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Encyclopedia > Global Positioning System
Artist's conception of GPS satellite in orbit
Artist's conception of GPS satellite in orbit
Civilian GPS receiver in a marine application.
Civilian GPS receiver in a marine application.

The Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). Utilizing a constellation of at least 24 Medium Earth Orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its location, speed, direction, and time. Other similar systems are the Russian GLONASS (incomplete as of 2008), the upcoming European Galileo positioning system, the proposed COMPASS navigation system of China, and IRNSS of India. For the global navigation satellite system operated by Russia, see GLONASS. Global Navigation Satellite System (GNSS) is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. ... GPS can refer to: Global Positioning System GPS (band), a progressive rock band Gunners Primary Sight, a part of the targeting and fire-control system on the M1 Abrams tank GNAT Programming Studio Generalized Processor Sharing General Problem Solver GPS Schools, an association of private boys schools Great Public... Image File history File links Download high resolution version (1006x806, 110 KB) Summary Artist Interpretation of GPS satellite, image courtesy of NASA [[1]] Licensing File links The following pages link to this file: Global Positioning System ... Image File history File links Download high resolution version (1006x806, 110 KB) Summary Artist Interpretation of GPS satellite, image courtesy of NASA [[1]] Licensing File links The following pages link to this file: Global Positioning System ... Image File history File links NAVSTAR_GPS_logo_shield-official. ... Image File history File links Size of this preview: 617 × 599 pixelsFull resolution (900 × 874 pixel, file size: 261 KB, MIME type: image/png) Please see the file description page for further information. ... Image File history File linksMetadata Download high resolution version (2560x1920, 758 KB) Summary Photo taken (25th Dec 2005) and supplied by Nachoman-au. ... Image File history File linksMetadata Download high resolution version (2560x1920, 758 KB) Summary Photo taken (25th Dec 2005) and supplied by Nachoman-au. ... For the global navigation satellite system operated by Russia, see GLONASS. Global Navigation Satellite System (GNSS) is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. ... A group of electronic satellites working in concert is known as a satellite constellation. ... Intermediate circular orbit (ICO), also called medium earth orbit (MEO), is used by satellites between the altitudes of low earth orbit (up to 1400 km) and geostationary orbit (ca. ... This article is about artificial satellites. ... This article is about the type of Electromagnetic radiation. ... In radio terminology, a receiver is an electronic circuit that receives a radio signal from an antenna and decodes the signal for use as sound, pictures, navigational-position information, etc. ... The geographic location of anything is measured by the latitude and longitude of it, as on a map or globe. ... GLONASS GLONASS (Russian ГЛОНАСС; ГЛОбальная НАвигационная Спутниковая Система; Globalnaya Navigatsionnaya Sputnikovaya Sistema. ... 2008 (MMVIII) will be a leap year starting on Tuesday of the Gregorian calendar. ... The Galileo positioning system is a planned Global Navigation Satellite System, to be built by the European Union (EU) and European Space Agency (ESA). ... The COMPASS system (also known as Beidou-2) is a project by China to develop an independent satellite navigation system. ... The Indian Regional Navigational Satellite System (IRNSS) is a proposed autonomous regional satellite navigation system to be constructed and controlled by the Indian government. ...


Developed by the United States Department of Defense, GPS is officially named NAVSTAR GPS (Contrary to popular belief, NAVSTAR is not an acronym, but simply a name given by John Walsh, a key decision maker when it came to the budget for the GPS program).[1] The satellite constellation is managed by the United States Air Force 50th Space Wing. The cost of maintaining the system is approximately US$750 million per year,[2] including the replacement of aging satellites, and research and development. The United States Department of Defense (DOD or DoD) is the federal department charged with coordinating and supervising all agencies and functions of the government relating directly to national security and the military. ... It has been suggested that this article or section be merged with Backronym and Apronym (Discuss) Acronyms and initialisms are abbreviations, such as NATO, laser, and ABC, written as the initial letter or letters of words, and pronounced on the basis of this abbreviated written form. ... USAF redirects here. ... The 50th Space Wing (50 SW) is a wing of the United States Air Force under the major command of Air Force Space Command (AFSPC). ... USD redirects here. ...


Following the shooting down of Korean Air Lines Flight 007 in 1983, President Ronald Reagan issued a directive making the system available for free for civilian use as a common good.[3] Since then, GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, scientific uses, and hobbies such as geocaching. GPS also provides a precise time reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks. Korean Air Lines Flight 007, also known as KAL 007 or KE007, was a Korean Air Lines civilian airliner shot down by Soviet jet interceptors on September 1, 1983 just west of Sakhalin island. ... Reagan redirects here. ... Radio navigation is the application of radio frequencies to determining a position on the earth. ... Cartography or mapmaking (in Greek chartis = map and graphein = write) is the study and practice of making maps or globes. ... Surveyor at work with a leveling instrument. ... A Geocache in Germany Geocaching is an outdoor treasure-hunting game in which the participants use a Global Positioning System (GPS) receiver or other navigational techniques to hide and seek containers (called geocaches or caches) anywhere in the world. ... Time transfer describes methods for transferring reference clock synchronization from one point to another, often over long distances. ... This article is about the natural seismic phenomenon. ... Synchronization (or Sync) is a problem in timekeeping which requires the coordination of events to operate a system in unison. ...

Contents

Simplified method of operation

A typical GPS receiver calculates its position using the signals from four or more GPS satellites. Four satellites are needed since the process needs a very accurate local time, more accurate than any normal clock can provide, so the receiver internally solves for time as well as position. In other words, the receiver uses four measurements to solve for four variables: x, y, z, and t. These values are then turned into more user-friendly forms, such as latitude/longitude or location on a map, then displayed to the user. For other uses, please see Satellite (disambiguation) A satellite is an object that orbits another object (known as its primary). ...


Each GPS satellite has an atomic clock, and continually transmits messages containing the current time at the start of the message, parameters to calculate the location of the satellite (the ephemeris), and the general system health (the almanac). The signals travel at the speed of light through outer space, and slightly slower through the atmosphere. The receiver uses the arrival time to compute the distance to each satellite, from which it determines the position of the receiver using geometry and trigonometry (see trilateration[4]) “Nuclear Clock” redirects here. ... An ephemeris (plural: ephemerides) (from the Greek word ephemeros = daily) is a device giving the positions of astronomical objects in the sky. ... A line showing the speed of light on a scale model of Earth and the Moon, taking about 1⅓ seconds to traverse that distance. ... A line showing the speed of light on a scale model of Earth and the Moon, taking about 1⅓ seconds to traverse that distance. ... Standing at B, you want to know your location relative to the reference points P1, P2, and P3. ...


Although four satellites are required for normal operation, fewer may be needed in some special cases. If one variable is already known (for example, a sea-going ship knows its altitude is 0), a receiver can determine its position using only three satellites. Also, in practice, receivers use additional clues (doppler shift of satellite signals, last known position, dead reckoning, inertial navigation, and so on) to give degraded answers when fewer than four satellites are visible. The Doppler effect is the apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves. ... Dead reckoning (DR) is the process of estimating ones current position based upon a previously determined position, or fix, and advancing that position based upon measured velocity, time, heading, as well as the effect of currents or wind. ... An inertial navigation system measures the position and altitude of a vehicle by measuring the accelerations and rotations applied to the systems inertial frame. ...


Technical description

Unlaunched GPS satellite on display at the San Diego Aerospace museum
Unlaunched GPS satellite on display at the San Diego Aerospace museum

Download high resolution version (1848x1018, 302 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (1848x1018, 302 KB) Wikipedia does not have an article with this exact name. ...

System segmentation

The current GPS consists of three major segments. These are the space segment (SS), a control segment (CS), and a user segment (US).[5]


Space segment

See also: GPS satellite and List of GPS satellite launches
A visual example of the GPS constellation in motion with the Earth rotating. Notice how the number of satellites in view from a given point on the Earth's surface, in this example at 45°N, changes with time.
A visual example of the GPS constellation in motion with the Earth rotating. Notice how the number of satellites in view from a given point on the Earth's surface, in this example at 45°N, changes with time.

The space segment (SS) comprises the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance. The GPS design originally called for 24 SVs, eight each in three circular orbital planes,[6] but this was modified to six planes with four satellites each.[7] The orbital planes are centered on the Earth, not rotating with respect to the distant stars.[8] The six planes have approximately 55° inclination (tilt relative to Earth's equator) and are separated by 60° right ascension of the ascending node (angle along the equator from a reference point to the orbit's intersection).[2] The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface.[9] The orbital plane of an object orbiting another is the geometrical plane in which the orbit is embedded. ... For the science fiction novella by William Shunn, see Inclination (novella). ... World map showing the equator in red For other uses, see Equator (disambiguation). ... Equatorial Coordinates Right ascension (abbrev. ... An orbital node is one of the two points where an inclined orbit crosses a plane of reference (e. ... When viewing a scene, as in optics, photography, or even hunting, the line of sight is the straight line between the observer and the target. ...


Orbiting at an altitude of approximately 20,200 kilometers (12,600 miles or 10,900 nautical miles; orbital radius of 26,600 km (16,500 mi or 14,400 NM)), each SV makes two complete orbits each sidereal day.[10] The ground track of each satellite therefore repeats each (sidereal) day. This was very helpful during development, since even with just four satellites, correct alignment means all four are visible from one spot for a few hours each day. For military operations, the ground track repeat can be used to ensure good coverage in combat zones. A nautical mile or sea mile is a unit of length. ... On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ...


As of September 2007, there are 31 actively broadcasting satellites in the GPS constellation. The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements. With the increased number of satellites, the constellation was changed to a nonuniform arrangement. Such an arrangement was shown to improve reliability and availability of the system, relative to a uniform system, when multiple satellites fail.[11] September 2007 is the ninth month of that year. ... A group of electronic satellites working in concert is known as a satellite constellation. ...


Control segment

The flight paths of the satellites are tracked by US Air Force monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, and Colorado Springs, Colorado, along with monitor stations operated by the National Geospatial-Intelligence Agency (NGA).[12] The tracking information is sent to the Air Force Space Command's master control station at Schriever Air Force Base in Colorado Springs, which is operated by the 2nd Space Operations Squadron (2 SOPS) of the United States Air Force (USAF). Then 2 SOPS contacts each GPS satellite regularly with a navigational update (using the ground antennas at Ascension Island, Diego Garcia, Kwajalein, and Colorado Springs). These updates synchronize the atomic clocks on board the satellites to within a few nanoseconds of each other, and adjust the ephemeris of each satellite's internal orbital model. The updates are created by a Kalman filter which uses inputs from the ground monitoring stations, space weather information, and various other inputs.[13] This article is about the U.S. State. ... Kwajalein Atoll - NASA NLT Landsat 7 (Visible Color) Satellite Image Kwajalein Atoll (Marshallese: Kuwajleen ; common English pronunciation , often nicknamed Kwaj by English-speaking residents of the U.S. facilities) is part of the Republic of the Marshall Islands (RMI). ... Anthem: God Save the Queen Capital Georgetown Largest city Georgetown Official languages English Government Dependency of St. ... For other uses, see Diego Garcia (disambiguation). ... Colorado Springs is most populous Home Rule Municipality in the State of Colorado. ... The National Geospatial-Intelligence Agency (NGA) is an agency of the United States Government with the primary mission of collection, analysis, and distribution of geospatial intelligence (GEOINT) in support of national security. ... Air Force Space Command (AFSPC) is a major command of the United States Air Force. ... Senior Airman Nayibe Ramos runs through a checklist during Global Positioning System satellite operations. ... USAF redirects here. ... “Nuclear Clock” redirects here. ... To help compare orders of magnitude of different times this page lists times between 10−9 seconds and 10−8 seconds (1 nanosecond and 10 nanoseconds) See also times of other orders of magnitude. ... An ephemeris (plural: ephemerides) (from the Greek word ephemeros = daily) is a device giving the positions of astronomical objects in the sky. ... The Kalman filter is an efficient recursive filter that estimates the state of a dynamic system from a series of incomplete and noisy measurements. ... Aurora australis observed by Discovery, May 1991. ...


