Method and a device for maintaining the performance quality of a code-division multiple access system in the presence of narrow band interference

• US 6,807,405 B1
• Filed: 04/28/1999
• Issued: 10/19/2004
• Est. Priority Date: 04/28/1999
• Status: Expired due to Term

• Current Assignee: ISCO International Inc.
• Original Assignee: ISCO International Inc.
• Inventors: Willetts, Mark N., Jagger, Charles E., Tobia, Micolino
• Primary Examiner(s): APPIAH, CHARLES NANA
• Application Number:
  US09/301,477
• Time in Patent Office: 2,001 Days
• Field of Search: 455/266, 455/296, 455/306, 455/303, 455/208, 455/278.1, 455/316, 375/144, 375/140, 375/147, 375/148, 370/318, 370/317
• US Class Current: 455/296
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• 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 1/71 the interference being narrowband interference
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 15/00 Suppression or limitation of noise or interference by means associated with receiver H04B1/10
• CPC Class Codes: H04B 2001/1063 using a notch filter
• CPC Class Codes: H04B 2201/709709 Methods of preventing interference
• CPC Class Codes: H04B 2201/709718 Determine interference
• CPC Class Codes: H04B 7/005 Control of transmission; Equalising
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 24/02 Arrangements for optimising operational condition
• CPC Class Codes: H04W 24/04 Arrangements for maintaining operational condition
• CPC Class Codes: H04W 24/08 Testing, supervising or monitoring using real traffic
• CPC Class Codes: H04W 24/10 Scheduling measurement reports ; Arrangements for measurement reports
• CPC Class Codes: H04W 28/04 Error control
• CPC Class Codes: H04W 28/16 Central resource management; Negotiation of resources or communication parameters, e.g. negotiating bandwidth or QoS [Quality of Service]
• CPC Class Codes: H04W 28/20 Negotiating bandwidth
• CPC Class Codes: H04W 52/243 taking into account interferences
• CPC Class Codes: H04W 52/245 taking into account received signal strength
• CPC Class Codes: H04W 72/0453 Resources in frequency domain, e.g. a carrier in FDMA
• CPC Class Codes: H04W 72/541 : using the level of interference
• CPC Class Codes: H04W 72/542 : using measured or perceived quality
• CPC Class Codes: H04W 88/02 : Terminal devices
• CPC Class Codes: H04W 88/08 : Access point devices

Abstract

A method and device which dynamically detects, tracks and filters interfering signals with sufficient speed (i.e. within one IS-95 CDMA data. frame period, or 20 ms) and fidelity to eliminate or greatly reduce the deleterious effects of narrow band interferer signals on a CDMA link. When inserted in an RF signal path an Adaptive Notch Filter (ANF) detects narrow band interferors above a threshold level within the CDMA signal. Detection is accomplished by continuous scanning of a preset excision band, e.g. a specified narrow band associated with an AMPS system. Detected interferors are then automatically acquired and suppressed. This is achieved by electronically placing a rejection notch at the frequency of the interferors. Multiple notch filters may be used to simultaneously suppress multiple interferors. In the absence of interferors a bypass mode is selected allowing the RF signal to bypass the notch. Upon detection of an interferer, a switch is made to a suppression mode where the interferor is steered through a first notch section and suppressed. Alternatively, an external control line may be used to select the bypass mode so that the signal is allowed to pass the notch section, regardless of interferer content.

Claims

1. A device for suppressing narrow band interference in a wideband telecommunications system, said system being operable in a wide frequency band, comprising:

means for rapidly analyzing said wide frequency band with respect to signal power levels in specified narrow frequency bands and detecting said narrow band signal power levels received within said specified bands,

means for deriving an average composite wideband power level from said narrow band signal power levels;

means for using said signal power levels to derive an adaptive threshold for identifying said narrow band interference;

means for setting one or more notch filters for suppressing said identified narrow band interference.

2. The device of claim 1, wherein said wideband system is a CDMA system and said specified frequency bands are determined from an AMPS system.

3. The device of claim 2, wherein said analysis means, said deriving means, said identifying means and said setting means all are accomplished within one IS-95 CDMA data frame period.

4. The device of claim 1, wherein said detecting means can be adapted to detect the presence of frequency hopped GSM signals and concurrently dehop multiple GSM interferors, transmitting the appropriate frequency hopping sequence to each of said notch filters.

5. The device of claim 1, wherein said notch filter comprises:

a first mixer;

a voltage controlled oscillator;

a narrowband fixed frequency filter with integral wider bandpass filter; and

a second mixer,

wherein said first mixer and said voltage controlled oscillator heterodyne a radio frequency signal to an intermediate frequency signal, said intermediate frequency signal then being both notch filtered and-bandpass filtered, wherein said second mixer translates said filtered signal back to said radio frequency.

