part ⅰ abstract
nowadays a new type of local area network is becoming widely accepted and promises to play a key role in the future of wireless communications. this new type of lan, which is called wireless lan, provides an alternative to the traditional lans based on twisted pair, coaxial cable, and optical fiber. in 1971, the first wireless lan was put together by the researchers, led by norman abramson, at the university of hawaii as a part of a research project called alohanet. the wireless lan serves the same purpose as that of a wired or optical lan: to convey information among the devices attached to the lan. but with the lack of physical cabling to tie down the location of a node on a network, the network can be much more flexible -- moving a wireless node is easy. this article will discuss about three techniques--spread spectrum, narrowband microwave, and infrared lan--and some products that are available to build up a wireless lan. each of the three techniques has its advantages and disadvantages. the problem is how to make use of the advantages and minimize the disadvantages. among them, the technique of frequency hopping spread spectrum is a key one, which was firstly initiated by hedy lamarr and george antheil, during the world war ⅱ. then four major standards of how the wlan should be set up will be introduced. finally it reaches the conclusion that although many techniques are available, the direct sequence spread spectrum (dsss) initiated by the ieee 802.11b working group is the most widely used one and has great potentials. however, if we combine the good technique solutions and the suitable products together, we can turn the wireless lan into practice in a large scale, which will surely benefit us.
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