Quantized coherent rake receiver
First Claim
1. A method for decoding a Code Division Multiple Access signal comprising the steps of:
- correlating at least two time shifts of a received signal against a spreading code, the received signal comprising successive transmitted data symbols, the at least two time shifts corresponding to a transmitted data symbol, and the spreading code and a complement of the spreading code corresponding to different respective transmitted data symbols;
weighting the results of the correlating step according to coefficients selected from a coefficient store, each coefficient having a sign and a value that is an inverse integer power of two and corresponding to a respective time shift;
summing the results of the weighting step for each time shift in a respective accumulator; and
determining a sign of the sums in the accumulators to decode the transmitted data symbol.
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Abstract
An implementation of coherent diversity combining in a RAKE receiver that uses energy in signal echoes by integrating information from main-path and bit-period-delayed signal propagation paths to remove echo distortion, or time dispersion, is described. If delayed by one chip in a CDMA system, such echoes appear as uncorrelated interference. The RAKE receiver correlates a despreading code with the current (main-path) signal samples and with the signal samples delayed by 1, 2, 4, . . . bit periods, and combines the correlation results to determine the information content of the signal. After appropriate conditioning, the received signal is digitized and the signal samples are stored. Groups of samples are Fast Walsh Transformed, and the real and imaginary transforms are scaled according to a table of coefficients; the scaled results are stored. Weighted, scaled transforms of groups shifted by 1, 2, 4, . . . samples are accumulated, and the index of the largest-magnitude accumulation is used to select real and imaginary transform values. The selected values are transferred to a RAKE coefficient computer and quantizer that determines from the sequence of values presented the mean value and trend of the real and imaginary components. A Kalman filter may use these values to estimate the values that will occur during the next group analysis period.
284 Citations
41 Claims
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1. A method for decoding a Code Division Multiple Access signal comprising the steps of:
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correlating at least two time shifts of a received signal against a spreading code, the received signal comprising successive transmitted data symbols, the at least two time shifts corresponding to a transmitted data symbol, and the spreading code and a complement of the spreading code corresponding to different respective transmitted data symbols; weighting the results of the correlating step according to coefficients selected from a coefficient store, each coefficient having a sign and a value that is an inverse integer power of two and corresponding to a respective time shift; summing the results of the weighting step for each time shift in a respective accumulator; and determining a sign of the sums in the accumulators to decode the transmitted data symbol. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An apparatus for decoding a Code Division Multiple Access signal comprising:
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means for correlating at least two time shifts of a received signal with a spreading code, the received signal comprising successive transmitted data symbols, the at least two time shifts corresponding to a transmitted data symbol, and the spreading code and a complement of the spreading code corresponding to different respective transmitted data symbols; means for weighting correlations produced by the correlating means according to respective ones of at least two coefficients, each coefficient having a sign and a value that is an inverse integer power of two and corresponding to a respective time shift; means for summing the weighted correlations produced by the weighting means for each time shift; and means for determining a sign of the sum produced by the summing means to decode the transmitted data symbol. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. An apparatus for decoding a Code Division Multiple Access signal comprising:
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means for correlating at least two time shifts of a received signal with at least two spreading codes, the received signal comprising successive transmitted data symbols and the spreading codes corresponding to different transmitted data symbols; means for weighting correlations produced by the correlating means according to coefficients selected from a coefficient store, the coefficients having values selected from the group comprising ±
1, ±
1/2, ±
1/4, . . . and 0, and each coefficient corresponding to a respective time shift and a respective spreading code;means for summing the weighted correlations produced by the weighting means for the time shifts for each spreading code; means for determining the largest sum produced by the summing means to decode a transmitted data symbol; and means for subtracting a waveform corresponding to the decoded transmitted data symbol from the received signal. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34, 35)
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36. An apparatus for receiving and decoding a Code Division Multiple Access signal comprising successive transmitted data symbols comprising:
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means for receiving the signal, wherein the receiving means includes means for generating successive samples of complex vector components of the signal and means for digitizing the samples; means for storing a plurality of the digitized samples of a transmitted data symbol; means for determining Fast Walsh Transforms of the stored digitized samples, wherein the determining means correlates at least two time-shifted groups of the stored digitized samples with each of a plurality of orthogonal codes, each orthogonal code corresponding to a respective transmitted data symbol, and generates correlation results, each correlation result having a real part and an imaginary part; means for determining respective weighting coefficients for the real part and the imaginary part of the correlation result for each code and for each time-shifted group and for applying the weighting coefficients to the real parts and the imaginary parts; means for summing the weighted parts over all time-shifted groups, the summing means comprising a respective accumulator for each code; and means for determining the accumulator containing the largest sum and thereby decoding the transmitted data symbol, wherein the weighting coefficient determining means determines the weighting coefficients for a succeeding transmitted data symbol from the correlation results and the decoded transmitted data symbol. - View Dependent Claims (37, 38, 39, 40, 41)
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Specification