Data bits modulate (modify) a carrier signal Basic modulation techniques: amplitude frequency phase.
Data bits are represented over the transmission channel by SYMBOLS Symbol rate is expressed in Baud (Symbols per Second) Modulation of a carrier is used to transmit data bits efficiently over the air interface The modulation process creates modulation symbols. A modulation Symbol is a sinusoidal signal (carrier) with specific parameters dictated by the data bit(s), transmitted for a finite period of time Carrier parameters do not change for the duration of the symbol
Prior to the transmission of data, the data bits are grouped and converted to symbols. These symbols are physically transmitted over the physical transmission channel. The symbols are transformed into phase and amplitude values of the RF-carrier.
A data bit is transmitted generally in the following way:
- Each data bit combination is coded into a symbo.
- The frequency fc is changed in phase or in phase and amplitude according to the symbol.