IEEE Transactions on Information Theory
Abelian Group Codes for Classical-Quantum Channels: One-Shot and Asymptotic Rate Bounds
James Chin-Jen Pang, S. Sandeep Pradhan, Hessam Mahdavifar
Abstract
We study the problem of transmission of information over classical-quantum (CQ) channels in the one-shot regime where the underlying codes are constrained to be shiftedgroup codes. Given a groupG, a group code of lengthnis a subgroup ofGn. In the achievability part, we introduce a new collection of input probability distributions that incorporates the encoding homomorphism and the underlying channel law. Using a random coding argument, we characterize the performance of group codes in terms of hypothesis testing relative-entropic quantities. In the converse part, we establish bounds by leveraging a hypothesis testing-based approach. Furthermore, we apply the one-shot result to the asymptotic stationary memoryless setting, and establish a single-letter lower bound on thegroup capacityof a CQ channel. Moreover, we derive a matching upper bound on the asymptotic group capacity.