Satellite maneuvers are not precise by GPS standards. So to change the orbit of a satellite, the satellite must be marked 'unhealthy', so receivers will not use it in their calculation. Then the maneuver can be carried out, and the resulting orbit tracked from the ground. Then the new ephemeris is uploaded and the satellite marked healthy again.


User segment

GPS receivers come in a variety of formats, from devices integrated into cars, phones, and watches, to dedicated devices such as those shown here from manufacturers Trimble, Garmin and Leica (left to right).
GPS receivers come in a variety of formats, from devices integrated into cars, phones, and watches, to dedicated devices such as those shown here from manufacturers Trimble, Garmin and Leica (left to right).

The user's GPS receiver is the user segment (US) of the GPS. In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock (often a crystal oscillator). They may also include a display for providing location and speed information to the user. A receiver is often described by its number of channels: this signifies how many satellites it can monitor simultaneously. Originally limited to four or five, this has progressively increased over the years so that, as of 2007, receivers typically have between 12 and 20 channels.[14] Download high resolution version (1000x619, 100 KB)GPS receivers from Trimble, Garmin und Leica Source: German Wikipedia DE:Bild:Gps empfaenger. ... Download high resolution version (1000x619, 100 KB)GPS receivers from Trimble, Garmin und Leica Source: German Wikipedia DE:Bild:Gps empfaenger. ... Trimble NASDAQ:TRMB is a provider of advanced positioning solutions, including GPS receivers. ... Garmin Ltd. ... Leica Geosystems formerly known as Wild based in eastern Switzerland produces products and systems for surveying and geographical measurement (geomatics). ... A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. ... 2007 is a common year starting on Monday of the Gregorian calendar. ...

A typical OEM GPS receiver module, based on the SiRF Star III chipset, measuring 15×17 mm, and used in many products.
A typical OEM GPS receiver module, based on the SiRF Star III chipset, measuring 15×17 mm, and used in many products.

GPS receivers may include an input for differential corrections, using the RTCM SC-104 format. This is typically in the form of a RS-232 port at 4,800 bit/s speed. Data is actually sent at a much lower rate, which limits the accuracy of the signal sent using RTCM. Receivers with internal DGPS receivers can outperform those using external RTCM data. As of 2006, even low-cost units commonly include Wide Area Augmentation System (WAAS) receivers. Image File history File linksMetadata Size of this preview: 800 × 534 pixelsFull resolution (1000 × 667 pixel, file size: 280 KB, MIME type: image/jpeg) Photographed by myself File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File linksMetadata Size of this preview: 800 × 534 pixelsFull resolution (1000 × 667 pixel, file size: 280 KB, MIME type: image/jpeg) Photographed by myself File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Original equipment manufacturer, or OEM, is a term that refers to containment-based re-branding, namely where one company uses a component of another company within its product, or sells the product of another company under its own brand. ... A modern SiRFstarIII chip based 20-channel GPS receiver with WAAS/EGNOS support. ... The Radio Technical Commission for Maritime Services (RTCM) is an international standards organization. ... RS-232 (also referred to as EIA RS-232C or V.24) is a standard for serial binary data interchange between a DTE (Data terminal equipment) and a DCE (Data communication equipment). ... WAAS System Overview The Wide Area Augmentation System (WAAS) is an extremely accurate navigation system developed for civil aviation by the Federal Aviation Administration (FAA), a division of the United States Department of Transportation (DOT). ...

SiRFstar III receiver and integrated antenna from UK company Antenova. This measures just 49 x 9 x 4 mm.
SiRFstar III receiver and integrated antenna from UK company Antenova. This measures just 49 x 9 x 4 mm.

Many GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol. NMEA 2000[15] is a newer and less widely adopted protocol. Both are proprietary and controlled by the US-based National Marine Electronics Association. References to the NMEA protocols have been compiled from public records, allowing open source tools like gpsd to read the protocol without violating intellectual property laws. Other proprietary protocols exist as well, such as the SiRF and MTK protocols. Receivers can interface with other devices using methods including a serial connection, USB or Bluetooth. Image File history File links Metadata Size of this preview: 800 × 353 pixelsFull resolution (2816 × 1242 pixel, file size: 1. ... Image File history File links Metadata Size of this preview: 800 × 353 pixelsFull resolution (2816 × 1242 pixel, file size: 1. ... A modern SiRFstarIII chip based 20-channel GPS receiver with WAAS/EGNOS support. ... The United Kingdom of Great Britain and Northern Ireland is a country in western Europe, and member of the Commonwealth of Nations, the G8, the European Union, and NATO. Usually known simply as the United Kingdom, the UK, or (inaccurately) as Great Britain or Britain, the UK has four constituent... This article or section does not adequately cite its references or sources. ... NMEA 2000® is a combined electrical and data specification for a marine data network for communication between marine electronic devices such as depth finders, chartplotters, navigation instruments, engines, tank level sensors, and GPS receivers. ... Proprietary indicates that a party, or proprietor, exercises private ownership, control or use over an item of property, usually to the exclusion of other parties. ... NMEA 0183 (or NMEA for short) is a combined electrical and data specification for communication between marine electronics and also, more generally, GPS receivers. ... Gpsd is a daemon that receives data from GPS receiver, and provides the data back to multiple applications such as Kismet. ... For the 2006 film, see Intellectual Property (film). ... SiRF is a brand of microcontroller designed to be used with GPS systems, which has its own programming language. ... The three-letter acronym MTK may refer to the following: MTK Hungária FC Main-Taunus-Kreis This page concerning a three-letter acronym or abbreviation is a disambiguation page—a list of articles associated with the same title. ... USB redirects here. ... This article is about the electronic protocol. ...


Navigation signals

GPS broadcast signal
GPS broadcast signal

Each GPS satellite continuously broadcasts a Navigation Message at 50 bit/s giving the time-of-week, GPS week number and satellite health information (all transmitted in the first part of the message), an ephemeris (transmitted in the second part of the message) and an almanac (later part of the message). The messages are sent in frames, each taking 30 seconds to transmit 1500 bits. Image File history File links GPS_signal_modulation_scheme. ... Image File history File links GPS_signal_modulation_scheme. ... In telecommunications and computing, bitrate (sometimes written bit rate, data rate or as a variable Rbit) is the number of bits that are conveyed or processed per unit of time. ... An ephemeris (plural: ephemerides) (from the Greek word ephemeros = daily) is a device giving the positions of astronomical objects in the sky. ...


The first 6 seconds of every frame contains data describing the satellite clock and its relationship to GPS time. The next 12 seconds contain the ephemeris data, giving the satellite's own precise orbit. The ephemeris is updated every 2 hours and is generally valid for 4 hours, with provisions for updates every 6 hours or longer in non-nominal conditions. The time needed to acquire the ephemeris is becoming a significant element of the delay to first position fix, because, as the hardware becomes more capable, the time to lock onto the satellite signals shrinks, but the ephemeris data requires 30 seconds (worst case) before it is received, due to the low data transmission rate.


The almanac consists of coarse orbit and status information for each satellite in the constellation, an ionospheric model, and information to relate GPS derived time to Coordinated Universal Time (UTC). A new part of the almanac is received for the last 12 seconds in each 30 second frame. Each frame contains 1/25th of the almanac, so 12.5 minutes are required to receive the entire almanac from a single satellite[16]. The almanac serves several purposes. The first is to assist in the acquisition of satellites at power-up by allowing the receiver to generate a list of visible satellites based on stored position and time, while an ephemeris from each satellite is needed to compute position fixes using that satellite. In older hardware, lack of an almanac in a new receiver would cause long delays before providing a valid position, because the search for each satellite was a slow process. Advances in hardware have made the acquisition process much faster, so not having an almanac is no longer an issue. The second purpose is for relating time derived from the GPS (called GPS time) to the international time standard of UTC. Finally, the almanac allows a single frequency receiver to correct for ionospheric error by using a global ionospheric model. The corrections are not as accurate as augmentation systems like WAAS or dual frequency receivers. However it is often better than no correction since ionospheric error is the largest error source for a single frequency GPS receiver. An important thing to note about navigation data is that each satellite transmits only its own ephemeris, but transmits an almanac for all satellites. UTC redirects here. ... ... Contents // Categories: Stub | Aircraft instruments ...


Each satellite transmits its navigation message with at least two distinct spread spectrum codes: the Coarse / Acquisition (C/A) code, which is freely available to the public, and the Precise (P) code, which is usually encrypted and reserved for military applications. The C/A code is a 1,023 chip pseudo-random (PRN) code at 1.023 million chips per second so that it repeats every millisecond. Each satellite has its own C/A code so that it can be uniquely identified and received separately from the other satellites transmitting on the same frequency. The P-code is a 10.23 megachip per second PRN code that repeats only every week. When the "anti-spoofing" mode is on, as it is in normal operation, the P code is encrypted by the Y-code to produce the P(Y) code, which can only be decrypted by units with a valid decryption key. Both the C/A and P(Y) codes impart the precise time-of-day to the user. A chip is the fundamental unit of transmission in a CDMA system. ... A pseudorandom number generator (PRNG) is an algorithm to generate a sequence of numbers that approximate the properties of random numbers. ...


Frequencies used by GPS include

  • L1 (1575.42 MHz): Mix of Navigation Message, coarse-acquisition (C/A) code and encrypted precision P(Y) code, plus the new L1C on future Block III satellites.
  • L2 (1227.60 MHz): P(Y) code, plus the new L2C code on the Block IIR-M and newer satellites.
  • L3 (1381.05 MHz): Used by the Nuclear Detonation (NUDET) Detection System Payload (NDS) to signal detection of nuclear detonations and other high-energy infrared events. Used to enforce nuclear test ban treaties.
  • L4 (1379.913 MHz): Being studied for additional ionospheric correction.
  • L5 (1176.45 MHz): Proposed for use as a civilian safety-of-life (SoL) signal (see GPS modernization). This frequency falls into an internationally protected range for aeronautical navigation, promising little or no interference under all circumstances. The first Block IIF satellite that would provide this signal is set to be launched in 2009[17].

