Wireless Sensor Network (WSN)

A wireless sensor network (WSN), also called a wireless sensor and actuator network, is a network composed of sensors which send their collected data through the network to a main location. At first invented for military motivations and applications, this type of network is principally used in the industry or at home for monitoring or control.

Applications 

There are a lot of applications for this kind of network:

-         The Area monitoring

-         The health care monitoring : there are a lot of possibility (location of persons, monitoring of ill patients in hospitals and at homes, collection of body information, … )

-         The environment sensing : the air pollution, the forest fire detection, the water quality monitoring, …

-         The industrial monitoring : machine health monitoring, data center monitoring, data logging, temperature/pressure/luminosity monitoring

Characteristics

-         The number of nodes in a network is very high : more than 65.000 sensors

-         The sensors have battery and so an autonomy: there must have an energy harvesting so, there are different sleep modes like the idle mode (the CPU is OFF and woken up by interrupts, all the peripherals are ON) or the Power down Mode.

IEEE 802.15.4

The IEEE 802.15.4 communication protocol is used in the wireless sensor network because he has a low power-consumption and a low range. This protocol specifies the physical layer and the media access control. So, it is the basis of the communication ways used in the WSN.

There are three bands of frequency for the IEEE 802.15.4 protocol: the 2.4 GHz one with 16 channels, the 902-928 MHz (American) one with 10 channels and the 868 MHz (European) one with 1 channel.

The communication programs 

The principal way of wireless communication in the WSN are:

-  The ZigBee

-  The WirelessHART

-  The ISA100.11a

-  The Thread

The Topology

The topology can vary from a simple star network to an advanced multi-hop wireless mesh network.

In a star topology, each node connects directly to a gateway. In a cluster tree network, all the nodes are connected to a node higher in the tree and then to a gateway. The data are routed from the lowest node to the gateway. Finally, to offer increased reliability, mesh networks feature nodes that can connect to multiple nodes in the system and pass data through the most reliable path available.

The IPv6 protocol

Some of the WSN technologies use the IPv6 protocol. In this section, we’re going to see why it is interesting for the applications and the advantages.

Internet Protocol version 6 (IPv6) is the most recent version of Internet Protocol, protocol that provides an identification and location system for computers on networks and routes traffic across the internet.

The first advantage of choosing an IPv6 addresses is to increase the number of possible address. Indeed, there are also:

-         Better efficiency for the routing : This principe can reduce the routing table size with a more hierarchical routing

-         Better efficiency for the packet processing: The packet headers are simplified and the IP-level checksum for IPv4 is eliminated.

-         Better data flows: IPv6 supports a superior multicast method saving network bandwidth.