2 Wireless technologies
2.4 Wireless Wide-Area Network (WWAN)

Wireless Wide Area Networks extend beyond 50 kilometers and typically use licensed frequencies. These types of networks can be maintained over large areas, such as cities or countries, via multiple satellite systems or antenna sites looked after by an internet services provider. There are mainly two available technologies: Digital cellular telephony and Satellites [1-3].

In the cellular system, the coverage area is divided into cells. A cell transmitter, at center of the cell, is designed to serve an individual cell. All transmitters are connected to a base station and these latter to a mobile telecommunications switching office which links the cellular and the wired telephone network. The system seeks to make efficient use of available channels by using low-power transmitters to allow frequency reuse at much smaller distances.

Different cellular generations have been developed since early 1980s. First generation, 1G, was analog and, conceived and designed purely for voice calls with almost no consideration of data services, with a speed of up to 2.4 kbps. The second generation, 2G, was based on digital technology and network infrastructure (GSM), enabling text messages, and with a data speed of up to 64 Kbps. The 2.5G generation was between the second and the third. Sometimes it has been referred as 2G + GPRS, it is an enhanced version of 2G, with a speed of up to 144 Kbps. The 3G generation was introduced in year 2000, with a data speed of up to 2 Mbps. The 3.5G is an enhanced version of the 3G that uses HSDPA to speed data transfers up to 14 Mbps. Finally the fourth generation, 4G, is capable of providing up to 1 Gbps speed and any kind of service at any time as per user requirements, anywhere. The 5G generation is expected by year 2020.

Wireless communications can also be developed via satellite. Due to its high altitude, satellite transmissions can cover a wide area over the surface of the earth. This can be very useful for users who are located in remote areas or islands where no submarine cables are in service. In these cases, satellite telephones are needed.

Each satellite is equipped with various transponders consisting of a transceiver and an antenna. The incoming signal is amplified and then rebroadcast on a different frequency.

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Figure 1.8 Satellite and cellular networks