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US 7,599,426 B2Granted
Use of adaptive filters in multiple access wireless systems employing predictable signals
AssigneeAcorn Technologies, Inc.
InventorAlvin M. Despain
Life of this patent
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Abstract
A code division multiple access (CDMA) radio system uses an adaptive filter in a receiver to mitigate multipath radio propagation and to filter out interfering signals. Characteristics of an initial stage of the filter preferably are determined by cross correlation of a generated pilot signal and the input signal with the integration of the correlation performed over a time period selected to be an integral number of symbol periods. The integration causes the portions of the cross correlation corresponding to the user subchannels to average substantially to zero, so that the pilot channel signal correlation is the primary contribution to the signal used to characterize the channel to establish the coefficients of the adaptive filter for the receiver.
Claims68
A CDMA wireless communication system, comprising:
- a receiver having an adaptive filter coupled to receive an input signal comprising a plurality of user signals and a pilot signal, the input signal characterized by a symbol period defined by a CDMA transmitter,
- wherein the adaptive filter comprises:
- a multiplier coupled to receive the input signal and to receive a synthesized pilot signal, the multiplier providing a multiplier output;
- and
- an integrator coupled to receive the multiplier output and to generate at least one filter coefficient determined from the input signal multiplied by a synthesized pilot signal with a result integrated over an integer number of symbol periods.
2 more elements
A CDMA wireless communication system, comprising:
- a receiver having an adaptive matched filter coupled to receive an input signal comprising a plurality of user signals and a generated pilot signal, the input signal characterized by a symbol period defined by a CDMA transmitter,
- the adaptive matched filter comprising cross correlation circuitry coupled to receive the input signal and the generated pilot signal,
- wherein the adaptive matched filter has at least one filter coefficient determined in the cross correlation circuitry by cross correlation of the input signal with the generated pilot signal where the cross correlation is performed over an integer number of symbol periods.
A CDMA wireless communication system, comprising:
- a receiver comprising an adaptive matched filter coupled to receive an input signal comprising a plurality of user signals and a pilot signal, the input signal characterized by a symbol period defined by a CDMA transmitter, the receiver further comprising reference signal generation circuitry for generating a reference signal,
- the adaptive matched filter comprising multiplication circuitry and averaging circuitry, the multiplication circuitry receiving the input signal and the reference signal and providing a multiplication output, the averaging circuitry coupled to receive the multiplication output and performing an averaging over an integer number of symbol periods to provide an averaged output,
- wherein the adaptive matched filter determines a set of filter coefficients from the averaged output, the adaptive matched filter filtering at least one of the user signals using the set of filter coefficients.
A CDMA wireless communication system, comprising:
- a receiver having an adaptive Wiener filter coupled to receive an input signal comprising a plurality of user signals and a pilot signal, the plurality of user signals characterized by an orthogonal code modulation, the receiver generating a reference signal,
- the adaptive Wiener filter comprising a correlator coupled to receive the input signal and the reference signal, the correlator performing a correlation process with the input signal and the reference signal with the correlation process comprising averaging for an integer number of orthogonal code periods,
- wherein the Wiener filter has at least one filter coefficient determined by the correlation process between the input signal and the reference signal generated by the receiver.
A CDMA wireless communication system, comprising:
- a receiver having an adaptive multistage Wiener filter coupled to receive an input signal comprising a plurality of user signals and a pilot signal, the plurality of user signals characterized by an orthogonal code modulation,
- the adaptive multistage Wiener filter comprising a cross correlator coupled to receive the input signal and the pilot signal, the cross corretator performing a cross correlation with the input signal and the pilot signal including an integration over of an integer number of orthogonal code periods,
- wherein the adaptive multistage Wiener filter has at least one set of filter coefficients determined from the cross correlation between the pilot signal and the input signal in one processing stage so that the cross correlation characterizes a channel between the receiver and a CDMA transmitter, the adaptive multistage Wiener filter filtering the input signal in the one processing stage and in other processing stages.
A CDMA wireless communication system, comprising:
- a receiver having an adaptive filter coupled to receive an input signal comprising a plurality of user signals and at least one pilot signal, with the plurality of user signals each modulated by a Walsh code, and with the plurality of Walsh code modulated signals and the pilot signal further modulated by at least one of a set of pseudo random codes,
- wherein the adaptive filter comprises a matched filter, the matched filter comprising a correlator receiving the input signal and the pilot signal, the matched filter having at least one matched filter coefficient determined by the correlator correlating the input signal and the pilot signal in time segments, magnitudes of correlations of the user signals averaging substantially to zero over the time segments so that the matched filter coefficients are obtained substantially from correlations of the pilot signal so that the correlating process characterizes a signal channel between the receiver and a CDMA transmitter, the matched filter filtering the input signal.
