Wireless communications systems and methods for short-code multiple user detection
First Claim
1. A method of processing short code spread spectrum waveforms transmitted by one or more users of a spread spectrum system, comprisinggenerating a matrix indicative of cross correlations among the waveforms as a composition of a first component that represents correlations among time lags and short codes associated with the waveforms transmitted by the users and a second component that represents correlations among multipath signal amplitudes associated with the waveforms transmitted by the users,generating, as a function of the correlation matrix, detection statistics corresponding to symbols generated by the users and encoded in the waveforms, and generating estimates of the symbols based on the detection statistics,wherein the first component is updated on a time scale commensurate with a rate of change of the time lags associated with the waveforms transmitted by the users and the second component is updated on a time scale commensurate with a rate of change of the multipath amplitudes associated with waveforms transmitted by the users.
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Abstract
The invention provides methods and apparatus for multiple user detection (MUD) processing that have application, for example, in improving the capacity CDMA and other wireless base stations. One aspect of the invention provides a multiprocessor, multiuser detection system for detecting user transmitted symbols in CDMA short-code spectrum waveforms. A first processing element generates a matrix (hereinafter, “gamma matrix”) that represents a correlation between a short-code associated with one user and those associated with one or more other users. A set of second processing elements generates, e.g., from the gamma matrix, a matrix (hereinafter, “R-matrix”) that represents cross-correlations among user waveforms based on their amplitudes and time lags. A third processing element produces estimates of the user transmitted symbols as a function of the R-matrix.
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Citations
19 Claims
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1. A method of processing short code spread spectrum waveforms transmitted by one or more users of a spread spectrum system, comprising
generating a matrix indicative of cross correlations among the waveforms as a composition of a first component that represents correlations among time lags and short codes associated with the waveforms transmitted by the users and a second component that represents correlations among multipath signal amplitudes associated with the waveforms transmitted by the users, generating, as a function of the correlation matrix, detection statistics corresponding to symbols generated by the users and encoded in the waveforms, and generating estimates of the symbols based on the detection statistics, wherein the first component is updated on a time scale commensurate with a rate of change of the time lags associated with the waveforms transmitted by the users and the second component is updated on a time scale commensurate with a rate of change of the multipath amplitudes associated with waveforms transmitted by the users.
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8. A method of processing short code spread spectrum waveforms transmitted by one or more users of a spread spectrum system, comprising
generating a matrix indicative of cross correlations among the waveforms as a composition of a first component that represents correlations among time lags and short codes associated with the waveforms transmitted by the users and a second component that represents correlations among multipath signal amplitudes associated with the waveforms transmitted by the users, generating estimates of symbols transmitted by the users and encoded in said waveforms as a function of the cross-correlation matrix, wherein the correlations among the short codes associated with the waveforms transmitted by the users are defined in accord with by the relation: wherein Γ
lk[m] represents correlation between l and k users corresponding to mth transmitted symbol,cl*[n] represents complex conjugate of the short code sequence associated with the lth user, ck [n−
m] represents the short code sequence associated with kth user,m is a symbol period, N represents the length of the code, and Nl represent the number of non-zero length of the code, wherein the first component is updated on a time scale commensurate with a rate of change of the time lags associated with the waveforms transmitted by the users and the second component is updated on a time scale commensurate with a rate of change of the multipath amplitudes associated with waveforms transmitted by the users. - View Dependent Claims (9, 10)
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11. A method of processing short code spread spectrum waveforms transmitted by one or more users of a spread spectrum system, comprising
generating a matrix indicative of cross correlations among the waveforms as a composition of a first component that represents correlations among time lags and short codes associated with the waveforms transmitted by the users and a second component that represents correlations among multipath signal amplitudes associated with the waveforms transmitted by the users, generating estimates of symbols transmitted by the users and encoded in said waveforms as a function of the cross-correlation matrix, wherein the correlations among the short codes associated with the waveforms transmitted by the users are defined in accord with by the relation: -
wherein Γ
lk[m] represents correlation between l and k users corresponding to mth transmitted symbol,cl*[n] represents complex conjugate of the short code sequence associated with the lth user, ck[n−
m] represents the short code sequence associated with kth user,m is a symbol period, N represents the length of the code, and Nl represent the number of non-zero length of the code, wherein the step of estimating the symbols further comprises generating, as a function of the correlation matrix, detection statistics corresponding to symbols generated by the users and encoded in the waveforms, and wherein the step of estimating the symbols comprises utilizing the detection statistics to estimate the symbols wherein the first component of the cross-correlation matrix is defined in accord with the relation; wherein g is a pulse shape vector, Nc is the number of samples per chip, τ
is a time lag, andΓ
represents the Γ
matrix defined above.- View Dependent Claims (12, 13, 14, 15, 16)
wherein m is a symbol period, Re denotes the real part of a complex expression, ak is a columnar matrix representing multipath amplitude components associated with the kth user, â
lq* is an estimate of alq* which is the complex conjugate of one multipath amplitude component of the lth user,akq′
is one multipath amplitude component associated with the kth user, andC denotes the C matrix defined above.
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13. The method of claim 12, wherein the detection statistics are obtained in accord with the following relation:
wherein yl[m] represents detection statistics for mth symbol transmitted by the lth user, rll[0]bl[m] represents a signal of interest, and remaining terms of the relation represent Multiple Access Interference (MAI) and noise.
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14. The method of claim 13, wherein the step of generating estimates comprises performing multi-stage decision-feedback interference cancellation (MDFIC).
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15. The method of claim 14, wherein the step of performing MDFJC includes estimating symbols in accord with the relation:
wherein {circumflex over (b)}l[m] represents an estimate of the mth symbol transmitted by the lth user.
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16. The method of claim 15, further comprising the step of updating the C-matrix upon occurrence of a change in a user'"'"'s delay lag time.
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17. A method of processing short code spread spectrum waveforms transmitted by one or more users of a spread spectrum system, comprising
generating a matrix indicative of cross correlations among the waveforms as a composition of a first component that represents correlations among time lags and short codes associated with the waveforms transmitted by the users and a second component that represents correlations among multipath signal amplitudes associated with the waveforms transmitted by the users, generating estimates of symbols transmitted by the users and encoded in said waveforms wherein the first component is updated on a time scale commensurate with a rate of change of the time lags associated with the waveforms transmitted by the users and the second component is updated on a time scale commensurate with a rate of change of the multipath amplitudes associated with waveforms transmitted by the users.
Specification