Figure 21.22 Applications of IEEE 802.16 (WiMax)

Figure 21.22 Applications of IEEE 802.16 (WiMax).
21.15 World Interoperability for MicroAccess, Inc. (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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