WIRELESS NETWORKS TECHNOLOGIES

Wireless communications are interfering more and more with the industrial automated applications. We can meet them in applications which need to establish dialogues between various types of terminals, to exchange data with sensors and machines, to register input data typed by mobile operators or to establish a link between a programming console and a control device.

These technologies are large, but they are not all relevant to an industrial environment. By the time now, the wireless systems the most often met in the industrial world are based on radio transmissions.

We have to take in account that the targeted objectives vary according each technique : the usage can be personal or collective, from a few people up to thousands of people for instance. As a technical solution, it will depend on the scale of distance between emitters and receivers, that is from a very short distance ( a few millimetres or a few centimetres for an RFID system for instance ) up to a very, very large one ( think about satellite communications ! ). Such networks can also be designed to interconnect digital systems only, or to connect any sensors with any control system. All that finally leads the design of the architecture and the features it is wanted for a specific application.

The main advantage we can get by using these techniques is a very versatile structure with a few cables, well adapted to communicate with mobile devices and mobile users, with the objective to exchange data with devices which can not be reached easily or to build flexible automated workshops. Some of their disadvantages are the high sensibility to the interactions with the environment ( the reflections of the electro-magnetic waves in an industrial context upset or block the radio transmissions for instance ), a very highest consumption of energy ( by the so popular Wifi networks compared with wired solutions for instance ), and the high sensibility to digital hacking and piracy.

Up to now, wireless digital data transmissions are mainly based on electromagnetic wave modulation ( using a wide range of frequencies while operating according to various methods ). Many other physical principles could be employed in order to exchange some data, but their usage stay limited in most of the cases unless experimentations are in progress in some research laboratories. In the past, a number of other solutions based on different physical principles have been proposed which are now obsolete as the transmission of informations using the telegraph for instance.

Data transfer using electromagnetic waves modulation.

In the industry, we can transmit data directly over radio waves using radio modems in association with some adequate communication protocols or in association with well adapted and compliant network technologies. Among the different possibilities, we can distinguish the Wifi technology and the ZigBee technology, all the technologies operated in cellular mobile phone networks, plus a number of technologies used to dialogue with satellites. We can also take in consideration the RFID technology ( radio frequency identification ) which is essentially used as a proximity interface for tracking or identification purposes. Out of the industrial applications, we can find the Bluetooth, wireless local loop ( WLL ), Wimax and Wusb ( wireless USB ) communication systems.

There is also high performing data exchange process operating beam of light modulation with laser wave generators. Unfortunately, one of their major weakness consist in a great sensibility to atmospheric perturbations, which allows to employ them in some specific situations only. In the same area we are talking below about Li-fi as en emergent technology.

The non radio-frequency-based alternative technologies.

For an industrial usage, we can sometimes meet the « power line communication » ( PLC ) technology.

For other usages, we can find technologies such as infrared or ultrasound waves modulation ( these techniques are currently used in the industry as basic methods employed in measurement process, but they are rarely used with the purpose to carry data ).

We can still find other methods to transport data such as infrasound waves modulation for instance or many other, but which concern only very specific and very particular situations. Right now, these too specialized solutions are not useful for a massive common usage ( yet ? ).

The emerging technologies.

One of the technologies to follow could be the Li-Fi technology which transmission process consists in the modulation of the light emitted by LED diodes in function of the data. Its greatest advantages are its very large bandwidth allowing a lot of communication channels, with a high frequency modulation allowing fast data transfers. Shortly, some of its features present highest performances than the Wifi technology. For all these reasons it will may be massively in use in the future for data transfer between automated systems.

The « Cisco » company provides useful and well illustrated educational papers related to the wireless technologies in general and particularly to the radio transmissions matter, giving a precise overview about. These papers develop technical details about these technologies according to many angles ( the topologies, the safety, the implementations, the services, the synchronisation, the performances and many more ).

• What are the different kind of wireless technologies ?
• What are the most used radio waves modulation techniques ?
• What are the available open standards for the wireless IP networks ?

• Which architecture for the multipoint wireless IP networks ?
• How to deploy a network ?
• How to access and how to manage a wireless network ?

• How to control admission ?
• And many other things …

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Here you will find a lot of technical resources related in radio communications in general. It is question of antennas, cellular telecommunication, radio-frequency technologies, radio wireless networks, satellite communication and telecommunication networks. In the « formulæ » section, you will find a useful formulas guide.

You will more particularly read the radio waves propagation and antennas folder, which is a very important matter to appreciate in an industrial context. This folder presents the electromagnetic waves, their spectrum, their characteristics, with a special sub folder related to their propagation. Then you can discover the different antennas technologies ( distributed antennas, MIMO technology ), the different radio antennas types, cable and connectors features, and finally some case studies.

www.electronics-notes.com

This interesting guide ( available in both html and pdf format ) is not exactly a technical document, although it contains a technical section. It is intended to the ( public ) community leaders, but we can think its reading offers a great interest for any organization leaders who are not skilled in computers, in the industry or anywhere else, while its contents is important in matter of strategy when building a wireless network.

