Take making calls or sending text messages on a mobile phone as an example to analyze the specific signals, messages and information involved in this communication process.

First of all, human voice is an analog signal, and then the process is: analog signal---A/D conversion (that is, converting the analog signal into a discrete signal, the process is sampling, quantization, and encoding) ---Then modulation----Transmit digital signals through radio, because digital signals have strong anti-interference ability. There are many measures in the middle to further enhance the anti-interference ability. It is sent to the remote receiving end, demodulated, and finally D/A converted, and then put into the power amplifier to drive the speaker, and then the other party can be heard.