Sensors_**2009**, \(9\), 3942-3957; doi:10.3390/s90503942  
_Article_  
**A Heterogeneous Wireless Identification Network for the Localization of Animals Based on Stochastic Movements**  
**[PERSON] \({}^{\star}\), [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON]**  
ETSI Telecomunicacion, Universidad Politecnica de Madrid, Avd. Complutense 30, 28040 Madrid, Spain; E-mails: [PERSON]DDRESS] (C.G. ); [PERSON]_ADDRESS] (J.J.L. ); [PERSON]DDRESS] (S.Z. ); [PERSON]_ADDRESS] (N.D.); [PERSON]L_ADDRESS] (I.R.) \({}^{\star}\) Author to whom correspondence should be addressed; E-mail: [PERSON]L_ADDRESS]; Tel. : +34 91-549-57-00 Ext. 2318  
_Received: 27 April 2009; in revised form: 14 May 2009 / Accepted: 22 May 2009 / Published: 25 May 2009_  
**Abstract:** The improvement in the transmission range in wireless applications without the use of batteries remains a significant challenge in identification applications. In this paper, we describe a heterogeneous wireless identification network mostly powered by kinetic energy, which allows the localization of animals in open environments. The system relies on radio communications and a global positioning system. It is made up of primary and secondary nodes. Secondary nodes are kinetic-powered and take advantage of animal movements to activate the node and transmit a specific identifier, reducing the number of batteries of the system. Primary nodes are battery-powered and gather secondary-node transmitted information to provide it, along with position and time data, to a final base station in charge of the animal monitoring. The system allows tracking based on contextual information obtained from statistical data. **Keywords:** stochastic transmission; energy harvesting; heterogeneous network; energy-aware network Introduction  
The effects of physical and biological factors on activity patterns and movements of animals are of major interest for biologists. A primary requisite for understanding certain aspects of animal behavior is knowing their location and mobility patterns. Tracking animals is important because they are often part of evolutionary and ecological experiments, they provide important ecosystem services and they are of conservation concern. The use of mobile sensor networks promises a fruitful future for animal behavioral sciences, although some difficulties arise when trying to insert electronic devices in a natural environment. In most wireless sensor networks, power is a constraint from both the technological and the ecological point of view. On the one hand, the power supply is a severe constraint in achieving a long lifetime in a wireless autonomous embedded system. In a battery operated system, the system lifetime is directly related to the node battery lifetime. Moreover, in an animal tracking case, if thousands of animals must be monitored, the thousands of nodes must be battery operated. Therefore, high maintenance costs result and a tedious task of battery replacement will come up during a long term experiment. On the other hand, working in an outdoor large environment, the use of batteries might be harmful for the ecosystem. If we spread a large amount of battery-powered nodes throughout the environment, there is a great possibility that some nodes get lost, and therefore an unexpected pollution might arise. A number of different strategies have been used to provide power to animal tracking systems avoiding battery restrictions (see Section 2). Although the use of battery-powered systems is probably not completely avoidable, researchers must try to develop systems where the use of batteries is reduced to a minimum. Following these lines of research, we have pursued the implementation of a heterogeneous network for animal tracking which tries to minimize the use of battery-powered nodes. This minimization is achieved by taking advantage of kinetic energy. During the day, animals perform different actions which imply the generation of kinetic energy because of their movement.