LANCOM 1811n Wireless – LANCOM 1821n Wireless
Chapter 1: Introduction
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EN
Payload data rate: Airborne data transmission is fundamentally unreli-
able. Even small glitches in the WLAN system can result in errors in data
transmission. Check sums are used to compensate for these errors, but
these take up a part of the available bandwidth. The payload data rate
indicates the ratio between theoretically available bandwidth and actual
payload. 802.11a/g can operate at payload rates of 1/2 or 3/4 while
802.11n can use up to 5/6 of the theoretically available bandwidth for
payload data.
These two features increase the maximum useable bandwidth of 54 Mbps for
802.11a/g to 65 Mbps for 802.11n. This increase is not exactly spectacular,
but it can be further improved by using the following features:
MIMO technology
MIMO (multiple input multiple output) is the most important new technology
contained in 802.11n. MIMO uses several transmitters and several receivers
to transmit up to four parallel data streams on the same transmission channel
(currently only two parallel data streams have been implemented). The result
is an increase in data throughput and improved wireless coverage.
20 MHz
20 MHz
IEEE 802.11a/b/g:
48 carrier signals
IEEE 802.11n:
52 carrier signals
Gross bandwidth
Payload rate for 802.11a/b/g: 1/2
Checksum
Payload data
Payload rate for 802.11a/b/g: 3/4
Maximum payload rate for 802.11n: 5/6
