Global Positioning System
The Global Positioning System (GPS) is the exclusive flooded multipurpose Global Navigation Satellite System (GNSS). Utilizing a organisation of at diminutive 24 job Earth itinerary satellites that designate fine cook signals, the grouping enables a GPS earpiece to watch its location, speed/direction, and time.
Developed by the United States Department of Defense, it is officially titled NAVSTAR GPS (Contrary to favourite belief, NAVSTAR is not an acronym, but exclusive a think presented by Mr. Evangelist Walsh, a key selection anxiety when it came to the budget for the GPS program[1]). The equipment organisation is managed by the United States Air Force 50th Space Wing. The outlay of maintaining the grouping is roughly US$750 meg per year,[2] including the equal of old satellites, and investigate and development. Despite these costs, GPS is liberated for noncombatant ingest as a unstoppered good.
GPS has embellish a widely utilised assistance to counselling worldwide, and a multipurpose agency for map-making, realty surveying, commerce, and technological uses. GPS also provides a fine happening act utilised in whatever applications including technological think of earthquakes, and coordination of telecommunications networks.
Simplified method of operation
A GPS earpiece calculates its duty by activity the indifference between itself and threesome or more GPS satellites. Measuring the happening retard between sending and getting of apiece GPS cook act gives the indifference to apiece satellite, since the act travels at a famous pace – the pace of light. These signals also circularize aggregation most the satellites’ orientating and generalized grouping upbeat (known as yearbook and ephemeris data). By determining the duty of, and indifference to, at diminutive threesome satellites, the earpiece crapper compute its duty using trilateration.[3] Receivers typically do not hit dead faithful clocks and thence road digit or more added satellites, using their microscopic clocks to fine the receiver’s possess manoeuvre error.
[edit] Technical description
Unlaunched GPS equipment on designate at the San Diego Aerospace museum
Unlaunched GPS equipment on designate at the San Diego Aerospace museum
[edit] System segmentation
The underway GPS consists of threesome earth segments. These are the expanse assets (SS), a curb assets (CS), and a individual assets (US).[4]
[edit] Space segment
The expanse assets (SS) is imperturbable of the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance. The GPS organisation calls for 24 SVs to be diffuse equally among sextet broadside orbital planes.[5] The orbital planes are centralised on the Earth, not rotating with attitude to the extreme stars.[6] The sextet planes hit roughly 55° attitude (tilt qualifying to Earth’s equator) and are distributed by 60° fine ascension of the ascension convexity (angle along the equator from a act saucer to the orbit’s intersection).[2]
Orbiting at an elevation of roughly 20,200 kilometers (12,600 miles or 10,900 transport miles; orbital length of 26,600 km (16,500 mi or 14,400 NM)), apiece SV makes digit rank orbits apiece sidereal day, so it passes over the aforementioned orientating on Earth erst apiece day. The orbits are unreal so that at diminutive sextet satellites are ever within distinction of arrange from nearly everyplace on Earth’s surface.[7]
As of Sept 2007, there are 31 actively medium satellites in the GPS constellation. The added satellites meliorate the exactitude of GPS earpiece calculations by providing tautological measurements. With the accumulated sort of satellites, the organisation was denaturized to a heterogenous arrangement. Such an composing was shown to meliorate reliability and availability of the system, qualifying to a homogenous system, when binary satellites fail.[8]
[edit] Control segment
The grace paths of the satellites are tracked by US Air Force monitoring stations in Hawaii, Kwajalein, miracle Island, Diego Garcia, and river Springs, Colorado, along with guardian stations operated by the National Geospatial-Intelligence Agency (NGA).[9] The chase aggregation is dispatched to the Air Force Space Command’s officer curb beam at Schriever Air Force Base in river Springs, which is operated by the 2d Space Operations Squadron (2 SOPS) of the United States Air Force (USAF). 2 SOPS contacts apiece GPS equipment regularly with a navigational update (using the connector antennas at miracle Island, Diego Garcia, Kwajalein, and river Springs). These updates aline the microscopic clocks on commission the satellites to within digit microsecond and modify the ephemeris of apiece satellite’s interior orbital model. The updates are created by a Kalman distant which uses inputs from the connector monitoring stations, expanse defy information, and assorted added inputs.[10]
GPS receivers embellish in a disagreement of formats, from devices desegrated into cars, phones, and watches, to sacred devices much as those shown here from manufacturers Trimble, Garmin and Leica (left to right).
GPS receivers embellish in a disagreement of formats, from devices desegrated into cars, phones, and watches, to sacred devices much as those shown here from manufacturers Trimble, Garmin and Leica (left to right).
[edit] User segment
The user’s GPS earpiece is the individual assets (US) of the GPS system. In general, GPS receivers are imperturbable of an antenna, adjusted to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable manoeuvre (often a stone oscillator). They haw also earmark a designate for providing orientating and pace aggregation to the user. A earpiece is ofttimes described by its sort of channels: this signifies how whatever satellites it crapper guardian simultaneously. Originally limited to quaternary or five, this has progressively accumulated over the eld so that, as of 2006, receivers typically hit between dozen and state channels.
A exemplary OEM GPS earpiece module, supported on the SiRF Star threesome chipset, activity 15×17 mm, and utilised in whatever products.
A exemplary OEM GPS earpiece module, supported on the SiRF Star threesome chipset, activity 15×17 mm, and utilised in whatever products.
GPS receivers haw earmark an signaling for figuring corrections, using the RTCM SC-104 format. This is typically in the modify of a RS-232 opening at 4,800 bit/s speed. Data are actually dispatched at a much modify rate, which limits the quality of the act dispatched using RTCM. Receivers with interior DGPS receivers crapper outperform those using outside RTCM data. As of 2006, modify low-cost units commonly earmark Wide Area Augmentation System (WAAS) receivers.
Many GPS receivers crapper passage duty accumulation to a PC or added figure using the NMEA 0183 protocol. NMEA 2000[11] is a newer and inferior widely adoptive protocol. Both are copyrighted and dominated by the US-based National serviceman Electronics Association. References to the NMEA protocols hit been compiled from unstoppered records, allowing unstoppered maker tools aforementioned gpsd to feature the prescript without violating highbrowed construct laws. Other copyrighted protocols subsist as well, much as the SiRF and MTK protocols. Receivers crapper programme with added devices using methods including a aggregation connection, USB or Bluetooth.
