Wireless networking is catching the attention of a lot of people these days. Its impact is growing and spreading out from its early focus on office network applications into a host of other areas.

In the industrial data communications space wireless local area networks (WLANs) are attracting attention in a similar way that wired Ethernet LANs did, albeit more quickly. Once Ethernet technology became commonplace, reliable and affordable, the industrial market started looking at it more seriously, considering how it could meet the unique and often stringent requirements of industrial applications.

Of course, proprietary wireless systems (point-to-point and networked) have been around for a while, but cost, lack of standardisation and performance limitations have been an impediment to their range of implementation. As the cost/performance ratio of IEEE802.11 wireless (WiFi) has improved, manufacturers and users have begun to develop products and systems specifically for industrial applications.

Now users are looking to WLANs for a wider range of needs. Inexpensive, reliable wireless networks allow industrial users to enhance data collection, human-machine interfaces (HMI) and web-based system monitoring, programming and management.

The ability to implement new projects without the time and expense of running cables is a compelling proposition. Maintenance departments can readily see the value in providing mobile access for updating, reprogramming and re-calibrating equipment over a wireless network.

Basics of the IEEE 802.11 standard
IEEE 802.11 is a set of standards - first introduced in 1997 - that defines how multiple devices can communicate on a wireless network.

The standard defines the physical and data link layers only. As a part of the IEEE family of standards, it is not surprising that 802.11 WLANs are easily connected to 802.3 (Ethernet) LANs. Higher layer LAN protocols, network operating systems and internetworking protocols such as TCP/IP integrate seamlessly.

Under the IEEE802.11 standard there can be two different types of devices on the network: stations and access points.
For wireless office networks a station is usually a desktop PC or laptop but the range of possibilities for industrial applications is wider. For example, a station could be a WiFi enabled PDA used as an HMI. Another possibility is an 802.11 wireless serial server connected directly to a programmable logic controller (PLC), HMI, or other field device.

An 802.11 access point is a radio with an interface that allows connection to a wired LAN. Access points run bridging software (specified by 802.11d) to facilitate the connection from wireless to wired network. The access point becomes the basestation for the WLAN. It aggregates access to the wired network for multiple wireless stations. An access point could be a standalone device or a card in a PC.

WiFi range
IEEE802.11 devices communicate via radio signals that must penetrate solid objects to reach other network nodes. These signals are attenuated to varying degrees depending on the type of material and its thickness.

The transmitter power output, the type of antenna used and the amount of attenuation through materials affects the useable range. Electromagnetic noise, the amount of network traffic, other radio devices operating in the same frequency band and reflections (multipathing) are also factors affecting range and overall performance.

In an infrastructure network the number of access points and their coverage pattern also affect how well the system operates. Typically an 802.11 device operating indoors will have a range from 100 to about 500 feet. Outdoors some products, using high gain antennae, may achieve line-of-sight ranges of five miles or more.

Security
Security is a significant concern for WLAN users and industrial users are not exempt. Whether security threats originate intentionally or unintentionally, wireless systems are more susceptible than wired systems.

IEEE802.11b uses wired equivalent privacy (WEP) protocol to encrypt transmitted data. Designed to provide the same level of
security as that of a wired LAN, WEP operates at the physical and data link layers of the network and has been found to be somewhat lacking.

IEEE 802.11g originally implemented a more robust security standard called WiFi protected access (WPA), a scheme designed to improve on WEP’s limitations. It has better encryption algorithms and uses a technique called authentication. WPA was considered an interim standard. IEEE’s 802.11i standard - which was adopted recently - incorporates WPA as well as additional security features and is expected to replace WPA.

Industrial applications challenge WLANs
Applying WLANs to industrial applications presents added challenges compared with home or enterprise applications.
Industrial environments often produce significant amounts of electrical noise. Variable frequency drives, competing radio systems, radar and microwave sources, and welders are a few examples of industrial noise sources. Signal attenuation and reflections can also compromise signal coverage in industrial buildings and worksites. Transmitter power levels, receiver sensitivity and access point placement is critical.

Reliability of individual components and the overall system can affect plant safety, security and downtime costs. Industrial users demand performance guarantees and these guarantees extend to system characteristics such as data latency and corruption levels.

In response many manufacturers are marketing equipment designed to address these challenges. For example, stations and access points targeting the industrial market implement higher transmitter power levels.

Industrially focused equipment increasingly offers weatherproof enclosures, industrial mounting options and connectors and other robust features. Manufacturers often include software to perform RF site surveys to assess the consistency and reliability of plant coverage. Some access points include remote management software.

The list of 802.11 modems, serial servers, repeaters, access points and other equipment grows daily. Quality and ruggedness continues to improve. At the same time the 802.11 standard continues to evolve while maintaining backward compatibility. Industrial equipment manufacturers and users are embracing wireless networking in concept and practice, and finding success in the process. IEEE802.11 compliant WLANs are a key part of that trend.

Sylvia Walsh-Flaherty is marketing manager at B&B Electronics