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83-424: COTSBot uses GPS to navigate. The first version was created in the early 2000s with an accuracy rate of about 65%. After training COTSBot with machine learning , its accuracy rate rose to 99% by 2019. COTSBot is capable of killing 200 crown-of-thorns starfish with its two liters capacity of poison. COTSBot is capable of performing about 20 runs per day, but multiple COTSBots will be necessary to significantly impact

166-408: A moving map display , or recorded or used by some other system, such as a vehicle guidance system. Although usually not formed explicitly in the receiver processing, the conceptual time differences of arrival (TDOAs) define the measurement geometry. Each TDOA corresponds to a hyperboloid of revolution (see Multilateration ). The line connecting the two satellites involved (and its extensions) forms

249-445: A changing environment. With the advent of MIMO Wi-Fi interfaces, which use multiple antennas, it is possible to estimate the AoA of the multipath signals received at the antenna arrays in the access points, and apply triangulation to calculate the location of client devices. SpotFi, ArrayTrack and LTEye are proposed solutions which employ this kind of technique. Typical computation of

332-690: A deliberate error introduced into the GPS data that military receivers could correct for. As civilian GPS usage grew, there was increasing pressure to remove this error. The SA system was temporarily disabled during the Gulf War , as a shortage of military GPS units meant that many US soldiers were using civilian GPS units sent from home. In the 1990s, Differential GPS systems from the US Coast Guard , Federal Aviation Administration , and similar agencies in other countries began to broadcast local GPS corrections, reducing

415-450: A directive making GPS freely available for civilian use, once it was sufficiently developed, as a common good. The first Block II satellite was launched on February 14, 1989, and the 24th satellite was launched in 1994. The GPS program cost at this point, not including the cost of the user equipment but including the costs of the satellite launches, has been estimated at US$ 5 billion (equivalent to $ 10 billion in 2023). Initially,

498-510: A full complement of 24 satellites in 2027. The GPS project was launched in the United States in 1973 to overcome the limitations of previous navigation systems, combining ideas from several predecessors, including classified engineering design studies from the 1960s. The U.S. Department of Defense developed the system, which originally used 24 satellites, for use by the United States military, and became fully operational in 1993. Civilian use

581-429: A liaison. The U.S. Department of Defense is required by law to "maintain a Standard Positioning Service (as defined in the federal radio navigation plan and the standard positioning service signal specification) that will be available on a continuous, worldwide basis" and "develop measures to prevent hostile use of GPS and its augmentations without unduly disrupting or degrading civilian uses". USA-203 from Block IIR-M

664-554: A manageable level to permit accurate navigation. During Labor Day weekend in 1973, a meeting of about twelve military officers at the Pentagon discussed the creation of a Defense Navigation Satellite System (DNSS) . It was at this meeting that the real synthesis that became GPS was created. Later that year, the DNSS program was named Navstar. Navstar is often erroneously considered an acronym for "NAVigation System using Timing And Ranging" but

747-457: A minimum, four satellites must be in view of the receiver for it to compute four unknown quantities (three position coordinates and the deviation of its own clock from satellite time). Each GPS satellite continually broadcasts a signal ( carrier wave with modulation ) that includes: Conceptually, the receiver measures the TOAs (according to its own clock) of four satellite signals. From the TOAs and

830-431: A receiver start-up situation. Most receivers have a track algorithm , sometimes called a tracker , that combines sets of satellite measurements collected at different times—in effect, taking advantage of the fact that successive receiver positions are usually close to each other. After a set of measurements are processed, the tracker predicts the receiver location corresponding to the next set of satellite measurements. When

913-404: A satellite fix would take too long. Such systems include assisted GPS, urban positioning services through hotspot databases, and indoor positioning systems . Wi-Fi positioning takes advantage of the rapid growth in the early 21st century of wireless access points in urban areas. The most common technique for positioning using wireless access points is based on a rough proxy for the strength of

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996-578: A simplified representation of the phase shifts experienced by each antenna as a function of the AoA of the propagation path: ϕ ( θ k ) = exp ⁡ ( − j ⋅ 2 π ⋅ d ⋅ sin ⁡ ( θ k ) ⋅ f / c ) {\displaystyle \phi (\theta _{k})=\exp(-j\cdot 2\pi \cdot d\cdot \sin(\theta _{k})\cdot f/c)} The AoA can then be expressed as

