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Wireless LANs, Part 1

Wireless computer networks are becoming a hot item not only for residences, but for commercial installations as well. When installing a wireless system in a home, the main wireless panel will be installed next to or near the main telecommunications entrance to the home, and will connect directly to the broadband device a cable modem or DSL hub. From there, the signal will be distributed electromagnetically,

Wireless computer networks are becoming a hot item not only for residences, but for commercial installations as well.

When installing a wireless system in a home, the main wireless panel will be installed next to or near the main telecommunications entrance to the home, and will connect directly to the broadband device — a cable modem or DSL hub. From there, the signal will be distributed electromagnetically, with each connected device being fitted with a receiver and connecting hardware.


Although hard-wired broadband installations will probably remain the most common type for some time, wireless is critically important for retrofitting existing homes for broadband service. Cabled systems have the advantages of both bandwidth and speed, and will be used in almost all new homes. But wireless is the answer for pre-existing homes. Very few people will want to fish new cables throughout a house, when they can just install a few pieces of equipment and get good service anyway. Fishing is slow, messy, destructive and requires the home owner to coordinate the broadband installer, plasterer, painter and perhaps a few other tradesmen. It is simply too difficult. Someone doing a major remodel might consider it, but very few others.

If you are familiar with the security business, you will remember that before wireless security systems, a lot of new homes got security systems, but not many existing homes. When good, inexpensive wireless security systems came along, everything changed: Lots of people bought wireless security systems for their existing homes. Today, wireless security systems keep many people employed. Broadband services should follow the same pattern.

The vast majority of homes in the United States are pre-existing, and the bulk of the long-term broadband installation market is there. Note, however, that work in existing homes will not be the initial rush. Right now, hard-wired (cabled) systems are making immense inroads, for the reasons we expressed earlier. For the moment, cabling is getting big quickly, and wireless is growing steadily, but less dramatically.

Broadband service becoming a new household utility will not happen overnight, especially for existing homes. It may become standard for new homes before long, but existing home owners will not be as eager to install broadband as new home buyers will be to have it built-in.

So, the likely acceptance pattern is cabled systems being bigger than wireless now, and wireless being bigger than cabled system five years from now — or at least something along those lines.


Wireless LANs frequently augment rather than replace wired LAN networks — providing the final few meters of connectivity between a backbone network and the mobile user. Some of the more common uses are:

  • Doctors and nurses using hand-held or notebook computers to deliver patient information instantly.

  • Small and/or mobile workgroups who need a quick network setup. (Teams of auditors, etc.)

  • To reduce the expense of moves, adds and changes to networks.

  • Temporary training sites.

  • Installing networked computers in older buildings where cabling is simply too difficult or expensive to install.

  • Retail stores or other locations that require frequent network reconfiguration.

  • Trade shows and similar situations where no local information technology people will be on-call.

  • As backup for mission-critical applications running on wired networks.

The primary benefits are:

  • Installation flexibility. Wireless technology allows the network to go where wire cannot go.

  • Reduced cost-of-ownership: While the initial investment required for wireless LAN hardware can be higher than the cost of wired LAN hardware, overall installation expenses and life-cycle costs can be significantly lower.

  • Scalability: (Another great computer term.) Wireless LAN systems can be configured in a variety of architectures to meet the needs of specific applications and installations. Configurations are easily and quickly changed.

  • Speed and simplicity of installation: Installing a wireless LAN system can be fast and easy and can eliminate the need to pull cable through walls and ceilings.

Wireless LANs should not be confused with wireless metropolitan-area networks (WMANs), packet radio often used for law-enforcement or utility applications or with wireless wide-area networks (WWANs), wide-area data transmission over cellular or packet radio. These systems are much more involved, more costly and have lower bandwidths.


Wireless LANs use electromagnetic waves (radio and infrared) to communicate information from one point to another without relying on any physical connection. The data being transmitted is superimposed on the radio carrier frequency, so that it can be accurately extracted at the receiving end. This is generally referred to as modulation of the carrier by the information being transmitted.

In a typical WLAN configuration, a transmitter/receiver (transceiver) device, called an access point, connects to the wired network from a fixed location using standard Ethernet cable. At a minimum, the access point receives, buffers and transmits data between the Wireless LAN and the wired network infrastructure. A single access point can support a small group of users and can function within a range of less than 100 to several hundred feet. The access point (or the antenna attached to the access point) is usually mounted high, but may be mounted essentially anywhere that is practical as long as the desired radio coverage is obtained. End users access the Wireless LAN through wireless LAN adapters, which are PC cards in notebook computers, ISA or PCI cards in desktop computers or fully integrated devices within hand-held computers. The adapters provide an interface between the network operating system (NOS) and the airwaves (via an antenna).

Refer to Fig. 1 (above) for a diagram of a simple wireless residential network.

The most simple Wireless LAN configuration is an independent (or peer-to-peer) WLAN that connects a set of PCs with wireless adapters. Any time two or more wireless adapters are within range of each other, they can set up an independent network. These on-demand networks typically require no administration or pre-configuration. Access points can extend the range of independent LANs by acting as a repeater, effectively doubling the distance between wireless PCs.


