Patent ID: 6545985
Filing Date: 2003-04-08
Classification: G10L,H04B,H04M

Abstract:
An arrangement for cancelling an echo returning to a first mobile station from a second mobile station in a mobile system comprising in addition to said mobile stations:at least one mobile exchange; a first transcoder and a second transcoder in such a way that the first and the second mobile stations are connected to said mobile exchanges through the first and the second transcoder, respectively, and the transcoders are arranged to convert a speech signal from a first coding format on the side of the mobile stations to a second coding format on the side of the mobile exchanges, and vice versa; tandem free operation for transmitting the speech signal entirely in the first coding format in response to the tandem free operation being active and both parties of a call being able to use the first coding format; at least one acoustic echo canceller between the mobile exchanges and the second mobile station; predefined criteria have been defined for the echo canceller upon the fulfilment of which the echo canceller replaces an uplink speech signal of the second mobile station by comfort noise coded in the second coding format; the echo canceller generates additional information if the tandem free operation is active and if the conditions for replacing the speech signal by the comfort noise are fulfilled at the same time; and in response to said additional information, the first transcoder encodes the speech signal to be transmitted to the first mobile station by using the comfort noise coded in the second coding format that is generated by the echo canceller.