26-06-2012, 01:17 PM
Seminar Report on LDPC codes
Report on LDPC.docx (Size: 954.39 KB / Downloads: 35)
Abstract:
LDPC codes are one of the hottest topics in coding theory today.
Originally invented in the early 1960's, they have experienced an
amazing come back in the last few years. Unlike many other classes
of codes LDPC codes are already equipped with very fast (probabilistic)
encoding and decoding algorithms. The question is that of the design
of the codes such that these algorithms can recover the original codeword
in the face of large amounts of noise. New analytic and combinatorial tools
make it possible to solve the design problem.
INTRODUCTION:
In the current century, the need for efficient and reliable digital data transmission and storage systems has been significantly highlighted. LOW density parity-check code (LDPC) is an
error correcting code used in noisy
communication channel to reduce the probability of loss of information. With LDPC, this probability can be reduced to as small as desired, thus the data
transmission rate can be as close to Shannon’s limit as desired. LDPC was developed by Robert Gallager in his
doctoral dissertation at MIT in 1960 .
.Error correction
In communication, errors can occur due to a lot of reasons , noisy channel, power surge in electronic circuits etc.
It is often desirable to detect these errors and correct them. An error correcting code is a technique for reducing the bit
error rate on a communication channel.
Forward error correction:
Error correcting involves transmitting
additional bits called redundancy ,along with the data bits. If no additional information is added to the original message, errors can turn a legal message into another legal bit pattern .Therefore redundancy is used in error correcting schemes .By adding redundancy a lot of bit patterns becomes illegal. These illegal patterns are used by the receiver to correct most of the errors in the data bits.