Abstract
Irrespective of time, location, and whether, Global Position System provides unparalleled range of services to commercial military and consumer applications. Majority of these services enables airborne, land, and sea users to know their exact velocity, location, and time whenever and wherever on Earth. The development and capabilities of the GPS technology have rendered obsolete and impractical, other traditional positioning and well-known navigation systems and technologies such as magnetic compasses, radio-based devices, and chronometers among others. Global Positioning System consists of 24 satellites, 21 of which are active while three (3) are spares and are located at an altitude of 10600 miles above the surface of the earth (El-Rabbany, 2002). GPS receivers on the ground is fitted with computers that are capable of triangulating its own sense after obtaining bearings from the other three (4) of the four (4) GPS satellites located in the same horizon. GPS segments are categorized into three distinct segments that include space segment, control segment, and user segment. Global Positioning systems perform an array of functions on land, in air, or at sea. There are specific features that make GPS systems be attractive. These includes the ability to provide high positioning accuracies, the capability to determine accurate time and velocity accuracies, readily available signals in any part of the world, the free services at no charge, and all all-weather service delivery system (Andrews, Weill, and Grewal, 2007). Despite the above advantages, a number of challenges that still impede the transmission of signals still exist within the limits of GPS technologies. Majority of these challenges includes errors such as inaccuracies associated with the reported location of satellites (orbital errors), receiver clock errors, signal multipath, and number of visible satellites, which can affect position reading or impede signal reception.
Global Positioning System
Irrespective of time, location, and whether, Global Position System provides unparalleled range of services to commercial military and consumer applications. Majority of these services enables airborne, land, and sea users to know their exact velocity, location, and time whenever and wherever on Earth. The development and capabilities of the GPS technology have rendered obsolete and impractical, other traditional positioning and well-known navigation systems and technologies such as magnetic compasses, radio-based devices, and chronometers among others. Twenty-four (24) GPS satellites are strategically located 10, 600 miles from Earth and they are in circular orbits with each other (El-Rabbany, 2002). The orbital period is 12 hours, and satellites are distributed in six orbital planes with equally spaced angles. Out of the 24 GPS satellites, twenty-one (21) are active while three (3) are spaces. The GPS satellites are spaced in such a manner that four (4) GPS satellites will always be beyond the horizon. In terms of structure and composition, each GPS satellite is equipped with an atomic clock, a computer, and a radio. Each radio understands its own clock and orbit thereby enabling it to broadcast continuously any changes in time and position. For instance, any minor corrections are made on each day after each GPS satellite verifies its own sense of position and time with other stations located on the ground.
GPS receivers on the ground are fitted with computers that are capable of triangulating its own sense after obtaining bearings from the other three (4) of the four (4) GPS satellites located in the same horizon (El-Rabbany, 2002). The display screen on GPS receivers shows a map whereby the position of the object can be drawn from the map. Identification of geographic positions and altitude becomes possible if signals from the fourth satellite are receivable. Interestingly, the receivers are capable of calculating direction and speed during movements, and this capability enables navigators to estimate the arrival times to specified locations. Readings in most receivers are obtained in the form of geographic positions, that is, latitude and longitude. Finally, advanced and specialized GPS receivers can be programmed to store vital data that are usable in map making and as well important for Geographic Information Systems.
