Wireless Ad Hoc and Sensor Networks

42 Wireless Ad Hoc and Sensor NetworksHome RF was initiated in 1998 and has similar goals to Bluetooth forWPAN. Its goal is shared data/voice transmission. It interfaceswith the Internet as well as the public switched telephone network.It uses the 2.4-GHz band and has a range of 50 m, suitable forhome and yard. A maximum of 127 nodes can be accommodatedin a single network.1.5.2 IEEE 1451 and Smart SensorsDesirable functionality of sensor nodes in a WSN include: ease of installation,self-indication, self-diagnosis, reliability, time awareness for coordinationwith other nodes, some software functions and DSP, andstandard control protocols and network interfaces (IEEE 1451 Expo 2001).There are many sensor manufacturers and many networks in the markettoday. It is too costly for manufacturers to make special transducers forevery network on the market. Different components made by differentmanufacturers should be compatible. Therefore, in 1993, the IEEE and theNational Institute of Standards and Technology (NIST) began work on astandard for smart sensor networks. IEEE 1451, the standard for smartsensor networks was the result. The objective of this standard is to makeit easier for different manufacturers to develop smart sensors and tointerface those devices to networks.Smart sensor, virtual sensor: A major outcome of IEEE 1451 studies isthe formalized concept of a smart sensor. A smart sensor is onethat provides extra functions beyond those necessary for generatinga correct representation of the sensed quality. Includedmight be signal-conditioning, signal-processing, and decisionmaking/alarmfunctions. Objectives of a smart sensor includemoving the intelligence closer to the point of measurement; makingit cost-effective to integrate and maintain distributed sensorsystems; creating a confluence of transducers, control, computation,and communications towards a common goal; and seamlesslyinterfacing numerous sensors of different types. The conceptof virtual sensor also needs to be discussed. A virtual sensor isthe physical sensor/transducer, plus the associated signal conditioningand digital signal processing (DSP) that is required toobtain reliable estimates of the required sensory information. Thevirtual sensor is a component of the smart sensor.1.5.3 Sensors for Smart EnvironmentsMany vendors now produce commercially available sensors of manytypes that are suitable for wireless network applications. See, for instance,