Combined acoustic echo canceller for the GSM network

When the implementation of an acoustic echo canceler is implemented in the Mobile Switching Center of a GSM network, it is necessary to take into account the non linearities introduced by the speech coder/decoder. A classical linear adaptive filter is not sufficient. The performances of a classical AEC are improved by noise reduction adaptive post-filter. The post-filter introduced, take into account implicitely the non linearity introduced by the GSM speech codecs cascaded with the linear echo path. It can reduce the quantization noise related to the coding/decoding operation. The proposed combined system presents better performances than that of the classic (linear) solution.