84 research outputs found
Construction of Near-Optimum Burst Erasure Correcting Low-Density Parity-Check Codes
In this paper, a simple, general-purpose and effective tool for the design of
low-density parity-check (LDPC) codes for iterative correction of bursts of
erasures is presented. The design method consists in starting from the
parity-check matrix of an LDPC code and developing an optimized parity-check
matrix, with the same performance on the memory-less erasure channel, and
suitable also for the iterative correction of single bursts of erasures. The
parity-check matrix optimization is performed by an algorithm called pivot
searching and swapping (PSS) algorithm, which executes permutations of
carefully chosen columns of the parity-check matrix, after a local analysis of
particular variable nodes called stopping set pivots. This algorithm can be in
principle applied to any LDPC code. If the input parity-check matrix is
designed for achieving good performance on the memory-less erasure channel,
then the code obtained after the application of the PSS algorithm provides good
joint correction of independent erasures and single erasure bursts. Numerical
results are provided in order to show the effectiveness of the PSS algorithm
when applied to different categories of LDPC codes.Comment: 15 pages, 4 figures. IEEE Trans. on Communications, accepted
(submitted in Feb. 2007
Development of rate-compatible structured LDPC CODEC algorithms and hardware IP
Issued as final reportSamsung Advanced Institute of Technolog
An Efficient Algorithm for Finding Dominant Trapping Sets of LDPC Codes
This paper presents an efficient algorithm for finding the dominant trapping
sets of a low-density parity-check (LDPC) code. The algorithm can be used to
estimate the error floor of LDPC codes or to be part of the apparatus to design
LDPC codes with low error floors. For regular codes, the algorithm is initiated
with a set of short cycles as the input. For irregular codes, in addition to
short cycles, variable nodes with low degree and cycles with low approximate
cycle extrinsic message degree (ACE) are also used as the initial inputs. The
initial inputs are then expanded recursively to dominant trapping sets of
increasing size. At the core of the algorithm lies the analysis of the
graphical structure of dominant trapping sets and the relationship of such
structures to short cycles, low-degree variable nodes and cycles with low ACE.
The algorithm is universal in the sense that it can be used for an arbitrary
graph and that it can be tailored to find other graphical objects, such as
absorbing sets and Zyablov-Pinsker (ZP) trapping sets, known to dominate the
performance of LDPC codes in the error floor region over different channels and
for different iterative decoding algorithms. Simulation results on several LDPC
codes demonstrate the accuracy and efficiency of the proposed algorithm. In
particular, the algorithm is significantly faster than the existing search
algorithms for dominant trapping sets
Performance of Coded Wireless Power Controllers for Wind Turbines Connected to a Smart Grid
Nowadays, with the advance of smart grid technologies, the participation of renewable energy in the power systems is changing for attend new requirements and increase efficiency of the systems. With a view of smart grid context, this work proposes the review of a modern wireless control system proposed based on for squirrel cage induction generators connected to the power grid. The wireless communication system applied transmits the reference power signals to the SCIG controller with the necessary reliability to ensure the power quality provided by the wind turbine employing the OFDM multi-carrier transmission technique associated with an LDPC coding scheme. The satisfactory results of this research endorse the operability and advantages of application of wireless control system for windy plants when some requirements and techniques, based on digital modulation and coding techniques, are employees
Network flow algorithms for wireless networks and design and analysis of rate compatible LDPC codes
While Shannon already characterized the capacity of point-to-point channels back in 1948, characterizing the capacity of wireless networks has been a challenging problem. The deterministic channel model proposed by Avestimehr, etc. (2007 - 1) has been a promising approach
for approximating the Gaussian channel capacity and has been widely studied recently. Motivated by this model, an improved combinatorial algorithm is considered for finding the unicast capacity for wireless information flow on such deterministic networks in the first part of this
thesis. Our algorithm fully explores the useful combinatorial features intrinsic in the problem. Our improvement applies generally with any size of finite fields associated with the channel model. Comparing with other related algorithms, our improved algorithm has very competitive
performance in complexity.
