2 Wireless technologies
2.3 Wireless Metropolitan-Area Network (WMAN)

Wireless Metropolitan Area Networks (WMANs) is the third group of wireless networks. WMANs are based on IEEE 802.16 standard which is often called WiMAX (Worldwide Interoperability for Microwave Access). WiMAX is a communications technology that supports point to multipoint architecture aimed at providing high-speed wireless data over metropolitan area networks [1-3]. This enables smaller wireless LANs to be interconnected by WiMAX creating a large WMAN. Thus, networking between cities can be achieved without the need for expensive cabling.

WiMAX is similar to Wi-Fi, but provides coverage over greater distances. While Wi-Fi is intended to provide coverage over relatively small areas, such as in offices or hot spots, WiMAX operates on two frequency bands, a mixture of licensed and unlicensed band, from 2 GHz to 11 GHz and from 10 GHz to 66 GHz, and can transfer around 70 Mbps over a distance of 50 km to thousands of users from a single base station, as depicted in Figure 1.7. As it can operate in two frequency bands WiMAX can work by line-of-sight and non-line-of-sight. At the 2 to 11GHz frequency range it works by non-line-of-sight, where a computer inside a building communicates with a tower/antenna outside the building. Short frequency transmissions are not easily disrupted by physical obstructions. Higher frequency transmissions are used for line-of-sight service. This enables to towers/antennae to communicate with each other over a greater distance.

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Figure 1.7 WiMaX network diagram