RTK Fundamentals - Revision history

Claudia.Prajanu at 14:30, 26 July 2018

2018-07-26T14:30:22Z

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	===Ambiguity Resolution===		===Ambiguity Resolution===
	As stated in the section above, one of the keys to obtain the best accuracy from RTK is to fix the carrier phase ambiguities to integer numbers. Normally, this is done in three steps:<ref name="GPS_WORLD_LAMBDA">~~[http://chromatographyonline.findanalytichem.com/lcgc/article/articleDetail.jsp?id=584852&sk=&date=&pageID=3~~ Bernd Eissfeller, Thomas Pany, Günter Heinrichs, Christian Tiberius, ''Real-Time Kinematic in the Light of GPS Modernization and Galileo'', Oct. 1, 2002, GPS Word]</ref>		As stated in the section above, one of the keys to obtain the best accuracy from RTK is to fix the carrier phase ambiguities to integer numbers. Normally, this is done in three steps:<ref name="GPS_WORLD_LAMBDA"> Bernd Eissfeller, Thomas Pany, Günter Heinrichs, Christian Tiberius, ''Real-Time Kinematic in the Light of GPS Modernization and Galileo'', Oct. 1, 2002, GPS Word</ref>
	* The ambiguities are first fixed to float numbers using standard least-square techniques.		* The ambiguities are first fixed to float numbers using standard least-square techniques.
	* The set of integer ambiguities is set to the one that optimizes the residuals in the surroundings of the float solution.		* The set of integer ambiguities is set to the one that optimizes the residuals in the surroundings of the float solution.

Filipe.Pelica: Included editor logo.

2014-09-18T17:14:01Z

Included editor logo.

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Carlos.Lopez at 11:40, 23 February 2012

2012-02-23T11:40:36Z

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Jose.Caro at 15:53, 5 December 2011

2011-12-05T15:53:26Z

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	With origin dating back to the mid-1990s, Real Time Kinematics (RTK) is a [[Differential GNSS\|differential GNSS]] technique which provides high positioning performance in the vicinity of a base station. The technique is based on the use of carrier measurements and the transmission of corrections from the base station, whose location is well known, to the rover, so that the main errors that drive the stand-alone positioning cancel out. A RTK base station covers a service area spreading about 10 or 20 kilometres, and a real time communication channel is needed connecting base and rover. RTK, which achieves performances in the range of a few centimetres, is a technique commonly used in surveying applications.<ref name="RTKIAG">[http://www.wasoft.de/e/iagwg451/ International Association of Geodesy (IAG) Working Group 4.5.1: Network RTK ] </ref><ref name="RTK_WIKI">[http://en.wikipedia.org/wiki/Real_Time_Kinematic RTK in Wikipedia]</ref><ref name="RTKWPNC06">[http://www.wpnc.net/fileadmin/WPNC06/Proceedings/34_Precise_Positioning_in_Real-Time_using_Navigation_Satellites_and.pdf Remote Sensing 2009, A. Rietdorf et al., ''Precise Positioning in Real-Time using Navigation Satellites and Telecommunication'', Proceedings of the 3rd Workshop on Positioning, Navigation and Communication (WPNC’06) ]</ref>		With origin dating back to the mid-1990s, [[Real Time Kinematics]] (RTK) is a [[Differential GNSS\|differential GNSS]] technique which provides high positioning performance in the vicinity of a base station. The technique is based on the use of carrier measurements and the transmission of corrections from the base station, whose location is well known, to the rover, so that the main errors that drive the stand-alone positioning cancel out. A RTK base station covers a service area spreading about 10 or 20 kilometres, and a real time communication channel is needed connecting base and rover. RTK, which achieves performances in the range of a few centimetres, is a technique commonly used in surveying applications.<ref name="RTKIAG">[http://www.wasoft.de/e/iagwg451/ International Association of Geodesy (IAG) Working Group 4.5.1: Network RTK ] </ref><ref name="RTK_WIKI">[http://en.wikipedia.org/wiki/Real_Time_Kinematic RTK in Wikipedia]</ref><ref name="RTKWPNC06">[http://www.wpnc.net/fileadmin/WPNC06/Proceedings/34_Precise_Positioning_in_Real-Time_using_Navigation_Satellites_and.pdf Remote Sensing 2009, A. Rietdorf et al., ''Precise Positioning in Real-Time using Navigation Satellites and Telecommunication'', Proceedings of the 3rd Workshop on Positioning, Navigation and Communication (WPNC’06) ]</ref>

