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Researching the Site

Which Type of Wireless LAN?

Intel(R) PRO/Wireless LAN adapter support a variety of network configurations, including 802.11b and 802.11a wireless LANs in both ad hoc and infrastructure modes. The following guidelines address the specific features of each type that must be taken into consideration when planning for installation of a wireless LAN.

802.11b and 802.11a Compared - What to Expect

The bullet items below provide an overview of the differences between the two types of wireless LAN. It is important to understand the strengths and weaknesses of each, in order to maximize overall system performance.

  • Range: Expect greater range from 802.11b, since technically the higher the frequency the faster the signal will decrease with distance.
  • Data Rate: Expect much greater throughput from 802.11a. At short range, this could be 4-5 times greater than that provided by 802.11b.
  • Reliability: Freedom from other legal signals in the same band makes 802.11a much less likely to have interference problems, which translates into better data transmission reliability.
  • Cost: 802.11a costs more to install, since more access points are required for a given area. However, on a "cost per transmitted bit" basis 802.11a is considerably less expensive than 802.11b.

With correct installation and implementation, both types of WLAN offer good performance. If speed and interference are not major considerations (for example, in a large open warehouse), 802.11b would be adequate. In a small office in a building with many other types of microwave devices, 802.11a would be a better choice. On-site testing via the site survey process is the best way to get accurate information on which type of network to use, or on how to create a network in a dual-mode 802.11b and 802.11a environment.

Note: A site survey done for an existing 802.11b network installation will not work for an 802.11a network that replaces the 802.11b network or is added to a site with an existing 802.11b network. A new site survey should be done and a new coverage area floor plan should be created.

Guidelines for Networks Using Dual 802.11a/802.11b Access Points

When designing and setting up an 802.11a and an 802.11b wireless LAN in the same location, using Intel(R) PRO/Wireless 5000 Dual Access Points, keep the following considerations in mind:

  • 802.11a and 802.11b devices differ in range, coverage, and channel specifications
  • Dual Access Points may provide greater coverage for 802.11b devices than for 802.11a devices. Site surveys involving Dual Access Points will need to consider the requirements for both technologies. In many cases it will be advisable to consider basing initial Access Point positioning primarily on 802.11a requirements, and then adjust 802.11b settings as needed.
  • 802.11b supports fewer non-overlapping channels than 802.11a. As a result, careful planning of channel selection and positioning is critical, especially for 802.11b networks using site surveys based on 802.11a requirements. 

Interaction with Wired Networks

Consider the degree to which the wireless LAN will interact with the conventional wired LAN. Some legacy systems, such as older mainframe networks, may not support WLANs without additional hardware or software.

Size and Shape of the Site

The size of the site determines what equipment you will need and where to place it. These parameters will be different for 802.11b and for 802.11a networks. See Which Type of Wireless Network for guidelines.

  • A small site requires fewer than 10 access points; two are usually sufficient.
  • A medium site requires between 10 and 20 access points.
  • A large site requires 20 to 100 access points and possibly some directional antennas.

The shape of the site is also a concern. Radio frequency (RF) transmissions propagate differently in a narrow space, such as a hallway, than in a large open area, such as an office filled with cubicles. Open doorways might also affect RF propagation.

Electrical Power

The right kind of power supply should be available for access points. The following are electrical installation alternatives listed in order of most to least desirable.

  1. Dedicated circuit with a Uninterrupted Power Supply (UPS) that also acts as a filter and surge suppressor.
  2. Non-dedicated circuit with a UPS.
  3. Non-dedicated circuit with a surge suppressor.

Configurations without a UPS are not recommended. A dedicated circuit is preferable to a non-dedicated circuit. Non-dedicated circuits have open receptacles; the load and type of use cannot be predicted at the time of installation. Although the current draw of the access points is minimal, other devices on the circuit can affect the access points.

If it is absolutely necessary to have a non-dedicated circuit, it is recommended that the circuit not support the following:

  • Non-network devices, such as lighting, powered directly from the circuit.
  • Devices with components that produce heat such as space heaters, laser printers, heat guns, soldering irons, or photocopiers.
  • Devices that often cause sudden sharp surges in the power line contain medium or large motors, such as electric staplers, refrigerators, floor cleaning equipment, air conditioners, fans, or any single device drawing more than 20 percent of the rated value the circuit.
  • Any combination of devices drawing more than 60 percent of the rated value of the circuit.

In all cases, the power to the access points must be unswitched and available 24 hours per day. It is recommended that the power never be provided from an energy management system.

Environmental Interference

Physical and environmental conditions affect the performance of wireless LAN equipment. Wireless LAN sites should not be excessively hot, cold, humid, or dusty. The area should also be relatively free of electronic equipment that generates background Radio Frequency (RF) noise, which can interfere with wireless LANs.

For optimal performance, do not locate access points near transformers, heavy-duty motors, fluorescent lights, microwave ovens, refrigerators, and other industrial equipment. See the site survey section for environment recommendations.

