Rake receiver for spread spectrum signal demodulation

• US 6,788,734 B2
• Filed: 05/08/2002
• Issued: 09/07/2004
• Est. Priority Date: 08/23/1996
• Status: Expired due to Term

• Current Assignee: III Holdings 1, LLC
• Original Assignee: TensorComm, Inc. (Rambus Inc.)
• Inventors: Kober, Wolfgang, Thomas, John K., Vis, Marvin L.
• Primary Examiner(s): DEPPE, BETSY LEE
• Application Number:
  US10/141,999
• Publication Number:
  US 20020176488A1
• Time in Patent Office: 853 Days
• Field of Search: 375/142, 375/144, 375/150, 375/147, 375/148, 375/343, 375/346, 375/347, 375/349, 375/267, 370/320, 370/335, 370/342, 370/441, 455/269, 455/272, 455/273, 455/278.1
• US Class Current: 375/148
• CPC Class Codes: H01Q 3/2605 Array of radiating elements provided with a feedback control over the element weights, e.g. adaptive arrays
• CPC Class Codes: H04B 1/1081 Reduction of multipath noise by equalising H04B7/005
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/71072 Successive interference cancellation
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop
• CPC Class Codes: H04B 7/0845 per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch rake receivers as such H04B1/7115
• CPC Class Codes: H04B 7/0891 Space-time diversity rake receivers H04B1/7115; space-time decoding H04L1/0631
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity

Abstract

The architecture of the present invention is premised upon an algorithm involving integration of oblique correlators and RAKE filtering to null interference from other spread spectrum signals. The oblique correlator is, of course, based on the non-orthogonal projections that are optimum for nulling structured signals such as spread spectrum signals. RAKE filtering is used to rapidly steer the beam of the multi-antenna system and to mitigate the effects of multipath.

Claims

1. A coded signal processor, comprising:

a plurality of projection filters m communication with a plurality of antennas, each of the plurality of projection filters projecting a corresponding composite signal space spanned by a respective composite coded signal output by the associated antenna onto a corresponding first signal space spanned by a respective first signal component of the respective composite coded signal along a corresponding projection space that is parallel to a corresponding second signal space spanned by at least a respective second signal component of the respective composite coded signal to determine a corresponding parameter of the respective first signal component.

2. The coded signal processor of claim 1, further comprising:

at least a first projection builder operable to determine a set of projection operators in accordance with the following mathematical expression;

3. The coded signal processor of claim 1, wherein the corresponding parameter is a time offset.

4. The coded signal processor of claim 1, wherein at least a portion of a noise portion of the respective composite coded signal is generated by a receiver.

5. The coded signal processor of claim 1, comprising a plurality of RAKE processors in communication with the plurality of projection filters, wherein each of the plurality of projection filters produces a corresponding projection filter output which is received as a RAKE processor input by a corresponding RAKE processor, the corresponding projection filter output of each of the plurality of projection filters being delayed relative to one another, each of the plurality of RAKE processors being adapted to align and scale their respective inputs to produce a corresponding compensated output.

6. The coded signal processor of claim 5, wherein the corresponding compensated output of each of the plurality of RAKE processors is delivered to a second projection builder in communication therewith for determining a refined oblique projection operator output corresponding to the compensated outputs using the equation of claim 2.

7. A method for processing a composite signal, comprising:

receiving a first composite coded signal, wherein a first composite signal space is spanned by the first composite coded signal; and

projecting the first composite signal space onto a first signal space spanned by a first signal component of the first composite coded signal along a projection space parallel to a first interference space spanned by a second signal component of the first composite coded signal to determine a parameter of the first signal component, wherein the first signal component is attributable to at least a first emitter and the second signal component is attributable to at least a second emitter other than the at least a first emitter.

8. The method of claim 7, wherein the method determines a parameter and the parameter is a time offset.

9. The method of claim 8, wherein the first and second signal components are transmitted asynchronously.

10. The method of claim 7, wherein the first signal component comprises a plurality of multipath signal segments and further comprising:

aligning at least one of a received time and phase of the multipath signal segments to produce an aligned first signal.

