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PCE-N15 WLAN Card User Manual
24
ASUS WLAN Card
COFDM (for 802.11a or 802.11g)
Signal power alone is not enough to maintain 802.11b-like distances in an
802.11a/g environment. To compensate, a new physical-layer encoding technology
was designed that departs from the traditional direct-sequence technology being
deployed today. This technology is called COFDM (coded OFDM). COFDM was
developed specically for indoor wireless use and offers performance much
superior to that of spread-spectrum solutions. COFDM works by breaking one
high-speed data carrier into several lowerspeed subcarriers, which are then
transmitted in parallel. Each high-speed carrier is 20MHz wide and is broken
up into 52 subchannels, each approximately 300KHz wide. COFDM uses 48 of
these subchannels for data, while the remaining four are used for error correction.
COFDM delivers higher data rates and a high degree of multipath reection
recovery, thanks to its encoding scheme and error correction.
Each subchannel in the COFDM implementation is about 300KHz wide. At the
low end of the speed gradient, BPSK (binary phase shift keying) is used to
encode 125Kbps of data per channel, resulting in a 6,000Kbps, or 6Mbps, data
rate. Using quadrature phase shift keying, you can double the amount of data
encoded to 250Kbps per channel, yielding a 12Mbps data rate. And by using
16-level quadrature amplitude modulation encoding 4bits per hertz, you can
achieve a data rate of 24Mbps. The 802.11a/g standard species that all 802.11a/
g-compliant products must support these basic data rates. The standard also lets
the vendor extend the modulation scheme beyond 24Mbps. Remember, the more
bits per cycle (hertz) that are encoded, the more susceptible the signal will be to
interference and fading, and ultimately, the shorter the range, unless power output
is increased.
Default Key
This option allows you to select the default WEP key. This option allows you to
use WEP keys without having to remember or write them down. The WEP keys
generated using the Pass Phrase is compatible with other WLAN products. The
Pass Phrase option is not as secure as manual assignment.
Device Name
Also known as DHCP client ID or network name. Sometimes provided by an ISP
when using DHCP to assign addresses.
DHCP (Dynamic Host Conguration Protocol)
This protocol allows a computer (or many computers on your network) to be
automatically assigned a single IP address from a DHCP server.
E6557_PCE-N15_Manual.indd 24 4/8/11 2:56:52 PM