Digital Signal Processing Reference
In-Depth Information
Figure 15-1.
802.11-based network communications scenario.
ously unconnected places, like shopping malls, libraries, trains and other means
of mass transportation, even private motor vehicles. As soon as seamless inte-
gration with wide-area coverage provided by 2.5G/3G cellular wireless infras-
tructures is reached, wireless access will likely become the most common form
of network access for an increasing number of users.
The IEEE 802.11 WLAN standard, based on the definition of the medium
access control (MAC) protocol and the physical layer (PHY) specifications, be-
came available in 1999 [1] and since then has emerged as the most success-
ful and most widely deployed WLAN standard. Figure 15-1 shows a simple
802.11-based network scenario, with two mobile stations and an access point
(AP) connected to a wired LAN.
So far, the main usage of Wireless LAN's has been limited to Internet based
services like Web browsing, e-mail, and file transfers. However, as already hap-
pened in the traditional wired LAN's, a strong interest is emerging towards mul-
timedia applications over WLAN's. Among them, interactive voice commu-
nication looks particularly appealing. WLAN-based telephony, in fact, could
not only replace and significantly extend traditional cordless telephony, but also
compete with cellular telephony in at least a certain number of scenarios. More-
over, such technology would have all the typical Voice over IP advantages, in-
cluding a single infrastructure for both data and voice, greater flexibility with
respect to traditional telephony, and the possibility of introducing new value-
added services.
