Kayla Tomizawa
Professor Ramsey
December 2, 2013
GPS: Technology Past Its Prime
We take for granted how easy it is to navigate and tell time. Our smart phones
conveniently help us with both, but twenty years ago, GPS was not public domain. As with most
technology of the day, GPS has improved tremendously since then, but it is beginning to reach
its threshold. In the case of GPS, the public funds the research. Therefore, we should be aware of
its capacity and applications. It is a public service that we forget we pay for because it is part of
our federal taxes, but we should keep in mind where our money is going and why it is being
spent. Past a certain degree of accuracy, GPS is not useful enough to continue funding the
research behind. If we look into what it means to enhance GPS and where its application may
have the room to grow, we will realize that the most current GPS model will be the technology’s
prime functionality.
GPS stands for Global Position
System. It is a method of pinpointing a
location on Earth and determining
accurate time. The system has three parts
(Fig. 1). The SV, or Satellite Vehicle,
sends a constant wave of signals to the
ground, to tell the ground stations where
it is. The Control Station calculates
Figure 1: The 3 parts of GPS
Source:
http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.ht
ml
where the satellites are and may send
correction information to the satellite. The consumer unit is the Receiver, and it merely waits for
time and coordinates from the satellite. [1]
There are several types of receivers and depending on whether or not the receiver is
moving or what sort of signal strength it needs, the receiver will be built differently. For
example, receivers on airplanes are designed to be able to receive a signal in a spherical
direction, which allows a plane to receive a GPS signal even while upside down. Other receivers
are placed around Earth to measure how the plate tectonics move for obvious weather and
disaster predictions. The most well-known receivers are those in people’s phones, which are built
under size and power consumption constraints. Smart phones constantly use GPS, because
phones rely on GPS for accurate time-telling. Turning on the tracking function on a smart phone,
however, will require the phone to find the GPS signal and calculate its specific location, which
uses extra processing power. This is why it is a manual function on smart devices.
The positioning algorithm is based on the concept
of triangulation (Fig. 2). At any time, the distance
from a satellite can easily be calculated. The
satellite sends off a radio signal, or in other words,
a simple beep. The receiver, either on the control
side or on the consumer side, can calculate the
time in between the beeps, and multiply it by the
speed of the signal, which is about the speed of
Figure 2: Triangulation Method
light as seen in the graphic, and solve for the
Source: http://gpstrianguler.blogspot.com/
distance. This equation only gives the distance
from the satellite. Calculations from a single satellite attain a spherical range of solution points.
Two calculations from two satellites will result in a circle of possible location points. The
solution circle is shown as the black circle in the visual above. Three calculations from three
satellites will result in only two possible location points, shown as black dots on the black circle
in the visual. Typically, one of these two points will be out of range of the surface of the Earth,
which leaves only one obvious answer. In general, receivers wait for four satellite signals to be
sure of its position on Earth. The United States government owns about thirty satellites, creating
a constellation that ensures coverage of at least four satellites simultaneously at any one place all
over the world. [2]
The method and math seem fairly simple and straightforward. With thirty satellites in the
sky, why do we sometimes see error on our GPS devices? Why do we continue to see
improvements in GPS tracking? The first system launched had an accuracy of within 250 meters
[3]. The system the government is currently launching, GPS III, includes accurate enough
models to ensure coordinates within one meter. This summer, the Air Force launched two GPS
III satellites into space. Awarded the $5 billion dollar contract five years ago, Lockheed Martin
leads the satellite update [4]. The goals are to make GPS accurate enough to track a position
within one meter. In order to meet this goal, engineers have upgraded the orbit models to account
for more errors and they’ve designed the new satellites that will last longer and send more
signals.