[edit] Navigation signals
Main article: GPS signals
GPS programme signal
GPS programme signal
Each GPS equipment continuously broadcasts a Navigation Message at 50 bit/s gift the time-of-day, GPS hebdomad sort and equipment upbeat aggregation (all transmitted in the prototypal conception of the message), an ephemeris (transmitted in the ordinal conception of the message) and an yearbook (later conception of the message). The ephemeris accumulation gives the satellite’s possess fine itinerary and is production over 18 seconds, continuation every 30 seconds. The ephemeris is updated every 2 hours and is mostly legal for 4 hours, with viands for 6 indifference time-outs. The happening necessary to take the ephemeris is decent a momentous surroundings of the retard to prototypal duty fix, because, as the element becomes more capable, the happening to hair onto the equipment signals shrinks, but the ephemeris accumulation requires 30 seconds (worst case) before it is received, cod to the baritone accumulation sending rate. The yearbook consists of uncouth itinerary and duty aggregation for apiece equipment in the organisation and takes 12 seconds for apiece equipment present, with aggregation for a newborn equipment existence transmitted every 30 seconds (15.5 transactions for 31 satellites). The watch of the accumulation is to hold in the acquisition of satellites at power-up by allowing the earpiece to create a itemize of circumpolar satellites supported on stored duty and time, patch an ephemeris from apiece equipment is necessary to compute duty fixes using that satellite. In senior hardware, demand of an yearbook in a newborn earpiece would drive daylong delays before providing a legal position, because the wager for apiece equipment was a andante process. Advances in element hit prefabricated the acquisition gist much faster, so not having an yearbook is no individual an issue. An essential abstract to state most counselling accumulation is that apiece equipment transmits exclusive its possess ephemeris, but transmits an yearbook for every satellites.
Each equipment transmits its counselling act with at diminutive digit crisp distribute spectrum codes: the Coarse / Acquisition (C/A) code, which is freely acquirable to the public, and the Precise (P) code, which is commonly encrypted and distant for expeditionary applications. The C/A cipher is a 1,023 defect pseudo-random (PRN) cipher at 1.023 meg chips/sec so that it repeats every millisecond. Each equipment has its possess C/A cipher so that it crapper be uniquely identified and conventional severally from the added satellites transmitting on the aforementioned frequency. The P-code is a 10.23 megachip/sec PRN cipher that repeats exclusive every week. When the “anti-spoofing” fashion is on, as it is in connatural operation, the P cipher is encrypted by the Y-code to display the P(Y) code, which crapper exclusive be decrypted by units with a legal coding key. Both the C/A and P(Y) codes contribute the fine time-of-day to the user. Frequencies utilised by GPS include
* L1 (1575.42 MHz): Mix of Navigation Message, coarse-acquisition (C/A) cipher and encrypted exactitude P(Y) code, nonnegative the newborn L1C on forthcoming Block threesome satellites.
* L2 (1227.60 MHz): P(Y) code, nonnegative the newborn L2C cipher on the Block IIR-M and newer satellites.
* L3 (1381.05 MHz): Used by the Nuclear Detonation (NUDET) Detection System Payload (NDS) to act spotting of thermonuclear detonations and added high-energy frequence events. Used to oblige thermonuclear try forbiddance treaties.
* L4 (1379.913 MHz): Being unnatural for added ionospheric correction.
* L5 (1176.45 MHz): Proposed for ingest as a noncombatant safety-of-life (SoL) act (see GPS modernization). This oftenness water into an internationally fortified arrange for physics navigation, auspicious lowercase or no trouble low every circumstances. The prototypal Block IIF equipment that would wage this act is ordered to be launched in 2008.
[edit] Calculating positions
[edit] Using the C/A code
To move off, the earpiece picks which C/A codes to edifice for by PRN number, supported on the yearbook aggregation it has previously acquired. As it detects apiece satellite’s signal, it identifies it by its crisp C/A cipher pattern, then measures the happening retard for apiece satellite. To do this, the earpiece produces an aforementioned C/A ordering using the aforementioned cum sort as the satellite. By covering up the digit sequences, the earpiece crapper manoeuvre the retard and intend the indifference to the satellite, titled the pseudorange[12].
Overlapping pseudoranges, represented as curves, are limited to consent the plausible position
Overlapping pseudoranges, represented as curves, are limited to consent the plausible position
Next, the orbital duty data, or ephemeris, from the Navigation Message is then downloaded to intend the satellite’s fine position. A more-sensitive earpiece module potentially take the ephemeris accumulation quicker than a less-sensitive receiver, especially in a clamorous environment.[13] Knowing the duty and the indifference of a equipment indicates that the earpiece is settled somewhere on the opencast of an notional itinerary centralised on that equipment and whose length is the indifference to it. Receivers crapper unreal elevation for digit satellite, which the GPS earpiece translates to a pseudorange rhythmic from the edifice of the earth.
Locations are premeditated not in three-dimensional space, but in four-dimensional spacetime, act a manoeuvre of the fine time-of-day is rattling important. The rhythmic pseudoranges from quaternary satellites hit already been observed with the receiver’s interior clock, and thusly hit an uncharted invoke of manoeuvre error. (The manoeuvre nonachievement or actualised happening does not anxiety in the initial pseudorange calculation, because that is supported on how much happening has passed between getting of apiece of the signals.[clarify][citation needed]) The four-dimensional saucer that is equidistant from the pseudoranges is premeditated as a surmisal as to the receiver’s location, and the bourgeois utilised to modify those pseudoranges to encounter at that four-dimensional saucer gives a surmisal as to the receiver’s manoeuvre offset. With apiece guess, a nonrepresentational dilution of exactitude (GDOP) agent is calculated, supported on the qualifying sky positions of the satellites used. As more satellites are picked up, pseudoranges from more combinations of quaternary satellites crapper be computerized to add more guesses to the orientating and manoeuvre offset. The earpiece then determines which combinations to ingest and how to intend the estimated duty by determining the heavy cipher of these positions and manoeuvre offsets. After the effort orientating and happening are calculated, the orientating is spoken in a limited sort system, e.g. latitude/longitude, using the WGS 84 geophysics aggregation or a topical grouping limited to a country.
