Going Forward - GPS Declassified: From Smart Bombs to Smartphones - page 187

five Beidou satellites. Add to all of these India's irnss, Japan's qzss, and numer-
ous satellite-based augmentation systems (waas, egnos, et al.), and by 2020
there could be about 150 navigation satellites broadcasting signals in the gps
bandwidth. This redundancy should be an unqualified boon to users, reduc-
ing the vulnerability from any single system failure while eliminating brown-
outs and poor reception in urban canyons, should it not? Unfortunately, the
answer is no. Each additional gnss signal increases the overall background
noise that receivers must sort through to lock onto a particular signal. It is like
trying to follow a conversation in a crowded room where everyone is talking
at once. Guenter Hein, head of esa's Galileo Operations and Evolution Depart-
ment, has calculated that once the number of combined signals approaches
seventy, the noise from satellites will exceed the natural cosmic noise floor,
and gnss systems will begin to interfere with themselves. 14 While this por-
tends an eventual international squabble over the total number and allocation
of gnss satellites and signals, the primary worry in the near term remains ter-
restrial interference. This can take the form of inadvertent disruptions by adja-
cent radio spectrum users like LightSquared or deliberate jamming by
pranksters, people trying to evade tracking, and even terrorists.
As noted previously, jamming gps with inexpensive transmitters is relatively
easy because the signals are so faint. Some have compared using a receiver on
the ground to detect a gps signal from space to standing in Los Angeles and
trying to see a sixty-watt lightbulb in New York. 15 An example of the serious
ramifications of jamming surfaced in 2010, when the faa investigated why a
new ground-based augmentation system (gbas) at Newark Airport randomly
lost gps signal reception and shut itself down multiple times per day over sev-
eral months. 16 gbas systems improve gps accuracy to allow Category I preci-
sion landings, but officials could not approve the Newark system until
determining the cause of the outages. The gbas antenna was within about a
few hundred feet of the New Jersey Turnpike, and the cause turned out to be
passing truck drivers using inexpensive gps jammers to thwart their fleet man-
agers' efforts to track their every move. 17 Experts estimated that one hundred
thousand such devices, which plug into vehicle cigarette lighters and can cost
as little as thirty dollars, were in use in the United States by 2009. 18 Market-
ing, selling, or using devices that jam signals such as gps, cell service, police
radar, or Wi-Fi is a federal crime in the United States, and the fcc announced
a crackdown in October 2011. 19 However, overseas sellers continue to offer a
wide array of jammers on the Internet.