A new metaconverse and outer region for finite-blocklength MACs

An outer rate region for the Discrete Memoryless Multiple Access Channel is given, and is shown to coincide with a recently derived inner rate region within a o(1/√n) term-except in the vicinity of the corner points of the Ahlswede-Liao pentagonal region, where the gap is O(1/√n). The derivation is based on a new metaconverse under the maximum error probability criterion and on strong large deviations for Neyman-Pearson tests.