1079-426: A single access point. Traditional fingerprinting is also RSSI-based, but it simply relies on the recording of the signal strength from several access points in range and storing this information in a database along with the known coordinates of the client device in an offline phase. This information can be deterministic or probabilistic. During the online tracking phase, the current RSSI vector at an unknown location

1162-414: A target client device can be employed to determine the device's location based on triangulation algorithms. A combination of these techniques may be used to improve the precision of a system. RSSI localization techniques are based on measuring rough relative signal strength at a client device from several different access points, and then combining this information with a propagation model to determine

1245-455: A two-step parametric and measurement-driven ray-tracing approach. This accounts for the absorption and reflection characteristics of various obstacles in the indoor environment. The location estimates are then computed using Bayesian filtering on sample sets derived by Monte Carlo sampling. This method has been found to provide good location estimates of users with sub-room precision using received signal strength indication (RSSI) readings from

1328-510: Is compared to those stored in the fingerprint and the closest match is returned as the estimated user location. Such systems may provide a median accuracy of 0.6m and tail accuracy of 1.3m. Its main disadvantage is that any changes to the environment, such as adding or removing furniture or buildings, may change the "fingerprint" that corresponds to each location, requiring an update to the fingerprint database. However, integration with other sensors such as cameras can be used in order to deal with

1411-525: Is given by the channel state information ( CSI ) matrix which can be extracted from modern wireless cards with special tools such as the Linux 802.11n CSI Tool. This is where the MUSIC algorithm is applied in, first by computing the eigenvectors of X X H {\displaystyle \mathbf {X} \mathbf {X} ^{H}} (where X H {\displaystyle \mathbf {X} ^{H}}

1494-458: Is one of the global navigation satellite systems (GNSS) that provide geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. It does not require the user to transmit any data, and operates independently of any telephone or Internet reception, though these technologies can enhance the usefulness of

1577-532: Is one steering vector for each propagation path, and the steering matrix A {\displaystyle \mathbf {A} } (of dimensions M ⋅ L {\displaystyle M\cdot L} ) is then defined as: A = [ a → ( θ 1 ) , … , a → ( θ L ) ] {\displaystyle \mathbf {A} =[{\vec {a}}(\theta _{1}),\dots ,{\vec {a}}(\theta _{L})]} and

1660-514: Is owned and operated by the United States government as a national resource. The Department of Defense is the steward of GPS. The Interagency GPS Executive Board (IGEB) oversaw GPS policy matters from 1996 to 2004. After that, the National Space-Based Positioning, Navigation and Timing Executive Committee was established by presidential directive in 2004 to advise and coordinate federal departments and agencies on matters concerning

1743-569: Is the attenuation experienced at any antenna of the array. The attenuation is the same in every antenna, except for a phase shift which changes for every antenna due to the extra distance traveled by the signal. This means that the signal arrives with an additional phase of − 2 π ⋅ d ⋅ sin ⁡ ( θ ) ⋅ ( f / c ) ⋅ ( 2 − 1 ) {\displaystyle -2\pi \cdot d\cdot \sin(\theta )\cdot (f/c)\cdot (2-1)} at

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1826-408: Is the conjugate transpose of X {\displaystyle \mathbf {X} } ) and using the vectors corresponding to eigenvalue zero to calculate the steering vectors and the matrix A {\displaystyle \mathbf {A} } . The AoAs can then be deduced from this matrix and used to estimate the position of the client device through triangulation . Though this technique

1909-455: Is the steering vector and given by: a → ( θ k ) = [ 1 ,   ϕ ( θ k ) ,   … ,   ϕ ( θ k ) M − 1 ] T {\displaystyle {\vec {a}}(\theta _{k})=[1,\ \phi (\theta _{k}),\ \dots ,\ \phi (\theta _{k})^{M-1}]^{T}} There

1992-904: Is the vector complex attenuations along the L {\displaystyle L} paths. OFDM transmits data over multiple different sub carriers, so the measured received signals x → {\displaystyle {\vec {x}}} corresponding to each sub carrier form the matrix X {\displaystyle \mathbf {X} } expressed as: X = [ x → 1 … x → L ] = A [ Γ → 1 … Γ → L ] = A F {\displaystyle \mathbf {X} =[{\vec {x}}_{1}\dots {\vec {x}}_{L}]=\mathbf {A} [{\vec {\Gamma }}_{1}\dots {\vec {\Gamma }}_{L}]=\mathbf {AF} } The matrix X {\displaystyle \mathbf {X} }

