Method and apparatus for determining an interference level on a fading channel

• US 20040209585A1
• Filed: 04/17/2003
• Published: 10/21/2004
• Est. Priority Date: 04/17/2003
• Status: Abandoned Application

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Wang, Michael Mao, Brown, Tyler A.
• Application Number:
  US10/417,874
• Publication Number:
  US 20040209585A1
• Time in Patent Office: Days
• US Class Current: 455/226.1
• CPC Class Codes: H04B 17/345 Interference values signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR] H04B17/336

Abstract

An interference level estimator 205 and corresponding method FIG. 6 can be used in a wireless communications device 200 and is operable to estimate an interference level of interference that is received over a fading channel. The interference level estimator comprises a processor 207 for processing a despread Code Division Multiple Access (CDMA) signal and the interference to remove a portion of the despread CDMA signal and a portion of the interference to provide a residual interference and for determining the estimate of the interference level from the residual interference, where the interference level is fading speed invariant.

Claims

1. A method in a communications receiver for ascertaining an interference level of interference that is received over a fading channel, the method comprising:

receiving a signal and the interference over the fading channel;

processing the signal and the interference as received to remove a portion of the signal and a portion of the interference to provide a residual interference; and

determining the interference level from the residual interference, the interference level being fading speed invariant.

2. The method of claim 1 wherein the processing the signal and the interference as received further comprises sampling the signal and the interference as received at a sampling rate that is higher than expected frequency components of the portion of the signal that result from the fading channel to provide a sampled signal and interference.

3. The method of claim 2 wherein the processing the signal and the interference as received further comprises filtering the sampled signal and interference with a filter that rejects the expected frequency components.

4. The method of claim 3 wherein the determining the interference level from the residual interference further comprises calculating a variance of the residual interference.

5. The method of claim 4 wherein the determining the interference level from the residual interference further comprises scaling the variance of the residual interference to correct for effects on the variance resulting from the filtering the sampled signal and interference to provide an accurate estimate of the interference level.

6. The method of claim 1 wherein the determining the interference level from the residual interference further comprises calculating a variance of the residual interference.

7. The method of claim 6 wherein the determining the interference level from the residual interference further comprises scaling the variance of the residual interference to correct for effects on the variance due to the processing the signal and the interference as received to provide an accurate estimate of the interference level.

8. The method of claim 7 wherein the scaling the variance of the residual interference further comprises adjusting the variance to account for attenuation of a high pass filter.

9. The method of claim 1 wherein the receiving the signal and the interference further comprises despreading a Code Division Multiple Access signal to provide the signal.

10. An interference level estimator for use in a wireless communications device to estimate an interference level of interference that is received over a fading channel, the interference level estimator comprising:

a processor for processing a despread Code Division Multiple Access (CDMA) signal and the interference to remove a portion of the despread CDMA signal and a portion of the interference to provide a residual interference; and

determining the estimate of the interference level from the residual interference, the interference level being fading speed invariant.

11. The interference level estimator of claim 10 wherein the processor for processing the despread CDMA signal and the interference further comprises a sampler for sampling the despread CDMA signal and the interference at a sampling rate that is higher than expected frequency components of the portion of the despread CDMA signal that result from the fading channel to provide a sampled despread CDMA signal and interference.

12. The interference level estimator of claim 11 wherein the processor for processing the despread CDMA signal and the interference further comprises a filter for filtering the sampled despread CDMA signal and interference to reject the expected frequency components.

13. The interference level estimator of claim 12 wherein the processor for determining the estimate of the interference level from the residual interference further calculates a variance of the residual interference.

14. The interference level estimator of claim 13 wherein the processor for determining the estimate of the interference level from the residual interference further scales the variance of the residual interference to correct for effects on the variance resulting from the filtering the sampled despread CDMA signal and interference to provide an accurate estimate of the interference level.

15. The interference level estimator of claim 10 wherein the processor for determining the estimate of the interference level from the residual interference further calculates a variance of the residual interference.

16. The interference level estimator of claim 15 wherein the processor for determining the estimate of the interference level from the residual interference further comprises a high pass filter for attenuating the portion of the despread CDMA signal and the interference and the processor scales the variance of the residual interference to correct for attenuation of the variance due to the high pass filter, thereby providing an accurate estimate of the interference level.

17. A wireless communications device including an interference level estimator for reporting an interference level of interference that is received over a fading channel, the wireless communications device comprising:

a receiver for receiving over the fading channel and despreading a Code Division Multiple Access (CDMA) signal and interference to provide a despread Code Division Multiple Access (CDMA) signal and interference;

a processor, coupled to the receiver, for processing the despread Code Division Multiple Access (CDMA) signal and interference to remove a portion of the despread CDMA signal and a portion of the interference to provide a residual interference and further for determining the interference level from the residual interference; and

a transmitter, coupled to the processor, for reporting information corresponding to the interference level, the interference level being fading speed invariant.

18. The wireless communications device of claim 17 wherein the processor for processing the despread CDMA signal and the interference further comprises a sampler for sampling the despread CDMA signal and the interference at a sampling rate that is higher than expected frequency components of the portion of the despread CDMA signal that result from the fading channel to provide a sampled despread CDMA signal and interference.

19. The wireless communications device of claim 18 wherein the processor for processing the despread CDMA signal and the interference further comprises a filter for filtering the sampled despread CDMA signal and interference to reject the expected frequency components.

20. The wireless communications device of claim 19 wherein the processor for determining the interference level from the residual interference further calculates a variance of the residual interference.

21. The wireless communications device of claim 20 wherein the processor for determining the interference level from the residual interference further weights the variance of the residual interference to correct for effects on the variance resulting from the filter to provide an accurate estimate of the interference level.

22. The wireless communications device of claim 17 wherein the processor for determining the interference level from the residual interference further calculates a variance of the residual interference.

23. The wireless communications device of claim 22 further including a high pass filter to attenuate the portion of the despread CDMA signal and the interference and wherein the processor further scales the variance of the residual interference to correct for attenuation of the variance due to the high pass filter, thereby providing an accurate estimate of the interference level.