11. The method of claim 7, further comprising:

determining an actual time of transmission of the first signal component;

determining an actual received time for the first signal component; and

repeating the projecting step using the actual time of transmission of the first signal component and the actual received time.

12. The method of claim 7, wherein in the projecting step:

generating a plurality of projection operators using a set of trial transmit times and candidate symbols associated with the first signal component using the following mathematical expression;

13. A method for processing a coded signal, comprising:

receiving a coded signal, the coded signal being decomposable into at least a first signal component; and

projecting obliquely a signal space spanned by the coded signal onto a first signal space spanned by the first signal component to determine a parameter of the first signal component, wherein the parameter is a time offset.

14. The method of claim 13, wherein the first signal component is attributable to a first emitter, and the coded signal includes at least a second signal component attributable to at least a second emitter different from the first emitter.

15. The method of claim 14, wherein in the projecting step:

generating a plurality of projection operators associated with the first signal component, each projection operator corresponding to a pairing of trial transmit times and candidate symbols, according to the following mathematical expression;

16. The method of claim 13, wherein the first signal component is attributable to a first emitter, the coded signal includes at least a second signal component attributable to at least a second emitter other than the first emitter and wherein the first and second signal components are transmitted asynchronously.

17. The method of claim 13, wherein the first signal component comprises a plurality of multipath signal segments and further comprising:

aligning at least one of a received time and phase of the multipath signal segments to produce an aligned first signal.

18. The method of claim 17, further comprising:

scaling the multipath signal segments.

19. The method of claim 13, wherein the first signal component comprises a plurality of multipath signal segments, each of the plurality of multipath signal segments being received at different times, and further comprising:

assigning to a portion of each of the plurality of multipath signal segments a respective time of receipt.

20. The method of claim 13, further comprising:

determining an actual time of transmission of the first signal component;

determining an actual received time for the first signal component; and

repeating the projecting step using the actual time of transmission of the first signal component and the actual received time.

21. A method for processing a composite signal, comprising:

receiving a first composite coded signal, wherein a first composite signal space is spanned by the first composite coded signal; and

projecting the first composite signal space onto a first signal space spanned by a first signal component of the first composite coded signal along a projection space that is parallel to at least a second interference space spanned by at least a second signal component of the first composite coded signal to determine at least one parameter of the first signal component, wherein the parameter is a time offset.

22. The method of claim 21, further comprising:

aligning and scaling the first signal component to form an aligned first signal;

selecting a first transmit time and symbol for the aligned first signal;

generating an interference code corresponding to the aligned first signal;

determining a projection operator corresponding to the aligned first signal;

generating a correlation function corresponding to the aligned first signal;

determining at least one of a second transmit time and symbol for the aligned first signal; and

based on the at least one of a second transmit time and symbol, decoding the aligned first signal.

23. A method for processing a composite signal, comprising:

receiving a first composite coded signal, wherein a first composite signal space is spanned by the first composite coded signal; and

projecting the first composite signal space onto a first signal space spanned by a first signal component of the first composite coded signal along a projection space that is parallel to at least a second interference space spanned by at least a second signal component of the first composite coded signal to determine at least one parameter of the first signal component, wherein the first signal component is attributable to at least a first emitter and the at least a second signal component is attributable to at least a second emitter other than the first emitter and wherein the first and second signal components are transmitted asynchronously.

24. The method of claim 23, wherein the projecting step comprises:

selecting a candidate symbol and trial time corresponding to the first signal component;

generating a candidate interference code corresponding to the first signal component;

determining a hypothetical projection operator corresponding to the first signal component;

generating a hypothetical correlation function corresponding to the first signal component; and

threshold detecting the hypothetical correlation function to determine temporal locations of a plurality of peaks.

25. The method of claim 23, further comprising:

aligning and scaling the first signal component to form an aligned first signal;

selecting a first transmit time and symbol for the aligned first signal;

generating an interference code corresponding to the aligned first signal;

determining a projection operator corresponding to the aligned first signal;

generating a correlation function corresponding to the aligned first signal;

determining at least one of a second transmit time and symbol for the aligned first signal; and

using the at least one of a second transmit time and symbol, decoding the aligned first signal.

