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FAQ

General FAQ

Determining Where to Place Wireless APs

It is important to locate the APs close enough together to provide ample wireless coverage but far enough apart to not interfere with each other and increase the error rate. The actual distance needed between any two APs depends upon the combination of the type of AP, the type of AP antenna, and the construction of the building, as well as on sources of signal degradation, shielding, and reflection. For specifications and guidelines for placing wireless APs, see the manufacturer’s documentation for the APs and the antennas used with them.

Maintain the best average ratio of wireless clients to APs. The greater the number of wireless clients that are associated with the AP, the lower the effective data transmission rate. Too many wireless clients attempting to use the same AP degrade the effective throughput or available bandwidth for each wireless client. By adding APs, you can increase throughput. To increase the number of APs per wireless client, you must increase the number of APs in a given coverage area. You can move APs closer together up to a point before they start to interfere with each other.

To determine where to place the wireless APs:

1.

On the architectural drawings, place wireless APs so that each wireless AP is no further than 300 feet from an adjacent wireless AP.

2.

To test the wireless AP placement, perform a site survey:

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Temporarily place wireless APs in the locations specified on the architectural drawings.

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Using a laptop equipped with an 802.11 wireless adapter and site survey software (site survey software ships with most wireless adapters), determine the signal strength within each coverage area.

3.

In coverage areas where signal strength is low, make any of the following adjustments:

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Reposition existing APs to increase the signal strength for that coverage area.

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Reposition or eliminate devices that interfere with signal strength (such as Bluetooth devices or microwave ovens).

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If possible, reposition or eliminate metal obstructions that interfere with signal propagation (such as filing cabinets and appliances).

•

Add additional wireless APs to compensate for the weak signal strength.

It is important to remember that radio frequency is three-dimensional. It can be conceptualized as a sphere of signal.

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Purchase antennas to meet the requirements of your building infrastructure.

For example, to eliminate interference between APs located on adjoining floors in your building, you can purchase directional antennas that flatten the signal (forming a donut-shaped signal distribution) to increase the horizontal range and decrease the vertical range.

4.

Update the architectural drawings to reflect the final number and placement of the wireless APs.

Example: An Enterprise Corporation Determines AP Location

An enterprise corporation used information from the manufacturer of its APs and from internal testing to determine the best locations for their APs when using IEEE 802.11b. They determined that a 30-foot radius for each AP (with 60 feet between adjacent APs) would provide the best coverage without interference between the APs.

To assist them in designing AP locations, the IT staff created a plan view of the building, with one drawing per floor. The floor plans displayed the location, name, IP address, and channel information for each AP. Based on the information in the floor plans, the IT staff determined that they could locate their APs in the plenum area between the lowered ceiling and the next floor up, which simplified troubleshooting for the AP equipment.