In the second part of our work, we consider the design and analysis of rate-compatible LDPC codes. Rate-compatible LDPC codes are basically a family of nested codes, operating at different code rates and all of them can be encoded and decoded using a single encoder and
decoder pair. Those properties make rate-compatible LDPC codes a good choice for changing channel conditions, like in wireless communications. The previous work on the design and analysis of LDPC codes are all targeting at a specific code rate and no work is known on
the design and analysis of rate-compatible LDPC codes so that the code performance at all code rates in the family is manageable and predictable. In our work, we proposed algorithms for the design and analysis of rate-compatible LDPC codes with good performance and make the code performance at all code rates manageable and predictable. Our work is based on E2RC codes, while our approaches in the design and analysis can be applied more generally not only to E2RC codes, but to other suitable scenarios, like the design of IRA codes. Most encouragingly, we obtain families of rate-compatible codes whose gaps to capacity are at most 0.3 dB across the range of rates when the maximum variable node degree is twenty, which is very promising compared with other existing results
Novel Code-Construction for (3, k) Regular Low Density Parity Check Codes
Communication system links that do not have the ability to retransmit generally rely
on forward error correction (FEC) techniques that make use of error correcting codes
(ECC) to detect and correct errors caused by the noise in the channel. There are
several ECC’s in the literature that are used for the purpose. Among them, the low
density parity check (LDPC) codes have become quite popular owing to the fact that
they exhibit performance that is closest to the Shannon’s limit.
This thesis proposes a novel code-construction method for constructing not only (3, k)
regular but also irregular LDPC codes. The choice of designing (3, k) regular LDPC
codes is made because it has low decoding complexity and has a Hamming distance,
at least, 4. In this work, the proposed code-construction consists of information submatrix
(Hinf) and an almost lower triangular parity sub-matrix (Hpar). The core design
of the proposed code-construction utilizes expanded deterministic base matrices in
three stages. Deterministic base matrix of parity part starts with triple diagonal matrix
while deterministic base matrix of information part utilizes matrix having all elements
of ones. The proposed matrix H is designed to generate various code rates (R) by
maintaining the number of rows in matrix H while only changing the number of
columns in matrix Hinf.
All the codes designed and presented in this thesis are having no rank-deficiency, no
pre-processing step of encoding, no singular nature in parity part (Hpar), no girth of
4-cycles and low encoding complexity of the order of (N + g2) where g2«N. The
proposed (3, k) regular codes are shown to achieve code performance below 1.44 dB
from Shannon limit at bit error rate (BER) of 10
−6
when the code rate greater than
R = 0.875. They have comparable BER and block error rate (BLER) performance
with other techniques such as (3, k) regular quasi-cyclic (QC) and (3, k) regular
random LDPC codes when code rates are at least R = 0.7. In addition, it is also shown
that the proposed (3, 42) regular LDPC code performs as close as 0.97 dB from
Shannon limit at BER 10
−6
with encoding complexity (1.0225 N), for R = 0.928 and
N = 14364 – a result that no other published techniques can reach
Multiple Parallel Concatenated Gallager Codes and Their Applications
Due to the increasing demand of high data rate of modern wireless communications, there is a significant interest in error control coding. It now plays a significant role in digital communication systems in order to overcome the weaknesses in communication channels. This thesis presents a comprehensive investigation of a class of error control codes known as Multiple Parallel Concatenated Gallager Codes (MPCGCs) obtained by the parallel concatenation of well-designed LDPC codes. MPCGCs are constructed by breaking a long and high complexity of conventional single LDPC code into three or four smaller and lower complexity LDPC codes. This design of MPCGCs is simplified as the option of selecting the component codes completely at random based on a single parameter of Mean Column Weight (MCW).
MPCGCs offer flexibility and scope for improving coding performance in theoretical and practical implementation. The performance of MPCGCs is explored by evaluating these codes for both AWGN and flat Rayleigh fading channels and investigating the puncturing of these codes by a proposed novel and efficient puncturing methods for improving the coding performance.
Another investigating in the deployment of MPCGCs by enhancing the performance of WiMAX system. The bit error performances are compared and the results confirm that the proposed MPCGCs-WiMAX based IEEE 802.16 standard physical layer system provides better gain compared to the single conventional LDPC-WiMAX system.
The incorporation of Quasi-Cyclic QC-LDPC codes in the MPCGC structure (called QC-MPCGC) is shown to improve the overall BER performance of MPCGCs with reduced overall decoding complexity and improved flexibility by using Layered belief propagation decoding instead of the sum-product algorithm (SPA).
A proposed MIMO-MPCGC structure with both a 2X2 MIMO and 2X4 MIMO configurations is developed in this thesis and shown to improve the BER performance over fading channels over the conventional LDPC structure
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