Filters for device-free indoor localization system based on RSSI measurement

Based on wireless sensor networks, device-free indoor localization technique has received much attention in the field of indoor localization system Due to different indoor environmental parameters, multipath fading, human presences and different system configurations, the WiFi-based received signal strength indicator values are affected. This problem leads the researchers to choose any filter or smoothing algorithm to get proper values of received signal strength in the indoor environment. The aim of using the filter or smoothing algorithm is to get a signal value which can clearly identify the changes in the signal values due to interferences caused by various factors in the indoor environment. Wi-Fi based device-free indoor localization technique has become more attractive because its simplicity, as well as it does not require extra hardware. However the implementation of this technique in the indoor environment becomes complex, sometimes because of imprecise and unreliable readings caused by multipath fading. There are various filters designed and tested to remove the inconsistencies occurring in RSSI readings due to the various environmental effects. This paper presents various types of filters which are used for smoothing the raw data received signal strength indicator values and also improving the strength of these values by mitigating multipath fading effects in an indoor environment.