Phone / radio / walkie-talkie communication theory

Is a half-duplex intercom communications tool, for example a so-called half duplex is A, B two intercom communication. When A and B is not talking at the same time to say, only when A finished, it can be said that there is a corresponding switching control of their transmission or acceptance on the radio, both at the same time is not acceptable,
it works: walkie-talkie headset and the microphone is analog to digital and digital to analog conversion. Microphone can convert said voice signal into a digital signal, which is the digital signal is a baseband signal , the low frequency band is, after modulation, the modulation can be sent to a high-frequency signal , it is transmitted through the antenna.
Transmitting and receiving process is a process of reverse process. When the antenna receives the other party sent over a high-frequency signal when, through a process called demodulation of the baseband signal from the high-frequency signal uninstall downloaded, converted into a voice signal,
in fact, walkie-talkies and cell phones have been very similar, and there the difference is that the phone can be said at the same time.