	==RTK Technique==		==RTK Technique==

Jose.Caro at 15:45, 5 December 2011

2011-12-05T15:45:06Z

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	===Ambiguity Resolution===		===Ambiguity Resolution===
	As stated in the section above, one of the keys to obtain the best accuracy from RTK is to fix the carrier phase ambiguities to integer numbers. Normally, this is done in three steps:		As stated in the section above, one of the keys to obtain the best accuracy from RTK is to fix the carrier phase ambiguities to integer numbers. Normally, this is done in three steps:<ref name="GPS_WORLD_LAMBDA">[http://chromatographyonline.findanalytichem.com/lcgc/article/articleDetail.jsp?id=584852&sk=&date=&pageID=3 Bernd Eissfeller, Thomas Pany, Günter Heinrichs, Christian Tiberius, ''Real-Time Kinematic in the Light of GPS Modernization and Galileo'', Oct. 1, 2002, GPS Word]</ref>
	* The ambiguities are first fixed to float numbers using standard least-square techniques.		* The ambiguities are first fixed to float numbers using standard least-square techniques.
	* The set of integer ambiguities is set to the one that optimizes the residuals in the surroundings of the float solution.		* The set of integer ambiguities is set to the one that optimizes the residuals in the surroundings of the float solution.
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	Of these three steps, the second one is quite complex, because the float ambiguity covariance ellipsoid in the measurement space is extremely elongated. As a consequence, the brute-force search process is inefficient, normally beyond the computational capabilities of the rover equipment. Several techniques have been developed to deal with this problem; please consult the [[Carrier Phase Ambiguity Fixing]] article for more information.		Of these three steps, the second one is quite complex, because the float ambiguity covariance ellipsoid in the measurement space is extremely elongated. As a consequence, the brute-force search process is inefficient, normally beyond the computational capabilities of the rover equipment. Several techniques have been developed to deal with this problem; please consult the [[Carrier Phase Ambiguity Fixing]] article for more information.

	==Notes==		==Notes==
	<references group="footnotes"/>		<references group="footnotes"/>

