Mismatched multi-letter successive decoding for the multiple-access channel

This paper studies channel coding for the discrete memoryless multiple-access channel with a given decoding rule. A multi-letter successive decoding rule depending on an arbitrary non-negative function q(x₁, x₂, y) is considered, and an achievable rate region and error exponent are derived. The rate region is compared with that of the maximum-metric decoder which uses the function q(x₁, x₂, y), and a numerical example is given for which successive decoding yields a strictly higher sum rate for a given pair of input distributions.