Wireless Networks for Industrial Automation, Fourth Edition

Richard Caro

• Publisher: International Society of Automation
• Year: 2014
• Print ISBN: 9780876640180
• eBook ISBN: 9781941546239
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

As commercial and residential networks rapidly go the wireless route, will industrial networks soon follow? This fourth edition includes the increasingly popular wireless application Radio Frequency Identification (RFID) and also provides a clear, unbiased view of the emerging wireless communications market. Author Dick Caro explores wireless communications from the factory and process automation viewpoint to help you make clear decisions on the timing and strategy for implementing wireless networks for automation projects. According to Caro, going wireless is more than just plugging in some wireless components to replace the wires. Residential networks are easily justified using today's inexpensive wireless components to avoid costly or unsightly wire installations. Industrial use is not quite so clear due to privacy and security concerns and the potential for signal loss in plant environments. Industrial use must have secure communications that never fails. However, the cost of industrial wiring is so high, that wireless can usually be justified. This fourth edition includes a general update of events that have occurred since the previous edition. Most importantly, it includes an extensive analysis of new wireless technology intended for process control, such as ISA100 Wireless (ISA100.11a), WirelessHART, WIA-PA, and WiFi, including IEEE 802.11n and 802.11ac.

Unit 1:
Wireless Network Technology

The changes in wireless technology for data networks over the past five years have been more dramatic than the changes in radio itself in the century since Guglielmo Marconi sent the first wireless telegraph signal across the Atlantic from Cornwall, England, to St. Johns, Newfoundland, on December 12, 1901. The progress in commercial radio transmission from telegraphy to voice to television was measured in decades. Commercial digital wireless transmission began in the mid-1990s when cellular digital telephony—known as PCS for Personal Communications Service—replaced Advanced Mobile Phone Service (AMPS), the then-dominant analog voice transmission protocol. Digital wireless telephony technology was then split into two competing technologies: time division multiple access (TDMA) and code division multiple access (CDMA). Older TDMA has now been replaced by Global System for Mobile Communications (GSM), a standard version of TDMA used by most European and Asian carriers as well as by some North American cell phone carriers. CDMA is used by some Japanese carriers as well as by two North American cell phone carriers. TDMA, GSM, and CDMA are not interoperable due to major protocol differences and frequency assignments.

As the cell phone industry has evolved, a much greater capability for digital data transmission has become necessary, particularly to support “smart phones.” Several different protocols have been tried, but the industry is now converging on LTE (Long Term Evolution), a protocol closely related to GSM. Even carriers using CDMA for voice are using LTE to achieve “4G” network speeds for digital data.

The wireless local area network (LAN) began to emerge in the late 1990s, when it became obvious that there was a need for wireless data networking. Wireless LANs required faster data transmission than was possible with cellular PCS (of any technology), and eventually suppliers settled upon using digital spread-spectrum as defined by the IEEE 802.11 standards. Spread-spectrum was originally developed for the U.S. military so wireless transmissions could be made in the presence of strong jamming signals. This work by the military was based on the spread-spectrum patent U.S. 2,292,387, which was originally granted to Hollywood actress Hedy Lamarr and her partner George Antheil.

Frequency hopping spread-spectrum (FHSS) and direct sequence spread-spectrum (DSSS), both operating up to 2.0 Mbps, were the first two IEEE 802.11 technologies. Neither is commercially available today. These initial technologies were improved upon until, in rapid succession, IEEE 802.11b (operating at up to 11 Mbps) and 802.11a, as well as 802.11g (both operating up to 54 Mbps) emerged. All of these are called Wi-Fi (wireless fidelity) after the name of the supporting industry association, the Wi-Fi Alliance, but 802.11b (and later 802.11g) became commercially successful technologies with a large home and office installed base. Both 802.11n and 802.11n/dual frequency have now essentially displaced 802.11g and IEEE802.11a. For the sake of simplicity, I will continue using the term Wi-Fi to represent any of the IEEE 802.11 standards.

