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Six Misconceptions About Industrial Wireless Networks

Wireless communication is an attractive option for many industrial worksites, especially in hard-to-wire locations or applications where tetherless network connectivity is required. However, unlike typical home/office wireless service where the quality of service is generally best-effort, many industrial wireless applications require a high level of service quality and improved determinism. For many industrial operators seeking wireless connectivity, wireless technology unfamiliarity can spawn many misconceptions about industrial wireless networks, which can ultimately result in an inefficient and ineffective platform for wireless network communication.

1. Radiation pattern characteristics are generally the same for all antennas

Directional antennas are used to focus transmission signals toward a specific direction or a targeted area with a beam width of approximately 30 degrees. Directional antennas are ideal for providing a dedicated link for point-to-point transmission, or for providing access for clients along a linear path.

Omni-directional antennas are used to radiate signals equally (360 degrees) in every direction. Omni-directional antennas are suitable for signal transmissions from a device, such as an access point, to provide network coverage from a central location.

See page 27 of the Industrial Wireless Guidebook for more information.

2. Increasing the antenna gain will increase wireless coverage area

Signal directivity and electrical efficiency are specified by the antenna gain value. The diagram below shows what happens when the gain is increased for a directional antenna. A lower gain value will typically have a more evenly distributed signal radiation pattern, and a higher gain value will emit radiation in a more specific direction.

The antenna is a passive component and does not amplify radio energy in anyway. Regardless of the type of antenna being used, the overall “volume” of the radiated energy will remain the same. Altering the gain of an antenna only changes how the energy is released, which will affect the shape of the energy radiation pattern.

The yellow balloons below illustrate how gain works for an omni-directional antenna. The balloon on the left represents the radiation pattern from a low-gain antenna, and the balloon on the right represents the radiation pattern from a high-gain antenna. Because the total “volume” of radiated energy will remain constant, the balloon has to sacrifice its vertical coverage in order to increase its horizontal coverage. The same concept applies for directional antennas; to reach a longer transmission distance, the energy beam field needs to be more focused and will have a smaller angle for alignment.

See page 25 of the Industrial Wireless Guidebook for more information.

3. Gain is the only factor of concern when selecting a type of antenna

While gain is definitely a very important characteristic for antenna selection, other factors, such as polarization, impedance matching, and VSWR (voltage standing wave ratio) should also be considered when choosing a suitable antenna.

Polarization
An improper antenna installation will decrease signal reception quality. It is important to know the polarization of the antennas in the WLAN to make sure that signals are being sent and received under optimal conditions.

Impedance Matching
Maximum power transfer from the transmitter to the antenna requires impedance matching of the antenna system. Mismatched impedance will cause energy loss and risk circuit damage from the reflected energy pulse.

VSWR
The voltage standing wave ratio (VSWR) is the ratio of the maximum voltage to the minimum voltage on the transmission line (cable) used to measure antenna efficiency. A higher VSWR means lower transmission efficiency and can result in heated transmission lines and damaged transmitters.

See page 24 of the Industrial Wireless Guidebook for more information.

4. Channel bonding will always improve the throughput of a wireless link

802.11n combines 2 adjacent 20 MHz channels to allow higher data rates. However, depending on the wireless landscape, channel bonding can be more susceptible to interference because it uses a 40 MHz spectrum. Some 802.11n devices will drop back to using only a 20 MHz band when excessive interference is detected.

See page 22 of the Industrial Wireless Guidebook for more information.

5. Higher data rates do not require more transmission power and modulation complexity

Many types of wireless technologies have been developed to meet the requirements of various wireless applications. Wireless technologies with relatively low data rates, such as ZigBee and Bluetooth, do not require much power for transmission using simple modulation schemes. Higher modulation formats will always consume more power for signal encoding.

See page 5 of the Industrial Wireless Guidebook for more information.

6. Any wireless device can be used in any wireless network, even for industrial applications

Any wireless device can be used to provide a best-effort level of service for home/office environments, where wireless network failures will not have serious consequences. Wireless network failures in industrial applications, however, can jeopardize the safety of onsite personnel, damage expensive machinery/equipment, and possibly translate into thousands of dollars per minute in production losses. In addition to network redundancy, industrial operators must also assess the application environment for elements that can impact network performance, compromise device reliability, and lead to unplanned system downtime.

See page 33 of the Industrial Wireless Guidebook for more information.

In addition to the convenience of mobile connectivity, benefits of wireless communication also include lower cost and faster deployment. Choosing a suitable wireless technology for a particular application is just the first step towards wireless connectivity, and building a reliable wireless network with optimized performance will require the right combination of antennas, RF cables, and connectors. Moxa’s Industrial Wireless Guidebook provides fundamental wireless knowledge and basic guidance for building a reliable wireless network with optimized capabilities. For more information on how to access the Industrial Wireless Guidebook,
please visit: http://www.moxa.com/Event/IW/2013/wireless_guidebook/Index.htm

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