Adaptive electrical echo canceller for telephone networks

Abstract

Echo in telephones is generally undesirable but inevitable. Impedance mismatch and acoustic coupling between the receiver and microphone circuit(s) respectively produce electric and acoustic echoes in a telephone network. There is therefore a need to develop an echo canceller that can be used to reduce these echoes in telephone networks. In this work, a model for electrical echo in telephone networks for varied echo-path delay was designed. This was with a view to implementing an adaptive electrical echo canceller based on a combination of the normalized least mean square (NLMS) and Geigel speech detector algorithms (GSD). Subsequently, the performance indices (convergence rate and efficiency) of the echo canceller implemented were obtained using error function, echo return loss enhancement (ERLE) and the mean squared error (MSE) for various echoes with varied round-trip delay according to the minimum requirement of ITU-T (International Telecommunication Union) Recommendations. The results obtained show that there was a 3 dB improvement over the NLMS algorithm. The developed adaptive electrical echo canceller is therefore suitable for reduction of echoes in telephone networks.