Decision feedback equalizer
First Claim
1. An adaptive equalizer for compensating a digital signal for dynamic variations in the transfer function of a communication channel, said digital signal being transmitted via the communication channel to said equalizer, said equalizer comprising:
- (A) first and second adaptive tapped delay lines each having an input and an output, the input of the first adaptive delay line for receiving the digital signal from the communication channel, the input of the second adaptive delay line for alternately receiving either a training signal or a decision result signal, the output of each adaptive delay line for producing an output signal which represents the product of the signal received at the respective input, delayed by a predetermined period which is a multiple a symbol period or of a fraction of the symbol period, multiplied by a preselected coefficient;
(B) a first summer for adding the output signals from the first and second delay lines to produce a compensated digital signal;
(C) decision means for receiving the compensated digital signal and responsively producing a decision result signal which represents an approximation of the digital signal transmitted by the transmitter;
(D) a switch for alternately passing either the decision result signal or the training signal to an output node in response to a switch control signal;
(E) a second summer for producing an error signal which represents the difference between the compensated digital signal and the signal present at the output node;
(F) coefficient adjustment means for receiving the error signal and a convergence control signal and responsively adjusting the coefficients of said first and second adaptive delay line means;
(G) an error detector for receiving the error signal and responsively producing an error decision signal which is indicative of whether the equalizer is accurately tracking changes in the communication channel'"'"'s characteristics; and
(H) a controller for receiving the error decision signal and responsively producing said switch control signal, whereby during a data receiving mode of operation the switch passes the decision result signal to the output node and during training or retraining modes of operation the switch passes the training or retraining signal, respectively, to the output node.
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Accused Products
Abstract
An improved decision feedback equalizer for use with digital communications. The equalizer includes an error detector, a process controller, a parameter selector and a data buffer for temporarily storing a digital data signal received from a communication channel. The error detector determines whether the equalizer is accurately tracking changes in the communication channel'"'"'s characteristics or is lost. When the error detector determines that the equalizer is lost, the process controller responsively generates control signals for initiating an optimal retraining/recovery method for the prevailing conditions. In some retraining/recovery methods, data is temporarily stored in the buffer. The stored data is later retrieved and processed once the equalizer is retrained. Retraining is performed using a retraining signal received via the communication channel or, if available, a portion of the data signal which is suitable for retraining, thereby permitting more rapid resumption of data reception. In addition, the parameter selector, in response to a control signal from the process controller and a signal which is indicative of the rate of change of the communication channel'"'"'s characteristics, dynamically adjusts the convergence rate of the equalizer to provide to an optimum value for performing retraining or tracking changes in the channel'"'"'s characteristics.
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Citations
30 Claims
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1. An adaptive equalizer for compensating a digital signal for dynamic variations in the transfer function of a communication channel, said digital signal being transmitted via the communication channel to said equalizer, said equalizer comprising:
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(A) first and second adaptive tapped delay lines each having an input and an output, the input of the first adaptive delay line for receiving the digital signal from the communication channel, the input of the second adaptive delay line for alternately receiving either a training signal or a decision result signal, the output of each adaptive delay line for producing an output signal which represents the product of the signal received at the respective input, delayed by a predetermined period which is a multiple a symbol period or of a fraction of the symbol period, multiplied by a preselected coefficient; (B) a first summer for adding the output signals from the first and second delay lines to produce a compensated digital signal; (C) decision means for receiving the compensated digital signal and responsively producing a decision result signal which represents an approximation of the digital signal transmitted by the transmitter; (D) a switch for alternately passing either the decision result signal or the training signal to an output node in response to a switch control signal; (E) a second summer for producing an error signal which represents the difference between the compensated digital signal and the signal present at the output node; (F) coefficient adjustment means for receiving the error signal and a convergence control signal and responsively adjusting the coefficients of said first and second adaptive delay line means; (G) an error detector for receiving the error signal and responsively producing an error decision signal which is indicative of whether the equalizer is accurately tracking changes in the communication channel'"'"'s characteristics; and (H) a controller for receiving the error decision signal and responsively producing said switch control signal, whereby during a data receiving mode of operation the switch passes the decision result signal to the output node and during training or retraining modes of operation the switch passes the training or retraining signal, respectively, to the output node. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. In an adaptive equalizer which receives a digital data signal from a communication channel, a method of recovering from an error condition comparing the steps of:
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using a training signal to cause said equalizer to converge; commencing a data receiving mode of operation in which said digital data signal is received from said channel and tracked by said equalizer; detecting that an error condition exists in said equalizer while said data signal is being received; following detection of the error condition, storing the data signal received from said channel in a memory; retraining the equalizer using a retraining signal received from the communication channel; and retrieving the stored data signal from the memory for tracking by the retrained equalizer. - View Dependent Claims (15, 16, 17)
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18. In an adaptive equalizer which receives a digital data signal from a communication channel, a method of receiving from an error condition comprising the steps of:
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using a training signal to cause said equalizer to converge; commencing a data receiving mode of operation in which said digital data signal is received from said channel and tracked by said equalizer; detecting that an error condition exists in said equalizer while said data signal is being received; determining whether a portion of the received data signal is sufficiently invariable to be used as a retraining signal; and retraining the equalizer using either a sufficiently invariable portion of the received data signal or a retraining signal received from the communication channel. - View Dependent Claims (19, 20, 21, 22, 23, 24)
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25. In an adaptive equalizer which receives a digital signal from a communication channel, a method of receiving from an error condition comprising the steps of:
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using a training signal to cause said equalizer to converge; commencing a data receiving mode of operation in which said digital data signal is received from said channel and tracked by said equalizer; detecting that an error condition exists in said equalizer while said data signal is being received; determining that a portion of the data signal is sufficiently invariable to be used as a retraining signal; and retraining the equalizer using said portion of the data signal. - View Dependent Claims (26, 27, 28, 29, 30)
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Specification