So many wireless technologies Which is the right one for my application?

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1 So many wireless technologies Which is the right one for my application? Don Dickinson Don Dickinson, Phoenix Contact USA, 586 Fulling Mill Road, Middletown, Pennsylvania, USA, (correspondence: , ext. 3868) KEYWORDS Bluetooth, Direct Sequence Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS), IEEE a/b/g/n, IEEE , Industrial Scientific & Medical (ISM) Bands, ISA100, Orthogonal Frequency Division Multiplexing (OFDM), Radio Frequency (RF), Spread Spectrum, Ultra High Frequency (UHF), WEP/WPA/WPA2, Wi-Fi, WirelessHART, Wireless Access Point (WAP), Wireless Ethernet, Wireless Local Area Network (WLAN) ABSTRACT Wireless technology has transformed our world. The demand for mobile communications and computing continues its dramatic growth driven by the proliferation of smart phones and tablets. The use of wireless in industry is growing rapidly as well. Wireless technology has been used in industry for many years and has provided reliable communications for monitoring and controlling remote processes, including mission-critical applications. However, new wireless technologies have emerged giving users even more options for solving application needs such as wireless networking for the mobile worker and, wireless sensor networks for process optimization and asset management. But which is the right technology for your application? Understanding the capabilities of the various wireless technologies will allow users to realize the benefits of wireless while avoiding the problems resulting from its misapplication. This paper provides an overview of the various license-free, Spread Spectrum technologies and their appropriate use for industrial applications. The capabilities and limitations of both proprietary and public wireless protocols will be discussed along with issues such as: moving data through a wireless medium, security and robustness of wireless transmission and, application considerations for the key wireless technologies used in industry. INTRODUCTION Wireless technology has come a long way since the development of wireless signaling techniques in the late 1800 s. Today, wireless technologies of many types are used in a variety of applications ranging from garage door openers to satellite communications. There are many types of wireless technologies and many questions that arise when considering which wireless technology to use. How far does it go? How fast can data be transmitted? Is it secure? Is it reliable? How much does it cost? The answers to these questions can vary greatly depending on which wireless technology is being considered. Generally speaking, there is no one technology that does everything you may want it to do. A wireless technology is chosen for a given application because the performance characteristics of that wireless technology best align with the application requirements. Which wireless technologies are suitable for use in an industrial application? An awareness of the fundamentals of wireless technology and ones used in industry will help determine which technology may be considered for a particular application. THE ELECTROMAGNETIC SPECTRUM We are surrounded by electromagnetic radiation that is both naturally occurring and man-made. The sun radiates energy that includes visible light and ultraviolet rays. Man generates electromagnetic radiation

2 Dickinson 2 such as TV station broadcasts and cell phone communications. Electromagnetic radiation is defined by its frequency measured in Hertz (Hz). The electromagnetic spectrum includes all electromagnetic radiation ranging from the extremely low frequencies, below 3000 Hz, to the extremely high frequencies, above 30 gigahertz. This spectrum includes the radio frequencies found at the lower end of the spectrum, microwaves, infrared rays, visible light, ultraviolet rays and, x-rays and gamma rays that are at the upper end of the spectrum. The radio frequencies (RF) are the lower frequencies in the spectrum and are well suited for communications. Generally, the lower the frequency the further it will travel and the better its ability to penetrate solid objects such as walls. However, the higher frequencies provide greater bandwidth allowing more data to be transmitted at higher speeds. Selecting a wireless technology usually requires a balance between distance and data rates. Within the RF spectrum the Ultra High Frequency (UHF) band is of greatest interest to the general public. The UHF band includes frequencies from 300 to 3000 MHz. The UHF band includes cell phone transmissions, licensed transmissions such as TV broadcasts and unlicensed transmissions such as Wireless Ethernet, also known as Wi-Fi. Most of the wireless technologies discussed in this paper operate in the UHF band. There are many types of wireless technologies used by the general public today. These technologies differ from one another in their modulation techniques, data transmission rates, transmission distance, security, cost, complexity and power consumption. When used in industrial applications robustness, reliability and ease of maintenance are important attributes. Some wireless technologies may be quite familiar and widely used by the general public such as Wi-Fi, Bluetooth and cellular. Other technologies may be unfamiliar. Some technologies are proprietary intended for specialized applications not addressed by other technologies. Certain technologies have been used in industrial applications for many years, primarily in industry market segments that have a decentralized infrastructure such as Water and Oil & Gas. Traditionally the use of wireless in industry has been driven by the need to monitor and control operations over long distances. However, wireless increasingly is providing new ways to address common needs in all industry segments. But with new technology comes new concerns - especially for mission-critical operations. Which wireless technologies are suitable for industrial applications? What are the advantages and limitations of each technology? WIRELESS FOR INDUSTRIAL APPLICATIONS Wireless technology must meet certain common requirements for use in an industrial control application. First, it must be reliable. Reliable performance and operation are essential for ensuring maximum uptime for an industrial process. If the appropriate wireless technology is selected for an application it can be as reliable as a wired connection. In some cases wireless can be more reliable than a wired connection. Machinery with moving components may require festooned cables or slip rings to send signals from moving components to fixed components. Repeated flexing of cables and wear on slip rings can create recurring problems for maintenance. Also, runs of copper cable that are thousands of feet long can become unreliable over time due to corrosion or electrical shorts resulting from deterioration or damage to wire insulation. Additionally, long cable runs may be prone to surges from lightning. Wireless can be an easy and cost effective solution to problems resulting from unreliable, wired connections. Because data is transmitted over air there is an inherent delay, or latency that must be taken into account when applying wireless. The latency of a given wireless technology must be appropriate for the application.