26. A method for processing a coded signal, comprising:

receiving a coded signal, the coded signal being decomposable into at least first and second signal components, wherein the first signal component is attributable to a first emitter and the second signal component is attributable to a second emitter different from the first emitter; and

determining a first correlation function associated with the first signal component according to the following mathematical expression;

27. The method of claim 26, further comprising:

projecting obliquely a signal space spanned by the coded signal onto a first signal space spanned by the first signal component to determine at least one parameter of the first signal component.

28. The method of claim 27, further comprising:

aligning and scaling the first signal component to form an aligned first signal;

selecting a transmit time and symbol for the aligned first signal;

generating an actual interference code corresponding to the aligned first signal;

determining a projection operator corresponding to the aligned first signal;

generating a correlation function corresponding to the aligned first signal;

determining at least one of a transmit time and symbol for the aligned first signal; and

using the at least one of a transmit time and symbol, decoding the aligned first signal.

29. The method of claim 27, wherein the projecting step comprises:

selecting a candidate symbol and trial time corresponding to the first signal component;

generating a candidate interference code corresponding to the first signal component;

generating a hypothetical correlation function corresponding to the first signal component; and

threshold detecting the hypothetical correlation function to determine temporal locations of a plurality of peaks.

30. A system for receiving a signal, comprising:

a plurality of antennas each of which is adapted to receive a respective signal, each respective signal being decomposable into a respective first coded signal segment attributable to a first emitter; and

a plurality of corresponding oblique projecting means for determining the respective first coded signal segment, the respective first coded signal segment spanning a corresponding first signal space, the plurality of oblique projecting means being in communication with the plurality of corresponding antennas and each of the plurality of oblique projecting means determining the respective first coded signal segment by projecting obliquely onto the corresponding first signal space a corresponding signal space spanned by the respective signal received by the corresponding antenna.

31. The system of claim 30, wherein at least one of the respective signals is also decomposable into a second signal segment attributable to an emitter other than the first emitter and wherein the corresponding signal space spanned by the respective signal is obliquely projected onto the corresponding first signal space along a corresponding projection space that is parallel to a second signal space spanned by the second signal segment.

32. The system of claim 30, further comprising:

a plurality of projection builders for outputting a plurality of hypothetical projection operators associated with the first coded signal segment; and

a plurality of corresponding RAKE processors in communication with the plurality of oblique projecting means, wherein each of the plurality of oblique projecting means produces a respective oblique projecting means output which is received as a RAKE processor input by each of the plurality of oblique projecting means'"'"' corresponding RAKE processor, the respective output of each of the plurality of oblique projecting means being delayed relative to one another, each of the plurality of RAKE processors being adapted to align and scale its respective input to produce a compensated output.

33. The system of claim 32, wherein the compensated output of each of the plurality of RAKE processors is delivered to a summing correlator.

34. The system of claim 30, further comprising:

a plurality of RAKE processing means, each RAKE processing means being in communication with a corresponding one of the plurality of oblique projecting means and producing a corresponding aligned first signal attributable to the first emitter; and

a demodulating means, in communication with the plurality of RAKE processing means, for demodulating at least a portion of each corresponding aligned first signal, the at least a portion of each corresponding aligned first signal defining a respective aligned first space, the demodulating means determining the corresponding aligned first signals by obliquely projecting a respective signal space defined by a corresponding aligned first signal onto the respective aligned first space.

35. A method for processing a composite signal, comprising:

(a) providing a first coded signal;

(b) outputting at least first and second channel signals corresponding to the first coded signal, wherein the first channel signal spans a first channel signal space and the second channel signal spans a second channel signal space;

(c) projecting the first channel signal space onto a first channel signal space spanned by a first channel signal component of the first channel signal along a first channel projection space parallel to a first channel interference space spanned by a first channel interference component of the first channel signal to determine a first parameter of the first channel signal component; and

(d) projecting the second channel signal space onto a second channel signal space spanned by a second channel signal component along a second channel projection space parallel to a second channel interference space spanned by a second channel interference component of the second channel signal to determine the first parameter of the second channel signal component, wherein the first and second channel signal components are attributable to at least a first emitter and the first and second channel interference components are attributable to at least a second emitter other than the at least a first emitter.

