On Locally Gabriel Geometric Graphs

Abstract

Let $P$ be a set of $n$ points in the plane. A geometric graph $G$ on $P$ is said to be locally Gabriel if for every edge $(u,v)$ in $G$, the Euclidean disk with the segment joining $u$ and $v$ as diameter does not contain any points of $P$ that are neighbors of $u$ or $v$ in $G$. A locally Gabriel graph(LGG) is a generalization of Gabriel graph and is motivated by applications in wireless networks. Unlike a Gabriel graph, there is no unique LGG on a given point set since no edge in a LGG is necessarily included or excluded. Thus the edge set of the graph can be customized to optimize certain network parameters depending on the application. The unit distance graph(UDG), introduced by Erdos, is also a LGG. In this paper, we show the following combinatorial bounds on edge complexity and independent sets of LGG: (i) For any $n$, there exists LGG with $\Omega (n^{5/4})$ edges. This improves upon the previous best bound of $\Omega (n^{1+\frac{1}{\log \log n}})$. (ii) For various subclasses of convex point sets, we show tight linear bounds on the maximum edge complexity of LGG. (iii) For any LGG on any $n$ point set, there exists an independent set of size $\Omega (\sqrt{n}\log n)$.