Capacity and speech quality aspects using adaptive multi-rate (AMR)

The AMR (adaptive multi-rate) is an emerging speech codec cellular standard in the ETSI. This standard should be ready during as a speech GSM evolution. It is a new concept for achieving a high speech quality maintaining an efficient spectrum usage. According to the channel quality and the traffic load, the radio resource algorithm allocates a half-rate or a full-rate channel in order to obtain the best balance between quality and capacity. Within this channel, the codec is quickly adapted to track changes in the radio link. An AMR system model has been developed to show the impact on speech quality by varying the capacity from only full-rate channels to only half-rate channels. The aim is also to show the gain provided by an AMR system compared with an existing GSM system using second generation EFR (enhanced full rate) and HR (half rate) coders. The results show that there is a trade-off between capacity increase and speech quality degradation. It is also very clear that there is a potential gain in quality by using AMR compared to existing speech codecs in GSM systems.