Interspeech'2005 - Eurospeech
In UMTS speech transmissions, the Adaptive Multi-Rate (AMR) speech codec is employed to allow for a dynamic assignment of data rates to individual users. The control of AMR modes is based on quality measurements of the transmission channel and aims at the maximization of speech quality by selecting the mode which is best suited to the current interference situation. In contrast to GSM, a reduction of AMR modes also leads to an increased cell capacity in UMTS. In this paper, a decentralized method for AMR mode switching is presented which is based on individual softbit measurements at the Viterbi channel decoder and optimizes the speech quality for a wide range of channel conditions. This method was developed by optimizing the AMR mode switching thresholds with respect to PESQ speech quality scores. The second part of the paper describes a new instrumental non-intrusive method for speech quality measurement by the evaluation of UMTS transmission parameters for application to UMTS-AMR speech transmissions. High correlations with the reference PESQ scores were observed.
Bibliographic reference. Werner, Marc / Vary, Peter (2005): "Quality control for UMTS-AMR speech channels", In INTERSPEECH-2005, 3157-3160.