1.1 Wireless Standards

The dynamic nature of wireless digital data communications stems from the standards committees of the Institute of Electrical and Electronic Engineers (IEEE), which develops most of these protocols. No illusion currently exists within the IEEE 802 committee, which is responsible for personal area networks (PAN), local area networks (LAN), and metropolitan area networks (MAN) that it will be possible to create a single network protocol useful over all of these four domains. Therefore, each application that has a special interest that is not accommodated by an existing protocol can form a new subcommittee to create a new protocol standard. IEEE ensures only that these subcommittees deliberate fairly, that they do not exclude a genuine interest, and that all proposed standards are publicly reviewed. All IEEE 802 standards are automatically submitted to the ISO/IEC (International Organization for Standardization and International Electrotechnical Commission) for consideration as international standards. Several of the IEEE 802 standards have failed in the marketplace, while others have succeeded.

In their efforts to make the family of IEEE 802 standards general, and independent of applications, all 802 committees develop their standards to define only Layers 1 and 2 of the ISO seven layer protocol stack (IEC/ISO 7498-1) shown in Table 1. By standardizing at this low level, many application-oriented upper layers can be added by standards committees and consortia focusing on specific application areas to take advantage of the commodity volume market for chips based on the IEEE 802 protocols.

Table 1. IEC/ISO 7498-1 Seven Layer Stack

Layer No.	Name	Function
7	Application	User interface
6	Presentation	Data format conversion
5	Session	Connection
4	Transport	Acknowledged service
3	Network	Network Addressing
2	Data Link	Local address and mastership
1	Physical	Hardware/Spectrum

Another source of wireless communications protocols is the International Telecommunications Union (ITU), the standards body for telephone networks. Telephony has rapidly changed from a purely wired circuit-switched analog service—also known as POTS (Plain Old Telephone Service) —to VoIP (Voice over Internet Protocol) on broadband service and now to wireless telephony.

Wireless telephone service began with AMPS, and rapidly progressed to 1G (first generation) digital service, which evolved to 2G, 2.5G, then to 3G and now 4G. Digital wireless telephony implementation has not been uniform, with a split between TDMA (especially since the GSM version of TDMA has been adopted in most countries) and CDMA, available in fewer countries.

Even though there are excellent reasons to keep CDMA, GSM, 3G, and 4G wireless in mind for in-plant voice networks and some mobile data applications, they are not presently being considered for industrial use. However, given the eventual availability of low-cost and low-power consumption 3G and 4G technologies, they should not be ignored.

A word of caution is in order about the standards documents for data communications. These very large documents are not intended to be read by general users. They are written for the implementer of networks and networking devices. If you really want to see some examples of such standards, however, most IEEE 802 network documents more than six months old are available for download on the IEEE standards website: http://standards.ieee.org/getieee802/ (look for the click here link in the last paragraph of the text). The IEEE and others often publish books about the standards, making them easier to understand.

1.1.1 IEEE 802.11, Wi-Fi

One factor causing rapid technological change in wireless communications is the ever-increasing capacity of commercial semiconductor processes such as CMOS (complementary metal oxide semiconductor) to handle higher frequencies. This factor alone is responsible for the recent rise in interest in IEEE 802.11n/dual frequency, which previously required more expensive GaAs (gallium arsenide) processes or higher-power bipolar semiconductors to use the 5-GHz frequency band. When 802.11n or dual frequency 802.11n chips are built in CMOS, they are as economical as the slower 802.11g chips.

With the ratification of 802.11n and the subsequent flood of new products on the market, we have witnessed another dramatic change in the Wi-Fi market. 802.11n, which is backwards-compatible with 802.11g, has completely displaced 802.11g for new wireless products. As the Wi-Fi band at 2.4 GHz becomes saturated, the benefits of dual frequency 802.11n become compelling since the 5.0-GHz band offers 24 non-overlapping channels, versus just three for service at 2.4 GHz. Chips that offer dual frequency 802.11n are already on the market, and soon all new Wi-Fi LANs will offer access at both 2.4- and 5-GHz service at little to no price premium. Additionally, IEEE 802.11ac chips that operate only in the 5-GHz band are also commercially available. Figure 1 illustrates a roadmap for these transitions in the Wi-Fi market.

