Method and apparatus for generating a time signal
First Claim
1. A system for producing a system time signal, the system including:
- A. a directional antenna that is focused to receive signals transmitted by a geostationary satellite; and
B. a receiver that processes the signal received by the antenna, the receiver including i. code and carrier tracking circuits for tracking a carrier and a PRN code included in the signals received by the antenna;
ii. a decoder for decoding timing information, satellite position information and ionospheric delay information from the signals received by the antenna; and
iii. a correction subsystem for producing a corrected timing signal that is based on the transmitted signal and corrected for associated propagation and atmospheric delays, and iv. a reference clock for producing a system time signal that is associated with the corrected timing signal.
1 Assignment
0 Petitions
Accused Products
Abstract
A time signal generation system produces a reference time signal based on the signals transmitted by geostationary satellites, such as the satellites in the Wide Area Augmentation System (WAAS). A receiver in the system includes a directional antenna that is focused on the signals transmitted by the geostationary satellite. The antenna rejects multipath signals, and the receiver thus tracks the satellite signal directly, without having to compensate for multipath distortion. Once the receiver is tracking the code and carrier, the receiver decodes the transmitted data to recover timing information, as well as satellite orbital correction information and an ionospheric model, or table, transmitted by the satellite. The receiver then uses the decoded information and timing pulses provided in synchronism with the transmitted PRN code to produce a corrected timing signal. The timing signal is provided to drive a reference clock that produces a system time signal that is essentially as stable as the Cesium clock signals utilized by the WAAS system.
11 Citations
24 Claims
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1. A system for producing a system time signal, the system including:
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A. a directional antenna that is focused to receive signals transmitted by a geostationary satellite; and
B. a receiver that processes the signal received by the antenna, the receiver including i. code and carrier tracking circuits for tracking a carrier and a PRN code included in the signals received by the antenna;
ii. a decoder for decoding timing information, satellite position information and ionospheric delay information from the signals received by the antenna; and
iii. a correction subsystem for producing a corrected timing signal that is based on the transmitted signal and corrected for associated propagation and atmospheric delays, and iv. a reference clock for producing a system time signal that is associated with the corrected timing signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
a. a PRN code generator that provides a timing signal that includes pulses that are synchronous with PRN code epochs, b. a correction processor that provides correction signals to compensate for delays, and c. a summation processor that combines the timing signal and the correction signals to produce a corrected timing signal. -
12. The system of claim 11 wherein
i. the receiver further includes a phase rotator for rotating the phase of a received signal, and ii. the correction subsystem provides a control signal to the phase rotator to control for doppler effects of satellite movement relative to the antenna. -
13. The system of claim 12 wherein the correction processor determines the doppler effects based on satellite velocity information transmitted by the satellite.
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14. The system of claim 11 wherein the PRN code generator further includes in the timing signal pulses that are synchronous with PRN code bits.
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15. The system of claim 1 further including a display for displaying the time.
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16. The system of claim 1 further producing a correction signal for an associated local clock, the correction signal providing phase shift information relating to a phase shift required to phase-lock the local clock to a time signal transmitted by the satellite.
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17. The system of claim 11 wherein the directional antenna is a parabolic dish antenna.
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18. The system of claim 11 wherein the directional antenna is a feed horn antenna.
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19. The system of claim 11 wherein the antenna is a geodetic choke ring antenna.
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20. A system for producing a system time signal, the system including:
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C. a directional antenna that is focused to receive signals transmitted by a geostationary satellite; and
D. a receiver that processes the signal received by the antenna, the receiver including i. code and carrier tracking circuits for tracking a carrier and a PRN code included in the signals received by the antenna;
ii. a decoder for decoding timing information, satellite position and velocity information from the signals received by the antenna; and
iii. a correction subsystem for determining associated ionospheric, tropospheric and propagation delays and producing a corrected timing signal that is based on the transmitted signal that is based on the transmitted signal and corrected for the delays, and iv. a reference clock for producing a system time signal that is associated with the corrected timing signal. - View Dependent Claims (21, 22, 23, 24)
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Specification