Selected Location Sensors Judy Kay CHAI: Computer human adapted interaction research group School of Information Technologies

GPS GPS – Global positioning System Position determined based on time difference on arrival of satellite signals Relies of access to the satellite signals Degrades indoors and around tall buildings Slow start up time Accuracy variable 5-10 metres for civillian GPS

AGPS Assisted GPS Increasingly widely available in consumer devices eg phones assisted to reduce startup and to operate indoors and near tall buildings –Cell tower location used to reduce possible location –Wifi access point mapping (eg Skyhooks – cars mapping continuously)‏

Active Badge – Cambridge BAT Indoor location sensors Infrared-based and ultrasound badges people wear Wall/ceiling mounted sensors Very fine-grained accuracy (cms)‏ Similar idea in Ubisense – based on ultra-wide band radio

WIFI Wi-Fi access points detected Fine grained – few metres Ekahau –Software to survey a building –Hardware active badges

Bluetooth Sensors detect devices that have discoverable Bluetooth communications protocol primarily designed for low power consumption Small range –Class 1 ~100 metres –Class 2 ~10 metres –Class 3 ~1 metre

RFID Radio-frequency identification –Active (powered)‏ –Passive –battery-assisted Range –Active ~10 m –Passive – max 2 m Increasingly widespread eg tollways, Walmart supply chain Attach to things