802.11A Rf Modulation Standard - ASCOM VoWiFi System System Description

System Description
Ascom VoWiFi System
The 802.11b and 802.11g specifications include the following restrictions:
Radio Band:
Maximum Data Rate:
Operating channels:
Maximum number of non-overlapping channels:
Typical Indoor Range
Typical Outdoor Range (Line of Sight)
a. With basic antenna and maximum power level.
Figure 4. The 2.4 GHz band with three non-overlapping channels (1, 6 and 11).
The standard specifies data rates up to 11 Mbps for 802.11b and 54 Mbps for 802.11g, but
this must be considered as a theoretical maximum, only available within a limited distance
from an AP. More resilient coding schemes are needed to decode signals with lower strength
at the expense of data rate. Also, note that this is the maximum data rate, which means that
the maximum throughput is more likely to be half of that because of data headers etc.
As a client moves away from the AP, data rate is reduced, and consequently the throughput.
The average throughput is, as a rule of thumb, half of the data rate. Therefore it is important
that APs are not placed too far apart.
2.2.2

802.11a RF Modulation Standard

WLAN products based on the 802.11a standard operate in the 5 GHz frequency range. This
is an unlicensed frequency band called the Unlicensed National Information Infrastructure
(UNII) band. It is divided into the UNII-1 band (5.15–5.25 GHz), the UNII-2 band (5.25–
5.35 GHz), the UNII-2 Extended band (5.47–5.710 GHz), and the UNII-3 band (5.725–
5.825 GHz) (depending on country regulations).
The UNII band is divided into 23 non-overlapping channels (depending on country
regulations) with a bandwidth of 20 MHz. The centre frequencies are 20 MHz apart.
Originally the UNII-1 band was intended for indoor operation, the UNII-3 band for outdoor
operation, and the UNII-2 and UNII-2 Extended band for both indoor and outdoor operation.
This distinction has been removed for FCC. For ETSI the UNII-1 and UNII-2 bands are still
intended for indoor operation, and the UNII-2 Extended band for both indoor and outdoor
operation. Also, the maximum power levels are lower for ETSI than FCC. The UNII-2 band's
primary users are radar and satellite systems. To avoid interference, all unlicensed
transmitters operating in the UNII-2 band must be able to detect the presence of radar
signals and to dynamically and automatically change to a different transmit frequency if
radar is discovered, see section
use these bands for voice traffic.
Above the UNII band there is a small part of the ISM band that can be used by 802.11a
products as well (5.825–5.875 GHz).
7 September 2011 / Ver. G
a
:
a
:
2.6 802.11h on page 16.Therefore, it is not recommended to
2.4 GHz
11 Mbps (802.11b)
54 Mbps (802.11g)
1–14 (depending on country
regulations)
ETSI: 1–13
FCC: 1–11
3
30 m / 100 ft
120 m / 400 ft
TD 92313EN
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