Project Objectives
This report limits itself to the discussion of the Global Positioning Systems, their structure, operations, and usefulness in different sectors and applications across the globe. This report aims to fulfill the following objectives:
- Explain what is meant by Global Position Systems and other GPS terminologies and as well shed some light on its history
- Discuss the structure and operations of GPS system
- Explain the different structures of GPS segments
- Outline the primary functions of GPS systems and technologies
- Examine the accuracy of GPS information and if possible, identify sources of errors that can affect the accuracy of GPS information
- Identify the primary users of GPS applications and other necessary conditions that should be fulfilled when purchasing GPS systems
- Identify other competitor versions of GPS systems
Global Positioning Systems and their History
Global Positioning Systems (GPS) refers to satellite-based radio-positioning systems and time-transfer systems that provide three-dimensional course, position, and time information to suitably equipped users. The radios sends, receives, and provides time and location information at any time, place, and weather provided the GPS radios are not obstructed from the four other orbital satellites. Other valuable information displayed by GPS technologies includes velocity and altitude. The U.S. Department of Defense designs, finances, and operates GPS systems while the USA owns the GPS technology. Other than the unparalleled advantages offered to the military, GPS systems have proven to be of fundamental benefits to the civilian community whereby GPS applications are used in rapidly expanding sets of applications. The Global Positioning System consists of 24 satellites that are in circular orbits around the Earth with the orbital period of approximately 12 hours (Kaplan, 1996). The satellites are distributed across six orbital planes that are equally spaced in angles. Each Global Positioning Satellite is built with an atomic clock, a computer, and a radio
The history of GPS systems can be traced to 1973 when the United States Department of Defense began to develop a 24-hour, all-weather global positioning system to provide support for the positioning requirements of US armed forces. The GPS was formerly referred to as the NAVSTAR (Navigation Satellite Timing and Ranging). Ideally, the GPS system was designed as a form of replacement to already large navigational system that was already in use, and as well, the need to obtain reliability and survivability for navigation systems in handling a wide variety of dynamics (Kaplan, 1996; Parkinson, and Spilker 1996). Other motives that initiated the development of GPS Technology included the need for a system to service unlimited users, and a system that does not require the transmission of signals from users to satellites. Eventually, it led to the design of a system that surpassed the intended concepts such that a one-way system was developed to transmit signals with no receiving functions. This function was essential in that enemies could not detect signals being relayed within the confines of the military. Additionally, the developed system used microwave transmission technology, was equipped with the latest atomic clocks, could transmit signals regardless of the prevailing weather conditions, and provided accurate navigation and positioning details (Parkinson, and Spilker 1996). Due to the relatively cheap cost and inexpensive equipment, the GPS technology was availed freely to the civilian population.
Structure and operations of the GPS
As earlier mentioned, the Global Positioning System consists of 24 satellites, 21 of which are active while three (3) are spares and are located at an altitude of 10600 miles above the surface of the earth (El-Rabbany, 2002). The satellites are strategically arranged in orbits such that at any time of the day, at least four satellites are visible above the earth’s horizon. The receivers on the ground detect their positions in reference to the GPS satellites. The primary navigation principle is obtained based on the measurement of pseudoranges between the four satellites and the user (Seeber, 2003). Equally, the stations located on the ground provide precise monitoring of the orbit at every level of the satellite and measures the travel time signals transmitted between the four satellites and the receiver. In turn, the accurate direction, location, and speed is the measure.
Structures of GPS Segments
GPS segments are categorized into three distinct segments that include control segment, user segment, and space segment. The space segment contains at least 24 GPS satellites that follow a specific pattern when orbiting the earth (Seeber, 2003). The satellites travel at an approximate speed of 7,000 miles per hour, and the satellites are spaced such that at least four GPS satellites can send signals to a GPS receiver located anywhere on earth. From each GPS receiver, coded radio signals are sent to earth and each signal contains particular information. The information includes the particular satellite sending the information, the exact position of the satellite, date and time the signal was sent, and whether the satellite was performing properly. Satellites use solar energy, but they are also powered by backup batteries in the absence of solar energy (Seeber, 2003). Majority of the satellites have been built to last for approximately 10 years after which they are replaced. Monitoring, control, and replacement of space satellites and GPS technology is done by the US Department of Defense.
The control segment entails constant monitoring of the health of satellites, the orbital configuration, and intensity of signals. The control segment is further subdivided into ground antennas, monitor stations, and master control station. There are at least six unmanned monitor stations all over the earth, each station is in constantly receiving, and monitoring information from GPS satellites and at the same time relays the clock and orbital information to master control stations (MCS). Similarly, Master Control Stations make precise corrections of orbital and clock information received from monitor stations. It sends the corrected information to ground antennas (Seeber, 2003). Last, the Ground Antennas are responsible for receiving corrected clock and orbital information from the Master Control Station and in turn, relays the corrected information to appropriate satellites.
Finally, the user segment of the GPS systems is made up of GPS receivers, which are responsible for collecting and processing signals received from GPS satellites that are in the range. It then uses the collected information to find and display the location, time, speed, and altitude of the receiver (Seeber, 2003). No information is transmitted from the receiver to the satellites.