36. The method of claim 35, wherein the first parameter is a time offset.

37. The method of claim 35, wherein the first and second channel signal components on the one hand and the first and second channel interference components on the other are transmitted asynchronously.

38. The method of claim 35, wherein the first and second channel signals respectively correspond to the in-phase and quadrature channels of the first coded signal.

39. The method of claim 35, further comprising filtering the first and second channel signals before the projecting steps (c) and (d).

40. The method of claim 35, wherein the first channel signal component comprises a plurality of multipath signal segments and further comprising the substep of:

aligning at least one of a received time and phase of the multipath signal segments to produce an aligned first signal.

41. The method of claim 35, further comprising, for each of the first and second channel signals, the steps of:

(e) determining an actual time of transmission of the first and second channel signal components, respectively;

(f) determining an actual received time for the first and second signal components, respectively; and

(g) repeating the projecting step using the actual time of transmission of the first and second channel signal components, respectively, and their corresponding actual received times.

42. The method of claims 35, further comprising:

generating a plurality of hypothetical projection operators corresponding to the first channel signal component according to an equation that includes the following mathematical expression;

43. The method of claim 35, further comprising:

(e) aligning and scaling the first channel signal component to form an aligned first signal;

(f) selecting a first transmit time and symbol for the aligned first signal;

(g) generating an interference code corresponding to the aligned first signal;

(h) determining a projection operator corresponding to the aligned first signal;

(i) generating a correlation function corresponding to the aligned first signal;

(j) determining at least one of a second transmit time and symbol for the aligned first signal; and

(k) based on the at least one of a second transmit time and symbol, decoding the aligned first signal.

44. The method of claim 35, wherein the projecting steps (c) and (d) collectively comprise:

selecting candidate symbols and trial times corresponding to the first and second channel signal components;

generating candidate interference codes corresponding to the first and second channel signal components;

determining hypothetical projection operators corresponding to the first and second channel signal components;

generating hypothetical correlation functions corresponding to the first and second channel signal components; and

threshold detecting the hypothetical correlation functions to determine temporal locations of a plurality of peaks.

45. A system for processing a coded signal, comprising:

an antenna operable to receive a coded signal;

an output operable to output first and second channel signals corresponding to the coded signal;

a correlator operable to output a correlation function, the correlator comprising (i) at least a first projection builder operable to determine at least a first oblique projection operator associated with the first and second channel signals and (ii) at least a first projection filter operable to project obliquely first and second channel signal spaces respectively spanned by the first and second channel signals onto at least one selected signal space spanned by at least one selected signal component to determine one or more parameters of the at least one selected signal component of the first and second channel signals, the at least one selected signal component being attributable to a first emitter having a first interference code matrix.

46. The system of claim 45, wherein the first and second channel signals correspond to the in-phase and quadrature components of the coded signal.

47. The system of claim 45, wherein the at least a first oblique projection operator is determined by the at least a first projection builder using an equation that includes the following mathematical expression:

48. The system of claim 45, further comprising:

a threshold timing device operable to generate timing information defining a temporal relationship among a plurality of peaks defined by the correlation function.

49. The system of claim 48, further comprising:

a timing reconciliation device operable to determine a reference time based on the timing information.

50. The system of claim 49, wherein the coded signal comprises a plurality of multipath signal segments associated with the at least one selected signal component of the coded signal and further comprising:

a RAKE processor operable to align the plurality of multipath signal segments for the first emitter in time and phase and output an aligned signal for the first emitter.

51. The system of claim 50, further comprising:

a demodulator operable to demodulate the aligned signal into a second correlation function.

52. The system of claim 51, further comprising:

a threshold detector operable to convert the second correlation function into digital information.

53. The system of claim 50, wherein the aligned signal output by the RAKE processor is delivered to a second oblique projection operator different from the at least a first oblique projection operator.

54. A system for processing a coded signal, comprising:

at least a first correlator operable to output at least a first correlation function corresponding to a first signal segment of a coded signal, the first correlator being configured to project obliquely a coded signal space spanned by the coded signal onto a first signal space spanned by the first signal segment, the first signal segment being attributable to a first emitter having a first interference code matrix.

