摘要:
Method and apparatus for measuring the delay of the distant echo in an echoancelling arrangement comprising a near echo canceller, a delay line and a distant echo canceller using the steps oftransmitting, by modulation of a carrier, a data sequence having a periodic autocorrelation function with sidelobes of negative or zero value, this sequence having a duration at least equal to the maximum value of the delay to be measured and a number of elements determined by the accuracy desired for measurement of the delay;calculating the correlation function between the data of a next transmitted sequence and the data formed by demodulating the received signal and storing calculated samples of the correlation function in a memory; and determining, among the samples stored, the sample corresponding to the maximum of the correlation function and the rank of that sample.
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; andon the basis of said sum signal, extraction of the coefficients of the echo cancellers during determined time windows.