Wiretap Channels: Roles of Rate Splitting and Channel Prefixing

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Csiszar and Korner's characterization of the rate-equivocation region of a general wiretap channel involves two auxiliary random variables: U, which represents rate splitting and V, which represents channel prefixing. For some channels, one or both of these auxiliary random variables are unnecessary, simplifying the expression and evaluation of the rate-equivocation region. In this paper, the authors provide new conditions under which channel prefixing or rate splitting does not improve the rate-equivocation region. In particular, they show that when the main channel is more capable than the eavesdropping channel, channel prefixing is unnecessary; the entire rate-equivocation region can be achieved by rate splitting alone.