Experimental analysis of the frequency diversity to improve localization in WSNs

Localization is becoming a very important and challenging task of Wireless Sensor Networks (WSN), especially in low cost and low data-rate networks that employ a large number of nodes. Since the data collected may have no meaning if the sensor positions are unknown, it becomes of fundamental importance to be able to locate each node of the network with respect to an absolute or relative coordinate system. Various algorithms that propose strategies to determine the nodes position of a network are present in literature. They are divided into range-based and range-free algorithms. Some of the range-based algorithms estimate distance from Received Signal Strength Indicator (RSSI) measurements between the unknown node and the reference nodes. Estimators of this method appreciate the fact that it does not require additional hardware, because indicators of RSSI are generally built-in in radio chipsets now on market. It can be considered a valid solution for localization both in terms of economic cost and in terms of energy consumption. However, this solution presents high uncertainty due to the high variability that influences the RSSI measurements and to the different choices that characterize the implemented RSSI measurement methods. The authors, inspired by previous works present in literature, are aimed in exploring the influence of the most relevant causes of RSSI variability, as the multipath, and their effect on the RSSI values for WSNs. In this context they propose a simple measurement method based on the frequency diversity able to mitigate these effects.