A variable channel coding scheme for adaptive multi rate (AMR)speech transmission over mobile radio channels is proposed. Although itwas developed for the GSM (Global System for Mobile Communications), thebasic concept of variable channel coding can be adopted to other digitalradio systems. The new AMR concept allows almost wire-line speechquality even for poor channel conditions by dynamically splitting thegross bit rate between source (speech) and channel coding according tothe channel quality. In this study we show some new aspects relating toAMR and show the advantage of recursive systematic convolutional (RSC)codes for mobile speech transmission. With some modification theyimprove not only the bit error rate but also the frame erasure rate. Itis derived that RSC codes can be decoded with a “standard”non-systematic Viterbi decoder and a simple transformation. A newpowerful approach is employed for the detection of the currently usedmode (in-band signaled information) where the mode bits are integratedin a long block and codes gain with their length
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