A Simple Yao-Yao-Based Spanner of Bounded Degree
  It is a standing open question to decide whether the Yao-Yao structure for unit disk graphs (UDGs) is a length spanner of not. This question is highly relevant to the topology control problem for wireless ad hoc networks. In this paper we make progress towards resolving this question by showing that the Yao-Yao structure is a length spanner for UDGs of bounded aspect ratio. We also propose a new local algorithm, called Yao-Sparse-Sink, based on the Yao-Sink method introduced by Li, Wan, Wang and Frieder, that computes a (1+e)-spanner of bounded degree for a given UDG and for given e > 0. The Yao-Sparse-Sink method enables an efficient local computation of sparse sink trees. Finally, we show that all these structures for UDGs -- Yao, Yao-Yao, Yao-Sink and Yao-Sparse-Sink -- have arbitrarily large weight. 
Mirela Damian