By Jai Belagur & Thomas M. Lebakken, P.E.
Until a decade ago, the utility industry had very few communication technology options to choose from, and those that were available were usually limited to supporting one application. In the last few years, however, there has been an explosion of new communication technologies-particularly in the wireless arena. Some are showing signs of maturity to support mission critical applications while others are worth a closer look. The most striking factors that make them worthwhile are their ability to support multiple applications, their compliance with industry standards, and their projected low costs of ownership.
Traditionally, utilities have relied on time-tested communication technologies such as analog leased lines, frame relay circuits and 900MHz wireless radio systems. Analog cellular, due to its excellent coverage, has been popular in some distribution automation implementations as well. However, all these technologies are capable of only supporting a handful of applications and many are proprietary in nature.
Somewhat interrelated and parallel developments in the automation and communication industries over the last decade have enabled substantial changes to take place. We truly seem to be in the middle of a revolution. The key enablers are:
- A general consensus within the automation industry that TCP/IP over Ethernet is the preferred solution;
- The emergence of wireless IP packet-based radio products that can support high bandwidth over long distances.
- Increasing support by relay, meter and device control suppliers of TCP/IP/Ethernet communications.
It is in this context that some of the newer wireless technologies offer distinct benefits both in terms of integrated solution and low costs.
Now established as an IEEE 802.11 standard, Wireless Fidelity or “WiFi” was originally developed to create and enable Ethernet access in conference rooms and to a local area network in a campus environment. In the last several years, WiFi applications have expanded to include public Internet access in coffee shops, hotels, airports and other locations, as well as private networks.
The 802.11 standard exists in three variants a, b and g. 802.11a operates in the unlicensed 5 GHz band between the frequencies of 5.15 GHz to 5.85 GHz. Speeds of 54 Mbps are achieved through implementing 64-level quadrature amplitude modulation (64QAM) to pack maximum amount of data possible.
802.11b and 802.11g differ from 802.11a at the physical layer, wherein the former transmits in the 2.4 GHz ISM band as compared to the 5 GHz band of the 802.11a. Consequently, they do not interoperate, but a significant benefit is they do not interfere with each other.
An emerging and promising application for some WiFi products is as a backhaul technology from substations. Some WiFi products when used with high-gain directional antennas can transport data more than 10 miles. Generally, however, utilities elect to use private 2.4-GHz spread-spectrum from their unlicensed list of product choices for substation-to-office backhaul vs. using WiFi.
The concept of using 802.11 or other high-speed wireless technologies as a community or utility network is starting to catch on. Within a utility enterprise, 802.11 is commonly used to support mobile workforce management data applications through the creation of “hotspots,” a term that has evolved to mean any wireless technology that has a central point with generally limited coverage but with bandwidth greater than 100 Kbps. Field crews can save valuable time by downloading work orders and service orders to their laptops via hotspots near substations. Laptops today routinely come equipped with an 802.11 modem at a cost of less than $30.
Utilities often are following two different tracks when using WiFi in the field as a hotspot technology. Many larger utilities have deployed laptops in their service vehicles and use their land mobile radio (LMR) system as the communications media. Because even the best LMR products can only deliver about 19.2 Kbps in bandwidth, adding WiFi in strategic locations can be helpful when accessing more bandwidth-intensive applications or for just shifting data off their shared LMR system.
Utilities that have not deployed a mobile service order program may also deploy WiFi hotspots as a cost-effective means to transport data for select applications (i.e. access to e-mail, remote access to SCADA, etc). Some WiFi products are made for outdoor use and are built with “carrier-grade” parts that are environmentally strong. Some products can come with the access point radio with an output power of 20 watts with coverage reaching up to a few miles. WiFi products for home use or coffee-shop use have output power of less than 1 watt and capabilities for less than 1,000 feet of coverage. Most WiFi works best when used while stationary vs. when the user is traveling at highway speeds.
The antenna design with WiFi is important. For most WiFi hotspot deployments an Omni (circular) antenna is most often used. When using WiFi as a backhaul technology, high gain directional antennas are used to blast the signal in a straight direction. Figure 1 illustrates this.
700MHz Broadband Technology
For some years now there have been wireless products that can deliver wide-area data with excellent coverage. They are available through an FCC license but are limited to about 33 Kbps in throughput. Other technologies (like 802.11) can deliver wireless broadband, but they often are limited to a few thousand feet of coverage and are unlicensed. However, the new 700-MHz products offer nearly 40 miles of coverage (more than 1,250 square miles), broadband speeds, and are licensed with frequency available through a frequency broker. Presently, there are six vendors with products available at 700 MHz.
The vendors of this equipment are likely not known to utilities as they come from the IP world, not the voice-radio world. Most of these players have strong financial backing and staying power.
Similar to what was described with the directional antennas of WiFi, the same type of antenna strategy can be used for 700 MHz. Therefore, sector antennas with a 90-degree radius are often used with 700 MHz. For 360 degrees of coverage, it is possible to combine four sector antennas together.
Wireless coverage is primarily a composite of the following:
- The spectrum used. Lower frequency spectrum propagates better than higher spectrum;
- The level of FCC approved output power of both the remote and master radios. The FCC defines the output power allowed on a product by product basis;
- FCC approved antenna gain; and
- Terrain and foliage.
