Detecting Location using Sensors Based on the 802:15:4 Wireless Standard

The 802:15:4 wireless standard is designed to provide low data-rate but very long battery life and very low complexity wireless networking. It operates in the industrial, scientific and medical radio bands; 868 MHz in Europe, 915 MHz in the USA and Australia, and 2.4 GHz worldwide. It is designed to be simpler and cheaper than other wireless standards such as Bluetooth and WiFi. It achieves greater range and noise immunity compared to Bluetooth at the expense of lower data rates by using a spread-spectrum modulation technique. As such it appears to be an attractive standard to use for wireless sensing. We have used the Jennic 5139, a single chip implementation of the 802:15.4 standard to develop a family of ‘smart’ sensors for data-collection in sports applications, including accelerometers, rate-gyroscopes and pressure sensors. One feature of the standard is the ability to read the received-signal-strength-indicator (RSSI). This gives an indicator of separation between a transmitter and a receiver and has been suggested as a means of triangulating location. The ability to cheaply and accurately detect location of an athlete in a realistic environment would be of great benefit in many sporting applications. Using our sensors we measured RSSI vs. separation, both in a free-field situation and when the transducer was worn by an athlete. We show that in real-life situations RSSI is able to locate an athlete to the nearest node, but not sufficient to pin-point their position between nodes. It is noted that the newly ratified 802.15.4a standard claims to deliver sub 1m accuracy ranging and may well provide a suitable low-cost wireless location technology