Primary Functions of Global Positioning Systems
Global Positioning systems perform an array of functions on land, in air, or at sea. There are specific features that make GPS systems be attractive. These includes the ability to provide high positioning accuracies, the capability to determine accurate time and velocity accuracies, readily available signals in any part of the world, the free services at no charge, and all all-weather service delivery system (Andrews, Weill, and Grewal, 2007). Above all, GPS technologies provide accurate position information in three dimensions (vertical and horizontal information). Currently, it is estimated that the number of civilian users exceeds the number of military users. In light of these characteristics, the global sectors are exceedingly utilizing the services of GPS technologies.
GPS systems were initially designed for military purposes and they have remained significant in facilitating military operations. Military ships, aircraft, tanks, and equipment use GPS technology for navigation purposes, provision of close air support, improving weapon technology, and determining target destination. In agriculture, GPS technologies are used in precision farming to monitor the process of applying fertilizer and pesticides in addition to proving accurate location information that enable farmers to plow, map fields, harvest, and identify potential disease areas or weed infestation. In the aviation industry, aircraft and airplane pilots utilize GPS technology to identify en route navigation and airport approaches. Additionally, the accurate location of aircraft can be identified from any place on or near the earth’s surface through the help of Satellite navigation (Andrews, Weill, and Grewal, 2007). In environmental management, GPS technology has been utilized in surveying disaster prone areas, and as well in mapping the movement of environmental phenomena such as hurricanes or forest fires. Interestingly, GPS technology can also be used in the identification of locations that have been altered or submerged by natural disasters.
Another area that utilizes GPS technology is Ground transportation. GPS technologies are used in vehicle tracking systems, in-vehicle navigation systems, and in automatic vehicle location systems. Majority of these systems shows the location of vehicles on an electronic sheet map thereby enabling drivers to track their exact locations and as well, get an overview of other destinations. Other systems are designed to automatically design a route and provide turn-by-turn directions to provide guidance to drivers. Furthermore, GPS technologies facilitates the process of monitoring and planning routes for emergency vehicles and delivery vans. Rail transport systems also use GPS technologies to estimate precise locations of trains, manage the flow of traffic, prevent collision of trains, and in the estimation of time, speed, and distance covered by trains (Andrews, Weill, and Grewal, 2007). In marine systems, GPS technologies assist in marine navigation, surveying underwater, routing traffic, locating navigational hazards, and marine mapping. Moreover, commercial fishing fleets use GPS technology to identify and navigate to areas with optimum fishing opportunities and as well to track the migration of fishes.
GPS technologies are also used for public safety such as locating emergency areas, and in recreation for finding bearings, estimating distance, time, and in returning to the original locations. Space science also utilizes GPS technologies to track and control the behavior and motions of satellites in orbit. Space shuttles and future rockets also depend on GPS technologies. Finally yet important, field of surveying heavily utilizes GPS technologies in both complex and basic tasks such as development of urban infrastructures and defining property lines respectively. Furthermore, mapping roads, rail systems, and surveying land maps is possible with the utilization of GPS technologies.
Accuracy of Global Position Systems
The accuracy of GPS systems depends with the precision of signals that emanate from GPS satellites to GPS receivers. Additionally, the number of obstacles that can obscure your receiver from the GPS systems are critical in the determining the precision and accuracy of information obtained from GPS systems. The types of receivers also play a significant role in the determination of GPS accuracy. Majority of GPS receivers have an accuracy range of +/- 10m. Other accurate forms of GPS receivers include Differential Global Positioning Systems (DGPS). The accuracy of most GPS systems is affected by errors.
Common sources of errors to GPS systems include inaccuracies associated with the reported location of satellites (orbital errors), receiver clock errors, signal multipath that makes GPS signals bounce off objects, and number of visible satellites, which can affect position reading or impede signal reception (Tsui, 2005). Satellite Shading also affects the accuracy of the information. For instance, the ideal satellite geometry is achieved when satellites are widely located at angles that are relative to one another.
Ideal Characteristics of Global Positioning Systems
In order to obtain accurate information from Global Positioning Systems, specific factors should be put into consideration during the acquisition of GPS tools. First, the GPS tool should be durable to ensure that it is capable of withstanding rigors work and continued usage. Second, the ability of the GPS tool to obtain and maintain the most reliable signal strength despite the existence of obstructions such as the location, changing weather conditions, and the sensitivity of the receiver (Tsui, 2005). Third, GPS components consume a lot of power and therefore, battery life is a critical factor to consider during the acquisition of GPS equipment. Other noteworthy features include the portability ranges, cellular signal reliability, the length of acquiring GPS signals from satellites, configuration complexities, and ease of use among others.
