GPS receiver and method for processing GPS signals
First Claim
1. A global positioning system (G PS) receiver, comprising:
- first circuitry for receiving and processing pseudorandom sequences transmitted by a plurality of orbiting satellites, said first circuitry configured to perform correlation operations on said pseudorandom sequences to determine pseudoranges from said GPS receiver to said satellites; and
second circuitry coupled to said first circuitry, said second circuitry configured for receiving and processing said pseudorandom sequences when said GPS receiver experiences blockage conditions, said second circuitry configured to perform said processing by digitizing and storing GPS data comprising a predetermined record length of said pseudorandom sequences and by performing fast convolution operations on said stored GPS data to determine said pseudoranges.
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Abstract
A global positioning system (GPS) receiver has first circuitry for receiving and processing pseudorandom sequences transmitted by a number of GPS satellites. The first circuitry is configured to perform conventional correlation operations on the received pseudorandom sequences to determine pseudoranges from the GPS receiver to the GPS satellites. The GPS receiver also includes second circuitry coupled to the first circuitry. The second circuitry is configured to receive and process the pseudorandom sequences during blockage conditions. The second circuitry processes the pseudorandom sequences by digitizing and storing a predetermined record length of the received sequences and then performing fast convolution operations on the stored data to determine the pseudoranges. The GPS receiver may have a common circuitry for receiving GPS signals from in view satellites and downconverting the RF frequency of the received GPS signals to an intermediate frequency (IF). The IF signals are split into two signal paths; a first of which provides the conventional correlation processing to calculate the pseudoranges. During blockage conditions, the IF signal is passed to the second signal path wherein the IF signals are digitized and stored in memory and later processed using the fast convolution operations to provide the pseudoranges. Alternative arrangements for the two signal paths include separate downconverters or shared digitizers. One embodiment provides both signal paths on a single integrated circuit with shared circuitry executing computer readable instructions to perform GPS signal processing appropriate to the reception conditions.
20 Citations
28 Claims
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1. A global positioning system (G PS) receiver, comprising:
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first circuitry for receiving and processing pseudorandom sequences transmitted by a plurality of orbiting satellites, said first circuitry configured to perform correlation operations on said pseudorandom sequences to determine pseudoranges from said GPS receiver to said satellites; and
second circuitry coupled to said first circuitry, said second circuitry configured for receiving and processing said pseudorandom sequences when said GPS receiver experiences blockage conditions, said second circuitry configured to perform said processing by digitizing and storing GPS data comprising a predetermined record length of said pseudorandom sequences and by performing fast convolution operations on said stored GPS data to determine said pseudoranges. - View Dependent Claims (2, 3)
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4. A global positioning system (GPS) receiver, comprising:
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an antenna for receiving GPS signals at an RF frequency from in view satellites;
a downconverter coupled to said antenna, said downconverter for reducing the RF frequency of said received GPS signals to an intermediate frequency (IF);
a conventional GPS receiver adaptable to be coupled to said downconverter, said conventional GPS receiver for acquiring and tracking a plurality of GPS satellite signals and for extracting Doppler information from said GPS satellite signals; and
first circuitry coupled to said conventional GPS receiver and adaptable to be coupled to said downconverted, said first circuitry configured for receiving and processing said received GPS signals when said GPS receiver experiences blockage conditions, said first circuitry configured to perform said processing by digitizing and storing GPS data comprising a predetermined record length of said IF GPS signals and by performing fast convolution operations on said stored GPS data to determine said pseudoranges. - View Dependent Claims (5, 6, 7, 8, 9, 10)
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11. A method for using a dual mode GPS receiver, said method comprising the steps of:
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activating said GPS receiver in a first mode of operation including, receiving GPS signals from in view satellites;
downconverting and demodulating said GPS signals to extract Doppler information regarding in view satellites and to compute pseudorange information;
storing said Doppler information;
detecting when said GPS receiver is experiencing blockage conditions and activating a second mode of operation in response thereto, the second mode including, digitizing said GPS signals at a predetermined rate to produce sampled GPS signals;
storing said sampled GPS signals in a memory; and
processing said sampled GPS signals to derive pseudoranges by performing fast convolution operations on said sampled GPS signals. - View Dependent Claims (12, 13, 14, 15, 16, 17, 19, 20, 21, 22, 25, 26, 27, 28)
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18. A tracking process utilizing global positioning system (GPS) satellites for determining the position of a remote sensor, the process comprising the steps of:
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receiving GPS signals at said remote sensor from a plurality of in view GPS satellites;
computing first pseudoranges utilizing said GPS signals and a conventional GPS receiver;
utilizing said first pseudoranges and satellite ephemeris data to compute a geographic location for said sensor;
detecting when said remote sensor is experiencing blockage conditions;
computing second pseudoranges utilizing digitized and buffered segments of said GPS signals, said computing comprising digital signal processing using fast convolution operations; and
utilizing said second pseudoranges and said satellite ephemeris data to compute said geographic location.
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23. A computer readable medium containing a computer program having executable code for a global positioning system (GPS) receiver, said computer program comprising:
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first instructions for receiving GPS signals from in view satellites, said GPS signals comprising pseudorandom (PN) codes;
second instructions for computing pseudoranges from said received GPS signals using a conventional GPS receiver;
third instructions for detecting when said GPS receiver is experiencing blockage conditions and digitizing said GPS signals at a predetermined rate to produce sampled GPS signals in response thereto;
fourth instructions for storing said sampled GPS signals in a memory; and
fifth instructions for processing said sampled GPS signals by performing fast convolution operations on said sampled GPS signals, said fifth instructions comprising a matched filtering operation to determine the relative timing between said PN codes and locally generated PN reference signals.
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24. A global positioning system (GPS) receiver apparatus, comprising:
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a first GPS receiver adaptable to be coupled to a source of GPS satellite signals, said first GPS receiver for acquiring and tracking a plurality of GPS satellite signals and for extracting Doppler information from said GPS satellite signals; and
a second GPS receiver adaptable to be coupled to said source of GPS satellite signals during blockage conditions, said second GPS receiver configured to sample and store said GPS signals at a predetermined rate to produce sampled GPS signals and to process said sampled GPS signals using fast convolution operations, said second GPS receiver further configured to respond to a signal indicating that said GPS receiver apparatus is experiencing blockage conditions and to initiate a snapshot GPS mode wherein said second GPS receiver is coupled to said source of said GPS satellite signals.
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Specification