One of the engineering journals I receive is "
Inside GNSS" which is
devoted to the "Global Navigation Satellite System Community".
GNSS is a blanket term which covers all satellite navigation systems, of
which most readers will be familiar with the US-built GPS network.
The magazine is generally filled with technical articles, with titles
such as "
Making Sense of GPS Inter-Signal Corrections - Satellite
Calibration Parameters in Legacy and Modernized Ionosphere Correction
Algorithms". Hardly the type of stuff that would generally cause one to
raise an eyebrow.
So it came somewhat as a surprise when I read in the latest March/April
edition that a battle was looming between the US GPS community and a
planned nationwide 4G wireless broadband network being built by a company
called
LightSquared.
In an article entitled "
GPS Community Confronts LightSquared
Move into L1 Spectrum", it seems as if a January 26th decision by the
Federal Communications Commission (FCC) to give LightSquared the go
ahead has the GPS community "seething", as the wireless network has the
"potential to overwhelm GPS receivers across the country".
Originally the LightSquared network was to use satellites augmented by
1,725 ground stations. However, LightSquared later requested to increase
the number of ground stations to some 40,000. The FCC put out a call for
comments over the Thanksgiving Holiday period and apparently only gave
interested parties ten days to respond rather than the usual thirty.
Apparently many federal agencies were caught off guard, and had to
scramble "to get their views in for consideration".
Technically, there are two major issues at the heart of the problem.
Firstly, wireless spectrum is only a finite resource and what limited
amounts exist are already extremely crowded. Secondly, when the GPS
signals reach Earth from satellites some 19,000 km away, they are
incredibly weak, in fact below what is termed the "RF noise floor". To
recover the spread-spectrum signals, GPS receivers have to pull them out
of the noise in an operation called "de-spreading". Preliminary modeling
and testing by some GPS receiver manufacturers and US Government
agencies show that the front-ends of the receivers will be overwhelmed
by the bllion-times more powerful 4G ground station transmissions in a
neighbouring band.
Among those concerned is the US aviation industry, including the
Federal Aviation Administration (FAA).
Quote:
|
Originally Posted by Inside GNSS
Each of these ground stations will put out a signal
that, when measured a half mile from the ATC, will be roughly 1 billion
times more powerful that a GPS signal, said GPS expert Brad Parkinson,
Edward C. Wells Professor of Aeronautics and Astronautics (Emeritus) at
Stanford University.
Preliminary tests by Garmin, a GPS equipment manufacturer, indicate that
the ground station signals will be so powerful that they will cause
receivers as far away as 5.6 miles to fail. Receivers in airplanes 12
miles in the air could also be jammed, said General William L. Shelton,
Commander, Air Force Space Command.
If we allow that system to be fielded and it does indeed jam GPS,
imagine the impact, Shelton told the Air Force Association Air Warfare
Symposium in Orlando, Fla., in February. We're talking about $110
billion industry in GPS; we're talking about dependence on so many
things in our infrastructure. This is just unbelievable."
|
In an article in Aviation Week -
Quote:
|
Originally Posted by Aviation Week
Because the signals transmitted by GPS and other global navigation-satellite systems
such as Galileo are extremely weak, they were located in a quiet part of
the L-band spectrum and designed to operate in the presence of other,
weak satellite signals. The LightSquared waiver is like a re-zoning law,
says Bradford Parkinson, emeritus professor at Stanford University's
Aeronautics and Astronautics Department.
|
Article here -
http://www.aviationweek.com/aw/gener...p26-307552.xml
Interested readers can find the Inside GNSS article here -
http://www.insidegnss.com/node/2508
LightSquared is a multi-billion dollar venture backed by Harbinger
Capital Partners and other hedge funds with personal links, it is
claimed, all the way back to the White House.
The US GPS industry is said to be worth US$110 billion and is apparently
in for a fight. They have formed a "Coalition to Save Our GPS". Their
web site is here -
http://www.saveourgps.org/
Companies and organizations such as the International Air Transport
Association (IATA), Garmin, TomTom, Magellan, the American Car Rental
Association, the Air Transport Association, the Aircraft Owners and
Pilots Association, the Amercan Congress of Surveying and Mapping,
Caterpillar, Deer & Company, UPS, FedEX and many more have put their
weight behind it.
The Coalition also have links to other articles on the issue -
http://www.saveourgps.org/related-articles.aspx
Apart from engineers, technologists, bureaucrats and politicians, there
will no doubt be armies of lawyers and lobbyists taking part in the
battle between the two groups.
In an article in the Wall Street Journal on 31 March, the Pentagon has
raised its concerns. See
http://online.wsj.com/article/SB1000...rss_Technology
Under pressure, the FCC has mandated that a Technical Working Group
(TWG) be formed to see whether the issues can be resolved.
As wireless spectrum grows more and more crowded, no doubt we will
see similar battles for the air waves in the years ahead.
Battle brews in the US to save GPS from proposed 4G broadband
