Cancellation of interference in a communication system with application to S-CDMA

• US 20050141460A9
• Filed: 05/08/2002
• Published: 06/30/2005
• Est. Priority Date: 08/31/1999
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Yousef, Nabil R., Kolze, Thomas J., Currivan, Bruce J., Ungerboeck, Gottfried
• Granted Patent: US 7,110,434 B2
• Time in Patent Office: Days
• US Class Current: 370/335
• CPC Class Codes: H04B 1/71 the interference being narrowband interference
• CPC Class Codes: H04B 1/7102 with transform to frequency domain
• CPC Class Codes: H04B 1/7105 Joint detection techniques, e.g. linear detectors
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: H04J 13/0003 Code application, i.e. aspects relating to how codes are applied to form multiplexed channels
• CPC Class Codes: H04J 13/16 Code allocation

Abstract

Cancellation of interference in a communication system with application to S-CDMA. A relatively straight-forward implemented, and computationally efficient approach of selecting a predetermined number of unused codes is used to perform weighted linear combination selectively with each of the input spread signals in a multiple access communication system. If desired, the predetermined number of unused codes is always the same in each implementation. Alternatively, the predetermined number of unused codes are selected from within a reordered code matrix using knowledge that is shared between the two ends of a communication system, such as between the CMs and a CMTS. While the context of an S-CDMA communication system having CMs and a CMTS is used, the solution is generally applicable to any communication system that seeks to cancel narrowband interference. Several embodiments are also described that show the generic applicability of the solution across a wide variety of systems.

Claims

1. A communication system that is operable to perform interference cancellation, comprising:

a transmitter that produces a spread signal that comprises a numerically constant-valued symbol spread across a first plurality of codes and data spread across a second plurality of codes and transmits the spread signal across a communication link;

a receiver, communicatively coupled to the transmitter via the communication link, that receives the spread signal after being transmitted across the communication link, the spread signal comprising interference, the receiver comprising;

a vector de-spreader that de-spreads the first plurality of codes and the second plurality of codes from the spread signal;

a weight computation functional block that calculates a plurality of complex-valued combining weights using the spread signal and the interference of the spread signal; and

a linear combiner that scales the de-spread first plurality of codes using the plurality of complex-valued combining weights and combines the scaled, de-spread first plurality of codes and one code selected from the de-spread second plurality of codes to perform interference cancellation on at least one code de-spread from the spread signal.

2. The communication system of claim 1, wherein the first plurality of codes comprises a plurality of unused codes;

and

the second plurality of codes comprises a plurality of used codes.

3. The communication system of claim 2, wherein the first plurality of codes and the second plurality of codes comprise a total number of 128 codes;

the first plurality of codes comprises at least 8 codes and no more than 32 codes;

the second plurality of codes comprises a remaining plurality of codes within the total number of 128 codes not included within the first plurality of codes; and

the communication system comprises a DOCSIS 2.0 S-CDMA operable communication system.

4. The communication system of claim 1, wherein the weight computation functional block calculates the plurality of complex-valued combining weights using both the de-spread first plurality of codes and the de-spread second plurality of codes.

5. The communication system of claim 1, wherein the weight computation functional block calculates the plurality of complex-valued combining weights using de-spread codes that are adjacent to the one code selected from the de-spread second plurality of codes.

6. The communication system of claim 5, wherein the adjacent codes comprise two codes immediately adjacent to the one code selected from the de-spread second plurality of codes.

7. The communication system of claim 1, wherein the weight computation functional block calculates the plurality of complex-valued combining weights using de-spread codes from at least one of the first plurality of codes and the second plurality of codes that bears preamble symbols.

8. The communication system of claim 1, wherein the weight computation functional block employs at least one of least means square processing and least square processing to calculate the plurality of complex-valued combining weights.

9. The communication system of claim 1, wherein the receiver is operable to demodulate the spread signal using at least one of Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8 Quadrature Amplitude Modulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and 1024 QAM.

10. The communication system of claim 1, wherein the receiver comprises at least one of a multi-channel headend physical layer burst receiver, a single chip wireless modem, a single chip DOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobile receiver, a satellite earth station, a tower receiver, a high definition television set top box receiver, and a transceiver.

11. A communication receiver that is operable to perform interference cancellation, comprising:

a vector de-spreader that de-spreads the first plurality of codes and the second plurality of codes from a spread signal, the spread signal comprising interference;

a weight computation functional block that calculates a plurality of complex-valued combining weights using the spread signal and the interference of the spread signal; and

a linear combiner that scales the de-spread first plurality of codes using the plurality of complex-valued combining weights and combines the scaled, de-spread first plurality of codes and one code selected from the de-spread second plurality of codes to perform interference cancellation on at least one code de-spread from the spread signal.

