CDMA subtractive demodulation
First Claim
1. A method for decoding a composite signal having overlapping, coded signals, comprising:
- (a) iteratively correlating said composite signal with a series of codewords and generating for each correlation a plurality of correlation signals;
(b) extracting a coded signal corresponding to a greatest correlation signal from said composite signal, said greatest correlation having an address associated with one of said correlated code words;
(c) periodically recorrelating a remaining portion of said composite signal with said codewords; and
(d) eliminating any correlation signal corresponding to said associated address of at least one codeword previously correlated in step (a) from said remaining composite signal.
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Accused Products
Abstract
Subtractive CDMA demodulation optimally decodes a coded information signal embedded in many other overlapping signals making up a received, composite signal. A radio receiver correlates a unique code corresponding to the desired signal to be decoded with the composite signal. Moreover, after each information signal is successfully decoded, it is recoded and removed from the composite signal. Subtractive CDMA demodulation is enhanced by decoding the composite signal in the order of strongest to weakest signal strength. The individual information signals are spread using block error correction codes which are correlated with the composite signal using Fast Walsh transforms. Correlated signals identified as the largest transform component are removed from the composite signal and the remaining composite signal is reformulated using an inverted Fast Walsh transform. Any residual error or interference caused during the extraction of a transform component is removed by recorrelating the composite signal using the index of that transform component.
295 Citations
40 Claims
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1. A method for decoding a composite signal having overlapping, coded signals, comprising:
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(a) iteratively correlating said composite signal with a series of codewords and generating for each correlation a plurality of correlation signals; (b) extracting a coded signal corresponding to a greatest correlation signal from said composite signal, said greatest correlation having an address associated with one of said correlated code words; (c) periodically recorrelating a remaining portion of said composite signal with said codewords; and (d) eliminating any correlation signal corresponding to said associated address of at least one codeword previously correlated in step (a) from said remaining composite signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A system for decoding a composite signal having overlapping, coded signals, comprising:
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means for iteratively performing orthogonal transformations on said composite signal with a series of codeword and generating for each transformation a plurality of transformation components, each transformation component being associated with a codeword and an index; means for iteratively extracting the coded signal corresponding to a greatest component from said composite signal; means for periodically performing at least one orthogonal transformation on a remaining portion of said composite signal with said codewords; and means for eliminating any transformation component corresponding to said associated index of at least one previous codeword. - View Dependent Claims (9, 10, 11, 12)
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13. A method for decoding a composite signal having overlapping, coded signals, comprising:
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(a) iteratively performing orthogonal transformations on said composite signal with a plurality of codeword and generating for each transformation a plurality of transformation components, each transformation component having an associated codeword and index; (b) iteratively extracting a coded signal corresponding to a greatest transformation component from said composite signal; (c) periodically performing at least one orthogonal transformation on a remaining portion of said composite signal using said codewords; and (d) eliminating any transformation component corresponding to said associated index of at least one previously extracted coded signal. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A system for decoding a composite signal having overlapping, coded signals, comprising:
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plural signal extraction stages, each stage having means for receiving said composite signal and a series of codewords and means for extracting from said composite signal a coded signal associated with one of said codewords, and at least one signal elimination stage having means for eliminating from a remaining portion of said composite signal a residual signal associated with one of said coded signals previously extracted by said extracting means. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30)
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31. A method for decoding a composite signal having overlapped, coded signals and time-delayed echoes of at least some of said coded signals, comprising:
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(a) correlating a series of codewords with a plurality of time-shifted versions of said composite signal and generating a set of correlations for each time-shifted composite signal; (b) combining all of said sets of correlations for said time-shifted composite signals to produce a combined set of correlations; (c) determining a codeword corresponding to a greatest correlation in said combined set; and (d) subtracting said determined codeword from at least one of said time-shifted composite signals. - View Dependent Claims (32, 33, 34, 35, 36, 37, 38, 39, 40)
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Specification