3 Dickinson 3 Second, it must be secure. Preventing intrusion and malicious jamming of frequencies are primary concerns when applying wireless technology. Some technologies inherently have higher levels of security than others due to the nature of the technology. Some technologies rely on encryption to protect sensitive data. Depending on the application, the required level of security can vary and may determine which wireless technology is suitable for use. Third, it must be rugged. It must be easy to setup and install and, it must be suitable for harsh industrial environments. Commercial products do not meet the demanding environmental standards required for industrial equipment. Typically industrial grade components meet specifications for temperature, shock and vibration, and noise immunity that far exceed the specifications for commercial or consumer grade equipment. Lastly, because an industrial control system is expected to have a long lifecycle, consideration must be given to the future environment in which a wireless system will operate. Over time, changes to the physical environment such as new structures or maturing vegetation could impact transmission paths. Additionally, the introduction of other wireless systems or devices emitting radio frequencies could result in radio frequency interference (RFI) impacting performance of new or existing wireless systems. A little planning at the beginning will minimize or eliminate potential issues with transmission paths in the future. LICENSED & UNLICENSED WIRELESS The use of the electromagnetic spectrum is tightly regulated in all jurisdictions throughout the world with different rules for use depending on the country and the operating frequency. In the United States the FCC (Federal Communications Commission) regulates use of the electromagnetic spectrum and manages the allocation of different frequency segments. International treaties between different country-specific regulators ensure that transmissions from one country do not negatively affect users in another country. In the USA the FCC allocates licensed and unlicensed portions of the spectrum called bands. For a licensed band, a user must get a license from the FCC in order to use equipment that uses that frequency band. On the other hand, in an unlicensed band, users do not require operating license provided that their equipment falls within specified frequency and power limits. For this paper, frequencies as regulated by the FCC will be used as examples. In general looking across the wireless spectrum, most wireless bands are licensed. In the US this requires a license from the FCC that authorizes transmission on a particular frequency over a defined geographic area. If another transmission interferes with a licensed transmission, the licensee has legal recourse to terminate the interfering transmission. Conversely, a licensee s transmission cannot interfere with a transmission on another frequency. Licensed radio transmissions have been used in industry for many years and will continue to be used when transmitting over long distances (many miles). However, there has been a dramatic growth in the use of license-free wireless technologies by the general public and industry. These technologies have greatly expanded the range of needs addressed by wireless and offer many new benefits for users. INDUSTRIAL, SCIENTIFIC & MEDICAL BANDS In 1985 the FCC allocated segments in the radio spectrum for license-free transmission. These segments are known as the Industrial, Scientific and Medical (ISM) bands. Many devices that we use daily such as cordless phones and wireless routers operate in the ISM bands. It s important to note that noncommunication devices emit electromagnetic waves at frequencies within the ISM bands. Microwave ovens cook food with electromagnetic waves in the 2.4 GHz band. Although a license is not needed there are specific requirements for frequency, power and technology used. Additionally, the manufacturer of

4 Dickinson 4 the wireless device must meet provisions of FCC part 15 that ensures unlicensed transmissions do not interfere with licensed transmissions. License-free transmissions are allowed in three bandwidths: 900 MHz, 2.4 GHz and 5.8 GHz. These are shorthand designations for the bands. The specific range of frequencies for each band is listed in Table 1. It is important to note that other countries may not recognize these same bands for license-free transmissions. All three bands can be used in the US but not in all countries. License-free transmissions in the 900 MHz band are not permitted in many countries; however, the 2.4 GHz band generally is considered license-free throughout most of the world. Confirm suitability before selecting a wireless device that will be used outside the US. Band Frequency Range 900 MHz MHz 2.4 GHz GHz 5.8 GHz GHz Table 1: The ISM Bands The performance of a wireless device is influenced greatly by the frequency band in which it operates. As previously noted, the lower the frequency the further it will travel and the better it can penetrate solid objects. Chart 1 shows the signal loss (attenuation) in free space for the three ISM bands. Differences in attenuation are even greater when objects are introduced into the signal path db db MHz Loss 900MHz 2.4GHz Loss 2.4GHz 5.8GHz Loss 5.8GHz Miles Miles Chart 1: Signal Loss in Free Space Why use the 2.4 or 5.8 GHz bands if a signal in the 900 MHz band goes further and is better at penetrating solid objects? The reason is more data can be sent faster in the higher frequencies. Which band is best depends on the application. A wireless link sending network data needs as much bandwidth as possible. Whereas a wireless device controlling a pump two miles away has to contend more with the challenge of distance than the speed or the amount of data being sent. The choice of which band to use is not determined by the user. Public wireless standards such as IEEE (wireless Ethernet or Wi-Fi)

