Information Theory, Inference, and Learning ... - Inference Group

Copyright Cambridge University Press 2003. On-screen viewing permitted. Printing not permitted. http://www.cambridge.org/0521642981You can buy this book for 30 pounds or $50. See http://www.inference.phy.cam.ac.uk/mackay/itila/ for links.564 47 — Low-Density Parity-Check Codesreceived:0 1 2 310 11 12 13→decoded:Figure 47.5. Iterative probabilistic decoding of a low-density parity-check code for a transmissionreceived over a channel with noise level f = 7.5%. The sequence of figures shows the bestguess, bit by bit, given by the iterative decoder, after 0, 1, 2, 3, 10, 11, 12, and 13 iterations.The decoder halts after the 13th iteration when the best guess violates no parity checks.This final decoding is error free.Probability of decoder error0.10.010.0010.00011e-051e-06GVC0 0.2 0.4 0.6 0.8 1Ratelow-densityparity-check codeShannon limitFigure 47.6. Error probability ofthe low-density parity-check code(with error bars) for binarysymmetric channel with f = 7.5%,compared with algebraic codes.Squares: repetition codes andHamming (7, 4) code; otherpoints: Reed–Muller and BCHcodes.