Chapter III-Coding and modulation

Code :

• Baseband signal: Band of digital signals with 0, 1 levels (from 0 to very high frequencies)
• Wideband signal: The baseband signal is modulated to the analog signal of the Frequency division multiplexing (because the analog channel cannot transmit the digital signal, so it needs to be modulated into an analog signal)

Baseband transmission signal: the baseband signal is fed directly into the channel transmission.

Frequency Division Multiplexing Transmission: In the same analog channel, the wideband signal is moved to different frequencies of transmission.

The probability of positive or negative occurrence is equal, there is no DC component-the transmission distance is nearly far;

Baseband signal transmission pulse waveform/Transmission code form-because it is a digital signal, the waveform is a rectangle:

1. Unipolar rectangular pulse (NRZ code): 1 yards and 0 yards, with or without pulses (corresponding to positive/negative level/0 level). So the polarity is single, but there is no interval between pulses, it is only suitable for near-distance transmission-no zero code.
2. Bipolar rectangular pulse: The pulse level is positive (0 yards), negative (1 yards), positive and negative occurrence probability is equal.
3. Unipolar Zero Code: relative to the NRZ code, 1 yards (pulse) occurs less than the width of the code element, so it can come back to 0 yards before the next code element--it is called Zero code.
4. Manchester Special code: With the pulse between the positive and negative jumps to represent the digital signal, is minus 1 yards, minus, and is 0 yards. Because of the jump through 0 levels-the Manchester special code is also a zero code.

Chapter III-Coding and modulation