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Wireless Protocols

EnOcean

EnOcean technology is a maintenance-free wireless sensor solution for use in building automation and industrial installations, produced by the German company EnOcean. The company was established in 2001 as a spin-off from Siemens AG. The product range of EnOcean has grown enormously in the last years and today wireless modules from EnOcean are used worldwide by more than 100 vendors to enable their system ideas for BAS.
The basic idea behind EnOcean technology is the fact that when a sensor measures a value, the energy state constantly changes. When a switch is pressed, the temperature changes or the luminance level variations generate enough energy to transmit wireless signals. So instead of using batteries, linear motion converters, solar cells and thermal converters are used to produce enough energy to transmit the signal. Figure below demonstrates this method.

wireless1


In a wireless sensor network, based on EnOcean technology there are three types of system components: sensor, repeater and end node, as shown in figure below.

wireless2

The Smart Routing or Smart Repeating, shown in figure above, is often sufficient in small systems such as residential homes. The Smart Repeating is a plug and play setup so no complex system configuration is needed. For larger system, the 2-level repeating is, however, not sufficient and therefore a mesh routing is required.

wireless3

In a normal (line powered) system, the routing concept is based on bidirectional transmission between all devices. In the EnOcean system this is not possible, due to energy aspects. This calls for a Mesh Routing concept as shown in figure above. Here the line powered end node also acts as a router and/or gateway. Even in this case the routing does not call for any special configuration and the network is self-organizing.

ZigBee

ZigBee is a wireless network standard, based on IEEE 802.15.4 Physical Layer, PHY, and Medium Access Control sub-layer, MAC. The ZigBee protocol is defined by ZigBee Alliance, which is a group of global companies, sharing the interest in creating wireless solutions for residential, commercial and industrial applications.

The main focus of ZigBee is to create a low power consumption, low cost wireless control/sensor network that has high density of nodes. By introducing an active (send/receive) and sleep mode, ZigBee manages to keep power consumption at the minimum, which is crucial for battery operated devices. The simplicity of ZigBee’s protocol and its small data packets, makes it suitable for control/sensor network and in the same time it reduces cost and  power consumption.
In order to make it possible for vendors to supply the lowest possible cost devices, IEEE standard defines two types of physical devices, full function devices, FFD, and reduced function devices, RFD. The full functioning one works on any topology, can be the network coordinator and is able to talk to any other device. The reduced function device can not become the network coordinator, is limited to star topology and can only talk to the network coordinator.
The ZigBee topology is determined by the devices included. As previously mentioned there are two types of nodes, FFD and RFD, and the composition of these types determines the structure as can be seen in figure below.


wireless4

In figure above it is shown how FFD can act as coordinator and router for the
network but a RFD can only work as end devices, with no routing possibilities,
and therefore limited to star topology. The coordinator is responsible
for starting and maintaining the devices on the network.

Z-wave

Z-Wave® is a mesh networking technology developed in 1999 to create a standard for wireless radio frequency (RF) communication for home devices. The key to the technology is that Z-Wave products are designed using a family of low-cost, low-power RF transceiver chips embedded with Z-Wave. Because all Z-Wave enabled devices use the same chip family, they communicate using a common communication protocol. Z-Wave communication is modeled after computer network protocols and is designed to afford high reliability. Z-Wave devices also act as signal repeaters, re-broadcasting signals to additional devices on the network.
Z-Wave Operating Characteristics
Z-Wave devices don't use the same frequency as other home devices like wireless phones, which typically operate at 2.4 GHz. The frequency used by Z-Wave varies based on country.
It also means that Z-Wave devices have a greater signal range. The range of a Z-Wave device is influenced by a number of factors, first being the presence of walls in the vicinity. Typical reported ranges are around 30 meters indoors and 100 meters in the open air.
Extending the normal range of these products is possible simply by adding more Z-Wave devices to the network. Because all Z-Wave devices are repeaters, the signal is passed along from one to the next and each time it is repeated, another 30 meters (approximately) of range is gained. Up to three additional devices (hops) can be used to extend the signal before the protocol terminates the signal.