Wireless communication is limited by how far a system's signals can reach. Wireless LANs use small cells, called microcells to extend their system's range. This is similar (as the name would indicate) to cellular telephone technology. At any point in time, a mobile PC equipped with a Wireless LAN adapter is associated with a single access point and its microcell, or area of coverage. Individual microcells overlap to allow continuous communication within wired network. They handle low-power signals and “hand off” users as they roam through a given geographic area.

Manufacturers of wireless LANs have a range of technologies to choose from when designing a wireless LAN solution. Each technology comes with its own set of advantages and limitations.

A narrowband radio system transmits and receives user information on a specific radio frequency. Narrowband radio keeps the signal frequency very narrow. Undesirable crosstalk between communications channels is avoided by coordinating users on different channel frequencies. The receiver filters out all radio signals except the ones on its designated frequency.

Many wireless LAN systems use spread-spectrum technology, a wide-band radio frequency technique developed by the military for use in secure communications systems. Spread-spectrum is designed to trade off bandwidth efficiency for reliability and security. More bandwidth is consumed than in the case of narrowband transmission, but the tradeoff produces a signal that is stronger and easier to detect. If a receiver is not tuned to the right frequency, a spread-spectrum signal is picked up only as background noise. There are two types of spread spectrum radio: frequency hopping and direct sequence.


The distance over which radio signals can be used to communicate is a function of product design (including transmitted power and receiver design) and the propagation path, especially in indoor environments. Interactions with typical building objects, such as walls, metal and even people, can affect how the magnetic energy propagates, and thus the range and coverage that a system achieves. Radio waves can penetrate many indoor walls and surfaces.

The range (or radius of coverage) for typical Wireless LAN systems varies from less than 100 feet to more than 500 feet. Coverage can be extended by using microcells.


As with wired LAN systems, actual amount of signal transfer (also called throughput) in wireless LANs is dependent on the product and the set-up. Factors that affect throughput include number of users, type of system used and bottlenecks on the wired portions of the system. Typical data rates range from 1 to 10 Mbps. Users of traditional Ethernet LANs generally experience little difference in performance when using a wireless LAN. Wireless LANs provide throughput sufficient for the most common office applications, including e-mail, and multi-user databases.


Another of the root technologies for wireless networks is military communications. That's why security has long been designed into most systems and why wireless networks are more secure than most wired networks. Complex encryption techniques make it impossible for all but the most sophisticated to gain unauthorized access to network traffic. In general, individual nodes must be security-enabled before they are allowed to participate in network traffic.

Building a wireless LAN includes infrastructure costs, for the wireless access points, and user costs, for the wireless LAN adapters. Infrastructure costs depend primarily on the number of access points deployed; access points range in price from $1,000 to $2,000. The number of access points required depends on the required coverage region and the number and type of users to be serviced. The coverage area is proportional to the square of the product's range. Wireless LAN adapters are required for standard computer platforms, and cost from $300 to $1,000.


The unlicensed nature of radio-based wireless LANs means that other products that transmit energy in the same frequency spectrum can potentially cause interference with a WLAN system. Microwave ovens are a potential concern, but most Wireless LAN manufacturers design their products to account for microwave interference. Another concern is the co-location of multiple systems. While co-located systems from different vendors may interfere with each other, others coexist without interference. This issue is best addressed directly with the appropriate vendors.


Access Point — A device that transports data between a wireless network and a wired network (infrastructure).

IEEE 802.X — A set of specifications for Local Area Networks (LAN) from The Institute of Electrical and Electronic Engineers (IEEE). Most wired networks conform to 802.3, the specification for CSMA/CD based Ethernet networks or 802.5 the specification for token ring networks. An 802.11 committee is working on a standard for 1 and 2 Mbps wireless LANs.

Independent network — A network that provides (usually temporarily) peer-to-peer connectivity without relying on a complete network infrastructure.

Infrastructure network — A wireless network centered about an access point. In this environment, the access point not only provides communication with the wired network but also mediates wireless network traffic in the immediate neighborhood.

Microcell — A bounded physical space in which a number of wireless devices can communicate. Because it is possible to have overlapping cells as well as isolated cells, the boundaries of the cell are established by rule or convention.

Multipath — The signal variation caused when radio signals take multiple paths from transmitter to receiver.

Radio Frequency (RF) Terms: GHz, MHz, Hz — The international unit for measuring frequency is Hertz (Hz). One Megahertz (MHz) is one million Hertz. One Gigahertz (GHz) is one billion Hertz. The standard U.S. electrical power frequency is 60 Hz, the AM broadcast radio frequency band is 0.55MHz to 1.6 MHz, the FM broadcast radio frequency band is 88 MHz to 108 MHz; microwave ovens typically operate at 2.45 GHz.

Roaming — Movement of a wireless node between two microcells. Roaming usually occurs in infrastructure networks built around multiple access points.

Wireless node — A user computer with a wireless network interface card (adapter).

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