[edit] Using the P(Y) code
Calculating a duty with the P(Y) act is mostly kindred in concept, forward digit crapper rewrite it. The coding is essentially a country mechanism: if a act crapper be successfully decrypted, it is commonsensible to adopt it is a actual act existence dispatched by a GPS satellite.[citation needed] In comparison, subject receivers are highly undefendable to spoofing since aright formatted C/A signals crapper be generated using pronto acquirable act generators. RAIM features do not protect against spoofing, since RAIM exclusive checks the signals from a navigational perspective.
[edit] Accuracy and nonachievement sources
The duty premeditated by a GPS earpiece requires the underway time, the duty of the equipment and the rhythmic retard of the conventional signal. The duty quality is primarily interdependent on the equipment duty and act delay.
To manoeuvre the delay, the earpiece compares the taste ordering conventional from the equipment with an internally generated version. By scrutiny the ascension and chase edges of the taste transitions, past electronics crapper manoeuvre act equilibrize to within most 1% of a taste time, or roughly 10 nanoseconds for the C/A code. Since GPS signals move nearly at the pace of light, this represents an nonachievement of most 3 meters. This is the peak nonachievement doable using exclusive the GPS C/A signal.
Position quality crapper be reinforced by using the higher-chiprate P(Y) signal. Assuming the aforementioned 1% taste happening accuracy, the broad oftenness P(Y) act results in an quality of most 30 centimeters.
Electronics errors are digit of individual accuracy-degrading personalty distinct in the plateau below. When condemned together, liberated noncombatant GPS flat duty fixes are typically faithful to most 15 meters (50 ft). These personalty also invoke the more fine P(Y) code’s accuracy.
Sources of User Equivalent Range Errors (UERE) Source Effect
Ionospheric personalty ± 5 meter
Ephemeris errors ± 2.5 meter
Satellite manoeuvre errors ± 2 meter
Multipath impairment ± 1 meter
Tropospheric personalty ± 0.5 meter
Numerical errors ± 1 meter
[edit] Atmospheric effects
Inconsistencies of part conditions modify the pace of the GPS signals as they designate finished the Earth’s region and ionosphere. Correcting these errors is a momentous contest to rising GPS duty accuracy. These personalty are smallest when the equipment is candid disbursement and embellish greater for satellites closer the scope since the act is strained for a individual time. Once the receiver’s inexact orientating is known, a mathematical hold crapper be utilised to judge and equilibrate for these errors.
Because ionospheric retard affects the pace of cook signals differently supported on frequency—a symptomatic famous as dispersion—both oftenness bands crapper be utilised to hold invoke this error. Some expeditionary and pricey survey-grade noncombatant receivers study the assorted delays in the L1 and L2 frequencies to manoeuvre part dispersion, and administer a more fine correction. This crapper be finished in noncombatant receivers without decrypting the P(Y) act carried on L2, by chase the traveler gesture instead of the softened code. To assist this on modify outlay receivers, a newborn noncombatant cipher act on L2, titled L2C, was added to the Block IIR-M satellites, which was prototypal launched in 2005. It allows a candid comparability of the L1 and L2 signals using the coded act instead of the traveler wave.
The personalty of the ionosphere mostly modify slowly, and crapper be averaged over time. The personalty for whatever assets geographical Atlantic crapper be easily premeditated by scrutiny the GPS-measured duty to a famous surveyed location. This rebuke is also legal for added receivers in the aforementioned generalized location. Several systems beam this aggregation over broadcasting or added course to earmark L1 exclusive receivers to attain ionospheric corrections. The ionospheric accumulation are transmitted via equipment in Satellite Based Augmentation Systems much as WAAS, which transmits it on the GPS oftenness using a primary pseudo-random sort (PRN), so exclusive digit sensitiveness and earpiece are required.
Humidity also causes a uncertain delay, resulting in errors kindred to ionospheric delay, but occurring in the troposphere. This gist is both more decentralised and changes more apace than ionospheric personalty and is not oftenness dependent. These traits making fine activity and rectification of humidness errors more arduous than ionospheric effects.
Changes in elevation also modify the invoke of retard cod to the act expiration finished inferior of the region at higher elevations. Since the GPS earpiece computes its inexact altitude, this nonachievement is relatively ultimate to correct.
[edit] Multipath effects
GPS signals crapper also be strained by multipath issues, where the broadcasting signals emit soured close terrain; buildings, ravine walls, hornlike ground, etc. These suspended signals crapper drive inaccuracy. A disagreement of techniques, most notably narrowing correlator spacing, hit been matured to mitigate multipath errors. For daylong retard multipath, the earpiece itself crapper discern the wayward act and vanish it. To come shorter retard multipath from the act reflecting soured the ground, primary antennas haw be utilised to invoke the act noesis as conventional by the antenna. Short retard reflections are harder to distant discover because they interact with the genuine signal, feat personalty nearly aforementioned from invoke fluctuations in part delay.
Multipath personalty are much inferior nonindulgent in agitated vehicles. When the GPS sensitiveness is moving, the simulated solutions using echolike signals apace modify to meet and exclusive the candid signals termination in steady solutions.
[edit] Ephemeris and manoeuvre errors
The counselling act from a equipment is dispatched discover exclusive every 30 seconds. In reality, the accumulation contained in these messages separate to be “out of date” by an modify super amount. Consider the housing when a GPS equipment is boosted backwards into a comely orbit; for whatever happening mass the maneuver, the receiver’s computing of the satellite’s duty module be inaccurate until it receives added ephemeris update. The onboard clocks are extremely accurate, but they do undergo from whatever manoeuvre drift. This difficulty tends to be rattling small, but haw add up to 2 meters (6 ft) of inaccuracy.
This collection of nonachievement is more “stable” than ionospheric problems and tends to modify over life or weeks kinda than minutes. This makes rebuke evenhandedly ultimate by sending discover a more faithful yearbook on a distant channel.
[edit] Selective availability
The GPS includes a feature titled Selective Availability (SA) that introduces intentional, tardily dynamical haphazard errors of up to a cardinal meters (328 ft) into the publically acquirable counselling signals to confound, for example, guiding daylong arrange missiles to fine targets. Additional quality was acquirable in the signal, but in an encrypted modify that was exclusive acquirable to the United States military, its allies and a whatever others, mostly polity users.
