Method and system for automatic gain control during signal acquisition

• US 8,363,758 B2
• Filed: 03/09/2010
• Issued: 01/29/2013
• Est. Priority Date: 04/03/2006
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Murthy, Vinay, Li, Linbo, Krishnamoorthi, Raghuraman
• Primary Examiner(s): Puente, Eva
• Application Number:
  US12/720,534
• Publication Number:
  US 20100158168A1
• Time in Patent Office: 1,057 Days
• Field of Search: 375/345, 375/260, 375/267, 375/285, 375/343, 455/127.2, 455/313, 455/419, 455/160.1, 370/280, 370/343, 370/350, 370/252
• US Class Current: 375/345
• CPC Class Codes: H03G 3/3052 in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver H03G3/32, H03G3/34 take precedence

Abstract

The disclosure is directed to a mobile communication device that includes automatic gain control (AGC) circuitry and operates in either a tracking mode or an acquisition mode. A received signal is sampled n times to calculate an energy estimate that is used to set the gain control values within the AGC circuitry. The value of n varies depending on whether the handset is operating in the acquisition mode or the tracking mode. Acquisition mode is typically considered to be the mode prior to coarse timing acquisition, also referred to as frame acquisition.

Claims

1. A mobile communications device comprising:

a receiver configured to operate in either an acquisition mode or a tracking mode and receive a signal comprising a plurality of Orthogonal Frequency Division Multiplex (OFDM) symbols; and

automatic gain control circuitry configured to set a gain control value based on a first number of samples of the received signal when the receiver is operating in the acquisition mode, where the first number of samples is less than a number of samples for a one of the plurality of OFDM symbols, and on a second number of samples of the received signal when the receiver is operating in the tracking mode.

2. The mobile communications device of claim 1, wherein the first number of samples is less than the second number of samples.

3. The mobile communications device of claim 1, wherein the second number of samples comprises the number of samples for the one of the plurality of OFDM symbols.

4. The mobile communications device of claim 1, wherein the first number of samples comprises a fraction of approximately one eighth or less of the number of samples of one of the plurality of OFDM symbols.

5. The mobile communications device of claim 1, wherein the first number of samples comprises one sixteenth or less of one of the plurality of OFDM symbols.

6. The mobile communications device of claim 1, wherein the received signal includes a TDM pilot signal.

7. The mobile communications device of claim 6, further comprising:

a processor configured to operate the receiver in the acquisition mode if the TDM pilot signal has not been acquired and operate the receiver in the tracking mode once the TDM pilot signal has been acquired.

8. The mobile communications device of claim 1, wherein the automatic gain control circuitry is further configured to determine an energy estimate of the received signal.

9. The mobile communications device of claim 1, wherein the automatic gain control circuitry is further configured to set the gain control value based on an energy estimate of the first number of samples when the receiver is operated in the acquisition mode.

10. The mobile communications device of claim 1, wherein the automatic gain control circuitry is further configured to set the gain control value based on an energy estimate of the second number of samples when the receiver is operated in the tracking mode.

11. The mobile communications device of claim 1, wherein the gain control value comprises a plurality of values.

12. The mobile communications device of claim 1, wherein the gain control value includes an analog control value and a digital control value.

13. A method for automatic gain control in a mobile communications device, comprising:

receiving a signal comprising a plurality of Orthogonal Frequency Division Multiplex (OFDM) symbols from a wireless network;

operating in either an acquisition mode or a tracking mode; and

setting a gain control value based on a first number of samples of the received signal when operating in the acquisition mode, where the first number of samples is less than a number of samples for a one of the plurality of OFDM symbols, and on a second number of samples of the received signal when operating in the tracking mode.

14. The method of claim 13, wherein the first number of samples is less than the second number of samples.

15. The method of claim 13, wherein the second number of samples comprises the number of samples for the one of the plurality of OFDM symbols.

16. The method of claim 13, wherein the received signal includes a TDM pilot signal.

17. The method of claim 16, further comprising:

operating in the acquisition mode if the TDM pilot signal has not been acquired; and

operating in the tracking mode once the TDM pilot signal has been acquired.

18. The method of claim 13, further comprising:

determining an energy estimate of the received signal.

19. The method of claim 18 further comprising:

determining an error signal which represents a power difference between the energy estimate and a desired reference level.

20. The method of claim 13, wherein the gain control value comprises a plurality of values.

28. The method of claim 13, wherein the first number of samples comprises a fraction of approximately one eighth or less of the number of samples of one of the plurality of OFDM symbols.

29. The method of claim 13, wherein the first number of samples comprises one sixteenth or less of one of the plurality of OFDM symbols.

30. The method of claim 13, wherein setting the gain control value is further based on an energy estimate of the first number of samples when operating in the acquisition mode.

31. The method of claim 13, wherein setting the gain control value is further based on an energy estimate of the second number of samples when operating in the tracking mode.

32. The method of claim 13, wherein the gain control value includes an analog control value and a digital control value.

21. A wireless communications device having a receiver configured to receive a signal from a wireless network, and operate in either an acquisition mode or a tracking mode, the device comprising:

means for estimating a received signal energy of the signal comprising a plurality of Orthogonal Frequency Division Multiplex (OFDM) symbols based on a first number of samples of the received signal when the receiver is operating in the acquisition mode and on a second number of samples of the received signal when the receiver is operating in the tracking mode, wherein the first number of samples is less than a number of samples for a one of the plurality of OFDM symbols; and

means for setting a gain control value based on the estimate of the received signal energy.