MegaHertz (MHz) is the name given to one million (106) Hertz, a measure of frequency. ... The United States Global Positioning System (GPS), having reached Fully Operational Capability on July 17, 1995[1] completed its original design goals. ... The United States Global Positioning System (GPS), having reached Fully Operational Capability on July 17, 1995[1] completed its original design goals. ...

Calculating positions

Using the C/A code

To start off, the receiver picks which C/A codes to listen for by PRN number, based on the almanac information it has previously acquired. As it detects each satellite's signal, it identifies it by its distinct C/A code pattern, then measures the received time for each satellite. To do this, the receiver produces an identical C/A sequence using the same seed number, referenced to its local clock, starting at the same time the satellite sent it. It then computes the offset to the local clock that generates the maximum correlation. This offset is the time delay from the satellite to the receiver, as told by the receiver's clock. Since the PRN repeats every millisecond, this offset is precise but ambiguous, and the ambiguity is resolved by looking at the data bits, which are sent at 50 Hz (20 ms) and aligned with the PRN code. A random seed (or seed state, or just seed) is a number (or vector) used to initialize a pseudorandom number generator. ...


This data is used to solve for x,y,z and t. Many mathematical techniques can be used. The following description shows a straightforward iterative way, but receivers use more sophisticated methods. (see below)


Conceptually, the receiver calculates the distance to the satellite, called the pseudorange[18]. The pseudorange (from pseudo and range) is a first-approximation measurement for the distance between a satellite and a navigation satellite receiver - for instance Global Positioning System (GPS) receivers. ...

Overlapping pseudoranges, represented as curves, are modified to yield the probable position
Overlapping pseudoranges, represented as curves, are modified to yield the probable position

Next, the orbital position data, or ephemeris, from the Navigation Message is then downloaded to calculate the satellite's precise position. A more-sensitive receiver will potentially acquire the ephemeris data more quickly than a less-sensitive receiver, especially in a noisy environment.[19] Knowing the position and the distance of a satellite indicates that the receiver is located somewhere on the surface of an imaginary sphere centered on that satellite and whose radius is the distance to it. Receivers can substitute altitude for one satellite, which the GPS receiver translates to a pseudorange measured from the center of the Earth. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... An ephemeris (plural: ephemerides) (from the Greek word ephemeros = daily) is a device giving the positions of astronomical objects in the sky. ...


When pseudoranges have been determined for four satellites, a guess of the receiver's location is calculated. Dividing the speed of light by the distance adjustment required to make the pseudoranges come as close as possible to intersecting results in a guess of the difference between UTC and the time indicated by the receiver's on-board clock. With each combination of four satellites, a geometric dilution of precision (GDOP) vector is calculated, based on the relative sky positions of the satellites used. As more satellites are picked up, pseudoranges from more combinations of four satellites can be processed to add more guesses to the location and clock offset. The receiver then determines which combinations to use and how to calculate the estimated position by determining the weighted average of these positions and clock offsets. After the final location and time are calculated, the location is expressed in a specific coordinate system, e.g. latitude/longitude, using the WGS 84 geodetic datum or a local system specific to a country. A line showing the speed of light on a scale model of Earth and the Moon, taking about 1â…“ seconds to traverse that distance. ... This article pertains to the Global Positioning System. ... This article is about the geographical term. ... Longitude is the east-west geographic coordinate measurement most commonly utilized in cartography and global navigation. ... WGS 84 is the 1984 revision of the World Geodetic System. ...


There are many other alternatives and improvements to this process. If at least four satellites are visible, for example, the receiver can eliminate time from the equations by computing only time differences, then solving for position as the intersection of hyperboloids. Also, with a full constellation and modern receivers, more than four satellites can be seen and received at once. Then all satellite data can be weighted by GDOP, signal to noise, path length through the ionosphere, and other accuracy concerns, and then used in a least squares fit to find a solution. In this case the residuals also give an estimate of the errors. Finally, results from other positioning systems such as GLONASS or the upcoming Galileo can be used in the fit, or used to double-check the result. (By design, these systems use the same bands, so much of the receiver circuitry can be shared, though the decoding is different). In regression analysis, least squares, also known as ordinary least squares analysis, is a method for linear regression that determines the values of unknown quantities in a statistical model by minimizing the sum of the residuals (the difference between the predicted and observed values) squared. ... In statistics and optimization, the concepts of error and residual are easily confused with each other. ... GLONASS GLONASS (Russian ГЛОНАСС; ГЛОбальная НАвигационная Спутниковая Система; Globalnaya Navigatsionnaya Sputnikovaya Sistema. ... The Galileo positioning system is a planned Global Navigation Satellite System, to be built by the European Union (EU) and European Space Agency (ESA). ...


Using the P(Y) code

Calculating a position with the P(Y) signal is generally similar in concept, assuming one can decrypt it. The encryption is essentially a safety mechanism: if a signal can be successfully decrypted, it is reasonable to assume it is a real signal being sent by a GPS satellite.[citation needed] In comparison, civil receivers are highly vulnerable to spoofing since correctly formatted C/A signals can be generated using readily available signal generators. RAIM features do not protect against spoofing, since RAIM only checks the signals from a navigational perspective. Raum the Old. ...


Accuracy and error sources

Sources of User Equivalent Range Errors (UERE)
Source Effect
Ionospheric effects ± 5 meter
Ephemeris errors ± 2.5 meter
Satellite clock errors ± 2 meter
Multipath distortion ± 1 meter
Tropospheric effects ± 0.5 meter
Numerical errors ± 1 meter

The position calculated by a GPS receiver requires the current time, the position of the satellite and the measured delay of the received signal. The position accuracy is primarily dependent on the satellite position and signal delay.


To measure the delay, the receiver compares the bit sequence received from the satellite with an internally generated version. By comparing the rising and trailing edges of the bit transitions, modern electronics can measure signal offset to within about 1% of a bit time, or approximately 10 nanoseconds for the C/A code. Since GPS signals propagate at the speed of light, this represents an error of about 3 meters. A line showing the speed of light on a scale model of Earth and the Moon, taking about 1â…“ seconds to traverse that distance. ...


Position accuracy can be improved by using the higher-chiprate P(Y) signal. Assuming the same 1% bit time accuracy, the high frequency P(Y) signal results in an accuracy of about 30 centimeters.


Electronics errors are one of several accuracy-degrading effects outlined in the table below. When taken together, autonomous civilian GPS horizontal position fixes are typically accurate to about 15 meters (50 ft). These effects also reduce the more precise P(Y) code's accuracy.


Atmospheric effects

Inconsistencies of atmospheric conditions affect the speed of the GPS signals as they pass through the Earth's atmosphere, especially the ionosphere. Correcting these errors is a significant challenge to improving GPS position accuracy. These effects are smallest when the satellite is directly overhead and become greater for satellites nearer the horizon since the path through the atmosphere is longer (see airmass). Once the receiver's approximate location is known, a mathematical model can be used to estimate and compensate for these errors. Air redirects here. ... Relationship of the atmosphere and ionosphere The ionosphere is the uppermost part of the atmosphere, distinguished because it is ionized by solar radiation. ... Horizon. ... Plot of the airmass calculations using the formulas discussed, The airmass in astronomy quantifies the path length that the light from a celestial source must travel through the Earths atmosphere to get to the observatory, relative to that for a source at the zenith. ...


Because ionospheric delay affects the speed of microwave signals differently depending on their frequency — a characteristic known as dispersion - delays measured on two more frequency bands can be used to measure dispersion, and this measurement can then be used to estimate the delay at each frequency[20]. Some military and expensive survey-grade civilian receivers measure the different delays in the L1 and L2 frequencies to measure atmospheric dispersion, and apply a more precise correction. This can be done in civilian receivers without decrypting the P(Y) signal carried on L2, by tracking the carrier wave instead of the modulated code. To facilitate this on lower cost receivers, a new civilian code signal on L2, called L2C, was added to the Block IIR-M satellites, which was first launched in 2005. It allows a direct comparison of the L1 and L2 signals using the coded signal instead of the carrier wave. Dispersion of a light beam in a prism. ... This article or section does not adequately cite its references or sources. ... In telecommunications, modulation is the process of varying a periodic waveform, i. ...


The effects of the ionosphere generally change slowly, and can be averaged over time. The effects for any particular geographical area can be easily calculated by comparing the GPS-measured position to a known surveyed location. This correction is also valid for other receivers in the same general location. Several systems send this information over radio or other links to allow L1-only receivers to make ionospheric corrections. The ionospheric data are transmitted via satellite in Satellite Based Augmentation Systems such as WAAS, which transmits it on the GPS frequency using a special pseudo-random noise sequence (PRN), so only one receiver and antenna are required. Augmentation of a Global Navigation Satellite System (GNSS) is a method of improving system attributes such as accuracy, reliability, and availability through the integrated of external information into the calculation process. ... Contents // Categories: Stub | Aircraft instruments ...


Humidity also causes a variable delay, resulting in errors similar to ionospheric delay, but occurring in the troposphere. This effect both is more localized and changes more quickly than ionospheric effects, and is not frequency dependent. These traits make precise measurement and compensation of humidity errors more difficult than ionospheric effects. The term humidity is usually taken in daily language to refer to relative humidity. ... Atmosphere diagram showing the mesosphere and other layers. ...


Changes in receiver altitude also change the amount of delay, due to the signal passing through less of the atmosphere at higher elevations. Since the GPS receiver computes its approximate altitude, this error is relatively simple to correct, either by applying a function regression or correlating margin of atmospheric error to ambient pressure using a barometric altimeter.


Multipath effects

GPS signals can also be affected by multipath issues, where the radio signals reflect off surrounding terrain; buildings, canyon walls, hard ground, etc. These delayed signals can cause inaccuracy. A variety of techniques, most notably narrow correlator spacing, have been developed to mitigate multipath errors. For long delay multipath, the receiver itself can recognize the wayward signal and discard it. To address shorter delay multipath from the signal reflecting off the ground, specialized antennas (e.g. a choke ring antenna) may be used to reduce the signal power as received by the antenna. Short delay reflections are harder to filter out because they interfere with the true signal, causing effects almost indistinguishable from routine fluctuations in atmospheric delay. PRIMERGY MultiPath PRIMERGY MultiPath supports redundant Fiber Channel paths, the configured connections between server and subsystem that are such an important component of disaster-tolerant servers and clusters. ... Magellan Navigation choke ring antenna and protective radome A tripod mounted choke ring antenna from Trimble Inc with no radome A choke ring antenna is a particular form of omnidirectional antenna for use at high frequencies. ...


Multipath effects are much less severe in moving vehicles. When the GPS antenna is moving, the false solutions using reflected signals quickly fail to converge and only the direct signals result in stable solutions.


Ephemeris and clock errors

While the ephemeris data is transmitted every 30 seconds, the information itself may be up to two hours old. Data up to four hours old is considered valid for calculating positions, but may not indicate the satellites actual position. If a fast TTFF is needed, it is possible to upload valid ephemeris to a receiver, and in addition to setting the time, a position fix can be obtained in under ten seconds. It is feasible to put such ephemeris data on the web so it can be loaded into mobile GPS devices. [21]


The satellite's atomic clocks experience noise and clock drift errors. The navigation message contains corrections for these errors and estimates of the accuracy of the atomic clock. However, they are based on observations and may not indicate the clock's current state. Clock drift refers to several related phenomena where a clock does not run in the exact right speed compared to another clock. ...


