Ashtech GPS Receivers

© Brooke Clarke 2009

Photo

Background

The L2 GPS signal can be either in plain text (P-code) or be encrypted by MOD 2 adding the secret A-code to get the Y-code.  In order to use the L2 signal for carrier phase surveying applications various ways can be used.  For example just squaring the L2 signal results in removing the Y-code and is used by a number of companies.  But the method developed by Ashtech (see patent5134407 below, provides the L2 carrier phase information with a lower noise figure and so is popular for precision applications.

Patents

4667203 Method and System for Determining Position using Signals from Satellites, Charles Counselman (Aero Service), May 19 1987 - multiply upper and lower sidebands of L2 to remove P-code
4928106 Global positioning system receiver with improved radio frequency and digital Processing, Javad Ashjaee, Roger J. Helkey, Robert G. Lorenz, Robert A. Sutherland (Ashtech), May 22, 1990, 342/352 - Squaring the signal to remove the P-code.
4972431 P-code-aided global positioning system receiver, Richard G. Keegan (Magnavox),  Nov 20, 1990, 375/1; 380/9; 342/357 - - adjust the phase of a locally generated replica of the known P-code until a strong demodulated signal appears out of the noise. This narrower bandwidth signal is then squared in order to eliminate the unknown modulation without hurting the signal-to-noise level as much as when the entire L2 signal is squared.  results in a half wavelength L2 carrier phase observable

5134407 Global positioning system receiver digital processing technique, Robert G. Lorenz, Roger J. Helkey, Kamran K. Abadi (Ashtech), Jul 28, 1992, 342/352; 342/357 -
Improved method to get around the P-code
Calls:
4426712Correlation system for global position receiverJan 17, 1984
4445118Navigation system and methodApr 24, 1984
4463357Method and apparatus for calibrating the ionosphere and application to surveillance of geophysical eventsJul 31, 1984
4468793Global position system (GPS) multiplexed receiverAug 28, 1984
4613977Digital Navstar receiverSep 23, 1986
4672629Receiver for bandspread signalsJun 9, 1987
4797677Method and apparatus for deriving pseudo range from earth-orbiting satellitesJan 10, 1989
4821294Digital signal processor and processing method for GPS receiversApr 11, 1989
4894662Method and system for determining position on a moving platform, such as a ship, using signals from GPS satellitesJan 16, 1990
4928106Global positioning system receiver with improved radio frequency and digital processingMay 22, 1990
4968981GPS receiver apparatusNov 6, 1990
4972431P-code-aided global positioning system receiverNov 20, 1990
Called By:
5216691Digital receiver for spread-spectrum signalsJun 1, 1993
5293170Global positioning system receiver digital processing techniqueMar 8, 1994
5325100Signal processing circuit for GPS receiverJun 28, 1994
5347546Method and apparatus for prefiltering a global positioning system receiverSep 13, 1994
5402442Receiving device for receiving and demodulating spread spectrum-modulated GPS waveMar 28, 1995
5515057GPS receiver with N-point symmetrical feed double-frequency patch antennaMay 7, 1996
5535278Global positioning system (GPS) receiver for recovery and tracking of signals modulated with P-codeJul 9, 1996
5548293System and method for generating attitude determinations using GPSAug 20, 1996
5561432Out of plane antenna vector system and methodOct 1, 1996
5572218System and method for generating precise position determinationsNov 5, 1996
5576715Method and apparatus for digital processing in a global positioning system receiverNov 19, 1996
5583513System and method for generating precise code based and carrier phase position determinationsDec 10, 1996
5633799Combined PC/104 and satellite positioning systemMay 27, 1997
5650785Low power GPS receiverJul 22, 1997
5684476Field navigation systemNov 4, 1997
5736961Dual Frequency global positioning systemApr 7, 1998
5825326Real-time high-accuracy determination of integer ambiguities in a kinematic GPS receiver Oct 20, 1998
5897605Spread spectrum receiver with fast signal reacquisitionApr 27, 1999
5901171Triple multiplexing spread spectrum receiverMay 4, 1999
5914685Relative position measuring techniques using both GPS and GLONASS carrier phase measurementsJun 22, 1999
5955973Field navigation systemSep 21, 1999
6018704GPS receiverJan 25, 2000
6041280GPS car navigation systemMar 21, 2000
6047017Spread spectrum receiver with multi-path cancellationApr 4, 2000
6061390P-code enhanced method for processing encrypted GPS signals without knowledge of the encryption codeMay 9, 2000
6125135System and method for demodulating global positioning system signalsSep 26, 2000
6125325GPS receiver with cross-track holdSep 26, 2000
6157341Method of processing signals of a satellite positioning systemDec 5, 2000
6181911Simplified receiver with rotator for performing position locationJan 30, 2001
6198765Spread spectrum receiver with multi-path correctionMar 6, 2001
6229479Relative position measuring techniques using both GPS and GLONASS carrier phase measurementsMay 8, 2001
6236937GPS receiver with cross-track holdMay 22, 2001
6249542Multipath processing for GPS receiversJun 19, 2001
RE37256System and method for generating precise position determinationsJul 3, 2001
6282231Strong signal cancellation to enhance processing of weak spread spectrum signalAug 28, 2001
6292749GPS receiver with cross-track holdSep 18, 2001
6393046Spread spectrum receiver with multi-bit correlatorMay 21, 2002
6400753Pseudo-noise correlator for a GPS spread spectrum receiverJun 4, 2002
6421609GPS receiver with cross-track holdJul 16, 2002
6466612Multipath processing for GPS receiversOct 15, 2002
6522682Triple multiplexing spread spectrum receiverFeb 18, 2003
6574558GPS receiver with cross-track holdJun 3, 2003
6633814GPS system for navigating a vehicleOct 14, 2003
6760364Multipath processing for GPS receiversJul 6, 2004
6768767GPS receiver capable of receiving C/A and P codes on multiple channelsJul 27, 2004
6788735Triple multiplexing spread spectrum receiverSep 7, 2004
6917644Spread spectrum receiver with multi-path correctionJul 12, 2005
7053826Extended range high sensitivity SPS positioning receiverMay 30, 2006
7064707Satellite-based positioning receiver with correction of cross correlation errorsJun 20, 2006
7116704Strong signal cancellation to enhance processing of weak spread spectrum signalOct 3, 2006
7184676Charging device and image forming apparatusFeb 27, 2007
7295633Triple multiplexing spread spectrum receiverNov 13, 2007
7301992Multipath processing for GPS receiversNov 27, 2007
7315569Method and system for locating a GPS correlated peak signalJan 1, 2008
7317752Method and system for locating a GPS correlated peak signalJan 8, 2008
7388539Carrier track loop for GNSS derived attitudeJun 17, 2008






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