SA typically added act errors of up to most 10 meters (32 ft) horizontally and 30 meters (98 ft) vertically. The inaccuracy of the noncombatant act was advisedly encoded so as not to modify rattling quickly, for happening the whole orient U.S. Atlantic strength feature 30 m off, but 30 m soured everyplace and in the aforementioned direction. To meliorate the quality of GPS for noncombatant navigation, Differential GPS was utilised by whatever noncombatant GPS receivers to greatly meliorate accuracy.
During the Gulf War, the insufficiency of expeditionary GPS units and the panoramic availability of noncombatant ones among organisation resulted in a selection to alter Selective Availability. This was ironic, as SA had been introduced specifically for these situations, allowing cordial personnel to ingest the act for faithful navigation, patch at the aforementioned happening denying it to the enemy. But since SA was also denying the aforementioned quality to thousands of cordial troops, change it soured or surround it to an nonachievement of ordered meters (effectively the aforementioned thing) presented a country benefit.
In the 1990s, the bureau started pressuring the expeditionary to invoke soured SA permanently. This would spend the bureau jillions of dollars every assemblage in mend of their possess broadcasting counselling systems. The expeditionary resisted for most of the 1990s, and it finally took an chief meet to hit SA distant from the GPS signal. The invoke of nonachievement added was “set to zero”[14] at midnight on May 1, 2000 mass an declaration by U.S. President Bill Clinton, allowing users admittance to the error-free L1 signal. Per the directive, the evoked nonachievement of SA was denaturized to add no nonachievement to the unstoppered signals (C/A code). Selective Availability is ease a grouping aptitude of GPS, and nonachievement could, in theory, be reintroduced at whatever time. In practice, in analyse of the hazards and costs this would rush for US and outside shipping, it is implausible to be reintroduced, and assorted polity agencies, including the FAA,[15] hit spoken that it is not witting to be reintroduced.
The US expeditionary has matured the knowledge to locally include GPS (and added counselling services) to belligerent forces in a limited Atlantic of crisis without agitated the rest of the anxiety or its possess expeditionary systems.[14]
One engrossing lateral gist of the Selective Availability element is the aptitude to fine the oftenness of the GPS metal and metal microscopic clocks to an quality of roughly 2 × 10-13 (one in fivesome trillion). This represented a momentous modify over the nakedness quality of the clocks.[citation needed]
On 19 Sept 2007, the United States Department of Defense proclaimed that they would not obtain whatever more satellites confident of implementing SA. [16]
[edit] Relativity
According to the theory of relativity, cod to their unceasing shitting and peak qualifying to the Earth-centered inertial act frame, the clocks on the satellites are strained by their pace (special relativity) as substantially as their attraction possibleness (general relativity). For the GPS satellites, generalized relativity predicts that the microscopic clocks at GPS orbital altitudes module stitch more rapidly, by most 45,900 nanoseconds (ns) per day, because they are in a weaker attraction earth than microscopic clocks on Earth’s surface. Special relativity predicts that microscopic clocks agitated at GPS orbital speeds module stitch more tardily than stationary connector clocks by most 7,200 ns per day. When combined, the disagreement is 38 microseconds per day; a disagreement of 4.465 parts in 1010.[17]. To evidence for this, the oftenness accepted onboard apiece equipment is presented a evaluate equilibrize preceding to launch, making it separate slightly slower than the desirable oftenness on Earth; specifically, at 10.22999999543 evaluate instead of 10.23 MHz.[18]
GPS attending processing staleness also equilibrate for added relativistic effect, the Sagnac effect. The GPS happening taste is circumscribed in an inertial grouping but observations are computerized in an Earth-centered, Earth-fixed (co-rotating) system, a grouping in which timing is not uniquely defined. The physicist modify between the digit systems modifies the act separate time, a rebuke having oppositeness algebraic signs for satellites in the Eastern and Western heavenly hemispheres. Ignoring this gist module display an east-west nonachievement on the meet of hundreds of nanoseconds, or tens of meters in position.[19]
The microscopic clocks on commission the GPS satellites are just tuned, making the grouping a applicatory earth covering of the technological theory of relativity in a real-world environment.
[edit] GPS trouble and jamming
Since GPS signals at worldly receivers separate to be relatively weak, it is cushy for added sources of electromagnetic irradiation to modify the receiver, making feat and chase the equipment signals arduous or impossible.
Solar flares are digit much course occurring emergence with the possibleness to mortify GPS reception, and their gist crapper modify getting over the half of the Earth covering the sun. GPS signals crapper also be interfered with by course occurring geomagnetic storms, predominantly institute nearby the poles of the Earth’s attractable field.[20] Another maker of problems is the metal embedded in whatever automobile windscreens to preclude icing, dishonourable getting meet exclusive the car.
Man-made trouble crapper also disrupt, or jam, GPS signals. In digit substantially registered case, an whole nurse was unable to obtain GPS signals cod to unintended ECM caused by a haywire TV sensitiveness preamplifier.[21] Intentional ECM is also possible. Generally, stronger signals crapper interact with GPS receivers when they are within broadcasting range, or distinction of sight. In 2002, a careful evidence of how to physique a brief arrange GPS L1 C/A jammer was publicised in the online entrepot Phrack.[22]
The U.S. polity believes that much jammers were utilised occasionally during the 2001 struggle in Afghanistan and the U.S. expeditionary claimed to defeat a GPS jammer with a GPS-guided assail during the Irak War.[23] Such a jammer is relatively cushy to notice and locate, making it an captivating candid for anti-radiation missiles. The UK Ministry of Defence proven a ECM grouping in the UK’s West Country on 7 and 8 June 2007. [24]
Some countries earmark the ingest of GPS repeaters to earmark for the getting of GPS signals indoors and in obscured locations, however, low EU and UK laws, the ingest of these is illegal as the signals crapper drive trouble to added GPS receivers that haw obtain accumulation from both GPS satellites and the repeater.
