Beyond the Cut-Set Bound: Uncertainty Computations in Network Coding with Correlated Sources

TL;DR

This paper introduces a new technique for deriving tighter bounds than traditional cut-set bounds in network coding with correlated sources, using the concept of an uncertainty region to characterize solvability constraints.

Contribution

It presents a novel method for proving converses in network coding with correlated sources, introducing the uncertainty region and providing a full characterization for two variables.

Findings

Tighter bounds than cut-set bounds for correlated sources.

Definition and characterization of the uncertainty region.

Constraints on source distributions for network solvability.

Abstract

Cut-set bounds on achievable rates for network communication protocols are not in general tight. In this paper we introduce a new technique for proving converses for the problem of transmission of correlated sources in networks, that results in bounds that are tighter than the corresponding cut-set bounds. We also define the concept of "uncertainty region" which might be of independent interest. We provide a full characterization of this region for the case of two correlated random variables. The bounding technique works as follows: on one hand we show that if the communication problem is solvable, the uncertainty of certain random variables in the network with respect to imaginary parties that have partial knowledge of the sources must satisfy some constraints that depend on the network architecture. On the other hand, the same uncertainties have to satisfy constraints that only depend on the joint distribution of the sources. Matching these two leads to restrictions on the statistical joint distribution of the sources in communication problems that are solvable over a given network architecture.