55. The system of claim 54, wherein the first correlator comprises:

at least a first projection builder operable to output a first set of projection operators.

56. The system of claim 55, wherein the at least a first projection builder generates each projection operator in the first set using the following mathematical expression:

57. The system of claim 55, wherein the first correlator comprises:

a user code generator operable to output a set of trial transmit times and candidate symbols corresponding to the first signal segment and, for each pairing of trial transmit times and candidate symbols in the set, generate a candidate user code for the first emitter and wherein the at least a first projection builder is configured to use the candidate user codes to determine the first set of projection operators.

58. The system of claim 57, wherein the first correlator further comprises:

a bank of projection filters, each projection filter in the bank of projection filters corresponding to each projection operator in the first set of projection operators, operable to output the at least a first correlation function.

59. The system of claim 58, wherein each of the projection filters is operable to output the at least a first correlation function attributable to the first emitter from the corresponding projection operator in the first set of projection operators while simultaneously nulling out interference attributable to emitters different from the first emitter.

60. The system of claim 59, further comprising:

a threshold detector operable to determine temporal locations of selected peaks in the at least a first correlation function.

61. The system of claim 60, further comprising:

a timing reconciliation device operable to determine a reference time based on the temporal locations of the selected peaks.

62. The system of claim 61, wherein the at least a first correlation function comprises a plurality of correlation functions and further comprising:

based on the reference time, a RAKE processor operable to scale and align in time and phase the plurality of correlation functions to form a plurality of aligned and scaled correlation functions and sum the plurality of aligned and scaled correlation functions to form a RAKE output.

63. The system of claim 62, further comprising:

a demodulator operable to determine, based on the RAKE output, an actual transmit time for the first signal segment.

64. The system of claim 63, wherein the demodulator comprises:

a second user code generator operable to output a second set of trial transmit times and candidate symbols corresponding to the first signal segment and, for each pairing of trial transmit times and candidate symbols in the set, generate at least a second candidate user code for the first emitter;

a second projection builder to determine, for the at least a second candidate user code and based on the RAKE output, a second set of projection operators; and

a second bank of projection filters, each filter being associated with a projection operator in the second set of projection operators, operable to output at least a second correlation function.

65. The system of claim 64, further comprising:

a second threshold detector operable to determine an actual transmit time and symbol based on the at least a second correlation function.

66. The system of claim 65, further comprising:

a decoder operable to despread the RAKE output using the actual transmit time and symbol.

67. The system of claim 54, further comprising:

at least one antenna operable to receive the coded signal and

at least one output operable to output first and second channel signals corresponding to the coded signal.

68. The system of claim 67, wherein the first channel signal corresponds to an in-phase portion of the coded signal and the second channel signal corresponds to a quadrature portion of the coded signal.

69. A method for processing a coded signal, comprising:

providing a coded signal, the coded signal comprising at least a first signal segment; and

projecting obliquely a coded signal space spanned by the coded signal onto a first signal space spanned by the first signal segment to provide a first output, the first signal segment being attributable to a first emitter having a first interference code matrix.

70. The method of claim 69, wherein the first output is at least a first correlation function corresponding to the first signal segment.

71. The method of claim 70, further comprising:

generating a first set of projection operators associated with the first signal segment.

72. The method of claim 71, wherein the generating step is performed using the following mathematical expression:

73. The method of claim 71, further comprising:

outputting a set of trial transmit times and candidate symbols corresponding to the first signal segment; and

for each pairing of trial transmit times and candidate symbols in the set, generating a candidate user code for the first emitter and wherein the candidate user codes are used to generate the first set of projection operators.

74. The method claim 73, further comprising

detecting temporal locations of selected peaks in the at least a first correlation function.

75. The method of claim 74, further comprising:

determining a reference time based on the temporal locations of the selected peaks.

76. The method of claim 75, wherein the at least a first correlation function comprises a plurality of correlation functions and further comprising:

based on the reference time, scaling and aligning in time and phase the plurality of correlation functions to form a plurality of aligned and scaled correlation functions; and

summing the plurality of aligned and scaled correlation functions to form a RAKE output.

