Here we see that this is the situation at the physical layer for any mobile communication scenario, where either you have brought voice-traffic or you have brought data-traffic. Voice is digitised and, if you have data, then it goes through a protocol. So, finally you are getting data which go through a block which we will call coding, scrambling or framing, and after that you feed it to the modulator and then to the transmitter. The channel is causing fade, channel experiences noise interference, distortion, doppler is dropping and then you receive the things.
In this particular lecture we are interested only in the coding and decoding parts of this particular block-diagram.