Basic concepts of communication
1. Channel: not identical with the circuit, the channel is a transmission medium signals . A communication line has two channels , one transmission channel, the other channel is acceptable.
2. Channel Model: transmission over the channel is an analog signal .
3. The digital channel: transmission channel is a digital signal .
4. The baseband signal: the digital signal 01 with two different voltages represented by the voltage signal .
5. wideband signal: the baseband signal (voltage signal) modulated into a frequency division multiplexed analog signal .