5 Dickinson 5 specify the frequency band to be used. The band for a proprietary device is selected by the manufacturer for the intended application. A key difference between the 2.4 and 5.8 GHz bands is channel allocation. As an example, when used for Wi-Fi the bands are segment into sections called channels. In the 2.4 GHz band there are eleven channels available for use in the US. Of the eleven, only three are non-overlapping. Communications on overlapping channels can interfere with one another and diminish performance of wireless transmissions. The 5.8 GHz band has eight channels. All are non-overlapping. The 5.8 GHz band offers the flexibility of having multiple networks that do not interfere with each other. However, there is greater attenuation in the 5.8 GHz band resulting in potentially shorter transmission distances than in the 2.4 GHz band. As stated previously the 2.4 GHz band generally is allocated for license-free transmissions throughout the world. There are many wireless devices operating in this band. As a result, congestion could be a potential issue for new or future installations. Regardless of the source, high concentrations of RF energy translate into possible interference for wireless devices. Different wireless technologies deal with interference in different ways. Knowing how the different wireless engines work is useful in understanding why different wireless technologies perform differently and, why one technology may be better than another for a given application. SPREAD SPECTRUM License-free, wireless transmissions in the ISM bands require the use of one of the Spread Spectrum technologies. Spread Spectrum refers to a method of transmitting a signal by spreading it over a broad range of frequencies, much wider than the minimum bandwidth needed to transmit. The benefits of Spread Spectrum technology are: Increased transmission speed for faster throughput Operation of multiple networks in the same area for greater flexibility in system layout and expansion Minimized impact on performance due to interference Reduced power consumption for battery-or solar powered installations There are three wireless technologies that come under the Spread Spectrum umbrella. They are Frequency Hopping, Direct Sequencing and Orthogonal Frequency Division Multiplexing. Each technology has its advantages and limitations. Frequency Hopping Spread Spectrum (FHSS) refers to a process of sending data on a carrier signal that hops from one frequency to the next in a pseudorandom hop sequence. The hop sequence is known by the transmitter and receiver and may include any number of frequencies in the hop sequence. Each hop generally is only a few milliseconds in duration. Should the hop sequence land on a particular frequency where there is interference, the data packet may be corrupted. However, that data packet can be ignored and the sequence continued to the next frequency. As a result, FHSS is said to tolerate interference and is well suited for industrial environments with high levels of electromagnetic interference (EMI) and radio frequency interference (RFI). Additionally, although not impossible, it would be very difficult to intercept or manipulate wireless transmissions using FHSS due to the pseudorandom hop sequence. As a result, FHSS is inherently a relatively secure means of transmitting data especially when encryption is added. The limitation of FHSS is lower data rates due to the short duration of each hop. FHSS is well suited for applications requiring robust performance in environments with high levels of EMI and RFI and, do not involve large amounts of data. Direct Sequence Spread Spectrum (DSSS) transmissions use a coding technique that acts somewhat as a software filter. DSSS spreads a signal over a large bandwidth before transmitting. The receiver despreads the data, recreating the original signal. This synchronized process of spreading and de-spreading

6 Dickinson 6 results in an improved signal to noise ratio referred to as process gain. Any signal that did not go through the spreading process is suppressed. DHSS is not immune to interference. When the jamming margin is reached, throughput goes from 100% to 0%. DHSS may be less immune to interference than FHSS but it provides higher data transmission rates. Generally DHSS is well suited for applications such as wireless networks where there are many nodes sending moderate amounts of data at speeds much faster than possible with FHSS. Despite its complex sounding name, Orthogonal Frequency Division Multiplexing (OFDM) is an easy technology to understand. OFDM uses multiple, parallel data streams to send data at much higher rates than DSSS. Although not technically a Spread Spectrum technology it is associated with the ISM bands. OFDM is optimal for a wireless network with a few nodes streaming large amounts of data. POWER LIMITATIONS As noted, the FCC authorizes license-free transmissions in any of the three ISM (Industrial, Scientific & Medial) bands using one of the three Spread Spectrum technologies. The third restriction for unlicensed transmissions is power. Unlicensed radio transmitters are limited to one Watt power output. There are additional limitations on the gain of antenna systems that vary depending on the type of transmission. Some wireless standards may specify or recommend a power output below the FCC s one Watt requirement in order to reduce transmission distance, minimizing interference between systems in close proximity. PUBLIC VERSES PROPRIETARY Wireless transmissions fall into one of two categories: Public Standard or Proprietary System. A wireless public standard involves a governing body that creates a specification guaranteeing performance and interoperability between devices from different