2075-391: Is traveled by the signal to reach the second antenna of the array. Considering that the k {\displaystyle k} -th propagation path arrives with angle θ k {\displaystyle \theta _{k}} with respect to the normal of the antenna array of the access point, γ k {\displaystyle \gamma _{k}}

2158-767: Is unhealthy For a more complete list, see List of GPS satellites On February 10, 1993, the National Aeronautic Association selected the GPS Team as winners of the 1992 Robert J. Collier Trophy , the US's most prestigious aviation award. This team combines researchers from the Naval Research Laboratory, the U.S. Air Force, the Aerospace Corporation , Rockwell International Corporation, and IBM Federal Systems Company. The citation honors them "for

2241-687: Is usually enough. The time measurements taken at the wireless interfaces are based on the fact that RF waves travel close to the speed of light, which remains nearly constant in most propagation media in indoor environments. Therefore, the signal propagation speed (and consequently the ToF) is not affected so much by the environment as the RSSI measurements are. Unlike traditional ToF-based echo techniques, such as those used in RADAR systems, Wi-Fi echo techniques use regular data and acknowledgement communication frames to measure

2324-539: Is usually more accurate than others, it may require special hardware in order to be deployed, such as an array of six to eight antennas or rotating antennas. SpotFi proposes the use of a superresolution algorithm which takes advantage of the number of measurements taken by each of the antennas of the Wi-Fi cards with only three antennas, and also incorporates ToF-based localization to improve its accuracy. Time of flight (ToF) localization approach takes timestamps provided by

2407-495: The Doppler effect , they could pinpoint where the satellite was along its orbit. The Director of the APL gave them access to their UNIVAC I computer to perform the heavy calculations required. Early the next year, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem: pinpointing the user's location, given the satellite's. (At the time,

2490-504: The navigation equations gives the position of the receiver along with the difference between the time kept by the receiver's on-board clock and the true time-of-day, thereby eliminating the need for a more precise and possibly impractical receiver based clock. Applications for GPS such as time transfer , traffic signal timing, and synchronization of cell phone base stations , make use of this cheap and highly accurate timing. Some GPS applications use this time for display, or, other than for

2573-430: The AoA is done with the MUSIC algorithm . Assuming an antenna array of M {\displaystyle M} antennas equally spaced by a distance of d {\displaystyle d} and a signal arriving at the antenna array through L {\displaystyle L} propagation paths, an additional distance of d sin ⁡ θ {\displaystyle d\sin \theta }

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2656-520: The Earth's center) and the offset of the receiver clock relative to the GPS time are computed simultaneously, using the navigation equations to process the TOFs. The receiver's Earth-centered solution location is usually converted to latitude , longitude and height relative to an ellipsoidal Earth model. The height may then be further converted to height relative to the geoid , which is essentially mean sea level. These coordinates may be displayed, such as on

2739-641: The GPS and related systems. The executive committee is chaired jointly by the Deputy Secretaries of Defense and Transportation. Its membership includes equivalent-level officials from the Departments of State, Commerce, and Homeland Security, the Joint Chiefs of Staff and NASA . Components of the executive office of the president participate as observers to the executive committee, and the FCC chairman participates as

2822-411: The GPS positioning information. It provides critical positioning capabilities to military, civil, and commercial users around the world. Although the United States government created, controls, and maintains the GPS system, it is freely accessible to anyone with a GPS receiver. The GPS project was started by the U.S. Department of Defense in 1973. The first prototype spacecraft was launched in 1978 and

2905-668: The GPS service, including new signals for civil use and increased accuracy and integrity for all users, all the while maintaining compatibility with existing GPS equipment. Modernization of the satellite system has been an ongoing initiative by the U.S. Department of Defense through a series of satellite acquisitions to meet the growing needs of the military, civilians, and the commercial market. As of early 2015, high-quality Standard Positioning Service (SPS) GPS receivers provided horizontal accuracy of better than 3.5 meters (11 ft), although many factors such as receiver and antenna quality and atmospheric issues can affect this accuracy. GPS

