A sensor node is made up of four basic components: sensing unit, processing unit, transceiver unit, and power unit. The sensing unit usually consists of two components: a sensor and an analog-to-digital converter (ADC). The processing unit acts as a tiny computer: a microprocessor and some RAM. The processing unit runs an embedded operating system and executes WSN applications that control the operations of the sensor and communication between sensor nodes. The transceiver unit is a low-power radio operating on an unlicensed frequency band. The power unit is a battery for regular sensor nodes. Note that in most cases a WSN will have a special sensor node that acts as the gateway for other sensor nodes with respect to ultimate data delivery. The gateway node interfaces to computers via RS232 or Ethernet links. As a result, the gateway node is different from other regular nodes, in both size and processing functionality, thus requiring more power supply.
Following is a list of sensor node characteristics that affect the design of WSN system architectures and applications:
» Size: Sensor nodes are very small, due to advancements in semiconductor technologies.
» Low power: Sensor nodes are expected to operate for a long time before the battery drains out. In many cases, it is prohibitive to replace batteries.
» Autonomous, unattended operations: Once deployed, sensor nodes should selforganize to work as programmed. Remote reprogramming is sometimes possible.
» Inexpensive: Their low cost makes it possible to deploy a large number of sensor notes at a moderate cost.
» Adaptive to environments and themselves: Sensor nodes are able to adapt to environmental and status changes.
Source of Information : Elsevier Wireless Networking Complete 2010