Digital radio frequency tranceiver system and method

• US 8,260,143 B2
• Filed: 03/12/2009
• Issued: 09/04/2012
• Est. Priority Date: 03/12/2008
• Status: Active Grant

• Current Assignee: Hypres, Inc.
• Original Assignee: Hypres, Inc.
• Inventors: Gupta, Deepnarayan, Mukhanov, Oleg
• Primary Examiner(s): Stafford, Patrick
• Assistant Examiner(s): NGUYEN, TUAN N
• Application Number:
  US12/403,326
• Publication Number:
  US 20090232507A1
• Time in Patent Office: 1,272 Days
• Field of Search: 398/67, 398/77, 398/202, 455/230, 455/74, 455/78, 455/114.3, 375/216, 375/296
• US Class Current: 398/115
• CPC Class Codes: H04B 10/2575 Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
• CPC Class Codes: H04B 10/25752 Optical arrangements for wireless networks
• CPC Class Codes: H04B 10/40 Transceivers
• CPC Class Codes: H04B 10/5561 Digital phase modulation
• CPC Class Codes: H04B 10/697 Arrangements for reducing noise and distortion
• CPC Class Codes: H04L 27/2096 Arrangements for directly or externally modulating an optical carrier optical modulation H04B10/503

Abstract

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.

Claims

1. A radio system, comprising:

an optoelectronic receiver configured to receive a predistorted signal from an optic communication medium comprising a radio frequency signal having at least one information-bearing electromagnetic wave component, wherein the predistorted signal comprises a predistortion and a signal component that partially cancel each other, to produce a signal having a remaining distortion;

an amplifier configured to amplify the signal having the remaining distortion and to generate a power radio frequency signal wherein the remaining distortion substantially compensates for a non-linearity of the amplifier, substantially without frequency translation between the received predistorted signal and the power radio frequency signal, the power radio frequency signal having spectral components at a frequency of between 698 MHz and 50 GHz;

an antenna port configured to emit the power radio frequency signal; and

a predistorter configured to generate the predistorted signal, comprising a digital processor having at least one look-up table, wherein the signal having the remaining distortion compensates for distortion by the amplifier, to increase an effective spur-free dynamic range of the power radio frequency signal by at least 3 dB by reducing a power of at least one intermodulation signal with respect to the signal component.

2. The radio system according to claim 1, further comprising a transmitter configured to communicate a feedback signal corresponding to the power radio frequency signal, wherein the predistortion is based on at least the feedback signal.

3. The radio system according to claim 1, wherein the power radio frequency signal has a spur-free dynamic range of at least 40 dB over a bandwidth of at least 19 MHz.

4. The radio system according to claim 1, further comprising a digital to analog converter, and an electrooptic transmitter, wherein the predistorter is configured to generate a signal which is converted by the digital to analog converter and transmitted by the electrooptic transmitter to the optoelectronic receiver as the predistorted signal.

5. The radio system according to claim 1, wherein the predistortion improves the effective spur-free dynamic range by at least 6 dB.

6. The radio system according to claim 1, further comprising:

a receive antenna port configured to receive a radio frequency signal having signal energy at a frequency of between 698 MHz and 50 GHz;

an amplifier and filter configured to amplify and filter the received radio frequency signal; and

an electrooptic transmitter configured to transmit a signal corresponding to the amplified and filtered received radio frequency signal.

7. The radio system according to claim 1, wherein the predistorter comprises a digital processor receiving digital samples representing a radio frequency signal at a rate of at least 10 Gigasamples per second.

8. The radio system according to claim 1, wherein the power radio frequency signal has spectral components having a frequency of at least 1.5 GHz.

9. The radio system according to claim 1, further comprising:

wherein the digital processor comprises a digital predistortion processor configured to produce a predistorted digital datastream, dependent on a source digital datastream and at least one of a distortion model and a distortion feedback signal;

an optical signal generator, configured to generate the predistorted signal corresponding to the predistorted digital datastream; and

at least one of a memory configured to store parameters of the distortion model and an optical signal receiver configured to receive the distortion feedback signal.

10. The radio system according to claim 9, wherein the optical signal receiver further receives a radio frequency signal;

further comprising a multiplex receiver, configured to extract information modulated on one of a plurality of information-carrying channels of the received radio frequency signal, substantially without interference with another of the information-carrying channels of the received radio frequency signal.

11. The radio system according to claim 9, wherein the digital predistortion processor is configured to produce a predistorted digital datastream dependent on a distortion model, and the radio system comprises the memory configured to store parameters of the distortion model.

12. The radio system according to claim 9, wherein the digital predistortion processor is configured to receive the distortion feedback signal, and the radio system comprises the optical signal receiver configured to receive the distortion feedback signal.

13. The radio system according to claim 9, wherein the digital datastream comprises a series of digital data representing a cellular radio transmission comprising a plurality of cellular radio channels, and wherein the digital predistortion processor is configured to reduce a peak to average power ratio of a signal emitted by a power amplifier receiving a representation of the predistorted digital datastream with respect to the source digital datastream.

14. The radio system according to claim 9, wherein the digital predistortion processor comprises a lookup table configured to supply predistortion data at a rate above a Nyquist rate of the carrier frequency.

15. The radio system according to claim 9, wherein the digital predistortion processor performs a proportional-integral-differential algorithm calculation.

16. The radio system according to claim 1, further comprising:

wherein the predistorter comprises a digital predistortion processor configured to produce a predistorted digital datastream, dependent on a source digital datastream comprising a digital radio frequency signal having a frequency of at least 1 GHz and a radio frequency distortion feedback signal; and

an optical fiber system configured to carry an analog representation of the predistorted digital datastream to optoelectronic receiver, and to receive an analog representation of a received radio frequency signal and the distortion feedback signal from the amplifier.