manufacturers. Interoperability gives consumers choices in product selection. A particular manufacturer s product may offer more features and benefits than another or, may offer cost advantages verses another manufacturer. Standards-based components can evolve as standards evolve protecting investments in earlier technology if backward compatibility is part of the standard. An example of a wireless standard is Wireless Ethernet, or Wi-Fi (short for Wireless-Fidelity). The standards for Wireless Ethernet were developed and are managed by the Institute of Electrical and Electronics Engineers (IEEE). The original standard was developed in the late 90 s and has evolved over time as technology and needs have changed. Public standards provide interoperability but also lead to concerns over security. With a public wireless standard everyone knows the radio language and everyone has access to equipment that can receive transmissions. Therefore, sensitive information transmitted using a public standard must be protected. Encryption and authentication techniques can provide secure transmission of sensitive information. Other than the recent development of standards for wireless sensor networks there are no other wireless standards developed specifically for industrial applications. However, there have been numerous proprietary, wireless products in the market for many years serving a wide range of industrial needs. With proprietary wireless systems the manufacturer controls the design and determines which products work together and how they work together. The word proprietary can have negative connotations; however, when considering wireless technology it may be helpful to think of proprietary simply as using available technology to meet a need where no public standard exists. Proprietary technology can often provide a significant benefit in terms of security. Although the wireless engine and the frequency range may be known for a wireless device (e.g. FHSS, 900 MHz), discovering how that device works would be extremely difficult for an outsider. As a result, proprietary technology

7 Dickinson 7 can provide a significant barrier to intrusion. Adding encryption increases the difficulty of intercepting or manipulating a wireless transmission especially if FHSS is used. As noted previously FHSS has an inherent element of security depending on its implementation. INDUSTRIAL WIRELESS There is no one wireless technology that satisfies all the needs of industry. As a result, numerous wireless technologies are being used in a variety of applications. As a general statement there are six segments of industrial wireless. They are: licensed proprietary, unlicensed proprietary, (wireless Ethernet), Bluetooth, sensor networks and cellular. As has been noted in this paper each wireless technology has its advantages and limitations. LICENSED TECHNOLOGY FOR INDUSTRY Licensed, proprietary wireless technology has been used for many years in industry. It is commonly used for transmission of data, usually serial, over long distances (many miles). Today, licensed proprietary wireless is commonly used for long-distance communications as part of a Supervisory Control and Data Acquisition (SCADA) System that monitors and controls operations over a large geographic area. The FCC issues licenses for transmissions in the VHF (very high frequencies) and UHF (ultra high frequencies). These frequencies generally are in the MHz range. A license allows transmissions with a maximum power output of five Watts. Although not difficult, there can be some challenges in obtaining a license. Frequency coordinators are helpful in determining which frequencies are available in a geographic area and submitting applications to the FCC. The greatest challenge in obtaining a license in the VHF and UHF bands is availability of open frequencies. Depending on the geographic location there may not be any available frequencies in the VHF band. Unless a user already has a license in the VHF band there may be no reason to consider new wireless systems in this band. Although UHF frequencies generally are available there may be limitations, especially in larger metropolitan areas. Generally, users already involved with licensed, proprietary technology will continue to use it as part of a wireless telemetry system. However, the rapid increase in the use wireless technology in industry is occurring in the unlicensed wireless technologies. LICENSE-FREE WIRELESS FOR INDUSTRY The use of license-free wireless in industry has increased dramatically in the past few years. In addition to displacing licensed technology for short to medium distance applications (several miles), many new uses for wireless have been discovered. Both standards-based and proprietary technologies are being used in a variety of applications. LICENSE-FREE PROPRIETARY License-free, proprietary wireless already has a proven track record for reliable performance in industrial applications. Although product packaging and functionality vary widely between manufacturers, most of the products in this segment use FHSS and operate in the 900 MHz band. For maximum application flexibility most proprietary wireless products use the full one Watt available for license-free transmissions. This technology is well suited for use in applications such as Wireless I/O (replacing wired connections between discrete and analog devices) or Data Radios (replacing wired serial connections between intelligent devices) for transmission distances from a few thousand feet to several miles. Depending on the manufacturer, system architecture can be point-to-point, point-to-multipoint or, multipoint-to-point. When end-to-end transmissions over long distances are not possible the Store & Forward function is useful. With Store & Forward, data is sent to an intermediate device (repeater) that relays data to a final destination.

