TIME REFERENCE SYSTEM
First Claim
1. A time reference system for generating a time reference from signals produced by a global navigation satellite constellation, wherein the system comprises:
- a satellite signal receiver having a radio frequency stage configured to receive and down convert code-modulated signals from a plurality of satellites and a correlator configured to receive, track and decode the down-converted satellite signals to provide signals containing partial pseudo-range measurements for respective satellites, anda data processing arrangement configured to receive signals containing assistance data from a source other than the received and down-converted satellite signals and the signals containing partial pseudo-range measurements, to perform data-bit synchronisation in which the bit edges of a data bit stream carried by the received satellite signals are identified, to perform correlation of pre-selected data sequences in the data stream to resolve time ambiguities, and to compute a time reference signal based on the assistance data, the partial pseudo-range measurements and code-tracking outputs from the satellite signal receiver, the data-bit synchronisation and the data sequence correlation.
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Accused Products
Abstract
A time reference system for generating a time reference from signals produced by a global navigation satellite constellation has a satellite signal receiver to receive and down-convert code-modulated signals from a plurality of satellites and a correlator to track and decode the down-converted signals to provide signals containing partial pseudo-range measurements for respective satellites. A data processing arrangement receives assistance data from an external source and performs data-bit synchronisation in which bit edges of a low frequency data bit stream carried by the received satellite signals are identified, to perform a preliminary position-velocity-time solution to provide an approximate time reference, and to perform auto-correlation of pre-selected data sequences in the data stream to resolve time ambiguities thereby to compute a precise time reference signal in weak received signal conditions. The pre-selected data sequences may be the repeated data preamble in the GPS navigation message constituted by the data stream.
54 Citations
16 Claims
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1. A time reference system for generating a time reference from signals produced by a global navigation satellite constellation, wherein the system comprises:
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a satellite signal receiver having a radio frequency stage configured to receive and down convert code-modulated signals from a plurality of satellites and a correlator configured to receive, track and decode the down-converted satellite signals to provide signals containing partial pseudo-range measurements for respective satellites, and a data processing arrangement configured to receive signals containing assistance data from a source other than the received and down-converted satellite signals and the signals containing partial pseudo-range measurements, to perform data-bit synchronisation in which the bit edges of a data bit stream carried by the received satellite signals are identified, to perform correlation of pre-selected data sequences in the data stream to resolve time ambiguities, and to compute a time reference signal based on the assistance data, the partial pseudo-range measurements and code-tracking outputs from the satellite signal receiver, the data-bit synchronisation and the data sequence correlation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of generating a time reference signal from signals produced by a global navigation satellite constellation, comprising:
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(a) receiving, down-converting, and tracking the signals transmitted by a plurality of satellites in the constellation to produce a plurality of receiver output signals, receiving assistance data signals from a source other than the directly received satellite signals, and producing from the receiver output signals and the assistance data signals representing a preliminary time solution, (b) correlating pre-selected data sequences, using a data processor, in a data stream carried by the signals transmitted by at least one of the satellites to resolve time ambiguities in the preliminary time solution, thereby to generate the time reference signal representing time to an accuracy of better than +/−
1 ms.
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15. A method of generating a time reference signal from signals produced by a global navigation satellite constellation, comprising:
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(a) receiving, down-converting, and tracking the signals transmitted by a plurality of satellites in the constellation to produce a plurality of receiver output signals, receiving assistance data signals from a source other than the directly received satellite signals, and producing from the receiver output signals and the assistance data signals representing a preliminary time solution, (b) performing data-bit synchronization, using a data processor, in which bit edges of a data stream carried by the signals transmitted by at least one of the satellites are identified, the data-bit synchronisation including performing frequency-shift-compensated integration of samples of the received data stream.
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16. A time reference system for generating a time reference signal from signals produced by a global navigation satellite constellation, wherein the system comprises:
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a satellite signal receiver having a radio frequency stage for receiving and down-converting code-modulated signals from a plurality of satellites and a correlator to receive, track and decode the down-converted satellite signals to provide signals containing partial pseudo-range measurements for respective satellites, and a data processing arrangement configured to receive signals containing assistance data from a source other than the received and down-converted satellite signals and the signals containing partial pseudo-range measurements, to perform data-bit synchronisation in which bit edges of a data bit stream carried by the received satellite signals are identified, to compute a position-velocity-time solution using time-of-arrival measurements of signals received by the receiver from the satellites, and to perform correlation of the data bit stream in the received and down-converted satellite signals with pre-selected data sequences, and, using all three of the data-bit synchronisation, the position-velocity-time solution, and the data bit stream correlation to compute a time reference signal.
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Specification