77. The method of claim 76, further comprising:

determining, based on the RAKE output, an actual transmit time for the first signal segment.

78. The method of claim 77, further comprising:

outputting a second set of trial transmit times and candidate symbols corresponding to the first signal segment; and

for each pairing of trial transmit times and candidate symbols in the set, generating at least a second candidate user code for the first emitter.

79. The method of claim 78, further comprising:

determining, for the at least a second candidate user code and based on the RAKE output, a second set of projection operators; and

based on the second set of projection operators, outputting at least a second correlation function.

80. The method of claim 79, further comprising:

determining an actual transmit time and symbol based on the at least a second correlation function.

81. The method of claim 80, further comprising:

despreading the RAKE output using the actual transmit time and symbol.

82. The method of claim 69, further comprising:

converting the coded signal into first and second channel signals.

83. The method of claim 82, wherein the first channel signal corresponds to an in-phase portion of the coded signal and the second channel signal corresponds to a quadrature portion of the coded signal.

84. A system for processing a coded signal, comprising:

at least a first projection filter operable to project obliquely a coded signal space spanned by the coded signal onto a first signal space spanned by a first signal segment of the coded signal, the first signal segment being attributable to a first emitter having a first interference code matrix.

85. The system of claim 84, wherein the at least a first projection filter outputs at least a first correlation function corresponding to the first signal segment.

86. The system of claim 85, further comprising:

at least a first projection builder operable to output a first set of projection operators.

87. The system of claim 86, wherein the at least a first projection builder generates each projection operator in the first set using the following mathematical expression:

88. The system of claim 86, further comprising:

a user code generator operable to output a set of trial transmit times and candidate symbols corresponding to the first signal segment and, for each pairing of trial transmit times and candidate symbols in the set, generate a candidate user code for the first emitter and wherein the at least a first projection builder is configured to use the candidate user codes to determine the first set of projection operators.

89. The system of claim 88, further comprising:

a bank of projection filters, each projection filter in the bank of projection filters corresponding to each projection operator in the first set of projection operators, operable to output the at least a first correlation function.

90. The system of claim 89, wherein each of the projection filters is operable to output the at least a first correlation function attributable to the first emitter from the corresponding projection operator in the first set of projection operators while simultaneously nulling out interference attributable to emitters different from the first emitter.

91. The system of claim 90, further comprising:

a threshold detector operable to determine temporal locations of selected peaks in the at least a first correlation function.

92. The system of claim 91, further comprising:

a timing reconciliation device operable to determine a reference time based on the temporal locations of the selected peaks.

93. The system of claim 92, wherein the at least a first correlation function comprises a plurality of correlation functions and further comprising:

based on the reference time, a RAKE processor operable to scale and align in time and phase the plurality of correlation functions to form a plurality of aligned and scaled correlation functions and sum the plurality of aligned and scaled correlation functions to form a RAKE output.

94. The system of claim 93, further comprising:

a demodulator operable to determine, based on the RAKE output, an actual transmit time for the first signal segment.

95. The system of claim 94, wherein the demodulator comprises:

a second user code generator operable to output a second set of trial transmit times and candidate symbols corresponding to the first signal segment and, for each pairing of trial transmit times and candidate symbols in the set, generate at least a second candidate user code for the first emitter;

a second projection builder to determine, for the at least a second candidate user code and based on the RAKE output, a second set of projection operators; and

a second bank of projection filters, each filter being associated with a projection operator in the second set of projection operators, operable to output at least a second correlation function.

96. The system of claim 95, further comprising:

a second threshold detector operable to determine an actual transmit time and symbol based on the at least a second correlation function.

97. The system of claim 96, further comprising:

a decoder operable to despread the RAKE output using the actual transmit time and symbol.

98. The system of claim 84, further comprising:

at least one antenna operable to receive the coded signal and

at least one output operable to output first and second channel signals corresponding to the coded signal.

99. The system of claim 98, wherein the first channel signal corresponds to an in-phase portion of the coded signal and the second channel signal corresponds to a quadrature portion of the coded signal.

