Wireless Sensor Networks and Systems

Wireless Technologies

Four main wireless technologies are applied to wireless sensor networks. Depending on the environment where it is going to be used, the type of use, the infrastructure conditions and/or the coverage extension needed, one of them (or a combination of two of them) can result the best option to develop the system.

Bluetooth is an open specification for wireless networks which is based on radiofrequency. It operates in the Industrial Scientific Medical (ISM) frequency band (2.4 GHz) forming wireless personal area networks (WPAN) (IEEE Std 802.15.1-2005, 2005). It has low energy consumption and its cost is quite low. Bluetooth controls its interference, and the susceptibility to the interference, by using spread spectrum modulation. It uses a frequency-hopping spread spectrum signaling method (FHSS). Bluetooth was formalized in IEEE 802.15.1 standard in its version 1.2. This technology uses a small area network without infrastructure (piconets). Nodes share a physical channel with a clock and a unique sequence of jumps in the same piconet. In Bluetooth, different channels can coexist. While a master can only belong to one piconet, any other device can belong to several piconets at the same time. This overlap is denominated scatternet (dispersed network), although there are not defined routing capacities among them. This technology appeared to be used for the devices interconnection like computers, mp3, PDAs, etc. at a distance of about 10m, although lasts products in the market achieve 100m. of coverage radius. Furthermore, this coverage range can be longer with higher antenna gain and even longer distances can be gotten using signal repeaters.