System for continuous wave rejection

• US 6,795,423 B1
• Filed: 02/04/2000
• Issued: 09/21/2004
• Est. Priority Date: 02/04/2000
• Status: Expired due to Fees

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Dick, Stephen G., Sezgin, Nadir
• Primary Examiner(s): CANGIALOSI, SALVATORE A
• Application Number:
  US09/497,413
• Time in Patent Office: 1,691 Days
• Field of Search: 370/342, 370/335, 370/386, 370/350, 704/233, 360/46, 375/134, 375/137, 375/149
• US Class Current: 370/342
• CPC Class Codes: H04B 1/71 the interference being narrowband interference
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers

Abstract

A method is disclosed for receiving transmitted signals in the presence of CW interference in a communication system that determines the presence of a code in a received signal by comparing with a detector threshold calculations made in accordance with a sample of a received signal. Such systems include but are not limited to those incorporating a Sequential Probability Ratio Test. The method includes obtaining a first input power value of the received signal at a first sample time and obtaining a second input power value of the received signal at a second sample time. The first and second power values are compared in order to provide an input sample comparison and the forgoing steps are repeated in order to provide a plurality of input sample comparisons. The detector threshold is adjusted in accordance with the plurality of sample comparisons.

The CW signal can be strongly correlated with a short code used for the acquisition purposes. Therefore in the CDMA systems if the received signal contains a CW signal, then the strong correlation between the CW signal and the short code used for acquisition may result in a false alarm. To prevent this, the following algorithm is suggested to be used for the cancellation of CW, if there is a CW signal present in the received CDMA signal.

Claims

1. A method for receiving transmitted signals in a CDMA communication system having a detector threshold for comparing with the detector threshold calculations made in accordance with a sample of a received signal in order to determine the presence of CW interference in the received signal, comprising the steps of:

(a) obtaining a first input sample of the received signal at a first sample time;

(b) obtaining a second input sample of the received signal at a second sample time;

(c) comparing the first and second samples in order to provide an input sample comparison;

(d) repeating steps (a)-(c) in order to provide a plurality of input sample comparisons; and

(e) adjusting the detector threshold in response to at least one of said input sample comparisons, thereby providing an adjustment of the detection threshold in response to detection of said CW interference.

2. The method for receiving transmitted signals of claim 1, comprising the adjusting the detector threshold in response to at least one of said input sample comparisons obtained from the comparison of the first and second samples.

3. The method for receiving transmitted signals of claim 2, comprising the step of determining whether the first and second input samples are representative of CW interference.

4. The method for receiving transmitted signals of claim 3, comprising the step of adjusting the detector threshold in accordance with the CW interference determination.

5. The method for receiving transmitted signals of claim 3, comprising the step of determining an average of the plurality of input sample comparisons.

6. The method for receiving transmitted signals of claim 5, comprising the step of adjusting the detector threshold in accordance with the CW interference .

7. The method for receiving transmitted signals of claim 6, wherein the detector threshold is an upper threshold comprising the step of adjusting the detector threshold upwards in accordance with the CW interference.

8. The method for receiving transmitted signals of claim 2, wherein the step of comparing the first and second input samples comprises performing a subtraction operation upon the first and second input samples.

9. The method for receiving transmitted signals of claim 8, wherein the step of comparing the first and second input samples comprises averaging the first and second input samples.

10. In a CDMA communications system, a method of receiving transmitted signals in the presence of CW interference comprising:

sampling a received signal to generate a plurality of signal samples;

converting each signal sample into a respective power value;

selecting and eliminating a maximum power value from the plurality of power values;

averaging the remaining power values to generate an average power value;

determining an average difference between each power value and the power value of an adjacent sample;

comparing the average power value to the average difference to generate an offset signal for adjusting a detection threshold in response to said CW interference.

