• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39C no.8
• /
• pp.637-642
• /
• 2014

In this paper, we propose a efficient shift index searching algorithm for design of the block LDPC codes. It is combined with the message-passing based cycle search algorithm and ACE algorithm. We can determine the shift indices by ordering of priority factors which are effect on the LDPC code performance. Using this algorithm, we can construct the LDPC codes with low complexity compare to trellis-based search algorithm and save the memory for storing the parity check matrix.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38A no.9
• /
• pp.744-749
• /
• 2013

We propose soft user data input on LDPC codes with parity encoded by the (1, 7) run length limited (RLL) code for perpendicular magnetic recording channel. The user data are encoded by maximum transition run (MTR) (3;11) code. In order to minimize the loss of code rate, the (1, 7) RLL code only encode the parity of LDPC. Also, to increase performance, we propose only user data part applied soft output Viterbi algorithm (SOVA). The performance using the SOVA showed good performance lower than 26 dB. In contrast, it showed worse performance high than 26 dB. This is because of incorrect soft information by high jitter noise and two different input types for LDPC decoder.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.19 no.8
• /
• pp.1839-1844
• /
• 2015

The low-density parity-check(LDPC) code has been adopted in many communication standards due to its error correcting performance, and the quasi-cyclic LDPC(QC-LDPC) is widely used because of implementation easiness. In the QC-LDPC decoder, a cyclic-shifter is required to rotate data in various sizes. This kind of cyclic-shifters are called multi-size circular shifter(MSCS), and this paper proposes a low-complexity structure for MSCS. In the conventional serially-placed two barrel-rotators, the unnecessary multiplexers are revealed and removed, leading to low-complexity. The experimental results show that the area is reduced by about 12%.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.10C
• /
• pp.1363-1369
• /
• 2004

LDPC(Low Density Parity Check) codes are described by bipartite graphs with bit nodes and parity-check nodes. Tanner derived minimum distance bounds of the regular LDPC code in terms of the eigenvalues of the associated adjacency matrix. In this paper we generalize the Tanner's results. We derive minimum distance bounds applicable to both regular and blockwise-irregular LDPC codes. The first bound considers the relation between bit nodes in a minimum-weight codeword, and the second one considers the connectivity between parity nodes adjacent to a minimum-weight codeword. The derived bounds make it possible to describe the distance property of the code in terms of the eigenvalues of the associated matrix.

• Journal of Communications and Networks
• /
• v.10 no.1
• /
• pp.5-9
• /
• 2008

Researchers have investigated many upper bound techniques applicable to error probabilities on the maximum likelihood (ML) decoding performance of turbo-like codes and low density parity check (LDPC) codes in recent years for a long codeword block size. This is because it is trivial for a short codeword block size. Previous research efforts, such as the simple bound technique [20] recently proposed, developed upper bounds for LDPC codes and turbo-like codes using ensemble codes or the uniformly interleaved assumption. This assumption bounds the performance averaged over all ensemble codes or all interleavers. Another previous research effort [21] obtained the upper bound of turbo-like code with a particular interleaver using a truncated union bound which requires information of the minimum Hamming distance and the number of codewords with the minimum Hamming distance. However, it gives the reliable bound only in the region of the error floor where the minimum Hamming distance is dominant, i.e., in the region of high signal-to-noise ratios. Therefore, currently an upper bound on ML decoding performance for turbo-like code with a particular interleaver and LDPC code with a particular parity check matrix cannot be calculated because of heavy complexity so that only average bounds for ensemble codes can be obtained using a uniform interleaver assumption. In this paper, we propose a new bound technique on ML decoding performance for turbo-like code with a particular interleaver and LDPC code with a particular parity check matrix using ML estimated weight distributions and we also show that the practical iterative decoding performance is approximately suboptimal in ML sense because the simulation performance of iterative decoding is worse than the proposed upper bound and no wonder, even worse than ML decoding performance. In order to show this point, we compare the simulation results with the proposed upper bound and previous bounds. The proposed bound technique is based on the simple bound with an approximate weight distribution including several exact smallest distance terms, not with the ensemble distribution or the uniform interleaver assumption. This technique also shows a tighter upper bound than any other previous bound techniques for turbo-like code with a particular interleaver and LDPC code with a particular parity check matrix.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37 no.3A
• /
• pp.179-187
• /
• 2012