8 Dickinson 8 Some manufactures offer unique proprietary products such as a 900 MHz Ethernet radio. Data rates may be much lower than an radio and, because it does not comply with IEEE standards it does not provide interoperability with other manufacturers radios. However, a one Watt, 900 MHz Ethernet radio transmits Ethernet data frames over the greatest distance possible without a license. WIRELESS ETHERNET Ethernet is the world-wide standard for local area network (LAN) technology. It is not surprising that Wireless Ethernet, commonly known as Wi-Fi, is widely used for wireless local area network (WLAN) technology. Although Ethernet communications can extend to the device level the most common use for Wi-Fi in industry is for wireless networking. Ethernet has become an integral part of industrial control networks and is well suited for communications between personal computers, PLCs, and a variety of other devices use in control systems. Wireless Ethernet extends the reach of wired networks to in-plant, near-plant and remote functions. Additionally, Ethernet has simplified the integration of control networks and business networks. Wireless and can be useful when implementing other technologies used in the plant such as RFID, VoIP and wireless security devices. Wi-Fi is based on the IEEE standard that defines four sub-standards: a, b, g & n. Each sub-standard defines the ISM band and Spread Spectrum technology to be used. Table 2 lists the standards and key attributes for each. IEEE established and maintains the standards that ensure products from different vendors are compatible. The Wi-Fi Alliance tests adherence to the standards and certifies that a product meets the standard. A product that is certified by the Wi-Fi alliance can display the Wi-Fi logo. Each standard has advantages and limitations a b g n ISM Band 5 GHz 2.4 GHz 2.4 GHz 2.4/5 GHz Speed (theoretical) 54 Mbps 11 Mbps 54 Mbps 54/300 Mbps Compatibility a b Backwards compatible to b Backwards compatible to a/b/g SS Technology OFDM DSSS OFDM, DSSS OFDM Table 2: IEEE Standards a operates in the 5.8 GHz band. It is unaffected by 2.4 GHz transmissions and can coexist with 2.4 GHz networks. As noted previously the 5.8 GHz band has eight, non-overlapping channels that provide flexibility when operating multiple networks in an area. However, the higher frequency means more signal attenuation. As a general statement a has not been widely deployed in industrial applications. The b standard was the first to be widely deployed but g became more commonly used due to the demand for higher data rates needed for network communications. A key advantage to g is that it is backwards compatible to b. A limitation of g is shorter transmission distance than b at the same frequency. Again, overlapping channels in the 2.4 GHz band may limit network layout for g n is the newest standard to be ratified and offers key advantages over the previous standards n provides significantly higher data rates, greater range and can operate in both the 2.4 and 5.8 GHz bands. A key provision for n is backward compatibility with g although there are performance limits when mixing devices on a network. Industrial grade n components are now readily available and are being deployed to take advantage of higher bandwidths and increased range.

