Graph-theoretical Constructions for Graph Entropy and Network Coding Based Communications

TL;DR

This paper introduces a graph-theoretical approach to analyze network coding solvability by relating the guessing number of a digraph to the independence number of an associated guessing graph, enabling new bounds and constructions.

Contribution

It presents a novel graph-based framework linking the guessing number to the independence number, simplifying network coding analysis and providing explicit constructions with high guessing numbers.

Findings

Guessing number equals the logarithm of the guessing graph's independence number.

Constructed digraphs with high guessing numbers based on cyclic codes.

Developed infinite classes of sparse digraphs with high guessing ratios.

Abstract

The guessing number of a directed graph (digraph), equivalent to the entropy of that digraph, was introduced as a direct criterion on the solvability of a network coding instance. This paper makes two contributions on the guessing number. First, we introduce an undirected graph on all possible configurations of the digraph, referred to as the guessing graph, which encapsulates the essence of dependence amongst configurations. We prove that the guessing number of a digraph is equal to the logarithm of the independence number of its guessing graph. Therefore, network coding solvability is no more a problem on the operations made by each node, but is simplified into a problem on the messages that can transit through the network. By studying the guessing graph of a given digraph, and how to combine digraphs or alphabets, we are thus able to derive bounds on the guessing number of digraphs. Second, we construct specific digraphs with high guessing numbers, yielding network coding instances where a large amount of information can transit. We first propose a construction of digraphs with finite parameters based on cyclic codes, with guessing number equal to the degree of the generator polynomial. We then construct an infinite class of digraphs with arbitrary girth for which the ratio between the linear guessing number and the number of vertices tends to one, despite these digraphs being arbitrarily sparse. These constructions yield solvable network coding instances with a relatively small number of intermediate nodes for which the node operations are known and linear, although these instances are sparse and the sources are arbitrarily far from their corresponding sinks.