Text A. The Global Positioning System (GPS)

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The Global Positioning System (GPS) is a U.S.-owned utility that provides users with positioning, navigation, and timing (PNT) services. This system consists of three segments:

1) The space segment constellation consists of 24 satellites, that transmit one-way signals that give the current GPS satellite position and time. 24 Space Vehicles (SVs) are distributed equally among six circular orbital planes. The orbital planes are centered on the Earth, not rotating with respect to the distant stars. Orbiting at an altitude of approximately 20,200 kilometers; orbital radius of 26,600 km, each SV makes two complete orbits each sidereal day.

2) The control segment consists of worldwide monitor and control stations that maintain the satellites in their proper orbits through occasional command maneuvers, and adjust the satellite clocks. It tracks the GPS satellites, uploads updated navigational data, and maintains health and status of the satellite constellation.

3) The user segment consists of the GPS receiver equipment, which receives the signals from the GPS satellites and calculates the user's three-dimensional position and time. In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock. Receivers typically have between twelve and twenty channels.

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GPS has become a widely used aid to navigation worldwide, and a useful tool for map- making, land surveying, commerce, and scientific uses. To meet the specific user requirements for PNT, a number of augmentations to the GPS are available. An augmentation is any system that aids GPS by providing accuracy, integrity, reliability, availability, or any other improvement that is not inherently part of GPS itself.

Nationwide Differential GPS System provides increased accuracy and integrity of the GPS to users on land and water. Modernization efforts include enhancing the performance and providing 10 to 15 centimeter accuracy throughout the coverage area. Over 50 countries around the world have implemented similar systems.

Wide Area Augmentation System provides aircraft navigation for all phases of flight.

Continuously Operating Reference Station archives and distributes GPS data for precision positioning and atmospheric modeling applications mainly through post-processing¹.

Global Differential GPS supports the real-time positioning, timing, and orbit determination requirements of the U.S. National Aeronautics and Space Administration (NASA) science missions. The U.S. Policy underscores the importance that all global navigation satellite systems and their augmentations be compatible with the GPS.

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In addition to longitude, latitude, and altitude, the Global Positioning System (GPS) provides a critical fourth dimension - time. Each GPS satellite contains multiple atomic clocks that contribute very precise time data to the GPS signals. GPS receivers decode these signals, effectively synchronizing each receiver to the atomic clocks. This enables users to determine the time to within 100 billionths of a second. Precise time is crucial to a variety of economic activities around the world. Communication systems, electrical power grids, scientific study of earthquakes and financial networks all rely on precision timing for synchronization and operational efficiency. Wireless telephone and data networks use GPS time to keep all of their base stations in perfect synchronization. Similarly, digital broadcast radio services use GPS time to ensure that the bits from all radio stations arrive at receivers in lockstep². Companies worldwide use GPS to time-stamp³ business transactions. Major investment banks use GPS to synchronize their network computers located around the world. Hollywood studios are incorporating GPS in their movie slates⁴, allowing for unparalleled control of audio and video data, as well as multi-camera sequencing.

4.______________________________________

It is estimated that delays from congestion⁵ on highways and streets throughout the world result in productivity losses in the hundreds of billions of dollars annually. GPS enables automatic vehicle location and in-vehicle navigation systems that are widely used throughout the world today. By combining GPS position technology with systems that can display geographic information a new dimension in surface transportation is realized. A geographic information system (GIS) stores, analyzes, and displays geographically referenced information. Today GIS enables effective strategies that can keep transit vehicles on schedule and inform passengers of precise arrival times. GPS is an essential element in the future of Intelligent Transportation Systems (ITS). Research is being conducted in the area of advanced driver assistance systems, which include road departure and lane change collision avoidance systems. These systems need to estimate the position of a vehicle relative to lane and road edge with an accuracy of 10 centimeters. With the continuous modernization of GPS, one can expect even more effective systems for crash prevention, distress alerts and position notification, electronic mapping, and in- vehicle navigation with audible instructions.

GPS receivers come in a variety of formats, from devices integrated into cars, phones, and watches, and many other devices.

Notes:

1) ¹post-processing - обработка данных (to perform mathematical and logical operations on data according to programmed instructions in order to obtain the required information).

2) ²in lockstep - зд. строго одновременно, букв. «шаг в ногу» (progressing at exactly the same speed and in the same direction as other people or things).

3) ³time-stamp - временная отметка (to assign an accurate time to a message, transaction, etc.) The database entry consists of the MAC address, the port that address was seen on, and a time- stamp to indicate when it was see.

4) ⁴slates - доска, которой хлопают перед очередным дублем (a pair of boards clapped together during film shooting in order to aid sound synchronization).

5) ⁵congestion - скопление (the state of being overcrowded, esp. with traffic or people).

4.8 Write out of text A phrases describing general uses of GPS.

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