WIRELESS SENSOR NETWORK

Wireless Sensor Network (WSN)?is an infrastructure-less wireless network that is deployed in a large number of wireless sensors in an ad-hoc manner that is used to monitor the system, physical or environmental conditions.?Sensor nodes are used in WSN with the onboard processor that manages and monitors the environment in a particular area. They are connected to the Base Station which acts as a processing unit in the WSN System.?

When a sensor node or a router runs out of power, it will disconnect from the WSN and negatively impact the application. In order to extend the network lifetime, energy conservation techniques must be used. Solar panels are the most popular solution for recharging the batteries of WSN components. Another approach to save energy is a technique called sleeping, which allows nodes, routers, and gateways to sleep during their idle times. The gateway is important because it coordinates the communication aspect of the WSN as well as its sleeping protocol. At a given time, the gateway wakes up nodes and routers. Data are exchanged, and then the nodes and routers go back to sleep. Sleeping is necessary for WSNs to save power. A sensor node generally spends 90% of its time sleeping. A communication protocol defines the rules of how data are exchanged. The most popular communication protocols for WSNs are Wi-Fi, Bluetooth, and ZigBee. Wi-Fi is excellent for data exchange and is ideal where the power supply is not a problem, like in household devices. Bluetooth is also popular and is present in many battery-powered devices, such as watches, mice, keyboards, and other electronics.

Bluetooth is a good option with low power consumption, short communication range, and high data rate. ZigBee requires even less power than Bluetooth and has a longer communication range, but it is quite slow. ZigBee would not be suitable for surfing the Internet or transmitting photos from a wireless camera, but it is well-suited for transmitting data from sensors in a field. In a very fast data-logging event, sensors and controllers usually report a simple dataflow (few bytes) each minute. Table 1 summarizes the three technologies accordingly with communication range and typical applications. ZigBee radios can operate at 2.4 GHz, 900 MHz (US), and 868 MHz (Europe), while Wi-Fi and Bluetooth operate at 2.4 GHz. The lower the radio frequency, the larger (broader) the communication range. For example, commercial wireless radios that use the ZigBee protocol operating in 900 MHz can communicate up to 14 miles (with directional antennas), while the 2.4 GHz radios have a communication range of 650 meters