12. The communication receiver of claim 11, wherein the first plurality of codes comprises a plurality of unused codes;

and

the second plurality of codes comprises a plurality of used codes.

13. The communication receiver of claim 12, wherein the first plurality of codes and the second plurality of codes comprise a total number of 128 codes;

the first plurality of codes comprises at least 8 codes and no more than 32 codes;

the second plurality of codes comprises a remaining plurality of codes within the total number of 128 codes not included within the first plurality of codes; and

the communication system comprises a DOCSIS 2.0 S-CDMA operable communication system.

14. The communication receiver of claim 11, wherein the weight computation functional block calculates the plurality of complex-valued combining weights using both the de-spread first plurality of codes and the de-spread second plurality of codes.

15. The communication receiver of claim 11, wherein the weight computation functional block calculates the plurality of complex-valued combining weights using de-spread codes that are adjacent to the one code selected from the de-spread second plurality of codes.

16. The communication receiver of claim 15, wherein the adjacent codes comprise two codes immediately adjacent to the one code selected from the de-spread second plurality of codes.

17. The communication receiver of claim 11, wherein the weight computation functional block calculates the plurality of complex-valued combining weights using de-spread codes from at least one of the first plurality of codes and the second plurality of codes that bears preamble symbols.

18. The communication receiver of claim 11, wherein the weight computation functional block employs at least one of least means square processing and least square processing to calculate the plurality of complex-valued combining weights.

19. The communication receiver of claim 11, wherein the communication receiver is operable to demodulate the spread signal using at least one of Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8 Quadrature Amplitude Modulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and 1024 QAM.

20. The communication receiver of claim 11, wherein the communication receiver comprises at least one of a multi-channel headend physical layer burst receiver, a single chip wireless modem, a single chip DOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobile receiver, a satellite earth station, a tower receiver, a high definition television set top box receiver, and a transceiver.

21. A communication receiver that is operable to perform interference cancellation, the communication receiver comprising:

a channel equalizer that receives a signal, from a communication channel, that comprises a portion of additive white noise; and

a canceler, communicatively coupled to the channel equalizer, that provides an inverse, zero forcing response to the received signal for substantial compensation of communication channel induced effects on the signal thereby generating a narrow peak at a frequency location of a null in a response of the communication channel; and

wherein the narrow peak causes the white noise to be colored and to include a white noise peak thereby generating narrowband colored noise; and

the canceler is operable to perform interference cancellation on the narrowband colored noise.

22. The communication receiver of the claim 21, wherein the canceler further comprises:

a vector de-spreader that de-spreads a first plurality of codes and a second plurality of codes from a colored signal;

a weight computation functional block that calculates a plurality of complex-valued combining weights using the signal and the narrowband colored noise that is added to the signal; and

a linear combiner that scales the de-spread first plurality of codes using the plurality of complex-valued combining weights and selectively sums the de-spread first plurality of codes and one code selected from the de-spread second plurality of codes to perform interference cancellation on at least one code de-spread from the spread signal.

23. The communication receiver of claim 22, wherein the first plurality of codes comprises a plurality of unused codes;

and the second plurality of codes comprises a plurality of used codes.

24. The communication receiver of claim 23, wherein the first plurality of codes and the second plurality of codes comprise a total number of 128 codes;

the first plurality of codes comprises at least 8 codes and no more than 32 codes;

the second plurality of codes comprises a remaining plurality of codes within the total number of 128 codes not included within the first plurality of codes; and

the communication system comprises a DOCSIS 2.0 S-CDMA operable communication system.

25. The communication receiver of claim 22, wherein the weight computation functional block calculates the plurality of complex-valued combining weights using both the de-spread first plurality of codes and the de-spread second plurality of codes.

26. The communication receiver of claim 22, wherein the weight computation functional block calculates the plurality of complex-valued combining weights using de-spread codes that are adjacent to the one code selected from the de-spread second plurality of codes.

27. The communication receiver of claim 26, wherein the adjacent codes comprise two codes immediately adjacent to the one code selected from the de-spread second plurality of codes;

and

the weight computation functional block calculates the plurality of complex-valued combining weights using de-spread codes from at least one of the first plurality of codes and the second plurality of codes that bears preamble symbols.

