Robust low-frequency spread-spectrum navigation system
Methods and apparatus are described for a navigation system. A process includes providing a plurality of transmitters distributed throughout a desired coverage area; locking the plurality of transmitters to a common timing reference; transmitting a signal from each of the plurality of transmitters. An apparatus includes a plurality of transmitters distributed throughout a desired coverage area; wherein each of the plurality of transmitters comprises a packet generator; and wherein the plurality of transmitters are locked to a common timing reference.
1. A radiolocation transmitter, comprising:
a packet generator configured to generate radiolocation data;
a pseudo-noise (PN) code generator configured to generate a PN code;
a radiolocation signal generator coupled to the packet generator and the PN code generator, where the radiolocation signal generator is configured to process the PN code and the radiolocation data to generate a spread-spectrum radiolocation signal; and
an output component configured to transmit the spread-spectrum radiolocation signal as a ground-wave or sky-wave signal.
2. The radiolocation transmitter of claim 1 , where the spread-spectrum radiolocation signal comprises a direct sequence spread-spectrum waveform.
3. The radiolocation transmitter of claim 1 , where the spread-spectrum radiolocation signal comprises a hybrid spread spectrum waveform that combines a direct sequence modulation with a frequency hopping, a time hopping, or a time gating protocol.
4. The radiolocation transmitter of claim 1 , where the radiolocation data comprises:
location information that indicates a geographic position of a radiolocation transmitter that sent the spread-spectrum radiolocation signal; and
time information that indicates a time when the spread-spectrum radiolocation signal was sent from the radiolocation transmitter.
5. The radiolocation transmitter of claim 1 , where the output component is configured to transmit the radiolocation signal in an 80-120 kHz frequency range.
6. The radiolocation transmitter of claim 5 , where the output component is configured to transmit the radiolocation signal split into an 80-90 kHz band and a 110-120 kHz band.
7. The radiolocation transmitter of claim 5 , where the output component is configured to transmit the radiolocation signal in a 90-110 kHz band.
8. The radiolocation transmitter of claim 1 , where the output component is configured to transmit the radiolocation signal in a frequency band with a center frequency around a 3.3 MHz.
9. The radiolocation transmitter of claim 1 , where the output component is configured to transmit the spread-spectrum radiolocation signal with a ground-wave propagation mode.
10. The radiolocation transmitter of claim 9 , where the radiolocation signal generator is configured to generate a second spread-spectrum radiolocation signal, and where the output component is configured to transmit the second spread-spectrum radiolocation signal with a sky-wave propagation mode.
11. A radiolocation transmitter, comprising:
a packet generator configured to generate radiolocation data;
a pseudo-noise (PN) code generator configured to generate a PN code;
a radiolocation signal generator coupled to the packet generator and the PN code generator, where the radiolocation signal generator is programmed to process the PN code and the radiolocation data to generate a constant-envelope hybrid spread spectrum waveform that combines direct sequence modulation with a frequency hopping, a time hopping, or a time gating protocol; and
an output component configured to transmit the hybrid spread-spectrum waveform as a radiolocation signal.
12. The radiolocation transmitter of claim 11 , where the radiolocation data comprises:
location information that indicates a geographic position of a radiolocation transmitter that sent the radiolocation signal; and
time information that indicates a time when the radiolocation signal was sent from the radiolocation transmitter.
13. The radiolocation transmitter of claim 12 , where the output component is configured to transmit the radiolocation signal in an 80-120 kHz frequency range.
14. The radiolocation transmitter of claim 13 , where the output component is configured to transmit the radiolocation signal split into an 80-90 kHz band and a 110-120 kHz band.
15. The radiolocation transmitter of claim 13 , where the output component is configured to transmit the radiolocation signal in a 90-110 kHz band.
16. The radiolocation transmitter of claim 11 , where the output component is configured to transmit the radiolocation signal in a frequency band with a center frequency around a 3.3 MHz.
17. The radiolocation transmitter of claim 11 , where the output component is configured to transmit the radiolocation signal around a 2.45 GHz frequency range.
18. The radiolocation transmitter of claim 11 , where the radiolocation signal generator is programmed to generate the hybrid spread spectrum waveform with a direct sequence modulation and a frequency hopping component that is orthogonal with respect to an underlying bit rate.
19. The radiolocation transmitter of claim 11 , where the radiolocation signal generator is programmed to generate the hybrid spread spectrum waveform with a direct sequence modulation and a time hopping protocol.
20. The radiolocation transmitter of claim 11 , where the output component is configured to transmit the hybrid spread-spectrum waveform with a ground-wave propagation mode.