Figure 21.22 Applications of IEEE 802.16 (WiMax)

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21 Wireless Local Area Networks
range of 4 to 6 miles, because mobility makes links vulnerable. The WiMAX 
technology can also provide fast and cheap broadband access to markets that lack 
infrastructure (fi ber optics or copper wire), such as rural areas and unwired coun-
tries. WiMAX can be used in disaster recovery scenes where the wired networks 
have broken down. It can be used as backup links for broken wired links.
WiMAX can typically support data rates from 500 kbps to 2 Mbps. WiMAX 
also has clearly defi ned QoS classes for applications with different requirements 
such as VoIP, real-time video streaming, fi le transfer, and web traffi c. A cellular 
architecture similar to that of mobile phone systems can be used with a central 
base station controlling downlink/uplink traffi c (see Figure 21.22).
WiMAX is a family of technologies based on IEEE 802.16 standards. There 
are two main types of WiMAX today, 
fi xed WiMAX
(IEEE 802.16d — 2004), and 
mobile WiMAX
(IEEE 802.16e — 2005). Fixed WiMAX is a point-to- multipoint 
technology, whereas mobile WiMAX is a multipoint-to-multipoint technology, 
similar to that of a cellular infrastructure. Both solutions are engineered to deliver 
ubiquitous high-throughput broadband wireless service at a low cost. Mobile 
WiMAX uses orthogonal frequency division multiple access (OFDMA) technol-
ogy which has inherent advantages in latency, spectral effi ciency, advanced antenna 
performance, and improved multipath performance in, an NLOS environment. 
Scalable OFDMA (SOFDMA) has been introduced in IEEE 802.16e to support 
scalable channel bandwidths from 1.25 to 20 MHz. Release 1 of mobile WiMAX 
will cover 5, 7, 8.75, and 10 MHz channel bandwidths for licensed worldwide 
spectrum allocations in 2.3 GHz, 2.5 GHz, 3.3 GHz, and 3.5 GHz
frequency 
bands. Also, next generation 4G wireless technologies (see Chapter 23) are evolv-
ing toward OFDMA and IP-based networks as they are ideal for delivering cost-
effective high-speed wireless data services.
The WiMAX specifi cation improves upon many of the limitations of the 
Wi-Fi standard (802.11b) by providing increased bandwidth and stronger en cryption. 
Table 21.19 provides comparisons of Wi-Fi and WiMAX.
The 802.16 standard was designed mainly for point-to-multipoint topolo-
gies, in which a base station distributes traffi c to many subscriber stations that are 
mounted on rooftops. The point-to-multipoint confi guration uses a scheduling 
mechanism that yields high effi ciency because stations transmit in their scheduled 
slots and do not contend with one another. WiMAX does not require stations to 
listen to one another because they encompass a larger area. This scheduling design 
suits WiMAX networks because subscriber stations might aggregate traffi c from 
several computers and have steady traffi c, unlike terminals in 802.11 hotspots, 
which usually have bursty traffi c. The 802.16 also supports a mesh mode, where 
subscriber stations can communicate directly with one another. The mesh mode 
can help relax the line-of-sight requirement and ease the deployment costs for high 
frequency bands by allowing subscriber stations to relay traffi c to one another. In 
this case, a station that does not have line-of-sight with the base station can get its 
traffi c from another station (see Figure 21.23).
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Mobile WiMAX systems offer scalability in both radio access technology 
and network architecture, thus providing a great deal of fl exibility in network 
deployment options and service offerings. Some of the salient features supported 
by WiMAX are:

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