An important component of context is location information, and much research has been focused on designing location systems which provide context-aware applications with the locations of people and objects. Location systems employ a variety of means to perform tracking. Particularly promising are ultrasonic location systems, which are robust, unobtrusive, and have been shown to reliably calculate the locations of people and objects to within several centimetres. However, current ultrasonic location systems utilize a very narrow range of frequencies. Consequently, they are limited in the rate at which they can report location readings, and they are susceptible to interference from ultrasonic noise, which occurs naturally in indoor environments. I have developed prototype broadband ultrasonic transmitters and receivers, collectively known as Dolphin. Using these to implement ultrasonic location systems, I have discovered that broadband ultrasound can yield the following advantages:

• higher aggregate update rate
• robustness in the presence of noise
• lower latency between the location readings of different tags
• enhanced identification encoding

1. M. Hazas, A. Hopper, "Broadband Ultrasonic Location Systems for Improved Indoor Positioning," IEEE Transactions on Mobile Computing, vol. 5, no. 5, pp. 536-547, IEEE, May 2006

2. Mike Hazas, Andy Ward, "A High Performance Privacy-Oriented Location System," First Conference on Pervasive Computing and Communications (PerCom 2003), IEEE Computer Society Press, Mar 2003

3. Mike Hazas, Andy Ward, "A Novel Broadband Ultrasonic Location System," UbiComp 2002, series LNCS, vol. 2498, pp. 264-280, Springer-Verlag, Sep 2002