Radio gracefulness of Moore graphs and beyond

Abstract

The study of radio graceful labelings is motivated by modeling efficient frequency assignment to radio towers, cellular towers, and satellite networks. For a simple, connected graph $G = (V(G), E(G))$, a radio labeling is a mapping $f: V(G) \rightarrow \mathbb{Z}^+$ satisfying (for any distinct vertices $u,v$) $$|f(u)-f(v)| + d(u,v) \geq diam(G)+1,$$ where $d(u,v)$ is the distance between $u$ and $v$ in $G$ and $diam(G)$ is the diameter of $G$. A graph is radio graceful if there is a radio labeling such that $f(V(G)) = \{1, \dots, |V(G)|\}$. In this paper, we determine the radio gracefulness of low-diameter graphs with connections to high-performance computing, including Moore graphs, bipartite Moore graphs, and approximate Moore graphs like $(r,g)-$cages, Erd\H{o}s-R\'enyi polarity graphs, and McKay-Miller-\v{S}ir\'a\v{n} graphs. We prove a new necessary and sufficient condition for radio graceful bipartite graphs with diameter $3$. We compute the radio number of $(r,g)-$cages arising from generalized $n-$gons. Additionally, we determine Erd\H{o}s-R\'enyi polarity graphs and McKay-Miller-\v{S}ir\'a\v{n} graphs are radio graceful.