Wireless Local Area Networks

Sept. 30, 2002
The following is a greatly expanded version of the article, under the same title, which appeared in the October 2002 issue of Buildings magazine.Super Joe, the company’s most successful road warrior, spends much of his life in airports. He leaves home early Monday morning, and seldom returns before Thursday evening. His sales territory encompasses one-third of the country, and he is always on the go. In fact, he seldom gets back to the office – everything is done from his laptop, usually from a hotel room or the airport waiting room.The trouble: This airport waiting room thing is getting a bit tedious; he has to get there at least an hour before flight time, and although there is a lot of material to send back to the home office, there are seldom adequate facilities for doing that. Wouldn’t it be nice, thought Joe, if he could sit with laptop at the ready, check his e-mail, and conveniently communicate with his assistant at the office?What he needs is a wireless local area network (WLAN) that will allow him to contact the office without searching for a pay phone with a special attachment.Sam and Susan are a couple of up-and-coming business people. Both work; both have demanding jobs; both bring their work home. Sam’s home office is in the front guest bedroom, and Susan’s office is in the alcove off of the kitchen. And the two rooms are not adjacent to each other. Furthermore, their line of work does, in fact, require that certain files be shared – and copying a file to a disk and carrying it to the other computer is not something that thrills them. Furthermore, e-mail always seems to arrive at the wrong computer. Finally, they would like to share the fax machine and laser printer.What they need is a wireless local area network that will allow a sharing of material and equipment.But what is a local area network – and, more specifically, what is a home network? Rich Annibaldi, senior manager of technical research for Pioneer New Media Technologies, said at a recent Society of Cable Telecommunications Engineers’ Conference on Emerging Technologies, “… it is a system of interconnections among a variety of devices in the home.” Today, these networks are mostly interconnections among PCs and printers and fax machines. And, externally, the Internet. This means that any device so equipped (including other devices that would be better identified as appliances) can communicate amongst themselves.A wireless local area network is not the only approach to problems such as these. In the office, there is the wired LAN, a network that links all workstations and peripherals. (In general, a network will link a community of interests, such as a home, an office, a hotel lobby, or even an airport waiting room.)Ethernet, a transmission system invented by Xerox some 25 years ago, holds forth as the undisputed leader so far as wired LANs are concerned. In fact, Ethernet is used to implement 80 percent of the wired LANs in the United States. But the very thought of stringing miles of Cat 5 cable around an existing building to access each terminal is not pleasant.Phone lines can also be used. A new industry standard technology, called HomePNA (Home Phoneline Network Alliance), can be used simultaneously with phone conversations. This works fine in a home, where there are likely an abundance of phone outlets, but in an airport? Well, no. That’s not a good solution.Another method that might be appropriate for a home is use of the home’s electrical power lines. Simply plug an adapter into a standard 110-volt outlet, and you are in business. But once again, an airport waiting room or a hotel lobby make such an approach rather unsatisfactory.And that brings us back to the wireless LAN.There are two dominant approaches to satisfying the needs of the wireless local area network: Bluetooth, and what is known as WLAN, a system built around the IEEE 802.11 standards. The IEEE approach is generally called Wi-Fi (for Wireless Fidelity). Both Bluetooth and 802.11 operate in the unlicensed spectrum, and both operate at very high speeds. And both have a limited range. BluetoothBluetooth operates in the unlicensed, 2.4 GHz band. It’s range is short – only 30 feet or so. Although the speed is high—about 1 megabit per second, it is still 10 times slower than 802.11. Also, Bluetooth is something of an infant; although there are more than 2,500 members of the Bluetooth Special Interest Group, and billions of dollars have been invested in the technology, most carriers remain unconvinced. It would seem that it is hard to be accepted until you are accepted.Bluetooth employs a spread spectrum frequency-hopping technology, using several random frequencies within a 79 MHz range, and hops very quickly – 1,600 hops per second. This means it is relatively tolerant of interference, since it is at one frequency for a very brief period of time. At the chip level, Bluetooth has a distinct advantage. The chips are small and highly integrated, making it easy for manufacturers to embed the technology in devices. It has been suggested that the cost of a chip will be as low as $4 by the end of 2002. (A wild card is the constant suggestion that Bluetooth will be used to do more than just communicate. Chips will be embedded in appliances, and these appliances will be networked. Thus, just about anything can be controlled from just about anywhere. To-date, some 150 products have been qualified to work with Bluetooth).IEEE 802.11First of all, let us recognize that there are two 802.11 specifications: 802.11a and 