In-band and out-of-band signal detection for automatic gain calibration systems

• US 20030012313A1
• Filed: 05/04/2001
• Published: 01/16/2003
• Est. Priority Date: 05/04/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Atheros Communications (Qualcomm, Inc.)
• Inventors: Husted, Paul, Ng, Tao Fei Samuel, Thon, Lars E., McFarland, William
• Granted Patent: US 6,721,547 B2
• Time in Patent Office: Days
• US Class Current: 375/345
• CPC Class Codes: H03G 5/165 Equalizers; Volume or gain control in limited frequency bands
• CPC Class Codes: H04B 1/1036 with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters H04B1/123 takes precedence; filter circuits H03H
• CPC Class Codes: H04B 1/109 by improving strong signal performance of the receiver when strong unwanted signals are present at the receiver input

Abstract

An embodiment of the present invention provides an automatic gain control system for a wireless receiver that quickly differentiates desired in-band signals from high power out-of-band signals that overlap into the target band. The system measures power before and after passing a received signal through a pair of finite impulse response filters that largely restrict the signal'"'"'s power to that which is in-band. By comparing the in-band energy of the received signal after filtering to the total signal energy prior to filtering, it is possible to determine whether a new in-band signal has arrived. The presence of this new in-band signal is then verified by a multi-threshold comparison of the normalized self-correlation to verify the presence of a new, desired in-band signal.

Claims

1. A method of estimating whether a received strong signal is an in-band signal based upon power estimates, the method comprising the steps of:

inputting the received strong signal;

measuring the power of the received strong signal;

providing the received strong signal to a filter section;

using the filter section to pass frequency components of the received strong signal within a desired band of frequencies to obtain a filtered signal;

measuring the power of the filtered signal and

comparing the power measurement of the received strong signal to the power measurement of the filtered signal to obtain an indication that the received signal is estimated as being in-band.

2. The method of claim 1, wherein measuring the power of the received strong signal and measuring the power of the filtered signal are performed by taking samples within windows of the received strong signal and the filtered signal, respectively.

3. The method of claim 2, wherein extreme samples in the measurement of the received strong signal and in the measurement of the filtered signal are not used in the respective measurements.

4. The method of claim 3, wherein highest magnitude samples in the measurement of the received strong signal and in the measurement of the filtered signal are not used in the respective measurements.

5. The method of claim 4 wherein prior to the step of measuring the power of the received strong signal there is included the step of removing DC offset from the input signal.

6. The method of claim 4 wherein the step of measuring the power of the received strong signal uses a different number of signal samples than the step of measuring the power of the filtered signal.

7. The method of claim 4 wherein the received signal power measurement is made based upon less than a received whole short training symbol.

8. The method of claim 4 wherein the received signal power measurement is made based on half of a period of a slowest frequency sinusoid that exists within a training symbol containing a plurality of sinusoids, with each of the plurality of sinusoids having a frequency that is an integer multiple of the slowest frequency sinusoid.

9. The method of claim 2 wherein prior to the step of measuring the power of the received strong signal there is included the step of removing DC offset from the input signal.

10. The method of claim 2 wherein the step of measuring the power of the received strong signal uses a different number of signal samples than the step of measuring the power of the filtered signal.

11. The method of claim 1, wherein comparing the power measurements of the received strong signal and the filtered signal includes determining whether the filtered signal power measurement is at least a certain portion of the received signal power measurement.

12. The method of claim 1 wherein prior to the step of measuring the power of the received strong signal there is included the step of removing DC offset from the input signal.

13. The method of claim 1, further including the step of determining that the received strong signal is a desired signal after the indication has been provided.

14. The method of claim 1 wherein the received signal power measurement is performed on less than a whole short training symbol.

15. The method of claim 14 wherein the received signal power measurement is performed on about one half of a received whole short training symbol.

17. The method of claim 16 further including the steps of:

reducing a gain provided by an automatic gain control circuit to an automatic gain control amplification section if saturation is determined; and

reducing a gain provided by the automatic gain control circuit to the automatic gain control amplification section if the power of the received digital signal is greater than the desired level.

18. The method of claim 16, wherein measuring the power of the received digial digital signal and measuring the power of the filtered signal are performed by taking samples within windows of the received digital signal and the filtered signal, respectively.

19. The method of claim 18, wherein extreme samples in the measurement of the received digital signal and in the measurement of the filtered signal are not used in the respective measurements.

20. The method of claim 19, wherein highest magnitude samples in the measurement of the received digital signal and in the measurement of the filtered signal are not used in the respective measurements.

21. The method of claim 20 wherein prior to the step of measuring the power of the received digital signal there is included the step of removing DC offset from the input signal.

22. The method of claim 20 wherein the step of measuring the power of the received digital signal uses a different number of signal samples than the step of measuring the power of the filtered signal.

23. The method of claim 20 wherein the received digital signal power measurement is performed on less than a received whole short training symbol.

24. The method of claim 23 wherein the received digital signal power measurement is performed on about one half of a received whole short training symbol.

25. The method of claim 18 wherein prior to the step of measuring the power of the received digital signal there is included the step of removing DC offset from the input signal.

26. The method of claim 18 wherein the step of measuring the power of the received digital signal uses a different number of signal samples than the step of measuring the power of the filtered signal.

27. The method of claim 18, wherein comparing the power measurements of the received strong signal and the filtered signal includes determining whether the filtered signal power measurement is at least a certain portion of the received signal power measurement.

28. The method of claim 16 wherein prior to the step of measuring the power of the received strong signal there is included the step of removing DC offset from the input signal.

29. The method of claim 16 wherein the received signal power measurement is determined base upon less than a whole short training symbol.

