Tunku Abdul Rahman College
2012/2013

ATGE 5053 Engineer in Society
Individual Assignment 2013
Advanced Diploma in Technology (Electronic Engineering)

Name : Chong Sai King
ID : 11WTA10497
Group : A

Objectives a. To study on the underlying knowledge used in the development of the GPS and how and why the GPS was developed.

b. To research on the use of the GPS including the profile and type of user, the purpose it is used for and the developments together with new knowledge created through the use of GPS.

Problem statement
In this developed society, it is obvious that mankind has arrived at yet another golden era with rapidly advancing technology. The 21st century has appeared that human are at busiest to compete to gain wealth by exploiting all possible resources. However, busy lifestyle has caused issues such as traffic congestion. Time always appears to be a resource easily hit scarcity. This era where information is the riches has invoked the demand of mankind on a tool to navigate so that time will not be wasted when they are lost in traffic. Therefore a tool to guide direction is developed and introduced to the society.

Introduction
The Global Positioning System (GPS) is selected as the tool in this assignment. Though GPS appears to be a common tool in the society, not everyone understands the process of development gone through by GPS. Global Positioning System is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. The system provides critical capabilities to military, civil and commercial users around the world. It is maintained by the United States government and is freely accessible to anyone with a GPS receiver.

Development of GPS

Why the GPS was developed?
In the early 1940s, the design of GPS is based partly on similar ground-based radio-navigation systems developed, and used during World War II.

Its aim was to provide global coverage of services to the US military which includes position, altitude, time and global detection of thermonuclear detonations.

There are two main GPS signals, a low accuracy one that is easy to pick up and a higher accuracy one that requires rough location information and the time in order to pick up.

The high accuracy signal is broadcast on two different frequencies and is encrypted. It can still only be decoded by military GPS systems although some professional civilian systems detect it and make use of it without actually understanding the data being transmitted.

How the GPS was developed?
The first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the Timation satellite that proved the ability to place accurate clocks in space, a technology required by GPS. In the 1970s, the ground-based Omega Navigation System, based on phase comparison of signal transmission from pairs of stations, became the first worldwide radio navigation system. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy [1].

While there were wide needs for accurate navigation in military and civilian sectors, almost none of those were seen as justification for the billions of dollars it would cost in research, development, deployment, and operation for a constellation of navigation satellites. During the Cold War arms race, the nuclear threat to the existence of the United States was the one need that did justify this cost in the view of the United States Congress. This deterrent effect is why GPS was funded. It is also the reason for the ultra-secrecy at that time. The nuclear triad consisted of the United States Navy's submarine-launched ballistic missiles (SLBMs) along with United States Air Force (USAF) strategic bombers and intercontinental ballistic missiles (ICBMs). Considered vital to the nuclear deterrence posture, accurate determination of the SLBM launch position was a force multiplier.

In 1964, the United States Army orbited its first Sequential Collation of Range (SECOR) satellite used for geodetic surveying. The SECOR system included three ground-based transmitters from known locations that would send signals to the satellite transponder in orbit. A fourth ground-based station at an undetermined position could then use those signals to fix its location precisely. The last SECOR satellite was launched in 1969. GPS can be thought of as an evolution of the SECOR system where the ground-based transmitters have been migrated into orbit [2].

By integrating ideas from predecessors, the GPS project was developed in 1973 to overcome the limitations of previous navigation systems, including a number of classified engineering design studies from the 1960s. GPS was created and realized by the U.S. Department of Defense (DoD) and was originally run with 24 satellites at the cost of twelve billion taxpayer dollars. It became fully operational in 1994. Roger L. Easton is generally credited as its inventor.

Satellites in each of three orbital planes spaced 120º apart, and their ground stations, formed the original GPS. GPS uses these satellites as reference points to calculate geographical positions, accurate to a matter of meters.

