Signals need to be transmitted in the channel
Simplex transmission, the transmission medium contains a channel
Half-duplex and full-duplex transmission, the transmission medium contains two channels
Encoding: Only transform the waveform of the digital signal without changing the nature of the signal
Modulation: Moves the range of the digital baseband signal to a higher frequency band and converts it to an analog signal
Symbol: The basic waveform that represents different discrete values when using the time domain to represent digital signals
In computer networks, constant digital baseband signals are encoded or modulated for transmission
Common codes:
Non-return to 0 coding: only positive and negative levels
There is a synchronization problem, do not use
Return to 0 code:
After the transmission of each symbol, the signal must return to 0, so the receiver only needs to sample after the signal returns to zero, and does not need a separate clock signal.
In fact, the return-to-zero encoding is equivalent to encoding the clock signal in the data in a "return-to-zero" manner, which becomes a "self-synchronizing " signal.
Most of the data bandwidth in the return-to-zero encoding is wasted for transmitting return-to-zero. (low efficiency)
Mantester code:
The transition in the middle of the symbol represents both the clock and the data
Differential Manchester encoding:
The transition only indicates the clock, whether the level at the beginning of the symbol changes indicates the data
Basic modulation method:
Mixed modulation: