Rapid acquisition methods and apparatus for GPS signals
First Claim
1. A method of receiving a signal with a receiver, said signal transmitted at a predetermined carrier frequency from one of a plurality of transmitters, said signal including a waveform modulated according to a periodically-repeating pseudonoise (PN) sequence that uniquely identifies the transmitter that sent the signal, said signal used in determining a location of the receiver, said method comprising:
- at the receiver, receiving electromagnetic energy in the vicinity of said carrier frequency, and digitizing said energy for a predefined period of time;
hypothesizing one of said plurality of transmitters and an associated hypothesized signal and providing a set of reference frequency samples corresponding to said hypothesized signal;
hypothesizing a first residual frequency;
selecting from said digitized energy a first subset of data of length at least equal to two repetitions of said periodically-repeating PN sequence, thereby defining a first data block;
responsive to said first data block, calculating a first set of data frequency samples;
pruning said first set of data frequency samples responsive to said hypothesized first residual frequency to provide a periodically-spaced first subset of said first set of data frequency samples, wherein said periodically-spaced first subset includes a plurality of samples having indices spaced relative to one another by an integer K, wherein K is the number of PN sequences in said first data block;
computing a first correlation series from said periodically-spaced first subset of said first set of data frequency samples and said set of reference frequency samples;
computing a first final correlation series comprising at least said first correlation series; and
examining said first final correlation series to determine whether a matched condition occurs between said transmitted signal and said hypothesized signal.
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Abstract
A method and apparatus for receiving a signal from transmitters such as GPS satellites, for fixing the location of the receiver. Each of the transmitted signals includes a unique periodically-repeating sequence. A received signal is stored by the receiver for at least two repetitions of the periodically-repeating sequence. FFT operations are performed, and the resulting data frequency samples are pruned responsive to a hypothesized residual frequency, a procedure which significantly reduces the total number of subsequent calculations and therefore significantly reduces processing time. A correlation series is determined from the pruned samples and reference frequency samples corresponding to a hypothesized transmitter. If a match is found in the examination of this series, a code phase offset is determined; if not the process is repeated with another hypothesized residual frequency. Multiple correlation series similarly obtained may also be incoherently combined prior to this examination. The apparatus and method disclosed herein is particularly useful for combined position location and communication systems, especially those that are unsynchronized, such as assisted GPS (“A-GPS”) utilized on GSM and UMTS cellular telephone systems.
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Citations
45 Claims
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1. A method of receiving a signal with a receiver, said signal transmitted at a predetermined carrier frequency from one of a plurality of transmitters, said signal including a waveform modulated according to a periodically-repeating pseudonoise (PN) sequence that uniquely identifies the transmitter that sent the signal, said signal used in determining a location of the receiver, said method comprising:
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at the receiver, receiving electromagnetic energy in the vicinity of said carrier frequency, and digitizing said energy for a predefined period of time; hypothesizing one of said plurality of transmitters and an associated hypothesized signal and providing a set of reference frequency samples corresponding to said hypothesized signal; hypothesizing a first residual frequency; selecting from said digitized energy a first subset of data of length at least equal to two repetitions of said periodically-repeating PN sequence, thereby defining a first data block; responsive to said first data block, calculating a first set of data frequency samples; pruning said first set of data frequency samples responsive to said hypothesized first residual frequency to provide a periodically-spaced first subset of said first set of data frequency samples, wherein said periodically-spaced first subset includes a plurality of samples having indices spaced relative to one another by an integer K, wherein K is the number of PN sequences in said first data block; computing a first correlation series from said periodically-spaced first subset of said first set of data frequency samples and said set of reference frequency samples; computing a first final correlation series comprising at least said first correlation series; and examining said first final correlation series to determine whether a matched condition occurs between said transmitted signal and said hypothesized signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of processing a signal that has been transmitted at a predetermined carrier frequency from one of a plurality of transmitters and that includes a waveform modulated according to a repeating pseudonoise (PN) sequence that identifies said one transmitter, the method comprising:
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receiving electromagnetic energy in a vicinity of said carrier frequency, and digitizing said energy for a predefined period of time; hypothesizing an identity of one of said transmitters and determining a signal associated therewith; providing a set of reference frequency samples corresponding to said determined signal; hypothesizing a first residual frequency of said determined signal; selecting from said digitized energy a first subset of data of length at least equal to two repetitions of said repeating PN sequence, thereby defining a first data block; responsive to said first data block, calculating a first set of data frequency samples using said first subset of data; pruning said first set of data frequency samples using said hypothesized first residual frequency to produce a periodically-spaced first subset of said first set of data frequency samples, wherein said periodically-spaced first subset includes a plurality of samples having indices spaced relative to one another by an integer K, wherein K is the number of PN sequences in said first data block; and computing a first final correlation series using as an input at least a first correlation series from said periodically-spaced first subset of said first set of data frequency samples and said set of reference frequency samples to produce an indication of whether a matched condition exists between said transmitted signal and said hypothesized signal. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A method of receiving at a mobile station a GPS signal transmitted at a GPS frequency from one of a plurality of satellite transmitters in earth orbit, to identify the satellite that transmitted the GPS signal and to determine a time of arrival at said mobile station of the GPS signal, said time of arrival used in determining the location of the mobile station, said GPS signal including a plurality of repetitions of a periodically-repeated PN sequence that uniquely identify the satellite that transmitted the GPS signal, the method comprising:
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at the mobile station, observing and digitizing a signal in the vicinity of the GPS frequency for a predefined period of time; hypothesizing a GPS satellite and providing a set of reference frequency samples corresponding to said hypothesized satellite; hypothesizing a first residual frequency; selecting from said digitized signal a first subset of data of length at least equal to two repetitions of said periodically-repeating PN sequence, thereby defining a first data block; responsive to said first data block, calculating a first set of data frequency samples; pruning said first set of data frequency samples responsive to said hypothesized first residual frequency to define a periodically-spaced first subset of said first set of data frequency samples wherein said periodically-spaced first subset includes a plurality of samples having indices spaced relative to one another by an integer K, wherein K is the number of repetitions of said PN sequence in said first data block; computing a first correlation series from said periodically-spaced first subset of said first set of data frequency samples and said set of reference frequency; selecting from said digitized signal a second subset of data of length at least equal to two repetitions of said periodically-repeating PN sequence, thereby defining a second data block; responsive to said second data block, calculating a second set of data frequency samples; pruning said second set of data frequency samples responsive to said hypothesized first residual frequency to define a periodically-spaced second subset of said second set of data frequency samples wherein said periodically-spaced second subset includes a plurality of samples having indices spaced relative to one another by an integer K, wherein K is the number of repetitions of said PN sequence in said second data block; computing a second correlation series from said periodically-spaced second subset of said second set of data frequency samples and said set of reference frequency samples; forming a final correlation series comprising at least a detecting and combining of said first correlation series and said second correlation series; and searching said final correlation data set to identify the presence of the GPS signal and if the presence of the GPS signal is identified, then determining a PN code phase offset. - View Dependent Claims (31, 32, 33, 34, 35)
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36. A method of processing a signal that has been transmitted from one of a plurality of transmitters, said signal containing a waveform modulated by a repeating PN sequence, the method comprising:
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hypothesizing a signal associated with one of said transmitters and a carrier frequency thereof; hypothesizing a residual frequency; extracting a first subset of data of length at least equal to two repetitions of said repeating PN sequence from electromagnetic energy received in a vicinity of a carrier frequency of said signal to be processed; pruning a first set of data frequency samples, computed from said first subset of data, in response to said hypothesized residual frequency, to produce a subset of said first set of data frequency samples, wherein said subset of said first set of data frequency samples comprises a plurality of samples having indices spaced relative to one another by an integer K, wherein K is the number of repetitions of said repeating PN sequence in said extracted first subset of data; computing a final correlation series using as inputs at least a correlation series determined from said subset of said first set of data frequency samples and a set of reference frequency samples corresponding to said hypothesized signal; and examining said final correlation series to determine whether a matched condition exists between said transmitted signal and said hypothesized signal.
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37. A mobile station that includes a position location system that receives a signal transmitted at a predetermined frequency from one of a plurality of transmitters, said transmitted signal including a periodically-repeating sequence that uniquely identifies the transmitter that sent the signal, the method comprising:
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means for observing and digitizing electromagnetic energy at the predetermined frequency for a predefined period of time; means for hypothesizing one of said plurality of transmitters and providing a set of reference frequency samples corresponding to a hypothesized signal transmitted from said hypothesized transmitter; means for hypothesizing a residual frequency; means for selecting a first portion of said digitized electromagnetic energy of length at least equal to two repetitions of said periodically-repeating sequences, thereby defining a first data block; means, responsive to said first data block, for calculating a first set of data frequency samples; means for pruning said first set of data frequency samples responsive to said hypothesized residual frequency to provide a periodically-spaced subset of said first set of data frequency samples, wherein said periodically-spaced subset comprises a plurality of samples having indices spaced relative to one another by an integer K, wherein K is the number of repetitions of said periodically-repeating sequence in said first data block; means for computing a first correlation series from said periodically-spaced subset of said first set of data frequency samples and said sat of reference frequency samples; means for computing a final correlation series comprising at least said first correlation series; and means for searching said final correlation series to identify whether a signal match condition occurs between said hypothesized signal and said received signal and if a matched condition is found between said hypothesized signal and said received signal, then determining timing information. - View Dependent Claims (38, 39, 40, 41, 42, 43, 44, 45)
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Specification