Outdoor localization system based on Android and ZigBee capable devices

Abstract: Context. Localization and positioning services are nowadays very extended and the growth is still continuing. Many places already provide wireless tracking systems to monitor the people or material movements, specially indoors. The new arising ZigBee wireless technology provides an efficient network management and a low battery consumption, making it appropriate for location purposes in portable devices like mobile phones. Objectives. The aim is to locate a ZigBee device located inside a golf ball that has been lost within an outdoors area. An Android phone connected to a ZigBee device via USB will serve as coordinator of the localization network and by giving on-screen instructions and guidance provided by the conceptual Decision Support System (DSS). Methods. The measurement used in the localization process is the Received Signal Strength (RSS). With this data, the distance between the sensors can be estimated. However to obtain an accurate position several readings from different sensors might be needed. This paper tests the precision levels of the ZigBee modules varying the number of sensors in the localization network and using the triangulation method. Results. The precision is the main variable measured in the results, which reaches distance variation of less than 1 meter in cases where the triangulation approach can be applied. For the localization process, the use of less than three sensors lead to very poor results, obtaining a wrong localization in around 30\% of the cases. Also, movement patterns were discovered to improve the localization process. All this data can be used as an input for the DSS for future improvements. Conclusions. This study proves that outdoor positioning with ZigBee devices is possible if the required level of precision is not very high. However, more studies concerning localization with less than three sensors have to be conducted to try to reach the goal of one-on-one localization. This study opens the door for further investigations in this matter.