Abstract: A hypothesis to take the physical channel and the Turbo decoder as a joint equivalent AWGN channel is presented. On the basis of this hypothesis, one can use the signal-to-noise ratio of the Turbo decoder output LLR as a criterion to stop the iterative procedure. To reduce the decoder complexity, one can make a decision for the symbol whose LLR is larger than a given threshold and output it. A theoretical threshold is given.

Key words: channel coding, Turbo codes, parallel concatenation coding