Jose.Caro at 15:38, 5 December 2011

2011-12-05T15:38:33Z

@@ Line 13: / Line 13: @@
 The technique is based on the following high-level principles:
-*In the neighbourhood of a clean-sky location, the main errors in the GNSS signal processing are constant, and hence they cancel out when differential processing is used. This includes the error in the satellite clock bias, the satellite orbital error, the ionospheric delay and the tropospheric delay. The main errors left without correction are multipath, interference and receiver thermal noise. Of the errors listed above, the only one which is truely constant with respect to the user location is the satellite clock bias; the rest will show a given dependency with the location as one moves away from the base station, being the tropospheric error the first to be fully decorrelated in a few kilometres from the base.
+*In the neighbourhood of a clean-sky location, the main errors in the GNSS signal processing are constant, and hence they cancel out when differential processing is used. This includes the error in the satellite clock bias, the satellite orbital error, the ionospheric delay and the tropospheric delay. The main errors left without correction are multipath, interference and receiver thermal noise. Of the errors listed above, the only one which is truly constant with respect to the user location is the satellite clock bias; the rest will show a given dependency with the location as the rover moves away from the base station, being the tropospheric error the first to be fully de-correlated in a few kilometres from the base.
 *The noise of carrier measurements is much smaller than the one of the pseudo-code measurements. The typical error of code pseudorange measurements is around 1 m, to compare with 5 mm for carrier phase measurements. However, the processing of carrier measurements is subject to the so-called carrier phase ambiguity, an unknown integer number of times the carrier wave length, that needs to be fixed in order to rebuild full range measurements from carrier ones.
-*The phase ambiguities can be fixed using differential measurements between two reference stations.There are different techniques available to fix them, some based on single frequency measurements with long convergence times, other taking benefit of dual frequency observables with shorter convergence. In general, the techniques either depend on a high precision knowledge of the ionosphere, or assume that the two stations are close enough so that the ionospheric differential delay is negligible when compared with the wave-length of the carriers, around 20 cm. The latter is the approached followed in RTK, limiting the service area to 10 or 20 km; the former is used in [[Wide Area RTK (WARTK)|WARTK]] to cover big service areas with base stations separated around hundreds of kilometers away. The RTK approach needs continuity in the tracked measurements to avoid re-initialization of the phase-ambiguity filters; this is a severe limitation in urban environments due to the big number of obstructions.
+*The phase ambiguities can be fixed using differential measurements between two reference stations. There are different techniques available to fix them, some based on single frequency measurements with long convergence times, other taking benefit of dual frequency observables with shorter convergence. In general, the techniques either depend on a high precision knowledge of the ionosphere, or assume that the two stations are close enough so that the ionospheric differential delay is negligible when compared with the wave-length of the carriers, around 20 cm. The latter is the approached followed in RTK, limiting the service area to 10 or 20 km; the former is used in [[Wide Area RTK (WARTK)|WARTK]] to cover big service areas with base stations separated around hundreds of kilometres away. The RTK approach needs continuity in the tracked measurements to avoid re-initialization of the phase-ambiguity filters; this is a severe limitation in urban environments due to the big number of obstructions.
 The base station broadcasts its well-known location together with the code and carrier measurements at frequencies L1 and L2 for all in-view satellites. With this information, the rover equipment is able to fix the phase ambiguities and determine its location relative to the base with high precision. By adding up the location of the base, the rover is positioned in a global coordinate framework.
@@ Line 23: / Line 23: @@
 ==RTK Algorithm==
-As stated inthe previous section, ofe of the main problems in the RTK technique is fixing the phase ambiguities.
+As stated in the previous section, one of the main problems in the RTK technique is fixing the phase ambiguities.
 The RTK Algorithm is based on double differenced observables that can eliminate selective availability effects as well as other biases. The highlights of the algorithm are described next. At a given epoch, and for a given satellite, the simplified carrier phase observation equation is the following:
@@ Line 62: / Line 62: @@
 ===Ambiguity Resolution===
-As it was said above the ambiguity resolution is the key of positioning precision in RTK Technique. It can be divided in mainly three steps, as shown in the figure.
+Of these three steps, the second one is quite complex, because the float ambiguity covariance ellipsoid in the measurement space is extremely elongated. As a consequence, the brute-force search process is inefficient, normally beyond the computational capabilities of the rover equipment. Several techniques have been developed to deal with this problem; please consult the [[Carrier Phase Ambiguity Fixing]] article for more information.
 ==Notes==
 <references group="footnotes"/>

