• Title/Summary/Keyword: Low Density Parity Check

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Protograph-Based Block LDPC Code Design for Marine Satellite Communications (해양 위성 통신을 위한 프로토그래프 기반 블록 저밀도 패리티 검사 부호 설계)

  • Jeon, Ki Jun;Ko, Byung Hoon;Myung, Se-Chang;Lee, Seong Ro;Kim, Kwang Soon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.39C no.7
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    • pp.515-520
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    • 2014
  • In this paper, the protograph-based block low density parity check (LDPC) code, which improves the performance and reduces the encoder/decoder complexity than the conventional Digital Video Broadcasting Satellite Second Generation (DVB-S2) LDPC code used for the marine satellite communication, is proposed. The computer simulation results verify that the proposed protograph-based LDPC code has the better performance in both the bit error rate (BER) and the frame error rate (FER) than the conventional DVB-S2 LDPC code. Furthermore, by analyzing the encoding and decoding computational complexity, we show that the protograph-based block LDPC code has the efficient encoder/decoder structure.

UEP Effect Analysis of LDPC Codes for High-Quality Communication Systems (고품질 통신 시스템을 위한 LDPC 부호의 UEP 성능 분석)

  • Yu, Seog Kun;Joo, Eon Kyeong
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.38A no.6
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    • pp.471-478
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    • 2013
  • Powerful error control and increase in the number of bits per symbol should be provided for future high-quality communication systems. Each message bit may have different importance in multimedia data. Hence, UEP(unequal error protection) may be more efficient than EEP(equal error protection) in such cases. And the LDPC(low-density parity-check) code shows near Shannon limit error correcting performance. Therefore, the effect of UEP with LDPC codes is analyzed for high-quality message data in this paper. The relationship among MSE(mean square error), BER(bit error rate) and the number of bits per symbol is analyzed theoretically. Then, total message bits in a symbol are classified into two groups according to importance to prove the relationship by simulation. And the UEP performance is obtained by simulation according to the number of message bits in each group with the constraint of a fixed total code rate and codeword length. As results, the effect of UEP with the LDPC codes is analyzed by MSE according to the number of bits per symbol, the ratio of the message bits, and protection level of the classified groups.

Row-splitting Algorithm for Low Density Parity Check Codes (LDPC 부호를 위한 행 분할 알고리즘)

  • Jung, Man-Ho;Lee, Jong-Hoon;Kim, Soo-Young;Song, Sang-Seob
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.45 no.2
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    • pp.92-96
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    • 2008
  • Practical communication systems need to operate at various different rates. This paper describes and analyzes low-density parity check codes for various different rates. From a specific mother code, it allows LDPC codes for different rate. The advantage of this technique is that each different rate LDPC codes have a same block length as mother code though the rate changes so it can make up for the weak points of puncturing and shortening which reduce their block length as the rate changes. Row-splitting method is to split the row, so that the rate changes from a higher rate to lower rate and cause of its own property, it can overcome the defect of row-combining method.

Performance of pilot-assisted coded-OFDM-CDMA using low-density parity-check coding in Rayleigh fading channels (레일리 페이딩 채널에서 파일럿 기법과 LDPC 코딩이 적용된 COFDM-CDMA의 성능 분석)

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

Low-Complexity Multi-Size Circular Shifter for QC-LDPC Decoder Based on Two Serial Barrel-Rotators (두 개의 직렬 Barrel-Rotator를 이용한 QC-LDPC 복호기용 저면적 Multi-Size Circular Shifter)

  • Kang, Hyeong-Ju
    • 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%.

Design of a Low-Power LDPC Decoder by Reducing Decoding Iterations (반복 복호 횟수 감소를 통한 저전력 LDPC 복호기 설계)

  • Lee, Jun-Ho;Park, Chang-Soo;Hwang, Sun-Young
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.32 no.9C
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    • pp.801-809
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    • 2007
  • LDPC Low Density Parity Check) code, which is an error correcting code determined to be applied to the 4th generation mobile communication systems, requires a heavy computational complexity due to iterative decodings to achieve a high BER performance. This paper proposes an algorithm to reduce the number of decoding iterations to increase performance of the decoder in decoding latency and power consumption. Measuring changes between the current decoded LLR values and previous ones, the proposed algorithm predicts directions of the value changes. Based on the prediction, the algorithm inverts the sign bits of the LLR values to speed up convergence, which means parity check equation is satisfied. Simulation results show that the number of iterations has been reduced by about 33% without BER performance degradation in the proposed decoder, and the power consumption has also been decreased in proportional to the amount of the reduced decoding iterations.

