Installation guide

TD 92408EN
9 December 2011 / Ver. G
System Planning
Ascom VoWiFi System
11
The following table lists the DFS and non-DFS channels on the 5 GHz band:
Band Channel ETSI (EU/EFTA etc) FCC (US etc)
UNII-1 36,40,44,48 Non-DFS Non-DFS
UNII-2 52,56,60,64 DFS DFS
UNII-2e 100,104,108,112,
116,120,124,128,
132,
136,140
DFS DFS
Note: 120, 124,
128 excluded.
a
a. For the FCC regulatory domain US and others countries the following
rules apply for the
UNII-2e band: 
- Devices will not transmit on channels which overlap the 5600
- 5650 MHz band (Ch 120,
124 and 128).
- For outdoor use any installation of either a master or a client de
vice within 35 km of a
Terminal Doppler Weather Radar (TDWR) location shall be separated by at least 30 MHz
(center-to-center) from the TDWR operating frequency. Table of current TWDR are to be
found in the FCC document “443999 D01 Approval of DFS UNII Devices v01” located at: 
https://apps.fcc.gov/kdb/GetAttachment.html?id=33781
UNII-3 149,153,157,161 n/a Non-DFS
ISM 165
Due to the regulations of the DFS channels, a client that does not
support radar detec
tion is
not allowed to actively scan for APs in these channels. The client will then have to perform
passive scanning which means that it only listens for beacons. For a voice client, this will
affect an ongoing call to some degree by introducing a slight increase in jitter in the voice
stream.
The VoWiFi Handset can use the DFS channels, b
ut t
he voice quality may be distorted and
roaming delayed. The DFS channel scan algorithm is optimized and uses both passive
scanning and active scanning when it is regulatory ensured that transmitting is allowed.
Note: Since the passive part of the scan phase is limited to 70 m
s, a beacon interval of less
than 70 ms (e.g. 60 ms) will give the best roaming performance.
2.4 802.11 n-radio Support in the VoWiFi Handset
The 802.11n standard uses advanced radio technology to boost high throughput levels and
more resilient communications links. This is achieved by using multiple antennas and
multiple radios in the WLAN equipment (MIMO). The technology can be used to achieve
higher speeds or extend the coverage area, where higher speeds will be available further
from the AP, and thus the transmission will take shorter time compared with a 802.11a/g
transmission.
In the 802.11n specification, a tighter use of the protocols has resulted in less overhead and
bett
er use of the channel. Th
is will improve the max speed from 54 Mbps to 75 Mbps.
In 802.11n networks it is also possible to double the
throughput by using channels twice as
wide (40MHz) than the 802.11b/g/a standards are using (20 MHz). The technique is called
channel bonding and combines two adjacent channels into a wider channel, and thus
effectively reduces the amount of channels to half.
The standard allows the use of clients that support single ch
annel or double channel width
at the same time, but with a reduced set of channels.
The 802.11n standard also allows the use of very large frames to redu
ce the amount of
ACKs needed. This reduces the large overhead known in WiFi, and throughput is raised
dramatically from the traditionally 50% up to 90% of the max bandwidth..