The principle of feedback
Turbocodes: achievements and prospects

In early telecommunications systems, error correction was performed after digital demodulation. The received analog signal was first converted into a frame of symbols, usually binary, and then the correction algorithms were applied. In one of their papers, Hartmann and Rudolph showed that it was possible to use the analog signal directly. This enabled them to build decoding algorithms whose performance was superior to existing algorithms. The downside is that their algorithm, for reasons of complexity, is limited to codes with...