Echo canceller utilizing correlation

Claim 2

An echo canceller for cancelling echoes reflected from the receiving path of a long-distance telephone circuit to the sending path through a four-wire to two-wire coupling circuit connected between said receiving and sending paths, comprising: cross-correlation means connected to said receiving path and said sending path for establishing the crosscorrelation between the instantaneous level of a received signal in said receiving path and the instantaneous level of a transmitted signal in said sending path and to provide a cross-correlation output signal representative of the cross-correlation; autocorrelation means connected to said receiving path for establishing the autocorrelation of the instantaneous level of said received signal and to provide an autocorrelation output signal representative of said autocorrelation; calculation means connected to said crosscorrelation means and said autocorrelation means and receptive of said crosscorrelation and autocorrelation signals for calculating the impulse response of an echo return path from the receiving path to the sending path through said four-wire to two-wire coupling circuit by solving for said impulse response the equation defining said cross-correlation as equal to the convolution of said impulse response with said autocorrelation; memory means connected to said calculation means for temporarily storing the calculated impulse response; integration means connected to said memory means and said receiving path for evaluating the convolution integral of the temporarily stored impulse response with the received signal to provide a convolution integral output signal representative of the echo component of the transmitted signal; and subtraction means connected to said sending path and said integration means for subtracting said convolution integral output signal from said transmitted signal.

Claim 3

An echo canceller for cancelling echoes reflected from the receiving path of a long-distance telephone circuit to the sending path through a four-wire to two-wire coupling circuit connected between said receiving and sending paths, comprising: cross-correlation means connected to said receiving path and said sending path for successively establishing in regular intervals the cross-correlation between the instantaneous level of a received signal in said receiving path and the instantaneous level of a transmitted signal in said sending path to provide successive cross-correlation output signals representative of the cross-correlation; autocorrelation means connected to said receiving path for successively establishing in said regular intervals the autocorrelation of the instantaneous level of the received signal to provide successive autocorrelation output signals representative of said autocorrelation; calculation means connected to said crosscorrelation means and said autocorrelation means and receptive of said cross-correlation and autocorrelation signals for calculating in regular intervals the impulse response of an echo return path from the receiving path to the sending path through said four-wire to two-wire coupling circuit by solving for said impulse response the equation defining said cross-correlation as equal to the convolution of said impulse response with said autocorrelation; memory means connected to said calculation means for temporarily storing the calculated impulse response; integration means connected to said memory means and said receiving path for evaluating the convolution integral of the temporarily stored impulse response with the received signal to provide a convolution integral output signal representative of the echo component of the transmittal signal; and subtraction means connected to said sending path and said integration means for subtracting said convolution integral output signal from said transmitted signal.

Claim 4

An echo canceller for cancelling echoes reflected from the receiving path of a long-distance telephone circuit to the sending path through a four-wire to two-wire coupling circuit connected between said receiving and sending paths, comprising: cross-correlation means connected to said receiving path and said sending path for successively establishing in regular intervals the cross-correlation between the instantaneous level of a received signal in said receiving path and the instantaneous level of a transmitted signal in said sending path to provide successive cross-correlation output signals representative of the cross-correlation; autocorrelation means connected to said receiving path for successively establishing in said regular intervals the autocorrelation of the instantaneous level of the received signal to provide successive autocorrelation output signals representative of said autocorrelation; calculation means connected to said crosscorrelation means and said autocorrelation means and receptive of said cross-correlation and autocorrelation signals for calculating in regular intervals the impulse response of an echo return path from the receiving path to the sending path through said four-wire to two-wire coupling circuit by solving for said impulse response the equation defining said cross-correlation as equal to the convolution of said impulse response with said autocorrelation; memory means connected to said calculation means for temporarily storing the calculated impulse response; integration means connected to said memory means and said receiving path for evaluating the convolution integral of the temporarily stored impulse response with the received signal to provide a convolution integral output signal representative of the echo component of the transmittal signal; and subtraction means connected to said sending path and said integration means for subtracting said convolution integral output signal from said transmitted signal.

Claim 5

An echo canceller according to claim 2, in which siad cross-correlation means comprises a first analogue-digital converter connected to said receiving path, a second analogue-digital converter connected to said sending path, a plurality of delay circuits in cascade and connected to said first analogue-digital converter to successively delay the digital output of the first analogue-digital converter by successive times to provide successively delayed digital outputs, a plurality of first multipliers connected to said second analogue-digital converter and the successively delayed digital outputs of said delay circuits respectively, and a plurality of first accumulators each connected to the output of a respective one of said first multipliers to provide said cross-correlation outputs.

Claim 6

An echo canceller according to claim 2, in which said auto-correlation means comprises a first analogue-digital converter connected to said receiving path, a plurality of delay circuits in cascade and connected to said first analogue-digital converter to successively delay the digital output of the first analogue-digital converter by successive times to provide successively delayed digital outputs, a plurality of second multipliers connected to said first analogue-digital converter and the successively delayed digital outputs of said delay circuits respectively, and a plurality of second accumulators each connected to the output of a respective one of said second multipliers to provide said autocorrelation outputs.

Claim 7

An echo canceller according to claim 2, in which said integration means comprises a plurality of third multipliers connected to said memory means and said successively delayed digital outputs, an adder circuit connected to the output of each of said third multipliers, and a digital-analogue converter connected to the output of said adder circuit to produce said convolution integral output.