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.

Interference from Equipment and Materials

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

Some of the items above apply to 802.11b networks but not 802.11a networks, and vice versa.

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

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:

In all cases, the power to the access points must not be switched and available 24 hours per day. It is recommended that the power never be provided from an energy management system.

Size and Shape of the Site

The size of the site determines what equipment you need and where to place it.

The shape of the site is also a concern. 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.

 


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