Performance assessment of tandem connection of cellular and satellite-mobile coders

In the near future, 16 and 8 kbit/s toll- or near-toll low-rate codecs are expected to be used together with 32 kbit/s digital circuit multiplication equipment, providing speech compression and digital speech interpolation. Additionally, a growing proportion of international calls originate from different digital cellular/satellite mobile (C/SM) systems. Knowledge of the end-to-end voice quality of tandem connections is fundamental in the planning of international circuits. Previous studies assessed tandem performance of cellular codecs and the fixed network, however satellite-mobile systems were not included. This paper presents a subjective evaluation of the voice quality of tandem connections of C/SM codecs in seven basic scenarios. This study concludes that the number of codecs used in tandem should be minimized and network capacity has to be increased for a given traffic load if voice quality cannot be compromised. In extreme cases, calls originating from C/SM terminals should be transmitted using clear channels