802.11b.802.11a, the newest, operates in the 5 GHz band, while 802.11b operates in the 2.4 GHz band (as does Bluetooth). At the present time, the 2.4 GHz system is the most popular. Both 802.11a and 802.11b use direct frequency-spreading techniques, and are therefore somewhat more susceptible to interference than is Bluetooth. The range of both is about 300 feet.Which is better? Who can say. At the present time the IEEE standard system is in the lead, but that could change. The two are not mutually exclusive; they should be able to co-exist seamlessly. Both have, as their primary function, the elimination of cable within a facility. In all cases this will make for greater physical comfort; in many cases, it will make the difference between being able to communicate and not being able to communicate. (As Sky Dayton, founder of EarthLink, said, “When you’re sitting in an airport without an Internet connection, it’s like someone cut off your oxygen supply.”) As should be evident, both 802.11 and Bluetooth most likely will be used to build geographically specific access zones to deliver fast data services for indoor environments. As an example, if you walk into a Starbucks coffee shop with a properly equipped PC, you can quickly be on the Internet at true broadband speeds, as if you were connected by wire to a DSL line or cable modem. Bluetooth is fast (1 Mbps); Wi-Fi is faster (802.11b up to 10 Mbps, 802.11a up to 54 Mbps).Standards But it is still anybody’s ball game. The most discouraging part about the “contest” is that the wireless industry is faced with yet another set of standards. What with FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access), CDMA (Code Division Multiple Access), and GSM (Global System for Mobile Communications) in the wide area wireless networks, there is more than a little disappointment that a similar situation is starting to take place.3GIt has been suggested by some that wireless LANs will cannibalize 3G revenues; that the ease, convenience, and low cost of a wireless LAN will retard its growth. Others, however, see the two augmenting each other. 3G will provide broadband instant availability, and will be designed around mobility. WLANs, on the other hand, will be limited by their nature to semi-stationary applications. Furthermore, the complexity and performance limitations of 3G – not to mention the slowness of its coming – will likely encourage deployment of WLANs.MarketWithout question, one of the most logical applications for a wireless LAN is in the home. The Yankee Group estimates that by 2003 more than 25 million homes in the United States will have more than one computer. These are obvious candidates for a WLAN; a home so equipped will be able to share Internet access and costly peripherals such as printers. It will also be able to share data in an efficient and effective manner.According to Gartner Dataquest, the worldwide WLAN market should hit $1.7 billion in 2002, and $3.8 billion by 2006. Although these are large numbers, it has been suggested that with the reduction in cost of WLAN equipment, they actually underestimate the potential market impact. The company estimates that adapter shipments will rise from 5 million in 2001, to 9 million in 2002, and more than 40 million in 2006. Whether or not these numbers prove to be accurate, they indicate that there is, and will continue to be, impressive growth in the WLAN market.A Yankee Group study in 2000 placed the number of installed home networks at 650,000, and suggested this would rise to 10 million by the end of 2003.But don’t stop with the home; think of all the other potential applications.  Beyond airports, think also of office buildings, hotel lobbies, hospitals, shopping malls, and convention centers. In each of these, the computer user is, for at least a period of time, in a fixed location. He or she would like to be networked with other departments in the store, or with other back-office facilities in the hotel, or the laboratory of the hospital, or to the Internet from the vendor’s booth at the convention center. Think of the main lobbies of all those corporations, where a salesman is trying to “sell” and access to the Internet is essential, but scurrying about searching for a telephone outlet is hardly professional. Ultimately, third-generation cellular may absorb some of this traffic, but that is—or will be – a more expensive solution. And it’s not available yet.How is It Done?The days of stringing Category 5 cable through a hot attic, or along the outside of a home, are gone. A wireless LAN will do the job. And it’s really quite easy. Simply connect a universal serial bus (USB) adapter to the desktop computers and the appropriate peripherals and follow the instructions to install the software that comes with the adapter. By so doing, the user of any of the connected computers can share a dial-up Internet connection, or printers, or special drives. You might say that the unit connecting to the Internet operates much like the base station of a cordless telephone; air interface within the facility, and cable or wire or fiber outside the facility. The software (run on the computers to which the adapters are attached) is quite simple: “Would you like to connect this computer to your home network? Would you like to share your hard drive and your printer?” When this is done, all the computers and devices in the home office with wireless adapters attached to them can simultaneously access each other, or the Internet, through the multi-user modem.SecurityYes, security poses a problem. Users, and potential