Deploying Your Wireless APs

Deploying Your Wireless APs

It is important to locate the wireless APs close enough together to provide ample wireless coverage, but also far enough apart to not interfere with each other. The actual distance needed between any two APs depends on the combination of the type of wireless AP, the type of wireless AP antenna, and the construction of the building; as well as sources of signal degradation, shielding, and reflection.

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For specifications and guidelines for placing wireless APs, see the manufacturer s documentation for the wireless APs and the antennas used with them.

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

To deploy your wireless APs, do the following:

1. Perform an analysis of wireless AP locations based on plans of floors and buildings.

2. Temporarily install your wireless APs.

3. Perform a site survey analyzing signal strength in all areas.

4. Relocate wireless APs or sources of RF attenuation or interference.

5. Verify the coverage volume.

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

These steps are discussed in more detail in the following sections.

Perform an Analysis of Wireless AP Locations

Obtain or create scaled architectural drawings of each floor for each building for which wireless access is being planned. On the drawing for each floor, identify the offices, conferences rooms, lobbies, or other areas where you want to provide wireless coverage.

It might be useful to enable wireless coverage for a building in its entirety rather than for specific locations within the building. This type of coverage can prevent connectivity problems that might result from undocking a laptop from an office for use in a different part of your building.

On the plans, indicate the devices that interfere with the wireless signals, and mark the building construction materials or objects that might attenuate, reflect, or shield wireless signals. Then indicate the locations of wireless APs so that each wireless AP is no further than 200 feet from an adjacent wireless AP.

After you have determined the initial locations of the wireless APs, you must determine their channels and then assign those channel numbers to each wireless AP.

To select the channels for the wireless APs

1. Identify the wireless networks owned by other organizations in the same building. Find out the placement of their wireless APs and the assigned channel.

   Wireless network signal waves travel through floors and ceilings, so wireless APs located near each other on different floors need to be set to nonoverlapping channels. If another organization located on a floor adjacent to your organization s offices has a wireless network, the wireless APs for that organization might interfere with the wireless APs in your network. Contact the other organization to determine the placement and channel numbers of their wireless APs to ensure that your own wireless APs that provide overlapping coverage use a different channel number.

2. Identify overlapping wireless signals on adjacent floors within your own organization.

3. After identifying overlapping coverage volumes outside and within your organization, assign channel numbers to your wireless APs.

To assign the channel numbers to the wireless APs

1. Assign channel 1 to the first wireless AP.

2. Assign channels 6 and 11 to the wireless APs that overlap coverage volumes with the first wireless AP, ensuring that those wireless APs do not also interfere with other coverage volumes with the same channel.

3. Continue assigning channel numbers to the wireless APs, ensuring that any two wireless APs with overlapping coverage are assigned different channel numbers.

Temporarily Install Your Wireless APs

Based on the locations and channel configurations indicated in your plans-based analysis of wireless AP locations, temporarily install your wireless APs.

Perform a Site Survey

Perform a site survey by walking around the building and its floors with a laptop computer equipped with an 802.11 wireless adapter and site survey software (site survey software ships with most wireless adapters and wireless APs). Determine the signal strength and bit rate for the coverage volume for each installed wireless AP.

Relocate Wireless APs or Sources of RF Attenuation or Interference

In locations where signal strength is low, you can make any of the following adjustments to improve the signal:

• Reposition the temporarily installed wireless APs to increase the signal strength for that coverage volume.

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

• Reposition or eliminate metal obstructions that interfere with signal propagation (such as filing cabinets and appliances).

• Add more wireless APs to compensate for the weak signal strength.

TIP
If you add a wireless AP, you might have to change the channel numbers of adjacent wireless APs.

• Purchase antennas to meet the requirements of your building infrastructure.

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

Verify Coverage Volume

Perform another site survey to verify that the changes made to the configuration or placement of the wireless APs eliminated the locations with low signal strength.

Update Your Plans

Update the architectural drawings to reflect the final number and placement of the wireless APs. Indicate the boundaries of the coverage volume and where the data rate changes for each wireless AP.