Modulation
Modulation is the process of adding information to a carrier signal to convert data into radio waves or other forms of electromagnetic signals.
The carrier signal is a steady waveform with a constant height and frequency.
Modulation is used to transmit multiple channels of information through a single communication medium, using frequency-division multiplexing (FDM)
Demodulation
Demodulation is the process of extracting the original signal from a modulated carrier wave.
Coherent Demodulation
the receiver recreates the exact carrier wave (with the same frequency and phase) to extract the original information from the received signal.
Baseband
It is the original, unmodulated form of a signal, which can be either analog or digital
In the Fourier domain, a baseband signal is a signal that occupies the frequency range from 0 Hz up to a certain cutoff