GNSS Markets and Applications - Understanding GPS: Principles and Applications - page 654

12.8 Creative Uses for GNSS

Location awareness is the ability to know where one is or where someone else is at a
given time. This knowledge can be applied in untold unique ways to provide service,
to understand the environment, to keep an eye on someone or something. The only
limitation is human ingenuity, which so far has proven to be unlimited when it
comes to GPS. Consider the following varied location awareness uses: tracking
sheep; guiding blind people; tracking the movement of ice floes; and geocaching ,
which is a sport where people find hidden packages at given GPS coordinates and
then add something of their own to the package. Other creative uses include plowing
roads hidden by snow; tracking race cars; mapping the location of victims of disas-
ters, such as was the case on September 11, 2001; keeping track of children and teen-
age drivers and adults with dementia. As receivers shrink to the size of a single chip
with concomitant low-power wireless communications, location awareness is pro-
vided by wearable devices like watches, pocket PDAs, or cell phones. Many new
applications become feasible, like tracking toddlers in an amusement park,
Alzheimer's patients, and teenage drivers [19, 20].
Another unique GNSS application involves the use of EGNOS and the Internet
[13]. Here, the GPS receiver takes corrections from EGNOS received via a wireless
Internet connection and combines them with the pseudorange measurements in
order to improve accuracy and availability. This is similar to assisted GPS, except
that SBAS data sent over the Internet is used to assist the GNSS receiver. Originally,
assisted GPS used the cellular network to provide acquisition and tracking aiding to
the GPS receiver. Qualcomm's SnapTrack System is prototypical of this type of
operation.
At the time of this writing, achieving GPS usage indoors remained a challenge.
Because of its weak signal, most commercial GPS receivers a decade ago did not
function well when the antenna did not have a clear view of the sky. This limitation
is being addresses in a variety of ways (see Sections 5.13 and 9.3).

12.9 Government and Military Applications

GPS is first and foremost a military system. Since its inception in the late 1960s, GPS
was designed to satisfy military requirements for a worldwide positioning, naviga-
tion, and timing service. Only a satellite-based system could ensure global coverage.
The signals had to enable very accurate fixes yet be resistant to enemy jamming.
Thus, the military developed user receivers that relied on what was called the P code.
This code was later encrypted to be today's Y code. Modernized GPS will transmit
the Y code for existing receivers and transmit the M code for new receivers. M code
is an even more robust signal whose dispersed spectrum properties allow for Allied
forces to jam in the band center to interfere with adversary receivers that are trying
to use C/A code signals, without disturbing their own use of M code.
Today, military use of other GNSS is limited primarily to the Russian
GLONASS. However, many of the world's militaries are using the C/A code of GPS.
Authorized users such as NATO forces and other countries with agreed-to access are
using the GPS P(Y) code for their military activities. It is expected that there will also