Wireless LAN – WLAN
22
3.1
What is a Wireless LAN?
BAT54-Rail/F..
Release
7.54
06/08
U IEEE 802.11a: 54 Mbps
IEEE 802.11a describes the operation of Wireless LANs in the 5 GHz fre-
quency band (5,15 GHz to 5,75 GHz), with up to 54 Mbps maximum transfer
rate. The real throughput depends however on the distance and/or on the
quality of the connection. With increasing distance and diminishing connect-
ing quality, the transmission rate lowers to 48 Mbps, afterwards to 36 Mbps
etc., up to a minimum of 6 Mbps. The distance of transmission ranges from
up to 125 m in open expanses, in buildings typically up to 25 m. The IEEE
802.11a standard uses OFDM (Orthogonal Frequency Division Multiplexing)
as modulation scheme.
OFDM
In the 5 GHz frequency band, the OFDM modulation scheme is used for IEEE
802.11a. OFDM is a modulation scheme, which utilizes multiple independent
carrier frequencies for the signal transmission, and which modulates these
multiple carriers each with a reduced data transfer rate. Thus the OFDM
modulation scheme is very insensitive in particular to echoes and other im-
pairments and enables high data transfer rates.
Turbo mode
In ’turbo mode’, BAT Wireless Router base stations are able to use simulta-
neously two radio channels and can so increase the transfer rate up to max-
imum 108 Mbps. The turbo mode can be used in conjunction with the IEEE
802.11a standard between BAT base stations and WLAN wireless network
cards. The increase of the transfer rate must be switched on in the base sta-
tion, but can also reduce the transmitting power and the range of the radio
connection.
U IEEE 802.11b: 11 Mbps
IIEEE 802.11b describes the operation of local Wireless LANs in the ISM fre-
quency band (Industrial, Scientific, Medical: 2.4 up to 2.483 GHz). The max-
imum transfer rate is up to 11 Mbps. The real through-put depends however
on the distance and/or on the quality of the connection. With increasing dis-
tance and diminishing connecting quality the transmission rate lowers to 5,5
Mbps, afterwards to 2 and finally to 1 Mbps. The range of the transmission
distances is between up to 150 m in open expanses and in buildings typically
up to 30 m. Due to different frequency bands in use, IEEE 802.11b is not
compatible to IEEE 802.11a.
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