It consists of a radio transmitter for digital data .The first step is the digital modulation of data into analog baseband signal according to one of the schemes presented in the following.The analog modulation then shifts the center frequency of analog signal up to the radio carrier .This signal is then transmitted via the antenna .
The model actually consist of digital modualtion box and analog modulation box.
The reciever receives the analog signal into analog baseband signal with the help of this known as carrier.This would be all that is needed for an analog radio tuned into the radio station .(the analog baseband signal would constitute the music)For digital data ,another step needed.Bits or frames have to be detected ,i.e the receiver must synchronise with the sender .How synchronisation is acheived ,depens on the digital modualtion scheme .After synchronistion ,the receiver has to decide the signal represents a digital 1 or 0 ,reconstructing the original data
The digital modulation schemes presented inthe following sections differ in many issues such as spectral efficeincy ,power efficiency ,and the robustness to multipath propagation
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