Underlying knowledge used in development of GPS
The GPS consists of three major segments. These are the space segment, a control segment, and a user segment. The U.S. Air Force develops, maintains, and operates the space and control segments. GPS satellites broadcast signals from space, and each GPS receiver uses these signals to calculate its three-dimensional location (latitude, longitude, and altitude) and the current time.
The space segment is composed of 24 to 32 satellites in medium Earth orbit and also includes the payload adapters to the boosters required to launch them into orbit. The control segment is composed of a master control station, an alternate master control station, and a host of dedicated and shared ground antennas and monitor stations. The user segment is composed of hundreds of thousands of U.S. and allied military users of the secure GPS Precise Positioning Service, and tens of millions of civil, commercial, and scientific users of the Standard Positioning Service.
The GPS receiver uses the messages it receives to determine the transit time of each message and computes the distance to each satellite using the speed of light. Each of these distances and satellites' locations define a sphere. The receiver is on the surface of each of these spheres when the distances and the satellites' locations are correct. These distances and satellites' locations are used to compute the location of the receiver using the navigation equations. This location is then displayed with a moving map display or latitude and longitude; elevation information may be included.
In typical GPS operation, four or more satellites must be visible to obtain an accurate result. Four sphere surfaces typically do not intersect. Therefore, it gives us the position of the receiver along with accurate time thereby eliminating the need for a very large, expensive, and power hungry clock. The very accurately computed time is used only for display or not at all in many GPS applications, which use only the location. A number of applications for GPS do make use of this cheap and highly accurate timing. These include time transfer, traffic signal timing, and synchronization of cell phone base stations.
Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known, a receiver can determine its position using only three satellites. For example, a ship or aircraft may have known elevation. Some GPS receivers may use additional clues or assumptions such as reusing the last known altitude, dead reckoning, inertial navigation, or including information from the vehicle computer, to give a position when fewer than four satellites are visible.
The usage, type of user and contributions of GPS
Car drivers use in-vehicle portable GPS devices to follow a route, find detours around traffic problems and with additional software receive traffic alerts and warnings on safety camera locations.
Pilots and captains use GPS devices to pinpoint their speed and position on air or sea with incredible accuracy.
Hikers and ramblers can use GPS receivers to ensure they are following their chosen route and to mark rendezvous points along the way.
Search and rescue teams at sea can use GPS to find their way to an incident quicker, to pinpoint the location of accidents and allow follow-up staff to find the scene quickly. This is particularly useful for and in extreme weather conditions on land where time can be a matter of life or death.
Scientists and engineers also have applications for GPS receivers, in scientific experiments, and in monitoring geological activity such as earth tremors, earthquakes and volcanic rumblings. They can use strategically positioned GPS devices to assist them in tracking climate change and other phenomena.
GPS is implemented in tracking individuals who are likely to wander and stray to being lost. Children and elders can be equipped with GPS devices. The satellite is able to pick up the signal and acquire the coordinate of their positions from the signal emitted by the device. Parents are able to keep track of the location of their children and prevent elders with Alzheimer’s disease from being lost.

