Tesi di laurea specialistica
Performance evaluation of the wireless standard IEEE 802.16 OFDMA mode
Corso di studi
Relatore Prof. Lenzini, Luciano
Relatore Prof. Mingozzi, Enzo
Relatore Prof. Mingozzi, Enzo
- Frame Allocation
Data inizio appello
Data di rilascio
The incredible explosion of ICT (Information and Communication Technology) field we assisted to during the last few years deeply influenced our life from many points of view, from our daily habits to the way of communicating to other peoples. A lot of telecommunication companies flourished, offering a continuously increasing number of heterogeneous services and researching new technologies to convey them. Services and technologies have been growing jointly: every new idea for a new service involved the adoption of a new technology to can support it. On the other hand the achievement of new network technologies opened the way to innovative as unpredictable services.<br><br>Until some years ago data and voice were conceived as two separated service categories: the former carried out with a packet switched approach, the latter with a circuit switched one. Thanks to higher bandwidth rates reached by later technologies, it has been possible to integrate data and voice on the same network backbone using a packet switched technique. At the same time, users began to getting familiar with new available solutions such as VoIP and video conference, also forcing access networks to evolve themselves. Many wired solutions (xDSL family, optical fibres) were proposed to face increasing bandwidth requests, offering digital transmissions to users. Moreover, the low prices of network devices modified the communication idea: cabled local area network (LAN) became very popular like a way to interconnect PC or to share common utility devices.<br><br>The main drawback in these scenarios is the big effort in term of time and money not only in cabling set up phase, but also in case of a new node addition.<br><br>In spite of wired solutions, wireless communication systems has a number of advantages, not least the mobility of the devices within the environment and the connectivity for rural areas not reached by wired infrastructures. <br><br>As regards the first aspect, we can talk about the employment of WiFi technology in Local Area Network. It is a simple matter to relocate a communicating device, and no additional cost of rewiring and excessive downtime is associated with such a move. It is also a simple matter to add in a communication device to the system or remove one from the system without any disruption to the remainder of the system itself. Other than the initial outlay on setting up the cell sites, the cost of running and maintaining a radio based communication solution is minimal. These, and other factors, show the appeal that a radio communication system has for the office environment.<br><br>Taking into account the second aspect, we can focus on the employment of WiMAX technology in Metropolitan Area Network. Just as Wi-Fi is based on the IEEE 802.11 standard, WiMAX (Worldwide Interoperability for Microwave Access) systems are based on the IEEE 802.16 standard, whose first version was approved in 2001 to define high-speed wireless service to stationary sites over distances up to 50 kilometers, while the maximum range for Wi-Fi is a few hundred meters. One reason for WiMAX's greater range is that it can transmit at higher power levels, depending on the radio band. WiMAX has the capability to run at 75 Mbps - many times the speed of digital subscriber lines (DSL) - but this capacity will usually be divided among many users. WiMAX was conceived to provide the same kind of fast Internet service afforded by DSL, cable modem and even fiber-optic systems. For this reason, it has also been called Wireless MAN (MAN stands for "metropolitan-area network"). The ability to provide these broadband connections wirelessly, without laying wire or cable in the ground, greatly lowers the cost to provide these services. So, WiMAX may change the economics for any place where the cost of laying or upgrading landlines to broadband capacity is prohibitively expensive, as in emerging countries. In countries like India, Mexico and China, for instance, where wired infrastuctures are currently insufficient or lacking, WiMAX can become part of the broadband backbone. <br><br>The first version of the standard 802.16 was followed by three amendments 802.16a, 802.16b and 802.16c to address issues of radio spectrum, quality of service and inter-operability respectively. This project ended in 2004 with the release of 802.16-2004  and the withdrawal of the earlier 802.16 documents including the a/b/c amendments. Despite the technology's origins, the WiMAX community more recently began to work on a mobile version of the standard, called IEEE 802.16e, which is popularly known as mobile WiMAX. Like Wi-Fi, it is intended to provide service to laptop computers and other mobile devices, but it will have greater range, probably up to a few kilometers.
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