2988-714: The Global Positioning System (GPS) its 60th Anniversary Award, nominated by IAF member, the American Institute for Aeronautics and Astronautics (AIAA). The IAF Honors and Awards Committee recognized the uniqueness of the GPS program and the exemplary role it has played in building international collaboration for the benefit of humanity. On December 6, 2018, Gladys West was inducted into the Air Force Space and Missile Pioneers Hall of Fame in recognition of her work on an extremely accurate geodetic Earth model, which

3071-474: The Navy TRANSIT system were too slow for the high speeds of Air Force operation. The Naval Research Laboratory (NRL) continued making advances with their Timation (Time Navigation) satellites, first launched in 1967, second launched in 1969, with the third in 1974 carrying the first atomic clock into orbit and the fourth launched in 1977. Another important predecessor to GPS came from a different branch of

3154-568: The Navy was developing the submarine-launched Polaris missile, which required them to know the submarine's location.) This led them and APL to develop the TRANSIT system. In 1959, ARPA (renamed DARPA in 1972) also played a role in TRANSIT. TRANSIT was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour. In 1967,

3237-595: The SLBM situation. In 1960, the Air Force proposed a radio-navigation system called MOSAIC (MObile System for Accurate ICBM Control) that was essentially a 3-D LORAN System. A follow-on study, Project 57, was performed in 1963 and it was "in this study that the GPS concept was born". That same year, the concept was pursued as Project 621B, which had "many of the attributes that you now see in GPS" and promised increased accuracy for U.S. Air Force bombers as well as ICBMs. Updates from

3320-520: The TOTs, the receiver forms four time of flight (TOF) values, which are (given the speed of light) approximately equivalent to receiver-satellite ranges plus time difference between the receiver and GPS satellites multiplied by speed of light, which are called pseudo-ranges. The receiver then computes its three-dimensional position and clock deviation from the four TOFs. In practice the receiver position (in three dimensional Cartesian coordinates with origin at

3403-510: The ToF. As in the RSSI approach, the ToF is used only to estimate the distance between the client device and access points. Then a trilateration technique can be used to calculate the estimated position of the device relative to the access points. The greatest challenges in the ToF approach consist in dealing with clock synchronization issues, noise, sampling artifacts and multipath channel effects. Some techniques use mathematical approaches to remove

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3486-602: The U.S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology required for GPS. In the 1970s, the ground-based OMEGA navigation system, based on phase comparison of signal transmission from pairs of stations, became the first worldwide radio navigation system. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy. Although there were wide needs for accurate navigation in military and civilian sectors, almost none of those

3569-442: The U.S. Secretary of Defense, William Perry , in view of the widespread growth of differential GPS services by private industry to improve civilian accuracy. Moreover, the U.S. military was developing technologies to deny GPS service to potential adversaries on a regional basis. Selective Availability was removed from the GPS architecture beginning with GPS-III. Since its deployment, the U.S. has implemented several improvements to

3652-416: The US government announced that the next generation of GPS satellites would not include the feature at all. Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS and implement the next generation of GPS Block III satellites and Next Generation Operational Control System (OCX) which was authorized by the U.S. Congress in 2000. When Selective Availability

3735-504: The United States military. In 1964, the United States Army orbited its first Sequential Collation of Range ( SECOR ) satellite used for geodetic surveying. The SECOR system included three ground-based transmitters at known locations that would send signals to the satellite transponder in orbit. A fourth ground-based station, at an undetermined position, could then use those signals to fix its location precisely. The last SECOR satellite

3818-451: The axis of the hyperboloid. The receiver is located at the point where three hyperboloids intersect. It is sometimes incorrectly said that the user location is at the intersection of three spheres. While simpler to visualize, this is the case only if the receiver has a clock synchronized with the satellite clocks (i.e., the receiver measures true ranges to the satellites rather than range differences). There are marked performance benefits to

3901-434: The basic position calculations, do not use it at all. Wi-Fi positioning system Wi-Fi positioning system ( WPS , WiPS or WFPS ) is a geolocation system that uses the characteristics of nearby Wi‑Fi access points to discover where a device is located. It is used where satellite navigation such as GPS is inadequate due to various causes including multipath and signal blockage indoors, or where acquiring

