On Capacity Formulation With Stationary Inputs and Application to a Bit-Patterned Media Recording Channel Model

• Published in: IEEE transactions on information theory 2015-11, Vol.61 (11), p.5906-5930
• Main Authors: Phan-Minh Nguyen, Armand, Marc A.
• Format: Article
• Language: English
• Subjects: bit-patterned media recording; bit-symmetry; Channel capacity; Channel models; Channels; Communication channels; Electronics; Ergodic processes; Joints; Low noise; lower/upper bounds; Magnetic recording; Magnetic separation; Mathematical models; Media; Noise; Recording; Series expansion; stationary and ergodic channel; stationary inputs; Transaction processing; Upper bound
• ISSN: 0018-9448; 1557-9654
• DOI: 10.1109/TIT.2015.2481878

In this correspondence, we illustrate among other things the use of the stationarity property of the set of capacity-achieving inputs in capacity calculations. In particular, as a case study, we consider a bit-patterned media recording channel model and formulate new lower and upper bounds on its capacity that yield improvements over existing results. Inspired by the observation that the new bounds are tight at low noise levels, we also characterize the capacity of this model as a series expansion in the low-noise regime. The key to these results is the realization of stationarity in the supremizing input set in the capacity formula. While the property is prevalent in capacity formulations in the ergodic-theoretic literature, we show that this realization is possible in the Shannon-theoretic framework where a channel is defined as a sequence of finite-dimensional conditional probabilities, by defining a new class of consistent stationary and ergodic channels.