Benign interference suppression for received signal quality estimation

• US 20050282500A1
• Filed: 06/16/2004
• Published: 12/22/2005
• Est. Priority Date: 06/16/2004
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Wang, Yi-Pin Eric, Bottomley, Gregory E., Ramesh, Rajaram
• Granted Patent: US 7,773,950 B2
• Time in Patent Office: Days
• US Class Current: 455/67.13
• CPC Class Codes: H04B 2201/709727 GRAKE type RAKE receivers
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0026 Transmission of channel quality indication
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04L 1/206 for modulated signals

Abstract

A receiver circuit suppresses effects of “benign” impairment from the calculation of received signal quality estimates, such that the estimate depends primarily on the effects of non-benign impairment. For example, a received signal may be subject to same-cell and other-cell interference plus noise, which is generally modeled using a Gaussian distribution, and also may be due to certain forms of self-interference, such as quadrature phase interference arising from imperfect derotation of the pilot samples used to generate channel estimates for the received signal. Such interference generally takes on a distribution defined by the pilot signal modulation, e.g., a binomial distribution for binary phase shift keying modulation. Interference arising from such sources is relatively “benign” as compared to Gaussian interference and thus should be suppressed or otherwise discounted in signal quality calculations. Suppression may be based on subtracting benign impairment correlation estimates from total impairment correlation estimates, or on filtering the benign impairment in channel estimation.

Claims

1. A method of estimating signal quality comprising:

calculating a signal-to-interference ratio estimate for a received signal subject to a total impairment comprising a first type of impairment that is relatively harmful with respect to demodulation of the received signal and a second type of impairment that is relatively benign with respect to demodulation of the received signal; and

suppressing effects of the second type of impairment from the calculation of the signal-to-interference ratio estimate such that the signal-to-interference ratio estimate depends primarily on the first type of impairment.

2. The method of claim 1, wherein the first type of impairment comprises Gaussian-type interference, and wherein the second type of impairment comprises non-Gaussian type interference.

3. The method of claim 1, wherein suppressing effects of the second type of impairment from the calculation of the signal-to-interference ratio estimate such that the signal-to-interference ratio estimate depends primarily on the first type of impairment comprises subtracting an estimate of the second type of impairment correlation from an estimate of the total impairment correlation to obtain a correlation estimate of the first type of impairment, and calculating the signal-to-interference ratio estimate based on the correlation estimate of the first type of impairment.

4. The method of claim 1, wherein suppressing effects of the second type of impairment from the calculation of the signal-to-interference ratio estimate such that the signal-to-interference ratio estimate depends primarily on the first type of impairment comprises suppressing the effects of the second type of impairment in a channel estimation process to thereby obtain modified channel estimates, and calculating the signal-to-interference ratio estimate based on the modified channel estimates.

5. A method of estimating signal quality comprising:

calculating a signal-to-interference ratio estimate for a received signal subject to a total impairment comprising both a first impairment and a second impairment;

suppressing the second impairment from the calculation of the signal-to-interference ratio estimate so that the signal-to-interference ratio estimate is greater than would be calculated based on the total impairment.

6. The method of claim 5, wherein the first impairment corresponds to interference that is well modeled as Gaussian interference, and wherein the second impairment corresponds to interference that is not well modeled as Gaussian interference.

7. The method of claim 5, further comprising mapping the signal-to-interference ratio estimate to a channel quality indicator, and reporting the channel quality indicator to a supporting wireless communication network.

8. The method of claim 7, wherein the received signal comprises at least a reference signal, and wherein reporting the channel quality indicator to a supporting wireless communication network comprises reporting the channel quality indicator to the supporting wireless communication network for data rate adaptation of a CDMA packet data channel signal.

9. The method of claim 8, wherein calculating a signal-to-interference ratio estimate for a received signal subject to a total impairment comprising both a first impairment and a second impairment comprises calculating the signal-to-interference ratio estimate from the reference channel signal.

10. The method of claim 9, further comprising adjusting the signal-to-interference ratio estimate for differences in power and spreading factor between the CDMA packet data channel signal and the reference channel signal.

11. The method of claim 5, wherein calculating a signal-to-interference ratio estimate for a received signal subject to a total impairment comprising both a first impairment and a second impairment comprises calculating a signal-to-interference-plus-noise ratio estimate for the received signal.

12. The method of claim 5, wherein calculating a signal-to-interference ratio estimate for a received signal subject to a total impairment comprising both a first impairment and a second impairment comprises calculating a total impairment correlation estimate, obtaining a correlation estimate for the first impairment by subtracting a correlation estimate for the second impairment from the total impairment correlation estimate, and calculating the signal-to-interference ratio estimate based on the correlation estimate for the first impairment.

13. The method of claim 12, further comprising calculating a correction term as a function of a rate of change of a multiplicative impairment, and scaling the correlation estimate for the-second impairment by the correction term.