To display the satellite orbit models on paper, we may draw the projected path of the
satellite orbit. We draw it as a perfect ellipse. We also draw the Earth as a perfect sphere, and we
leave out all the other planets and celestial bodies in the solar system. In reality, the satellite’s
orbit is not an ellipse, the Earth is not spherical, and there are definitely large bodies with
enormous amounts of gravitational force affecting our planet and the satellites orbiting it. A large
part of the research behind GPS is put towards calculating the exact path of the satellite’s orbit,
based on the gravitational fluctuations from the moving solar system. Since a satellite is out in
space, it is impossible to ever be certain where it is, so scientists take measurements and use
filtering algorithms to determine where the satellites most likely are. [5]
What may be the least accredited, but the most crucial contribution of GPS is time
keeping. The satellites help measure the speed of the Earth’s rotation. We measure our days with
sunrises and sunsets, but the sun does not orbit around the Earth. The Earth spins and orbits
around the sun; therefore, our sense of time is based on the rotational and orbital speed of the
Earth. GPS is what allows us to keep accurate track of leap years, even leap seconds, which keep
our banks and transportation running precisely. The satellites’ trajectories are used in helping
measure the speed of the Earth’s rotation. Therefore, all the corrections calculated for the
trajectory based on the gravitational pulls from other celestial bodies must also be used to
calculate the time delay. [5]
Those are just some of the problems the satellite’s orbit faces. There are also obstacles
the signals must face. When a receiving device cannot find signal in an underground parking
structure, that’s because the radio signal cannot travel through several feet of concrete. On the
other extreme, any particle, even air and light, affects the pathway of the signal. Signal delay
caused by particles inside the Earth’s atmosphere is called tropospheric delay [6]. Signals
received from satellites further from the zenith direction travel slower than signals received from
directly above the satellite (Fig. 3). The more of Earth’s atmosphere the signal must travel
through, the longer it will take to get to the receiver, resulting in a positional error. While the
error caused by tropospheric delay is very small compared to the satellite orbit corrections, the
process to calculate the tropospheric delay is
tedious and expensive. Measurements from all
over the Earth during different times and
weather conditions at different levels of
atmosphere must constantly be taken in order
for the delay calculations to be useful. The
Figure 3: Tropospheric Delay
correction obtained from calculating the
Source:
tropospheric delay may not seem worth the
http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.
html
work. It’s a new requirement for GPS III
[5] and if there were to be a next generation GPS, there would need to be more research in this
area. Past the one meter accuracy GPS III promises, the correction is not worth the cost.
The satellite trajectory and signal delays are examples of problems the government
tackles to build a more accurate GPS model. NASA, along with the help of the IERS, or the
International Earth Reference Systems Service, takes measurements of the environment outside
and inside the Earth’s atmosphere to calculate better models of the satellites and signals. Aside
from these, engineers work to develop satellites and launch systems. Most of the money spent is
in building and launching the satellites. That’s what Lockheed Martin is contracted to do [4].
Development and launching will cost $5 billion alone. The measurements and research are done
by NASA and a number of other companies, which are paid separately from Lockheed Martin.
We can now begin to sense how immense the GPS project is.
The final general research topic within GPS is signal processing. The satellites send down
simple radio signals to communicate with the control stations and receivers. How is it that
receivers know which signal to look for, or how does the government protect the signal? The
satellite’s signal is made of three waves: a carrier, the data, and an encryption code. The carrier is
just the frequency the signal rides on. The data is the positional information the satellite sends
down, and the encryption code is how the receiver finds the right signal. The receiver knows the
exact code and the carrier frequency so that it may match it and read the data hidden in the signal
modulation. [7]
GPS III satellites will each send four signals, one shared globally by all nations, one
specifically for military, and two extra for civilians. With each satellite sending multiple signals
on different frequencies, they could be used to error check against each other, aiding in accuracy.
Multiple signals can also be used to strengthen the signal, so that the receiver may find the signal
easier and quicker. For the military signal, engineers have added a stronger encryption code and
increased the power capacity. This aspect of the project is worth researching further. The
encryption method is essential to the safety of our nation. Both the encryption and adding signal
capacity is an easy and inexpensive fix. Once the satellites are launched (part of Lockheed’s
contract), the receivers must be retrofitted to be able to search for the new signals. What this
means is that consumer will need to buy a new receiver, but that would fall under the commercial
aspect of GPS. It will not be government funded, and therefore, is not a shared cost among the
public.
Another obstacle satellite signals face are reflective surfaces. Especially in urban areas,
the signals will bounce off buildings and cars, creating a multipath effect [7]. Mainly GPS
devices in their cars deal with multipath effects. The receiver moves so that there is no way to
predict the possible reflections of the signal. This is an example of a commercial product
problem. The GPS receiver must install software to correct multipath effects. The satellite and
the government control stations are not equipped to solve each individual receiver problem.
