Lancom Systems LCOS 3.50 - Manual (Page 204)

LANCOM Reference Manual LCOS 3.50 ̈ Chapter 11: Wireless LAN – WLAN
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IEEE 802.11a: 54 Mbps
IEEE 802.11a describes the operation of Wireless LANs in the 5 GHz frequency
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 connecting quality, the
transmission rate lowers to 48 Mbps, afterwards to 36 Mbps etc., up to a min-
imum 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 mod-
ulation scheme is very insensitive in particular to echoes and other impair-
ments and enables high data transfer rates.
Turbo mode In ’turbo mode’, LANCOM Wireless base stations are able to use simultane-
ously two radio channels and can so increase the transfer rate up to maximum
108 Mbps. The turbo mode can be used in conjunction with the IEEE 802.11a
standard between LANCOM base stations and AirLancer 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.
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 maxi-
mum 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 com-
patible to IEEE 802.11a.
DSSS For shielding against interferences by other transmitters, which have possibly
the same frequency band, the DSSS procedure (Direct Sequence Spread Spec-
trum) is used for IEEE 802.11b in the 2,4 GHz frequency band. A transmitter
normally uses only a very narrow range of the available frequency band for