Simplified 2-Dimensional Scaled Min-Sum Algorithm for LDPC Decoder

  • Cho, Keol;Lee, Wang-Heon;Chung, Ki-Seok
    • Journal of Electrical Engineering and Technology
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    • v.12 no.3
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    • pp.1262-1270
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    • 2017
  • Among various decoding algorithms of low-density parity-check (LDPC) codes, the min-sum (MS) algorithm and its modified algorithms are widely adopted because of their computational simplicity compared to the sum-product (SP) algorithm with slight loss of decoding performance. In the MS algorithm, the magnitude of the output message from a check node (CN) processing unit is decided by either the smallest or the next smallest input message which are denoted as min1 and min2, respectively. It has been shown that multiplying a scaling factor to the output of CN message will improve the decoding performance. Further, Zhong et al. have shown that multiplying different scaling factors (called a 2-dimensional scaling) to min1 and min2 much increases the performance of the LDPC decoder. In this paper, the simplified 2-dimensional scaled (S2DS) MS algorithm is proposed. In the proposed algorithm, we figure out a pair of the most efficient scaling factors which multiplications can be replaced with combinations of addition and shift operations. Furthermore, one scaling operation is approximated by the difference between min1 and min2. The simulation results show that S2DS achieves the error correcting performance which is close to or outperforms the SP algorithm regardless of coding rates, and its computational complexity is the lowest comparing to modified versions of MS algorithms.

Bit-to-Symbol Mapping Strategy for LDPC-Coded Turbo Equalizers Over High Order Modulations (LDPC 부호 기반의 터보 등화기에 적합한 고차 변조 심볼사상)

  • Lee, Myung-Kyu;Yang, Kyeong-Cheol
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.35 no.5C
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    • pp.432-438
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    • 2010
  • In this paper we study the effect of bit-to-symbol mappings on the convergence behavior of turbo equalizers employing low-density parity-check (LDPC) codes over high order modulations. We analyze the effective SNR of the outputs from linear minimum mean-squared error (MMSE) equalizers and the convergence property of LDPC decoding for different symbol mappings. Numerical results show that the bit-reliability (BR) mapping provides better performance than random mapping in LDPC-coded turbo equalizers over high order modulations. We also verify the effect of symbol mappings through the noise threshold and error performance.

Performance of Noise-Predictive Turbo Equalization for PMR Channel (수직자기기록 채널에서 잡음 예측 터보 등화기의 성능)

  • Kim, Jin-Young;Lee, Jae-Jin
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.33 no.10C
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    • pp.758-763
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    • 2008
  • We introduce a noise-predictive turbo equalization using noise filter in perpendicular magnetic recording(PMR) channel. The noise filter mitigates the colored noise in high-density PMR channel. In this paper, the channel detectors used are SOVA (Soft Output Viterbi Algorithm) and BCJR algorithm which proposed by Bahl et al., and the outer decoder used is LDPC (Low Density Parity Check) code that is implemented by sum-product algorithm. Two kinds of LDPC codes are experimented. One is the 0.5Kbyte (4336,4096) LDPC code with the code rate of 0.94, and the other is 1Kbyte (8432,8192) LDPC code with the code rate of 0.97.

Design and Performance Evaluation of Improved Turbo Equalizer (개선된 터보 등화기의 설계와 성능 평가)

  • An, Changyoung;Ryu, Heung-Gyoon
    • Journal of the Institute of Electronics and Information Engineers
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    • v.50 no.8
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    • pp.28-38
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    • 2013
  • In this paper, we propose a improved turbo equalizer which generates a feedback signal through a simple calculation to improve performance in single carrier system with the LMS(least mean square) algorithm based equalizer and LDPC(low density parity check) codes. LDPC codes can approach the Shannon limit performance closely. However, computational complexity of LDPC codes is greatly increased by increasing the repetition of the LDPC codes and using a long parity check matrix in harsh environments. Turbo equalization based on LDPC code is used for improvement of system performance. In this system, there is a disadvantage of very large amount of computation due to the increase of the repetition number. To less down the amount of this complicated calculation, The proposed improved turbo equalizer adjusts the adoptive equalizer after the soft decision and the LDPC code. Through the simulation results, it's confirmed that performance of improved turbo equalizer is close to the SISO-MMSE(soft input soft output minimum mean square error) turbo equalizer based on LDPC code with the smaller amount of calculation.