Installation guide

TD 92408EN
9 December 2011 / Ver. G
System Planning
Ascom VoWiFi System
39
This experience can be gained from installations performed, and from practical
measurements done in different typical environments either in situ or in the lab, and should
concentrate on the radio performance of a handset or laptop. The technician should also
gain this knowledge by using different brands of the same client type in different
environments.
The planning tool from Ekahau uses a normalization
prof
ile that is compared to a standard
client, which is defined for each vendor that is supported by the tool so the software can
calculate the recommended position for the APs. A technician may then compare the
performance of different clients.
If a site is using mixed clients of the same type, like for example two brands or series
of
VoWiFi phones, their performance in different environment must be fully understood.
Probably an installer only works with a couple of different APs which are very well
documented from
the vendor, and that he feels familiar with but he may meet a plethora of
different clients that need to be supported.
Each client has it its own design depending on what components are used for example,
an
tenna design, firmware and device drivers, power levels, housing etc.
This could mean that a WLAN where a specific type of WiFi phone works with sufficient
perf
ormance may not support another handset with the same voice quality. This has been
seen several times when the i75 has been chosen to replace other vendor’s handsets.
For laptops and other data clients, the differences between netw
ork card manufacturers are
less noticeable since most applications used by a laptop user are forgiving in their nature
due to the protocol used and that they normally do not have to roam.
We are likely to see more and more problems for different data clients as sm
aller devices
such as smart phones and handheld tablet/pad computers are used by staff ‘on the run’.
A.6.3 Can I Replace the i75 VoWiFi Handset
with the i62?
The i62 is designed to have similar perfor
mance as the i75. Nevertheless there are some
major differences between the two families of handset:
Radio chip different vendors are used, which of course use different
firmware and device drivers
Radio sensitivity due to the different chips used the radi
o s
e
nsitivity is different
RSSI measurements the software that calculates the RSSI values shown on the
screen is different for the
two phone models and thus the values
are not easily compared. For instance, the RSSI presented by the
i75 VoWiFi Handset is in general higher than the true value.
Roaming algorithm the firmware difference will re
sult
in different roaming
algorithms
Antenna design the i75 VoWiFi Handset antennas are optimized for
2.4 GHz
while the antenna in the i62 has to function at both 2.4 and 5
GHz and cannot be optimized to the same extent. The different
physical characteristics of the phones will also mean the
radiation pattern differs.
Typically the above topics are visible when a walk
-through of the site is done with a
connected phone call between the two
handsets. Reading the RSSI values at the same spot
may show differences and the handover location may be different for the two handsets.
Conclusion: