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International Conference on Communications

High-rate low-density parity check codes based on anti-Pasch affine geometries

Bane V. Vasic

Published Jun 25, 2003• 12 citations
Publisher

Abstract

We introduce a combinatorial construction of regular low-density parity check codes based on balanced incomplete block designs whose bipartite graphs have girth six. Our construction employs a special type of anti-Pasch affine geometry that result in codes having minimum distance of at least six. We are primarily concerned with very high-rate codes and low column weights, but the proposed construction can be used to generate long codes as well as codes of arbitrary column weight.

DOI
10.1109/icc.2002.997067

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We introduce a combinatorial construction of regular low-density parity check codes based on balanced incomplete block designs whose bipartite graphs have girth six. Our construction employs a special type of anti-Pasch affine geometry that result in codes having minimum distance of at least six. We are primarily concerned with very high-rate codes and low column weights, but the proposed construction can be used to generate long codes as well as codes of arbitrary column weight.
In this paper we construct three types of low-density parity-check codes with column weight j = 3 based on geometries in graphical models. Low-density parity-check codes with j > 2 are desired because their minimum distance improves linearly with the code block length n. The codes we present here have girth 8 and girth 10. All codes are regular and well-structured. These codes have flexible block lengths and code rates, and may be used in the area of communications and data storage. Our simulation results show that they have better bit-error-rate decoding performance and lower error floors in additive white Gaussian noise channels than randomly constructed low-density parity-check codes.
This paper presents a method to construct regular low-density parity-check (LDPC) codes of short block length and high rate based on a special type of combinatoric designs, i.e., balanced incomplete block designs (BIBDs) with lambda = 2 whose construction are based on cyclic difference families. Although the Tanner graph of the codes constructed contains some cycles of length 4, simulation results show that they perform well under belief propagation (BP) decoding. Further, these codes are quasi-cyclic (QC) codes and hence can be encoded efficiently
This paper,based on algebra and graph,proposes a method for constructing structured low-density parity-check(LDPC) codes.In this method,the authors design a connected graph with three kinds of special path to ensure that the Tanner graph of the parity check matrix mapped from the connected graph is without short cycles.The construction method results in two classes of(3,k)-regular quasi-cyclic LDPC codes with girth 8 and 12 respectively.Furthermore,by extending this construction method,two classes of LDPC codes with column weight 2,whose girths are respectively 16 and 24,can be obtained.The simulation studies show that these codes can achieve better performance than randomly constructed regular LDPC codes over AWGN channels with iterative decoding.At the BER of 10-5,the new proposed(3,6)-regular(4356,2205) QC-LDPC code performs 1.48dB from the Shannon limit.Moreover,it outperforms the random regular LDPC code of comparable parameters by 0.1dB.For the new proposed structured LDPC codes with column weight 2,they can achieve about 2dB coding gains with respect to the random regular LDPC codes with similar block lengths and code rates.
This paper introduces several new combinatorial constructions of low-density parity-check (LDPC) codes, in contrast to the prevalent practice of using long, random-like codes. The proposed codes are well structured, and unlike random codes can lend themselves to a very low-complexity implementation. Constructions of regular Gallager codes based on cyclic difference families, cycle-invariant difference sets, and affine 1-configurations are introduced. Several constructions of difference families used for code design are presented, as well as bounds on the minimal distance of the codes based on the concept of a generalized Pasch configuration.
This article describes the different methods to design regular low density parity-check (LDPC) codes with large girth. In graph terms, this corresponds to designing bipartite undirected regular graphs with large girth. Large girth speeds the convergence of iterative decoding and improves the performance at least in the high SNR range, by slowing down the onsetting of the error floor. We reviewed several existing constructions from exhaustive search to highly structured designs based on Euclidean and projective finite geometries and combinatorial designs. We describe GB and TS LDPC codes and compared the BER performance with large girth to the BER performance of random codes. These studies confirm that in the high SNR regime these codes with high girth exhibit better BER performance. The regularity of the codes provides additional advantages that we did not explore in this article like the simplicity of their hardware implementation and fast encoding.