New knowledge created through the use of GPS
The invention of GPS has created the new knowledge regarding to the issue of radio wave signal degradation. Realizing the knowledge, developers start to pay attention on improving the accuracy and reliability of GPS. There are various factors contributing to radio signal deterioration and developers are currently utilizing all possible existing knowledge for counterfeiting.
Atmospheric effect which is caused by the change in atmospheric condition can affect GPS radio signals as signals travel through the thick layer of the atmosphere. Both ionosphere and troposphere can leave little or more impact on the speed of the radio signals. Dual frequency measurement by comparing the two frequencies can reduce the error and also define a precise location of the receiver.
Multipath effect occurs when signals are get reflected or bounced by coming in contact with surrounding hills, buildings or any kind of hard core object before it reaches the receiver. Thus, increase in travel time of signals cause error. However, with the help of the technique named narrow collector spacing the receiver recognizes the long delay signals and does not take into account while calculating the precise time and location. Also there are some specialized antennas are used to measure the exact data from the signals that are slightly deviated or delayed. But it’s a bit difficult as the fluctuation is very little in atmospheric delay.
At times, the receiver enabled with a clock that is not as accurate as the atomic clock in satellite and so produces a little timing error.
Orbital error occurs when the satellite’s orbital location is calculated wrongly. As the right location of the satellites position in the orbit is essential, even a small error can leave a large difference as far as accuracy is concerned.
Satellite geometry is the exact position of the satellite at a given period of time. Ideally when satellites are located in wide angles from each other, it becomes easy to measure distance. However, poor satellite geometry occurs when they are in a line or in a tight grouping.
Artificial degradation of the satellite signal occurs when there is a limitation on the propagation of radio signal. The Department of Defense of US recently restricted certain highly accurate GPS signals (military related) from public use as these can be misused and so intentionally degraded. This is called Selective Availability (SA) in which kinds of intentional errors like creating noise in the satellite clock or transmitting some false orbital data to the satellite that can come back to the receiver at the ground. However, receivers of Defense Department have the capability of rectifying those errors [3].
Moreover, the developers realized an important issue from the invention of the GPS. GPS is developed into handheld device, mobile phones, integrated in automobiles and everywhere except underground and indoors. As GPS signals cannot penetrate into the ground it cannot be used in caves or mines. It is found that metals and concretes reduce or even block the propagation of radio waves which is used to transmit the GPS signal from the satellite. This new knowledge on the flaw of satellite has become a motivating factor for developers to create new technology. A Swiss company found a smart solution to this problem and presents now the first Underground GPS. It's now even possible to follow a caver in real time.
The newly developed system consists of a mobile emitter located underground, and four receivers at fixed positions on the surface determined by GPS, a radio link between the receivers and a computer with custom software to analyze and visualize the signals. The receivers are placed on the surface, roughly on top of the underground passage to be measured. They are automatically self-located using GPS. The underground transmitter sends a signal that is detected by the receivers located at the surface. The computer then calculates the exact position and visualises it, making it possible to follow the moving object in real time covering a surface of 300 m x 300 m without the need to move the surface receivers. This design enables the positioning system to be used underground.

Conclusion
The technology of the Global Positioning System is allowing for huge changes in society. The applications using GPS are constantly growing. The cost of the receivers is dropping while at the same time the accuracy of the system is improving. Even though the system was originally developed for military purposes, civil sales now exceed military sales. The GPS is gradually becoming popular in the society for its benefits to mankind.

In order to perfect the applications of GPS in the society, it is now undergoing development to become more reliable and accurate measurements, less costly to corporations. The error removing equipment will no longer be needed with more affordable and accessible to consumers. This would be a greater incentive for the development of new uses.

GPS is a fantastic tool of the 21st century offering many functions. The future of GPS appears to be virtually unlimited; technological fantasies abound. The system provides a novel, unique, and instantly available address for every square yard on the surface of the planet–a new international standard for locations and distances. To the computers of the world, at least, our locations may be defined not by a street address, a city, and a state, but by a longitude and latitude. With the GPS location of services stored with phone numbers in computerized indices, the search for a local restaurant or the nearest gas station in any city, town, or suburb will be completed in an instant. With GPS, the world has been given a technology of unbounded promise, born in the laboratories of scientists who were motivated by their own curiosity to probe the nature of the universe and our world, and built on the fruits of publicly supported basic research.

References

[1]. Bright Hub (2010) Who Invented the GPS? The Minds Behind the Invention of GPS. [online] Available at: http://www.brighthub.com/electronics/gps/articles/68261.aspx [Accessed: 21 Feb 2013].

[2]. Bellis, M. (1912) History of the Global Positioning System - GPS. [online] Available at: http://inventors.about.com/od/gstartinventions/a/gps.htm [Accessed: 21 Feb 2013].

[3]. Roseindia.net (2008) Factors responsible for GPS signal errors. [online] Available at: http://www.roseindia.net/technology/gps/gps-signal-errors.shtml [Accessed: 21 Feb 2013].