DECISION AID FOR WIRELESS STANDARDS – WHEN TO USE WHICH WIRELESS SYSTEM

Publication date: 15 April 2008

DECISION AID FOR WIRELESS STANDARDS  – WHEN TO USE WHICH WIRELESS SYSTEM

- By Armin Anders, head of product marketing, and Frank Schmidt, head of research, EnOcean GmbH

Compared to wired systems, wireless offers much greater flexibility and convenience in building installation. There are a variety of different systems on the market.

Increasingly therefore, system integrators, electrical planners, architects and property owners are spoilt for choice. Here we look at the established wireless technologies with their major performance parameters.

A systematic analysis of the individual requirements for performance, cost and flexibility in the intended wireless technology will soon narrow down the choice.

What follows are the major decision criteria.

Summary of established wireless systems 

DECISION 1:

HIGH OR LOW DATA VOLUME

Do you want to transmit moving pictures, network computers or operate a printer wirelessly? If so you need a wireless system with a high data rate that can carry large data quantities in a short time. The WLAN and Bluetooth standards offer this capability, but at the price of medium to high energy needs.

Consequently they are unsuitable for battery powering over a long period. Most automated functions in a building however only require shortterm wireless transmission of small amounts of information. These include switching lights and devices, operating curtains and especially transmitting the information of wireless sensors like air-conditioning controls, position signalling switches and smoke detectors.

So when low energy need takes priority, you can move on to the next decision to narrow down the choice of candidates.

DECISION 2:

MULTIPLE SIMULTANEOUSLY TRANSMITTING DEVICES

When communication interference appears, it is invariably caused by wireless transmitters in the immediate vicinity operating in the same frequency band. Given high radio density, this can result in substantial delays in time to transmit and even data losses.

A safeguard against other wireless transmitters combined with fast system response can be produced by making use of a frequency band that is less crowded. There is a very pronounced increase in the wireless networking of PCs, printers and other IT devices using the 2.4 GHz band, which is licence-free all over the world.

This makes the 868 MHz band, for example, much more suitable for reliable building automation and covering a large area. It is also licence-free in Europe, allowing no continuous transmissions but only very short transmitted pulses.

In addition, the laws of physics mean that 868 MHz radio waves have twice the range of 2.4 GHz signals and double the penetration through materials like walls and furniture – and all for the same transmitted power.

A 2.4 GHz system consequently requires about four times more receiving nodes over its area. That increases its cost compared to an 868 MHz solution. The need for security against collision of the wireless telegrams within your own system increases with the number of transmitters.

The radio data simultaneously sent by multiple transmitters can collide close to a receiver, and the latter will then be unable to decode them properly.

The problems are fewer in a small installation as long as a radio channel is not overloaded by the relatively small number of wireless sensors and switches. But in larger installations you find very many wireless components in what can be tight confines. So it is important to choose a wireless system that is suitably robust in its rejection of data collisions.

One effective method is to keep each of the transmissions very short. Extremely short wireless telegrams of only about a thousandth of a second and an intelligent strategy of multiply repeating each transmission create excellent collision safety in the EnOcean wireless standard, safeguarding against sporadic and periodic sources of interference.

As many as 500 closely located transmitters, all signalling once per minute, can be received with more than 99.9% certainty.

DECISION 3:

BATTERIES

If the servicing of wireless sensors and switches needed to replace batteries is a disadvantage for an application, is not wished or even out of the question, it is of course possible to do away with batteries. EnOcean is currently the sole provider of such technology. What makes it possible is the extremely low energy need.

The wireless protocol requires only about 0.12 µWs to securely transmit one bit of information over a distance of 300 meters in free space. A batteryless wireless switch consumes about 50 µWs for a complete radio command – some 100 times less than the more usual, battery-powered wireless switch.

So a conventional wireless switch, powered by an electrodynamic generator, would require 100 times the actuating force, and a conventional wireless sensor in a living room would need a solar cell 100 times in size.

DECISION 4:

INTEROPERABILITY

Of all wireless standards, batteryless EnOcean wireless technology offers the largest spectrum of end-products for building automation. To date some 50 manufacturers have created a selection totalling more than 200 compatible devices. About 200,000 devices have gone into use over the past three years, proving their ruggedness and reliability in thousands of buildings.

The devices of the different manufacturers all work on the same wireless interface. So signals sent by wireless switches from Osram, Zumtobel, Bticino or Peha, for example, can be received by thermostats from Thermokon, Stuhl or Omnio and by wireless receivers from ABB, Siemens, Wago, Beckhoff, Wieland or Phoenix. Gateways provide for integration into all common building bus systems like EIB/KNX, LON, TCP/IP and BACnet.

General-purpose and specific switch inserts allow integration into the switch ranges with their different designs of all installation material producers on the German market. In addition to unidirectional switches and sensors, bidirectional wireless modules are obtainable for creating intelligent networks for instance.

CONCLUSION

Wireless systems are now firmly in place in building installation. But no wireless system can satisfy all the different requirements to the full. The WLAN and Bluetooth standards are more suited for data-heavy applications. Flexible control of building functions or detection of sensor data produce a need for cableless sensors or switches.

This is where batteries are often not wanted or unacceptable because of the service investment. And EnOcean is the only standard enabling the implementation of such batteryless plus wireless systems. With this technology it is possible to create maintenance-free systems even for large buildings with many hundred transmitting devices in one radio cell.