Jose.Caro at 14:47, 5 December 2011

2011-12-05T14:47:33Z

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	Real Time ~~Kinematic~~ (RTK) ~~satellite navigation~~ is a ~~DGNSS~~ technique ~~used~~ in ~~land survey and in hydrographic survey~~ based on the use of carrier ~~phase~~ measurements of the ~~GNSS signals where a single reference~~ station ~~provides~~ the real-time ~~corrections~~, ~~providing up to centimeter-level accuracy. When referring to GPS~~ in ~~particular~~, ~~the system~~ is ~~also~~ commonly ~~referred to as Carrier-Phase Enhancement, CPGPS~~.<ref name="RTK_WIKI"/>		With origin dating back to the mid-1990s, Real Time Kinematics (RTK) is a [[Differential GNSS\|differential GNSS]] technique which provides high positioning performance in the vicinity of a base station. The technique is based on the use of carrier measurements and the transmission of corrections from the base station, whose location is well known, to the rover, so that the main errors that drive the stand-alone positioning cancel out. A RTK base station covers a service area spreading about 10 or 20 kilometres, and a real time communication channel is needed connecting base and rover. RTK, which achieves performances in the range of a few centimetres, is a technique commonly used in surveying applications.<ref name="RTKIAG">[http://www.wasoft.de/e/iagwg451/ International Association of Geodesy (IAG) Working Group 4.5.1: Network RTK ] </ref><ref name="RTK_WIKI">[http://en.wikipedia.org/wiki/Real_Time_Kinematic RTK in Wikipedia]</ref><ref name="RTKWPNC06">[http://www.wpnc.net/fileadmin/WPNC06/Proceedings/34_Precise_Positioning_in_Real-Time_using_Navigation_Satellites_and.pdf Remote Sensing 2009, A. Rietdorf et al., ''Precise Positioning in Real-Time using Navigation Satellites and Telecommunication'', Proceedings of the 3rd Workshop on Positioning, Navigation and Communication (WPNC’06) ]</ref>

	==RTK Technique==		==RTK Technique==
	~~The~~ RTK ~~technique follows~~ the ~~same general principle as [[DGNSS Fundamentals\|classical DGNSS]], but instead of using corrections~~ to ~~C/A code pseudoranges, it uses~~ the ~~carrier phase as its signal~~.~~<ref name="RTK_WIKI"/>~~		From an architectural point of view, RTK consists of a base station, one or several rover users, and a communication channel with which the base broadcasts information to the users at real time.

	The ~~RTK~~ technique ~~consists~~ on a ~~rover user that applies real~~-~~time corrections provided by a base station~~. In the ~~classical [[DGNSS Fundamentals\|DGNSS Technique]]~~, ~~there~~ are ~~also 2 receivers~~, one at a ~~known~~ location (base station~~) and one at an unknown position~~, ~~that see~~ the ~~same GNSS satellites~~ in ~~common~~. ~~By fixing~~ the ~~location~~ of the ~~base station~~, the ~~other location may~~ be ~~found either by computing corrections~~ to the ~~position~~ of the ~~unknown receiver~~ or ~~by computing corrections to~~ the ~~pseudoranges~~. In the ~~classical DGNSS technology~~, ~~only corrections~~ to ~~C/A code pseudoranges are being transmitted, which brings rover positional errors down~~ to ~~values about 1 m for distances between rover and~~ base ~~station~~ of a ~~few tens~~ of ~~kilometers~~.~~<ref name="RTK_WIKI"/>~~		The technique is based on the following high-level principles:
			*In the neighbourhood of a clean-sky location, the main errors in the GNSS signal processing are constant, and hence they cancel out when differential processing is used. This includes the error in the satellite clock bias, the satellite orbital error, the ionospheric delay and the tropospheric delay. The main errors left without correction are multipath, interference and receiver thermal noise. Of the errors listed above, the only one which is truely constant with respect to the user location is the satellite clock bias; the rest will show a given dependency with the location as one moves away from the base station, being the tropospheric error the first to be fully decorrelated in a few kilometres from the base.
			*The noise of carrier measurements is much smaller than the one of the pseudo-code measurements. The typical error of code pseudorange measurements is around 1 m, to compare with 5 mm for carrier phase measurements. However, the processing of carrier measurements is subject to the so-called carrier phase ambiguity, an unknown integer number of times the carrier wave length, that needs to be fixed in order to rebuild full range measurements from carrier ones.
			*The phase ambiguities can be fixed using differential measurements between two reference stations.There are different techniques available to fix them, some based on single frequency measurements with long convergence times, other taking benefit of dual frequency observables with shorter convergence. In general, the techniques either depend on a high precision knowledge of the ionosphere, or assume that the two stations are close enough so that the ionospheric differential delay is negligible when compared with the wave-length of the carriers, around 20 cm. The latter is the approached followed in RTK, limiting the service area to 10 or 20 km; the former is used in [[Wide Area RTK (WARTK)\|WARTK]] to cover big service areas with base stations separated around hundreds of kilometers away. The RTK approach needs continuity in the tracked measurements to avoid re-initialization of the phase-ambiguity filters; this is a severe limitation in urban environments due to the big number of obstructions.