In this paper, we propose an adaptive DFE (Decision Feedback Equalizer) based on LDPC (Low Density Parity Check) code for phase noise suppression and performance improvement. The proposed equalizer in this paper is applied for wireless repeater system. So as to meet ever increasing requirements on higher wireless access data rate and better quality of service (QoS), the wireless repeater system has been studied. The echo channel and RF impairments such as phase noise produce performance degradation. In order to remove echo channel and phase noise, we suggest a novel adaptive DFE equalizer based on LDPC code. The proposed equalizer helps to compensate RF impairments and improve the performance significantly better than used independently. In addition, proposed equalizer has less iteration number of LDPC code. So, the proposed equalizer system has low complexity.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.5C
• /
• pp.532-538
• /
• 2003

In this paper we have investigated a novel approach applying low-density parity-check coding to a COFDM-CDMA system, which operates in a multi-path fading mobile channel. Developed as a linear-block channel coder, the LDPC code is known for a superior signal reception capability in AWGN and/or flat fading channels with respect to increased encoding rates, however, its performance degrades when the communication channel becomes multi-path fading. For a typical multi-path fading mobile channel with a SNR of 16㏈ or lower. in order to obtain a BER lower than 1 out of 10000, the LDPC code with encoding rates below 1:3 requires not only the inherent parity check information but also the piloting information for refreshing front-end equalizer taps of COFDM-CDMA, periodically. For instance, while the 1:3-rate LDPC coded transmission symbol is consisted of data bits and parity-check bits in 1 to 3 proportion, on the other hand, in the proposed method the same rate LDPC transmission symbol contains data bits, parity check bits, and pilot bits in 1 to 2 to 1 proportion, respectively. The included pilot bits are effective not only for channel estimation and channel equalization but for symbol decoding by assisting the parity-check bits, hence, improving SNR vs BER performance over the conventional 1:3-rate LDPC code. The proposed system performance has been verified using computer simulations in multi-path, Rayleigh fading channels, and the results show us that the proposed method out-performs the general LDPC channel coding methods in terms of SNR vs BER measurements.

• 전자공학회논문지 IE
• /
• v.43 no.4
• /
• pp.115-121
• /
• 2006

In this paper, we proposed about data error check and correction on channel transmission in the communication system. LDPC codes are used for minimizing channel errors by modeling AWGN Channel as a VDSL system. Because LDPC Codes use low density parity bit, mathematical complexity is low and relating processing time becomes shorten. Also the performance of LDPC code is better than that of turbo code in long code word on iterative decoding algorithm. This algorithm is better than conventional algorithms to correct errors, the proposed algorithm assigns weights for errors concerning parity bits. The proposed weighted Bit-flipping algorithm is better than the conventional Bit-flipping algorithm and we are recognized improve gain rate of 1 dB.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.11C
• /
• pp.901-906
• /
• 2010

Low density parity check (LDPC) code, first introduced by Gallager and re-discovered by MacKay et al, has attracted researcher's interest mainly due to their performance and low decoding complexity. It was remarkable that the performance is very close to Shannon capacity limit under the assumption of having long codeword length and iterative decoder. However, comparing to turbo codes widely used in the current mobile communication, the encoding complexity of LDPC codes has been regarded as the drawback. This paper proposes a solution for DVB-S2 LDPC encoder to reduce the encoder latency. We use the fast IRA encoder that use the transformation of the parity check matrix into block-wise form and the partial parallel process to reduce the number of system clocks for the IRA code encoding. We compare the proposed encoder with the current DVB-S2 encoder to show that the performance of proposal is better than that of the current DVB-S2 encoder.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.8 no.8
• /
• pp.1149-1154
• /
• 2013

In this paper, an algorithm having new edge growth with depth constraints for constructing Tanner graph of LDPC(Low density parity check) codes is proposed. This algorithm reduces effectively the number of small stoping set in the graph and has lower complexity than other algorithm. The simulation results shows the improved performance of the LDPC codes constructed by this algorithm.