Error exponent regions for multi-user channels

In modern communication systems, different users have different requirements for quality of service (QoS). In contrast to existing QoS schemes, there is currently no framework in information theory concerning QoS in multi-user systems. In this work an information-theoretic groundwork is proposed to study communication systems which provide heterogeneous reliabilities for the users. This is done by defining individual codeword error probabilities for the users in the network and obtaining their fundamental tradeoff. This tradeoff is quantified by introducing the concept of the error exponent region. Using this framework, a system can be realized, which can provide a tradeoff of reliabilities among the users for a fixed vector of users' rates. This adds a completely new dimension to the performance tradeoff in such networks, which is unique to multi-terminal communication systems, and is beyond what is given by the conventional performance-versus-rate tradeoff in single-user systems. Although this is a very general concept and can be applied to any multi-terminal communication system, in this work we focus on broadcast and multiple access channels. We show the existence of a tradeoff among the users' error exponents by deriving inner and outer bounds for the error exponent region.