IISc Logo    Title

etd AT Indian Institute of Science >
Division of Electrical Sciences >
Computer Science and Automation (csa) >

Please use this identifier to cite or link to this item: http://hdl.handle.net/2005/523

Title: Experimental Studies On A New Class Of Combinatorial LDPC Codes
Authors: Dang, Rajdeep Singh
Advisors: Shankar, Priti
Keywords: Computer Mathematics
Low Density Parity Check Codes
Graph Construction Technique
Sum-Product Algorithm
Decoding Algorithms
Progressive Edge Growth (PEG) Codes
Almost Regular High Girth (ARG) Codes
Additive White Gaussian Noise (AWGN)
Binary Erasure Channel (BEC)
High Girth Construction
LDPC Codes
Submitted Date: May-2007
Series/Report no.: G22223
Abstract: We implement a package for the construction of a new class of Low Density Parity Check (LDPC) codes based on a new random high girth graph construction technique, and study the performance of the codes so constructed on both the Additive White Gaussian Noise (AWGN) channel as well as the Binary Erasure Channel (BEC). Our codes are “near regular”, meaning thereby that the the left degree of any node in the Tanner graph constructed varies by at most 1 from the average left degree and so also the right degree. The simulations for rate half codes indicate that the codes perform better than both the regular Progressive Edge Growth (PEG) codes which are constructed using a similar random technique, as well as the MacKay random codes. For high rates the ARG (Almost Regular high Girth) codes perform better than the PEG codes at low to medium SNR’s but the PEG codes seem to do better at high SNR’s. We have tried to track both near codewords as well as small weight codewords for these codes to examine the performance at high rates. For the binary erasure channel the performance of the ARG codes is better than that of the PEG codes. We have also proposed a modification of the sum-product decoding algorithm, where a quantity called the “node credibility” is used to appropriately process messages to check nodes. This technique substantially reduces the error rates at signal to noise ratios of 2.5dB and beyond for the codes experimented on. The average number of iterations to achieve this improved performance is practically the same as that for the traditional sum-product algorithm.
URI: http://etd.iisc.ernet.in/handle/2005/523
Appears in Collections:Computer Science and Automation (csa)

Files in This Item:

File Description SizeFormat
G22223.pdf5.83 MBAdobe PDFView/Open

Items in etd@IISc are protected by copyright, with all rights reserved, unless otherwise indicated.


etd@IISc is a joint service of SERC & IISc Library ||
|| Powered by DSpace || Compliant to OAI-PMH V 2.0 and ETD-MS V 1.01