Đang chuẩn bị liên kết để tải về tài liệu:
Lý thuyết mạng không dây P9

The growth of Wireless Local Area Network (WLANs) commenced in the mid-1980s and was triggered by the US Federal Communications Commission (FCC) decision to authorize the public use of the Industrial, Scientific and Medical (ISM) bands. This decision eliminated the need for companies and end users to obtain FCC licenses to operate their wireless products. Since then, there has been a substantial growth in the area of WLANs. Lack of standards, however, enabled the appearance of many proprietary products thus dividing the market into several, possibly incompatible parts. Consequently, the need for standardization in the area appeared. . | Wireless Networks. P. Nicopolitidis M. S. Obaidat G. I. Papadimitriou and A. S. Pomportsis Copyright 2003 John Wiley Sons Ltd. ISBN 0-470-84529-5 9 Wireless Local Area Networks 9.1 Introduction The growth of Wireless Local Area Network WLANs commenced in the mid-1980s and was triggered by the US Federal Communications Commission FCC decision to authorize the public use of the Industrial Scientific and Medical ISM bands. This decision eliminated the need for companies and end users to obtain FCC licenses to operate their wireless products. Since then there has been a substantial growth in the area of WLANs. Lack of standards however enabled the appearance of many proprietary products thus dividing the market into several possibly incompatible parts. Consequently the need for standardization in the area appeared. The first attempt to define a standard was made in the late 1980s by IEEE Working Group 802.4 which was responsible for the development of the token-passing bus access method. The group decided that token passing was an inefficient method to control a wireless network and suggested the development of an alternative standard. As a result the Executive Committee of IEEE Project 802 decided to establish Working Group IEEE 802.11 which has been responsible since then for the definition of physical and MAC sublayer standards for WLANs. The first 802.11 standard was finalized in 1997 and was developed by taking into consideration existing research efforts and market products in an effort to address both technical and market issues. It offered data rates up to 2 Mbps using spread spectrum modulation in the ISM bands. In September 1999 two supplements to the original standard were approved by the IEEE Standards Board. The first standard 802.11b extends the performance of the existing 2.4 GHz physical layer with potential data rates up to 11 Mbps. The second 802.11a aims to provide a new higher data rate from 20 up to 54 Mbps physical layer in the 5 GHz band. The .