users, are concerned about transmitting credit card numbers across a wireless LAN. Are there answers? Of course; coding techniques that “guarantee” privacy can be employed – but for every engineer who can create a security protocol there is another who can break it. The jury is still out on this one.IntegrationIs there an advantage to being part of a national system? Perhaps. Fragmentation is usually not a good idea. And if a national system would encourage a consistent standard, a consistent method of operation, and perhaps economy of scale, then why not?Some people are betting on it. Sky Dayton, the founder of EarthLink, is pushing his newest venture, Boingo Wireless in trying to unite a growing number of independent Wi-Fi networks. The network, if you can call it that, will be based on the IEEE 802.11b Wi-Fi standard. Currently, he has just more than 500 access points in its system, but insists that by the end of 2002 there will be 5,000. Is there a market? Dayton claims that there are an untold number of small businesses, such as coffee houses, bars, and restaurants. At a higher level, of course, there are hotels, airlines, convention centers, clubhouses, and shopping malls. John Stanton, chairman of mobile giant VoiceStream Wireless, says, “I view Wi-Fi to be 3G with training wheels. It’s so early that it’s still hard to see how relationships between carriers – and I’ll use that term loosely, but I think it needs to be more broadly defined – are going to evolve.”Dayton agrees. “At some point, it’s going to be, ‘Your chocolate fell into my peanut butter,’ and we’ll have the ideal network for everyone.”Campus WLAN DesignSo far we’ve talked about relatively small geographic areas – hotel lobbies, airport waiting rooms, private homes, and the like. But what happens if a total campus, or a huge office building, or a sprawling mall, must be interconnected? The range of each wireless LAN is short, so somehow we must interconnect several – even many  – wireless LANs. But there is the ever-present danger of interference – just as there is in cellular systems if the engineering is not done right.Fortunately, we can take a page from the book of the cell phone operators, and use the short range of the system to our advantage.In the case of WLANs, operating at a base frequency of 2.4 GHz, there is a bandwidth of 83.5 MHz available. There are up to 11 channels that can be used, but they must be used judiciously, since they overlap from a frequency standpoint, and thus can interfere with each other. Fortunately, channels 1, 6, 11 do not overlap with each other, and therefore may be used adjacent to each other. This overlapping system can be continued as is done with the layout of cellular radio, and we never run out of available cell frequency channels. (802.11a, operating at 5 GHz, offers eight non-overlapping channels).This seems simple enough, but all too frequently the campus (or building, or airport, or mall) we are attempting to cover is not geographically simple. For instance, it may be appropriate to place an access point (with antenna) at the corner of an office building. Certainly, the antenna (if it is omni-directional) will “see” rooms within its range within the building – but it will also see things that are outside the building, and this may not be what is desired. In this case, directional antennas may be used – and, in fact, because we are often dealing with three-dimensional structures, we must consider the up/down view of the landscape as well as the right/left view. In short, a good knowledge of RF technology, and the lay of the land, will permit almost any large geographical area to be covered by a wireless LAN.ConclusionThe LAN is exactly what it is purported to be: a local area network. The LAN can be of several forms: Hard wired, using Category 5 cable. This is the conventional method in offices across the country. Ethernet is used as a transmission means, frequently at 10 Mbps; occasionally at 100 Mbps.Wired, using the telephone wires already in place. Usually the twisted-pair phone line is divided (frequency wise) into three parts: from 0 to 3.4 kHz handles the plain old telephone services; the midrange of 25 kHz to 1.1 MHz is used for ADSL; and the top area, about 4-10 MHz, is used for home networking. A new industry standard technology called Home Phoneline Network Alliance has made it possible to send computer data at speeds of up to 10 Mbps over a home’s existing phone wires.Wired, using 110-VAC power wiring. Power outlets are everywhere, so the desirability of this approach is understandable. Unfortunately, security is poor, since the transmitted signal can travel outside of the building as well as inside.Wireless, using one of several standards. IEEE Standard 802.11b operates at a base frequency of 2.4 GHz, and can transmit at 11 Mbps. IEE Standard 802.11a operates in the 5 GHz band, and can transmit at up to 50 Mbps. Bluetooth operates in the 2.4 GHz band, and can transmit 1 Mbps.These systems are not designed with mobility in mind. They are small in size, and expanding a system to include a plurality of “cells” is not all that easy. But they are designed for convenience and high-speed data transmission. Above all, they obviate the need for stringing miles of cable. As a realtor from Raleigh, NC, notes, “If you’re faced with stringing new Cat-5 wiring, a wireless LAN is going to be your savior.”Read L. Ballew, P.E., is senior vice president at Carter & Burgess (www.c-b.com), a Fort Worth, TX-based engineering consulting firm.

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