Optimal Redundancy in Exact Channel Synthesis

We consider the redundancy of the exact channel synthesis problem under an i.i.d. assumption. Existing results provide an upper bound on the unnormalized redundancy that is logarithmic in the block length. We show, via an improved scheme, that the logarithmic term can be halved for most channels and eliminated for all others. For full-support discrete memoryless channels, we show that this is the best possible.