Innovative techniques for extending the range and node limits in Bluetooth-based wireless sensor networks

Wireless networks for sensor applications are required to support an adequate data throughput, range, node density and must consume as little power as possible. The Bluetooth specification has been designed for low power, medium data rate, cable replacement solutions and is therefore useful for wireless sensor networks. However it has a limitation of a maximum number of eight active devices per Bluetooth network (piconet). To be useful in wireless sensor networks a Bluetooth piconet requires a means to communicate to more than the maximum of eight active devices. This paper demonstrates techniques for expanding the usefulness of Bluetooth for wireless sensor networks. This has been done by using multiple access points, sharing the active member addresses of the Bluetooth piconet and utilising multiple piconet and scatternet tree structures. A comparison of existing piconet handoff mechanisms has been conducted and these have been evaluated for feasibility with the available hardware's limitations. Scatternet and piconet sharing mechanisms have been developed that allow a Bluetooth structure to support more than eight devices. These structures have been implemented with existing Bluetooth hardware and are compared via theoretical simulation and experimental results. The developed network of multiple Bluetooth access points combined with the developed Bluetooth structures provides several wireless networks suitable for sensor applications.