3984-642: The clocks on GPS satellites, as observed by those on Earth, run 38 microseconds faster per day than those on the Earth. The design of GPS corrects for this difference; because without doing so, GPS calculated positions would accumulate errors of up to 10 kilometers per day (6 mi/d). When the Soviet Union launched its first artificial satellite ( Sputnik 1 ) in 1957, two American physicists, William Guier and George Weiffenbach, at Johns Hopkins University 's Applied Physics Laboratory (APL) monitored its radio transmissions. Within hours they realized that, because of

4067-493: The crown of thorns starfish populations. A smaller version of COTSBot called "RangerBot" is also being developed by QUT. This robotics-related article is a stub . You can help Misplaced Pages by expanding it . GPS The Global Positioning System ( GPS ), originally Navstar GPS , is a satellite-based radio navigation system owned by the United States Space Force and operated by Mission Delta 31 . It

4150-457: The distance between the client device and the access points. Trilateration (sometimes called multilateration) techniques can be used to calculate the estimated client device position relative to the expected position of access points. Though one of the cheapest and easiest methods to implement, its disadvantage is that it does not provide very good precision (median of 2–4m), because the RSSI measurements tend to fluctuate according to changes in

4233-496: The distance from the satellite to the ground station. With the distance information collected from multiple ground stations, the location coordinates of any satellite at any time can be calculated with great precision. Each GPS satellite carries an accurate record of its own position and time, and broadcasts that data continuously. Based on data received from multiple GPS satellites , an end user's GPS receiver can calculate its own four-dimensional position in spacetime ; However, at

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4316-451: The distance traveled between two position measurements drops below or near the random error of position measurement. GPS units can use measurements of the Doppler shift of the signals received to compute velocity accurately. More advanced navigation systems use additional sensors like a compass or an inertial navigation system to complement GPS. GPS requires four or more satellites to be visible for accurate navigation. The solution of

4399-407: The effect of both SA degradation and atmospheric effects (that military receivers also corrected for). The U.S. military had also developed methods to perform local GPS jamming, meaning that the ability to globally degrade the system was no longer necessary. As a result, United States President Bill Clinton signed a bill ordering that Selective Availability be disabled on May 1, 2000; and, in 2007 ,

4482-454: The environment or multipath fading . Cisco uses RSSI to locate devices through its access points. Access points collect the location data and update the location on the Cisco cloud called Cisco DNA Spaces . Monte Carlo sampling is a statistical technique used in indoor Wi-Fi mapping to estimate the location of wireless nodes. The process involves creating wireless signal strength maps using

4565-408: The first step to determine a device's position is to determine the distance between the target client device and a few access points. With the known distances between the target device and access points, trilateration algorithms may be used to determine the relative position of the target device, using the known position of access points as a reference. Alternatively, the angles of arriving signals at

4648-428: The full constellation of 24 satellites became operational in 1993. After Korean Air Lines Flight 007 was shot down when it mistakenly entered Soviet airspace, President Ronald Reagan announced that the GPS system would be made available for civilian use as of September 16, 1983; however, initially this civilian use was limited to an average accuracy of 100 meters (330 ft) by use of Selective Availability (SA),

4731-407: The highest-quality signal was reserved for military use, and the signal available for civilian use was intentionally degraded, in a policy known as Selective Availability . This changed on May 1, 2000, with U.S. President Bill Clinton signing a policy directive to turn off Selective Availability to provide the same accuracy to civilians that was afforded to the military. The directive was proposed by

4814-473: The increased use of augmented reality , social networking , health care monitoring, personal tracking, inventory control and other indoor location-aware applications. In wireless security , it is an important method used to locate and map rogue access points . The popularity and low price of Wi-Fi network interface cards is an attractive incentive to use Wi-Fi as the basis for a localization system and significant research has been done in this area in

4897-528: The most significant development for safe and efficient navigation and surveillance of air and spacecraft since the introduction of radio navigation 50 years ago". Two GPS developers received the National Academy of Engineering Charles Stark Draper Prize for 2003: GPS developer Roger L. Easton received the National Medal of Technology on February 13, 2006. Francis X. Kane (Col. USAF, ret.)

