There are two technologies for transmission.
1> Narrowband Technology
2> Spread Spectrum Technology
1) Narrowband Technology
A narrowband radio system transmits and receives user information on a specific radio frequency. Narrowband radio keeps the radio signal frequency as narrow as possible just to pass the information. Undesirable cross talk between communications channels is avoided by carefully coordinating different users on different channel frequencies.
A private telephone line is much like a radio frequency. When each home in a neighborhood has its own private telephone line, people in one home can not listen to calls made to other homes. In a radio system, privacy and noninterference are accomplished by the use of separate radio frequencies. The radio receiver filters out all radio signals except the ones on its designated frequency.
2) Spread Spectrum Technology
Most wireless LAN systems use spread spectrum technology, a wideband radio frequency technique developed by the military for use in reliable, secure, mission critical communications systems.
Spread spectrum is designed to trade off bandwidth is consumed than in the case of narrowband transmission, but the tradeoff produces a signal that is, in effect, louder and thus easier to detect, provided that the receiver knows the parameters of the spread spectrum signal being broad cast.
If a receiver is not tuned to the right frequency, a spread spectrum signal looks like background noise. Spread spectrum simply means that data is sent in small pieces over a number of the discrete frequencies available for use at any time in the specified range.
There are further 2 types of this technology.
1> Frequency Hopping Spread Spectrum Technology
2> Direct Sequence Spread Spectrum Technology
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