AMR & FEED: Channel Coding Concepts for Speech Transmission

In mobile communications systems the channel quality is determined by two physical effects: The short term fading due to scattering, reflections and interference and the long term fading due to the change of the geographical surroundings. Since the influence of the short term fading can be easily reduced by using interleaving techniques, the main channel coding task is to cope with the long term fading. In this paper two channel coding concepts for speech transmission over a mobile communication system are presented and compared to each other as well as to a conventional coding system. The first concept is the Adaptive Multi-Rate Codec (AMR-Codec) based on channel adapted mode switching. The second concept is the Far End Error Decoder (FEED) based on high memory convolutional codes and sequential decoding.