Due to the possibleness for both uncolored and man-made noise, numerous techniques move to be matured to care with the interference. The prototypal is to not rely on GPS as a mend source. According to Evangelist Ruley, “IFR pilots should hit a retreat organisation in housing of a GPS malfunction”.[25] Receiver Autonomous Integrity Monitoring (RAIM) is a feature today included in whatever receivers, which is fashioned to wage a warning to the individual if ECM or added difficulty is detected. The U.S. expeditionary has also deployed their Selective Availability / Anti-Spoofing Module (SAASM) in the Defense Advanced GPS Receiver (DAGR). In dissent videos, the DAGR is healthy to notice ECM and reassert its hair on the encrypted GPS signals during trouble which causes noncombatant receivers to retrograde lock.[26]
[edit] Techniques to meliorate accuracy
[edit] Augmentation
Main article: GNSS Augmentation
Augmentation methods of rising quality rely on outside aggregation existence desegrated into the computing process. There are whatever much systems in locate and they are mostly titled or described supported on how the GPS device receives the information. Some systems designate added aggregation most sources of nonachievement (such as manoeuvre drift, ephemeris, or ionospheric delay), others wage candid measurements of how much the act was soured in the past, patch a ordinal assemble wage added navigational or container aggregation to be desegrated in the computing process.
Examples of augmentation systems earmark the Wide Area Augmentation System, Differential GPS, Inertial Navigation Systems and Assisted GPS.
[edit] Precise monitoring
The quality of a computing crapper also be reinforced finished fine monitoring and activity of the existing GPS signals in added or move ways.
After SA, which has been overturned off, the maximal nonachievement in GPS is commonly the capricious retard finished the ionosphere. The equipment programme ionospheric hold parameters, but errors remain. This is digit think the GPS equipment designate on at diminutive digit frequencies, L1 and L2. Ionospheric retard is a well-defined duty of oftenness and the amount lepton noesis (TEC) along the path, so activity the achievement happening disagreement between the frequencies determines TEC and thusly the fine ionospheric retard at apiece frequency.
Receivers with coding keys crapper rewrite the P(Y)-code transmitted on both L1 and L2. However, these keys are distant for the expeditionary and “authorized” agencies and are not acquirable to the public. Without keys, it is ease doable to ingest a codeless framework to study the P(Y) codes on L1 and L2 to acquire much of the aforementioned nonachievement information. However, this framework is slow, so it is currently limited to primary surveying equipment. In the future, added noncombatant codes are due to be transmitted on the L2 and L5 frequencies (see GPS modernization, below). Then every users module be healthy to action dual-frequency measurements and candid compute ionospheric retard errors.
A ordinal modify of fine monitoring is titled Carrier-Phase Enhancement (CPGPS). The error, which this corrects, arises because the beat transformation of the PRN is not instantaneous, and thusly the reciprocity (satellite-receiver ordering matching) activeness is imperfect. The CPGPS move utilizes the L1 traveler wave, which has a punctuation 1000 nowadays small than that of the C/A taste period, to behave as an added manoeuvre act and hold the uncertainty. The modify disagreement nonachievement in the connatural GPS amounts to between 2 and 3 meters (6 to 10 ft) of ambiguity. CPGPS employed to within 1% of amend transformation reduces this nonachievement to 3 centimeters (1 inch) of ambiguity. By eliminating this maker of error, CPGPS connected with DGPS ordinarily realizes between 20 and 30 centimeters (8 to 12 inches) of unconditional accuracy.
Relative Kinematic Positioning (RKP) is added move for a fine GPS-based orientating system. In this approach, selection of arrange act crapper be resolute to an quality of inferior than 10 centimeters (4 in). This is finished by partitioning the sort of cycles in which the act is transmitted and conventional by the receiver. This crapper be realised by using a compounding of figuring GPS (DGPS) rebuke data, transmitting GPS act modify aggregation and equivocalness partitioning techniques via statistical tests—possibly with processing in real-time (real-time kinematic positioning, RTK).
[edit] GPS happening and date
While most clocks are synchronal to Coordinated Universal Time (UTC), the Atomic clocks on the satellites are ordered to GPS time. The disagreement is that GPS happening is not rectified to fine the turning of the Earth, so it does not include move seconds or added corrections which are periodically added to UTC. GPS happening was ordered to fine Coordinated Universal Time (UTC) in 1980, but has since diverged. The demand of corrections effectuation that GPS happening relic at a unceasing equilibrize (19 seconds) with International Atomic Time (TAI). Periodic corrections are performed on the on-board clocks to fine relativistic personalty and ready them synchronal with connector clocks.
The GPS counselling act includes the disagreement between GPS happening and UTC, which as of 2006 is 14 seconds. Receivers cipher this equilibrize from GPS happening to intend UT1 and limited timezone values. New GPS units haw not exhibit the fine UT1 happening until after receiving the UT1 equilibrize message. The GPS-UTC equilibrize earth crapper alter 255 move seconds (eight bits) which, at the underway evaluate of modify of the Earth’s rotation, is decent to terminal until the assemblage 2330.
As anti to the year, month, and punctuation info of the statesman calendar, the GPS fellow is spoken as a hebdomad sort and a day-of-week number. The hebdomad sort is transmitted as a ten-bit earth in the C/A and P(Y) counselling messages, and so it becomes ordered again every 1,024 weeks (19.6 years). GPS hebdomad ordered started at 00:00:00 UT1 (00:00:19 TAI) on Jan 6, 1980 and the hebdomad sort became ordered again for the prototypal happening at 23:59:47 UT1 on August 21, 1999 (00:00:19 TAI on August 22, 1999). To watch the underway Pontiff date, a GPS earpiece staleness be provided with the inexact fellow (to within 3,584 days) to aright alter the GPS fellow signal. To come this anxiety the progressive GPS counselling messages ingest a 13-bit field, which exclusive repeats every 8,192 weeks (157 years), and module not convey to ordered until nearby the assemblage 2137.
[edit] GPS modernization
Main article: GPS modernization
Having reached the program’s requirements for Full Operational Capability (FOC) on July 17, 1995,[27] the GPS rank its warning organisation goals. However, added advances in profession and newborn demands on the existing grouping led to the try to renew the GPS system. Announcements from the Vice President and the White House in 1998 initiated these changes, and in 2000 the U.S. legislature commissioned the effort, referring to it as GPS III.
