What is a WLAN?

A wireless local area network (also reffered to as a LAWN) is a type of local area network that uses high frequency radio waves rather than wires to communicate between base points.

What is 802.11?

802.11 refers to a family of specifications developed by the IEEE for wireless LAN technology. 802.11 basically specifies a wireless interface between a wireless client and a base station or between two wireless clients.

What are the different specifications?

• 802.11 - applies to wireless LANS and provides 1 or 2 Mbps transmission in the 2.4Ghz band. It uses Frequency Hopping Spread Spectrum (FHSS) or Direct Sequence Spread Spectrum (DSSS) see below for more on FHSS and DSSS
• 802.11a is an extension to 802.11 which provides up to 54Mbps in the 5Ghz band. It uses a different encoding scheme to 802.11 called Orthogonal Frequency Division Multiplexing (OFDM) see below for more on OFDM
• 802.11b is an extension to 802.11 which provides up to 11Mbps in the 2.4Ghz band. 802.11b uses DSSS
• 802.11g is an extension to 802.11 which provides 20+Mbps in the 2.4Ghz band

What is FHSS?

Frequency Hopping Spread Spectrum is one of two types of spread spectrum radio. It is a transmission technology synonymous with wireless LAN. It is used in transmissions where the data signal is modulated with a narrowband carrier signal which 'hops' in a random, predictable sequence from frequency to frequency. The signal is spread in time domain rather than cutting it up into small pieces in frequency domain. By doing this, interference is reduced because a signal from a narrowband system will only affect the spread spectrum if both are transmitting at the same time. If synchronised properly, a single logical channel is maintained. The transmission frequencies are determined by a 'hopping' code. The receiver must be set to the same hopping code and must listen to the incoming signal at the correct frequency and time in order to receive it

What is DSSS?

Direct Sequence Spread Spectrum is the second type of spread spetrum radio. It works in wireless LAN transmissions where a data signal at the sending station is combined with a higher data rate bit sequence (or chipping code) which divides the user data according to a spreading ratio. The chipping code is a redundant bit pattern for each bit that is transmitted, which increases the signals resistwnce to interference. If one or more bits in the pattern are damaged during transmission, the original data can be recovered due to the redundancy of the transmission.

What is OFDM?

Orthogonal Frequency Division Multiplexing, is a frequency division mulitplexing modulation technique for transmitting large amounts of digital data over a radio wave. OFDM works by splitting the radio signal into multiple smaller sub-signals that are then transmitted simultaneously at different frequencies to the receiver. OFDM reduces the amount of crosstalk in signal transmissions.