Abstract: Optical signal transmission is improved by reducing the variance in light output level and OSNR by adjusting optical signal intensity and gain tilt, taking SRS influence into consideration.

Abstract: An acoustic echo canceller for cancelling an acoustic echo component produced when a signal on a receiving communication line appears on a transmitting communication line via an acoustic echo path. In the acoustic echo canceller, a variable coefficient series is divided into blocks, among which selected is a block requiring a coefficient correction amount update operation conforming to the attenuation characteristic of an impulse response in a sound field. A coefficient fitted to the attenuation characteristic of the impulse response in the sound field is set for the selected block. Therefore, convergence speed degradation of the acoustic echo cancellation characteristic involved in divided update can be compensated, and even if an echo path characteristic fluctuates, an excellent follow-up characteristic is provided, so that stable and high-speed acoustic echo cancellation can always be executed.