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Wire and Wireless Communication Applications Chap. 8
TABLE 8–17
WIFI STANDARDS
Item 802.11a 802.11b 802.11g 802.11n
Band 5.0 GHz 2.4 GHz 2.4 GHz 2.4 GHz
Max data rate 54 Mb/s 11 Mb/s 54 Mb/s 120 MB/s
Modulation OFDM DSSS OFDM DSSS & OFDM
Bandwidth (typical) 20 MHz 20 MHz 20 MHz 20 MHz
Diversity None None None MIMO
Range (max) 500 ft 500 ft 500 ft 1,500 ft
Compatible with 802.11a 802.11b 802.11b, 802.11g
DSSS = Direct-sequence spread spectrum
MIMO = Multiple input and multiple output
WiMAX
The WiMAX concept is completely different from the WiFi concept. WiMAX is more like a
cellular telephone system. It is designed strictly for data transmission and it is connected to
the internet. WiMAX is a WMAN (Wireless Metropolitan Area Network) and the WiMAX
standards are developed and approved by the IEEE 802.16 Working Group.
WiMAX base-station antennas are placed at elevated locations, such as on the top of
buildings or towers, and they can share tower space on cellular telephone towers.
The WiMAX system service provider may operate in one of two different ways:
Licensed Service or Unlicensed Service. For licensed service the operator has to buy
spectral space and a license for WiMAX service from the FCC. For unlicensed service
the operator can install and operate the system without a license; however, any unlicensed
system is subject to signal interference from other unlicensed systems, present or future.
Either type of system requires professional installation. That is, the base station antennas
are selected (antenna gain and pattern) and mounted at the proper orientation so that the
desired coverage area is obtained and so that the signal from the antenna produces minimum
interfere to other cells.
Table 8–18 gives the WiMAX standards for both licensed service and unlicensed
service. The unlicensed service has the advantages of a faster rollout and lower costs. The
licensed service has the advantages of less interference and better signal reception since
the licensed service operates at lower frequencies (2.5 GHz) where signals have less building
attenuation and better NLOS (Non Line Of Sight) characteristics.
In the United States, Clearwire is building a licensed WiMAX network with national
coverage. The network is already “rolled out” in major U.S. cities. Sprint and Clearwire have
signed an agreement for Clearwire to provide 4G WiMAX service for Sprint. (Clearwire is
financed by its publically traded stock, as well as partial ownership by Sprint, Intel, Time
Warner Cable, Bright House, Google, and Comcast.) As indicated in Section 8–8, this
WiMAX network is a 4G cellular network, and it is in competition with LTE 4G technology
provided by other carriers.
WiMAX uses 802.16 standards. For the latest information and references on this developing
technology, see the topic IEEE 802.16 in Wikipedia.