Figure 3 reflects the impact of frequency and coverage.
Considering distance of propagation and bandwidth delivered, licensed 700-MHz products are very attractive to electric utilities. Figure 4 , on the next page, reflects a comparison of technologies.
Satellite technologies make it possible to provide communication access to remote and otherwise hard-to-reach areas. Compared to conventional solutions, satellite technologies offer the advantage of wide coverage, point-to-multipoint transmission capabilities, and seamless transmission independence from terrestrial communication infrastructure. Thus, on an affordable and timely basis, satellite technology could provide connectivity to substations and feeders located in rural and remote areas where terrestrial communication infrastructure is practically non-existent or its rollout is prohibitive.
Characterized by excellent coverage but low bandwidth and high latency, satellite communications can support some of the utility applications that are not sensitive to latency. Applications such as mobile workforce management and mobile data consisting of text e-mails can make use of satellite services for communicating with field crews in areas that have poor coverage through terrestrial networks.
Mobile cellular communications has experienced the highest growth in the past decade with a significant impact in the voice communication industry. Second generation (2G) services were provided on CDMA and GSM networks, with GSM being a late entrant in the North American market. 2G provides basic data services such as text messaging, while its later version, dubbed 2.5G, can provide higher data rates but is still limited in data throughput. The emerging 3G services provide higher data bandwidth that can support bandwidth-thirsty applications. Qualcomm’s original “High Data Rate” which is now referred to as CDMA 1XEV is currently being offered by Sprint as a business solution for mobile broadband data applications. Other major vendors such as Verizon and Cingular offer similar services. Claims are being made that users could experience data rates as high as 400 to 700 kbps with peaks around 2 Mbps.
Using cellular as a primary technology for key utility automation programs can present significant risk, but it does have its place as a “gap-filler.” For example, assume a utility has fiber for 10 percent of its substations in its urban areas. This is a big investment. It makes sense to place a new cellular service 2.5G/3G with a data-only service plan as a backup technology in the event the fiber is cut. Therefore, for about $20 per month, cellular could be used as a backup technology at a substation.
Let’s assume a utility selects spread-spectrum radio as the primary communications technology for distribution automation. The utility may be able to reduce some of the spread-spectrum costs by using cellular for some locations. Distribution automation often comes with slightly lower reliability expectations than other applications. Maybe 99.9 percent uptime is OK vs. 99.999 percent.
Cellular can also provide an attractive backup and gap filler for the land mobile radio system. Sometimes the cellular ability to support a private call and full duplex communications is very valuable. The challenge of deploying too many applications with cellular is the fact that during major events, the track record of cellular reliability is very poor.
Unlicensed Fixed Systems-802.16 (WiMAX)
Also known as WiMAX, 802.16 is a new and emerging standard that operates in 2 GHz to 66 GHz, both licensed and unlicensed spectrum. Backed by majors such as Intel, Fujitsu, Alvarion and Nokia, WiMAX is set to revolutionize the communication industry. The 802.16x IEEE standards define wireless networking protocols geared toward “metropolitan” area networks with a range of about zero to 35 miles. 802.16 starts from the premise of delivering broadband data to fixed points. The standards are in varying stages of development. 802.16a was ratified in January 2003 and holds a lot of promise for rural scenarios with non-line-of-sight connectivity. The 802.16e specification will extend WiMAX to mobile clients by means of PC cards. This would allow true mobile wireless connectivity at broadband speeds throughout a cell that is potentially 30 miles in radius. As an extension to 802.16a, the 802.16e architecture is optimized for (and backward-compatible with) fixed base stations.
Both 802.16a and 802.16e support robust quality-of-service (QoS) functionality that allows them to dynamically assign a modulation scheme that lowers throughput to increase range when necessary.
WiMAX has been in development for at least three years now, with product launches targeted for mid to late 2006. The success of broadband wireless access technologies has been restrained by the lack of interoperability between different manufacturers’ equipment and mass production of components built to a single standard. Therefore, the promise of WiMAX is designed to address the key objective of an open standard solution. This will allow equipment from a variety of manufacturers to work together just like WiFi presently does.
WiMAX will use orthogonal frequency division multiplexing (OFDM) as its modulation means. The WiMAX industry association is claiming that their products will be non-line-of-site. This will have to be determined on a case-by-case basis.
Several companies including Intel, Alvarion, Airspan, Fujitsu, Hughes Network Systems and Nokia have formed the WiMAX forum to promote the development of broadband wireless access networks that support the 802.16 standard. Utilities should watch closely for the developments of WiMAX in 2006.
Thomas M. Lebakken, P.E., is vice president of engineering at Power System Engineering, Inc. He has more than 18 years experience supporting utilities of all types coast-to-coast on automation system solutions that meet their business needs. Tom has experience with SCADA, substation automation, feeder automation, outage management systems, GIS, AMR, load management, system integration and a wide range of communication technologies.
Jai S. Belagur is an engineering consultant with Power System Engineering, Inc. Jai has more than 15 years of experience in electric utility system integration, radio systems for protection and SCADA, distribution system automation, SCADA project implementation, AMR, advanced metering infrastructure and load management applications. His current interests include IP networks for real-time applications, communications security and mobile work force management applications.