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In this paper, we employ to provide a method which combines Turbo codes and Low-Density Parity-Check (LDPC) codes based on Orthogonal Frequency Division Multiplexing (OFDM) system by adaptive encoding. The technique of channel estimation is used. The code rate and encoding scheme are all adaptive selection in the light of different channel conditions, so that we can make good use of these two types...
Message-Passing is the main decoding algorithm for Low-Density Parity Check (LDPC) Codes, in which Logarithmic Belief Propagation (Log-BP) algorithm is the most popularly used one. Particle Swarm Optimization (PSO) can also be regarded as an optimization algorithm by message-passing, which makes it possible to combine Log-BP algorithm with PSO. PSO was introduced into Log-BP algorithm by regarding...
A coding scheme for the Gaussian wiretap channel based on low-density parity-check (LDPC) codes is presented. The messages are transmitted over punctured bits to hide data from eavesdroppers. It is shown by means of density evolution that the BER of an eavesdropper, who operates below the code's SNR threshold and has the ability to use a bitwise MAP decoder, increases to 0.5 within a few dB. It is...
We derive the exact log-likelihood ratio (LLR) for iterative decoding of low-density parity-check codes for pilot-symbol-assisted BPSK transmission over flat Rayleigh fading channels. The bit-error rate (BER) performances of this metric are studied for various interleavers and different pilot spacings. We further compare this metric with the approximate metric, which has been commonly used in the...
In this paper the issue of improving the performance of iterative decoders based on sub-optimal calculation of the messages exchanged during iterations (L-values) is addressed. It is well known in the literature that a simple-yet very effective-way to improve the performance of suboptimal iterative decoders is based on applying a scaling factor to the L-values. In this paper, starting with a theoretical...
In this paper, we consider multiple access schemes with correlated sources. Distributed source coding is not used; rather, the correlation is exploited at the access point (AP). In particular, we assume that each source uses a channel code to transmit, through an additive white Gaussian noise (AWGN) channel, its information to the AP, where component decoders, associated with the sources, iteratively...
Low density parity check (LDPC) codes have stimulated a lot of interest in recent years due to their capacity approaching performance and availability of fast decoding algorithms. The existing encoding scheme for LDPC code usually incurs too high complexity and should be changed to encoding scheme with low complexity. An elementary turbo structured Tanner graph construction and encoding scheme for...
The recently proposed split-row decoding algorithm provides significant improvements in the throughput, hardware efficiency and energy efficiency when compared to existing soft decision decoding algorithms at the cost of some error performance loss. In this paper we propose split-row threshold which outperforms the split-row algorithm while maintaining the same level of complexity. Simulation results...
The error-correcting performance of low-density parity check (LDPC) codes, when decoded using practical iterative decoding algorithms, is known to be very close to Shannon limits in the asymptotic limit of large blocklengths. A substantial limitation to the use of finite-length LDPC codes is the presence of an error floor in the low frame error rate (FER) region. This paper develops two methods, a...
The paper presents a novel approach to reduce the bit error rate (BER) in iterative belief propagation (BP) decoding of low density parity check (LDPC) codes. The behavior of the BP algorithm is first investigated as a function of number of decoder iterations, and it is shown that typical uncorrected error patterns can be classified into 3 categories: oscillating, nearly-constant, or random-like,...
Unequal error protection is the key to future transport of multimedia data. The paper presents an overview of some new approaches realizing UEP properties in physical transport, especially multicarrier modulation, or with LDPC and turbo codes. For multicarrier modulation, a UEP bit-loading method is described allowing for an arbitrary number of classes, arbitrary SNR margins between the classes and...
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