Agile navigation transmitter system
A direct digital synthesis transmitter that uses a programmable digital circuit to generate a digital signal representing at least one radio frequency signal, the generated signal is filtered, amplified by an amplifier, and provided to a transmission antenna without upconversion. The transmitter generating the digital signal at a desired output frequency range such that a frequency upconverter is not needed to produce signals in the desired radio frequency range.
1. A transmission system for providing navigation signals, the system comprising:
a digital processing circuit configured to generate digital navigation signals based on signal characteristics specifying at least one of a carrier frequency, modulation type, waveform, power, data structure, and timing information; and
a radio frequency (RF) amplifier operationally connected to the digital processing circuit and configured to amplify RF signals for transmission to at least one navigation receiver via at least one RF antenna,
wherein the RF signals are derived from the digital navigation signals and maintained with substantially the same carrier frequency as that of the digital navigation signals without an up-conversion to a higher frequency prior to transmission via the at least one RF antenna.
2. The transmission system of claim 1 , wherein the carrier frequency of the generated digital navigation signals is substantially equal to a carrier frequency of the amplified RF signals after amplification by the RF amplifier.
3. The transmission system of claim 1 , further comprising a digital to analog converter circuit operationally connected to the digital processing circuit and configured to convert the digital navigation signals to the RF signals in analog form prior to delivery of the RF signals to the RF amplifier.
4. The transmission system of claim 1 , further comprising a signal descriptor circuit operationally connected to the digital processing circuit and configured to provide the digital processing circuit with the signal characteristics based on pre-stored signal characteristics specifying a plurality of navigation signals.
5. The transmission system of claim 1 , further comprising a non-volatile memory device configured to store the signal characteristics at time of manufacturing of the transmission system and maintain integrity of and ability to retrieve the signal characteristics after a loss of power to the transmission system.
6. The transmission system of claim 5 , wherein the non-volatile memory device is configured to receive via a wireless receiver new signal characteristics specifying new navigation signals from a remote location for storage of the new signal characteristics.
7. The transmission system of claim 1 , further comprising a reference timing source and ephemeris reference source in communication with the digital processing circuit.
8. The transmission system of claim 1 , wherein the digital processing circuit is configured to access and retrieve digital signal values from a lookup table storing a list of digital signal values that correspond to a plurality of predefined signal characteristics.
9. The transmission system of claim 1 , wherein the RF amplifier comprises a preamplifier, a bandpass filter, and a power amplifier.
10. The transmission system of claim 1 , wherein the digital processing circuit calculates and applies a noise cancellation signal to remove undesired noise in regions of the target spectrum of the GHz range or spectrum.
11. The transmission system of claim 1 , further comprising a noise cancellation signal generator in communication with the digital processing circuit, the noise cancellation signal generator being configured to produce a digital data stream that represents an inverse of an undesirable noise signal such that the undesirable noise signal is substantially eliminated from the output of the digital processing circuit when communicated to the RF amplifier.
12. A method of providing navigation signals, the method comprising:
generating by a hardware processing circuit digital navigation signals pursuant to signal characteristics specifying at least one of a carrier frequency, modulation type, data structure, and timing information;
deriving radio frequency (RF) signals from the digital navigation signals while maintaining substantially the same carrier frequency for the RF signals as that of the digital navigation signals and without an up-conversion to a higher frequency; and
amplifying by a RF amplifier the derived RF signals for transmission to at least one navigation receiver via at least one RF antenna at a transmission frequency.
13. The method of claim 12 , further comprising:
receiving the signal characteristics from a signal descriptor circuit to generate the digital navigation signals based on the carrier frequency;
adjusting amplitudes of the navigation signals to account for gain characteristics of the RF antenna by frequency;
converting the digital navigation signals directly to the RF signals in analog form at the carrier frequency or frequencies without the need to upconvert to the transmission frequency via the RF antenna;
minimizing noise by instructing a tunable amplifier to generate one or more pass bands; and
transmitting with the RF antenna the amplified RF signals without upconverting to the transmission frequency.
14. The method of claim 12 , further comprising applying noise cancellation for undesirable noise signals within a frequency spectrum of the RF signals to substantially eliminate the undesirable noise signals from the amplified RF signal.
15. The method of claim 12 , wherein the carrier frequency of the generated digital navigation signals is substantially equal to a carrier frequency of the amplified RF signals after amplification by the RF amplifier.
16. The method of claim 12 , further comprising converting the digital navigation signals using a digital-to-analog converter to the RF signals in analog form prior to delivery of the RF signals to the RF amplifier.
17. The method of claim 12 , further comprising providing the digital processing circuit with the signal characteristics based on pre-stored signal characteristics specifying a plurality of navigation signals.
18. The method of claim 12 , further comprising storing the signal characteristics at time of manufacturing of the transmission system in a non-volatile memory device and maintaining integrity of and ability to retrieve the signal characteristics after a loss of power to the non-volatile memory device.
19. The method of claim 18 , wherein the non-volatile memory device is configured to receive via a wireless receiver new signal characteristics specifying new navigation signals from a remote location for storage of the new signal characteristics.
20. The method of claim 18 , further comprising producing a digital data stream that represents an inverse of an undesirable noise signal such that the undesirable noise signal is substantially eliminated from the RF signals when communicated to the RF amplifier.