Methods and apparatus for interference cancellation using complex interference orthogonalization techniques

• US 6,515,980 B1
• Filed: 09/22/1999
• Issued: 02/04/2003
• Est. Priority Date: 09/22/1999
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Bottomley, Gregory Edward
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): Milord, Marceau
• Application Number:
  US09/401,565
• Time in Patent Office: 1,231 Days
• Field of Search: 370/342, 370/503, 370/509, 370/441, 370/335, 370/328, 370/329, 375/130, 375/350, 375/343, 375/230, 375/324, 375/229, 375/147, 375/148, 455/213, 455/307, 455/296, 455/226.3, 455/222
• US Class Current: 370/342
• CPC Class Codes: H04B 1/7105 Joint detection techniques, e.g. linear detectors

Abstract

A communications signal including components associated with desired and interfering signals that are modulated according to respective first and second modulation sequences is processed to generate a baseband signal. The baseband signal is correlated with the first modulation sequence, e.g., a combination of a first scrambling sequence and a first spreading sequence, to produce a first correlation output. The baseband signal is also correlated with a combination of the first modulation sequence and a complex component (e.g., a second scrambling sequence) of the second modulation sequence, to generate a second correlation output. The first and second correlation outputs are combined to generate an estimate of information represented by the first signal, for example, by combining the first and second correlation outputs to produce a first RAKE finger output and combining the first RAKE finger output with a second RAKE finger output to generate an estimate of information represented by the desired signal. Related receiver apparatus is also discussed.

Claims

1. A method of recovering information from a communications signal that includes components associated with first and second signals that are modulated according to respective first and second modulation sequences, the method comprising the steps of:

processing the communications signal to generate a baseband signal;

correlating the baseband signal with the first modulation sequence to produce a first correlation output;

correlating the baseband signal with a combination of the first modulation sequence and a complex component of the second modulation sequence to generate a second correlation output; and

combining the first and second correlation outputs to generate an estimate of information represented by the first signal.

2. A method according to claim 1, wherein the second signal is modulated according to a complex scrambling sequence, and wherein said step of correlating the baseband signal with a combination of the first modulation sequence and a complex component of a second modulation sequence comprises the step of correlating the baseband signal with a combination of the first modulation sequence and the complex scrambling sequence.

3. A method according to claim 1, wherein the first signal is modulated according to a combination of a first scrambling sequence and a first spreading sequence, wherein the second signal is modulated according to a combination of a second scrambling sequence and a second spreading sequence, and:

wherein said step of correlating the baseband signal with the first modulation sequence comprises the steps of;

descrambling the baseband signal with a complex conjugate of the first scrambling sequence to generate a first plurality of descrambled values;

correlating the first plurality of descrambled values with the first spreading sequence to generate the first correlation output;

wherein said step of correlating the baseband signal with a combination of the first modulation sequence and a complex component of the second modulation sequence comprises the steps of;

descrambling the baseband signal with the first scrambling sequence to generate a second plurality of descrambled values; and

correlating the second plurality of descrambled values with a product of the first spreading sequence, an in-phase component of the second scrambling sequence and a quadrature component of the second scrambling sequence to generate the second correlation output.

4. A method according to claim 3, wherein said step of correlating the second plurality of descrambled values is preceded by the step of identifying the second scrambling sequence.

5. A method according to claim 4, wherein said step of identifying the second scrambling sequence comprises the step of detecting a signal encoded according to the second scrambling sequence.

6. A method according to claim 5:

wherein said step of detecting comprises the step of detecting a plurality of signals; and

wherein said step of identifying the second scrambling sequence comprises the step of identifying a scrambling sequence associated with a strongest one of the detected plurality of signals.

7. A method according to claim 3, wherein said step of combining comprises the steps of:

combining the first and second correlation outputs to produce a first RAKE finger output; and

combining the first RAKE finger output with a second RAKE finger output to generate an estimate of information represented by the first signal.

8. A method according to claim 3, wherein said step of combining the first and second correlation outputs comprises the step of combining the first and second correlation outputs according to channel estimates for the first and second signals.

9. A method according to claim 8, further comprising the step of estimating noise power and interference power, and wherein said step of combining the first and second correlation outputs comprises the step of combining the first and second correlation outputs according to the estimated noise power and interference power.

10. A method according to claim 3, further comprising the step of determining a set of weighting factors, and wherein said step of combining the first and second correlation outputs comprises the step of combining the first and second correlation outputs according to the determined set of weighting factors.

11. A method according to claim 10, wherein said step of determining a set of weighting factors comprises the step of adaptively determining weighting factors from at least one of known information or estimated information.

12. A method according to claim 3, wherein the communications signal includes a component associated with a third signal that is modulated according to a combination of the first scrambling sequence and a third spreading sequence that is orthogonal to the first spreading sequence, and:

wherein said step of combining the first and second correlation outputs is preceded by the step of determining a minimum rotation angle that minimizes interference associated with the third signal; and

wherein said step of combining the first and second correlation outputs comprises the step of combining the first and second correlation outputs according to the determined minimum rotation angle.

