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 synchronization 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.
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Citations
15 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 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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15. 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