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Wireless Fear Factor

Fear is often the biggest hurdle to overcome when evaluating wireless networking as a way to reduce cabling and maintenance costs and to maximize networking flexibility.

This fear is based on valid concerns: What equipment do I need? Does the manufacturer understand my application? Who will be there for me if I need help?

The first step in overcoming fear is to face it. Likewise, the first thing to realize about wireless networking is to recognize that it takes more than wireless technology to make wireless communication work in harsh, demanding and cost-conscious industrial automation applications. From the perspective of the integrator or end user, communications expertise and comprehensive technical support are key considerations that distinguish ordinary wireless products from the robust wireless communication solutions required by industrial users.

The first considerations are frequency ranges and power levels. These are often geographically regulated. For North America, New Zealand and Australia, frequency ranges and power levels are usually no problem. Operation of wireless industrial Ethernet within Europe still requires some adjustments, as the approval authority remains with each country.

Is it programmable?

Many radios on the market today do not meet local country regulations, because they transmit too much power or operate on frequencies that are not approved for unlicensed use. Therefore, it is important to determine whether or not the radio can be programmed to meet these regulations.

The 2.4 GHz ISM band can be used and sold without license or on-going usage fees anywhere in the world, whereas 900 MHz systems are more highly restricted and cannot be used in Europe.

Use of 5 GHz systems, such as 802.11a, with its wider bandwidth than 2.4 GHz making it more line-of-sight capable, is more broadly allowed than 900 MHz, but still has some country-specific rules.

The next consideration is whether Direct Sequence Spread Spectrum (DSSS) or Frequency Hopping Spread Spectrum (FHSS) is better for the application.

FHSS industrial modems typically enable the user to choose from 150 or more hopping patterns, and, within each data channel, the modem will hop among a large number of frequency channels—75 or more in the United States. With this flexibility, FHSS modems can be programmed to hop around electrical interference. If transmission is blocked at one frequency, the modem will automatically hop to the next frequency in the pattern, so reliable communication is maintained.

Security tricks

Security is an important issue in any data network. With wireless communication, there is the added worry of outside interference preventing your data from being received correctly. FHSS technology provides inherent security against jamming or the unintentional electrical interference, typical of industrial automation environments.

Critical information that should be considered before purchasing a wireless network includes data transmission distance, line-of-sight obstacles and environmental factors within the plant.

Antenna selection depends upon such factors as antenna path, mounting, cable type and loss, and distance.

Whip antennas are normally connected directly to the radio and receive and transmit in all directions, and are a good choice if either radio is moving.

Yagi array antennas are an array of linear elements, parallel to one another and attached perpendicularly to and along the length of a metal boom. These transmit and receive radio waves from the direction they are aimed and are good for long-range links.

Parabolic reflector antennas also transmit and receive radio waves to and from the direction they are aimed, and are generally used for long-range links to fixed radios.

Effective evaluation of the key components should alleviate the fear factor inherent in implementing wireless networking.

Kevin Zamzow, kzamzow@prosoft-technology, is the RadioLinx Product Manager, and Wallace Gastreich, wgastreich@prosoft-technology, is an Application Engineer, for ProSoft Technology Inc.

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