9 Dickinson 9 Regardless of the standard used it is important to note that Ethernet-based industrial protocols may not function as required on a wireless LAN as they do on a wired LAN. Consideration must be given to the suitability of a given industrial protocol for use over a wireless medium. There may be limits on performance or specialized configurations required to ensure proper operation. Ethernet radios can be used three ways: Wireless Access Point (WAP), Bridge and Client. A WAP connects client devices to a wired Ethernet network via a wireless link. Client devices, such as laptops use an internal, wireless network interface card (NIC) to communicate with a WAP. If a client device such as a PLC does not have a NIC, an Ethernet radio in Client mode provides the connection to a WAP. Some manufacturers may offer specialized functions for Wi-Fi radios such as Bridge mode that allow a number of radios to form a wireless mesh LAN. In Bridge mode an Ethernet radio communicates with other Ethernet radios that are in the same bridge network. Only the radios designated as part of a specific bridge network can communicate with one another adding a degree of security. A WAP can be added if client devices are to have access to the bridge WLAN. WI-FI SECURITY Because Wi-Fi is a public standard, the security and integrity of wireless transmissions are important concerns. There are a number of measures that can be taken to make transmissions secure but encryption techniques are the most common. WEP (Wired Equivalent Privacy) was the first encryption technique but now can be compromised with limited know-how. WPA (Wi-Fi Protected Access) was introduced to improve upon WEP. WPA provides better security than WEP but still is vulnerable to attacks. Today, WPA2 provides the highest level of security for wireless Ethernet networks and is considered un-hackable by today s standards. BLUETOOTH Bluetooth is based on a public standard (IEEE ) intended for short-range, low-power wireless transmissions. Originally conceived for connecting consumer electronics such as a wireless keyboard or mouse to a PC, Bluetooth is being used in industry for close-proximity, machine-to-machine (M2M) communications and other short-range wireless applications. Bluetooth is useful for replacing slip rings or festooned cables between a fixed component on a machine and a component that is moving or rotating. Also, replacing a serial cable with a wireless Bluetooth connection could eliminate the tether between a PC and PLC allowing a programmer to move around freely. Lastly, Bluetooth has been used as a simple wire replacer between groups of I/O enabling machine modularity and portability. The Bluetooth Special Interest Group (SIG) certifies that products meet the standard ensuring interoperability of products from different manufacturers. Bluetooth uses FHSS and operates in the 2.4 GHz band, the same as b/g. When channels become overloaded, later versions Bluetooth use adaptive frequency hopping to remove overloaded channels from the hop sequence. This is one example of how wireless standards evolve to minimize interference between unlicensed technologies. Bluetooth is considered a very short range wireless technology. The standard identifies three classes of devices based on transmission power and approximate range. Class 3 devices (1 mw max) have an approximate range of one meter, Class 2 devices (2.5 mw max) 10 meters and Class 1 devices (up to 100 mw max) 100 meters. However, some Bluetooth installations with line-of-site easily exceed 100 meters. Because most Bluetooth applications are very short range with limited data exchange security may not be a critical concern. Regardless, as with any public standard security is important. Bluetooth uses a number of techniques to ensure secure transmission of data. Password protection ensures only devices with identical passwords can participate in the protected data communication. Additional security comes

10 Dickinson 10 from controlling the pairing process to determine which products can communicate. Also, devices can be made invisible so they cannot be discovered by other devices. WIRELESS SENSOR NETWORKS The IEEE standard defines the fundamental provisions of a low-power, wireless, mesh network that is the basis for several wireless standards including WirelessHART and ISA100.11a - part of the ISA100 family of wireless standards. Unlike other wireless standards, WirelessHART and ISA100.11a have been specifically developed for the industrial automation environment where reliability, robustness and security are critical. Both are low-rate, low-power, mesh networks operating in the 2.4 GHz band. Both employ channel hopping and DSSS for communications between the nodes and the gateway that connects the WSN to the plant network or host system. Although the two standards differ in scope and implementation, because they are based on IEEE there are commonalities in their general application relating to wireless field devices and the establishment of a wireless sensor network (WSN). As a general statement a WSN consists of nodes that are able to discover and communicate with neighboring nodes forming a mesh network that communicates to a host system via a gateway. Although a star topology is possible, a mesh network allows devices to connect and reconnect in any number of ways creating multiple, redundant paths that increase the reliability and range of the network. Another benefit of a mesh network is that nodes do not have to communicate directly with the gateway, only to nodes in close proximity. Shorter transmission distances translate into lower power requirements and enable the use of battery-powered field devices and other energy harvesting techniques. Truly wireless devices can be relocated as needed or used for temporary monitoring. Although a mesh network has many advantages there are limits in its application within an industrial process. As the mesh