14. The method of claim 12, wherein the first impairment comprises Gaussian impairment and the second impairment comprises non-Gaussian impairment, and wherein obtaining a correlation estimate for the first impairment by subtracting a correlation estimate for the second impairment from the total impairment correlation estimate comprises subtracting a non-Gaussian impairment correlation estimate from the total impairment correlation estimate to obtain a Gaussian impairment correlation estimate used for calculation of the signal-to-interference ratio estimate.

15. The method of claim 5, wherein suppressing the second impairment from the calculation of the signal-to-interference ratio estimate comprises filtering effects of the second impairment in a channel estimation process to obtain modified channel estimates, calculating a correlation estimate for the first impairment based on the modified channel estimates, and calculating the signal-to-interference ratio estimate based on the correlation estimate for the first impairment.

16. The method of claim 15, wherein the first impairment comprises Gaussian impairment and the second impairment comprises non-Gaussian impairment, and wherein filtering effects of the second impairment in a channel estimation process to obtain modified channel estimates comprises suppressing effects of the non-Gaussian impairment from the channel estimation process, and wherein calculating a correlation estimate for the first impairment based on the modified channel estimates comprises calculating a Gaussian impairment correlation estimate from the modified channel estimates.

17. The method of claim 15, wherein filtering effects of the second impairment in a channel estimation process to obtain modified channel estimates for the received signal comprises calculating filter coefficients for an interpolation filter, and calculating the modified channel estimates based on applying the interpolation filter to despread values of a reference channel signal received as part of the received signal.

18. The method of claim 17, further comprising configuring the interpolation filter to have a filter bandwidth large enough to track a multiplicative impairment term corresponding to the second impairment.

19. A receiver circuit for estimating received signal quality comprising:

a signal quality calculation circuit configured to calculate a signal-to-interference ratio estimate for a received signal subject to a total impairment comprising both a first impairment and a second impairment;

an impairment suppression circuit configured to suppress the second impairment from the calculation of the signal-to-interference ratio estimate so that the signal-to-interference ratio estimate depends primarily on the first impairment.

20. The receiver circuit of claim 19, wherein the calculation circuit is configured to map the signal-to-interference ratio estimate to a channel quality indicator for reporting to a supporting wireless communication network.

21. The receiver circuit of claim 20, wherein the received signal comprises at least a reference channel signal, and wherein reporting the channel quality indicator to a supporting wireless communication network comprises reporting the channel quality indicator to the supporting wireless communication network for data rate adaptation of a CDMA packet data channel signal.

22. The receiver circuit of claim 21, wherein the calculation circuit is configured to calculate the signal-to-interference ratio estimate for the received signal based on calculating the signal-to-interference ratio estimate from the reference channel signal.

23. The receiver circuit of claim 22, wherein the calculation circuit is configured to adjust the signal-to-interference ratio estimate for differences in power and spreading factor between the CDMA packet data channel signal and the reference channel signal.

24. The receiver circuit of claim 19, wherein the calculation circuit is configured to calculate the signal-to-interference ratio estimate as a signal-to-interference-plus-noise ratio for the received signal.

25. The receiver circuit of claim 19, wherein the suppression circuit is configured to calculate a total impairment correlation estimate, obtain a correlation estimate for the first impairment by subtracting a correlation estimate for the second impairment from the total impairment correlation estimate, and to calculate the signal-to-interference ratio estimate based on the correlation estimate for the first impairment.

26. The receiver circuit of claim 25, wherein the suppression circuit includes a correction term calculation circuit that is configured to calculate a correction term as a function of a multiplicative impairment term arising from the second impairment, and wherein the suppression circuit is configured to scale the correlation estimate for the second impairment by the correction term.

27. The receiver circuit of claim 19, wherein the suppression circuit includes a channel estimation with filter circuit, and wherein the suppression circuit is configured to suppress the second impairment from the calculation of the signal-to-interference ratio estimate by filtering effects of the second impairment in a channel estimation process to thereby obtain modified channel estimates for the received signal, and to calculate a first impairment correlation estimate based on the modified channel estimates.

28. The receiver circuit of claim 27, wherein the calculation circuit is configured to calculate the signal-to-interference ratio estimate based on the modified channel estimates.

29. The receiver circuit of claim 27, wherein the channel estimation with filter circuit comprises an interpolation filter and wherein the suppression circuit is configured to calculate filter coefficients for the interpolation filter, and calculate the modified channel estimates based on applying the interpolation filter to despread values of a reference channel signal that is part of the received signal, or that is received in association with the received signal.

30. The receiver circuit of claim 29, wherein the interpolation filter is configured to have a filter bandwidth sufficient to track a multiplicative impairment term associated with the second impairment.

