TWO-STEP INITIALIZATION PROCEDURE FOR ADAPTIVE ANALOG ECHO CANCELLATION

摘要

The present invention relates to a communication unit comprising an echo canceler (140) for generating an echo suppression signal (ECHOSUP) to be superimposed at a receiver input to a receive analog signal comprising at least one of a far-end signal (RXSIG) received from a transmission medium (200) and an echo signal (ECHOSIG) resulting from a near-end signal (TXSIG) being transmitted from a transmitter output over the transmission medium and coupling through an echo coupling path ( h E k ) into the receiver input; and a controller (150) for controlling the operation of the echo canceler. The controller applies at least one first gain value (±1, ²1, ³1) across the echo coupling path for the receive analog signal to be power-constrained below a first power threshold at the receiver input, receives first measurements of the receive analog signal performed while the near-end signal is being transmitted with the at least one first gain value in force and without the echo suppression signal being generated, and determines a first estimate h ^ E k of the echo coupling path from the first measurements. The echo canceler generates the echo suppression signal based on the first estimate. The controller thereupon substitutes at least one nominal gain value (±2, ²2, ³2) used for regular communication over the transmission medium for the respective at least one first gain value, receives second measurements of the receive analog signal performed while the near-end signal is being transmitted with the at least one nominal gain value in force and while the echo suppression signal based on the first estimate is being generated and superimposed to the receive analog signal, and determines a second estimate h ^ ^ E k of the echo coupling path from the second measurements. The echo canceler then adjusts the echo suppression signal based on the second estimate. The present invention also relates to a method for controlling an echo suppression signal.