network increases in size so do the number of hops to get data from a node to the gateway. As the number of hops increase so does the latency of the system. This is not an issue when used for non-critical monitoring and control functions. A WSN can provide valuable information for asset management and process optimization that might have been difficult or impossible to obtain otherwise. WirelessHART and ISA100.11a are best suited for the process industries where there are higher densities of smart instrumentation; however, because they are true industrial, wireless standards both are expected to be widely deployed over time and further enhanced as each standard evolves. To ensure proper integration into current and future control architectures a more thorough understanding of each standard s performance and application considerations is highly recommended and is beyond the scope of this paper. The following information is offered to highlight broad distinctions between the two. WirelessHART WirelessHART is based on the HART (Highway Addressable Remote Transducer) protocol. HART was developed in the 1980 s by Rosemount Inc. as a protocol for smart instrumentation. HART allows the transmission of digital signals over 4-20mA analog signal lines and has been used primarily to commission and calibrate intelligent field devices. Originally proprietary, HART is published for free use without royalties by the HART Communications Foundation (HCF). The HCF is a not-for-profit organization that manages and controls the HART communications protocol. HART 7, the latest major revision of the HART protocol introduced WirelessHART as a physical medium for the protocol. WirelessHART has been adopted by the International Electrotechnical Commission (IEC) as an international standard, IEC Per the HCF, HART is the most widely used field communication protocol for intelligent process instruments with more than 30 million HART-enabled devices installed worldwide. In addition to the

11 Dickinson 11 primary process variable, HART provides access to other useful data available from a HART-enabled device such as device status, diagnostics and, additional measured and calculated values. In reality the vast majority of devices (85% per the HCF) use only the process data communicated via the 4-20mA signal. The additional data is stranded in the device. WirelessHART provides access to the stranded information via a wireless link without disturbing existing wiring. As a benefit of wireless mesh networking existing HART-enabled devices can be brought together into a WirelessHART network that easily can be expanded with new WirelessHART devices when needed. ISA100 ISA100 is a family of wireless standards developed by the International Society of Automation (ISA). ISA is a nonprofit organization that has developed standards and provided certification programs, educational programs, and conferences for industry for more than 65 years. Additionally, ISA is an accredited member organization of the American National Standards Institute (ANSI) and works with standards bodies around the world to develop and hone standards methodologies. The ISA100 committee establishes standards, recommended practices, technical reports and related information to define technologies and procedures for implementing wireless systems in automation and control system environments with a focus on the field level. The ISA100 committee also works with other ISA committees such as ISA99 (control system security) and ISA84 (process safety) that wish to incorporate wireless technology into future revisions of their work. The ISA100 Wireless Compliance Institute (WCI) provides independent testing and certification of wireless devices to the ISA100 standards. Planned additions to the ISA100 family of standards include support for backhaul functionality, factory automation, power management, asset and people tracking and other key-use cases. As noted previously ISA100.11a is part of the ISA100 standards, is based on IEEE and provides interoperability of ISA100 compliant devices comprising a wireless sensor network. A key difference from WirelessHART that supports only the HART protocol, ISA100.11a supports native ISA100 protocols and other protocols including wired HART. As a result ISA100.11a may offer greater flexibility in the establishment of a WSN especially when combined with other ISA100 standards currently under development. ISA100.11a is expected to become an IEC standard (IEC 62734) indicating its recognition as an international wireless standard. For more information on the WirelessHART and ISA100 standards visit or respectively. CELLULAR TECHNOLOGY Of all the wireless technologies available to the general public none has had a greater impact as Cellular. Cellular has empowered smartphone technology and provides instant global connectivity. Cellular is proving useful for industry as well especially for the SCADA industries where communications with geographically dispersed assets is a common requirement. Traditionally telemetry has relied on a variety of connection types for remote communications such as analog phone lines, wired network connections (copper, fiber, cable) and, wireless telemetry systems that can be costly and difficult to maintain. Users of cellular technology are able to leverage a highly capitalized wireless infrastructure providing global connectivity that would be cost prohibitive or impossible with traditional telemetry systems. In industry there are many applications well-suited for cellular technology such as remote monitoring and control, data logging and, machine-to-machine (M2M) applications. Consideration must be given to the suitability of cellular for time-critical or mission-critical functions. Although cellular networks have very high up-time, when loss of communications would result in loss of critical functions, cellular may not be appropriate unless there is no other means of communication.

