Wi-Fi Technology
The IEEE 802.11n standard was conceived with the goal of increasing wireless local area
network (WLAN) data throughput to a theoretical level of 540Mbps, or 10 times the speed
of 802.11g. Built on OFDM technology used in the 802.11g standard, 802.11n achieves its
higher throughput, in part, by increasing channel spectrum from 20MHz to 40MHz.
In addition to increasing channel utilization through MAC aggregation techniques, 802.11n
also incorporates multiple antennas using a scheme called multiple-input multiple-output
antenna technology, or MIMO. MIMO provides spatial diversity and spatial multiplexing for
increased range and throughput, respectively. A summary of the IEEE 802.11 standard
features is shown in the table below.
The 802.11n standardization process has not yet been completed, and 802.11n remains a
pre-standard as debate continues about final details of the standard. 802.11n consumes
two of the three non-overlapping 2.4GHz channels. In a pure 802.11n network this is not an
issue, however, it is a problem in a hybrid network. Chipset manufacturer Airgo Networks1
has publicly stated that pre-standard 802.11n products would degrade or even disable
existing 802.11b and 802.11g networks, and the following graphic depicts the conflict.
Additionally, 802.11n uses OFDM modulation, while 802.11b does not. This means that if
OFDM clients want to communicate in the presence of 802.11b clients, they must use the
slower and less-efficient 802.11b protocol to protect any higher-rate OFDM transmissions.
Failure to do so will affect both 802.11b signaling and 802.11n throughput. Pre-standard
802.11n-based devices now on the market, most of which are consumer products, have
been confirmed to cause interference with 802.11b/g devices.
The 802.11n standard is expected to be ratified in 2007, and wide-scale enterprise
adoption of 802.11n should commence in 2008. Concerned about interference with
existing WLAN infrastructure and clients, IT managers are seeking assurances today that
WLANs they purchase now can coexist with 802.11n networks that are deployed in the
future.
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