28. The communication receiver of claim 22, wherein the weight computation functional block employs at least one of least means square processing and least square processing to calculate the plurality of complex-valued combining weights.

29. The communication receiver of claim 21, wherein the communication receiver is operable to demodulate the signal using at least one of Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8 Quadrature Amplitude Modulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and 1024 QAM.

30. The communication receiver of claim 21, wherein the communication receiver comprises at least one of a multi-channel headend physical layer burst receiver, a single chip wireless modem, a single chip DOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobile receiver, a satellite earth station, a tower receiver, a high definition television set top box receiver, and a transceiver.

31. A communication receiver that is operable to perform interference cancellation, comprising:

a vector de-spreader that de-spreads a first plurality of codes and a second plurality of codes from a spread signal;

a linear combiner that comprises a plurality of feed-forward equalizers; and

wherein each feed-forward equalizer being communicatively coupled to outputs from each of the first plurality of codes;

each feed-forward equalizer comprises a tapped delay line and a plurality of combining weights;

each feed-forward equalizer sums its corresponding output code with delayed and scaled versions of its corresponding output code, the delaying and scaling being performed using the tapped delay line and the plurality of combining weights for each feed-forward equalizer;

the plurality of feed-forward equalizers cooperatively provide a plurality of feed-forward equalizer outputs; and

a linear combiner that combines the plurality of feed-forward equalizer outputs with at least one code, selected from the second plurality of codes, to perform interference cancellation on at least one code de-spread from the spread signal.

32. The communication receiver of claim 31, wherein each feed-forward equalizer comprises a plurality of equalizer taps;

and

each equalizer tap comprising a frequency selective response.

33. The communication receiver of claim 31, wherein the first plurality of codes comprises a plurality of unused codes;

and

the second plurality of codes comprises a plurality of used codes.

34. The communication receiver of claim 31, wherein the communication receiver is operable to demodulate the signal using at least one of Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8 Quadrature Amplitude Modulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and 1024 QAM.

35. The communication receiver of claim 31, wherein the communication receiver comprises at least one of a multi-channel headend physical layer burst receiver, a single chip wireless modem, a single chip DOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobile receiver, a satellite earth station, a tower receiver, a high definition television set top box receiver, and a transceiver.

36. A communication receiver that is operable to perform interference cancellation, comprising:

a vector de-spreader that de-spreads a first plurality of codes and a second plurality of codes from a spread signal;

a weight computation functional block that calculates a plurality of complex-valued combining weights using the spread signal and interference contained within the spread signal;

a linear combiner that scales the de-spread first plurality of codes using the plurality of complex-valued combining weights and selectively sums the scaled, de-spread first plurality of codes and one code selected from the de-spread second plurality of codes to perform interference cancellation on at least one code de-spread from the spread signal; and

an iterative adaptive weight functional block that is operable to perform error calculation of a hard decision corresponding to the at least one code de-spread from the spread signal; and

wherein the iterative adaptive weight functional block updates the plurality of complex-valued combining weights using the calculated error.

37. The communication receiver of claim 36, wherein the iterative adaptive weight functional block performs least means square error processing to calculate the error that is used to update the plurality of complex-valued combining weights.

38. The communication receiver of claim 36, wherein the first plurality of codes comprises a plurality of unused codes;

and

the second plurality of codes comprises a plurality of used codes.

39. The communication receiver of claim 36, wherein the communication receiver is operable to demodulate the signal using at least one of Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8 Quadrature Amplitude Modulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and 1024 QAM.

40. The communication receiver of claim 36, wherein the communication receiver comprises at least one of a multi-channel headend physical layer burst receiver, a single chip wireless modem, a single chip DOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobile receiver, a satellite earth station, a tower receiver, a high definition television set top box receiver, and a transceiver.

41. An interference cancellation method, comprising:

receiving a spread signal that comprises interference;

de-spreading the received signal using a first plurality of codes and a second plurality of codes;

calculating a plurality of complex-valued combining weights using the spread signal and the interference contained within the spread signal;

scaling the de-spread first plurality of codes using the plurality of complex-valued combining weights; and

selectively summing the scaled, de-spread first plurality of codes and one code selected from the de-spread second plurality of codes.

42. The method of claim 41, wherein the first plurality of codes comprises a plurality of unused codes;

and

the second plurality of codes comprises a plurality of used codes.

