714
21 Wireless Local Area Networks
WLANs are fl exible data communications systems
implemented as an extension
or as an alternative for wired LANs. Using radio frequency (RF) technology, WLANs
transmit
and receive data over the air, minimizing the need for wired connections.
Thus, WLANs combine data connectivity with user mobility [3–6,8,14–16].
Recently, manufacturers have deployed WLANs for process and control
applications. Retail applications have expanded to include
wireless point of sale
(WPOS). The health-care and education industry are also fast-growing markets
for WLANs.
WLANs provide high-speed, reliable data communications in a
building or campus environment as well as coverage in rural areas. WLANs are
simple to install. Figure 21.2 provides application fi elds of WLANs.
In WLANs, the connection between the client and
the user is accomplished
by the use of a wireless medium such as RF or Infrared (IR) communications
instead of a cable. This allows a remote user to stay
connected to the network
while mobile or not physically attached to the network. The wireless connection
802.2 LLC
802.1 Bridging
802.11 MAC
802.11a
OFDM
5 GHz
802.11g
OFDM
>20 Mbps
802.11n
OFDM/
MIMO
>100 Mbps
802.11b
DSSS
Wi-Fi
PHY
