Wireless Sensor Networks - Smoothing algorithms for RSSI-based Device-free Passive Localisation

In recent years, the use of wireless sensor networks has increased. This is due in part to the increasing miniaturization, decreasing costs and the identification of real-world scenarios where sensors can be deployed. Device-free Passive (DfP) localisation is the identification of a person without the need for any physical devices i.e. tags or sensors. A DfP Localisation system uses the Received Signal Strength Indicator (RSSI) for monitoring and tracking changes in a Wireless Network infrastructure. The changes in the signal along with prior fingerprinting of a physical location allow identification of a person's location. This paper is focused on implementing DfP Localisation built using a Wireless Sensor Network (WSN). The main reason for deploying Wireless Sensor Network DfP Localisation is due in part to the benefits of deploying when a wireless network infrastructure is not available. RSSI-based localisation techniques became more attractive because of their simplicity but also because they do not require additional hardware. The human body contains more than 70% water and it is known that resonance frequency of water is 2.4 GHz. Thus the human body is reacting as an absorber attenuating the wireless signal. Many of the proposed RSSI-based technologies use the fingerprinting method for estimating the location of the tracked person. Fingerprinting in location estimation systems refers to a method that compares the fingerprint of some characteristic of a signal that is location dependent.