	~~When using carrier phase signals sent by the same satellites the accuracy can improved to about 30 cm.~~ The ~~difficulty of~~ the ~~use of~~ carrier ~~phase data comes~~ at ~~a cost~~ in ~~terms of overall system complexity because the measurements are ambiguous by an integer (i~~.~~e. every cycle of~~ the ~~carrier~~ is ~~similar~~ to ~~every other)~~. ~~Therefore,~~ the ~~key~~ of the RTK technique ~~is the [[RTK Fundamentals\|~~"~~Ambiguity Resolution~~"~~]].~~ <ref name="~~RTK_WIKI~~">[~~http://en~~.~~wikipedia.org/wiki/Real_Time_Kinematic~~ RTK in ~~Wikipedia]</ref>~~		The base station broadcasts its well-known location together with the code and carrier measurements at frequencies L1 and L2 for all in-view satellites. With this information, the rover equipment is able to fix the phase ambiguities and determine its location relative to the base with high precision. By adding up the location of the base, the rover is positioned in a global coordinate framework.

			The RTK technique can be used for distances of up to 10 or 20 kilometres,<ref name="RTKIAG"/><ref name="RTKWPNC06"/> yielding accuracies of a few centimetres in the rover position, to be compared with 1 m that is achieved with code-based [[Differential GNSS\|differential GPS]]. Because of its high precision in controlled environments, RTK is extensively used in surveying applications.

	==RTK Algorithm==		==RTK Algorithm==

	~~The difficulty in making an RTK system is properly aligning the signals.<ref name="RTK_WIKI"/>~~ As stated ~~in [http://www.septentrio.com/ Septentrio] homepage~~, ''the ~~carrier phase measurements are extremely precise (down to~~ the ~~fractions of millimeter), but they contain an unknown integer initialization constant,~~ the ~~so-called “phase ambiguity”. Therefore RTK positioning has to resolve integer~~ ambiguities ~~to achieve the high level of precision.''<ref>[http://www.septentrio~~.~~com/support/about-gnss/dgps-vs-rtk DGPS vs RTK, Septentrio]</ref>~~		As stated inthe previous section, ofe of the main problems in the RTK technique is fixing the phase ambiguities.

	The RTK Algorithm is based on double differenced observables that can eliminate selective availability effects as well as other biases. The highlights of the algorithm are described next. At a given epoch, and for a given satellite, the simplified carrier phase observation equation is the following:		The RTK Algorithm is based on double differenced observables that can eliminate selective availability effects as well as other biases. The highlights of the algorithm are described next. At a given epoch, and for a given satellite, the simplified carrier phase observation equation is the following:
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	In the above equation receiver and satellite clock offsets and hardware biases cancel~~, since double differencing is effectively differencing between satellites and between receivers~~. The single difference ambiguities difference <math>N_a^{12}-N_b^{12}</math> is commonly parameterized as a new ambiguity parameter <math>~~N_a~~^{12}</math>. The advantage of double differencing is that the new ambiguity parameter <math>~~N_a~~^{12}</math> is an integer because the non-integer terms in the GPS carrier phase observation, due to clock and hardware delays in the transmitter and receiver, are eliminated.		In the above equation receiver and satellite clock offsets and hardware biases cancel out. The single difference ambiguities difference <math>N_a^{12}-N_b^{12}</math> is commonly parameterized as a new ambiguity parameter <math>N_{ab}^{12}</math>. The advantage of double differencing is that the new ambiguity parameter <math>N_{ab}^{12}</math> is an integer because the non-integer terms in the GPS carrier phase observation, due to clock and hardware delays in the transmitter and receiver, are eliminated.