These problems tend to be very small, but may add up to a few meters (10s of feet) of inaccuracy.[22]


Selective availability

GPS includes a (currently disabled) feature called Selective Availability (SA) that can introduce intentional, slowly changing random errors of up to a hundred meters (328 ft) into the publicly available navigation signals to confound, for example, the guidance of long range missiles to precise targets. When enabled, the accuracy is still available in the signal, but in an encrypted form that is only available to the United States military, its allies and a few others, mostly government users. Even those who have managed to acquire military GPS receivers would still need to obtain the daily key, whose dissemination is tightly controlled. A key is a piece of information that controls the operation of a cryptography algorithm. ...


Prior to being turned off, SA typically added signal errors of up to about 10 meters (32 ft) horizontally and 30 meters (98 ft) vertically. The inaccuracy of the civilian signal was deliberately encoded so as not to change very quickly. For instance, the entire eastern U.S. area might read 30 m off, but 30 m off everywhere and in the same direction. To improve the usefulness of GPS for civilian navigation, Differential GPS was used by many civilian GPS receivers to greatly improve accuracy. Differential Global Positioning System (DGPS) is an enhancement to Global Positioning System that uses a network of fixed ground based reference stations to broadcast the difference between the positions indicated by the satellite systems and the known fixed positions. ...


During the Gulf War, the shortage of military GPS units and the ready availability of civilian ones caused many troops to buy their own civilian GPS units: their wide use among personnel resulted in a decision to disable Selective Availability. This was ironic, as SA had been introduced specifically for these situations, allowing friendly troops to use the signal for accurate navigation, while at the same time denying it to the enemy—but the assumption underlying this policy was that all U.S. troops and enemy troops would have military-specification GPS receivers and that civilian receivers would not exist in war zones. But since many American soldiers were using civilian devices, SA was also denying the same accuracy to thousands of friendly troops; turning it off (by removing the added-in error) presented a clear benefit to friendly troops. For other uses, see Iraq war (disambiguation). ...


In the 1990s, the FAA started pressuring the military to turn off SA permanently. This would save the FAA millions of dollars every year in maintenance of their own radio navigation systems. The amount of error added was "set to zero"[23] at midnight on May 1, 2000 following an announcement by U.S. President Bill Clinton, allowing users access to the error-free L1 signal. Per the directive, the induced error of SA was changed to add no error to the public signals (C/A code). Clinton's executive order required SA to be set to zero by 2006; it happened in 2000 once the US military developed a new system that provides the ability to deny GPS (and other navigation services) to hostile forces in a specific area of crisis without affecting the rest of the world or its own military systems.[23] FAA redirects here. ... Radio navigation is the application of radio frequencies to determining a position on the earth. ... is the 121st day of the year (122nd in leap years) in the Gregorian calendar. ... Year 2000 (MM) was a leap year starting on Saturday. ... William Jefferson Bill Clinton (born William Jefferson Blythe III[1] on August 19, 1946) was the 42nd President of the United States, serving from 1993 to 2001. ...


Selective Availability is still a system capability of GPS, and error could, in theory, be reintroduced at any time. In practice, in view of the hazards and costs this would induce for US and foreign shipping, it is unlikely to be reintroduced, and various government agencies, including the FAA,[24] have stated that it is not intended to be reintroduced. FAA may refer to: Federal Aviation Administration in the United States Fleet Air Arm in the UK Royal Navy Fuerza Aérea Argentina in Argentina This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...


One interesting side effect of the Selective Availability hardware is the capability to correct the frequency of the GPS cesium and rubidium atomic clocks to an accuracy of approximately 2 × 10-13 (one in five trillion). This represented a significant improvement over the raw accuracy of the clocks.[citation needed] General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Standard atomic weight 132. ... General Name, Symbol, Number rubidium, Rb, 37 Chemical series alkali metals Group, Period, Block 1, 5, s Appearance grey white Standard atomic weight 85. ... An atomic clock is a type of clock that uses an atomic resonance frequency standard as its counter. ...


On 19 September 2007, the United States Department of Defense announced that future GPS III satellites will not be capable of implementing SA,[25] eventually making the policy permanent.[26] is the 262nd day of the year (263rd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... The United States Department of Defense (DOD or DoD) is the federal department charged with coordinating and supervising all agencies and functions of the government relating directly to national security and the military. ...


Relativity

Satellite clocks are slowed by its orbital speed but sped up by its distance out of the earth's gravitational well.
Satellite clocks are slowed by its orbital speed but sped up by its distance out of the earth's gravitational well.

According to the theory of relativity, due to their constant movement and height relative to the Earth-centered inertial reference frame, the clocks on the satellites are affected by their speed (special relativity) as well as their gravitational potential (general relativity). For the GPS satellites, general relativity predicts that the atomic clocks at GPS orbital altitudes will tick more rapidly, by about 45.9 microseconds (μs) per day, because they are in a weaker gravitational field than atomic clocks on Earth's surface. Special relativity predicts that atomic clocks moving at GPS orbital speeds will tick more slowly than stationary ground clocks by about 7.2 μs per day. When combined, the discrepancy is about 38 microseconds per day; a difference of 4.465 parts in 1010.[27]. To account for this, the frequency standard onboard each satellite is given a rate offset prior to launch, making it run slightly slower than the desired frequency on Earth; specifically, at 10.22999999543 MHz instead of 10.23 MHz.[28] Since the atomic clocks on board the GPS satellites are precisely tuned, it makes the system a practical engineering application of the scientific theory of relativity in a real-world environment.-1... For a generally accessible and less technical introduction to the topic, see Introduction to special relativity. ... For a generally accessible and less technical introduction to the topic, see Introduction to special relativity. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... “Nuclear Clock” redirects here. ... A microsecond is an SI unit of time equal to one millionth (10-6) of a second. ...


Sagnac distortion

GPS observation processing must also compensate for the Sagnac effect. The GPS time scale is defined in an inertial system but observations are processed in an Earth-centered, Earth-fixed (co-rotating) system, a system in which simultaneity is not uniquely defined. A Lorentz transformation is thus applied to convert from the inertial system to the ECEF system. The resulting signal run time correction has opposite algebraic signs for satellites in the Eastern and Western celestial hemispheres. Ignoring this effect will produce an east-west error on the order of hundreds of nanoseconds, or tens of meters in position.[29] The Sagnac effect manifests itself in an experimental setup called ring interferometry. ... In physics, an inertial frame of reference, or inertial frame for short (also descibed as absolute frame of reference), is a frame of reference in which the observers move without the influence of any accelerating or decelerating force. ... ECEF stands for Earth-Centered, Earth-Fixed, and is a Cartesian coordinate system used for GPS, and is sometimes known as a conventional terrestrial system[1]. It represents positions as an X, Y, and Z coordinate. ... Simultaneity is the property of two events happening at the same time in at least ONE Reference frame. ... In physics, the Lorentz transformation converts between two different observers measurements of space and time, where one observer is in constant motion with respect to the other. ...


GPS interference and jamming

Natural sources

Since GPS signals at terrestrial receivers tend to be relatively weak, it is easy for other sources of electromagnetic radiation to desensitize the receiver, making acquiring and tracking the satellite signals difficult or impossible. For telecommunications, desensitization is a form of electromagnetic interference where a radio receiver is unable to receive the full strength of a radio signal. ...


Solar flares are one such naturally occurring emission with the potential to degrade GPS reception, and their impact can affect reception over the half of the Earth facing the sun. GPS signals can also be interfered with by naturally occurring geomagnetic storms, predominantly found near the poles of the Earth's magnetic field.[30] GPS signals are also subjected to interference from Van Allen Belt radiation when the satellites pass through the South Atlantic Anomaly. A solar flare observed by Hinode in the G-band. ... A geomagnetic storm is a temporary disturbance of the Earths magnetosphere. ... The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. ... Van Allen belts The Van Allen radiation belt is a torus of energetic charged particles around Earth, trapped by Earths magnetic field. ... The Van Allen radiation belts and the point of the South Atlantic Anomaly. ...


Artificial sources

Metallic features in windshields[31], such as defrosters, or car window tinting films[32] can act as a Faraday cage, degrading reception just inside the car. Entrance to a Faraday room A Faraday cage or Faraday shield is an enclosure formed by conducting material, or by a mesh of such material. ...


Man-made EMI can also disrupt, or jam, GPS signals. In one well documented case, an entire harbor was unable to receive GPS signals due to unintentional jamming caused by a malfunctioning TV antenna preamplifier.[33] Intentional jamming is also possible. Generally, stronger signals can interfere with GPS receivers when they are within radio range, or line of sight. In 2002, a detailed description of how to build a short range GPS L1 C/A jammer was published in the online magazine Phrack.[34] Electromagnetic interference (or EMI, also called radio frequency interference or RFI) is a (usually undesirable) disturbance caused in a radio receiver or other electrical circuit by electromagnetic radiation emitted from an external source. ... Radio jamming is the (usually deliberate) transmission of radio signals that disrupt communications by decreasing the signal to noise ratio. ... Phrack is an underground ezine made by and for hackers that has been around since November 17, 1985. ...


The U.S. government believes that such jammers were used occasionally during the 2001 war in Afghanistan and the U.S. military claimed to destroy a GPS jammer with a GPS-guided bomb during the Iraq War.[35] Such a jammer is relatively easy to detect and locate, making it an attractive target for anti-radiation missiles. The UK Ministry of Defence tested a jamming system in the UK's West Country on 7 and 8 June 2007. [36] United States Government redirects here. ... For other uses of War in Afghanistan, see War in Afghanistan. ... For other uses, see Iraq war (disambiguation). ... HARM on a US Navy F-18C Three ALARMs on an RAF Tornado GR4 An anti-radiation missile is a missile which is designed to detect and home in on the emissions of an enemy radar installation. ...


Some countries allow the use of GPS repeaters to allow for the reception of GPS signals indoors and in obscured locations, however, under EU and UK laws, the use of these is prohibited as the signals can cause interference to other GPS receivers that may receive data from both GPS satellites and the repeater.


Due to the potential for both natural and man-made noise, numerous techniques continue to be developed to deal with the interference. The first is to not rely on GPS as a sole source. According to John Ruley, "IFR pilots should have a fallback plan in case of a GPS malfunction".[37] Receiver Autonomous Integrity Monitoring (RAIM) is a feature now included in some receivers, which is designed to provide a warning to the user if jamming or another problem is detected. The U.S. military has also deployed their Selective Availability / Anti-Spoofing Module (SAASM) in the Defense Advanced GPS Receiver (DAGR). In demonstration videos, the DAGR is able to detect jamming and maintain its lock on the encrypted GPS signals during interference which causes civilian receivers to lose lock.[38] It has been suggested that Air traffic control#Instrument Flight Rules (IFR) be merged into this article or section. ... Raum the Old. ... An SAASM, Selective Availability / Anti-Spoofing Module, is used by military Global Positioning System receivers to allow decryption of precision GPS coordinates, while the accuracy of civilian GPS receivers may be reduced by the US military through Selective Availability. ... The Defense Advanced GPS Receiver (DAGR) The Defense Advanced GPS Receiver (DAGR) is a handheld GPS receiver used by the United States Department of Defense and select foreign military services. ...


