Decimated noise estimation and/or beamforming for wireless communications

• US 6,563,885 B1
• Filed: 10/24/2001
• Issued: 05/13/2003
• Est. Priority Date: 10/24/2001
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Magee, David Patrick, Hosur, Srinath
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): TRAN, KHANH C
• Application Number:
  US09/999,721
• Publication Number:
  US 20030076900A1
• Time in Patent Office: 566 Days
• Field of Search: 375/144, 375/147, 375/148, 375/260, 375/278, 375/284, 375/285, 375/254, 375/316, 375/346, 375/348, 375/349, 375/350, 370/317, 370/320, 370/332, 370/334, 370/342, 370/441, 370/465, 370/525, 370/526, 370/529, 455/67.3, 455/135, 455/222, 455/561, 455/456, 455/65, 455/277.1, 455/277.2, 455/296
• US Class Current: 375/316
• CPC Class Codes: H04L 1/206 for modulated signals
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

A system and method facilitate estimating noise in a received signal. The received signal includes a plurality of data tones. Noise is estimated for a selected subset of data tones for each data burst, such that noise estimates for all data tones can be computed over a plurality of data bursts. As a result of spreading the noise estimates over more than one burst, the overall computations associated with obtaining the noise estimates can be reduced based on the size of the respective subsets. The updated data tone noise estimates further can be employed in subsequent processing, such as in beamforming calculations.

Claims

1. A signal processing system for use in a receiver, comprising:

a data tone selector that identifies a subset of data tones from a received data signal having a plurality of identifiable data tones;

a noise estimator that computes a noise estimate for each data tone in the subset of data tones; and

a hard decision component which computes a hard decision for each data tone in the subset of data tones, the noise estimator employing the hard decision for each data tone in the subset of data tones to compute the noise estimate for each respective data tone in the subset of data tones.

2. The system of claim 1, further comprising a counter that increments a count value in response to receiving each data signal, the data tone selector identifying a subset of the plurality of data tones based on the count value.

3. The system of claim 1, the data tone selector determining a size of the subset of data tones as a function of a maximum count value for the counter and the plurality of data tones.

4. The system of claim 1, further comprising an averager operative to compute an average noise estimate for each data tone.

5. The system of claim 4, the averager being operative to compute an average noise estimate for a selected subset of the plurality of data tones, the selected subset of data tones being different from the data tones for which noise estimates were computed for a present data signal.

6. The system of claim 4, further comprising a register in which updated average noise estimates are stored, the average noise estimates for the subset of data tones being employed to update previously determined average noise estimates for corresponding data tones in the subset of data tones.

7. The system of claim 1, further comprising a register in which noise estimates are stored, the noise estimates for the subset of data tones being employed to update previously determined noise estimates for corresponding data tones in the subset of data tones.

8. The system of claim 7, further comprising a beamformer operative to perform beamforming computations for each of the plurality of data tones based on the noise estimates stored for the respective data tones.

9. The system of claim 8, the beamforming computations further comprising computing at least one of soft decisions and noise-to-signal ratio estimates for each of the plurality of data tones based on the noise estimates stored for the respective data tones.

10. The system of claim 1, further comprising a covariance function operative to compute the variance and correlation of the noise estimate for each respective data tone in the identified subset of data tones.

11. The system of claim 1, the received data signal corresponding to a multiple carrier communications technique.

12. The system of claim 1 forming part of an application specific integrated circuit.

13. The system of claim 1 being implemented as executable instructions programmed in a digital signal processor.

14. A noise estimation system comprising:

a data tone identifier operative to identify a subset of data tones from a plurality of data tones for processing with a given data burst;

a hard decision component operative to compute hard decisions for the subset of data tones in the given data burst; and

a noise estimator operative to compute a data tone noise estimate for each data tone in the desired subset of data tones based on the respective hard decisions, the noise estimator being operative to provide an indication of the computed data tone noise estimate for each data tone of the subset of data tones in the given data burst.

15. The noise estimator of claim 14, the given data burst conforming to a multiple carrier modulation format.

16. A beamforming system comprising:

an aggregator that includes stored noise estimates for a plurality of data tones, the noise estimates for a selected subset of the plurality of data tones being updated for a received data signal based on noise estimates computed for the selected subset of the plurality of data tones in the received data signal; and

a beamformer that computes at least one of a soft decision and noise-to-signal ratio estimate for each of the plurality of data tones in the received data signal based on the stored noise estimate for each respective data tone.

17. The system of claim 16, the at least one of soft decision and noise-to-signal ratio estimate for each of the plurality of data tones being computed for each of the plurality of data tones as a function of the stored noise estimate, a channel estimate and a data signal value for each respective data tone.

18. The system of claim 17, the channel estimate for each of the plurality of data tones being stored, at least one of the stored noise estimate and the stored channel estimate being updated for at least some of the plurality of data tones in the received data signal according to a respective decimation rate.

19. The system of claim 16, the beamformer computing a soft decision and noise-to-signal ratio estimate for each of the plurality of data tones in the received data signal, each of the soft decision and noise-to-signal ratio estimates being computed as a quotient having a common denominator for each data tone.

