Installation guide

TD 92408EN
9 December 2011 / Ver. G
System Planning
Ascom VoWiFi System
25
7 AP Placement for Optimal Performance
There is a contradiction between the two essential requirements for optimal AP placement.
Good performance requires good coverage, but “over-coverage” will reduce the
performance.
As described in 5 Basic Cell Planning on page 18, enough
overlap between adjacent cells is
needed in order to have sufficient radio signal strength at all pla
ces and enough margin
when roaming between cells. However, the co-channel interference problem, described in 6
Co-Channel Interference on page 22,
is reduced by increasing the distance between APs
working on the same channel.
This means that for every unique combination in the ce
ll planning, these two requirements
must be proved against each other to obtain the optimal placement.
The AP distance to avoid co-channel interference is described in 6.1 Clear
Channel
Assessment, CCA on page 22. The CCA will not introduce any transmission interrupts if th
e
APs or STAs are separated to -76 dBm. However, if two APs on the same
channel are
transmitting at the same time, the VoWiFi Handset will require the interfering signal to be
attenuated at least 15 dB compared to their “own” signal.
Different systems have different RF characteristics i
n terms of co-channel interference
suppression, adjacent channel rejection and clear channel assessment. This might have
some effect and different systems behave differently with the same set-up.
It is important not only to think of coverage but also on people´s moving patterns, and
place the APs so it gives cover
age around corners, along walking paths and through thick
doors. For optimal coverage around corners, it is recommended to place an AP in the
crossroad, see figure 6 below.
Figure 8.
Figure 6. Recommended placement of AP to receive coverage around corners.