A CDMA wireless communication system, comprising:
- a receiver having an adaptive filter coupled to receive an input signal comprising a plurality of user signals and at least one pilot signal, with the plurality of user signals modulated by Walsh codes, the modulated user signals and the pilot signal further modulated by at least one of a set of pseudo random codes,
- wherein the adaptive filter comprises at least a matched filter, the matched filter comprising a correlator receiving the input signal and the pilot signal, the matched filter having matched filter coefficients determined by the correlator averaging correlations of the input signal and the pilot signal over one or more Walsh code periods, magnitudes of correlations from user signal components of the input signal averaging substantially to zero over the one or more Walsh code periods so that the at least one adaptive filter coefficient is obtained from at least the pilot signal so that correlations characterize a signal channel between the receiver and a CDMA base station, the matched filter filtering the plurality of user signals.
A CDMA wireless communication system, comprising:
- a receiver having an adaptive filter coupled to receive an input signal comprising a plurality of user signals and at least one pilot signal, with at least the plurality of user channels signals modulated by Walsh codes, the plurality of user signals and the pilot signal modulated by at least one of a set of pseudo random codes,
- wherein the adaptive filter comprises at least a matched filter comprising an integrator, the matched filter having matched filter coefficients determined by the integrator integrating a correlation signal generated from the input signal over one or more Walsh code periods, magnitudes of user signals integrating substantially to zero over the one or more Walsh code periods so that the matched filter coefficients are obtained from at least the pilot signal in the matched filter that characterizes a signal channel between the receiver and a CDMA base station, and wherein the matched filter filters the plurality of user signals.
A CDMA wireless communication system, comprising:
- a receiver having an adaptive filter coupled to receive an input signal comprising a plurality of user signals and a known signal, the known signal comprising a known version of a sync signal, the input signal characterized by a symbol period defined by a CDMA transmitter,
- the adaptive filter comprising multiplication and integration circuitry, the multiplication and integration circuitry coupled to receive the input signal and the known signal and adapted to output at least one filter coefficient,
- wherein the at least one filter coefficient is determined from the input signal multiplied by the known signal with a result integrated over one or more complete symbol periods.
A CDMA wireless communication system, comprising:
- a receiver having an adaptive filter coupled to receive an input signal comprising a plurality of user signals and known signals, the known signals comprising a pilot signal and a sync signal, the input signal characterized by a symbol period defined by a CDMA transmitter,
- the adaptive filter comprising multiplication and integration circuitry, the multiplication and integration circuitry coupled to receive the input signal and at least a portion of the known signals and adapted to output at least one filter coefficient,
- wherein the adaptive filter has at least one filter coefficient determined by the multiplication and integration circuitry by multiplying the input signal by a locally generated reference signal which is a composite of signals corresponding to the one or more of the known signals to generate a multiplication result with the multiplication result integrated over one or more complete symbol periods.
A multiple access wireless communication system, comprising:
- a receiver having an adaptive filter coupled to receive an input signal comprising one or more user signals, the input signal characterized by an encoding identifying a base station that transmitted the input signal, the receiver generating a reference signal,
- the adaptive filter comprising correlation circuitry, the correlation circuitry coupled to receive the input signal and the reference signal and adapted to output at least one filter coefficient,
- wherein the correlation circuitry determines from the input signal at least one filter coefficient prior to the adaptive filter decoding the input signal, the correlation circuitry identifying a component of the input signal that is predictable only over a portion of a time interval, the correlation circuitry providing an output signal, the adaptive filter determining at least one filter coefficient from an average of two or more values respectively determined from two or more successive occurrences of the component of the input signal.
A receiver for a multiple access wireless communication system, the receiver comprising:
- an adaptive filter coupled to receive an input signal comprising one or more user signals, the input signal characterized by an encoding identifying a base station that transmitted the input signal;
- and
- a reference signal generator that generates a local reference signal synchronized with the input signal,
- the adaptive filter comprising correlation circuitry, the correlation circuitry coupled to receive the input signal and the local reference signal, the correlation circuitry performing correlations over time intervals,
- wherein the correlation circuitry performs correlations between the input signal and the local reference signal to remove unpredictable portions and to isolate predictable portions of the input signal, the adaptive filter using the correlation to determine coefficients of a matched filter prior to decoding the input signal and using the matched filter to at least in part filter the input signal,
- wherein the adaptive filter determines coefficients of the matched filter from an average of two or more of the correlations using successive portions of the input signal.
3 more elements
Dependencies are inferred from the claim text.