13. A method according to claim 3, wherein the communications signal includes a component associated with a third signal that is modulated according to a combination of the first scrambling sequence and a third spreading sequence that is orthogonal to the first spreading sequence, and:

wherein said step of combining the first and second correlation outputs is preceded by the step of equalizing the first and second correlation outputs to control interference associated with the third signal; and

wherein said step of combining the first and second correlation outputs comprises the step of combining the equalized first and second correlation outputs.

14. A method according to claim 13:

wherein said step of correlating the first plurality of descrambled values with the first spreading sequence comprises the steps of;

multiplying the first plurality of descrambled values by the first spreading sequence to generate scaled descrambled values;

sorting the scaled descrambled values into first and second sets based on corresponding values of an indicator function comprising a product of in-phase and quadrature components of the first and second scrambling sequences; and

accumulating respective ones of the first and second sets of scaled descrambled values to generate respective first and second sets of partial correlation output values;

wherein said step of correlating the second plurality of descrambled values with a product of the first spreading sequence, an in-phase component of the second scrambling sequence and a quadrature component of the second scrambling sequence comprises the steps of;

multiplying the second plurality of descrambled values by a product of the first spreading sequence, an in-phase component of the second scrambling sequence and a quadrature component of the second scrambling sequence to generate scaled descrambled values;

sorting the scaled descrambled values into third and fourth sets based on corresponding values of the indicator function; and

accumulating respective ones of the third and fourth sets of scaled descrambled values to generate respective third and fourth sets of partial correlation output values; and

wherein said step of combining the first and second correlation outputs comprises the step of combining the first, second, third and fourth sets of partial correlation output values.

15. A method according to claim 14, wherein the first, second, third and fourth partial correlation outputs are accumulated using weights that are each functions of channel estimates, noise power estimates and interference power estimates.

16. A receiver for processing a communications signal that includes components associated with first and second signals that are modulated according to respective first and second modulation sequences, the receiver comprising:

a converter operative to produce a baseband signal from the communications signal; and

a complex interference orthogonalizing baseband processor responsive to the converter and operative to correlate the baseband signal with the first modulation sequence to produce a first correlation output, to correlate the baseband signal with a combination of the first modulation sequence and a complex component of the second modulation sequence to generate a second correlation output, and to combine the first and second correlation outputs to generate an estimate of information represented by the first signal.

17. A receiver according to claim 16, wherein the complex interference orthogonalizing baseband processor comprises:

a first correlator operative to correlate the baseband signal with the first modulation sequence to produce a first correlation output;

a second correlator operative to correlate the baseband signal with a combination of the first modulation sequence and a complex component of the second modulation sequence to generate a second correlation output; and

a combiner responsive to the first and second correlators and operative to combine the first and second correlation outputs to generate an estimate of information represented by the first signal.

18. A receiver according to claim 17, wherein the second signal is modulated according to a complex scrambling sequence, and wherein the second correlator is operative to correlate the baseband signal with a combination of the first modulation sequence and the complex scrambling sequence.

19. A receiver according to claim 17, wherein the first signal is modulated according to a combination of a first scrambling sequence and a first spreading sequence, wherein the second signal is modulated according a combination of a second scrambling sequence and a second spreading sequence, and:

wherein the first correlator comprises;

a first descrambler operative to descramble the baseband signal with a complex conjugate of the first scrambling sequence to generate a first plurality of descrambled values;

a first despreader operative to correlate the first plurality of descrambled values with the first spreading sequence to generate the first correlation output;

wherein said second correlator comprises;

a second descrambler operative to descramble the baseband signal with the first scrambling sequence to generate a second plurality of descrambled values; and

a second despreader operative to correlate the second plurality of descrambled values with a product of the first spreading sequence, an in-phase component of the second scrambling sequence and a quadrature component of the second scrambling sequence to generate the second correlation output.

20. A receiver according to claim 19, wherein said combiner comprises:

a first combiner operative to combine the first and second correlation outputs to produce a first RAKE finger output; and

a second combiner operative to combine the first RAKE finger output with a second RAKE finger output to generate an estimate of information represented by the first signal.

21. A receiver according to claim 19, wherein said combiner is operative to combine the first and second correlation outputs according to channel estimates for the first and second signals.

22. A receiver according to claim 21, wherein said combiner is operative to combine the first and second correlation outputs according to estimates of noise power and interference power.

23. A receiver according to claim 19, wherein the complex interference orthogonalizing baseband processor further comprises a weighting factor determiner operative to determine a set of weighting factors, and wherein the combiner is operative to combine the first and second correlation outputs according to the determined weighting factors.

24. A receiver according to claim 23, wherein said weighting factor determiner is operative to adaptively determine weighting factors from at least one of known information or estimated information.

25. A receiver, comprising:

means for producing a baseband signal from a communications signal that includes components associated with first and second signals that are modulated according to respective first and second modulation sequences;

means for correlating the baseband signal with the first modulation sequence to produce a first correlation output;

means for correlating the baseband signal with a combination of the first modulation sequence and a complex component of the second modulation sequence to generate a second correlation output; and

means for combining the first and second correlation outputs to generate an estimate of information represented by the first signal.