30. The method of claim 29 wherein the received signal power measurement is determined based upon about one half of a received whole short training symbol.

31. The method of claim 16 further including the step of making a fine automatic gain control adjustment if it was determined that an in-band signal exists.

16. A method of estimating whether an input signal is an in-band signal, the method comprising the steps of:

inputting the input signal;

converting the input signal to a received digital signal using an analog to digital converter;

determining whether the received digital signal is saturating the analog to digital converter and if so identifying the digital signal as a strong signal type;

measuring the power of the received digital signal;

determining whether the power of the received digital signal is greater than a desired level and if so identifying the received digital signal as the strong signal type;

providing the received digital signal to a filter section;

using the filter section to pass frequency components of the received digital signal within a desired band of frequencies to obtain a filtered signal;

measuring the power of the filtered signal and comparing the power measurement of the received digital signal to the power measurement of the filtered digital signal to obtain an indication that the received signal is an in-band signal type; and

determining that the received digital signal is an in-band signal if the received digital signal is indicated as being of the in-band type and is identified as being of the strong signal type.

32. A method of determining that a received digital signal of the strong signal type exists within an input signal including the steps of:

converting the input signal to a received digital signal using an analog to digital converter;

measuring the power of the received digital signal; and

determining whether the power of the received digital signal is greater than a desired level and if so identifying the received digital signal as the strong signal type;

33. The method of claim 32 further including the step of reducing a gain provided by an automatic gain control circuit to an automatic gain control amplification section if the power of the received digital signal is greater than the desired level.

34. The method of claim 33 wherein the step of reducing the gain reduces the gain by an amount that is based upon the determined power and a predetermined gain target value.

35. The method of claim 32 further including the steps of:

determining whether the received digital signal saturates the analog to digital converter and if so identifying the digital signal as the strong signal type.

36. The method of claim 35 further including the steps of:

determining whether the received digital signal saturates the analog to digital converter; and

reducing a gain provided by an automatic gain control circuit to an automatic gain control amplification section if the received digital signal is determined to saturate the analog to digital converter.

37. The method of claim 36 wherein the step of reducing the gain reduces the gain a predetermined amount.

38. The method of claim 35 wherein the step of determining whether the received digital signal saturates the analog to digital converter includes the steps of:

counting a number of times that a plurality of samples of the received digital signal exceeded the predetermined saturation threshold; and

comparing the number of times with a predetermined saturation count threshold, such that when the predetermined saturation threshold is exceeded, the received digital signal is determined to saturate the analog to digital converter.

40. The system of claim 39, wherein the filter section includes a finite impulse response filter.

41. The system of claim 39, wherein the filter section includes a decimation filter.

42. The system of claim 39, wherein the filter section includes a low-pass filter.

43. The system of claim 36, wherein the power detector includes separate power detectors for measuring the received digital signal and the filtered signal.

44. The system of claim 43, wherein each of the power detectors includes a sampler configured to take samples of its respective signal within windows thereof.

45. The system of claim 43 wherein each of the power detectors does not use highest magnitude samples in the measurement of its respective signal.

46. The system of claim 39, wherein the filtered signal power measurement uses at least certain signal samples from the received signal power measurement.

47. The system of claim 39 further including a DC offset control unit for removing DC offset from the input signal.

48. The system of claim 39 wherein the control logic includes:

means for determining whether the power of the received digital signal is greater than a desired level and if so identifying the received digital signal as the strong signal type;

49. The system of claim 48 further including:

means for reducing a gain provided by an automatic gain control circuit to an automatic gain control amplification section if the power of the received digital signal is greater than the desired level.

50. The system of claim 49 wherein the means for reducing the gain reduces the gain by an amount that is based upon the determined power and a predetermined gain target value if the power of the received digital signal is greater than the desired level.

51. The system of claim 49 further including:

means for determining whether the received digital signal saturates the analog to digital converter and if so identifying the digital signal as the strong signal type.

52. The system of claim 51 wherein the means for determining includes means for counting a number of times that a plurality of samples of the received digital signal exceeded a predetermined saturation threshold;

and

means for comparing the number of times with a predetermined saturation count threshold, such that when the predetermined saturation threshold is exceeded, the received digital signal is determined to saturate the analog to digital converter

53. The system of claim 51 further including:

means for reducing the gain provided by the automatic gain control circuit to the automatic gain control amplification section if the received digital signal is determined to saturate the analog to digital converter.

54. The method of claim 36 wherein the means for reducing the gain reduces the gain a predetermined amount if the received digital signal is determined to saturate the analog to digital converter.

39. A system for detecting in-band signals, the system comprising:

a filter section for filtering a received digital signal to pass frequency components of the received digital signal within a desired band of frequencies to obtain a filtered signal;

a power detector for measuring power of the filtered signal and for measuring power of the received digital signal; and

control logic for, based on the measured power of the received digital signal and the filtered signal, determining whether the received signal is an in-band signal.

55. A method of determining that a received digital signal of the strong signal type exists within an input signal including the steps of:

converting the input signal to a received digital signal using an analog to digital converter;

determining whether the received digital signal saturates the analog to digital converter; and

reducing a gain provided by an automatic gain control circuit to an automatic gain control amplification section if the received digital signal is determined to saturate the analog to digital converter.

56. The method of claim 55 wherein the step of reducing the gain reduces the gain a predetermined amount.

57. The method of claim 55 wherein the step of determining whether the received digital signal saturates the analog to digital converter includes the steps of:

counting a number of times that a plurality of samples of the received digital signal exceeded the predetermined saturation threshold; and

comparing the number of times with a predetermined saturation count threshold, such that when the predetermined saturation threshold is exceeded, the received digital signal is determined to saturate the analog to digital converter.