• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.2
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• pp.432-438
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• 2011

This paper describes an analysis of optimal design conditions of multi-mode LDPC(low density parity check) decoder which supports three block lengths (648, 1296, 1944) and four code rates (1/2, 2/3, 3/4, 5/6) for IEEE 802.11n WLAN system. A fixed-point model of LDPC decoder, which adopts min-sum algorithm and layered decoding scheme, is implemented using Matlab. From fixed-point simulation results for various bit-width parameters such as internal bit-width, integer/fractional part bit-widths, optimal design conditions and decoding performance of LDPC decoder are analyzed.

• Journal of Communications and Networks
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• v.15 no.2
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• pp.217-221
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• 2013

Quantum low-density parity-check (LDPC) codes based on the Calderbank-Shor-Steane construction have low encoding and decoding complexity. The sum-product algorithm(SPA) can be used to decode quantum LDPC codes; however, the decoding performance may be significantly decreased by the many four-cycles required by this type of quantum codes. All four-cycles can be eliminated using the entanglement-assisted formalism with maximally entangled states (ebits). The proposed entanglement-assisted quantum error-correcting code based on Euclidean geometry outperform differently structured quantum codes. However, the large number of ebits required to construct the entanglement-assisted formalism is a substantial obstacle to practical application. In this paper, we propose a novel class of entanglement-assisted quantum LDPC codes constructed using classical Euclidean geometry LDPC codes. Notably, the new codes require one copy of the ebit. Furthermore, we propose a construction scheme for a corresponding zigzag matrix and show that the algebraic structure of the codes could easily be expanded. A large class of quantum codes with various code lengths and code rates can be constructed. Our methods significantly improve the possibility of practical implementation of quantum error-correcting codes. Simulation results show that the entanglement-assisted quantum LDPC codes described in this study perform very well over a depolarizing channel with iterative decoding based on the SPA and that these codes outperform other quantum codes based on Euclidean geometries.

• Journal of Communications and Networks
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• v.17 no.4
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• pp.351-361
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• 2015

In this paper, a new decoding scheme is proposed to improve the error correcting performance of low-density parity-check (LDPC) codes in high signal-to-noise ratio (SNR) region by using post-processing. It behaves as follows: First, a conventional LDPC decoding is applied to received LDPC codewords one by one. Then, we count the number of word errors in a predetermined number of decoded codewords. If there is no word error, nothing needs to be done and we can move to the next group of codewords with no delay. Otherwise, we perform a proper post-processing which produces a new soft-valued codeword (this will be fully explained in the main body of this paper) and then apply the conventional LDPC decoding to it again to recover the unsuccessfully decoded codewords. For the proposed decoding scheme, we adopt a simple product code structure which contains LDPC codes and simple algebraic codes as its horizontal and vertical codes, respectively. The decoding capability of the proposed decoding scheme is defined and analyzed using the parity-check matrices of vertical codes and, especially, the combined-decodability is derived for the case of single parity-check (SPC) codes and Hamming codes used as vertical codes. It is also shown that the proposed decoding scheme achieves much better error correcting capability in high SNR region with little additional decoding complexity, compared with the conventional LDPC decoding scheme.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.05a
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• pp.771-774
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• 2010

In this paper, BER performance of LDPC(Low-Density Parity-Check) decoder for WiMAX is analyzed, and optimal design conditions of LDPC decoder are derived. The min-sum LDPC decoding algorithm which is based on an approximation of LLR sum-product algorithm is modeled and simulated by Matlab, and it is analyzed that the effects of LLR approximation bit-width and maximum iteration cycles on the bit error rate(BER) performance of LDCP decoder. The parity check matrix for IEEE 802.16e standard which has block length of 2304 and code rate of 1/2 is used, and AWGN channel with QPSK modulation is assumed. The simulation results show that optimal BER performance is achieved for 7 iteration cycles and LLR bit-width of (8,6).

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

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.4
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• pp.569-574
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• 2017

In order to transmit information in a channel environment in which noise exists, a coding technique of information is required. One of the coding techniques used for error detection and correction close to the Shannon limit is Low Density Parity Code(LDPC). LDPC and decoding characteristic features by Sum-product algorithm are matched for the performance to Turbo Code, RA(Repeat Accumulate) code, in case of very long code length of LDPC surpass their performance. This paper explains LDPC coding scheme of image data and decoding scheme, implements LDPC decoder in FPGA.

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

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

• Journal of Korea Multimedia Society
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• v.9 no.6
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• pp.728-734
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• 2006

Carrier interferometry code is considered as a promising scheme that provides significant performance improvement via frequency diversity effect. Space-time coding is commonly employed to achieve a performance gain through space diversity. The combination of these techniques and forward error correction coding will lead to enhanced system capacity and performance. This paper presents a low-density parity check (LDPC) coded space-time orthogonal frequency division multiplexing (OFDM) transmission scheme with carrier interferometry code for high-capacity and high-performance mobile multimedia communications. Computer simulations demonstrate that the proposed mobile multimedia transmission system offers a considerable performance improvement of approximately 9dB in terms of Eb/No in the Rayleigh fading channel with relatively low delay spread, in comparison with space-time OFDM. Performance gains are further increased, comparing with traditional OFDM systems.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.55-58
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• 2004

This this paper, we propose vertical Bell laboratories layered space time (V-BLAST) system based on variable rate Low-Density Parity Check (LDPC) codes to improve performance of receiver when QR decomposition interference suppression combined with interference cancellation is used over independent Rayleigh fading channel. The different rate LDPC codes can be made by puncturing some rows of a given parity check matrix. This allows to implement a single encoder and decoder for different rate LDPC codes. The performance can be improved by assigning stronger LDPC codes in lower layer than upper layer because the poor SNR of first detected data streams makes error propagation. Keeping the same overall code rates, the V-BLAST system with different rate LDPC codes has the better performance (in terms of Bit Error Rate) than with constant rate LDPC code in fast fading channel.