GPS Competitors
The closest competitor of GPS technology is the Wide Are Augmentation System (WAAS) that consists of satellites and ground stations capable of providing accurate positioning. The WAAS technology was developed by the Federal Aviation Administration (FAA). A good example of WAAS is the European Geostationary Navigation Overlay Service (EGNOS). The WAAS program was specifically developed to assist pilots is determining direct en route paths, identifying precision approach services to runways, and to ensure maximum capacity and safety improvements in all weather conditions (Tsui, 2005). WAAS users are required to have WAAS-capable receivers to enable them obtain signals in areas covered by WAAS satellites.
Results and Conclusions
The analysis and discussion of Global Positioning System concepts has revealed that GPS technology is a force in the force. Perhaps the system designers had different intentions when developing and designing GPS technologies but these applications have added to the versatility of usage of GPS not only as a system for estimating the precise positioning of objects but also in the provision of accurate and reliable navigation information. Irrespective of time, location, and whether, Global Position System provides unparalleled range of services to commercial military and consumer applications. Majority of these services enables airborne, land, and sea users to know their exact velocity, location, and time whenever and wherever on Earth. Indeed, the GPS technology supports numerous positioning and navigation applications that satisfy a multitude of user needs. At this moment, the widespread usage of GPS applications in different sectors of the economy makes it exceedingly difficult to think of a life without Global Positioning Systems. It is evident that creating a complex system such as the GPS technology is not an easy task and this can be proven from the few competitors of GPS technology. GPS technologies and systems are used in different sectors of society. This includes road and rail transportation, marine navigation, agriculture, the airline industry, space science, recreation, military, and in the provision of public safety among others. Information and signals relayed by GPS systems are safe and reliable thereby making GPS technology the ideal navigation and positioning equipment.
The evaluation and analysis of the structure, operation, and application of GPS systems have shown that maintaining the GPS technology is a complex activity given the nature of the GPS technologies. Notwithstanding these complexities, GPS services are maintained and offered free of charge thereby making it available for an unlimited number of users and applications. Global Positioning Systems have a potential future judging from the current technological advancements. Virtually, every communication and navigation device is manufactured or fitted with a GPS receiver. From basic consumer electronic products such as mobile phones to complex navigation and military tools such as ships, aircrafts, and weapons, are both built with GPS technologies (Tsui, 2005). Importantly, the Global Positioning System is also advancing at an increasing rate and therefore, more is still to be expected with regard to the future of GPS tools and applications.
Despite the above advantages, a number of challenges that still impede the transmission of signals still exist within the limits of GPS technologies. Majority of these challenges includes errors such as inaccuracies associated with the reported location of satellites (orbital errors), receiver clock errors, signal multipath, and number of visible satellites, which can affect position reading or impede signal reception. These errors have an effect of affecting the signal strength and in turn, leading to inaccurate positioning and navigation information. Nonetheless, these challenges can be avoided by ensuring that GPS receivers and equipment are evaluated to test their reliability. Factors that must be considered during the evaluation of GPS systems include durability, the capability to obtain and maintain the most reliable signal strength, and power consumption (Tsui, 2005). As such, a number of procedures can be followed in evaluating GPS tools and equipment. These includes conducting an evaluation and testing exercise to ascertain the ideal characteristics, identifying the credibility of vendors, examining the legal considerations, and lastly, identifying ways of overcoming the challenges. Overall, there is potential in GPS technology provided corrective measures be taken and as well, there is the need to conduct immense research and innovation in GPS technology to ensure its sustainability.
References
Andrews, A., P., Weill, L. R., and Grewal, S. G. (2007). Global Positioning Systems, Inertial Navigation, and Integration. John Wiley & Sons
El-Rabbany, A. (2002). Introduction to GPS: the Global Positioning System. Artech House
Kaplan, E. D. ed. (1996). Understanding GPS: Principles and Applications. Boston: Artech House Publishers.
Parkinson, B. W., and Spilker. J. J. eds. (1996). Global Positioning System: Theory and Practice. Volumes I and II. Washington, DC: American Institute of Aeronautics and Astronautics, Inc.
Seeber, G. (2003). Satellite Geodesy (2nd Edition). Walter de Gruyter Inc.
Tsui, B. J. (2005). Fundamentals of Global Positioning System receivers: A software Approach. John Wiley and Sons