Load balancing computational methods in a short-code spread-spectrum communications system
First Claim
1. A method of processing spread spectrum waveforms transmitted by a plurality of users of a spread spectrum system, comprisingdistributing among a plurality of logic units parallel tasks each for computing a portion of a matrix indicative of cross correlations among the waveforms transmitted by the users,partitioning computation of the cross-correlation matrix such that a computational load associated with a task distributed to one of said logic units is substantially equal to computational load associated with another task distributed to another logic unit,executing with the plurality of logic units the distributed tasks,generating detection statistics corresponding to symbols transmitted by the users and encoded in the waveforms as a function of the cross correlation matrix, andgenerating estimates of the symbols based on the detection statistics.
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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.
75 Citations
13 Claims
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1. A method of processing spread spectrum waveforms transmitted by a plurality of users of a spread spectrum system, comprising
distributing among a plurality of logic units parallel tasks each for computing a portion of a matrix indicative of cross correlations among the waveforms transmitted by the users, partitioning computation of the cross-correlation matrix such that a computational load associated with a task distributed to one of said logic units is substantially equal to computational load associated with another task distributed to another logic unit, executing with the plurality of logic units the distributed tasks, generating detection statistics corresponding to symbols transmitted by the users and encoded in the waveforms as a function of the cross correlation matrix, and generating estimates of the symbols based on the detection statistics.
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7. A method of processing spread spectrum waveforms transmitted by a plurality of users of a spread spectrum system, comprising
partitioning computation of a matrix representing cross-correlations among the waveforms transmitted by the users in accord with a pre-defined metric, distributing among a plurality of logic units parallel tasks each corresponding to one of said partitions for computing a portion of the matrix, executing with the plurality of logic units the distributed tasks, assembling said computed portions to generate the cross-correlation matrix, representing the cross-correlation matrix as a composition of a first component that represents correlations among time lags and code sequences 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 detection statistics corresponding to symbols transmitted by the users and encoded in the waveforms as a function of the cross correlation matrix, and estimating the symbols based on the detection statistics.
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9. A method of processing spread spectrum waveforms transmitted by a plurality of users of a spread spectrum system, comprising
partitioning computation of a matrix representing cross-correlations among the waveforms transmitted by the users in accord with a pre-defined metric, distributing among a plurality of logic units parallel tasks each corresponding to one of said partitions for computing a portion of the matrix, executing with the plurality of logic units the distributed tasks, assembling said computed portions to generate the cross-correlation matrix, representing the cross-correlation matrix as a composition of a first component that represents correlations among time lags and code sequences 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 detection statistics corresponding to symbols transmitted by the users and encoded in the waveforms as a function of the cross correlation matrix, and generating estimates of the symbols based on the detection statistics wherein correlations among the code sequences associated with the respective users are computed in accord with the relation: -
wherein Γ
lk[m] represents correlation between l and k user codes corresponding to a shift of m chips,c*l[n] represents complex conjugate of the code sequences associated with the lth user, ck[n−
m] represents the code sequences associated with kth user,N represents the length of the code, and Nl represent the number of non-zero length of the code. - View Dependent Claims (10, 11, 12, 13)
wherein g is a pulse shape vector, Nc is the number of samples per chip, τ
is a time lag, andΓ
lk[m] represents correlation between l and k user codes corresponding to a shift of m chips.
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11. The method of claim 10, further comprising the step of computing the cross-correlation matrix (herein referred to as r matrix) in accord with the relation:
wherein â
lq* is an estimate of α
lq*, which represents a complex conjugate of one multipath amplitude component of the 1th user,α
kq, is one multipath amplitude component associated with the kth user, andC denotes the aforesaid C matrix.
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12. The method of claim 11, wherein the step of generating detection statistics comprises computing the detection statistics in accord with the relation:
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wherein yl[m] represents detection statistic for the mth symbol transmitted by the lth user, rll[0]bl[m] represents a signal of interest, and remaining terms of the relations represent Multiple Access Interference (MAI) and noise.
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13. The method of claim 12, wherein the step of generating symbol estimates comprises computing the estimates in accord with the relation:
wherein {circumflex over (b)}l[m] represents an estimate of the mth symbol transmitted by the lth user, g is a pulse shape vector, Nc is the number of samples per chip, τ
is a time lag, andΓ
represents the Γ
matrix.
Specification