Good quality virtual realization of unit ball graphs

  • Authors:
  • Sriram V. Pemmaraju;Imran A. Pirwani

  • Affiliations:
  • Department of Computer Science, University of Iowa, Iowa City, IA;Department of Computer Science, University of Iowa, Iowa City, IA

  • Venue:
  • ESA'07 Proceedings of the 15th annual European conference on Algorithms
  • Year:
  • 2007

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Abstract

The quality of an embedding Φ : V → R2 of a graph G = (V,E) into the Euclidean plane is the ratio of max{u,v}∈E ∥Φ(u)-Φ(v)∥2 to min{u,v}∉E ∥Φ(u)-Φ(v)∥2. Given a unit disk graph G = (V,E), we seek algorithms to compute an embedding Φ : V → R2 of best (smallest) quality. This paper presents a simple, combinatorial algorithm for computing a O(log2.5 n)-quality 2-dimensional embedding of a given unit disk graph. Note that G comes with no associated geometric information. If the embedding is allowed to reside in higher dimensional space, we obtain improved results: a quality-2 embedding in RO(1). Our results extend to unit ball graphs (UBGs) in fixed dimensional Euclidean space. Constructing a "growth-restricted approximation" of the given unit disk graph lies at the core of our algorithm. This approach allows us to bypass the standard and costly technique of solving a linear program with exponentially many "spreading constraints". As a side effect of our construction, we get a constant-factor approximation to the minimum clique cover problem on UBGs, described without geometry. Our problem is a version of the well known localization problem in wireless networks.