Echo canceller in a communication system at a terminal

An echo processing method in a communication system at a terminal having a first transducer receiving a first signal including a part due to activity of a distant user and a second transducer emitting a second signal including a useful part due to activity of a local user, a background noise part, and an echo part due to coupling between said transducers, said method comprising:

• a first adaptive echo cancellation step including (a) calculating, from the first signal received by said first transducer, an estimate of said echo part of the second signal emitted by said second transducer, and (b) subtracting said estimate of said second signal emitted by said second transducer in order to produce an output signal;
• a second step of processing the echo remaining after said echo cancellation step, said second step including (a) distinguishing components which make up said echo part, (b) identifying components which make up said background noise part, and (c) determining a gain variation law modifying said output signal so as to reduce to the maximum extent the levels of said elements making up said echo part without substantially affecting said useful part;
• and
• compensating for the effects of said gain variation law on said components making up said background noise part by (a) modifying the gain determined by said variation law so that the output signal modified is at the level of said component making up said background noise part if the level of the output signal as it should be after application of said gain variation law is less than the level of a corresponding component making up said determined background noise part, and (b) keeping the gain as determined by the gain variation law if the level of the output signal as it should be after application of said gain variation law is not less than the level of a corresponding component making up said determined background noise part.

A terminal for processing an echo, the terminal being part of a communication system, the terminal comprising a first transducer for receiving a signal, the signal including a part due to activity of a distant user and a second transducer for emitting a second signal, the second signal including (a) a useful part due to the activity of a local user, (b) a background noise part and (c) an echo part due to coupling between the transducers, an adaptive echo cancellation device being adapted to (a) calculate, from the first signal received by said first transducer, an estimate of the echo part of the second signal emitted by said second transducer and (b) subtract the estimate of the second signal emitted by said second transducer to produce an output signal from the echo cancellation device, a device for processing the residual echo at the output of said adaptive echo cancellation device, the said residual echo processing device comprising a gain controller for modifying said output signal of the echo cancellation device, said gain controller including a first analyzer tar distinguishing components which make up said echo part, a second analyzer for identifying components which constitute said background part, and a calculator for determining a gain variation law, so as to reduce to the maximum possible extent the levels of said components making up said echo part without substantially affecting said useful parts, a compensator for compensating for the effects of said gain variation law on said components making up said background noise part, said compensator being arranged for (a) comparing the level of the output signal as it should be after application of said gain variation law at the level of a corresponding component making up said background noise part determined by the said second analyzer and (b) modifying the gain determined by said variation law so that the output signal modified by said gain controller is at the level of said component making up said background noise part in response to the determined level of said output signal being less than said level of said component;

• wherein the compensator comprises a simulation signal generator for reproducing the characteristics of said background noise part in response to said output signal being modified by said gain controller.

Echo processing method in a communication system at a terminal having a first transducer receiving a first signal including a pert due to the activity of a distant user and a second transducer emitting a second signal including a useful part due to the activity of a local user, a background noise part, as well as an echo part due to coupling between said transducers, said method comprising:

• a first adaptive echo cancellation step including (a) calculating, from the first signal received by said first transducer, an estimate of said echo part of the second signal emitted by said second transducer, and (b) subtracting said estimate of said second signal emitted by said second transducer in order to produce an output signal,
• a second step of processing the echo remaining after said echo cancellation step, said second step including (a) distinguishing components which make up said echo part, (b) identifying components which make up said background noise part, and (c) determining a gain variation law modifying said output signal so as to reduce to the maximum extent the levels of said elements making up said echo part without substantially altering said useful part, and
• compensating for the effects of said gain variation law on said components making up said background noise part by (a) comparing the level of the output signal as it should be after application of said gain variation law with the level of a corresponding component making up said determined background noise part, and (b) modifying the gain determined by said variation law so that the output signal modified is at the level of said component making up said background noise part in response to the comparison indicating said level of said output signal is less than said level of said component, the compensating step including simulating reproduction of the characteristics of said background noise part in response to said output signal being modified by said gain controller.