The most appealing technology embedded into 802.11n, in addition to its dual frequency band, and in IEEE 802.11ac is called MIMO (Multiple Inputs, Multiple Outputs), most easily recognized by several antennas on dual frequency 802.11n and 802.11ac products. The “n” and “ac” standards require that all signals be simultaneously transmitted on each of the antennas. Due to the spatial separation of these antennas (they are a few centimeters apart) signals transmitted by all antennas will be received by the multiple antennas of the receiver slightly out of phase with each other. MIMO technology provides a way for the receiver to mathematically realign the phases of the received signals such that the resulting resolved signal is now stronger and more reliable than any single signal. Note also that reflected signals, often called multipath signals, are also out of phase with the original. MIMO offers a technical solution to the multipath problem, which is often associated with networks built in large plant units in the process and metals industries, often referred to as the “canyons of steel.”

Figure 1. Market Size for Versions of Wi-Fi

IEEE 802.11n can also bond channels in both the 2.4- and 5-GHz ISM (Industrial, Scientific, and Medical) bands that were formerly assigned to 802.11g and 802.11a, respectively. Channel bonding in 802.11n may be used to achieve a higher data rate. While a single channel for either “a” or “g” can achieve a theoretical maximum 54 Mbps, bonding two channels in 802.11n can achieve a theoretical rate of 108 Mbps. 802.11n can achieve theoretical data rates as high as 600 Mbps by bonding four channels.

Channels may only be bonded within bands. This means that currently, an IEEE 802.11n dual-channel device requires two radios, one for each band. Many inexpensive 802.11n devices may not be able to implement the dual radio part of IEEE 802.11n simply because they do not have a 5-GHz radio, and as a result, will not be able to achieve the higher data rates that can come from channel bonding.

The successor to 802.11n in the Wi-Fi market is IEEE 802.11ac, which is very much like IEEE 802.11n except for its ability to bond more channels in the 5-GHz band to achieve a maximum data rate greater than 1.0 Gbps. This becomes a wireless equivalent of Gigabit Ethernet. While the standard has not yet been completed (as of 2013) there are already products on the market. By the end of 2014, IEEE 802.11ac should be the dominant Wi-Fi protocol.

Table 2. IEEE 802.11 Standards

Another recent standard is IEEE 802.11ad (2012), which deviates from the 2.4-/5-GHz ISM band by using an ISM band at 60 GHz that currently is lightly used. It uses multiple antennas to form a virtual “beam” between the transmitter and receiver. This makes IEEE 802.11ad almost as effective as a directional antenna such as a Yagi (Figure 2) but not quite as effective as a parabolic antenna (Figure 3). The beam forming is performed with advanced mathematics setting both the amplitude and phase shifting of the signal sent to and received from each of the up to eight antennas. This is an implementation of the phased array antennas discussed in section 1.4.5. By using the 60-GHz band, sufficient bandwidth can be allocated to allow data rates up to 6.67 Gbps, which is known as WiGig. It is not intended for conventional LANs, but is directed at cable replacement for high definition video and audio signals.

As mentioned above, the Wi-Fi market is supported by the Wi-Fi Alliance, which in its own words is “a nonprofit international association formed in 1999 to certify interoperability of wireless Local Area Network products based on IEEE 802.11 specifications.” The Wi-Fi Alliance currently has more than 200 member companies from around the world, and more than 1000 products have received Wi-Fi® certification since certification began in March of 2000. The goal of the Wi-Fi Alliance’s members is “to enhance the user experience through product interoperability.” The Wi-Fi Alliance website is: http://www.wi-fi.org/

1.1.2 IEEE 802.15.1, Bluetooth

Bluetooth is a wireless communications technology that was created to eliminate the wires connecting cellular telephones and other portable electronics to a headset or earphones. Bluetooth has already been applied in many commercial products and almost all wireless telephones, but at a much slower pace than its developers ever dreamed. Bluetooth has just enough networking capability to interest a wide variety of companies in extending its use beyond its original scope.

In fact, Bluetooth is far more than a communications protocol; it is also a full communications application stack. The lower two communications layers of Bluetooth (Layers 1 and 2) have been published as IEEE standard 802.15.1. For the original task of device connection, the upper layers of Bluetooth offer a rich suite of fu...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• Acknowledgments
• Contents
• Preface
• About the Fourth Edition
• Unit 1: Wireless Network Technology
• Unit 2: Wireless Network Standards
• Unit 3: Industrial Automation Requirements
• Unit 4: Application of Wireless Networks to Industrial Automation
• Unit 5: On the Bleeding Edge
• Unit 6: Recommendations for Wireless Networking
• Unit 7: Radio Frequency Tagging
• About the Author