As the author Robert WILLIAMS has written, using the Internet to provide services is not a bed of roses.

In the first chapter, you can find considerations about budgeting a wireless connectivity in a very practical way. The second chapter is more technical, in which you will read considerations about data transfer rates, protocols, operating systems, how to build a local area network, what are wide area networks ( WAN ), how the radio frequency connections are working, and finally how can we secure a wireless network and how important is it ?

Robert L. WILLIAMS - www.tsl.texas.gov

The oldest technique used in industrial wireless networking is the data transmission through radio modems, which modulate and demodulate the radio electromagnetic waves. The radio waves are only a medium, and the modem modulate the radio waves in function of the data to be transmit. By this way, the radio modems are compatible with all the networks and protocols you want, such as the IP networks, the field networks and so on, through virtual private networks ( VPN ) if you need it.

This wireless radio-transmission technique is more and more operated in industrial applications because it offers a great compatibility with common industrial communication protocols and networks. We use it to transfer data between machines, to collect informations, to enable synchronization between production lines or to make production and maintenance management easier.

What are the advantages this solution could afford ?

• Less cabling and data enrichment due to mobile terminal connections ( for maintenance operators for instance ).

What could be its disadvantage ?

• A high power consumption and a great sensibility in relation with electromagnetic perturbations or/and with electromagnetic wave propagation disturbances.
• High sensibility according to hacking ( intrusions, data stealing, virus etc ) which can propagate from network to network since they are more and more interconnected. Talking of that, we could take some benefits when using some networks analysis and survey software with the objective to analyse data exchanges and to be able to detect any bad-intention access trial.

This transmission method operates several technologies we have to grasp well enough before implementing them in an industrial environment.

When installing a Wifi network in an industrial context the most sensible stages are a priori :

• A good knowledge and a good mastery about wave propagation matters in very constrained and very disturbed locations.
• The knowledge we have got in the expected usage of the installation, plus the context in which it will be opened out.
• Knowledge and techniques to be operated in order to warrant a quite good digital security.

Although this document is not up to date ( it has been published in year 2002 ; it is not question of the 802.11n standard for instance ), these 93 pages are a complete reference concerning the 802.11 standard bases. You will find in this paper detailed informations about medium access control ( MAC ), about MAC management, about the physical layers and their extensions to the standard, about design considerations, about the protocols in usage, about the frame format and many more.

Mustafa ERGEN - University of Koç ( Turkey )

http://home.ku.edu.tr/~mergen/Site/Home.html

This document quickly resumes pretty well the wifi technology and its main features through its history, the benefits it offers, its growth and its architecture. After that, the paper presents some brief technical overviews about the physical layer, the media access control ( « MAC » ), the logical link control ( « LLC » ), the infrastructure, the security and the wi-fi protected setup.

• Wifi development history through the 1990 to 2015 years.

  The evolution of the technology according to the 802.11 standard, the 802.11a standard, the 802.11b standard, WEP, the ODFM modulation, Bluetooth 3.0 + High Speed and finally the 802.11ac standards.

• The benefits.

  We can find especially among them : the mobility, the IP compatibility, the high speed data transfer, the easy and fast installation plus the low cost aspect.

• Physical layer.
  • The spread spectrum technology with FHSS, DSSS and OFDM modulations.
  • The channel list with their place in the frequency band and where there are in use.
  • The list of the standards from 802.11 up to 802.11n with their respective frequency, bandwidth and modulation features.
• Infrastructure.

  A brief presentation about the services ( BBS, IBBS, ESS, AP client service ) and the system ( DS, DSS ).

• Security.
  • A short introduction to association, authentication, access control, encryption, data integrity and data confidentiality functionalities.
  • Plus a quick description of some protocols such as WEP, WPA, WAPI ( defined by the chinese government for the cell phones used in China ) and WPA2.

www.silabs.com

This technical paper published in 2008 introduces the 802.11n technology, how it works and what could be the benefits by using it. The first chapter talks about the main concepts such as MIMO ( Multiple Inputs Multiple Outputs ), the bandwidth, the modulation and the MAC layer. The second chapter introduces the 802.11n interoperability, while the third chapter introduces the 802.11n network management ( planning, surveying and securing ).

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To manage a wireless network, it is necessary to use some tools to configure it, to survey it, to register how it is performing in a specific context and to diagnostic it. Below are some useful tools dedicated to wireless networks, and you can find other networks utility software working with them ( Wireshark, NMap or NTOPNG for instance ), usable for all the networks in general.

