Why factories struggle with wireless technology

Factories have much to gain from wireless technology, such as robot control, RFID tag monitoring, and local area network (LAN) communications. Wireless systems can cost less and offer more flexibility than cabled systems. But factories are challenging environments for wireless systems, as verified by tests conducted recently by the National Institute of Standards and Technology (NIST) in the US.

Heavy industrial plants can be highly reflective environments, scattering radio waves erratically and interfering with wireless transmissions. Electromagnetic interference may hinder manufacturing sectors, particularly the car industry, when they try to take full advantage of wireless networking.

The NIST tests aim to quantify what has been, until now, a nebulous problem. In a partnership with the US Council for Automotive Research (USCAR), NIST plans to develop a statistical representation of the radio propagation environment of a production floor, as a basis for developing standards to pre-qualify wireless devices for factories. NIST researchers conducted the initial tests at a car assembly plant in August 2006, and completed additional tests recently at an engine plant and a metal stamping plant.

The manufacturing plants tested were crowded with stationary and mobile metal structures, such as fabrication and testing machinery, platforms, fences, beams, conveyors, mobile forklifts, maintenance vehicles and automobiles in various stages of production. NIST monitored frequencies below 6 GHz for 24-hour periods to understand the background ambient radio environment. This spectrum survey showed that interference from heavy equipment ("machine noise') can impair signals for low-frequency applications such as those used in some controllers on the production floor.

A detailed analysis of a common wireless LAN frequency band (channels from 2.4 to 2.5 GHz) found heavy, constant traffic by data transmitting nodes, wireless scanners and industrial equipment. Signal-scattering tests showed the potential for high levels of multipath interference, where radio signals travel in multiple complicated paths from transmitter to receiver, arriving at slightly different times.

NIST researchers will use the data in studies aimed at pre-qualifying wireless devices for use in industrial environments. Meanwhile, the study has identified a number of steps that can be taken to minimise radio interference on the factory floor. These include using licensed frequency bands where possible and restricting the use of personal electronics in high-traffic frequency bands, such as 2.4 GHz.

Other suggestions include the installation of absorbing material in key locations, use of wireless systems with high immunity to electromagnetic interference, use of equipment that emits little machine noise and use of directional antennas to help mitigate multipath interference when transmitter and receiver are close together.