33. The device of claim 21, wherein the first number of samples is less than the second number of samples.

34. The device of claim 21, wherein the second number of samples comprises the number of samples for the one of the plurality of OFDM symbols.

35. The device of claim 21, wherein the first number of samples comprises a fraction of approximately one eighth or less of the number of samples of one of the plurality of OFDM symbols.

36. The device of claim 21, wherein the first number of samples comprises one sixteenth or less of one of the plurality of OFDM symbols.

37. The device of claim 21, wherein the received signal includes a TDM pilot signal.

38. The device of claim 37, further comprising:

means for operating the receiver in the acquisition mode if the TDM pilot signal has not been acquired and operating the receiver in the tracking mode once the TDM pilot signal has been acquired.

39. The device of claim 21, wherein the means for setting the gain control value is further configured to determine an energy estimate of the received signal.

40. The device of claim 21, wherein the means for setting the gain control value is further configured to set the gain control value based on an energy estimate of the first number of samples when the receiver is operated in the acquisition mode.

41. The device of claim 21, wherein the means for setting the gain control value is further configured to set the gain control value based on an energy estimate of the second number of samples when the receiver is operated in the tracking mode.

42. The device of claim 21, wherein the gain control value comprises a plurality of values.

43. The device of claim 21, wherein the gain control value includes an analog control value and a digital control value.

22. A mobile communications device comprising:

a receiver configured to receive a signal from a wireless network, the signal comprising a plurality of Orthogonal Frequency Division Multiplex (OFDM) symbols, and operate in either an acquisition mode or a tracking mode; and

automatic gain control circuitry configured to set a gain control value periodically at a first rate that is higher than an OFDM symbol rate when the receiver is operating in the acquisition mode and periodically at a second rate when the receiver is operating in the tracking mode.

23. The mobile communications device of claim 22, wherein the first rate is more frequent than the second rate.

44. The mobile communications device of claim 22, wherein the automatic gain control circuitry is further configured to determine an energy estimate of the received signal.

45. The mobile communications device of claim 22, wherein the gain control value comprises a plurality of values.

46. The mobile communications device of claim 22, wherein the gain control value includes an analog control value and a digital control value.

55. The mobile communications device of claim 22, wherein the second rate comprises the OFDM symbol rate.

56. The mobile communications device of claim 22, wherein the first rate comprises a number approximately eight times or more than the OFDM symbol rate.

57. The mobile communications device of claim 22, wherein the first rate comprises a number approximately sixteen times or more than the OFDM symbol rate.

58. The mobile communications device of claim 22, wherein the received signal includes a TDM pilot signal.

59. The mobile communications device of claim 58, further comprising:

a processor configured to operate the receiver in the acquisition mode if the TDM pilot signal has not been acquired and operate the receiver in the tracking mode once the TDM pilot signal has been acquired.

60. The mobile communications device of claim 22, wherein the automatic gain control circuitry is further configured to set the gain control value based on an energy estimate of the first rate when the receiver is operated in the acquisition mode.

61. The mobile communications device of claim 22, wherein the automatic gain control circuitry is further configured to set the gain control value based on an energy estimate of the second rate when the receiver is operated in the tracking mode.

24. A computer-readable memory unit encoded with a computer program for automatic gain control in a mobile communications device, which upon execution cause one or more processors to:

receive a signal comprising a plurality of Orthogonal Frequency Division Multiplex (OFDM) symbols from a wireless network;

operate in either an acquisition mode or a tracking mode; and

set a gain control value based on a first number of samples of the received signal when operating in the acquisition mode, where the first number of samples is less than a number of samples for a one of the plurality of OFDM symbols, and on a second number of samples of the received signal when operating in the tracking mode.

25. The computer-readable memory unit of claim 24, wherein the first number of samples is less than the second number of samples.

26. The computer-readable memory unit of claim 24, wherein the second number of samples comprises the number of samples for the one of the plurality of OFDM symbols.

27. The computer-readable memory unit of claim 24, wherein the received signal includes a TDM pilot signal.

47. The computer-readable memory unit of claim 24, wherein the first number of samples comprises a fraction of approximately one eighth or less of the number of samples of one of the plurality of OFDM symbols.

48. The computer-readable memory unit of claim 24, wherein the first number of samples comprises one sixteenth or less of one of the plurality of OFDM symbols.

49. The computer-readable memory unit of claim 27, wherein the computer program causes the one or more processors to operate in the acquisition mode if the TDM pilot signal has not been acquired and operate in the tracking mode once the TDM pilot signal has been acquired.

50. The computer-readable memory unit of claim 24, wherein the computer program causes the one or more processors to determine an energy estimate of the received signal.

51. The computer-readable memory unit of claim 24, wherein the computer program causes the one or more processors to set the gain control value based on an energy estimate of the first number of samples when operating in the acquisition mode.

52. The computer-readable memory unit of claim 24, wherein the computer program causes the one or more processors to set the gain control value based on an energy estimate of the second number of samples when operating in the tracking mode.

53. The computer-readable memory unit of claim 24, wherein the gain control value comprises a plurality of values.

54. The computer-readable memory unit of claim 24, wherein the gain control value includes an analog control value and a digital control value.