100. The system of claim 84, wherein the at least a first projection filter is a plurality of projection filters operable to project obliquely a respective coded signal space corresponding to a respective coded signal onto a respective first signal space spanned by a respective first signal segment of the respective coded signal.

101. A system for processing a coded signal, comprising:

an input for receiving at least one coded signal, the at least one coded signal being decomposable into first and second signal segments, the first signal segment being attributable to a first emitter and the second signal segment being attributable to a second emitter different from the first emitter;

at least a first projection filter operable to output at least a first correlation function corresponding to the first signal segment using the following mathematical expression;

102. The system of claim 101, wherein the at least a first projection filter is operable to project obliquely a coded signal space spanned by the coded signal onto a first signal space spanned by a first signal segment of the coded signal.

103. The system of claim 101, wherein the at least a first projection filter uses a first set of projection operators to output the at least a first correlation function.

104. The system of claim 103, further comprising:

a user code generator operable to output a set of trial transmit times and candidate symbols corresponding to the first signal segment and, for each pairing of trial transmit times and candidate symbols in the set, generate a candidate user code for the first emitter and wherein at least a first projection builder is configured to use the candidate user codes to determine the first set of projection operators.

105. The system of claim 104, wherein the at least a first projection filter is a bank of first projection filters and each filter in the bank of projection filters corresponds to each projection operator in a first set of projection operators and is operable to output a corresponding first correlation function.

106. The system of claim 105, wherein each of the first projection filters is operable to output the corresponding first correlation function from the corresponding projection operator in the first set of projection operators while simultaneously nulling out interference attributable to emitters different from the first emitter.

107. The system of claim 106, further comprising:

a threshold detector operable to determine temporal locations of selected peaks in the at least a first correlation function.

108. The system of claim 107, further comprising:

a timing reconciliation device operable to determine a reference time based on the temporal locations of the selected peaks.

109. The system of claim 108, wherein the at least a first correlation function comprises a plurality of correlation functions and further comprising:

based on the reference time, a RAKE processor operable to scale and align in time and phase the plurality of correlation functions to form a plurality of aligned and scaled correlation functions and sum the plurality of aligned and scaled correlation functions to form a RAKE output.

110. The system of claim 109, further comprising:

a demodulator operable to determine, based on the RAKE output, an actual transmit time for the first signal segment.

111. The system of claim 110, wherein the demodulator comprises:

a second user code generator operable to output a second set of trial transmit times and candidate symbols corresponding to the first signal segment and, for each pairing of trial transmit times and candidate symbols in the set, generate at least a second candidate user code for the first emitter;

a second projection builder to determine, for the at least a second candidate user code and based on the RAKE output, a second set of projection operators; and

a second bank of projection filters, each filter being associated with a projection operator in the second set of projection operators, operable to output at least a second correlation function.

112. The system of claim 111, further comprising:

a second threshold detector operable to determine an actual transmit time and symbol based on the at least a second correlation function.

113. The system of claim 112, further comprising:

a decoder operable to despread the RAKE output using the actual transmit time and symbol.

114. The system of claim 101, further comprising:

at least one antenna operable to receive the coded signal and

at least one output operable to output first and second channel signals corresponding to the coded signal.

115. The system of claim 114, wherein the first channel signal corresponds to an in-phase portion of the coded signal and the second channel signal corresponds to a quadrature portion of the coded signal.

116. The system of claim 101, wherein the at least a first projection filter is a plurality of projection filters operable to project obliquely a respective coded signal space corresponding to a respective coded signal onto the first signal space spanned by a respective first signal segment of the respective coded signal.

117. A method for processing a coded signal, comprising:

providing a coded signal, the coded signal comprising at least first and second signal segments, the first signal segment being attributable to a first emitter and the second signal segment being attributable to a second emitter different from the first emitter; and

generating at least a first correlation function associated with the first signal segment, wherein the generating step is performed using the following mathematical expression;

118. The method of claim 117, wherein the generating step comprises:

projecting obliquely a coded signal space spanned by the coded signal onto a first signal space spanned by the first signal segment to provide the at least a first correlation function.

119. The method of claim 117, wherein the at least a first correlation function is generated in the generating step using a first set of projection operators.

