Combined Source/Channel Decoding: When Minimizing Bit Error Rate is Suboptimal

AT&T Labs – Research Florham Park, NJ 07932, USA ftim,thomas,rvc,[email protected] Abstra t | Convolutional coding as a means of error correction is widely used in mobile communications, where the effects of channel noise have to be taken into account. Channel decoders usually aim at minimizing the frame, symbol or residual bit error rate of the source bits. In this contribution we show how the residual bit error rate can be reduced by using a priori knowledge about the source statistics within the channel decoding process. This usually helps the source decoder to perform better. If the source decoder also uses a priori knowledge, however, we show that the best overall system performance is reached at a higher residual bit error rate after channel decoding. This gives new insight into optimization criteria of combined source/channel decoding.