A Dual-Domain Achievability of the Typical Error Exponent

For random-coding ensembles with pairwise-independent codewords, we show that the probability that the exponent of a given code from the ensemble being smaller than an upper bound on the typical random-coding exponent is vanishingly small. This upper bound is known to be tight for i.i.d. ensembles over the binary symmetric channel and for constant-composition codes over memoryless channels. Our result recovers these as special cases and remains valid for arbitrary alphabets and channel memory, as well as arbitrary ensembles with pairwise independent codewords.