TD 92685EN
28 June 2012 / Ver. A
Troubleshooting Guide
Ascom i62 VoWiFi Handset
8
2. WLAN Overview
2.3 The Importance of Pre- and Post-Site Surveys
Modern site survey tools are valuable for pinpointing potential RF propagation problems,
especially for large sites.
Modern site survey tools can do a lot more than just create th
e traditional heat maps that
show the RF coverage areas from all access points. They can display co-channel interference
areas, Signal-to-noise ratio (SNR levels), rogue access points and more.
Furthermore, most tools also include a pre-sit
e survey WLAN CAD planning tool which a
designer can use to do a simulation of RF coverage by using building drawings for a site.
This computer based plan must be verified on place, once the APs have been installed and
configured, by doing a live site survey at the site.
This pre-site survey is an aid to help the designe
r to plan for the placements of the APs in a
new installation. The designer should make sure that the information gathered about the
site is:
• Accurate and complete regarding the layout of the site
• The materials use in the construction
of the building and their effects on RF propagation
are fully appreciated
• The types of antennas to be used and deployed are provisioned for
• The power levels to use are fully understood.
Otherwise, the result of the survey will not a
ccurately represent the anticipated RF
propagation at the site. Performance problems will immediately manifest themselves once
the WLAN is commissioned.
If a pre-site survey was performed in the traditiona
l way, it should be followed up with a
post-site survey after a network is deployed. This can be done by an installer requesting the
site survey report and using the report to check that the installation is optimized for voice
and that AP configurations are consistent and compliant with the vendors
recommendations.
If the support engineer is subsequently required to visit a site
to troubleshoot problems, he
or she should initially verify that the content of the site survey still is accurate when it
comes to AP placements, traffic load, and channel plans, etcetera. Special attention should
be paid to areas where the layout of the building or concentration of VoWiFi clients may
cause problems. The site survey features built into the handset described later in this guide
are very useful in verifying the accuracy of the coverage predicted in the site survey and can,
in some situations, quickly identify holes in the RF coverage.
2.4 WLAN Dynamics
Consideration must also be made that a WLAN is not a one-time installation. It changes
constantly as people move around. The physical characteristics of the site may also change
over time as furniture is moved, office partitions are redesigned and walls are build or
removed. All of these factors can affect the propagation of RF signals.
2.5 Troubleshooting Implications and WLAN Design
It is beyond the scope of this guide to provide information about setting up a new WLAN to
accommodate voice traffic or upgrading a legacy WLAN to do the same, except to
emphasize the importance of those issues described in previous sections. In general, the role
of the support engineer should be one of troubleshooting a system that once appeared to
adequately meet the requirements of the enterprise (otherwise it wouldn’t have been
signed off) but is now experiencing problems because of physical site changes, increasing
personnel numbers, new applications and other factors that were never envisaged.
Documentation that was completed during the setting up and deployments of the new site
can therefore be a valuable reference in troubleshooting subsequent problems:
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