12 Dickinson 12 It is hard to image anyone who doesn t already have a good understanding of cell phone technology, at least in terms of personal communications. Regardless, even experienced users can be confused by the cellular jargon commonly heard on TV commercials for cellular providers. Since its inception there have been several major advances in cellular technology beginning with 2G (second generation) that was widely deployed in the 1990 s, followed by 3G in the mid-2000 s and now, 4G. It s important to note that the designation of a generation is a generic term that does not specify a particular technology. Generally, a new generation implies a significant increase in data transmission rates without backward compatibility to the previous generation. The tremendous cost of upgrading the cellular infrastructure to a new generation technology means it takes many years to deploy a new generation nationally. Providers deploy the newest technologies in large metropolitan areas first, followed by increasing smaller populations. Such is the case with 4G service that now is readily available in large to medium population centers but won t be fully deployed in all areas of the US for a number of years. As noted, a generation label can represent multiple technologies. Common 2G and 2.5G technologies are GSM and CDMA. GSM (Global System for Mobile Communications) is the dominant cellular technology used around the world with estimates of 85% of all cellular devices employing GSM. Major providers in the US that employ GSM are AT&T and T-Mobile. Use of CDMA (Code Division multiple access) technology is generally limited to the US. Verizon is the major provider using CDMA technology for cellular communications. Currently 2G, 2.5G and 3G technologies are being commonly used for industrial applications although support of the 2G technologies is expected to be phased out in the coming years. The most common application is the transmission of process data between cellular modems via the cellular data network. Cellular can also be used to monitor and control remote operations through the use of SMS (Short Message Service) messages also known as text messages. SMS messages are sent via the voice network and can be useful for cost-effective annunciation of alarm and status conditions at remote facilities. A key issue with cellular is the recurring costs for monthly service. Depending on the provider there are a variety of call plan options for both data and texting. Data plan charges are based on the amount of data sent each month. Charges for text-only plans for SMS-based devices are usually based on the number of messages sent with each message costing a few cents. Unlimited text and data plans that are common with cell phones may not apply for SCADA or M2M applications. Although cellular service can be obtained directly from the major cellular providers users may find it helpful to work with the major resellers that specialize in M2M communications. These resellers have extensive expertise in M2M applications and offer call plans tailored to the needs of industrial users. This service is extremely helpful when data from multiple locations involve several service providers using different technologies and call plans. Additionally, the third party may offer web services that allow data collected from remote sites to be displayed on an internet web page or sent to a central database. Information can be easily accessed and operations monitored from any location with an internet connection. GENERAL COMPARISON OF WIRELESS Table 3 lists typical transmission distances and common industrial applications for the wireless technologies discussed in this paper. Transmission distances are influenced by many factors and can vary greatly even for the same wireless technology due to differences in transmission paths, antenna systems and application performance requirements. The chart is useful as a general guide in determining the suitability of a wireless technology for a given installation.

13 Dickinson 13 Wi-Fi a/b/g/n Proprietary Cellular Bluetooth WirelessHART ISA100.11a UHF/VHF Typical Range* Hundreds to thousands of feet Thousands of feet to several miles Global A few hundred feet A few hundred feet Many miles Frequency Band 2.4 / 5.8 GHz 900 MHz 850/900/ 1800/1900 MHz 2.4 GHz 2.4 GHz MHz Enterprise Ethernet Network SCADA Ethernet Network Serial Data Digital & Analog I/O Table 3: Typical transmission distances and applications for wireless technologies SUMMARY Wireless has a well-established role in industry today but its use will grow dramatically in the coming years as wireless technologies find mainstream acceptance and standards intended for industrial applications are further developed and deployed. Understanding the advantages and limitations of the various wireless technologies will allow users to realize the benefits of wireless while avoiding unnecessary costs and lost time resulting from its misapplication.

14 Dickinson 14 LIST OF ACCRONYMS ANSI CDMA DSSS EMI FCC FHSS IEEE GSM HART HCF I/O ISA ISM LAN M2M NIC OFDM PC PLC RF RFI RFID SCADA SIG UHF VHF VoIP WAP WCI WEP WLAN WPA WSN American National Standards Institute Code Division Multiple Access Direct Sequence Spread Spectrum Electromagnetic Interference Federal Communications Commission Frequency Hopping Spread Spectrum Institute of Electrical and Electronics Engineers Global System for Mobile Communications Highway Addressable Remote Transducer HART Communications Foundation Inputs/Outputs International Society of Automation Industrial, Scientific and Medical Local Area Network Machine to Machine Network Interface Card Orthogonal Frequency-Division Multiplexing Personal Computer Programmable Logic Controller Radio Frequency Radio Frequency Interference Radio Frequency Identification Supervisory Control and Data Acquisition Special Interest Group Ultra High Frequencies Very High Frequencies Voice over Internet Protocol Wireless Access Point Wireless Compliance Institute Wired Equivalent Privacy Wireless Local Area Network Wi-Fi Protected Access Wireless Sensor Network About the author: Don Dickinson has more than 28 years of sales, marketing and product application experience in Industrial Controls and Automation, involving a wide range of products and technologies in various industry segments. Don is the Senior Business Development Manager Water Sector, Phoenix Contact USA. He is the past chair of the NC AWWA-WEA Automation Committee and the current chair of the Automation Committee s Security Subcommittee.