6. The device of claim 5, wherein said notch filter is bypassed by means of a radio frequency switching circuit when no interferer is detected, wherein said switching circuit has a switching threshold which is higher for switching in the notch filter than for bypassing the notch filter.

7. A method for suppressing narrow band interference in a wideband telecommunications system, said system being operable in a wide frequency band, comprising the steps of:

rapidly analyzing said wide frequency band with respect to signal power levels in specified narrow frequency bands and detecting said narrow band signal power levels received within said specified bands,

deriving an average composite wideband power level from said narrow band signal power levels;

using said signal power levels to derive an adaptive threshold for identifying said narrow band interference; and

setting one or more notch filters for suppressing said identified narrow band interference.

8. The method of claim 7, wherein said wideband system is a CDMA system and said specified frequency bands are determined from an AMPS system.

9. The method of claim 8, wherein said analyzing step, said deriving step, said identifying step and said setting step all are accomplished within one IS-95 CDMA data frame period.

10. The method of claim 7, wherein said detecting step includes means for selectively detecting the presence of frequency hopped GSM signals and concurrently dehoping multiple GSM interferors, transmitting the appropriate frequency hopping sequence to each of said notch filters.

11. A method of detecting and eliminating narrowband interference in a wideband communication signal having a frequency bandwidth with narrowband channels disposed therein, the method comprising:

scanning at least some of the narrowband channels to determine signal strengths in at least some of the narrowband channels;

determining a threshold based on the signal strengths in at least some of the narrowband channels; and

filtering the wideband communication signal at a frequency corresponding to a narrowband channel having a signal strength exceeding the threshold.

12. The method of claim 11, wherein a signal strength at which filtering is enabled is higher than a signal strength at which filtering is disabled.

13. The method of claim 11, wherein the wideband communication signal comprises a spread spectrum signal.

14. The method of claim 11, wherein the wideband communication signal comprises a code-division multiple access (CDMA) signal.

15. The method of claim 11, wherein the narrowband channels comprise channels of an analog cellular telephone system.

16. The method of claim 15, wherein the analog cellular telephone system comprises an analog mobile phone system (AMPS).

17. The method of claim 11, wherein filtering the wideband communication signal comprises filtering the wideband communication signal at a frequency corresponding to a narrowband channel having the strongest signal strength.

18. The method of claim 11, wherein determining the threshold comprises averaging at least some of the signal strengths in at least some of the narrowband channels.

19. The method of claim 18, wherein determining the threshold comprises not including a number of the largest signal strengths when determining the average of at least some of the signal strengths in at least some of the narrowband channels.

20. The method of claim 18, wherein determining the threshold comprises adding an offset to the average of at least some of the signal strengths in at least some of the narrowband channels.

21. The method of claim 11, wherein filtering the wideband communication signal comprises tuning a notch filter to suppress a frequency of the wideband communication signal corresponding to a narrowband channel having a signal strength exceeding the threshold.

22. The method of claim 11, further comprising filtering the wideband communication signal at a plurality of frequencies corresponding to a plurality of narrowband channels having signal strengths exceeding the threshold.

23. The method of claim 22, wherein the plurality of frequencies that are filtered are the frequencies corresponding to narrowband channels having signal strengths that exceed the threshold by the largest margins.

24. The method of claim 22, wherein the plurality of frequencies that are filtered are prioritized according to margins by which their signal strengths exceed the threshold.

25. The method of claim 11, wherein filtering comprises:

frequency shifting the wideband communication signal from an original frequency position until one of the narrowband channels having a signal strength exceeding the threshold is at a notch frequency of a notch filter, thereby producing a frequency shifted wideband communication signal;

removing interference from the frequency shifted wideband communication signal by filtering the frequency shifted wideband communication signal to produce a filtered wideband communication signal; and

frequency shifting the filtered wideband communication signal back to the original frequency position.

26. The method of claim 25, wherein filtering comprises:

frequency shifting the filtered wideband communication signal from the original frequency position until a second one of the narrowband channels having a signal strength exceeding the threshold is at a notch frequency of a notch filter, thereby producing a second frequency shifted wideband communication signal;

removing interference from the second frequency shifted wideband communication signal by filtering the second frequency shifted wideband communication signal to produce a second filtered wideband communication signal; and

frequency shifting the second filtered wideband communication signal back to the original frequency position.

