Digital Microwave Communication System Model

Signal source of the transmit end is the equipment that provides original signals, it outputs digital signals.
Channel coding is to improve the reliability of transmitting digital signals. For noise and interference may inevitably exist in the channel, the digital signals transmitted may generate error bit. To make the code element automatically checked and corrected at the receive end, channel coder is used to add some additional code elements to the input digital hierarchy based on certain rules, and form new digital hierarchy. At the receive end, signals are checked based on the rules of the new digital code element hierarchy.
Modulation is to modulate the digital signals to the carrier of higher frequencies to make it adapt to radio channel transmission.
Functions of demodulation and channel decoding at the receive end are opposite to that of modulation and channel code at the transmit end. Please see below Figure.