Wireless local area network is the product of the combination of computer network and wireless communication technology. Generally speaking, a wireless local area network (WLAN) provides all the functions of a traditional wired local area network without using a traditional cable. The infrastructure needed by the network does not need to be buried underground or hidden in the wall, and the network can be moved or changed according to actual needs. Also called local area network, because it will be limited by the distance between wireless connection equipment and computer, which will affect the transmission range, so it must be within the regional scope to connect to the network.

Wireless LAN is based on traditional wired LAN, which is an extension and replacement of wired LAN. It only realizes wireless communication through wireless hubs, wireless access nodes, wireless bridges, wireless network cards and other devices on the basis of wired LAN. Like wired networks, wireless LANs also need transmission media. Only the transmission medium used in WLAN is not twisted pair or optical fiber, but infrared or radio waves, and the latter is often used.

Infrared system

Infrared LAN uses infrared ray with wavelength less than 1 micron as transmission medium, which has strong directivity. Because it uses part of the spectrum below visible light as the transmission medium, its use is not restricted by the radio management department. Infrared signals need line-of-sight (line-of-sight) transmission, so it is difficult to eavesdrop and will not interfere with similar systems in neighboring areas. In practical application, infrared ray has a high background noise, which is greatly influenced by sunlight and environmental lighting. And generally requires high transmission power. At present, infrared wireless local area network is a feasible choice of "high cost-effective network above 100 Mbit/s".

radio wave

Using radio waves as the transmission medium of WLAN is the most widely used at present, mainly because of its wide coverage and wide application. When spread spectrum communication is used, especially the direct sequence spread spectrum modulation mode has strong anti-interference and anti-noise ability and anti-fading ability because the transmission power is lower than the natural background noise. On the one hand, it makes communication very safe, basically avoids eavesdropping and stealing communication signals, and has high usability. On the other hand, the frequency band used in wireless local area is mainly S-band (2.4 GHz ~ 2.4835 GHz band), also called ISM (industrial scientific medical treatment), which is not restricted by the Federal Communications Commission in the United States, and belongs to the industrial free radiation frequency band, which will not cause harm to human health. Therefore, radio waves become the most commonly used wireless transmission media in WLAN.

Except that the transmission medium is different from the traditional LAN, one of the characteristics of WLAN technology is that the standards are not uniform, and different standards have different applications. At present, there are 802. 1 1 standards (including 802.1a, 802.1/b and 802.11g.