Modulation
An RF arresting has characteristics that accredit it to be beatific from an antenna, through the air medium,
and accustomed by addition antenna at the destination. RF signals are analog in nature. A computer,
though, uses agenda signals to represent $.25 of information.
Before transmitting abstracts through the air, the transceiver aural the radio cards and admission points
must catechumen agenda signals into analog signals acceptable for manual through the air medium.
As allotment of accepting an 802.11 frame, a radio agenda or admission point charge catechumen the analog signal
back into a agenda anatomy that is accepted by the accretion device. This about-face action is
known as accentuation and demodulation, respectively.
802.11 defines several types of modulation, depending on which concrete band and abstracts rate
is in use by the 802.11 station. In general, it is accessible to attune an RF carrier arresting by
changing its amplitude, frequency, or phase, as apparent in Figure G-9. For example, 802.11b uses
phase about-face keying (PSK) to represent agenda data. 802.11a and 802.11g, though, apparatus a
combination of amplitude and appearance shifts, which is referred to as quadrature amplitude
modulation (QAM).
Figure G-9 Attributes of an RF Signal
Amplitude
Time
Frequency = 1/T
Reference
Phase