GPS III has several promises for exciting breaks in technology to come in the next ten
years. This includes, Amazon Prime Air which is a drone delivery service, and automated
vehicles [7]. California has already passed laws legalizing automated cars [8]. Along with the
new consumer market that will open up, there will be great advances in the safety of
transportation. GPS will be able to track how much cargo trains stretch and contract with
extreme weather, minimizing crashes.
However, the use for such an accurate GPS stops here. There seems to be no use for the
public to have accuracy closer than a meter. Past that point, GPS becomes a terribly dangerous
weapon. The military backs up GPS research to make sure the bombs they send hit their target
and not innocent citizens. Closer than a meter, though, makes way for precise weapons such as
lasers. It’s something out of a sci-fi film, but we should consider the dangers of the research
before we support it.
Medical uses, such as tracking the body, or business uses, such as indoor navigation, may
argue for more accurate GPS models. To this we should refer to how GPS works. The main
challenge with GPS is the fact that the satellites, or the points of reference, are out of our view.
We cannot ever be absolutely sure where the satellites are, since we could never physically
measure their positions. Had we been able to, the entire system would not need NASA’s
continued research and data collections from the past few decades to predict the solar system
orbits. For indoor systems, or even systems completely enclosed within the Earth’s atmosphere,
the calculations for GPS becomes much simpler; the cost of the system becomes much simpler,
and the exact position coordinates are much more easily attainable. In fact, businesses are
already investing in systems for indoor tracking, as seen with the Caesar’s Palace application
[10].
This doesn’t mean that we should not continue to learn about GPS. It is necessary to
continue researching encryption methods in order to keep our military signals out of the wrong
hands and project our soldiers on the field. If we are hiding somewhere, we don’t want the
enemy to be able to detect our signal. Regardless of whether or not we agree with the war, it
would be for the safety of our soldiers that are already on the field. However, this is not the same
as continuing to calculate more accurate GPS signals.
What it may become is an extension of the Cold War. Centimeter accurate GPS is a way
to fuel the creation of massive weapons. In the end, it will terrorize citizens, similarly to nuclear
weapons. Hopefully we can learn from our mistakes and see some technologies as more
dangerous to pursue than to create. It is not necessary to continue pushing the boundaries of GPS
accuracy, and once the current GPS III contract is over, we should push to cease heavy funding
for research.
Works Cited
[1] Peter H. Dana. (2000, May 1). Global Positioning System Overview. [Online]. Available:
http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html
[2] National Coordination Office for Space-Based Position, Navigation, and Timing. (2013,
October 22). Space Segment. [Online]. Available: http://www.gps.gov/systems/gps/space/
[3] Mary E. Reece. (2000 April). Navigation History. [Online]. Available:
http://infohost.nmt.edu/~mreece/gps/cover.html
[4] Lockheed Martin Corporation. (2013). Global Position System. [Online]. Available:
http://www.lockheedmartin.com/us/products/gps.html
[5] Gérard Petit and Brian Luzum, “Technical Notes No. 36” in IERS Conventions, Frankfurt
am Main, 2010, pp. 33-67.
[6] Wang Xinlong. (1929). The applicability analysis of troposphere delay error model in
GPS positioning. [Online]. Available:
http://www.emeraldinsight.com/journals.htm?articleid=1810553&show=html
[7] Timothy S. Stombaugh. Unraveling the GPS Mystery. [Online]. Available:
http://ohioline.osu.edu/aex-fact/0560.html
[8] Adario Strange. (2013, December 1). Amazon Unveils Flying Delivery Drones on '60
Minutes. [Online]. Available: http://mashable.com/2013/12/01/amazon-unveils-flyingrobot-delivery-drones/
[9] Arion McNicoll and Nick Glass. (2013, June 7). Future of transport is self-driving cars,
says GPS inventor. [Online]. Available: http://www.cnn.com/2013/06/07/tech/selfdriving-cars-inventor-gps/
[10] Dean Takahashi. (2011, November 1). CST demos technology for tracking mobile
devices indoor. [Online]. Available: http://venturebeat.com/2011/11/01/csr-demostechnology-for-tracking-mobile-devices-indoors/