4980-519: The need for clock synchronization. More recently, the Wi-Fi Round Trip Time standard has provided fine ToF ranging capabilities to Wi‑Fi. Citing the specific privacy concerns arising out of WPS, Google suggested a unified approach for excluding a particular access point from taking part in determining location using WPS, supposedly by every access point owner deliberately opting out for each access point to be excluded. Appending "_nomap" to

5063-440: The new measurements are collected, the receiver uses a weighting scheme to combine the new measurements with the tracker prediction. In general, a tracker can (a) improve receiver position and time accuracy, (b) reject bad measurements, and (c) estimate receiver speed and direction. The disadvantage of a tracker is that changes in speed or direction can be computed only with a delay, and that derived direction becomes inaccurate when

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5146-481: The nuclear triad, also had requirements for a more accurate and reliable navigation system. The U.S. Navy and U.S. Air Force were developing their own technologies in parallel to solve what was essentially the same problem. To increase the survivability of ICBMs, there was a proposal to use mobile launch platforms (comparable to the Soviet SS-24 and SS-25 ) and so the need to fix the launch position had similarity to

5229-428: The past 15 years. The problem of Wi‑Fi–based indoor localization of a device is that of determining the position of client devices with respect to access points. Many techniques exist to accomplish this, and these may be classified based on the four different criteria they use: received signal strength indication ( RSSI ), fingerprinting , angle of arrival ( AoA ) and time of flight ( ToF ). In most cases

5312-429: The path of the user. To minimize fluctuations in the received signal, there are certain techniques that can be applied to filter the noise. In the case of low precision, some techniques have been proposed to merge the Wi-Fi traces with other data sources such as geographical information and time constraints (i.e., time geography ). Accurate indoor localization is becoming more important for Wi‑Fi–based devices due to

5395-419: The precision depends on the number of discovered nearby access points with (accurate) entries in the database and the precisions of those entries. The access point location database gets filled by correlating mobile device location data (determined by other systems, such as Galileo or GPS) with Wi‑Fi access point MAC addresses. The possible signal fluctuations that may occur can increase errors and inaccuracies in

5478-514: The precision needed for GPS. The design of GPS is based partly on similar ground-based radio-navigation systems, such as LORAN and the Decca Navigator System , developed in the early 1940s. In 1955, Friedwardt Winterberg proposed a test of general relativity —detecting time slowing in a strong gravitational field using accurate atomic clocks placed in orbit inside artificial satellites. Special and general relativity predicted that

5561-644: The reason for the ultra-secrecy at that time. The nuclear triad consisted of the United States Navy's submarine-launched ballistic missiles (SLBMs) along with United States Air Force (USAF) strategic bombers and intercontinental ballistic missiles (ICBMs). Considered vital to the nuclear deterrence posture, accurate determination of the SLBM launch position was a force multiplier . Precise navigation would enable United States ballistic missile submarines to get an accurate fix of their positions before they launched their SLBMs. The USAF, with two thirds of

5644-405: The received signal ( received signal strength indicator , or RSSI ) and the method of "fingerprinting". Typically a wireless access point is identified by its SSID and MAC address , and these data are compared to a database of supposed locations of access points so identified. The accuracy depends on the accuracy of the database (e.g. if an access point has moved its entry is inaccurate), and

5727-541: The received signal vector x → {\displaystyle {\vec {x}}} is: x → = A Γ → {\displaystyle {\vec {x}}=\mathbf {A} {\vec {\Gamma }}} where Γ → = [ γ → 1 … γ → L ] {\displaystyle {\vec {\Gamma }}=[{\vec {\gamma }}_{1}\dots {\vec {\gamma }}_{L}]}

5810-408: The reference atomic clocks at the ground control stations; any drift of the clocks aboard the satellites from the reference time maintained on the ground stations is corrected regularly. Since the speed of radio waves ( speed of light ) is constant and independent of the satellite speed, the time delay between when the satellite transmits a signal and the ground station receives it is proportional to

5893-441: The second antenna and − 2 π ⋅ d ⋅ sin ⁡ ( θ ) ⋅ ( f / c ) ⋅ ( m − 1 ) {\displaystyle -2\pi \cdot d\cdot \sin(\theta )\cdot (f/c)\cdot (m-1)} at the m {\displaystyle m} -th antenna. Therefore, the following complex exponential can be used as

5976-403: The user carrying a clock synchronized with the satellites. Foremost is that only three satellites are needed to compute a position solution. If it were an essential part of the GPS concept that all users needed to carry a synchronized clock, a smaller number of satellites could be deployed, but the cost and complexity of the user equipment would increase. The description above is representative of

