Variable baud rate demodulator

• US 6,282,248 B1
• Filed: 07/14/1998
• Issued: 08/28/2001
• Est. Priority Date: 07/14/1998
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.), Lucent Technologies, Inc. (Nokia Corporation), Processor Innovations Corp.
• Original Assignee: Agere Systems Guardian Corp. (Broadcom, Inc.)
• Inventors: Udovic, Daniel, Farrow, Cecil William, Raghunath, Kalavai Janardhan
• Primary Examiner(s): Le, Amanda T.
• Application Number:
  US09/114,948
• Time in Patent Office: 1,141 Days
• Field of Search: 375/261, 375/324, 375/326, 375/340, 329/304, 329/306, 329/308, 348/554, 348/555
• US Class Current: 375/324
• CPC Class Codes: H04L 27/38 Demodulator circuits; Receiver circuits
• CPC Class Codes: H04L 7/0029 interpolation of received data signal

Abstract

A method of efficiently demodulating and isolating a signal within a fixed possibly wider band spectral region, having any of a wide range of baud rates. The signal is sampled at a fixed, first frequency which remains fixed no matter what the baud rate. Thus, the sample rate does not necessarily correspond to the desired baud rate. The sampled signal is then demodulated and low pass filtered to create baseband samples at the first frequency, which are then subject to user-specified arbitrary rate change in a continuously variable interpolator/decimator (continuously variable digital delay (CVDD) device), and decimated by a programmable power of 2, to produce samples at a second frequency. The second frequency is preferably determined to be a whole number multiple of the desired baud rate, e.g., twice the desired baud rate. The samples are equalized to produce output symbols at the target baud rate. Based on this method, a demodulator can receive signals of varying bandwidth and baud rates at arbitrary spectral locations within a possibly wider bandwidth aggregate channel span, and can adapt its target baud rate for each signal to be the actual baud rate of the derived incoming data signal within the possibly wider bandwidth aggregate channel span.

Claims

1. A method of demodulating a signal including a digital signal having any of a range of baud rates, comprising:

sampling said signal at a fixed frequency to provide a sampled signal;

demodulating said sampled signal to create samples at said fixed frequency;

variably adjusting a rate of said samples to an arbitrary rate; and

decimating said arbitrary rate samples to decimated samples having a rate equal to an integer multiple of a target baud rate.

2. The method of demodulating a signal including a digital signal having any of a range of baud rates according to claim 1, further comprising:

equalizing said decimated samples to output data symbols at said target baud rate.

3. The method of demodulating a signal including a digital signal having any of a range of baud rates according to claim 1, wherein:

said variably adjusted rate is a decimated rate.

4. The method of demodulating a signal including a digital signal having any of a range of baud rates according to claim 1, wherein:

said variably adjusted rate is an interpolated rate.

5. The method of demodulating a signal including a digital signal having any of a range of baud rates according to claim 1, wherein:

said decimating decimates by powers of 2.

6. The method of demodulating a signal including a digital signal having any of a range of baud rates according to claim 1, wherein:

said integer multiple rate is twice said target baud rate.

7. The method of demodulating a signal including a digital signal having any of a range of baud rates according to claim 1, wherein:

said integer multiple rate is less than said arbitrary rate.

8. The method of demodulating a signal including a digital signal having any of a range of baud rates according to claim 1, wherein:

said fixed frequency is not an even number multiple of said arbitrary rate.

9. The method of demodulating a signal including a digital signal having any of a range of baud rates according to claim 1, wherein:

said fixed frequency is not an even number multiple of said target baud rate.

10. The method of demodulating a signal including a digital signal having any of a range of baud rates according to claim 1, wherein:

said range of baud rates includes a range through a factor of 10.

11. The method of demodulating a signal including a digital signal having any of a range of baud rates according to claim 1, wherein:

said range of baud rates includes a range through a factor of 100.

12. A demodulator adapted to receive a data stream having any of a wide range of baud rates, comprising:

an interpolator/decimator adapted to receive a stream of samples at a fixed rate and produce a stream of samples at a second rate;

a decimator adapted to receive said stream of samples at said second rate and produce a stream of samples at a third rate slower than said second rate; and

an equalizer adapted to receive said stream of samples at said third rate and produce a stream of symbols at a fourth rate.

13. The demodulator adapted to receive a data stream having any of a wide range of baud rates according to claim 12, wherein:

said fourth rate is a target baud rate.

14. The demodulator adapted to receive a data stream having any of a wide range of baud rates according to claim 13, wherein:

said third rate is an integer multiple of said target baud rate.

15. The demodulator adapted to receive a data stream having any of a wide range of baud rates according to claim 14, wherein:

said integer multiple is two.

16. The demodulator adapted to receive a data stream having any of a wide range of baud rates according to claim 13, wherein:

said second rate is an integer multiple of said third rate.

