Installation guide
TD 92408EN
9 December 2011 / Ver. G
System Planning
Ascom VoWiFi System
18
5 Basic Cell Planning
Cell planning for traditional cordless telephony systems (DECT) deals with coverage and
additional capacity reinforcement. Normally, a sufficient number of channels are available to
plan the cells for frequency reuse at a distance large enough to limit the effects of co-
channel interference.
2.4 GHz-radio b/g/n, VoWiFi Handsets
IEEE 802.11 operation in the 2.4 GHz band only pr
ovides the use of three non-overlapp
ing
channels, channel 1, 6 and 11. Use of other channels than 1, 6 and 11 has a negative impact
on performance in the system since those channels will interfere with each other. The usage
of channels other than 1, 6 and 11 will cause a performance reduction. This is not only due
to RF interference, but also due to the protocol specification.
Note: The use of 802.11n 40
MHz double channels i
s not recommended since the amount of
channels will be reduced to only two (ETSI) or one (FCC).
5.0 GHz-radio a/n, VoWiFi Handsets
In the 5 GHz band there are plenty of non-overl
a
p
ping channels to choose from. The specific
usage and amount of channels that can be used varies with country regulations. The
support of the 802.11d in an AP and in the VoWiFi Handset will automatically adjust the
usage to the so called regulatory domain.
The 5 GHz band consists of several sets of channels listed in th
e table below. See also
802.11a Radar
Protection, Dynamic Frequency Selection (DFS) on page 10.
Radio ET
SI FCC
2.4GHz, 802.11b/g/n 20MHz 3 3
5GHz, 802.11a/n 20MHz 4 + 15 (DFS) 9 + 12 (DFS)
2.4GHz, 802.11n 40MHz 2 1
5GHz, 802.11n 40MHz 2 + 7 (DFS) 4 + 5 (DFS)
Note: The VoWiFi H
and
set supports, but does not make use of, 40 MHz channel bonding.
The channels to support in the VoWiFi Handset can be configured using PDM, or the Device
Manager (IMS3 or UniteCM).
Note: For examples on channel placing layouts r
efer to manufacturers planning
documentation.
For a multi-cell system based on 802.11 the following factors affects the cell planni
ng:
• Coverage
• Capacity
•Roaming
• Noise interference
The wireless cell planning is done u
sing an AP placement tool which estimates the
placement of APs based on the building/campus characteristics. It is recommended that a
site survey is done using the built-in tools in the VoWiFi Handset. The tool provides a true
measurement of the RF environment based upon the radio of the VoWiFi Handset. Other
wireless analysers can be used to provide additional assistance during a site survey.
The basic approach to cell planning
is to ha
ve sufficient overlap between adjacent cells in
order to ensure that sufficient radio signal strength is present during a handover between