ISA TR100.00.01

Scope and Purpose

In this technical report, “radio” means “the wirelesstransmission of information between two or more locations usingelectromagnetic waves”. The name “radio” (derived from “radiation”)was officially adopted at the 1906 Berlin RadiotelegraphConvention, although the alternative “wireless” remained inparallel use and is now gaining precedence over its competitor.This change in nomenclature is particularly relevant where radiotechnology is replacing wires. For example the telephone companies’copper pair subscriber loops are rapidly losing ground to cellularphones, Category 5 (CAT5) cable is giving way to 802.11 wirelesslocal area networks (LANs), and even fiber optic cables can bereplaced over short distances by line-of-sight free-space laserlinks.

The industrial instrumentation and automation field hastraditionally relied on wired connections, but the need for greaterflexibility and lower costs favors growing applications of wirelesstechnology. In esponse to this need, the ISA-SP100 Committee wasformed to address wireless manufacturing and control systemsapplications such as the following:

• field sensors used for monitoring, control, alarm, andshutdown;

• wireless real time field-to-business systems (e.g., wirelessequipment interfacing work order systems, control LAN, businessLAN, voice).

This covers all industries including fluid processing, materialprocessing, and discrete parts manufacturing environments.

Equipment cost will be an important factor. It is easy toimagine new and useful monitor and control applications which,although not feasible today because of the cost of the wiredconnections, will become practical when the cost of wirelessnetworks has been reduced sufficiently.

The broad scope of these applications suggests that there isunlikely to be an optimum “one size fits all” wireless solution.The bandwidth, throughput, signal latency (transmission delay), biterror ratio, availability and reliability requirements of awireless local area network carrying large volumes of file transferor voice traffic or a link used for real-time control of criticaltemperature or pressure parameters in a process tank are verydifferent from those of a link used to monitor the water level in aremote reservoir, where only a few bytes may need to be transmittedthree or four times a day. This technical report focuses on radiosusing the unlicensed industrial, scientific and medical (ISM) andUnlicensed National Information Infrastructure (UNII) bands. Inthis technical report where there are references to the ISM bandsthe UNII bands should also be considered to be included.

These bands have certain aspects in common:

• They are required to comply with regulations set by governmentagencies, such as the Federal Communications Commission (FCC) inthe United States. For example, both transmitter output power andradiated power density are capped, to limit the potential forinterference. In general, the regulations are very flexible andprovide ample scope for developing innovative solutions to wirelesscommunications problems.

• They are exposed to the constant threat of radio frequencyinterference from other equipment operating in the same bands.

This technical report presents a general tutorial on the basicprinciples of radio communications, and then discusses theperformance of spread spectrum radio systems in the presence ofinterference from other ISM band users and non-ideal propagationconditions, such as may be expected in the industrial plantenvironment. Its objective is to give readers a realisticunderstanding of how radio links can complement and/or replacewired connections, the factors influencing link range, and thepitfalls for the unwary. Industrial applications for wirelesscommunications range from the relatively non-critical, such asasset monitoring to support preventive maintenance programs, allthe way to the highly-critical, involving plant, personnel andpublic safety. The technical report will show that welldesignedradio systems can satisfy these varying needs, but that theassociated tradeoffs of performance vs. security and reliabilityresult in different system solutions for differentapplications.

In general, the radio links analyzed in the technical report areassumed to operate in the ISM bands, and to carry information inthe form of digital bit streams. Discussions are limited to thephysical layer and error-control portions of the data-link layer ofthe seven layer open systems interconnection (OSI) model. Wirelessnetworking concepts are touched on only superficially, in thecontext of spectrum sharing and spectrum management; furtherdetails may be incorporated in a future publication. Where examplesare given, they are based on the 2.4 GHz ISM band and the rules ineffect in North America.

Section 2 of the technical report deals first with theperformance of a single, one-way radio link in ideal “free space”conditions, assuming unobstructed line-of-sight propagation of thecarrier waves and no sources of interference (such as othertransmitters, electrical machinery or electronic equipment), theonly sources of impairment being the thermal noise generated in thereceiver and the reduction in signal strength due to pathlosses.

Section 3 of the technical report covers various aspects ofradio wave propagation, including reductions in signal strength dueto increasing distance from the transmitter and transmissionthrough “lossy” (partially-conducting) media, reflection ofelectromagnetic waves at conducting, nonconducting orpartially-conducting surfaces, multipath signal fading caused byreflections and techniques for mitigating these effects, and thedesign, selection and deployment of antennas.

Section 4 of the technical report deals with the “real world”issue of how multiple radio systems can “co-exist” withoutsuffering unacceptable levels of radio frequency interference fromother users sharing the same frequency bands. Topics discussedinclude the traditional regulatory approach to spectrum management,the constraints applicable to the unlicensed frequency bands,sources of interference and the effects of interference on radioperformance, and techniques to mitigate the effects ofinterference.

The final section of the technical report addresses the issue ofwireless communication standards and how they might be rationalizedto facilitate the secure and reliable deployment of radio links inthe industrial environment for applications in all categories fromnon-critical to highly critical.

Edition:

06

Published:

01/01/2006

Number of Pages:

68

File Size:

1 file , 3.2 MB