Techniques to improve accuracy

Augmentation

Main article: GNSS Augmentation

Augmentation methods of improving accuracy rely on external information being integrated into the calculation process. There are many such systems in place and they are generally named or described based on how the GPS sensor receives the information. Some systems transmit additional information about sources of error (such as clock drift, ephemeris, or ionospheric delay), others provide direct measurements of how much the signal was off in the past, while a third group provide additional navigational or vehicle information to be integrated in the calculation process. Augmentation of a Global Navigation Satellite System (GNSS) or Blended navigation is a method of improving the navigation systems attributes, such as accuracy, reliability, and availability, through the integration of external information into the calculation process. ...


Examples of augmentation systems include the Wide Area Augmentation System, Differential GPS, Inertial Navigation Systems and Assisted GPS. WAAS System Overview The Wide Area Augmentation System (WAAS) is an extremely accurate navigation system developed for civil aviation by the Federal Aviation Administration (FAA), a division of the United States Department of Transportation (DOT). ... Differential Global Positioning System (DGPS) is an enhancement to Global Positioning System that uses a network of fixed ground based reference stations to broadcast the difference between the positions indicated by the satellite systems and the known fixed positions. ... An inertial navigation system measures the position and altitude of a vehicle by measuring the accelerations and rotations applied to the systems inertial frame. ... GPS is a satellite based positioning system. ...


Precise monitoring

The accuracy of a calculation can also be improved through precise monitoring and measuring of the existing GPS signals in additional or alternate ways.


After SA, which has been turned off, the largest error in GPS is usually the unpredictable delay through the ionosphere. The spacecraft broadcast ionospheric model parameters, but errors remain. This is one reason the GPS spacecraft transmit on at least two frequencies, L1 and L2. Ionospheric delay is a well-defined function of frequency and the total electron content (TEC) along the path, so measuring the arrival time difference between the frequencies determines TEC and thus the precise ionospheric delay at each frequency. TEC is an important descriptive quantity for the ionosphere of the Earth. ...


Receivers with decryption keys can decode the P(Y)-code transmitted on both L1 and L2. However, these keys are reserved for the military and "authorized" agencies and are not available to the public. Without keys, it is still possible to use a codeless technique to compare the P(Y) codes on L1 and L2 to gain much of the same error information. However, this technique is slow, so it is currently limited to specialized surveying equipment. In the future, additional civilian codes are expected to be transmitted on the L2 and L5 frequencies (see GPS modernization, below). Then all users will be able to perform dual-frequency measurements and directly compute ionospheric delay errors.


A second form of precise monitoring is called Carrier-Phase Enhancement (CPGPS). The error, which this corrects, arises because the pulse transition of the PRN is not instantaneous, and thus the correlation (satellite-receiver sequence matching) operation is imperfect. The CPGPS approach utilizes the L1 carrier wave, which has a period 1000 times smaller than that of the C/A bit period, to act as an additional clock signal and resolve the uncertainty. The phase difference error in the normal GPS amounts to between 2 and 3 meters (6 to 10 ft) of ambiguity. CPGPS working to within 1% of perfect transition reduces this error to 3 centimeters (1 inch) of ambiguity. By eliminating this source of error, CPGPS coupled with DGPS normally realizes between 20 and 30 centimeters (8 to 12 inches) of absolute accuracy. A pseudorandom number generator (PRNG) is an algorithm to generate a sequence of numbers that approximate the properties of random numbers. ... In statistics, the term cross-correlation is sometimes used to refer to the covariance cov(X, Y) between two random vectors X and Y, in order to distinguish that concept from the covariance of a random vector X, which is understood to be the matrix of covariances between the scalar... Periodicity is the quality of occurring at regular intervals (e. ... In electronics and especially synchronous digital circuits, a clock signal is a signal used to coordinate the actions of two or more circuits. ... Differential Global Positioning System (DGPS) is an enhancement to Global Positioning System that uses a network of fixed ground based reference stations to broadcast the difference between the positions indicated by the satellite systems and the known fixed positions. ...


Relative Kinematic Positioning (RKP) is another approach for a precise GPS-based positioning system. In this approach, determination of range signal can be resolved to a precision of less than 10 centimeters (4 in). This is done by resolving the number of cycles in which the signal is transmitted and received by the receiver. This can be accomplished by using a combination of differential GPS (DGPS) correction data, transmitting GPS signal phase information and ambiguity resolution techniques via statistical tests—possibly with processing in real-time (real-time kinematic positioning, RTK). cm redirects here, alternate uses: cm (disambiguation) A centimetre (symbol cm; American spelling: centimeter) is an SI unit of length. ... Real Time Kinematic (RTK) land survey is based on a differential use of carrier phase measurements of the GPS, Glonass and/or Galileo signals where a single reference station provides the real-time corrections of even to a centimetre level of accuracy. ...


GPS time and date

While most clocks are synchronized to Coordinated Universal Time (UTC), the atomic clocks on the satellites are set to GPS time. The difference is that GPS time is not corrected to match the rotation of the Earth, so it does not contain leap seconds or other corrections which are periodically added to UTC. GPS time was set to match Coordinated Universal Time (UTC) in 1980, but has since diverged. The lack of corrections means that GPS time remains at a constant offset (19 seconds) with International Atomic Time (TAI). Periodic corrections are performed on the on-board clocks to correct relativistic effects and keep them synchronized with ground clocks.[citation needed] UTC redirects here. ... “Nuclear Clock” redirects here. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... UTC redirects here. ... International Atomic Time (TAI, from the French name Temps Atomique International) is a high-precision atomic time standard that tracks proper time on Earths geoid. ...


The GPS navigation message includes the difference between GPS time and UTC, which as of 2006 is 14 seconds due to the leap second added to UTC December 31st of 2005. Receivers subtract this offset from GPS time to calculate UTC and specific timezone values. New GPS units may not show the correct UTC time until after receiving the UTC offset message. The GPS-UTC offset field can accommodate 255 leap seconds (eight bits) which, at the current rate of change of the Earth's rotation, is sufficient to last until the year 2330.[citation needed] 2006 is a common year starting on Sunday of the Gregorian calendar. ...


As opposed to the year, month, and day format of the Gregorian calendar, the GPS date is expressed as a week number and a day-of-week number. The week number is transmitted as a ten-bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years). GPS week zero started at 00:00:00 UTC (00:00:19 TAI) on January 6, 1980 and the week number became zero again for the first time at 23:59:47 UTC on August 21, 1999 (00:00:19 TAI on August 22, 1999). To determine the current Gregorian date, a GPS receiver must be provided with the approximate date (to within 3,584 days) to correctly translate the GPS date signal. To address this concern the modernized GPS navigation messages use a 13-bit field, which only repeats every 8,192 weeks (157 years), and will not return to zero until near the year 2137.[citation needed] For the calendar of religious holidays and periods, see liturgical year. ... This article is about the unit of information. ... is the 6th day of the year in the Gregorian calendar. ... Year 1980 (MCMLXXX) was a leap year starting on Tuesday (link displays the 1980 Gregorian calendar). ... is the 233rd day of the year (234th in leap years) in the Gregorian calendar. ... Events of 2008: (EMILY) Me Lesley and MIley are going to China! This article is about the year. ... is the 234th day of the year (235th in leap years) in the Gregorian calendar. ... Events of 2008: (EMILY) Me Lesley and MIley are going to China! This article is about the year. ... (Redirected from 2137) (21st century - 22nd century - 23rd century - other centuries) The twenty-second century comprises the years 2101 to 2200. ...


GPS modernization

Main article: GPS modernization

Having reached the program's requirements for Full Operational Capability (FOC) on July 17, 1995,[39] the GPS completed its original design goals. However, additional advances in technology and new demands on the existing system led to the effort to modernize the GPS. Announcements from the U.S. Vice President and the White House in 1998 initiated these changes, and in 2000 the U.S. Congress authorized the effort, referring to it as GPS III. The United States Global Positioning System (GPS), having reached Fully Operational Capability on July 17, 1995[1] completed its original design goals. ... is the 198th day of the year (199th in leap years) in the Gregorian calendar. ... Year 1995 (MCMXCV) was a common year starting on Sunday. ... Dick Cheney 46th and current Vice President (2001- ) The Vice President of the United States is the second-highest executive official of the United States government, the person who is a heartbeat from the presidency. ... For other uses, see White House (disambiguation). ... Year 1998 (MCMXCVIII) was a common year starting on Thursday (link will display full 1998 Gregorian calendar). ... Year 2000 (MM) was a leap year starting on Saturday. ... The Congress of the United States is the legislative branch of the federal government of the United States of America. ...


The project aims to improve the accuracy and availability for all users and involves new ground stations, new satellites, and four additional navigation signals. New civilian signals are called L2C, L5 and L1C; the new military code is called M-Code. Initial Operational Capability (IOC) of the L2C code is expected in 2008.[40] A goal of 2013 has been established for the entire program, with incentives offered to the contractors if they can complete it by 2011 (See GPS signals). The United States Global Positioning System (GPS), having reached Fully Operational Capability on July 17, 1995[1] completed its original design goals. ... L5 or L-5 may be: The fifth lumbar vertebra in Human anatomy The fifth Lagrange Point in an astronomical Solar System The filk song Home on Lagrange (The L5 Song) The Gibson L5 electric guitar in Musical instruments The french female pop music group L5 This page expands a... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance with the Gregorian calendar. ... 2013 (MMXIII) will be a common year starting on Tuesday of the Gregorian calendar. ... The Global Positioning System (GPS) satellites broadcast a variety of signals to receivers (termed the user segment of the system) to enable the determination of location and synchronized time. ...


Applications

The Global Positioning System, while originally a military project, is considered a dual-use technology, meaning it has significant applications for both the military and the civilian industry.


