How WLAN works

How does WLAN work?
WLANs use radio, infrared and microwave transmission to transmit data from one point to another without cables. Therefore WLAN offers way to build a Local Area Network without cables. This WLAN can then be attached to an allready existing larger network, the internet for example.

A wireless LAN consists of nodes and access points. A node is a computer or a peripheral (such as a printer) that has a network adapter, in WLANs case with an antenna. Access points function as transmitters and receivers between the nodes themselves or between the nodes and another network. More on this later.

WLAN data transfer in itself is implemented by one of the following technologies:

Frequency Hopping Spread Spectrum (FHSS)
Direct Sequence Spread Spectrum (DSSS)
Infrared (IR)
In the following is a brief dicussion about each of them.

Frequency Hopping Spread Spectrum
Frequency Hopping Spread Spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse noise.

Direct Sequence Spread Spectrum
Direct Sequence Spread Spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a chip (or chipping code). The longer the chip, the greater the probability that the original data can be recovered (the more bandwidth required also). Even if one or more bits in the chip are damaged during transmission, statistical techniques can recover the original data without the need for retransmission. To an unintended receiver, DSSS appears as low-power wideband noise and is ignored by most narrowband receivers.

Infrared Technology
Infrared (IR) systems use very high frequencies, just below visible light in the electromagnetic spectrum, to carry data. Like light, IR cannot penetrate opaque objects; it is either directed (line-of-sight) or diffuse technology. Inexpensive directed systems provide very limited range (3 ft) and are occasionally used in specific WLAN applications. High performance directed IR is impractical for mobile users and is therefore used only to implement fixed subnetworks. Diffuse (or reflective) IR WLAN systems do not require line-of-sight, but cells are limited to individual rooms.