17. The demodulator adapted to receive a data stream having any of a wide range of baud rates according to claim 16, wherein:

said integer multiple is a power of two.

18. The demodulator adapted to receive a data stream having any of a wide range of baud rates according to claim 12, further comprising:

a timing recovery circuit adapted to receive an indication of said target baud rate and to control an output rate of at least one of said interpolator/decimator, decimator and equalizer based thereon.

19. The demodulator adapted to receive a data stream having any of a wide range of baud rates according to claim 18, wherein:

said timing recovery circuit receives an indication of a stream of samples output from at least one of said decimator and said equalizer.

20. The demodulator adapted to receive a data stream having any of a wide range of baud rates according to claim 12, further comprising:

an analog-to-digital converter adapted to produce said stream of samples at said fixed rate irrespective of a target baud rate.

21. The demodulator adapted to receive a data stream having any of a wide range of baud rates according to claim 20, wherein:

said analog-to-digital converter receives a quadrature amplitude modulated signal.

22. The demodulator adapted to receive a data stream having any of a wide range of baud rates according to claim 21, further comprising:

a demodulator circuit adapted to receive said stream of samples at said fixed rate and produce baseband in-phase and quadrature samples therefrom;

wherein said interpolator/decimator is adapted to receive both said in-phase and quadrature samples.

23. The demodulator adapted to receive a data stream having any of a wide range of baud rates according to claim 20, further comprising:

a master clock adapted to provide a master clock signal to said analog-to-digital converter, said interpolator/decimator, said decimator and said equalizer.

24. A demodulator adapted to receive a data stream having any of a wide range of baud rates, comprising:

an interpolator/decimator adapted to receive a stream of samples at a fixed rate and produce a stream of samples at a second rate;

a decimator adapted to receive said stream of samples at said second rate and produce a stream of samples at a third rate slower than said second rate;

an equalizer adapted to receive said stream of samples at said third rate and produce a stream of symbols at a fourth rate; and

a timing recovery circuit adapted to receive an indication of said target baud rate and to control an output rate of at least one of said interpolator/decimator, decimator and equalizer based thereon;

wherein said timing recovery circuit controls each of said interpolator/decimator, decimator and equalizer.

25. Apparatus for demodulating a signal including a digital signal having any of a range of baud rates, comprising:

means for sampling said signal at a fixed frequency to provide a sampled signal;

means for demodulating said sampled signal to create samples at said fixed frequency;

means for variably adjusting a rate of said samples to an arbitrary rate; and

means for decimating said arbitrary rate samples to decimated samples having a rate equal to an integer multiple of a target baud rate.

26. The apparatus for demodulating a signal including a digital signal having any of a range of baud rates according to claim 25, further comprising:

means for equalizing said decimated samples to output data symbols at said target baud rate.

27. The apparatus for demodulating a signal including a digital signal having any of a range of baud rates according to claim 25, wherein:

said means for decimating decimates by powers of 2.

28. The apparatus for demodulating a signal including a digital signal having any of a range of baud rates according to claim 25, wherein:

said integer multiple rate is twice said target baud rate.

29. The apparatus for demodulating a signal including a digital signal having any of a range of baud rates according to claim 25, wherein:

said range of baud rates includes a range through a factor of 10.

30. The apparatus for demodulating a signal including a digital signal having any of a range of baud rates according to claim 25, wherein:

said range of baud rates includes a range through a factor of 100.

31. A method of demodulating a data signal contained within a possible wider frequency span signal and having any of a range of baud rates, said method comprising:

sampling said possibly wider frequency span signal at a fixed frequency to provide a sampled signal;

demodulating said sampled signal to create samples at said fixed frequency;

configuring two continuously variable digital rate interpolators/decimators to produce two output streams at a nominal rate equal to a rational rate multiple of the expected nominal baud rate of said data signal;

activating a timing recovery feedback element to provide a sampling time offset adjustment to said two continuously variable digital rate interpolators/decimators, said feedback element adjusting a digital sample rate of said two continuously variable digital rate interpolator/decimators to equal a rational rate multiple of an actual baud rate of said data signal; and

digitally equalizing to generate data symbols at said actual baud rate of said received data signal.

32. The method of demodulating a data signal contained within a possible wider frequency span signal and having any of a range of baud rates according to claim 31, wherein:

said digital equalization includes carrier phase tracking.

33. A method of demodulating a signal contained within a possible wider frequency span signal or arbitrary bandwidth, said method comprising:

sampling said possibly wider frequency span sampled input signal at a fixed frequency to provide a sampled signal;

demodulating said sampled signal to create samples at said fixed frequency;

configuring two continuously variable digital rate interpolator/decimators to produce two high spectral fidelity output streams of a frequency sub-band signal having a sample rate equal to a desired rate which is greater than twice a frequency span of said frequency sub-band signal.