31. A mobile terminal for use in a wireless communication network comprising:

a transmitter to transmit signals to the network;

a receiver to receive signals from the network;

said receiver including a receiver circuit comprising;

a signal quality calculation circuit configured to calculate a signal-to-interference ratio estimate for a received signal subject to a total impairment comprising both a first impairment and a second impairment;

an impairment suppression circuit configured to suppress the second impairment from the calculation of the signal-to-interference ratio estimate so that the signal-to-interference ratio estimate is based primarily on the first impairment.

32. The mobile terminal of claim 31, wherein the calculation circuit is configured to map the signal-to-interference ratio estimate to a channel quality indicator, and wherein the mobile terminal is configured to transmit the channel quality indicator to the network.

33. The mobile terminal of claim 32, wherein the received signal comprises at least a reference channel signal, and wherein the mobile terminal is configured periodically to transmit an updated channel quality indicator for data rate adaptation of a CDMA packet data channel signal by the wireless communication network.

34. The mobile terminal of claim 33, wherein the calculation circuit is configured to calculate the signal-to-interference ratio estimate for the received signal based on calculating the signal-to-interference ratio estimate from the reference channel signal, and to adjust the signal-to-interference ratio estimate for differences in power and spreading factor between the reference channel signal and the CDMA packet data channel signal.

35. The mobile terminal of claim 31, wherein the suppression circuit is configured to calculate a total impairment correlation estimate, obtain a correlation estimate for the first impairment by subtracting a correlation estimate for the second impairment from the total impairment correlation estimate, and wherein the calculation circuit is configured to calculate the signal-to-interference ratio estimate from the correlation estimate for the first impairment.

36. The mobile terminal of claim 35, wherein the first impairment is Gaussian impairment and the second impairment is non-Gaussian impairment, and wherein the suppression circuit is configured to obtain a Gaussian impairment correlation estimate as the correlation estimate for the first impairment by subtracting a non-Gaussian impairment correlation estimate from the total impairment correlation estimate.

37. The mobile terminal of claim 35, wherein the suppression circuit includes a correction term calculation circuit that is configured to calculate a correction term as a function of a multiplicative impairment term arising from the second impairment, and further configured to scale the correlation estimate for the second impairment by the correction term.

38. The mobile terminal of claim 31, wherein the suppression circuit includes a channel estimation with filter circuit, and wherein the suppression circuit is configured to suppress the second impairment from the calculation of the signal-to-interference ratio estimate by filtering effects of the second impairment in a channel estimation process and thereby obtain modified channel estimates for the received signal and to calculate a first impairment correlation estimate based on the modified channel estimates.

39. The mobile terminal of claim 38, wherein the calculation circuit is configured to calculate the signal-to-interference ratio estimate based on the modified channel estimates.

40. The mobile terminal of claim 38, wherein the channel estimation with filter circuit comprises an interpolation filter and wherein the suppression circuit is configured to calculate filter coefficients for the interpolation filter, and to calculate the modified channel estimates based on applying the interpolation filter to despread values of a reference channel signal that is part of the received signal, or that is received in conjunction with the received signal.

41. A method of estimating signal quality comprising:

suppressing benign interference from the calculation of a signal-to-interference ratio estimate for a received signal that is subject both to benign and non-benign interference; and

reporting signal quality to a wireless communication network as a function of the signal-to-interference ratio estimate.

42. The method of claim 41, wherein the received signal is subject to benign, non-Gaussian interference and to non-benign, Gaussian interference, and wherein suppressing benign interference from the calculation of the signal-to-interference ratio estimate for the received signal comprises suppressing the effects of the non-Gaussian interference from the calculation of the signal-to-interference ratio estimate.

43. The method of claim 42, wherein suppressing the effects of the non-Gaussian interference from the calculation of the signal-to-interference ratio estimate comprises filtering the non-Gaussian interference in a channel estimation process to obtain modified channel estimates, and calculating the signal-to-interference ratio based on the modified channel estimates.

44. The method of claim 42, wherein suppressing the effects of the non-Gaussian interference from the calculation of the signal-to-interference ratio estimate comprises calculating a total impairment correlation estimate for the Gaussian and non-Gaussian interference, calculating a non-Gaussian impairment correlation estimate for the non-Gaussian interference, subtracting the non-Gaussian impairment correlation estimate from the total impairment correlation estimate to obtain a Gaussian impairment correlation estimate for the Gaussian interference, and calculating the signal-to-interference ratio estimate based on the Gaussian impairment correlation estimate.

45. A computer readable medium storing a computer program comprising:

program instructions to calculate a signal-to-interference ratio estimate for a received signal subject to a total impairment comprising a first type of impairment that is relatively harmful with respect to demodulation of the received signal and a second type of impairment that is relatively benign with respect to demodulation of the received signal; and

program instructions to suppress effects of the second type of impairment from the calculation of the signal-to-interference ratio estimate such that the signal-to-interference ratio estimate depends primarily on the first type of impairment.