following things matter:

  1. The LightSquared folks are right about how the GPS guys knew this day would come and conveniently chose to do nothing. But in the short term it doesn’t matter, because the FCC will not allow anything to happen to GPS.
  2. On the other hand, if the GPS guys get their way, it means taking another 40 MHz of prime spectrum and rendering it useless forever. That also isn’t going to happen. That suggests a phase in/compromise.
  3. Whether LightSquared actually survives the compromise as a viable service will depend on a lot of things. The dimensions of any such compromise will depend on the interference tests. While it is clear that LightSquared’s system as proposed causes interference with GPS systems, a lot of questions remain about what ought to happen to make it so that GPS and LightSquared can live together in harmony.

And the precedent of how to deal with annoying neighbors is almost more important than what actually happens to LightSquared. If the GPS guys get their “sit on your rear-end veto,” then we can pretty much kiss off spectrum reform in the most useful spectrum bands. Every potentially useful band has neighbors that built systems on the assumption that nothing would ever change. So the FCC either finds a way to balance the interest of incumbents with fostering the expanded use we need for our expanding wireless demand, or we forget about “spectrum flexibility” and resign ourselves to the current state of the universe pumped up by the occasional auction.

The FCC isn’t going to let anything happen to GPS. That doesn’t mean the GPS guys will be happy.

Here is really the most important thing. The FCC’s engineers on spectrum issues are extremely conservative. They recognize that making predictions about possible interference is not nearly the precise science that people like to think it is. From an engineering standpoint, it is easier to loosen interference restrictions later than try to mitigate interference if you were too optimistic. But from an economic standpoint, this approach can take a service that was economically feasible and make it into something simply not worth doing. The FCC tries to balance these competing interests, taking into consideration things such as how important (economically and politically) is the existing service and how useful (from the FCC’s perspective) the new service would be.

So for LightSquared and GPS, the tests mandated by the FCC show that, if LightSquared turned on its network tomorrow, it would have fairly widespread impact on existing GPS systems. So is the show over for LightSquared? Not necessarily. LightSquared is trying to demonstrate to the FCC that it can take “mitigation measures” to bring the risk of harmful interference down to safe levels.

Here are the standard kinds of interference mitigation measures in these sorts of situations.

Require upgrades for the existing systems. LightSquared has already indicated it will pay to protect “critical” systems related to national security, public safety, and extremely expensive precision applications. This probably also applies to other wireless providers collocated in the same area whose towers rely on the GPS for precision timing rather than the location function. This approach alone cannot possibly work for millions of already deployed consumer GPS systems, and will probably be resisted by the GPS coalition as underinclusive. Which brings us to the next popular choice.

Offer an internalized guard band. The problem of energy leaking out of the band allocated to one service into another service is an old one, and the traditional solution is to require a “guard band” between the services. LightSquared can be required to limit the actual operation in its system to something far smaller than its actual 40 MHz. The idea is that by increasing the separation between the LightSquared operations and the frequencies GPS units receive, you attenuate the strength of the energy that interferes. LightSquared has offered to begin transmissions only in the lower 10 MHz of spectrum it has, in order to mitigate GPS interference.

Phase in over time to replace deployed systems. A third approach is a gradual phase in on the theory that consumer GPS units, the most numerous and with the worst shielding, will be replaced over time with better units designed to shield against the increased energy generated by LightSquared’s operations. This is what LightSquared has proposed Thursday to get it to eventually be able to use its full 40 MHz. The Commission can also require that, as LightSquared ramps up operation, it must work with providers to notify consumers about the possible need to upgrade their GPS units.

None of these is mutually exclusive, and a combination play seems the most likely – if the FCC does anything at all. But, does a solution leave LightSquared financially viable? The most likely problem for LightSquared is if it has to sacrifice too much capacity for an internal guard band. LightSquared’s business model depended on access to 40 MHz of spectrum. If LightSquared must take too much spectrum out of action, or if it needs to eliminate the large contiguous blocks that make LTE more efficient, it may jeopardize its ability to sell enough wholesale capacity to give adequate rate of return.

In theory, this entire proceeding involves one licensee and its direct neighbors. But the reality is that what happens here will dramatically impact whether investors try to innovate and repurpose spectrum for wireless broadband generally. LightSquared has spent well over a billion dollars already. If the FCC indicates it will pull the plug on that kind of investment because of political pressure, only the most well-connected incumbents will take any kind of risk, and then only for the most conventional kinds of investment.

Harold Feld blogs at Wetmachine and is also the legal director at Public Knowledge.

1 Comment


They received a conditional license, that condition being non interference with GPS products and services. Rather than actually work on filters etc LightSquared wants the GPS industry to accommodate them.

There are boatloads of unused spectrum out there like the 75mhz that the US DOT holds, never mind Spectrum Co. Use it or lose it at auction -that should be the rule.

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