27. A system adapted to detect and eliminate narrowband interference in a wideband communication signal having a frequency bandwidth with narrowband channels disposed therein, the system comprising:

a scanner adapted to scan at least some of the narrowband channels to determine signal strengths in at least some of the narrowband channels;

a notch module adapted to receive the wideband communication signal and to selectively remove narrowband interference from the wideband communication signal to produce a filtered wideband communication signal; and

a controller coupled to the scanner and to the notch module, wherein the controller is adapted to determine a threshold based on the signal strengths in at least some of the narrowband channels and to control the notch module to filter the wideband communication signal at a frequency corresponding to a narrowband channel having a signal strength exceeding the threshold.

28. The system of claim 27, wherein a signal strength at which the controller controls the notch module to remove narrowband interference is higher than a signal strength at which the controller controls the notch module not to remove narrowband interference.

29. The system of claim 27, wherein the wideband communication signal comprises a spread spectrum signal.

30. The system of claim 27, wherein the wideband communication signal comprises a code-division multiple access (CDMA) signal.

31. The system of claim 27, wherein the narrowband channels comprise channels of an analog cellular telephone system.

32. The system of claim 31, wherein the analog cellular telephone system comprises an analog mobile phone system (AMPS).

33. The system of claim 27, wherein the controller is further adapted to store a list of narrowband channels having signal strengths that exceed the threshold.

34. The system of claim 33, wherein the controller is further adapted to prioritize the list of narrowband channels based on their signal strengths.

35. The system of claim 33, wherein the controller is further adapted to output the list of narrowband channels having signal strengths that exceed the threshold.

36. The system of claim 35, wherein the system uses the list for diagnostic purposes including signal analysis functions.

37. The system of claim 27, wherein the controller is further adapted to control the notch module to filter the wideband communication signal at a frequency corresponding to a narrowband channel having the strongest signal strength that exceeds the threshold.

38. The system of claim 27, wherein the controller is adapted to determine the threshold by determining an average of at least some of the signal strengths of the narrowband channels.

39. The system of claim 27, wherein the notch module is a first notch module and the filtered wideband communication signal is a first filtered wideband communication signal, the system further comprising a second notch module adapted to receive the first filtered wideband communication signal from the first notch module and to selectively filter the first filtered wideband communication signal at a frequency corresponding to a second narrowband channel to produce a second filtered wideband communication signal.

40. The system of claim 39, wherein the second notch module is tuned to a frequency corresponding to a narrowband channel having a signal strength exceeding the threshold.

41. The system of claim 39, wherein the first notch module removes a first narrowband interference signal from the wideband communication signal and the second notch module removes a second narrowband interference signal from the wideband communication signal.

42. The system of claim 41, wherein the first and second narrowband interference signals have different center frequencies.

43. The system of claim 37, wherein the notch module comprises:

a programmable phase locked loop coupled to the controller, the programmable phase locked loop adapted to generate a reference signal;

a first mixer adapted to receive the wideband communication signal and the reference signal and to shift the wideband communication signal in frequency from an original frequency position until one of the narrowband channels having a signal strength exceeding the threshold is located at an intermediate frequency, thereby creating a frequency shifted wideband communication signal;

a filter coupled to the first mixer and having a notch located at the intermediate frequency, the filter adapted to receive the frequency shifted wideband communication signal from the first mixer and to reduce frequency components of the wideband communication signal that are located at the intermediate frequency to produce a filtered wideband communication signal; and

a second mixer coupled to the filter and adapted to receive the filtered wideband communication signal and the reference signal and to shift the filtered wideband communication signal in frequency back to the original frequency position.

44. The system of claim 43, further comprising a second notch module comprising:

a second programmable phase locked loop coupled to the controller, the second programmable phase locked loop adapted to generate a second reference signal;

a third mixer adapted to receive the filtered wideband communication signal and the second reference signal and to shift the filtered wideband communication signal in frequency from the original frequency position until a second one of the narrowband channels having a signal strength exceeding the threshold is located at the intermediate frequency, thereby creating a second frequency shifted wideband communication signal;

a second filter coupled to the third mixer and having a notch located at the intermediate frequency, the second filter adapted to receive the second frequency shifted wideband communication signal from the third mixer and to reduce frequency components of the second filtered wideband signal that are located at the intermediate frequency to produce a second filtered wideband communication signal; and

a fourth mixer coupled to the second filter and adapted to receive the second filtered wideband communication signal and the second reference signal and to shift the second filtered wideband communication signal in frequency back to its original frequency position.

45. The system of claim 27, wherein the notch module further comprises a bypass switch coupled to the controller and adapted to be controlled by the controller to bypass the notch module when no narrowband channel has a signal strength exceeding the threshold.

46. A method of detecting, eliminating and reporting narrowband interference in a wideband communication signal having a frequency bandwidth with narrowband channels disposed therein, the method comprising:

scanning at least some of the narrowband channels to determine signal strengths in at least some of the narrowband channels;

determining a threshold based on the signal strengths in at least some of the narrowband channels;

filtering the wideband communication signal at a frequency corresponding to a narrowband channel having a signal strength exceeding the threshold;

storing a list of narrowband channels having signal strengths that exceed the threshold; and

outputting the list of narrowband channels having signal strengths that exceed the threshold.

