Adaptive multi-rate. A speech service adapted to cellular radio network quality

Adaptive multi-rate (AMR) is an emerging speech service currently being standardized in the ETSI for the GSM system. The new AMR standard will be flexible by adapting the error protection level and the allocated radio resources. A trade-off between speech quality and system capacity can be achieved for a variety of radio channel and operating conditions. The adaptation of the protection level will be fast and speech service specific. Besides the basic source and channel codec for speech signal payload, the AMR system concept further includes channel state tracking and inband transmission of adaptation data. We review the general AMR system concept and discuss the capacity and quality benefits that can be achieved. An example solution for GSM is described including speech coding, channel coding, inband signaling, and the adaptation scheme.