21. The system of claim 19, the soft decisions ({circumflex over (Z)}[k]) being computed as $\hat{Z}$

[k]=[H1*

[r]⋯

Hn*

[r]]

[adj

 



Ravg

[r]]

[Y1

[r]⋮

Yn

[r]][H1*

[r]⋯

Hn*

[r]]

[adj

 



Ravg

[r]]

[H1

[r]⋮

Hn

[r]]

where

H_n is a channel estimate for the n^th antenna;

R_avg is the average noise estimate;

Y_n is the received data signal for the n^th antenna;

r is a data tone index functionally related to k ε

{0,1, . . . , N_data−

1},

 

where N_data is the number of data tones; and

n is a number of antennas at which the received data signal is received.

22. The system of claim 16 in combination with a noise estimation system, the combination comprising:

the noise estimation system comprising;

a data tone identifier operative to identify the selected subset of data tones from a plurality of data tones for processing with the received data signal;

a hard decision component which computes hard decisions for the selected subset of data tones in the received data signal; and

a noise estimator operative to compute a data tone noise estimate for each data tone in the selected subset of data tones based on the respective hard decisions, the computed data tone noise estimates being provided to update the noise estimates of the aggregator.

23. The system of claim 16, the subset of data tones being selected based on the received signal.

24. A wireless communications system, comprising:

at least one antenna operative to receive a wireless signal and convert the received signal into a corresponding electrical signal;

a preprocessing system operative to process the electronic signal and convert the electrical signal from the at least one antenna into a digital signal and perform desired preprocessing of the digital signal to provide a preprocessed digital signal in the frequency domain having a plurality of data tones and training tones for each data burst;

a decimated noise estimator operative to estimate noise for a subset of the plurality of data tones for a given data burst; and

a hard decision component which computes a hard decision for each data tone in the reduced subset of data tones for the given data burst, the noise estimator employing the hard decision for each data tone in the subset of data tones to estimate noise for each respective data tone in the reduced subset of data tones.

20. The system of claim 26, the denominator being computed and updated for a selected subset of the plurality of data tones of the received data signal according to a decimation rate.

25. The system of claim 24, further comprising a counter that increments a count value in response to receiving a subsequent data burst, the subset of data tones being determined based on the count value for the given data burst.

26. The system of claim 25, further comprising an averager operative to compute an average noise estimate for at least some of the data tones.

27. The system of claim 24, further comprising a register in which updated noise estimates are stored, the noise estimates for the reduced subset of data tones in the given data burst being employed to update previously determined noise estimates for corresponding data tones in the reduced subset of data tones.

28. The system of claim 27, further comprising a beamformer operative to perform beamforming computations for each of the plurality of data tones in the given data burst based on the updated noise estimates for the respective data tones.

29. The system of claim 28, the beamformer computing a soft decision and noise-to-signal ratio estimate for each of the plurality of data tones in the given data burst, each of the soft decision and noise-to-signal ratio estimates being computed as a quotient having a common denominator for each data tone in the given data burst.

30. The system of claim 29, the denominator being computed and updated for a selected subset of the plurality of data tones of the given data burst according to a decimation rate.

31. The system of claim 24, further comprising a selector operative to identify the data tones in the subset of data tones for the given data burst and provide information to the noise estimator based on which the subset of the plurality of data tones are identified to the noise estimator.

32. A receiver system, comprising:

means for receiving at least one digitized signal in the frequency domain corresponding to a data burst having a plurality of data tones;

means for identifying a subset of the plurality of data tones from the data burst in the at least one digitized signal;

means for estimating noise for the identified subset of the plurality of data tones;

means for providing an indication of the data tone noise estimates for the identified subset of the plurality of data tones; and

a count means for incrementing a count value in response to each data burst received, the means for identifying further identifying the identified subset of the plurality of data tones based on the count value.

33. The system of claim 32, further comprising means for computing a hard decision for each data tone in the identified subset of the plurality of data tones, the means for estimating employing the hard decision for each data tone in the identified subset of the plurality of data tones to estimate noise for each respective data tone in the identified subset of the plurality of data tones.

34. The system of claim 33, further comprising means for updating previously determined data tone noise estimates for corresponding data tones in the identified subset of the plurality of data tones based on the indication of data tone noise estimates for the identified subset of the plurality of data tones.

35. The system of claim 34, further comprising means for performing at least one beamforming computation for each data tone in the given data burst based on the updated noise estimates for each respective data tone.

36. A method for processing a digitized frequency domain signal having a plurality of data tones at different carrier frequencies, comprising:

decimating a received data burst to provide a subset of a plurality of data tones associated with the received data burst;

estimating noise for each of the data tones in the subset of data tones;

providing an indication of the estimated noise for each data tone in the subset; and

updating the estimated noise for the remaining data tones in the plurality of data tones by repeating the decimation and the estimation for different subsets of data tones over a plurality of data bursts.

37. The method of claim 36, further comprising performing at least one beamforming computation for each data tone in each given data burst based on the updated noise estimates for each respective data tone.

38. The method of claim 36, further comprising computing a soft decision and noise-to-signal ratio estimate for each of the plurality of data tones in the received data burst, each of the soft decision and noise-to-signal ratio estimates being computed as a quotient having a common denominator for each data tone in the received data burst.

39. The method of claim 38, further comprising computing and updating the denominator for a selected subset of the plurality of data tones of the received data burst according to a decimation rate.

40. The method of claim 36, further comprising computing a hard decision for each data tone in the identified subset of data tones, the estimation employing the computed hard decision for each data tone in the subset of data tones to estimate noise for each respective data tone in the subset of data tones.

41. A digital signal processor having computer-executable instructions for performing the method of claim 36.

42. An application specific integrated circuit configured to implement the method of claim 36.