This is one of those odd stories that illustrate the way
business and government sometimes work together to build new and powerful
communications systems. The outcome could affect many consumers who own and use
GPS guidance systems in their cars or for outdoor recreation. To a certain
degree, it could affect radio engineers.
The story began with an FCC allocation for a satellite
communication system in the spectrum 1525 to 1559 MHz — an allocation that
until now has had limited commercial appeal and is not heavily used.
Along came a company with a vision to help supply
wireless data services, what we used to know as the cell phone industry.
Wireless data is in short supply and high demand.
The company, LightSquared, came up with an idea to make
this L Band spectrum useful for terrestrial data: Use the spectrum to build a
terrestrial network and connect it up with satellites. The plan had a lot to
like. An underutilized segment of spectrum would be converted into a highly
profitable and useful segment of the wireless data industry.
This is where the government help comes in. When this
spectrum was allocated, it was for satellite communications; it was not a
license to build a terrestrial network. So a petition for an exemption was
filed, quietly and just before the Thanksgiving holiday, on Nov. 19, 2010.
Instead of the normal 30-day comment period, the petition was “fast-tracked,”
which allowed only a few days for comment.
The FCC then ruled in favor of LightSquared and gave it
the permit to build a new terrestrial network of high-power transmitters for
high-speed data. The permit allows up to 40,000 of
these repeaters to be built at effective radiated powers of up to 15,000
JUST ONE PROBLEM …
Although the proposal was fast-tracked at the
commission, there were technical concerns. Specifically, LightSquared spectrum
was perilously close to a satellite system that has been in place for many
years: the network of GPS satellites used for civilian and military purposes.
Generally, it isn’t a good idea to mix terrestrial and
satellite uses on the same or nearby frequencies. Satellite communications
require receivers to be able to detect very low signals coming from outside the
earth’s atmosphere. That requires a receiver that has exceptional sensitivity.
Terrestrial services, on the other hand, use relatively high-power signals to
convey large amounts of data over a wide geographical distance.
This table from the
Garmin report describes the effect of Lightsquared service on a Garmin aviation
In this case, the GPS system requires receivers to not only
detect low-power signals but simultaneously to detect a range of satellites
that are spread across the visible sky. Now mix in a huge number of terrestrial
amplifiers on a close frequency that require omnidirectional antenna systems
and high power. Due to their proximity and power requirements, these
terrestrial amplifiers likely will overwhelm the sensitive GPS receivers that
are trying to pick out very weak satellite signals.
And that is just what happened, in spite of
LightSquared’s claims that its own extensive testing indicated little to no
interference would occur.
The main L1 band of frequencies used by the GPS system is
centered on 1575.42 MHz and extends down to 1559 MHz. Testing by Garmin Corp.
showed that operations proposed by LightSquared would cause a typical consumer
GPS receiver to fail within 3.6 miles of its terrestrial repeaters. An
FAA-certified General Aviation receiver that employs GPS to help determine
aircraft height began to fail within 13.8 miles of a terrestrial transmitter,
according to the report, which was sent to the FCC in January. (The study can
be found at http://tinyurl.com/rwgps.)
As I do the math, this comes out to approximately 1.6
million square miles of interference to consumer units and about 6.4 million
square miles of interference to aviation uses. Ouch.
It makes the engineer in me just sigh. Wouldn’t you
think the possibility of massive interference would be obvious before investors
and regulators wrote contracts and rules that committed billions of dollars?
This calls to mind the recent pleas from the Society of
Broadcast Engineers to mandate that FCC commissioners retain at least one staff
member with an engineering background. If such a rule were in place, would this
proposal have received fast-track approvals from Julius “Cell Man” Genachowski?
The whole affair reminds me of the history of the
satellite radio industry.
It may seem like I am dredging up buried garbage. But
when initially proposed and awarded, this was supposed to be a satellite
service that delivered programs directly to a consumer receiver. When that
failed to be possible technically, a decision to allow the service instead to
become a second terrestrial radio band was made without comment, even though
doing so changed the terms of the original license and altered the competitive
Satellite radio eventually became a competitive
Frankenstein, vowing to destroy the existing terrestrial radio industry and
sowing the market with devices intended to interfere with standard FM band. And
when the two satellite radio companies mismanaged their way to bankruptcy with
their impossible giveaways and contracts for high-priced programming, they were
allowed to merge, eliminating any inconvenient direct competition.
OK, I know this is politics and that the FCC has a
mission to assist pioneering uses of the electromagnetic spectrum. But as
someone who has worked in an industry that is both successful and highly
regulated for my entire career, it does seem as if certain rule changes happen
too easily and without a proper evaluation of the potential consequences. This
doesn’t seem, well, fair. Or even sensible at times.
Rule shifts of this kind can greatly change the value of
a spectrum allocation that suddenly has newfound abilities. LightSquared is
boasting that its proposed 4G data services eventually will be worth $120
billion. If the original spectrum allocation had included the right to build
out a terrestrial network, it would have likely raised more bidders and a
higher market value in auction. Observers are rightly uncomfortable when such
sudden shifts in rules allow one company to suddenly own valuable property after
a supposedly open auction process.
The lure of business may obscure potential harm to
established users from changes that are poorly thought out and motivated by a
desire to create fabulous new profits.
FOR THE BEST
GPS uses are numerous in radio. Many studios use
professional clock systems that synchronize via the GPS system. Station groups
with single-frequency networks rely on GPS timing to keep their signals in
sync. Timing drift results in coverage being converted to interference. Consultants
use them to determine tower locations and antenna elevations. GPS is used
widely for measuring broadcast radials for AM and FM service.
LightSquared says it will fix the problem and is
designing its systems to protect GPS with exceptional attention to minimizing
out-of-band interference. Its latest proposal offers to use only the lowest 10
MHz of its frequency allocation in the initial buildout to provide protection
to existing GPS systems.
It also turns the blame on the GPS industry for relying
on receivers that are prone to interference. Somehow this claim seems hollow
given the massive change in use that has been permitted to LightSquared and the
secretive way in which its license was changed.
FCC has stated that LightSquared must prove it has resolved the GPS
interference issue before it can continue its deployment. Let’s hope both
parties take this responsibility seriously — and that no more “Midnight Fixes”
emerge from this important regulatory agency.