METHOD AND APPARATUS FOR ESTIMATING A SIGNAL-TO-INTERFERENCE RATIO

• US 20120127884A1
• Filed: 01/30/2012
• Published: 05/24/2012
• Est. Priority Date: 02/26/2008
• Status: Active Grant

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Vanganuru, Kiran K., Sternberg, Gregory S., Lawton, William E.
• Granted Patent: US 8,780,749 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception

Abstract

A method and apparatus for estimating a signal-to-interference ratio (SIR) are disclosed. A received signal includes signal energy on multiple basis functions. Desired signal energy in the received signal is transformed onto a first basis function with constant polarity. The desired signal energy is estimated by coherently averaging signal energy on the first basis function. A noise power is estimated by averaging signal energy on each basis function other than the first basis function and accumulating the averaged signal energy from the basis function other than the first basis function and scaling the accumulated signal energy to account for a noise estimate from the first basis function. An SIR is estimated by dividing the desired signal energy by the noise power.

Claims

1. A method of estimating signal power, the method comprising:

receiving a signal, wherein the signal carries modulated symbols and includes noise;

transforming symbol energy of the signal to a real part and noise energy of the signal to an imaginary part by multiplying the signal with a complex conjugate of a second signal, wherein the second signal has a real component and an imaginary component; and

computing signal power from the real part of the signal after the transformation.

2. The method of claim 1 wherein the second signal is an estimate of a transmitted signal.

3. The method of claim 1 wherein the second signal is a pilot signal that is a priori known and represents the signal uncorrupted by noise.

4. The method of claim 1 wherein the computing signal power from the real part of the signal after the transformation includes filtering the real part of the signal after the transformation and computing the signal power from the filtered real part of the signal after the transformation.

5. The method of claim 1 wherein the signal is received over a common pilot channel (CPICH), or a dedicated physical control channel (DPCCH).

6. The method of claim 1 wherein the symbols are modulated according to pulse amplitude modulation (PAM), or M-phase shift keying (MPSK).

7. The method of claim 1 wherein the modulated symbols are capable of being represented in complex notation having a real component and an imaginary component and the signal is capable of being represented in complex notation having a real component and an imaginary component.

8. A method of estimating noise power, the method comprising:

receiving a signal, wherein the signal carries modulated symbols and includes noise;

transforming symbol energy of the signal to a real part and noise energy of the signal to an imaginary part by multiplying the signal with a complex conjugate of a second signal, wherein the second signal has a real component and an imaginary component; and

computing noise power from the imaginary part of the signal after the transformation.

9. The method of claim 8 wherein the second signal is an estimate of a transmitted signal.

10. The method of claim 8 wherein the second signal is a pilot signal that is a priori known and represents the signal uncorrupted by noise.

11. The method of claim 8 wherein the modulated symbols are capable of being represented in complex notation having a real component and an imaginary component and the signal is capable of being represented in complex notation having a real component and an imaginary component.

12. The method of claim 11 wherein on a condition that the noise is identically distributed between real component of the signal and the imaginary component of the signal, the computing noise power from the imaginary part of the signal after the transformation includes squaring the imaginary part of the signal after the transformation and scaling by a factor of two the squared imaginary part of the signal after the transformation and filtering the scaled imaginary part of the signal after the transformation.

13. The method of claim 8 wherein the symbols are modulated according to pulse amplitude modulation (PAM), or M-phase shift keying (MPSK).

14. A method for estimating a signal-to-interference ratio (SIR), the method comprising:

acquiring signal power for a first channel;

acquiring noise power for a second channel;

scaling the noise power based on a spreading factor associated with the first channel and a spreading factor associated the second channel; and

computing SIR based on the signal power and the scaled noise power.

15. The method of claim 14 wherein the noise power is scaled by multiplying the noise power by a ratio of the spreading factor associated with the first channel and the spreading factor associated with the second channel.

16. The method of claim 14 wherein the first channel is a data or control channel and the second channel is a pilot channel.

17. An apparatus for estimating signal power, the apparatus comprising:

a receiver configured to receive a signal, wherein the signal carries modulated symbols and includes noise;

a computation unit configured to transform symbol energy of the signal to a real part and noise energy of the signal to an imaginary part by multiplying the signal with a complex conjugate of a second signal, wherein the second signal has a real component and an imaginary component; and

a power computation unit configured to compute signal power from the real part of the signal after the transformation.

18. The apparatus of claim 17 wherein the second signal is an estimate of a transmitted signal.

19. The apparatus of claim 17 wherein the second signal is a pilot signal that is a priori known and represents the signal uncorrupted by noise.

20. The apparatus of claim 17 wherein the power computation unit is configured to filter the real part of the signal after the transformation and compute the signal power from the filtered real part of the signal after the transformation.

21. The apparatus of claim 17 wherein the signal is received over a common pilot channel (CPICH), or a dedicated physical control channel (DPCCH).

22. The apparatus of claim 17 wherein the symbols are modulated according to pulse amplitude modulation (PAM), or M-phase shift keying (MPSK).

23. The apparatus of claim 17 wherein the modulated symbols are capable of being represented in complex notation having a real component and an imaginary component and the signal is capable of being represented in complex notation having a real component and an imaginary component.

24. An apparatus for estimating noise power, the apparatus comprising:

a receiver configured to receive a signal, wherein the signal carries modulated symbols and includes noise;

a computation unit configured to transform symbol energy of the signal to a real part and noise energy of the signal to an imaginary part by multiplying the signal with a complex conjugate of a second signal, wherein the second signal has a real component and an imaginary component; and

a power computation unit configured to compute noise power from the imaginary part of the signal after the transformation.

25. The apparatus of claim 24 wherein the second signal is an estimate of a transmitted signal.

26. The apparatus of claim 24 wherein the second signal is a pilot signal that is a priori known and represents the signal uncorrupted by noise.

27. The apparatus of claim 24 wherein the modulated symbols are capable of being represented in complex notation having a real component and an imaginary component and the signal is capable of being represented in complex notation having a real component and an imaginary component.

28. The apparatus of claim 27 wherein the power computation unit is configured to, on a condition that the noise is identically distributed between real component of the signal and the imaginary component of the signal, compute noise power from the imaginary part of the signal after the transformation by squaring the imaginary part of the signal after the transformation and scaling by a factor of two the squared imaginary part of the signal after the transformation and filtering the scaled imaginary part of the signal after the transformation.

29. The apparatus of claim 24 wherein the symbols are modulated according to pulse amplitude modulation (PAM), or M-phase shift keying (MPSK).

30. An apparatus for estimating a signal-to-interference ratio (SIR), the apparatus comprising:

a first unit configured to acquire signal power for a first channel;

a second unit configured to acquire noise power for a second channel;

a scaling unit configured to scale the noise power based on a spreading factor associated with the first channel and a spreading factor associated the second channel; and

a computation unit configured to compute SIR based on the signal power and the scaled noise power.

31. The apparatus of claim 30 wherein the scaling unit scales the noise power is scaled by multiplying the noise power by a ratio of the spreading factor associated with the first channel and the spreading factor associated with the second channel.

32. The apparatus of claim 30 wherein the first channel is a data or control channel and the second channel is a pilot channel.