17. A wideband radio receiver comprising:

at least one tower unit mounted on a tower, each tower unit comprising an antenna configured to receive an incident wideband radio frequency signal having spectral energy between 698 MHz and 50 GHz and a bandwidth of at least 39 MHz, an amplifier configured to amplify the wideband radio frequency signal, and an electro-optic converter configured to convert the amplified wideband radio frequency signal to an analog optical signal for communication over an optical fiber communications link; and

a base unit remote from the tower, configured to receive the analog optical signal from the optical fiber communications link, comprising an opto-electric converter configured to convert the optical signal received from the optical fiber communications link to an analog radio frequency signal corresponding to the wideband radio frequency signal incident on the antenna, an analog-to-digital converter having a sampling rate of at least 2 GHz configured to directly digitize the entire analog radio frequency signal within the at least 39 MHz bandwidth, and a digital linearizer comprising a digital signal processing having at least one lookup table, configured to digitally compensate the digitized analog radio frequency signal for at least nonlinear distortion, to substantially reconstruct a digitally sampled equivalent of the signal incident on the antenna, having a spur-free dynamic range greater than a spur-free dynamic range of the optical signal over said bandwidth of at least 39 MHz.

18. A radio system, comprising:

an optoelectronic receiver configured to receive an input from an optic communication medium comprising a radio frequency signal having a bandwidth of at least 59 MHz at a band frequency lower band limit higher that 698 MHz and less than 50 GHz;

an amplifier configured to generate a power radio frequency signal corresponding to the radio frequency signal having an average power of at least 36 dBm wherein the power radio frequency signal has a distortion with an error vector magnitude of at least 1% with respect to the radio frequency signal communicated by the optical communication medium;

an interface port to an antenna configured to transmit the power radio frequency signal; and

a digital signal processor having at least one lookup table, configured or define an input to the optic communication medium which is predistorted, such that the power radio frequency signal produced by the amplifier has a distortion with respect to an undistorted signal provided to the digital signal processor of the at least 3 dB less than the distortion of the power radio frequency signal produced by the amplifier with respect to the radio frequency signal communicated by the optical communication medium.

19. The radio system according to claim 18, wherein the digital signal processor is clocked at at least 5 GHz.

20. The radio system according to claim 18, wherein the error vector magnitude of the distortion is at least 2%.

21. The radio system according to claim 18, wherein the error vector magnitude of the distortion is at least 4% and the digital signal processor is configured to precompensate the radio frequency signal to achieve a reduction in error vector magnitude of the power radio frequency signal with respect to the an undistorted signal provided to the digital signal processor of at least 3%.

22. A radio system, comprising:

a digital predistorter comprising a digital processor having at least one look-up table, configured to receive and modify a digital datastream having a data sample rate in excess of 1.4 GHz, and representing a radio frequency signal having a carrier frequency of at least 700 MHz and less than 50 GHz, to produce a predistorted digital datastream;

a module configured to convert the predistorted digital datastream into a predistorted radio frequency optical signal;

a converter configured to receive the predistorted radio frequency optical signal and produce a corresponding electrical signal;

a power amplifier configured to amplify corresponding electrical signal for transmission, to produce a power radio frequency signal; and

a coupler configured to deliver the power radio frequency signal to an antenna;

wherein the digital predistorter is configured to compensate for both of a distortion introduced by the power amplifier and a distortion introduced by the module to increase an effective spur-free dynamic range of the power radio frequency signal by at least 3 dB.

23. The radio system according to claim 22, wherein the coupler is configured to present the power radio frequency signal, having a spur-free dynamic range of at least 40 dB over a bandwidth of at least 19 MHz.

24. The radio system according to claim 22, wherein at least the power amplifier has an associated intermodulation distortion, and the digital predistorter is configured to predistort the digital datastream in a manner to compensate for at least a portion of the associated intermodulation distortion, to increase an spur-free dynamic range of the radio system.

25. The radio system according to claim 24, wherein the predistortion improves the effective spur-free dynamic range by at least 6 dB.

26. The radio system according to claim 24, wherein the optical signal comprises an analog optical signal.

27. The radio system according to claim 22, wherein the digital predistorter comprises a digital superconducting circuit.

28. The radio system according to claim 27, wherein the digital superconducting circuit comprises a plurality of Josephson junctions configured in at least one rapid-single-flux-quantum logic element.

29. The radio system according to claim 22, wherein the digital datastream comprises a cellular radio transmit signal having a bandwidth of at least 19 MHz.

30. The radio system according to claim 22, further comprising:

a coupler configured to receive a radio frequency signal of at least 700 MHz and less than 50 GHz;

a amplifier and filter configured to amplify the received radio frequency signal; and

an electrooptic transmitter configured to generate a received optical signal corresponding to the received radio frequency signal.

31. The radio system according to claim 30, wherein the received optical signal is used as a feedback signal for the digital predistorter.

32. The radio system according to claim 30, wherein the received optical signal is digitized and presented to a digital post-distorter.

33. The radio system according to claim 30, wherein the received optical signal is digitized and digitally demodulated.

34. The radio system according to claim 30, wherein the received optical signal comprises a cellular radio receive signal having a bandwidth of at least 19 MHz.

35. The radio system according to claim 22, wherein the module is configured to introduce a distortion into the optical signal with respect to the digital datastream, and the digital predistorter is configured to predistort the digital datastream in a manner to compensate for at least a portion of the introduced distortion.