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.

## Sources

* http://www.iec.ch/whitepaper/pdf/iecWP-internetofthings-LR-en.pdf
* http://www.ni.com/white-paper/7142/en/
* https://fr.wikipedia.org/wiki/Réseau\_de\_capteurs\_sans\_fil