	Among the different challenges to achieve high-level precision, i.e. cm-level positioning, there is the ''Integer Ambiguity Resolution'', as the method used to solve the unknown integer ambiguities of the double-differenced carrier phase observables, that is the key in RTK algorithm.

			Although it would be possible to estimate the double difference ambiguity using a float approach instead of an integer one, this would lead to dm-level accuracy instead of cm-level. Hence, standard RTK fixes the ambiguities to integer figures.

	===Ambiguity Resolution===		===Ambiguity Resolution===
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	==Credits==		==Credits==
	Edited by GMV. The text in the introduction and the section ''RTK Technique'' is mostly taken from Wikipedia with minor adaptation,<ref name="RTK_WIKI"/> provided under [http://creativecommons.org/licenses/by-sa/3.0/ Creative Commons Attribution-ShareAlike License].

	The section ''Ambiguity Resolution'' has been taken from the article ''Real-Time Kinematic in the Light of GPS Modernization and Galileo''<ref name="GPS_WORLD_LAMBDA"/> and TU Delft University web-page dedicated to the LAMBDA Method <ref name="TU_Delf_Lambda"/>.		The section ''Ambiguity Resolution'' has been taken from the article ''Real-Time Kinematic in the Light of GPS Modernization and Galileo''<ref name="GPS_WORLD_LAMBDA"/> and TU Delft University web-page dedicated to the LAMBDA Method <ref name="TU_Delf_Lambda"/>.

Timo.Kouwenhoven at 23:27, 12 November 2011

2011-11-12T23:27:25Z

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	\|Category=Fundamentals		\|Category=Fundamentals
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	\|YearOfPublication=2011		\|YearOfPublication=2011
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	==RTK Technique==		==RTK Technique==

	The RTK technique follows the same general principle as [[DGNSS Fundamentals\|classical DGNSS]], but instead of using corrections to C/A code pseudoranges, it uses the carrier phase as its signal.<ref name="RTK_WIKI"/>		The RTK technique follows the same general principle as [[DGNSS Fundamentals\|classical DGNSS]], but instead of using corrections to C/A code pseudoranges, it uses the carrier phase as its signal.<ref name="RTK_WIKI"/>

Irene.Hidalgo at 11:56, 11 November 2011

2011-11-11T11:56:37Z

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	\|Authors=See ''Credits'' section		\|Authors=See ''Credits'' section
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	\|YearOfPublication=2011		\|YearOfPublication=2011
	\|Logo=GMV		\|Logo=GMV
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	}}		}}
			Real Time Kinematic (RTK) satellite navigation is a DGNSS technique used in land survey and in hydrographic survey based on the use of carrier phase measurements of the GNSS signals where a single reference station provides the real-time corrections, providing up to centimeter-level accuracy. When referring to GPS in particular, the system is also commonly referred to as Carrier-Phase Enhancement, CPGPS.<ref name="RTK_WIKI"/>
	Real Time Kinematic (RTK) satellite navigation is a DGNSS technique used in land survey and in hydrographic survey based on the use of carrier phase measurements of the ~~GPS, GLONASS and/or Galileo~~ signals where a single reference station provides the real-time corrections, providing up to centimeter-level accuracy. When referring to GPS in particular, the system is also commonly referred to as Carrier-Phase Enhancement, CPGPS.<ref name="RTK_WIKI"/>

	==RTK Technique==		==RTK Technique==
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	Once the ambiguity fixing is solved by LAMBDA Method explained above, the problem comes when baseline distance is larger than a few tens of kms. In this case, the compensation of atmospheric effects is not complete and the ambiguity fixing is less reliable due to error decorrelation, which increases proportionately with baseline distance. To solve this issue, information from a network of base stations is used, this is known as Network RTK techniques.		Once the ambiguity fixing is solved by LAMBDA Method explained above, the problem comes when baseline distance is larger than a few tens of kms. In this case, the compensation of atmospheric effects is not complete and the ambiguity fixing is less reliable due to error decorrelation, which increases proportionately with baseline distance. To solve this issue, information from a network of base stations is used, this is known as Network RTK techniques.