Military

The military applications of GPS span many purposes:

  • Navigation: GPS allows soldiers to find objectives in the dark or in unfamiliar territory, and to coordinate the movement of troops and supplies. The GPS-receivers commanders and soldiers use are respectively called the Commanders Digital Assistant and the Soldier Digital Assistant.[41][42][43][44]
  • Target tracking: Various military weapons systems use GPS to track potential ground and air targets before they are flagged as hostile.[citation needed] These weapon systems pass GPS co-ordinates of targets to precision-guided munitions to allow them to engage the targets accurately. Military aircraft, particularly those used in air-to-ground roles use GPS to find targets (for example, gun camera video from AH-1 Cobras in Iraq show GPS co-ordinates that can be looked up in Google Earth[citation needed]).
  • Missile and projectile guidance: GPS allows accurate targeting of various military weapons including ICBMs, cruise missiles and precision-guided munitions. Artillery projectiles with embedded GPS receivers able to withstand accelerations of 12,000G have been developed for use in 155 mm howitzers.[45]
  • Search and Rescue: Downed pilots can be located faster if they have a GPS receiver.
  • Reconnaissance and Map Creation: The military use GPS extensively to aid mapping and reconnaissance.
  • The GPS satellites also carry a set of nuclear detonation detectors consisting of an optical sensor (Y-sensor), an X-ray sensor, a dosimeter, and an Electro-Magnetic Pulse (EMP) sensor (W-sensor) which form a major portion of the United States Nuclear Detonation Detection System.[46][47]

BOLT-117 laser guided bomb Precision-guided munitions (smart munitions or smart bombs) are self-guiding weapons intended to maximize damage to the target while minimizing collateral damage. Because the damage effects of an explosive weapon scale as a power law with distance, quite modest improvements in accuracy (and hence... A ground-attack aircraft is an aircraft that is designed to operate in direct support of ground forces such as infantry, tanks and other fighting vehicles. ... Gun cameras are cameras used in military vehicles to help measure tactical effectiveness. ... The Bell AH-1 Cobra is an attack helicopter. ... Google Earth is a virtual globe program that was originally called Earth Viewer and was created by Keyhole, Inc. ... A Minuteman III missile soars after a test launch. ... A Taurus KEPD 350 cruise missile of the German Luftwaffe A cruise missile is a guided missile which carries an explosive payload and uses a lifting wing and a propulsion system, usually a jet engine, to allow sustained flight; it is essentially a flying bomb. ... BOLT-117 laser guided bomb Precision-guided munitions (smart munitions or smart bombs) are self-guiding weapons intended to maximize damage to the target while minimizing collateral damage. Because the damage effects of an explosive weapon scale as a power law with distance, quite modest improvements in accuracy (and hence... For other uses, see Artillery (disambiguation). ... A projectile is any object sent through space by the application of a force. ... The term g force or gee force refers to the symbol g, the force of acceleration due to gravity at the earths surface. ... 19th century 12 pounder (5 kg) mountain howitzer displayed by the National Park Service at Fort Laramie in Wyoming, USA A howitzer is a type of artillery piece that is characterized by a relatively short barrel and the use of comparatively small explosive charges to propel projectiles at trajectories with... Mixed reconnaissance patrol of the Polish Home Army and the Soviet Red Army during Operation Tempest, 1944 Reconnaissance is the military term for the active gathering of information about an enemy, or other conditions, by physical observation. ... Vela was the name of a group of satellites developed as the Vela Hotel element of Project Vela by the United States to monitor compliance with the 1963 Partial Test Ban Treaty by the Soviet Union, and other nuclear-capable states. ...

Civilian

See also: GNSS applications and GPS navigation device
This antenna is mounted on the roof of a hut containing a scientific experiment needing precise timing.
This antenna is mounted on the roof of a hut containing a scientific experiment needing precise timing.

Many civilian applications benefit from GPS signals, using one or more of three basic components of the GPS: absolute location, relative movement, and time transfer. A Global Navigation Satellite System (GNSS) receiver, which may use the GPS, GLONASS, or Beidou system, is capable of being used in many applications. ... Download high resolution version (760x1288, 180 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (760x1288, 180 KB) Wikipedia does not have an article with this exact name. ...


The ability to determine the receiver's absolute location allows GPS receivers to perform as a surveying tool or as an aid to navigation. The capacity to determine relative movement enables a receiver to calculate local velocity and orientation, useful in vessels or observations of the Earth. Being able to synchronize clocks to exacting standards enables time transfer, which is critical in large communication and observation systems. An example is CDMA digital cellular. Each base station has a GPS timing receiver to synchronize its spreading codes with other base stations to facilitate inter-cell hand off and support hybrid GPS/CDMA positioning of mobiles for emergency calls and other applications. Finally, GPS enables researchers to explore the Earth environment including the atmosphere, ionosphere and gravity field. GPS survey equipment has revolutionized tectonics by directly measuring the motion of faults in earthquakes. Surveyor at work with a leveling instrument. ... This article is about determination of position and direction on or above the surface of the earth. ... General Information Generically (as a multiplexing scheme), code division multiple access (CDMA) is any use of any form of spread spectrum by multiple transmitters to send to the same receiver on the same frequency channel at the same time without harmful interference. ... Enhanced 911 service or E911 service is a North American telephone network feature that automatically associates the physical address with the calling partys telephone number. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... Global earthquake epicenters, 1963–1998. ...


To help prevent civilian GPS guidance from being used in an enemy's military or improvised weaponry, the US Government controls the export of civilian receivers. A US-based manufacturer cannot generally export a GPS receiver unless the receiver contains limits restricting it from functioning when it is simultaneously (1) at an altitude above 18 kilometers (60,000 ft) and (2) traveling at over 515 m/s (1,000 knots).[48] These parameters are well above the operating characteristics of the typical cruise missile, but would be characteristic of the reentry vehicle from a ballistic missile. A Taurus KEPD 350 cruise missile of the German Luftwaffe A cruise missile is a guided missile which carries an explosive payload and uses a lifting wing and a propulsion system, usually a jet engine, to allow sustained flight; it is essentially a flying bomb. ... This page is a candidate for speedy deletion. ... Diagram of V-2, the first ballistic missile. ...


GPS functionality has now started to move into mobile phones en masse. The first handsets with integrated GPS were launched already in the late 1990’s, and were available for broader consumer availability on networks such as those run by Nextel, Sprint and Verizon in 2002 in response to US FCC mandates for handset positioning in emergency calls. Capabilities for access by third party software developers to these features were slower in coming, with Nextel opening those APIs up upon launch to any developer, Sprint following in 2006, and Verizon soon thereafter.


History

The design of GPS is based partly on the similar ground-based radio navigation systems, such as LORAN and the Decca Navigator developed in the early 1940s, and used during World War II. Additional inspiration for the GPS came when the Soviet Union launched the first Sputnik in 1957. A team of U.S. scientists led by Dr. Richard B. Kershner were monitoring Sputnik's radio transmissions. They discovered that, because of the Doppler effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them. They realized that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion. LORAN (LOng RAnge Navigation) is a terrestrial navigation system using low frequency radio transmitters that use the time interval between radio signals received from three or more stations to determine the position of a ship or aircraft. ... Decca Navigator Mk 12 The Decca Navigator System was a hyperbolic low frequency radio navigation system (also known as multilateration) that was first deployed during World War II when the Allied forces needed a system which could be used to achieve accurate landings. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... Sputnik redirects here. ... A source of waves moving to the left. ...


The first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. Using a constellation of five satellites, it could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology the GPS relies upon. In the 1970s, the ground-based Omega Navigation System, based on signal phase comparison, became the first world-wide radio navigation system. Operational Transit satellite The TRANSIT system, also known as NAVSAT (for Navy Navigation Satellite System), was the first satellite navigation system to be used operationally. ... USN redirects here. ... The Timation satellites were conceived, developed, and launched by the Naval Research Laboroatory in Washington, D.C. begining in 1964. ... Omega is the name for the first truly global radionavigation system for aircraft operated by the United States of America in cooperation with six partner nations. ...


The first experimental Block-I GPS satellite was launched in February 1978.[40] The GPS satellites were initially manufactured by Rockwell International (now part of Boeing) and are now manufactured by Lockheed Martin (IIR/IIR-M) and Boeing (IIF). Rockwell International was the ultimate incarnation of a series of companies under the sphere of influence of Willard Rockwell, who had made his fortune after the invention and successful launch of a new bearing system for truck axles in 1919. ... The Boeing Company (NYSE: BA, TYO: 7661) is a major aerospace and defense corporation, originally founded by William Edward Boeing. ... Lockheed/BAE/Northrop F-35 Lockheed Trident missile C-130 Hercules; in production since the 1950s, now as the C-130J Lockheed Martin (NYSE: LMT) is an aerospace manufacturer formed in 1995 by the merger of Lockheed Corporation with Martin Marietta. ... The Boeing Company (NYSE: BA, TYO: 7661) is a major aerospace and defense corporation, originally founded by William Edward Boeing. ...


Timeline

  • In 1972, the US Air Force Central Inertial Guidance Test Facility (Holloman AFB) conducted developmental flight tests of two prototype GPS receivers over White Sands Missile Range, using ground-based pseudo-satellites.
  • In 1978 the first experimental Block-I GPS satellite was launched.
  • In 1983, after Soviet interceptor aircraft shot down the civilian airliner KAL 007 that strayed into restricted Soviet airspace due to navigational errors, killing all 269 people on board, U.S. President Ronald Reagan announced that the GPS would be made available for civilian uses once it was completed.[49][50]
  • By 1985, ten more experimental Block-I satellites had been launched to validate the concept.
  • On February 14, 1989, the first modern Block-II satellite was launched.
  • In 1992, the 2nd Space Wing, which originally managed the system, was de-activated and replaced by the 50th Space Wing.
  • By December 1993 the GPS achieved initial operational capability.[51]
  • By January 17, 1994 a complete constellation of 24 satellites was in orbit.
  • Full Operational Capability was declared by NAVSTAR in April 1995.
  • In 1996, recognizing the importance of GPS to civilian users as well as military users, U.S. President Bill Clinton issued a policy directive[52] declaring GPS to be a dual-use system and establishing an Interagency GPS Executive Board to manage it as a national asset.
  • In 1998, U.S. Vice President Al Gore announced plans to upgrade GPS with two new civilian signals for enhanced user accuracy and reliability, particularly with respect to aviation safety.
  • On May 2, 2000 "Selective Availability" was discontinued as a result of the 1996 executive order, allowing users to receive a non-degraded signal globally.
  • In 2004, the United States Government signed a historic agreement with the European Community establishing cooperation related to GPS and Europe's planned Galileo system.
  • In 2004, U.S. President George W. Bush updated the national policy, replacing the executive board with the National Space-Based Positioning, Navigation, and Timing Executive Committee.
  • November 2004, QUALCOMM announced successful tests of Assisted-GPS for mobile phones.[53]
  • In 2005, the first modernized GPS satellite was launched and began transmitting a second civilian signal (L2C) for enhanced user performance.
  • On September 14, 2007, the aging mainframe-based Ground Segment Control System was transitioned to the new Architecture Evolution Plan.[54]
  • The most recent launch was on March 15, 2008.[55] The oldest GPS satellite still in operation was launched on July 4, 1991, and became operational on August 30, 1991.[56]
Satellite numbers[57][58]
Block Launch Period Satellites launched Currently in service
I 1978–1985 10+11 0
II 1985–1990 9 0
IIA 1990–1997 19 13
IIR 1997–2004 12+11 12
IIR-M 2005–2008 6+22 6
IIF 2009– 0+102 0
Total 58+21+122 31
1Failed
2In preparation.
(Last update: 12 April 2008)

The MiG-25 is a Russian interceptor that was the mainstay of the Soviet air defence. ... Korean Air Lines Flight 007, also known as KAL 007 or KE007, was a Korean Air Lines civilian airliner shot down by Soviet jet interceptors on September 1, 1983 just west of Sakhalin island. ... Reagan redirects here. ... is the 45th day of the year in the Gregorian calendar. ... Year 1989 (MCMLXXXIX) was a common year starting on Sunday (link displays 1989 Gregorian calendar). ... The 50th Space Wing (50 SW) is a wing of the United States Air Force under the major command of Air Force Space Command (AFSPC). ... is the 17th day of the year in the Gregorian calendar. ... Year 1994 (MCMXCIV) The year 1994 was designated as the International Year of the Family and the International Year of the Sport and the Olympic Ideal by the United Nations. ... William Jefferson Bill Clinton (born William Jefferson Blythe III[1] on August 19, 1946) was the 42nd President of the United States, serving from 1993 to 2001. ... The Interagency GPS Executive Board (IGEB) was an agency of the United States Federal Government that sought to integrate the needs and desires of various governmental agencies into formal Global Positioning System Planning. ... This article is about the former Vice President of the United States. ... is the 122nd day of the year (123rd in leap years) in the Gregorian calendar. ... Year 2000 (MM) was a leap year starting on Saturday. ... George Walker Bush (born July 6, 1946) is the forty-third and current President of the United States of America, originally inaugurated on January 20, 2001. ... Qualcomm (NASDAQ: QCOM) is a wireless telecommunications research and development company based in San Diego, California. ... GPS is a satellite based positioning system. ... A stylised representation of a mobile phone A mobile phone is a device which behaves as a normal telephone whilst being able to move over a wide area ( cordless phone which acts as a telephone only within a limited range). ... is the 257th day of the year (258th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 185th day of the year (186th in leap years) in the Gregorian calendar. ... Year 1991 (MCMXCI) was a common year starting on Tuesday (link will display full calendar) of the Gregorian Calendar. ... is the 242nd day of the year (243rd in leap years) in the Gregorian calendar. ... Year 1991 (MCMXCI) was a common year starting on Tuesday (link will display full calendar) of the Gregorian Calendar. ...

