METHOD OF INITIALIZING THE FILTER COEFFICIENTS IN A COMPENSATION DEVICE FOR NEAR AND FAR ECHOES, AND DEVICE FOR PERFORMING THIS METHOD

摘要

The filter coefficients of an echo cancelling arrangement having a near echo canceller and a distant echo canceller are initialized in accordance with a method and apparatus wherein the following steps are performed: transmission of at least two training sequences each comprising a pair of complementary S and C sequences having autocorrelation functions such that, if added, their sidelobes cancel, each S and C sequence being followed by a variable time interval DELTA , determined as a function of the measured distant echo delay tau so that a distant echo produced in response to a training sequence occurs immediately after the near echo produced in response to by a following training sequence; after the first training sequence transmitted, calculation of correlation signals giving the correlation between the received signal and reference signals derived from an S sequence and a C sequence respectively during the first half and the second half of a training sequence of a duration T; application of a delay T/2 to the correlation signal formed on the basis of the S sequence; production of a sum signal of said delayed correlation signal and the correlation signal formed on the basis of the C sequence; and on the basis of said sum signal, extraction of the coefficients of the echo cancellers during determined time windows.