Abstract — We consider data communication over a discrete memoryless channel where neither the sender nor the receiver knows the channel law. The setup is universal in the sense that no training sequence is allowed, i.e. no position of the channel code is allowed to be fixed to a certain symbol. We discuss a variety of approaches for solving this problem efficiently. It turns out that it is worthwhile to design decoders which try to minimize the symbol error probability. This is in contrast to the usual approach where the block error probability is minimized. As a side result, we present a very simple derivation of the so-called one-sweep algorithm by Johansson and Zigangirov. In the context of universal channel decoding, this algorithm has certain structural advantages over the BCJR algorithm. I
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