Method and apparatus for detecting interference using correlation

• US 7,525,942 B2
• Filed: 09/01/2005
• Issued: 04/28/2009
• Est. Priority Date: 09/01/2005
• Status: Active Grant

• Current Assignee: ISCO International Inc.
• Original Assignee: ISCO International Inc.
• Inventors: Cordone, Sean S.
• Primary Examiner(s): D AGOSTA, STEPHEN M
• Application Number:
  US11/217,717
• Publication Number:
  US 20070047494A1
• Time in Patent Office: 1,335 Days
• Field of Search: 370/310, 370/310.2, 370/335, 370/338, 455/63.1, 455/65, 455/67.13, 455/114.2, 455/296, 455/501
• US Class Current: 370/335
• 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
• CPC Class Codes: H04B 17/345 Interference values signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR] H04B17/336
• CPC Class Codes: H04B 2201/709709 Methods of preventing interference

Abstract

A system and/or a method for detecting interference using correlation may be used in a communication system to protect against, or to report the presence of, narrowband interference, which has deleterious effects on the performance of the wideband communication system. The interference detection system described herein may be used to determine presence of narrowband interference by calculating correlation factors for a plurality of narrowband channels disposed within the wideband communication system and comparing the correlation factors with a threshold correlation factor.

Claims

1. A method, performed by a mobile unit or base station, for detecting narrowband interference in a wideband communication signal having a frequency bandwidth with a narrowband channel disposed therein, the method comprising:

scanning the narrowband channel a plurality of times to determine a plurality of signal strengths at each of the plurality of scans;

determining a correlation factor for the narrowband channel based on the plurality of signal strengths;

comparing the correlation factor with a threshold correlation factor to determine presence of the narrowband interference in the narrowband channel;

wherein scanning the narrowband channel a plurality of times further comprises

continuously scanning the narrowband channel to generate a plurality of narrowband scans, and

storing a plurality of signal strength observations, each of the plurality of signal strength observations corresponding to one of the plurality of narrowband scans; and

wherein determining the correlation factor further comprises using a subset of the plurality of signal strength observations, wherein the subset of the plurality of signal strength observations are the most recent of the plurality of signal strength observations.

2. The method of claim 1, wherein the wideband communication signal is a direct sequence spread spectrum signal.

3. The method of claim 1, wherein the wideband communication signal is at least one of:

(1) an IS-95 code division multiple access signal;

(2) an IS-2000 code division multiple access signal;

(3) a universal mode telephone service/wide-band code division multiple access signal;

or (4) an IS-856 code division multiple access signal.

4. The method of claim 1, wherein:

scanning the narrowband channel a plurality of times further includes scanning a plurality of narrowband channels a plurality of times;

determining the correlation factor for the narrowband channel further includes determining a plurality of correlation factors for each of the plurality of narrowband channels; and

comparing the correlation factor with a threshold correlation factor further includes comparing each of the plurality of correlation factors with the threshold correlation factor to determine presence of narrowband interference in each of the plurality of narrowband channels.

5. The method of claim 4, further comprising:

for each scanning of the plurality of channels, determining a group of narrowband channels that have the highest signal strengths during the scan; and

determining if any of the group of narrowband channels is present in groups of channels having the highest signal strengths in at least two subsequent scans.

6. The method of claim 5, wherein determining if any of the group of narrowband channels is present in groups of channels having the highest signal strengths in at least two subsequent scans comprises determining if at least two of the group of narrowband channels are present in groups of channels having the highest signal strengths in the at least two subsequent scans.

7. The method of claim 4, further comprising:

calculating an average signal strength during a particular scan of the plurality of narrowband channels; and

determining a particular narrowband channel having narrowband signal strength above the average signal strength by at least a first threshold to determine presence of narrowband interference in each of the plurality of narrowband channels.

8. The method of claim 7, further comprising:

receiving a first criteria; and

in response to the first criteria determining a narrowband channel having interference by selecting one of;

(1) a particular narrowband channel having narrowband signal strength above the average signal strength by at least a first threshold;

or (2) a particular narrowband channel having a correlation factor above a threshold correlation factor.

9. A method, performed by a mobile unit or base station, for detecting narrowband interference in a wideband communication signal having a frequency bandwidth with a plurality of narrowband channels disposed therein, the method comprising:

scanning the plurality of narrowband channels a plurality of times to determine a plurality of signal strengths, each of the plurality of signal strengths corresponding to a particular scan of a particular narrowband channel;

selecting a first number of narrowband channels, wherein the first number of narrowband channels have highest signal strengths for the first scan;

selecting a second number of narrowband channels, wherein the second number of narrowband channels have highest signal strengths for the second scan;

determining if any of the first number of narrowband channels corresponds to any of the second number of narrowband channels to identify a narrowband channel having interference;

determining a first threshold based on the plurality of narrowband signal strengths for the first number of narrowband channels; and

determining a second threshold based on the plurality of narrowband signal strengths for the second number of narrowband channels.

10. The method of claim 9, wherein the wideband communication signal is at least one of:

(1) an IS-95 code division multiple access signal;

(2) an IS-2000 code division multiple access signal;

(3) a universal mode telephone service/wide-band code division multiple access signal;

or (4) an IS-856 code division multiple access signal.

11. The method of claim 9, wherein:

selecting a first number of narrowband channels further comprises selecting narrowband channels with signal strengths for the first scan above the first threshold; and

selecting a second number of narrowband channels further comprises selecting narrowband channels with signal strength for the second scan above the second threshold.

12. The method of claim 9, further comprising removing the narrowband interference using a notch filter.

13. An interference detection system for detecting narrowband interference within a wideband communication signal with a plurality of narrowband channels disposed therein, the system comprising:

a wideband signal receiver to receive the wideband signal;

a narrowband signal strength scanner to scan a plurality of narrowband channels to determine narrowband channel signal strengths for each of the plurality of scans; and

a digital signal processor to process the plurality of narrowband channel signal strengths for each of the plurality of scans to determine a plurality of correlation factors and to compare the plurality of correlation factors to a threshold correlation factor to determine a narrowband channel having the narrowband interference, wherein the digital signal processor is further to;

determine average signal strengths for each of the plurality of scans;

calculate a plurality of threshold signal strengths corresponding to the plurality of scans based on the average signal strengths for each of the plurality of scans; and

determine a group of narrowband channels for each of the plurality of scans having signal strengths above the threshold signal strength corresponding to each of the plurality of scans.

14. The system of claim 13, wherein the digital signal processor is further to determine if any of the group of narrowband channels are present in at least two subsequent scans.

15. The system of claim 13, further comprising a notch filter to receive information identifying the narrowband channel having the interference signal from the digital signal processor and to remove the interference signal from the wideband communication signal.

16. The system of claim 13, wherein the wideband signal receiver is further to receive at least one of:

(1) an IS-95 code division multiple access signal;

(2) an IS-2000 code division multiple access signal;

(3) a universal mode telephone service/wide-band code division multiple access signal;

or (4) an IS-856 code division multiple access signal.