Comparison between RSSI-based and TOF-based Indoor Positioning Methods


A location-based service (LBS) cannot be realized unless solutions of the positioning problem are available at hand. For the outdoor positioning, GPS based practical solutions have been introduced. Using GPS they have developed so many commercial LBS systems. Navigation, logistics, troop management and fleet management are all examples of LBS. LBS is so useful that it should be available in doors. However, GPS signal is so weak inside buildings that we cannot determine the location of a moving object in doors with GPS only. Therefore, so many indoor positioning researches have been performed. Cricket, Active Badge and BAT are pioneers in the field of indoor positioning. They are very accurate but they require special equipments dedicated for positioning. Using special equipments is not economical. Therefore, many researchers have suggested using wireless local area networks (WLAN) in positioning. Among the methods they are using, the fingerprinting methods are most accurate. The deployment of the fingerprinting methods consists of two phases: the offline phase and the on-line phase. During the off-line phase a site-survey of the received signal strength indices (RSSIs) from access points (APs) is performed. The vector of the RSSI values at a point is called the location fingerprint of that point. A lot of location fingerprints must be collected at each of the points in the site during the off-line phase. This is extremely tedious and time consuming. An alternative choice is the trilateration method. This method converts RSSIs from APs into distances and determines the location of the moving object with the distances and the locations of the APs. That is, we only need the coordinates of the APs in the site to get ready to run the trilateration positioning program. The conversion rule of RSSIs into distances is based on the RF propagation loss model. The model is a simple mathematical expression representing the relationship between the RSSI and the distance. However, the RSSI is influenced by obstructions, reflections and multipath and the RF propagation loss model is very erroneous. As a result, WLAN based trilateration is much less accurate than the fingerprinting method. Nevertheless, the trilateration method could be more practical than the fingerprinting method because it does not require the time consuming offline phase process. Therefore, they established IEEE 802.15.4 A where the distance is determined by the speed of RF and TOF (Time of Flight). Ubi-nanoLOC mote complies with IEEE 802.15.4 A. This paper discusses the advantages and disadvantages of the WLAN-based trilateration indoor positioning and the Ubi-nanoLOC indoor positioning draws our final conclusions.

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@inproceedings{Yim2012ComparisonBR, title={Comparison between RSSI-based and TOF-based Indoor Positioning Methods}, author={Jaegeol Yim}, year={2012} }