In wireless sensor networks (WSNs) the position information of individual nodes is a matter of vital importance because allows the implementation of necessary network functions such as routing, querying and other applications. The objective of this paper is to propose an algorithm of threedimensional distributed range-free localization for WSNs, using an unmanned aerial vehicle (UAV) equipped with a rotary and tilting directional antenna. This algorithm, denominated as the three-dimensional azimuthally defined area localization algorithm (3D-ADAL), is executed in each sensor node and is based only on the analysis of the information received from the UAV, therefore is energy efficient and contributes to extend the lifetime of the sensor network. Additionally the proposed algorithm has the advantage of being simple and economical. The simulation results show that the proposed algorithm is a practical, effective and accurate method for a three-dimensional location of sensor nodes in a WSN.Keywords -Three-dimensional localization, wireless sensor network, unmanned aerial vehicle, directional antenna.

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The travelling repairman problem (TRP) is a scheduling problem in which a repairman must visit locations to perform some task. Each location has a time window in which the repairman is allowed to arrive. The objective of this problem is to maximize the number of tasks performed. In this paper, we consider a special case in which all the locations are on a straight line, the tasks have no processing time, and all time-windows are of unit length. We present an improvement on the analysis of the 4-approximation algorithm presented by S. L. Pérez Pérez et al. in 2014.