Duality of channels and codes

Abstract

For any given channel $W$ with classical inputs and possibly quantum outputs, a dual classical-input channel $W^{\perp }$ can be defined by embedding the original into a channel $\mathcal{N}$ with quantum inputs and outputs. Here we give new uncertainty relations for a general class of entropies that lead to very close relationships between the original channel and its dual. Moreover, we show that channel duality can be combined with duality of linear codes, whereupon the uncertainty relations imply that the performance of a given code over a given channel is entirely characterized by the performance of the dual code on the dual channel. This has several applications. In the context of polar codes, it implies that the rates of polarization to ideal and useless channels must be identical. Duality also relates the tasks of channel coding and privacy amplification, implying that the finite blocklength performance of extractors and codes is precisely linked, and that optimal rate extractors can be transformed into capacity-achieving codes, and vice versa. Finally, duality also extends to the EXIT function of any channel and code. Here it implies that for any channel family, if the EXIT function for a fixed code has a sharp transition, then it must be such that the rate of the code equals the capacity at the transition. This may give a different route to proving a code family achieves capacity by establishing sharp EXIT function transitions.

v2: 22 pages. fixed idempotency of duality for symmetric channels and added a statement about binary-input channels; v1: 23 pages, 2 figures

References in corpus (7)

• Coding Theorem and Strong Converse for Quantum Channels
• Quantum Information Processing with Finite Resources -- Mathematical Foundations
• Conjectured Strong Complementary Information Tradeoff
• Physical Underpinnings of Privacy
• Duality of privacy amplification against quantum adversaries and data compression with quantum side information
• Investigating Properties of a Family of Quantum Renyi Divergences
• Alignment of Polarized Sets

Cited by in corpus (7)

• Reed-Muller Codes on BMS Channels Achieve Vanishing Bit-Error Probability for All Rates Below Capacity
• Belief Propagation with Quantum Messages for Quantum-Enhanced Classical Communications
• On privacy amplification, lossy compression, and their duality to channel coding
• Reliability Function of Classical-Quantum Channels
• Smoothing of binary codes, uniform distributions, and applications
• Tight lower bound on the error exponent of classical-quantum channels
• Equivalence of three classical algorithms with quantum side information: Privacy amplification, error correction, and data compression