Summary This chapter has focused on the area of localisation. Some of the main techniques used and the types of positioning system have been explained. The most successful wide area systems have been discussed along with the different issues which prohibits their use indoors. Indoor or local RTLS have been introduced along with the primary test case for this study using 802.11 Wi-Fi – indoors. The strengths and weaknesses of each of these positioning techniques have been outlined along with some of the current methods to overcome these. Areas where research still needs to be conducted have been identified. Table 2.4: Comparison table of Local Area Positioning Systems Accuracy System Approach (and Scale Cost Constraints precision) Active Bat Ultrasound 1 cell: 10 Dense sensor 3 cm Moderate (Addlesee et al., proximity m2 grid needed 2001) 9.14 m w/o Ultrasound/RF 300 US$ Dense sensor Cricket 6 cm/ 3-5o any TOF per node grid needed (Gu et al., 2009) obstacles Low accuracy, Active Badge IR cellular Room Very low Room scale low up-date (Want et al., proximity occupancy cost rate 1992) 1 m (50% RSS WLAN Requires Ekahau within 2 Moderate Fingerprinting range calibration (Ekahau, 2011) m) RADAR WLAN RSS ranging and 4.3 m WLAN (Bahl and Low adapters SNR analysis (50%) range Padmanabhan, needed on tags 2000) RSS Cellular GPS required PlaceLab >20 m ( Fingerprinting, network Free for calibration, (La Marca et al., 50%) GSM, Bluetooth range accuracy poor 2005) High Ubisense UWB (TDOA 15 cm 1 cell: room $15,000 Expensive (Steggles and and AOA) (100%) size for kit Gschwind, 2005)
Summary This chapter has focused on the area of localisation. Some of the main techniques used and the types of positioning system have been explained. The most successful wide area systems have been discussed along with the different issues which prohibits their use indoors. Indoor or local RTLS have been introduced along with the primary test case for this study – using 802.11 Wi-Fi indoors. The strengths and weaknesses of each of these positioning techniques have been outlined along with some of the current methods to overcome these. Areas where research still needs to be conducted have been identified. Table 2.4: Comparison table of Local Area Positioning Systems System Approach Accuracy (and precision) Scale Cost Constraints Active Bat (Addlesee et al., 2001) Ultrasound proximity 3 cm 1 cell: 10 m2 Moderate Dense sensor grid needed Cricket (Gu et al., 2009) Ultrasound/RF TOF 6 cm/ 3-5o 9.14 m w/o any obstacles 300 US$ per node Dense sensor grid needed Active Badge (Want et al., 1992) IR cellular proximity Room occupancy Room scale Very low cost Low accuracy, low up-date rate Ekahau (Ekahau, 2011) RSS Fingerprinting 1 m (50% within 2 m) WLAN range Moderate Requires calibration RADAR (Bahl and Padmanabhan, 2000) RSS ranging and SNR analysis 4.3 m (50%) WLAN range Low WLAN adapters needed on tags PlaceLab (La Marca et al., 2005) RSS Fingerprinting, GSM, Bluetooth >20 m ( 50%) Cellular network range Free GPS required for calibration, accuracy poor Ubisense (Steggles and Gschwind, 2005) UWB (TDOA and AOA) 15 cm (100%) 1 cell: room size High $15,000 for kit Expensive