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IEEE International Symposium on Information Theory (ISIT)

On a class of finite geometry low density parity check codes

Shu Lin, Heng Tang, Yu Kou

Published Nov 13, 2002• 7 citations
Publisher

Abstract

A new class of geometry LDPC codes is presented which contains the class of Kou-Lin-Fossorier codes (see IEEE International Symposium on Information Theory, p.200, June 2000) as a subclass. If the code construction is based on Euclidean geometry (EG) and projective geometry (PG) over finite fields, we obtain four classes of LDPC codes, namely: (1) type-I EG-LDPC codes; (2) type-II EG-LDPC codes; (3) type-I PG-LDPC codes; and (4) type-II PG-LDPC codes.

DOI
10.1109/isit.2001.935865

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A new class of geometry LDPC codes is presented which contains the class of Kou-Lin-Fossorier codes (see IEEE International Symposium on Information Theory, p.200, June 2000) as a subclass. If the code construction is based on Euclidean geometry (EG) and projective geometry (PG) over finite fields, we obtain four classes of LDPC codes, namely: (1) type-I EG-LDPC codes; (2) type-II EG-LDPC codes; (3) type-I PG-LDPC codes; and (4) type-II PG-LDPC codes.
Finite geometries, such as Euclidean and projective geometries, are powerful mathematical tools for constructing error-control codes. In the 1960s and 1970s, finite geometries were successfully used to construct many classes of easily implementable majority-logic decodable codes. In 2000, Kou, Lin, and Fossorier [1–3] showed that finite geometries can also be used to construct LDPC codes that perform well and close to the Shannon theoretical limit with iterative decoding based on belief propagation. These codes are called finite-geometry (FG) -LDPC codes. FG-LDPC codes form the first class of LDPC codes that are constructed algebraically. Since 2000, there have been many major developments in construction of LDPC codes based on various structural properties of finite geometries [4–18]. In this chapter, we put together all the major constructions of LDPC codes based on finite geometries under a unified frame. We begin with code constructions based on Euclidean geometries and then go on to discuss those based on projective geometries. Construction of LDPC Codes Based on Lines of Euclidean Geometries This section presents a class of cyclic LDPC codes and a class of quasi-cyclic (QC) LDPC codes constructed using lines of Euclidean geometries. Before we present the constructions of these two classes of Euclidean-geometry (EG)-LDPC codes, we recall some fundamental structural properties of a Euclidean geometry that have been discussed in Chapter 2.
This paper presents a geometric approach to the construction of low-density parity-check (LDPC) codes. Four classes of LDPC codes are constructed based on the lines and points of Euclidean and projective geometries over finite fields. Codes of these four classes have good minimum distances and their Tanner (1981) graphs have girth 6. Finite-geometry LDPC codes can be decoded in various ways, ranging from low to high decoding complexity and from reasonably good to very good performance. They perform very well with iterative decoding. Furthermore, they can be put in either cyclic or quasi-cyclic form. Consequently, their encoding can be achieved in linear time and implemented with simple feedback shift registers. This advantage is not shared by other LDPC codes in general and is important in practice. Finite-geometry LDPC codes can be extended and shortened in various ways to obtain other good LDPC codes. Several techniques of extension and shortening are presented. Long extended finite-geometry LDPC codes have been constructed and they achieve a performance only a few tenths of a decibel away from the Shannon theoretical limit with iterative decoding.
The finite Euclidean and Projective geometry codes are the most known among One-Step Majority-Logic Decodable codes that are Low-Density Parity-Check codes as well. Unfortunately, these codes are rare, and we do not have a great diversity when designing communication systems with a fixed code-length and code rate. Regarding the non-binary Euclidian and projective geometric Codes, each code is restricted to a unique alphabet. To offer a bigger range of possible alphabets for each code, we propose new construction by redefining the incidence vector of the lines of Euclidean and projective geometries over finite fields. This approach leads to an enrichment of the class of EG and PG codes. An error performance study of some new codes has been carried out and shows good results.
Low density parity check (LDPC) codes with iterative decoding based on belief propagation achieve astonishing error performance close to Shannon limit. No algebraic or geometric method for constructing these codes has been reported and they are largely generated by computer search. As a result, encoding of long LDPC codes is in general very complex. This paper presents two classes of high rate LDPC codes whose constructions are based on finite Euclidean and projective geometries, respectively. These classes of codes a.re cyclic and have good constraint parameters and minimum distances. Cyclic structure adows the use of linear feedback shift registers for encoding. These finite geometry LDPC codes achieve very good error performance with either soft-decision iterative decoding based on belief propagation or Gallager's hard-decision bit flipping algorithm. These codes can be punctured or extended to obtain other good LDPC codes. A generalization of these codes is also presented.
A new class of quantum low-density parity-check (LDPC) codes whose parity-check matrices are dual-containing matrices constructed based on lines of Euclidean geometries (EGs) is presented. The parity-check matrices of our quantum codes contain one and only one 4-cycle in every two rows and have better distance properties. However, the classical parity-check matrix constructed from EGs does not satisfy the condition of dual-containing. In some parameter conditions, parts of the rows in the matrix maybe have not any nonzero element in common. Notably, we propose four families of fascinating structure according to changes in all the parameters, and the parity-check matrices are adopted to satisfy the requirement of dual-containing. Series of matrix properties are proved. Construction methods of the parity-check matrices with dual-containing property are given. The simulation results show that the quantum LDPC codes constructed by this method perform very well over the depolarizing channel when decoded with iterative decoding based on the sum-product algorithm. Also, the quantum codes constructed in this paper outperform other quantum codes based on EGs.
A new method for constructing quasi-cyclic (QC) low-density parity-check (LDPC) codes based on the structural properties of Euclidean geometries is presented. The proposed method changes the incidence vectors of some lines in the original Euclidean geometry method to construct much more parity check matrices and results in a large class of QC-LDPC codes with girth of at least 6. Simulations show that some codes in this class have better performance and lower error floor than the original Euclidean geometry codes.