6059-401: The vector a → ( θ k ) γ k {\displaystyle {\vec {a}}(\theta _{k})\gamma _{k}} of received signals due to the k {\displaystyle k} -th propagation path, where a → ( θ k ) {\displaystyle {\vec {a}}(\theta _{k})}

6142-472: The wireless interfaces to calculate the ToF of signals and then use this information to estimate the distance and relative position of one client device with respect to access points. The granularity of such time measurements is in the order of nanoseconds and systems which use this technique have reported localization errors in the order of 2m. Typical applications for this technology are tagging and locating assets in buildings, for which room-level accuracy (~3m)

6225-557: Was allowed from the 1980s. Roger L. Easton of the Naval Research Laboratory , Ivan A. Getting of The Aerospace Corporation , and Bradford Parkinson of the Applied Physics Laboratory are credited with inventing it. The work of Gladys West on the creation of the mathematical geodetic Earth model is credited as instrumental in the development of computational techniques for detecting satellite positions with

6308-420: Was concerned with the curving of the paths of radio waves ( atmospheric refraction ) traversing the ionosphere from NavSTAR satellites. After Korean Air Lines Flight 007 , a Boeing 747 carrying 269 people, was shot down by a Soviet interceptor aircraft after straying in prohibited airspace because of navigational errors, in the vicinity of Sakhalin and Moneron Islands , President Ronald Reagan issued

6391-485: Was destroyed in a launch failure). The effect of the ionosphere on radio transmission was investigated in a geophysics laboratory of Air Force Cambridge Research Laboratory , renamed to Air Force Geophysical Research Lab (AFGRL) in 1974. AFGRL developed the Klobuchar model for computing ionospheric corrections to GPS location. Of note is work done by Australian space scientist Elizabeth Essex-Cohen at AFGRL in 1974. She

6474-700: Was discontinued, GPS was accurate to about 5 meters (16 ft). GPS receivers that use the L5 band have much higher accuracy of 30 centimeters (12 in), while those for high-end applications such as engineering and land surveying are accurate to within 2 cm ( 3 ⁄ 4  in) and can even provide sub-millimeter accuracy with long-term measurements. Consumer devices such as smartphones can be accurate to 4.9 m (16 ft) or better when used with assistive services like Wi-Fi positioning . As of July 2023 , 18 GPS satellites broadcast L5 signals, which are considered pre-operational prior to being broadcast by

6557-595: Was inducted into the U.S. Air Force Space and Missile Pioneers Hall of Fame at Lackland A.F.B., San Antonio, Texas, March 2, 2010, for his role in space technology development and the engineering design concept of GPS conducted as part of Project 621B. In 1998, GPS technology was inducted into the Space Foundation Space Technology Hall of Fame . On October 4, 2011, the International Astronautical Federation (IAF) awarded

6640-621: Was launched in 1969. With these parallel developments in the 1960s, it was realized that a superior system could be developed by synthesizing the best technologies from 621B, Transit, Timation, and SECOR in a multi-service program. Satellite orbital position errors, induced by variations in the gravity field and radar refraction among others, had to be resolved. A team led by Harold L. Jury of Pan Am Aerospace Division in Florida from 1970 to 1973, used real-time data assimilation and recursive estimation to do so, reducing systematic and residual errors to

6723-539: Was never considered as such by the GPS Joint Program Office (TRW may have once advocated for a different navigational system that used that acronym). With the individual satellites being associated with the name Navstar (as with the predecessors Transit and Timation), a more fully encompassing name was used to identify the constellation of Navstar satellites, Navstar-GPS . Ten " Block I " prototype satellites were launched between 1978 and 1985 (an additional unit

6806-515: Was seen as justification for the billions of dollars it would cost in research, development, deployment, and operation of a constellation of navigation satellites. During the Cold War arms race , the nuclear threat to the existence of the United States was the one need that did justify this cost in the view of the United States Congress. This deterrent effect is why GPS was funded. It is also

6889-520: Was ultimately used to determine the orbit of the GPS constellation. On February 12, 2019, four founding members of the project were awarded the Queen Elizabeth Prize for Engineering with the chair of the awarding board stating: "Engineering is the foundation of civilisation; ...They've re-written, in a major way, the infrastructure of our world." The GPS satellites carry very stable atomic clocks that are synchronized with one another and with

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