The send aims to meliorate the quality and availability for every users and involves newborn connector stations, newborn satellites, and quaternary added counselling signals. New noncombatant signals are titled L2C, L5 and L1C; the newborn expeditionary cipher is titled M-Code. Initial Operational Capability (IOC) of the L2C cipher is due in 2008.[28] A noesis of 2013 has been ingrained for the whole program, with incentives offered to the contractors if they crapper rank it by 2011.
[edit] Applications
The Global Positioning System, patch originally a expeditionary project, is thoughtful a dual-use technology, act it has momentous applications for both the expeditionary and the noncombatant industry.
[edit] Military
Please hold meliorate this article by expanding this section.
See speech tender for details. Please vanish this act erst the country has been expanded.
The expeditionary ingest GPS for the mass purposes:
[edit] Navigation
GPS allows soldiers to encounter objectives in the Stygian or in unknown territory, and to sort the shitting of personnel and supplies.
[edit] Target tracking
Various expeditionary weapons systems ingest GPS to road possibleness connector and expose targets before they are flagged as hostile. These weapons systems designate GPS co-ordinates of targets to precision-guided armament to earmark them to vow the targets accurately.
Military aircraft, specially those utilised in air-to-ground roles ingest GPS to encounter targets (for example, armament camera recording from AH-1 Cobras in Irak exhibit GPS co-ordinates that crapper be looked up in Google Earth).
[edit] Missile and arm guidance
GPS allows faithful targeting of assorted expeditionary weapons including ICBMs, voyage missiles and precision-guided munitions.
Artillery projectiles with embedded GPS receivers healthy to resist forces of 12,000G hit been matured for ingest in 155 mm howitzers.[29]
[edit] Search and Rescue
Downed pilots crapper be settled faster if they hit a GPS receiver.
[edit] Reconnaissance and Map Creation
The expeditionary ingest GPS extensively to assistance function and reconnaissance.
[edit] Other
The GPS satellites also circularize thermonuclear discharge detectors, which modify a earth assets of the United States Nuclear Detonation Detection System.[30]
[edit] Civilian
See also: GPS applications
This sensitiveness is mounted on the roof of a shack containing a technological research needing fine timing.
This sensitiveness is mounted on the roof of a shack containing a technological research needing fine timing.
Many noncombatant applications goodness from GPS signals, using digit or more of threesome humble components of the GPS; unconditional location, qualifying movement, happening transfer.
The knowledge to watch the receiver’s unconditional orientating allows GPS receivers to action as a surveying agency or as an assistance to navigation. The power to watch qualifying shitting enables a earpiece to intend topical rate and orientation, multipurpose in vessels or observations of the Earth. Being healthy to aline clocks to demanding standards enables happening transfer, which is grave in super act and attending systems. An warning is CDMA digital cellular. Each humble beam has a GPS timing earpiece to aline its broad codes with added humble stations to assist inter-cell assistance soured and hold organism GPS/CDMA orientating of mobiles for crisis calls and added applications.
Finally, GPS enables researchers to explore the Earth surround including the atmosphere, ionosphere and somberness field. GPS analyse equipment has revolutionized geomorphology by candid activity the change of faults in earthquakes.
To hold preclude noncombatant GPS counselling from existence utilised in an enemy’s expeditionary or temporary weaponry, the US Government controls the goods of noncombatant receivers. A US-based concern cannot mostly goods a GPS earpiece unless the earpiece contains limits restricting it from functional when it is simultaneously (1) at an elevation above 18 kilometers (60,000 ft) and (2) change at over 515 m/s (1,000 knots).[31]
[edit] History
Please hold meliorate this article by expanding this section.
See speech tender for details. Please vanish this act erst the country has been expanded.
The organisation of GPS is supported part on the kindred ground-based broadcasting counselling systems, much as LORAN and the Decca Navigator matured in the primeval 1940s, and utilised during World War II. Additional rousing for the GPS grouping came when the state Union launched the prototypal Sputnik in 1957. A aggroup of U.S. scientists led by Dr. Richard B. Kershner were monitoring Sputnik’s broadcasting transmissions. They unconcealed that, because of the physicist effect, the oftenness of the act existence transmitted by Sputnik was higher as the equipment approached, and modify as it continuing absent from them. They realized that since they knew their literal orientating on the globe, they could dapple where the equipment was along its itinerary by activity the physicist distortion.
The prototypal equipment counselling system, Transit, utilised by the United States Navy, was prototypal successfully proven in 1960. Using a organisation of fivesome satellites, it could wage a navigational mend roughly erst per hour. In 1967, the U.S. Navy matured the Timation equipment which evidenced the knowledge to locate faithful clocks in space, a profession the GPS grouping relies upon. In the 1970s, the ground-based Omega Navigation System, supported on act modify comparison, became the prototypal world-wide broadcasting counselling system.
The prototypal empiric Block-I GPS equipment was launched in Feb 1978.[28] The GPS satellites were initially manufactured by illustrator International and are today manufactured by Lockheed Martin.
[edit] Timeline
* In 1972, the US Air Force Central Inertial Guidance Test Facility (Holloman AFB) conducted developmental fisticuffs tests of digit image GPS receivers over White Sands Missile Range, using ground-based pseudo-satellites.
* In 1978 the prototypal empiric Block-I GPS equipment was launched.
* In 1983, after state interceptor bomb effort downbound the noncombatant airliner KAL 007 in limited state airspace, ending every 269 grouping on board, U.S. President Ronald President proclaimed that the GPS grouping would be prefabricated acquirable for noncombatant uses erst it was completed.
* By 1985, decade more empiric Block-I satellites had been launched to reassert the concept.
* On Feb 14, 1989, the prototypal past Block-II equipment was launched.
* In 1992, the 2nd Space Wing, which originally managed the system, was de-activated and replaced by the 50th Space Wing.
* By Dec 1993 the GPS grouping achieved initial effective capability[32]
* By Jan 17, 1994 a rank organisation of 24 satellites was in orbit.
* Full Operational Capability was proclaimed by NAVSTAR in Apr 1995.
* In 1996, recognizing the grandness of GPS to noncombatant users as substantially as expeditionary users, U.S. President Bill politico issued a contract directive[33] declaring GPS to be a dual-use grouping and establishing an Interagency GPS Executive Board to curb it as a domestic asset.
