Controller Based WLANs

How should I space my APs for optimum Wi-Fi voice coverage?

Aruba Employee

Product and Software: This article applies to all Aruba controllers and ArubaOS versions.

 

Although nearly all currently-available Wi-Fi phones support only 2.4 GHz radios (802.11b and 802.11g), the infrastructure should support 802.11a/b/g everywhere, because the 5 GHz band (802.11a) has many more available channels and is less prone to interference.

 

Wi-Fi coverage for voice requires more planning than for data users, due to the importance of avoiding dead spots. This is a significant concern because people are inclined to attempt voice calls from places where they would never think of using their PC. The best practice today is to upload a floor plan to the Aruba RF Plan or VisualRF planning tool to identify access point (AP) locations, and then perform a "walk-around" site survey to identify any special situations such as large metal objects, thick reinforced concrete walls, and so on.

 

For voice, continuous coverage is important, but the APs should not be too close together. Very closely-spaced APs result in extra handover events and can make it more difficult for the client to make a good handover decision. The usual parameters for a planning tool would be for a minimum data rate of 6 Mb/s (802.11g) with a 50% overlap between cells (in the Aruba planning tool, set overlap to 150%). As a general rule, it is best to have a minimum RF coverage of -67 dBm and not higher.

 

AP spacing will generally be about 20-25 meters (60-75 feet) for data-only networks and 15-20 meters (45-60 feet) where voice is used. Modern WLANs automatically adjust AP transmit power levels and channels for optimum coverage after the APs are installed. The objective should be to install APs more densely than would be necessary if all APs were running at maximum power (consistent with the 6 Mb/s minimum data rates suggested here).

 

Polycom recommends that their phones have a minimum of -65 dBm for 802.11a band phones. Vocera requirements are different, and this article does not cover the use of Vocera phones.

 

For more information, see the "Understanding Design Principles for Roaming Devices" chapter in the Virtual Optimizing Aruba WLANs for Roaming Devices document.

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Last update:
‎07-02-2014 06:39 PM
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