Awards

Two GPS developers received the National Academy of Engineering Charles Stark Draper Prize for 2003: Founded in 1964, the National Academy of Engineering (NAE) in the United States provides engineering leadership in service to the nation. ... The Charles Stark Draper Prize is awarded by the National Academy of Engineering for the advancement of engineering and the education of the public about engineering. ...

One GPS developer, Roger L. Easton, received the National Medal of Technology on February 13, 2006 at the White House.[59] An American Physicist and Electrical Engineer, credited (along with Bradford Parkinson) with the development of the Global Positioning System (GPS). ... The Aerospace Corporation is a nonprofit engineering and science organization headquartered in El Segundo, California. ... Look up engineer in Wiktionary, the free dictionary. ... “MIT” redirects here. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... LORAN (LOng RAnge Navigation) is a terrestrial navigation system using low frequency radio transmitters that use the time interval between radio signals received from three or more stations to determine the position of a ship or aircraft. ... Dr Bradford Parkinson is a professor at Stanford University and is credited as the co-inventor of the Global Positioning System. ... Six F-16 Fighting Falcons with the U.S. Air Force Thunderbirds aerial demonstration team fly in delta formation in front of the Empire State Building. ... Astronautics is the branch of engineering that deals with machines designed to work outside of Earths atmosphere, whether manned or unmanned. ... Stanford redirects here. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... The National Medal of Technology is an honor granted by the President of the United States to inventors and innovators that have made significant contributions to the development of new and important technology. ... is the 44th day of the year in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... For other uses, see White House (disambiguation). ...


On February 10, 1993, the National Aeronautic Association selected the Global Positioning System Team as winners of the 1992 Robert J. Collier Trophy, the most prestigious aviation award in the United States. This team consists of researchers from the Naval Research Laboratory, the U.S. Air Force, the Aerospace Corporation, Rockwell International Corporation, and IBM Federal Systems Company. The citation accompanying the presentation of the trophy honors the GPS Team "for the most significant development for safe and efficient navigation and surveillance of air and spacecraft since the introduction of radio navigation 50 years ago." is the 41st day of the year in the Gregorian calendar. ... Year 1993 (MCMXCIII) was a common year starting on Friday (link will display full 1993 Gregorian calendar). ... The primary mission of NAA is the advancement of the art, sport, and science of aviation and space flight by fostering opportunities to participate fully in aviation activities and by promoting public understanding of the importance of aviation and space flight to the United States. ... The Collier Trophy is the most prestigious award in the aviation field, given once a year to those that have made the greatest achievement in aeronautics or astronautics in America, with respect to improving the performance, efficiency, and safety of air or space vehicles, the value of which has been... -1... Seal of the Air Force. ... The Aerospace Corporation is a nonprofit engineering and science organization headquartered in El Segundo, California. ... Rockwell International was the ultimate incarnation of a series of companies under the sphere of influence of Willard Rockwell, who had made his fortune after the invention and successful launch of a new bearing system for truck axles in 1919. ... For other uses, see IBM (disambiguation) and Big Blue. ...


Other systems

Other satellite navigation systems in use or various states of development include: For the global navigation satellite system operated by Russia, see GLONASS. Global Navigation Satellite System (GNSS) is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. ...

The Beidou navigation system is a project by the Peoples Republic of China to develop an independent satellite navigation system. ... The COMPASS system (also known as Beidou-2) is a project by China to develop an independent satellite navigation system. ... The Galileo positioning system is a planned Global Navigation Satellite System, to be built by the European Union (EU) and European Space Agency (ESA). ... GLONASS GLONASS (Russian ГЛОНАСС; ГЛОбальная НАвигационная Спутниковая Система; Globalnaya Navigatsionnaya Sputnikovaya Sistema. ... The Indian Regional Navigational Satellite System (IRNSS) is a proposed autonomous regional satellite navigation system to be constructed and controlled by the Indian government. ... There are very few or no other articles that link to this one. ...

See also

Nautical Portal

Image File history File links No higher resolution available. ... GPS is a satellite based positioning system. ... Bowditchs American Practical Navigator was written by Nathaniel Bowditch and published in 1802 and has remained the textbook of American sailors. ... The goals of the Degree Confluence Project are to visit each of the latitude and longitude integer degree intersections on Earth, and post photographs of each location on the World Wide Web. ... Exchangeable image file format (Exif) is a specification for the image file format used by digital cameras. ... Geotagging, sometimes referred to as Geocoding, is the process of adding geographical identification metadata to various media such as websites, RSS feeds, or images and is a form of geospatial metadata. ... A Geocache in Germany Geocaching is an outdoor treasure-hunting game in which the participants use a Global Positioning System (GPS) receiver or other navigational techniques to hide and seek containers (called geocaches or caches) anywhere in the world. ... A method of drawing that uses GPS to create large scale drawings. ... This article does not cite any references or sources. ... GSM localization is the use of multilateration to determine the location of GSM mobile phones, usually with the intent to locate the user. ... GPS/INS refers to the use of GPS satellite signals to correct or calibrate a solution from an Inertial Navigation System. ... An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntax constraints imposed by XML itself. ... There are very few or no other articles that link to this one. ... A GPS Phone is a mobile phone with an integrated GPS system which can be used for traveling and tracking purposes. ... The ID Sniper rifle is an art project, a fictional, hoax weapon devised by Jakob Boeskov, a Danish artist from New York and Danish industrial designer Kristian von Bengtson. ... OpenStreetMap of Chester OpenStreetMap is a collaborative, project create Free maps using data from portable GPS devices. ... Free content is any kind of functional work, artwork, or other creative content upon which no legal restriction has been placed that significantly interferes with peoples freedom to use, understand, redistribute, improve, and share the content. ... A point of interest, or POI, is a specific point location that someone may find useful or interesting. ... Radio navigation is the application of radio frequencies to determining a position on the earth. ... Raum the Old. ... In Norse Mythology, Sigi is a one of the sons of Odin. ... The term telematics is used in a number of ways: The integrated use of telecommunications and informatics, also known as ICT (Information and Communications Technology). ... A taxi in Kyoto, equipped with GPS navigation system An automotive navigation system is a satellite navigation system designed for use in automobiles. ... Height Modernization is the name of a series of state-by-state programs recently begun by the United States National Geodetic Survey, a division of the National Oceanic and Atmospheric Administration. ... NextGen or Next Generation Air Transportation System is the name given to the project which is set to completely overhaul the national airspace system(NAS). ... Standing at B, you want to know your location relative to the reference points P1, P2, and P3. ... Skyhook Wireless is a service for determining geographical location by looking up the MAC Addresses of nearby Wireless Access Point in a proprietary database and inferring the position of the device by the relative strength of the signals. ...

