User's Manual

AppendixD:GlossaryofTerms
3Com®AirProtectPlannerUserGuide
113
802.11b supports bandwidth up to 11 Mbps.
802.11b uses the same radio signaling frequency
– 2.4 GHz, as the original 802.11 standard. Being
an unregulated frequency, 802.11b gear can incur
interference from microwave ovens, cordless
phones, and other appliances using the same 2.4
GHz range. However, you can easily avoid
interference by installing 802.11b gear at a
reasonable distance from other appliances.
Vendors often prefer using unregulated
frequencies to lower their production costs.
802.11g Wireless Protocol
In 2002 and 2003, WLAN products supporting a
new standard called 802.11g began to appear on
the scene. 802.11g attempts to combine the best
of both 802.11a and 802.11b. 802.11g supports
bandwidth up to 54 Mbps, and it uses the 2.4 GHz
frequency for greater range. 802.11g is
backwards compatible with 802.11b, which means
that 802.11g APs will work with 802.11b Wireless
Network Adapters and vice versa.
802.11n Wireless Protocol
This is an emerging standard for wireless local
area networks that promises higher data rates and
longer range as compared to its predecessors
802.11a, b, and g. 802.11n brings many new
features at the medium access control and
physical layers (for example, multiple-input-
multiple-output (MIMO), wider 40 MHz channels,
frame aggregation).
MIMO configuration
Multiple-Input-Multiple-
Output configuration
Multiple-Input-Multiple-Output (MIMO) stands for
multiple radio chains at the transmitter and
receiver, often depicted as n x m, where n is the
number of transmitting radios and m is the
number of receiving radios. MIMO can be
leveraged in many ways for increasing the range
of a WLAN using spatial diversity and for
increasing the data transmission rate using spatial
multiplexing. Spatial diversity is achieved by
transmitting or receiving copies of the same signal
over multiple radios. Spatial multiplexing is
achieved by transmitting and receiving unique
data streams over multiple radios. The maximum
number of spatial streams is limited by min (n,
m), that is, the minimum among the number of
radio chains at the transmitter and receiver. IEEE
802.11n draft 2.0 makes it mandatory for APs to
support a minimum of two spatial streams and
support for up to four streams optionally.
Channel width
Legacy 802.11 protocols operate on 20 MHz
channels. IEEE 802.11n allows bonding of two 20
MHz channels so that a net channel width of 40
MHz can be used. In 40 MHz mode, one channel is
assigned as the “primary” channel and the other is
assigned as the “secondary” channel. The
secondary channel is identified as “upper” or
“lower” with respect to the primary channel. For
example, in 2.4 GHz, if channel 6 is the primary
channel then channel 10 could be assigned as the
upper secondary and channel 2 as the lower
secondary channel.
Guard Interval (GI)
The guard interval is the spacing between
consecutive symbol transmissions. IEEE 802.11n
draft 2.0 prescribes a mandatory long Guard
Interval of 800 ns and an optional short Guard
Interval of 400 ns.