Digital radio frequency transceiver system and method
A transceiver architecture for wireless base stations wherein a broadband radio frequency signal is carried between at least one tower-mounted unit and a ground-based unit via optical fibers, or other non-distortive media, in either digital or analog format. Each tower-mounted unit (for both reception and transmission) has an antenna, analog amplifier and an electro-optical converter. The ground unit has ultrafast data converters and digital frequency translators, as well as signal linearizers, to compensate for nonlinear distortion in the amplifiers and optical links in both directions. In one embodiment of the invention, at least one of the digital data converters, frequency translators, and linearizers includes superconducting elements mounted on a cryocooler.
1. A communication system, comprising:
an optoelectronic receiver configured to receive an optic signal conveyed from an electrooptic transmitter to an optic communication medium, comprising an analog domain representation of a radio frequency signal having frequencies above 698 MHz modulating the optic signal, and to produce an electrical analog domain signal corresponding to radio frequency signal frequencies above 698 MHz, including at least one intermodulation distortion product of the radio frequency signal;
a digitizer configured to quantize the electrical analog domain signal to a digital stream having a sampling rate of at least 1.4 gigasamples per second; and
a digital signal processor configured receive the digital stream and digitally reduce a representation of an amplitude of at least one intermodulation distortion product, dependent on a model of the intermodulation distortion properties of the at least one of the optoelectronic receiver and the electrooptic transmitter, and to produce a processed signal output.
2. The communication system according to claim 1 , wherein the digital signal processor is configured to reduce a representation of an amplitude of at least one intermodulation distortion product over a range of a frequency band greater than about 20 MHz.
3. The communication system according to claim 2 , wherein the digital signal processor is configured to reduce a representation of an amplitude of at least one intermodulation distortion product over a range of a frequency band greater than about 60 MHz.
4. The communication system according to claim 1 , wherein the digital signal processor is configured to improve a effective spur-free dynamic range of the digitized analog domain representation by at least 3 dB.
5. The communication system according to claim 4 , wherein the digital signal processor is configured to improve a effective spur-free dynamic range of the digitized analog domain representation by at least 6 dB.
6. The communication system according to claim 1 , further comprising:
an interface configured to receive a radio frequency signal having a frequency above than 698 MHz; and
the electrooptic transmitter configured to produce the optic signal conveyed in the optic communication medium, comprising an analog domain representation of the radio frequency signal from the interface having frequencies above 698 MHz modulating the optic signal.
7. The communication system according to claim 1 , wherein the digital processor comprises a plurality of lookup tables, and is configured to deconvolve a non-linear distortion.
8. The communication system according to claim 1 , wherein the digitizer comprises a Josephson junction configured to digitize the analog domain signal at a rate of at least 40 GHz.
9. The communication system according to claim 1 , further comprising a digital channelizer configured to segregate a broadband signal represented in the processed signal output into a plurality of different independent communication channels.
10. A communication method, comprising:
receiving an optic signal conveyed from an electrooptic transmitter to an optic communication medium to an optoelectronic receiver, comprising an analog domain representation of a radio frequency signal having frequencies above 698 MHz modulating the optic signal;
producing an electrical analog domain signal corresponding to radio frequency signal frequencies above 698 MHz, including at least one intermodulation distortion product of the radio frequency signal;
quantizing the electrical analog domain signal to a digital stream having a sampling rate of at least 1.4 gigasamples per second; and
digitally reducing a representation of an amplitude of at least one intermodulation distortion product, dependent on a model of the intermodulation distortion properties of the at least one of the optoelectronic receiver and the electrooptic transmitter.
11. The method according to claim 10 , wherein a representation of an amplitude of at least one intermodulation distortion product is reduced over a range of a frequency band greater than about 20 MHz.
12. The method according to claim 10 , wherein a effective spur-free dynamic range of the digitized analog domain representation is improved by at least 3 dB.
13. The method according to claim 10 , further comprising:
receiving a radio frequency signal having a frequency above than 698 MHz; and
producing the optic signal conveyed in the optic communication medium, comprising an analog domain representation of the received radio frequency signal having frequencies above 698 MHz modulating the optic signal.
14. The method according to claim 10 , wherein said model is represented by data stored in a plurality of lookup tables, which is used to deconvolve a non-linear distortion.
15. The method according to claim 10 , further comprising segregating a broadband signal represented in the processed signal output into a plurality of different independent communication channels with a digital channelizer.
16. A method of reducing a crest factor in a digital representation of an analog radio frequency signal which is adapted for amplification through a power amplifier and transmission as a radio frequency signal through an antenna, comprising:
receiving a plurality of oversampled digital representations of radio frequency signals having different frequencies;
determining that a combination of the plurality of oversampled digital representations of radio frequency signals having different frequencies will produce a first composite signal having an excessive peak-to-average power ratio and thereby reduce an efficiency of the power amplifier;
digitally modifying the combination of the plurality of oversampled digital representations of radio frequency signals having different frequencies to produce a second composite signal having a reduced peak-to-average power ratio with respect to the peak-to-average power ratio of the first composite signal while meeting at least one predetermine signal distortion criterion; and
outputting the second composite signal.
17. The method according to claim 16 , wherein the plurality of oversampled digital representations of radio frequency signals having different frequencies are representative of digital signals having a bit rate above 1.4 GHz.
18. The method according to claim 16 , further comprising digitally predistorting the second composite signal to reduce an intermodulation distortion present in an output of the power amplifier.
19. The method according to claim 18 , further comprising converting a multibit parallel representation of the second composite signal into a single bit serial representation digital stream.
20. The method according to claim 19 , wherein the single bit serial representation digital stream has a bit rate greater than 1.4 GHz, and a power insufficient to directly drive an output device, further comprising digitally amplifying a power of the single bit serial representation digital stream to a power level sufficient for directly driving the output device.