	Network RTK has been established in several countries during the last years. The first-generation of Network RTK systems is consolidated, and the objectives of the International Association of Geodesy ''Commission 4: Positioning & Applications'' to develop the next generation RTK are mainly:<ref>[http://www.gmat.unsw.edu.au/iag/iag_sc45.htm International Association of Geodesy ''Commission 4'' ~~webpage~~]</ref> <ref name=NET_RTK>[http://www.wasoft.de/e/iagwg451/ ''Introduction to Network RTK '', International Association of Geodesy (IAG) Working Group 4.5.1: Network RTK ] </ref>		Network RTK has been established in several countries during the last years. The first-generation of Network RTK systems is consolidated, and the objectives of the International Association of Geodesy ''Commission 4: Positioning & Applications'' to develop the next generation RTK are mainly:<ref>[http://www.gmat.unsw.edu.au/iag/iag_sc45.htm International Association of Geodesy ''Commission 4'' web-page]</ref> <ref name=NET_RTK>[http://www.wasoft.de/e/iagwg451/ ''Introduction to Network RTK '', International Association of Geodesy (IAG) Working Group 4.5.1: Network RTK ] </ref>

	* investigation on important technical issues for next generation RTK system development: e.g. the improvement of algorithms for the prediction of atmospheric corrections or the mitigation of station-dependent errors (mainly multipath) at the reference stations		* investigation on important technical issues for next generation RTK system development: e.g. the improvement of algorithms for the prediction of atmospheric corrections or the mitigation of station-dependent errors (mainly multipath) at the reference stations
	* development of data standards and operational procedures, including the communication protocols and message formats.		* development of data standards and operational procedures, including the communication protocols and message formats.
	* ~~establishement~~ of strong collaborations with other international ~~organisations~~, such as [http://igscb.jpl.nasa.gov/ IGS], and also with the industry sector.		* establishment of strong collaborations with other international organizations, such as [http://igscb.jpl.nasa.gov/ IGS], and also with the industry sector.

	==Credits==		==Credits==
	Edited by GMV. The text in the introduction and the section ''RTK Technique'' is mostly taken from Wikipedia with minor adaptation,<ref name="RTK_WIKI"/> provided under [http://creativecommons.org/licenses/by-sa/3.0/ Creative Commons Attribution-ShareAlike License].		Edited by GMV. The text in the introduction and the section ''RTK Technique'' is mostly taken from Wikipedia with minor adaptation,<ref name="RTK_WIKI"/> provided under [http://creativecommons.org/licenses/by-sa/3.0/ Creative Commons Attribution-ShareAlike License].

	The section ''Ambiguity Resolution'' has been taken from the article ''Real-Time Kinematic in the Light of GPS Modernization and Galileo''<ref name="GPS_WORLD_LAMBDA"/> and TU Delft University ~~webpage~~ dedicated to the LAMBDA Method <ref name="TU_Delf_Lambda"/>.		The section ''Ambiguity Resolution'' has been taken from the article ''Real-Time Kinematic in the Light of GPS Modernization and Galileo''<ref name="GPS_WORLD_LAMBDA"/> and TU Delft University web-page dedicated to the LAMBDA Method <ref name="TU_Delf_Lambda"/>.

	The section ''RTK on-going Research'' has been taken from the article ''Introduction to Network RTK'' <ref name=NET_RTK/> and the [http://www.gmat.unsw.edu.au/iag/iag_sc45.htm International Association of Geodesy ~~Commision~~ 4 (Positioning & Applications) ~~webpage~~].		The section ''RTK on-going Research'' has been taken from the article ''Introduction to Network RTK'' <ref name=NET_RTK/> and the [http://www.gmat.unsw.edu.au/iag/iag_sc45.htm International Association of Geodesy Commission 4 (Positioning & Applications) web-page].