43. The method of claim 42, wherein the first plurality of codes and the second plurality of codes comprise a total number of 128 codes;

the first plurality of codes comprises at least 8 codes and no more than 32 codes;

the second plurality of codes comprises a remaining plurality of codes within the total number of 128 codes not included within the first plurality of codes; and

the communication system comprises a DOCSIS 2.0 S-CDMA operable communication system.

44. The method of claim 41, further comprising calculating the plurality of complex-valued combining weights using both the de-spread first plurality of codes and the de-spread second plurality of codes.

45. The method of claim 41, further comprising calculating the plurality of complex-valued combining weights using de-spread codes that are adjacent to the one code selected from the de-spread second plurality of codes.

46. The method of claim 45, wherein the adjacent codes comprise two codes immediately adjacent to the one code selected from the de-spread second plurality of codes.

47. The method of claim 41, further comprising calculating the plurality of complex-valued combining weights using a de-spread code from at least one of the first plurality of codes and the second plurality of codes that bears preamble symbols.

48. The method of claim 41, further comprising employing at least one of least means square processing and least square processing to calculate the plurality of complex-valued combining weights.

49. The method of claim 41, further comprising demodulating the spread signal using at least one of Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8 Quadrature Amplitude Modulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and 1024 QAM.

50. The method of claim 41, wherein the method is performed in at least one of a multi-channel headend physical layer burst receiver, a single chip wireless modem, a single chip DOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobile receiver, a satellite earth station, a tower receiver, a high definition television set top box receiver, and a transceiver.

51. A synchronous code division multiple access interference (S-CDMA) interference cancellation method, comprising:

selecting a plurality of used codes from a plurality of available codes;

selecting a plurality of unused codes from the plurality of available codes;

spreading a signal using the plurality of used codes;

transmitting a spread signal;

receiving the spread signal, the received spread signal comprising interference; and

employing a used projection of the received spread signal onto the plurality of used codes and an unused projection of the received spread signal onto the plurality of unused codes to perform interference cancellation on the received spread signal.

52. The method of claim 51, further comprising:

computing the used projection of the received spread signal onto the plurality of used codes; and

computing the unused projection of the received spread signal onto the plurality of unused codes.

53. The method of claim 51, further comprising de-spreading the received spread signal using the plurality of used codes and the plurality of unused codes to generate the de-spread signal.

54. The method of claim 51, wherein the plurality of available codes comprises at least one of a plurality of DOCSIS 2.0 S-CDMA orthogonal codes and Walsh-Hadamard codes.

55. The method of claim 51, wherein the plurality of unused codes comprises at least one of a plurality of adjacent codes and a plurality of maximally spaced apart codes within the plurality of available codes.

56. The method of claim 51, wherein the plurality of unused codes are selected employing an optimality criterion that comprises at least one of:

selecting unused codes that have maximal correlation with the interference;

minimizing enhancement of white noise resulting from the interference cancellation; and

minimizing residual interference power within the received spread signal after performing interference cancellation.

57. The method of claim 51, wherein the method is performed in at least one of a multi-channel headend physical layer burst receiver, a single chip wireless modem, a single chip DOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobile receiver, a satellite earth station, a tower receiver, a high definition television set top box receiver, and a transceiver.

58. An interference cancellation method, comprising:

selecting a plurality of used basis waveforms from a plurality of substantially orthogonal waveforms;

selecting a plurality of unused basis waveforms from the plurality of substantially orthogonal waveforms;

transmitting a signal using the plurality of used basis waveforms;

receiving the signal, the received signal comprising interference; and

employing a used projection of the received signal onto the plurality of used basis waveforms and an unused projection of the received signal onto the plurality of unused basis waveforms to perform interference cancellation on the received signal.

59. The method of claim 58, further comprising:

computing the used projection of the received signal onto the plurality of used basis waveforms; and

computing the unused projection of the received signal onto the plurality of unused basis waveforms.

60. The method of claim 58, further comprising transmitting at least one of a zero valued symbol and a training symbol using the plurality of unused basis waveforms.

61. The method of claim 58, wherein a number of the plurality of unused basis waveforms is less than a number of the plurality of used basis waveforms.

62. The method of claim 58, further comprising:

computing an interference projection of the interference onto the plurality of unused basis waveforms; and

subtracting the interference projection from the used projection.

63. The method of claim 58, wherein the method is performed in at least one of a multi-channel headend physical layer burst receiver, a single chip wireless modem, a single chip DOCSIS/EuroDOCSIS cable modem, a base station receiver, a mobile receiver, a satellite earth station, a tower receiver, a high definition television set top box receiver, and a transceiver.