This paper deals with a new class of convolutional codes called Turbo-codes, whose performances in terms of Bit Error Rate (BER) are close to the SHANNON limit. The Turbo-Code encoder is built using a parallel concatenation of two Recursive Systematic Convolutional codes and the associated decoder, using a feedback decoding rule, is implemented as P pipelined identical elementary decoders. I -INTRODUCTION Consider a binary rate R=1/2 convolutional encoder with constraint length K and memory

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... 1. The input to the encoder at time k is a bit dk and the corresponding codeword Ck is the binary couple ( X k , Y k ) with K -I i=O x k = z g I i d k -; m d . 2 gli =0,1 (la)