120. The method of claim 119, further comprising:

outputting a set of trial transmit times and candidate symbols corresponding to the first signal segment; and

for each pairing of trial transmit times and candidate symbols in the set, generating a candidate user code for the first emitter and wherein the candidate user codes are used to generate the first set of projection operators.

121. The method of claim 120, further comprising

detecting temporal locations of selected peaks in the at least a first correlation function.

122. The method of claim 121, further comprising:

determining a reference time based on the temporal locations of the selected peaks.

123. The method of claim 122, wherein the at least a first correlation function comprises a plurality of correlation functions and further comprising:

based on the reference time, scaling and aligning in time and phase the plurality of correlation functions to form a plurality of aligned and scaled correlation functions; and

summing the plurality of aligned and scaled correlation functions to form a RAKE output.

124. The method of claim 123, further comprising:

determining, based on the RAKE output, an actual transmit time for the first signal segment.

125. The method of claim 124, further comprising:

outputting a second set of trial transmit times and candidate symbols corresponding to the first signal segment; and

for each pairing of trial transmit times and candidate symbols in the set, generating at least a second candidate user code for the first emitter.

126. The method of claim 125, comprising:

determining, for the at least a second candidate user code and based on the RAKE output, a second set of projection operators; and

based on the second set of projection operators, outputting at least a second correlation function.

127. The method of claim 126, further comprising:

determining an actual transmit time and symbol based on the at least a second correlation function.

128. The method of claim 127, further comprising:

despreading the RAKE output using the actual transmit time and symbol.

129. The method of claim 117, further comprising:

converting the coded signal into first and second channel signals.

130. The method of claim 129, wherein the first channel signal corresponds to an in-phase portion of the coded signal and the second channel signal corresponds to a quadrature portion of the coded signal.

131. A method for processing a coded signal, comprising:

providing a coded signal, the coded signal comprising at least first and second signal segments, the first signal segment being attributable to a first emitter and the second signal segment being attributable to a second emitter different from the first emitter;

generating at least one first projection operator using the following mathematical expression;

132. The method of claim 131, wherein the determining step comprises the substep of:

projecting obliquely a coded signal space spanned by the coded signal onto a first signal space spanned by the first signal segment to provide at least a first correlation function.

133. The method of claim 132, wherein the oblique projection is based on the at least one first projection operator.

134. The method of claim 133, further comprising:

outputting a set of trial transmit times and candidate symbols corresponding to the first signal segment; and

for each pairing of trial transmit times and candidate symbols in the set, generating a candidate user code for the first emitter and wherein the candidate user codes are used to generate the at least a first projection operator.

135. The method of claim 134, further comprising

detecting temporal locations of selected peaks in the at least a first correlation function.

136. The method of claim 135, further comprising:

determining a reference time based on the temporal locations of the selected peaks.

137. The method of claim 136, wherein the at least a first correlation function comprises a plurality of correlation functions and further comprising:

based on the reference time, scaling and aligning in time and phase the plurality of correlation functions to form a plurality of aligned and scaled correlation functions; and

summing the plurality of aligned and scaled correlation functions to form a RAKE output.

138. The method of claim 137, further comprising:

determining, based on the RAKE output, an actual transmit time for the first signal segment.

139. The method of claim 138, further comprising:

outputting a second set of trial transmit times and candidate symbols corresponding to the first signal segment; and

for each pairing of trial transmit times and candidate symbols in the set, generating at least a second candidate user code for the first emitter.

140. The method of claim 139, further comprising:

determining, for the at least a second candidate user code and based on the RAKE output, at least a second projection operator; and

based on the at least a second projection operator, outputting at least a second correlation function.

141. The method of claim 140, further comprising:

determining an actual transmit time and symbol based on the at least a second correlation function.

142. The method of claim 141, further comprising:

despreading the RAKE output using the actual transmit time and symbol.

143. The method of claim 131, further comprising:

converting the coded signal into first and second channel signals.

144. The method of claim 143, wherein the first channel signal corresponds to an in-phase portion of the coded signal and the second channel signal corresponds to a quadrature portion of the coded signal.