Turbo code
Its performance is close to the best performance that information theory can achieve, so it is a revolutionary progress in coding theory. Such codes, especially decoding operations, are very complex, and only a brief introduction to their basic concepts is given here.
Fundamental
Since the complexity of block codes and convolutional codes increases exponentially with the increase of code block length or constraint degree, in order to improve the error correction ability, most people do not simply increase the length of one code, but combine two or Multiple simple codes are combined into composite codes.
The encoder of the turbo code adds an interleaver between two parallel or series component code encoders, so that it has a large code group length and can obtain near-ideal performance under the condition of low signal-to-noise ratio.
The relationship between interleaver capacity and bit error rate
From this curve, it can be seen that the bit error rate is low when the interleaver capacity is large, because the large interleaving range can better randomize the input symbols of the interleaver.
TCM
Basic Concepts of Trellis Coded Modulation (TCM)
Directly decode the modulated signal (such as: 8PSK signal), the difference between the symbols is the difference of the carrier phase, and this difference is the Euclidean distance.
The greater the Euclidean distance between the two signal sequences, that is, the greater the difference between them, the less likely they are to be confused with each other due to interference. The signal points in the diagram represent a modulated signal waveform with a certain phase.
error control method
Error Control Necessity
White noise causes additive interference, causing random errors in the transmitted signal
Fading causes multiplicative interference, resulting in burst errors in the transmitted signal
Error control means : all means of correcting errors including channel coding
Automatic Repeat Request (ARQ)
Forward Error Correction (FEC)
Hybrid Error Correction (HEC)
Automatic Repeat Request (ARQ)
Forward Error Correction (FEC)
Hybrid Error Correction (HEC)
Summarize:
The above three error control methods have their own characteristics, and can be reasonably selected according to the actual situation