Wednesday, February 15, 2012
Coasean Positioning System
Ronald Coase's theory of reciprocal causation is alive, well, and interfering with GPS. Yesterday, the FCC pulled the plug on a plan by LightSquared to build a new national wireless network that combines cell towers and satellite coverage. The FCC went along with a report from the NTIA that LightSquared's network would cause many GPS systems to stop working, including the ones used by airplanes and regulated closely by the FAA. Since there's no immediately feasible way to retrofit the millions of GPS devices out in the field. LightSquared had to die so that GPS could live.
LightSquared's "harmful interference" makes this sound like a simple case of electromagnetic trespass. But not so fast. LightSquared has had FCC permission to use the spectrum between 1525 and 1559 megahertz, in the "mobile-satellite spectrum" band. That's not where GPS signals are: they're in the next band up, the "radionavigation satellite service" band, which runs from 1559 to 1610 megahertz. According to LightSquared, its systems would be transmitting only in its assigned bandwidth--so if there's interference, it's because GPS devices are listening to signals in a part of the spectrum not allocated to them. Why, LightSquared plausibly asks, should it have a duty of making its own electromagnetic real estate safe for trespassers?
The underlying problem here is that "spectrum" is an abstraction for talking about radio signals, but real-life uses of the airwaves don't neatly sort themselves out according to its categories. In his 1959 article The Federal Communications Commission, Coase explained:
What does not seem to have been understood is that what is being allocated by the Federal Communications Commission, or, if there were a market, what would be sold, is the right to use a piece of equipment to transmit signals in particular way. Once the question is looked at in this way, it is unnecessary to think in terms of ownership of frequencies of the ether.
Now add to this point Coase's observation about nuisance: that the problem can be solved either by the polluter or the pollutee altering its activities, and so in a sense should be regarded as being caused equally by both of them. So here. "Interference" is a property of both transmitters and receivers; one man's noise is another man's signal. GPS devices could have been designed with different filters from the start, filters that were more aggressive in rejecting signals from the mobile-satellite band. But those filters would have added to the cost of a GPS unit, and worse, they'd have degraded the quality of GPS reception, because they would have thrown out some of the signals from the radionavigation-satellite band. (The only way to build a completely perfect filter is to make it capable of traveling back in time. No kidding!) Since the mobile-satellite band wasn't at the time being used anywhere close to as intensively as LightSquared now proposes to use it, it made good sense to build GPS devices that were sensitive rather than robust.
There are multiple very good articles on property, tort, and regulatory lurking in this story. There's one on the question Coase was concerned with: regulation versus ownership as means of choosing between competing uses (like GPS and wireless broadband). There's another on the difficulty of even defining property rights to transmit, given the failure of the "spectrum" abstraction to draw simple bright lines that avoid conflicting uses. There's one on the power of incumbents to gain "possession" over spectrum not formally assigned to them. There's another on investment costs and regulatory uncertainty: LightSquare has already launched a billion-dollar satellite. And there's one on technical expertise and its role in regulatory policy. Utterly fascinating.
The problem is that the difference between the originally proposed use (i.e. terrestrial receivers only) and the new proposed use (terrestrial transmitters and receivers) are so different as to be one of kind rather than degree.
At the ground level GPS signal power is around 1 x 10^-16 W. The signal that LightSquare wanted to broadcast in the neighboring spectra would have been 9 orders of magnitude stronger.
Human beings don't deal every day with nine orders of magnitude, but to put it in perspective, going to the other direction going from 1 watt to 1x10^9W moves from enough power for a tiny LED flashlight, to the amount of power put out by the largest nuclear power plants.
It isn't a matter of just a little better filter. I can't imagine what LightSquare was thinking - the physics just don't work.
Posted by: Brad | Feb 15, 2012 11:37:06 AM
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