	==Notes==		==Notes==

Irene.Hidalgo: /* RTK Technique */

2011-11-11T11:40:27Z

RTK Technique

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	==RTK Technique==		==RTK Technique==

	The classical ~~GNSS receivers compare a~~ C/A code pseudoranges signal being sent from the satellite with an internally generated copy of the same signal. Since the signal from the satellite takes time to reach the receiver, the two signals do not "line up" properly; the satellite's copy is delayed in relation to the local copy. By progressively delaying the local copy more and more, the ~~two signals will eventually line up properly. That delay is the time needed for the~~ signal ~~to reach the receiver, and from this the distance from the satellite can be calculated~~.<ref name="RTK_WIKI"/>		The RTK technique follows the same general principle as [[DGNSS Fundamentals\|classical DGNSS]], but instead of using corrections to C/A code pseudoranges, it uses the carrier phase as its signal.<ref name="RTK_WIKI"/>

	The ~~accuracy of the resulting range measurement is generally~~ a ~~function of the ability of the receiver's electronics to accurately compare the two signals~~. In ~~general receivers are able to align~~ the ~~signals to about 1% of one bit-width. For instance~~, ~~the coarse-acquisition (C/A) code sent on the GPS system sends a bit every 0.98 microsecond~~, so a ~~receiver is accurate to 0.01 microsecond, or about 3 metres in terms of distance. The military-only P~~(Y) ~~signal sent by~~ the same satellites ~~is clocked ten times as fast~~, ~~so with similar techniques~~ the receiver ~~will be accurate~~ to ~~about 30 cm~~. ~~Other effects introduce errors much greater than this~~, ~~and accuracy based on an uncorrected~~ C/A ~~signal is generally~~ about 15 m.<ref name="RTK_WIKI"/>		The RTK technique consists on a rover user that applies real-time corrections provided by a base station. In the classical [[DGNSS Fundamentals\|DGNSS Technique]], there are also 2 receivers, one at a known location (base station) and one at an unknown position, that see the same GNSS satellites in common. By fixing the location of the base station, the other location may be found either by computing corrections to the position of the unknown receiver or by computing corrections to the pseudoranges. In the classical DGNSS technology, only corrections to C/A code pseudoranges are being transmitted, which brings rover positional errors down to values about 1 m for distances between rover and base station of a few tens of kilometers.<ref name="RTK_WIKI"/>

	~~RTK follows~~ the same ~~general concept, but uses~~ the ~~satellite's~~ carrier phase ~~as its signal, not the messages contained within. The improvement possible using this signal is potentially very high if one continues to assume~~ a ~~1% accuracy~~ in ~~locking. For instance,~~ the ~~GPS coarse-acquisition~~ (~~C/A) code broadcast in the L1 signal changes phase at 1~~.~~023 MHz, but~~ the L1 carrier ~~itself~~ is ~~1575~~.~~42 MHz~~, ~~over a thousand times as fast. This frequency corresponds to a wavelength~~ of ~~19 cm for~~ the ~~L1 signal. Thus a ±1% error in L1 carrier phase measurement corresponds to a ±1.9mm error in baseline estimation~~.<ref name="RTK_WIKI">[http://en.wikipedia.org/wiki/Real_Time_Kinematic RTK in Wikipedia]</ref>		When using carrier phase signals sent by the same satellites the accuracy can improved to about 30 cm. The difficulty of the use of carrier phase data comes at a cost in terms of overall system complexity because the measurements are ambiguous by an integer (i.e. every cycle of the carrier is similar to every other). Therefore, the key of the RTK technique is the [[RTK Fundamentals\|"Ambiguity Resolution"]]. <ref name="RTK_WIKI">[http://en.wikipedia.org/wiki/Real_Time_Kinematic RTK in Wikipedia]</ref>

	==RTK Algorithm==		==RTK Algorithm==