Signal loss can occur when metal, concrete, walls, or floors block transmission. Locate access points in open areas or add access points as needed to improve performance.

The Vertical Dimension

For simplicity, we talk of "moving around," but signals will also travel up and down. This can be good or bad, depending on your situation.

The good news is that, in a multistory building, you can usually communicate between floors using one access point. As usual, the actual range depends on the floor material, which can only be checked with a site survey. Expect some dead spots directly over (or under) large metal air conditioning ducts, and similar metal surfaces. The bad news is that another company on the floor above or below you may innocently install its own system, and, for example, place an access point directly below your desk. A bit of diplomatic mutual planning helps both systems to operate at maximum efficiency. The placement of access points, and the choice of channels, needs to be worked out between users.

Elevators

Some elevators are transparent to microwaves, and others act as a closed metal box. In the latter case, if network operation in the elevator is required, you may have to install an access point in the elevator. This requirement should be incorporated into your site survey.

Interference from Equipment and Materials

Some of the equipment and materials that can interfere with wireless LAN transmissions include:

  • Equipment that produces radio waves in the 2.4 or 5 GHz range
  • Existing wireless LANs
  • Cordless telephones or cordless telephone stations except for cellular telephones
  • Microwave ovens closer than three meters (ten feet) from the antenna
  • Radio frequency identification tags
  • Ceiling-mounted sprinkler heads closer than 60 centimeters (two feet) to the antenna
  • Outdoor broadcast television used by mobile television cameras
  • Uninterruptible power supply (UPS) devices
  • Pine trees with needles near wavelength or half wavelength
  • Large heat-producing machines or chambers
  • Fluorescent lights
  • Overhead cranes
  • Overhead conveyors
  • Elevator shafts
  • Heavy-duty motors
  • Lead paint
  • Plants and trees
  • Power surge protectors
  • Refrigerators
  • Sulfur plasma lighting
  • Transformers


Relative Attenuation of RF Obstacles

Obstruction

Degree of Attenuation

Example

Open Space

None

Cafeteria, courtyard

Wood

Low

Inner wall, office partition, door, floor

Plaster

Low

Inner wall (old plaster lower than new plaster)

Synthetic Materials

Low

Office partition

Cinder block

Low

Inner wall, outer wall

Asbestos

Low

Ceiling

Glass

Low

Non-tinted window

Wire Mesh in Glass

Medium

Door, partition

Metal Tinted Glass

Medium

Tinted window

Human Body

Medium

Large group of people

Water

Medium

Damp wood, aquarium, organic inventory

Bricks

Medium

Inner wall, outer wall, floor

Marble

Medium

Inner wall, outer wall, floor

Ceramic (Metal Content or Backing)

High

Ceramic tile, ceiling, floor

Paper

High

Roll or stack of paper stock

Concrete

High

Floor, outer wall, support pillar

Bulletproof Glass

High

Security booth

Silvering

Very High

Mirror

Metal

Very High

Desk, office partition, reinforced concrete, elevator shaft, filing cabinet, sprinkler system, ventilator

Site Survey Overview

The key to successful setup and installation of your wireless LAN is the site survey. The main tools of the site survey are:

  • An access point, or a laptop, set up as the "transmitter." It should be mounted at the same height, and as close as possible to the same spot, as you plan to use for your final installation
  • Another laptop, on a cart, to use as the mobile receiver. It must be loaded with your site survey software
  • A copy of a building or area map, to plot your field strength data
  • If you are installing an 802.11b system, verify that all of the above-mentioned interfering systems, devices and gadgets are off, or if they must be on, that they are indeed turned on. In the event of problems, try turning all other systems off anyway, and repeat the tests. This will at least identify your problem area.

The Site Survey Procedure

The survey procedure is simple: Move around your area and plot the strength of your signal at various locations. Repeat the process for each intended access point location. As you move around, you will probably encounter some problems. Major area problems are usually associated with your "transmitter" location. If you placed the transmitter on a wall containing a metal air conditioning duct or similar metal surface, you will have a serious problem with range, and a very large dead spot. Move the transmitting unit and repeat the tests.

Localized problems can be due to some hidden building characteristic. If you draw connecting "equal strength" signal level lines on your map, it will help you visualize problem areas, and may hint towards the best method of addressing them. These tests will show you where to mount your access points, and how many you will need to get good building coverage.

Seamless coverage means that you can move around the entire coverage area, and always stay connected. This requires software that can detect the fact that your signal is dropping down at one access point, and going up at another, thus triggering a seamless handoff between them. Keep in mind that this process will not work unless there is a reasonable signal level overlap of the signals in the two areas. If you lay out your system without this signal overlap, the user will experience an annoying signal dropout as he moves around.

Done with your building survey? Now go outside your facility, and repeat the above measuring process. Check how far down the street your signal goes. You can move your transmitter to increase or decrease this range as appropriate.

For detailed information about conducting a site survey, see the Site Survey section of this guide. For instructions on how to use site survey software, see Using the Site Survey Tool.

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Copyright (c) 2003 Intel Corporation.