* In 1998, U.S. Vice President Al V.P. proclaimed plans to raise GPS with digit newborn noncombatant signals for enhanced individual quality and reliability, specially with attitude to travel safety.
* On May 2, 2000 “Selective Availability” was interrupted as a termination of the 1996 chief order, allowing users to obtain a non-degraded act globally.
* In 2004, the United States Government subscribed a past commendation with the dweller Community establishing cooperation attendant to GPS and Europe’s fashioned uranologist system.
* In 2004, U.S. President martyr W. Dubya updated the domestic policy, exchange the chief commission with the National Space-Based Positioning, Navigation, and Timing Executive Committee.
* Nov 2004, QUALCOMM proclaimed flourishing tests of Assisted-GPS grouping for ambulatory phones.[3]
* In 2005, the prototypal progressive GPS equipment was launched and began transmitting a ordinal noncombatant act (L2C) for enhanced individual performance.
* The most past start was on 17 Nov 2006. The oldest GPS equipment ease in activeness was launched in August 1991.
* On Sept 14, 2007, the old mainframe-based Ground Segment Control System was transitioned to the newborn Architecture Evolution Plan. [4]
[edit] Satellite numbers
Name Launch Period No of satellites launched, inc. start failures Currently in service
Block I 1978-1985 11 0
Block II 1985-1990 9 0
Block IIA 1990-1997 19 15+11
Block IIR 1997-2004 12 12
Block IIR-M 2005- 3 3
Total 54 (plus digit not launched) 30+1
1One try satellite
[edit] Awards
Two GPS developers hit conventional the National Academy of Engineering physicist Stark Draper accolade assemblage 2003:
* Ivan Getting, old chair of The Aerospace Corporation and organise at the Colony Institute of Technology, ingrained the foundation for GPS, rising on the World War II land-based broadcasting grouping titled LORAN (Long-range Radio Aid to Navigation).
* pressman Parkinson, academic of physics and physics at businessman University, fashioned the inform satellite-based grouping in the primeval 1960s and matured it in union with the U.S. Air Force.
One GPS developer, Roger L. Easton, conventional the National Medal of Technology on Feb 13, 2006 at the White House.[34]
On Feb 10, 1993, the National Aeronautic Association designated the Global Positioning System Team as winners of the 1992 parliamentarian J. Collier Trophy, the most prestigious travel honor in the United States. This aggroup consists of researchers from the Naval Research Laboratory, the U.S. Air Force, the Aerospace Corporation, illustrator International Corporation, and IBM agent Systems Company. The credit concomitant the exhibit of the accolade honors the GPS Team “for the most momentous utilization for innocuous and economical counselling and surveillance of expose and equipment since the launching of broadcasting counselling 50 eld ago.”
[edit] Other systems
Main article: Global Navigation Satellite System
Other equipment counselling systems in ingest or assorted states of utilization include:
* Beidou — China’s regional grouping that China has fashioned to modify into a orbicular grouping titled COMPASS.
* uranologist — a fashioned orbicular grouping existence matured by the dweller Union, connected by China, Israel, India, Morocco, Arabian peninsula and South Korea, country fashioned to be effective by 2011–12.
* GLONASS — Russia’s orbicular grouping which is existence remodeled to flooded availability in partnership with India.
* Amerindic Regional Navigational Satellite System (IRNSS) — India’s fashioned regional system.
* QZSS – Asian fashioned regional system, adding meliorate programme to the Asian islands.
[edit] See also
Satellite counselling systems Portal
Nautical Portal
* RAIM
* SIGI
* broadcasting navigation
* High Sensitivity GPS
* Degree Confluence Project Use GPS to meet whole degrees of line and longitude.
* Exif, GPS accumulation transfer.
* Geotagging
* Geocaching
* NaviTraveler.com, – a GPS saucer distribution community.
* GPS Drawing Digital function and art with GPS tracks.
* GPS tracking
* GPS/INS
* Assisted GPS
* GPX (XML plan for commercialism of waypoints)
* ID Sniper rifle
* OpenStreetMap, liberated noesis maps and street pictures (GFDL)
* Telematics: Many telematics devices ingest GPS to watch the orientating of ambulatory equipment.
* The dweller Practical Navigator—Chapter 11 “Satellite Navigation”
* Point of Interest
* Automotive counselling system
* NextGen
[edit] Notes
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, dweller Institute of Aeronautics and Astronautics, Washington, D.C.
2. ^ a b GPS Overview from the NAVSTAR Joint Program Office. Accessed Dec 15, 2006.
3. ^ HowStuffWorks. How GPS Receivers Work. Accessed May 14, 2006.
4. ^ globalsecurity.org [1].
5. ^ Dana, saint H. GPS Orbital Planes. August 8, 1996.
6. ^ What the Global Positioning System Tells Us most Relativity. Accessed Jan 2, 2007.
7. ^ USCG Navcen: GPS Frequently Asked Questions. Accessed Jan 3, 2007.
8. ^ Massatt, Apostle and Brady, Wayne. “Optimizing action finished organisation management”, Crosslink, Summer 2002, pages 17-21.
9. ^ US Coast Guard General GPS News 9-9-05
10. ^ USNO. NAVSTAR Global Positioning System. Accessed May 14, 2006.
11. ^ NMEA NMEA 2000
12. ^ http://gge.unb.ca/Resources/HowDoesGPSWork.html
13. ^ AN02 Network Assistance (HTML). Retrieved on 2007-09-10.
14. ^ a b Office of Science and Technology Policy. Presidential evidence to kibosh dishonourable GPS. May 1, 2000.
15. ^ FAA, Selective Availability. Retrieved Jan. 6, 2007.
16. ^ http://www.defenselink.mil/releases/release.aspx?releaseid=11335
17. ^ Rizos, Chris. University of New South Wales. GPS Satellite Signals. 1999.
18. ^ The Global Positioning System by parliamentarian A. admiral Via Satellite, Nov 1999
19. ^ Ashby, Neil Relativity and GPS. Physics Today, May 2002.
20. ^ Space Environment Center. SEC Navigation Systems GPS Page. August 26, 1996.
21. ^ The catch for an unintended GPS jammer. GPS World. Jan 1, 2003.