47. The method of claim 46, wherein the list of narrowband channels having signal strengths that exceed the threshold is prioritized based on signal strength.

48. The method of claim 47, wherein diagnostic purposes comprises signal analysis functions.

49. The method of claim 46, wherein the wideband communication signal comprises a spread spectrum signal.

50. The method of claim 46, wherein the wideband communication signal comprises a code-division multiple access (CDMA) signal.

51. The method of claim 46, wherein the narrowband channels comprise channels of an analog cellular telephone system.

52. The method of claim 51, wherein the analog cellular telephone system comprises an analog mobile phone system (AMPS).

53. A method of selecting a threshold for use in detecting narrowband interference within a bandwidth of a wideband communication signal, the method comprising:

tuning a receiver to a plurality of frequencies within the bandwidth having substantially no narrowband interference to produce a plurality of signal strength indications;

comparing a threshold voltage to a voltage representation of each of the plurality of signal strength indications;

setting the threshold voltage until the threshold voltage exceeds each of the plurality of signal strength indications;

tuning the receiver to a frequency having narrowband interference to produce an interference signal strength indication;

comparing the threshold voltage to a voltage representation of the interference signal strength indication; and

ensuring that the voltage representation of the interference signal strength indication exceeds the voltage representation of the threshold.

54. The method of claim 53, wherein tuning the receiver to a plurality of frequencies within the bandwidth having substantially no narrowband interference comprises tuning the receiver to a plurality of narrowband channels within the wideband communication signal.

55. The method of claim 53, wherein tuning the receiver to a plurality of frequencies within the bandwidth having substantially no narrowband interference comprises sweeping the tuning of the receiver across a plurality of frequencies.

56. An interference detection and suppression system adapted to detect and eliminate narrowband interference in a wideband communication signal having a frequency bandwidth with narrowband channels disposed therein, the system comprising:

a notch filter for filtering the wideband communication signal at a frequency corresponding to a selected one of the narrowband channels;

a bypass switch adapted to selectively bypass the wideband communications signal around the notch filter;

a receiver adapted to be tuned to a narrowband channel and to produce a voltage signal strength indication pertaining to the channel to which the receiver is tuned;

a threshold setting device adapted to produce a voltage signal representative of a threshold to which the device is set; and

a comparator coupled to the receiver, the threshold setting device and the bypass switch, wherein the comparator controls the bypass switch to selectively bypass the notch filter based on a comparison of the voltage signal representative of the threshold and the voltage signal strength indication.

57. The system of claim 56, wherein the receiver comprises a scanning receiver adapted to sequentially tune to the narrowband channels and to produce a voltage signal strength indication pertaining to each channel to which the receiver is tuned.

58. The system of claim 57, further comprising a sample and hold circuit adapted to prevent the scanning receiver from scanning when the comparator detects that the voltage signal strength indication exceeds the voltage signal representative of the threshold.

59. The system of claim 56, wherein the comparator controls the bypass switch not to bypass the notch filter when the voltage signal strength indication exceeds the voltage signal representative of the threshold.

60. The system of claim 59, wherein the comparator controls the bypass switch to bypass the notch filter when the voltage signal representative of the threshold exceeds the voltage signal strength indication.

61. A method of detecting and suppressing interference in a wideband communication signal having a frequency bandwidth with narrowband channels disposed therein, the method comprising:

tuning a receiver to a narrowband channel to produce a voltage signal strength indication corresponding to the channel to which the receiver is tuned;

setting a threshold to produce a voltage signal representative of a threshold;

selectively filtering with an adaptive notch filter a selected one of the narrowband channels based on a comparison of the voltage signal representative of the threshold and the voltage signal strength indication; and

selectively bypassing a selected one of the narrowband channels based on a comparison of the voltage signal representative of the threshold and the voltage signal strength indication.

62. The method of claim 61, further comprising scanning the receiver across a frequency range to sequentially tune to the narrowband channels and to produce a voltage signal strength indication pertaining to each channel to which the receiver is tuned.

63. The method of claim 62, further comprising the step of stopping the receiver from scanning when the voltage signal strength indication exceeds the voltage signal representative of the threshold.

64. The method of claim 61, wherein the adaptive notch filter does not filter the selected one of the narrowband channels when the voltage signal representative of the threshold exceeds the voltage signal strength indication.

65. The method of claim 61, wherein the adaptive notch filter filters the selected one of the narrowband channels when the voltage signal strength indication exceeds the voltage signal representative of the threshold.