References

  1. ^ Parkinson, B.W. (1996), Global Positioning System: Theory and Applications, chap. 1: Introduction and Heritage of NAVSTAR, the Global Positioning System. pp. 3-28, American Institute of Aeronautics and Astronautics, Washington, D.C.
  2. ^ a b GPS Overview from the NAVSTAR Joint Program Office. Accessed December 15, 2006.
  3. ^ "History of GPS", usinfo.state.gov, February 3, 2006. 
  4. ^ HowStuffWorks: How GPS Receivers WorkAccessed May 14, 2006.
  5. ^ globalsecurity.org [1].
  6. ^ P. Daly. Navstar GPS and GLONASS: global satellite navigation systems. IEEE.
  7. ^ Dana, Peter H. GPS Orbital Planes. August 8, 1996.
  8. ^ What the Global Positioning System Tells Us about Relativity. Accessed January 2, 2007.
  9. ^ USCG Navcen: GPS Frequently Asked Questions. Accessed January 3, 2007.
  10. ^ Agnew, D.C. and Larson, K.M. (2007). "Finding the repeat times of the GPS constellation". GPS Solutions 11: 71--76. Springer. doi:10.1007/s10291-006-0038-4.  This article from author's web site, with minor correction.
  11. ^ Massatt, Paul and Brady, Wayne. "Optimizing performance through constellation management", Crosslink, Summer 2002, pages 17-21.
  12. ^ The additional stations are: Washington, DC, England, Argentina, Ecuador, Bahrain and Australia. Source: US Coast Guard General GPS News 9-9-05
  13. ^ USNO NAVSTAR Global Positioning System. Accessed May 14, 2006.
  14. ^ Note that though there are many receiver manufacurers, they almost all use one of the chipsets produced for this purpose. An example: GPS Receiver Chip Performance Survey. GPS Technology Reviews.
  15. ^ NMEA NMEA 2000
  16. ^ Interface Specification IS-GPS-200, Revision D: Navstar GPS Space Segment/Navigation User Interfaces. Navstar GPS Joint Program Office. Page 103.
  17. ^ First GPS IIF Satellite Undergoes Environmental Testing. GPS World. November 5, 2007.
  18. ^ How Does GPS Work?
  19. ^ AN02 Network Assistance (HTML). Retrieved on 2007-09-10.
  20. ^ The same principle, and the math behind it, can be found in descriptions of pulsar timing by astronomers.
  21. ^ http://www.tdc.co.uk/index.php?key=ephemeris Ephemeris Server Example
  22. ^ UNit 1 - Introduction to GPS.
  23. ^ a b Statement by the President regarding the United States' Decision to Stop Degrading Global Positioning System Accuracy. Office of Science and Technology Policy (May 1, 2000). Retrieved on 2007-12-17.
  24. ^ GNSS - Frequently Asked Questions - GPS: Will SA ever be turned back on?. FAA (June 13, 2007). Retrieved on 2007-12-17.
  25. ^ DoD Permanently Discontinues Procurement Of Global Positioning System Selective Availability. DefenseLink (September 18, 2007). Retrieved on 2008-02-20.
  26. ^ Selective Availability. National space-based Positioning, Navigation, and Timing Executive Committee. Retrieved on 2008-02-20.
  27. ^ Rizos, Chris. University of New South Wales. GPS Satellite Signals. 1999.
  28. ^ The Global Positioning System by Robert A. Nelson Via Satellite, November 1999
  29. ^ Ashby, Neil Relativity and GPS. Physics Today, May 2002.
  30. ^ Space Environment Center. SEC Navigation Systems GPS Page. August 26, 1996.
  31. ^ I-PASS Mounting for Vehicles with Special Windshield Features.
  32. ^ 3M Automotive Films.. Note that the 'Color Stable' films are specifically described as not interfering with satellite signals.
  33. ^ The hunt for an unintentional GPS jammer. GPS World. January 1, 2003.
  34. ^ Low Cost and Portable GPS Jammer. Phrack issue 0x3c (60), article 13]. Published December 28, 2002.
  35. ^ American Forces Press Service. Centcom charts progress. March 25, 2003.
  36. ^ MoD's tests will send satnav haywire so take a road atlas | the Daily Mail
  37. ^ Ruley, John. AVweb. GPS jamming. February 12, 2003.
  38. ^ Commercial GPS Receivers: Facts for the Warfighter. Hosted at the Joint Chiefs website, linked by the USAF's GPS Wing DAGR program website. Accessed on 10 April, 2007
  39. ^ US Coast Guard news release. Global Positioning System Fully Operational
  40. ^ a b Hydrographic Society Journal. Developments in Global Navigation Satellite Systems. Issue #104, April 2002. Accessed April 5, 2007.
  41. ^ http://peosoldier.army.mil/factsheets/SWAR_LW_DBCS.pdf Commanders Digital Assistant explanation and photo
  42. ^ Latest version Commanders Digital Assistant
  43. ^ http://www.army-technology.com/contractors/computers/lago/lago6.html Soldier Digital Assistant explanation and photo
  44. ^ http://www.gcn.com/print/22_20/22893-1.html Commanders and Soldiers' GPS-receivers
  45. ^ XM982 Excalibur Precision Guided Extended Range Artillery Projectile. GlobalSecurity.org (2007-05-29). Retrieved on 2007-09-26.
  46. ^ Sandia National Laboratory's Nonproliferation programs and arms control technology.
  47. ^ Dr. Dennis D. McCrady. The GPS Burst Detector W-Sensor. Sandia National Laboratories.
  48. ^ Arms Control Association.Missile Technology Control Regime. Accessed May 17, 2006.
  49. ^ Dietrich Schroeer, Mirco Elena (2000). Technology Transfer. Ashgate, p80. ISBN 075462045X. Retrieved on 2008-05-25. 
  50. ^ Michael Russell Rip, James M. Hasik (2002). The Precision Revolution: GPS and the Future of Aerial Warfare. Naval Institute Press. ISBN 1557509735. Retrieved on 2008-05-25. 
  51. ^ United States Department of Defense. Announcement of Initial Operational Capability. December 8, 1993.
  52. ^ National Archives and Records Administration. U.S. Global Positioning System Policy. March 29, 1996.
  53. ^ 3g.co.uk
  54. ^ losangeles.af.mil
  55. ^ sidt.gpsworld.com
  56. ^ United States Naval Observatory. GPS Constellation Status. Accessed on October 17, 2007.
  57. ^ United States Naval Observatory ((USNO) - Block II Satellite Information.
  58. ^ GPS constellation status. Russian Space Agency. April 9, 2008
  59. ^ United States Naval Research Laboratory. National Medal of Technology for GPS. November 21, 2005

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A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Aerial view of USNO. The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States. ... is the 134th day of the year (135th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... NMEA 0183 (or NMEA for short) is a combined electrical and data specification for communication between marine electronics and also, more generally, GPS receivers. ... is the 309th day of the year (310th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 253rd day of the year (254th in leap years) in the Gregorian calendar. ... Dispersion of a light beam in a prism. ... Congress established Office of Science and Technology Policy (OSTP) in 1976 with a broad mandate to advise the President and others within the Executive Office of the President on the effects of science and technology on domestic and international affairs. ... is the 121st day of the year (122nd in leap years) in the Gregorian calendar. ... Year 2000 (MM) was a leap year starting on Saturday. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... December 17 is the 351st day of the year (352nd in leap years) in the Gregorian calendar. ... is the 164th day of the year (165th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... December 17 is the 351st day of the year (352nd in leap years) in the Gregorian calendar. ... is the 261st day of the year (262nd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance with the Gregorian calendar. ... is the 51st day of the year in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance with the Gregorian calendar. ... is the 51st day of the year in the Gregorian calendar. ... The University of New South Wales, also known as UNSW or colloquially as New South, is a university situated in Kensington, a suburb in Sydney, New South Wales, Australia. ... Physics Today magazine, created in 1948, is the flagship publication of The American Institute of Physics. ... The Space Environment Center (SEC) is a laboratory in the National Oceanic and Atmospheric Administration (NOAA)/Office of Oceanic and Atmospheric Research (OAR). ... is the 238th day of the year (239th in leap years) in the Gregorian calendar. ... Year 1996 (MCMXCVI) was a leap year starting on Monday (link will display full 1996 Gregorian calendar). ... is the 1st day of the year in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... Phrack is an underground ezine made by and for hackers that has been around since November 17, 1985. ... is the 362nd day of the year (363rd in leap years) in the Gregorian calendar. ... Also see: 2002 (number). ... is the 84th day of the year (85th in leap years) in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... is the 43rd day of the year in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... is the 95th day of the year (96th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... GlobalSecurity. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 149th day of the year (150th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 269th day of the year (270th in leap years) in the Gregorian calendar. ... is the 137th day of the year (138th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance with the Gregorian calendar. ... is the 145th day of the year (146th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance with the Gregorian calendar. ... is the 145th day of the year (146th in leap years) in the Gregorian calendar. ... The United States Department of Defense (DOD or DoD) is the federal department charged with coordinating and supervising all agencies and functions of the government relating directly to national security and the military. ... is the 342nd day of the year (343rd in leap years) in the Gregorian calendar. ... Year 1993 (MCMXCIII) was a common year starting on Friday (link will display full 1993 Gregorian calendar). ... The National Archives building in Washington, DC The United States National Archives and Records Administration (NARA) is an independent agency of the United States federal government charged with preserving and documenting government and historical records. ... is the 88th day of the year (89th in leap years) in the Gregorian calendar. ... Year 1996 (MCMXCVI) was a leap year starting on Monday (link will display full 1996 Gregorian calendar). ... Aerial view of USNO. The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States. ... is the 290th day of the year (291st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 99th day of the year (100th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance with the Gregorian calendar. ... Bust of Thomas Edison at the front gate of the Naval Research Laboratory. ... is the 325th day of the year (326th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ...

External links

Government links

  • GPS.gov — General public education website created by the U.S. Government
  • National Space-Based PNT Executive Committee—Established in 2004 to oversee management of GPS and GPS augmentations at a national level.
  • USCG Navigation Center—Status of the GPS constellation, government policy, and links to other references. Also includes satellite almanac data.
  • Air Force Space Command GPS Operations Center homepage
  • The GPS Program Office (GPS Wing)—Responsible for designing and acquiring the system on behalf of the US Government.
  • U.S. Naval Observatory's GPS constellation status
  • U.S. Army Corps of Engineers manual: NAVSTAR HTML and PDF (22.6 MB, 328 pages)
  • PNT Selective Availability Announcements
  • Global Positioning System Systems Engineering Case Study (A detailed history of GPS development)
  • Federal Aviation Administration's GPS FAQ

Introductory / tutorial links

  • How GPS Works at HowStuffWorks
  • GPS Academy Garmin interactive video web site explaing what exactly GPS is and what it can do for you.
  • GPS Basics / u-blox GPS basics tutorial
  • GPS and GLONASS Simulation(Java applet) Simulation and graphical depiction of space vehicle motion including computation of dilution of precision (DOP)
  • How does GPS work? TomTom explains GPS, navigation, and digital maps
  • How does eGPS work? CSR's online tutorial introduces the concept and principles of enhanced GPS techniques to improve A-GPS performance and provide indoor positioning
  • HowStuffWorks Simplified explanation of GPS and video about how GPS works.
  • Trimble's Online GPS Tutorial Tutorial designed to introduce you to the principles behind GPS

Technical, historical, and ancillary topics links

  • GPS SPS Performance Standard — The official Standard Positioning Service specification.
  • GPS PPS Performance Standard — The official Precise Positioning Service specification.
  • Dana, Peter H. "Global Positioning System Overview"
  • Satellite Navigation: GPS & Galileo (PDF)—16-page paper about the history and working of GPS, touching on the upcoming Galileo
  • History of GPS, including information about each satellite's configuration and launch.
  • Chadha, Kanwar. "The Global Positioning System: Challenges in Bringing GPS to Mainstream Consumers" Technical Article (1998)
  • GPS Weapon Guidance Techniques
  • RAND history of the GPS (PDF)
  • GPS-guided educational experience based on the history of a location
  • GPS Anti-Jam Protection Techniques
  • Crosslink Summer 2002 issue by The Aerospace Corporation on satellite navigation.
  • Improved weather predictions from COSMIC GPS satellite signal occultation data.
  • David L. Wilson's GPS Accuracy Web Page A thorough analysis of the accuracy of GPS.
  • Innovation: Spacecraft Navigator, Autonomous GPS Positioning at High Earth Orbits Example of GPS receiver designed for high altitude spaceflight.
  • The Navigator GPS Receiver GSFC's Navigator spaceflight receiver.
  • Neil Ashby's Relativity in the Global Positioning System
  • Ralph Bucher's Hyperbolic Positioning Algorithm [2]
  • Average Latitude & Longitude of Countries
Wikimedia Commons has media related to:
Global Positioning System


  Results from FactBites:
 
Global Positioning System Overview (4381 words)
The approximate orbital data is used to preset the receiver with the approximate position and carrier Doppler frequency (the frequency shift caused by the rate of change in range to the moving SV) of each SV in the constellation.
Receiver position is computed from the SV positions, the measured pseudo-ranges (corrected for SV clock offsets, ionospheric delays, and relativistic effects), and a receiver position estimate (usually the last computed receiver position).
Applying a simple position correction from the reference receiver to the remote receiver has limited effect at useful ranges because both receivers would have to be using the same set of SVs in their navigation solutions and have identical GDOP terms (not possible at different locations) to be identically affected by bias errors.
Global Positioning System (663 words)
A receiver for the Global Positioning System must lock onto the signals from four of the GPS satellites to give a full three-dimensional position.
Position accuracies to about +/- 2 meters can be obtained by comparison of a field GPS receiver with a fixed receiver at a known position.
Receivers for this kind of positioning differ from the popular hand-held units in that they have memories for storage of data in both the moving and stationary units and are calibrated to take data at the same time.
  More results at FactBites »

 
 

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