Multiplex communications – Wide area network – Packet switching
Patent
1989-12-01
1991-10-29
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
379388, 379410, 379406, H04M 908
Patent
active
050621025
ABSTRACT:
In a data transmission system where a first signal partially leaks as an echo from a first transmission line to a second transmission line through a hybrid circuit to form a mixed signal of the echo and a second signal on the second transmission line, an echo canceller is used for cancelling the echo by producing an echo replica at a transversal filter according to filter coefficients and subtracting the echo replica from the mixed signal. In order to reliably generate the filter coefficient for a reduced time duration, a series of autocorrelation coefficients of the first signal and a series of cross-correlation coefficients between the first and the mixed signals are calculated at calculators and the filter coefficients are determined from both of the autocorrelation and the cross-correlation coefficient series at a coefficient determining circuit. The coefficient determining circuit may be an arithmetic circuit for solving simultaneous linear equations. Another circuit for determining the filter coefficients may be a circuit where a first filter coefficient is determined by detecting the maximum value and the corresponding delay time from the series of cross-correlation coefficients, making a fresh series of cross-correlation coefficients with reference to the maximum values, the delay time and the first filter coefficient, then, determining a second filter coefficient from the fresh series. Then, filter coefficients are determined by repetition of the similar operation.
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patent: 4785445 (1988-11-01), Guidoux
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patent: 4937813 (1990-06-01), Schenk
patent: 4956838 (1990-09-01), Gilloire et al.
NEC Corporation
Olms Douglas W.
Ton Dang
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