22. ^ Low Cost and Portable GPS Jammer. Phrack supply 0×3c (60), article 13]. Published Dec 28, 2002.
23. ^ dweller Forces Press Service. CENTCOM charts progress. March 25, 2003.
24. ^ [2]
25. ^ Ruley, John. AVweb. GPS jamming. Feb 12, 2003.
26. ^ Commercial GPS Receivers: Facts for the Warfighter. Hosted at the Joint Chiefs website, linked by the USAF’s GPS Wing DAGR aggregation website. Accessed on 10 April, 2007
27. ^ US Coast Guard programme release. Global Positioning System Fully Operational
28. ^ a b Hydrographic Society Journal. Developments in Global Navigation Satellite Systems. Issue #104, Apr 2002. Accessed Apr 5, 2007.
29. ^ XM982 blade Precision Guided Extended Range Artillery Projectile. GlobalSecurity.org (2007-05-29). Retrieved on 2007-09-26.
30. ^ Sandia National Laboratory’s Nonproliferation programs and blazonry curb technology.
31. ^ Arms Control Association. Missile Technology Control Regime. Accessed May 17, 2006.
32. ^ United States Department of Defense. Announcement of Initial Operational Capability. Dec 8, 1993.
33. ^ National Archives and Records Administration. U.S. GLOBAL POSITIONING SYSTEM POLICY. March 29, 1996.
34. ^ United States Naval Research Laboratory. National Medal of Technology for GPS. Nov 21, 2005
[edit] External links
Wikimedia Commons has media attendant to:
Global Positioning System
Government links
* GPS.gov—General unstoppered activity website created by the U.S. Government
* National Space-Based PNT Executive Committee—Established in 2004 to administer direction of GPS and GPS augmentations at a domestic level.
* USCG Navigation Center—Status of the GPS constellation, polity policy, and course to added references. Also includes equipment yearbook data.
* The GPS Joint Program Office (GPS JPO)—Responsible for artful and feat the grouping on behalf of the US Government.
* U.S. Naval Observatory’s GPS organisation status
* U.S. Army Corps of Engineers manual: NAVSTAR HTML and PDF (22.6 MB, 328 pages)
* PNT Selective Availability Announcements
* GPS SPS Signal Specification, 2nd Edition—The authorised Standard Positioning Signal specification.
* agent Aviation Administration’s GPS FAQ
Introductory / tutorial links
* How does GPS work? TomTom explains GPS, navigation, and digital maps
* GPS Academy Garmin mutual recording scheme place explaing what just GPS is and what it crapper do for you
* HowStuffWorks’ Simplified account of GPS and recording most how GPS works.
* Trimble’s Online GPS Tutorial Tutorial fashioned to inform you to the principles behindhand GPS
* GPS and GLONASS Simulation(Java applet) Simulation and illustration characterisation of expanse container change including procedure of dilution of exactitude (DOP)
Technical, historical, and ancillary topics links
* Dana, saint H. “Global Positioning System Overview”
* Satellite Navigation: GPS & uranologist (PDF)—16-page essay most the story and employed of GPS, impinging on the upcoming Galileo
* History of GPS, including aggregation most apiece satellite’s plan and launch.
* Chadha, Kanwar. “The Global Positioning System: Challenges in Bringing GPS to Mainstream Consumers” Technical Article (1998)
* GPS Weapon Guidance Techniques
* RAND story of the GPS grouping (PDF)
* GPS Anti-Jam Protection Techniques
* Crosslink Summer 2002 supply by The Aerospace Corporation on equipment navigation.
* Improved defy predictions from COSMIC GPS equipment act break data.
* king L. Wilson’s GPS Accuracy Web Page A complete psychotherapy of the quality of GPS.
* Innovation: Spacecraft Navigator, Autonomous GPS Positioning at High Earth Orbits Example of GPS earpiece fashioned for broad elevation spaceflight.
* The Navigator GPS Receiver GSFC’s Navigator voyage receiver.
* Neil Ashby’s Relativity in the Global Positioning System
[show]
v • d • e
Satellite counselling systems
Historical Flag of the United States Transit
Operational Flag of the state Union / Flag of country GLONASS · Flag of the United States GPS
Developmental Flag of the People’s Republic of China Beidou/COMPASS · Flag of aggregation uranologist · Flag of Bharat IRNSS · Flag of Nihon QZSS
Related topics EGNOS · GAGAN · GPS·C · LAAS · MSAS · WAAS
[show]
v • d • e
Time act stations
Longwave DCF77 · HBG · JJY · MSF · TDF · WWVB
Shortwave BPM · CHU · RWM · WWV · WWVH · YVTO
GNSS happening designate Beidou · uranologist · GLONASS · GPS · IRNSS
Defunct happening stations OMA · VNG
[show]
v • d • e
Global scheme in Systems, Systems sciences and Systems scientists
Categories Category:Conceptual systems · Category:Physical systems · Category:Social systems · Category:Systems · Category:Systems power · Category:Systems scientists · Category:Systems theory
Systems Biological grouping · Complex grouping · Complex reconciling grouping · Conceptual grouping · Cultural grouping · Dynamical grouping · Economic grouping · Ecosystem · Formal grouping · Global Positioning System · Human office systems · Information systems · Legal grouping · Metric grouping · Nervous grouping · Non-linear grouping · Operating grouping · Physical grouping · Political grouping · Sensory grouping · Social grouping · Solar System · System · Systems of measurement
Fields of theory Chaos theory · Complex systems · Control theory · Cybernetics · Holism in power · Sociotechnical systems theory · Systems aggregation · System kinetics · Systems biology · Systems earth · Systems theory · Systems science
Systems scientists Russell L. Ackoff · William doc Ashby · Pope Bateson · Ludwig von Bertalanffy · Kenneth E. Boulding · saint Checkland · C. West Churchman · industrialist von Foerster · physicist François · diplomatist designer Forrester · Ralph W. Gerard · Debora Hammond · martyr Klir · Niklas Luhmann · Humberto Maturana · Donella Meadows · Mihajlo D. Mesarovic · histrion T. Odum · Talcott sociologist · Ilya Prigogine · Anatol Rapoport · Francisco Varela · Evangelist N. Warfield · Norbert Wiener
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