26. A receiver according to claim 25, wherein the second signal is modulated according to a complex scrambling sequence, and wherein said means for correlating the baseband signal with a combination of the first modulation sequence and a complex component of a second modulation sequence comprises means for correlating the baseband signal with a combination of the first modulation sequence and the complex scrambling sequence.

27. A receiver according to claim 25, wherein the first signal is modulated according to a combination of a first scrambling sequence and a first spreading sequence, wherein the second signal is modulated according a combination of a second scrambling sequence and a second spreading sequence, and:

wherein said means for correlating the baseband signal with the first modulation sequence comprises;

means for descrambling the baseband signal with a complex conjugate of the first scrambling sequence to generate a first plurality of descrambled values;

means for correlating the first plurality of descrambled values with the first spreading sequence to generate the first correlation output;

wherein said means for correlating the baseband signal with a combination of the first modulation sequence and a complex component of the second modulation sequence comprises;

means for descrambling the baseband signal with the first scrambling sequence to generate a second plurality of descrambled values; and

means for correlating the second plurality of descrambled values with a product of the first spreading sequence, an in-phase component of the second scrambling sequence and a quadrature component of the second scrambling sequence to generate the second correlation output.

28. A receiver according to claim 27, further comprising means for identifying the second scrambling sequence.

29. A receiver according to claim 28, wherein said means for identifying the second scrambling sequence comprises means for detecting a signal encoded according to the second scrambling sequence.

30. A receiver according to claim 29:

wherein said means for detecting comprises means for detecting a plurality of signals; and

wherein said means for identifying the second scrambling sequence comprises means for identifying a scrambling sequence associated with a strongest one of the detected plurality of signals.

31. A receiver according to claim 27, wherein said means for combining comprises:

means for combining the first and second correlation outputs to produce a first RAKE finger output; and

means for combining the first RAKE finger output with a second RAKE finger output to generate an estimate of information represented by the first signal.

32. A receiver according to claim 27, wherein said means for combining the first and second correlation outputs comprises means for combining the first and second correlation outputs according to channel estimates for the first and second signals.

33. A receiver according to claim 32, further comprising means for estimating noise power and interference power, and wherein said means for combining the first and second correlation outputs comprises means for combining the first and second correlation outputs according to the estimated noise power and interference power.

34. A receiver according to claim 27, further comprising means for determining a set of weighting factors, and wherein said means for combining the first and second correlation outputs comprises means for combining the first and second correlation outputs according to the determined weighting factors.

35. A receiver according to claim 34, wherein said means for determining a set of weighting factors comprises means for adaptively determining weighting factors from at least one of known information or estimated information.

36. A receiver according to claim 27, wherein the communications signal includes a component associated with a third signal that is modulated according to a combination of the first scrambling sequence and a third spreading sequence that is orthogonal to the first spreading sequence, wherein the receiver further comprises means for determining a minimum rotation angle that minimizes interference associated with the third signal, and wherein said means for combining the first and second correlation outputs comprises means for combining the first and second correlation outputs according to the determined minimum rotation angle.

37. A receiver according to claim 27, wherein the communications signal includes a component associated with a third signal that is modulated according to a combination of the first scrambling sequence and a third spreading sequence that is orthogonal to the first spreading sequence, wherein the receiver further comprises means for equalizing the first and second correlation outputs to control interference associated with the third signal, and wherein said means for combining the first and second correlation outputs comprises means for combining the equalized first and second correlation outputs.

38. A receiver according to claim 37:

wherein said means for correlating the first plurality of descrambled values with the first spreading sequence comprises;

means for multiplying the first plurality of descrambled values by the first spreading sequence to generate scaled descrambled values;

means for sorting the scaled descrambled values into first and second sets based on corresponding values of an indicator function comprising a product of in-phase and quadrature components of the first and second scrambling sequences; and

means for accumulating respective ones of the first and second sets of scaled descrambled values to generate respective first and second sets of partial correlation output values;

wherein said means for correlating the second plurality of descrambled values with a product of the first spreading sequence, an in-phase component of the second scrambling sequence and a quadrature component of the second scrambling sequence comprises;

means for multiplying the second plurality of descrambled values by a product of the first spreading sequence, an in-phase component of the second scrambling sequence and a quadrature component of the second scrambling sequence to generate scaled descrambled values;

means for sorting the scaled descrambled values into third and fourth sets based on corresponding values of the indicator function; and

means for accumulating respective ones of the third and fourth sets of scaled descrambled values to generate respective third and fourth sets of partial correlation output values; and

wherein said means for combining the first and second correlation outputs comprises means for combining the first, second, third and fourth sets of partial correlation output values.

39. A receiver according to claim 38, wherein the first, second, third and fourth set of partial correlation output values are accumulated using weights that are each functions of channel estimates, noise power estimates and interference power estimates for the first and second signals.