Airtraft 1.0 is a radio frequency wireless network sniffer. It detects and establishes exactly the data being transmitted over a Wifi 802.11 network. It tracks and identifies all the access points ( legitimate or not ), it provides statistics on performing ( by user or / and by protocol ), it measures the strength of the signal for the different devices on the network and delivers many other functionalities. This open source software is distributed under the GPL licence. It is designed to run under the Linux operating system.

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Kismet is a software used to detect all the Wifi 802.11 networks - hidden networks and visible networks - and to detect all the intrusive attempts in a passive way. An Add-on is available to allow Kismet working on other protocols and networks.

https://kismetwireless.net/

Stumbler is a software running under the MS windows operating system, which allows detecting all the Wifi networks respecting the 802.11 a, 802.11 b or 802.11 g standards. It allows to check the configuration of a Wifi network, to detect the locations where the Wifi signal is weak, to detect interferences between several wireless networks and to detect intrusive attempts.

www.stumbler.net

Wavemon is a software designed to monitor the wireless networks. It allows to know at first sight the most important informations relative to your network, such as the configuration of the devices, the power management parameters and the status of the network.

• You can visually estimate the quality of the radio transmissions, the amplitude of the radio waves and the signal / noise rate.
• It displays the list of all the connected nodes.

For learning purpose, the wavemon tutorial available on www.raspberrypi-spy.co.uk, shows you how to monitor WiFi connections with Wavemon from a RaspBerryPi .

https://github.com/uoaerg/

This is a radio-frequency communication network intended for personal usage, providing a low transmission range, from 10 meters to 100 meters maximum according to the class of the emitter. Its main objective is to interconnect digital devices, such as peripherals, computers and tablets.

This loop is a wireless communication medium installed and provided by the telecommunication or internet access providers to interconnect their subscribers in general inside a wide area ( one city or more for instance ). So, the operators avoid to build a wired infrastructure. One of its application is the WiMax network.

This consists in a wireless remote communication technique. It allows emitting data by modulating the light of lighting devices using LED.

The objective of the technology is to establish a network inside a building or inside a house, without using the radio frequencies, but at the opposite of the other available technologies, the transmission is uni-directional ( up to now ), and the communication must be direct without any visual obstacle.

The data flow rate could be hundred times faster than using a wifi network ( up to 1 gigabits per second ) and depends on several parameters ( on the amount of connected users for instance ), but right now the transmission range does not exceed 10 meters.

The Li-Fi main features are a low energy consumption, a very large bandwidth with an almost infinite amount of channels, direct data transmission, a low transmission range with classical bulbs ( nevertheless, laser beam can be used with other visible light communication - VLC - technologies, in this way, the transmission range is about up to 60 kilometres ), no electromagnetic interferences and a natural indoor robustness according to hacking.

While the users must be located in front of the light beam in order to detect the modulation, this technology is right now - according to the current state of the research - used in network intended for personal and limited needs only, although it is well adapted in some situations.

Such a communication technique is similar to the Li-Fi one, in the way it is a modulation of light, excepted it is in the area of the non visible waves inside the electromagnetic spectrum.

It is often used for personal usage, in the cars and in the medical world ( there are none electromagnetic interference with the medical devices ).

By now the flow data rate is about 1 gigabits per second and the transmission range is about 10 meters.

This wireless technique uses the radio frequency modulation to transmit data. Its objective is to provide fast Internet access by covering a large surface of a territory ( a range of several square kilometres ) for hundreds up to several thousands of subscribers. The Wimax networks are using the wireless local loops ( WLL ) and are compatible with other IP networks and with Wifi networks.

This implementation is the wireless version of the universal serial bus standard ( USB ). Such as USB, WUSB is designed to interconnect personal peripherals and digital devices inside a small area. The data transmission rate is about 480 megabits per second within a distance of 3 meters.

ZigBee use the radio frequency modulation to transmit the data. At the beginning, it has been designed to interconnect sensors and other wireless networks at the lowest cost.

www.bluetooth.org - The consortium provides all the Bluetooth specifications with some articles related to the security, the architecture and the topology. The association provides some technical folders and papers too.

www.ctia.org - CTIA is an international association involved in all the wireless technologies ( cellular networks, personal communication services, mobile applications and more ).

www.lificonsortium.org - The Li-Fi consortium is an international association of manufacturers and searchers, involved in optical wireless communication technologies ( The Li-Fi technology itself, the infrared laser communications technology and more other ). On the web site, you can discover some technical overviews in relation with the Li-Fi networks, the optical mobility technologies, fast data transfer, infrared connections and more.

www.wi-fi.org - The Wi-fi consortium is an industrial manufacturers association promoting the Wi-fi technology, which certifies the products using its technologies.

www.usb.org/developers/wusb/ - Wireless USB is a part of the USB consortium. The association develops and delivers the specifications of the WUSB standard, with a few tools.

www.zigbee.org - The ZigBee alliance specifies and promotes the ZigBee network technologies. On its web site, you can find the overviews about the different ZigBee technologies, with some technical papers to download.