11. A CDMA communications system having a noise rejection subsystem, the CDMA system receiving transmitted signals having a detection threshold for detecting codes in the received signals in the presence of CW interference, the CDMA communications system comprising:

a first filter for sampling a received signal and generating a power value for each sample;

a second filter for determining a difference value between power values of adjacent samples;

an averaging device which determines an average power value;

a second averaging device which determines an average difference value; and

,

a comparator for comparing a ratio of the average power value per the average difference value to a threshold and generating an offset signal for adjusting the threshold in response to the ratio.

12. The noise rejection subsystem of claim 11 further comprising a maximum value device for selecting a maximum power value from the samples.

13. The noise rejection subsystem of claim 12 wherein the averaging device is configured to subtract the selected maximum power value prior to determining the average power value.

14. The noise rejection subsystem of claim 11 further comprising a second maximum value device for selecting a maximum difference value from the samples.

15. The noise rejection subsystem of claim 14 wherein the second averaging device is configured to subtract the selected maximum difference value prior determining the average difference value.

16. A method for a user equipment (UE) to receive transmitted signals in a CDMA communication system having a detection threshold for detecting codes in the received signals in the presence of CW interference in the received signal, characterized by the steps of:

(a) obtaining a first input sample of the received signal at a first sample time;

(b) obtaining a second input sample of the received signal at a second sample time;

(c) comparing the first and second samples in order to provide a first correlation; and

(d) adjusting the detection threshold in response to said first correlation when the presence of said CW interference is detected.

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

(f) obtaining at said first sample time a third input sample of the received signal;

(g) obtaining at said second sample time a fourth input sample of the received signal; and

(h) comparing said third and fourth input sample and generating therefrom a second correlation;

whereby a relationship between said first correlation and said second correlation determines the adjustment to said threshold.

18. The method of claim 17 wherein said comparison of said first and second correlations is equivalent to the amount of CW interference present in said received signal.

19. The method of claim 18 wherein said comparison of said third and fourth correlations is equivalent to the amount of background noise present in said received signal.

20. The method of claim 18 wherein said steps (a)-(c) are repeated in order to provide a plurality of first correlations and steps (f)-(h) are repeated in order to provide a plurality of second correlations.

21. The method of claim 16 wherein said steps (a)-(c) are repeated in order to provide a plurality of first correlations.

22. The method of claim 21 wherein said plurality of first correlations are averaged and said plurality of second correlations are averaged;

and whereby the relationship between said first correlation and said second correlation is an adjustment to the detection threshold.

23. A user equipment (UE) for receiving transmitted signals in a CDMA communication system having a detection threshold for detecting codes in the received signals in the presence of CW interference, the UE comprising:

a first filter for obtaining a first input sample at a first sample time and a second input sample at a second sample time;

a second filter responsive to said first and second input samples, for generating a first correlation b_R between said first and second samples; and

an adjustment unit for adjusting the detection threshold in response to said first correlation to ensure detection of said codes.

24. The UE of claim 23 wherein said first correlation is equivalent to the amount of CW interference and said second correlation is equivalent to background noise present in said received signal.

25. The UE of claim 24 further comprising:

a third filter for obtaining a third input sample at the first sample time and obtaining a fourth input sample at the second sample time, respectively;

a fourth filter responsive to said third and fourth input samples, for generating a second correlation b_AR between said third and fourth input samples; and

a comparator, coupled to said second and fourth filters, for comparing said first and second correlations; and

said adjustment units adjusting said detection threshold in response to said comparison.

26. The UE of claim 25 wherein said plurality of first correlations are averaged, said averaged first correlations being equivalent to the amount of CW interference present in the received signal.

27. The UE of claim 26 wherein said plurality of second correlations are averaged, said averaged second correlations being equivalent to the amount of background noise in said received signals.

28. The UE of claim 27 wherein said averaged first and second correlations are divided, said comparator comparing said divided correlations to a ratio threshold and generating an offset equivalent to the difference between said divided correlations and said ratio threshold.