• Title/Summary/Keyword: LDPC부호

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Adaptive Hard Decision Aided Fast Decoding Method in Distributed Video Coding (적응적 경판정 출력을 이용한 고속 분산 비디오 복호화 기술)

  • Oh, Ryang-Geun;Shim, Hiuk-Jae;Jeon, Byeung-Woo
    • Journal of the Institute of Electronics Engineers of Korea SP
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    • v.47 no.6
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    • pp.66-74
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    • 2010
  • Recently distributed video coding (DVC) is spotlighted for the environment which has restriction in computing resource at encoder. Wyner-Ziv (WZ) coding is a representative scheme of DVC. The WZ encoder independently encodes key frame and WZ frame respectively by conventional intra coding and channel code. WZ decoder generates side information from reconstructed two key frames (t-1, t+1) based on temporal correlation. The side information is regarded as a noisy version of original WZ frame. Virtual channel noise can be removed by channel decoding process. So the performance of WZ coding greatly depends on the performance of channel code. Among existing channel codes, Turbo code and LDPC code have the most powerful error correction capability. These channel codes use stochastically iterative decoding process. However the iterative decoding process is quite time-consuming, so complexity of WZ decoder is considerably increased. Analysis of the complexity of LPDCA with real video data shows that the portion of complexity of LDPCA decoding is higher than 60% in total WZ decoding complexity. Using the HDA (Hard Decision Aided) method proposed in channel code area, channel decoding complexity can be much reduced. But considerable RD performance loss is possible according to different thresholds and its proper value is different for each sequence. In this paper, we propose an adaptive HDA method which sets up a proper threshold according to sequence. The proposed method shows about 62% and 32% of time saving, respectively in LDPCA and WZ decoding process, while RD performance is not that decreased.

Low Complexity Iterative Detection and Decoding using an Adaptive Early Termination Scheme in MIMO system (다중 안테나 시스템에서 적응적 조기 종료를 이용한 낮은 복잡도 반복 검출 및 복호기)

  • Joung, Hyun-Sung;Choi, Kyung-Jun;Kim, Kyung-Jun;Kim, Kwang-Soon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.8C
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    • pp.522-528
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    • 2011
  • The iterative detection and decoding (IDD) has been shown to dramatically improve the bit error rate (BER) performance of the multiple-input multiple-output (MIMO) communication systems. However, these techniques require a high computational complexity since it is required to compute the soft decisions for each bit. In this paper, we show IDD comprised of sphere decoder with low-density parity check (LDPC) codes and present the tree search strategy, called a layer symbol search (LSS), to obtain soft decisions with a low computational complexity. In addition, an adaptive early termination is proposed to reduce the computational complexity during an iteration between an inner sphere decoder and an outer LDPC decoder. It is shown that the proposed approach can achieve the performance similar to an existing algorithm with 70% lower computational complexity compared to the conventional algorithms.

Estimation of soft decision channel gain for coded MIMO system (부호화된 MIMO 시스템에서 연판정 채널 이득값의 계산)

  • Kim, Young-Min;Shang, Ping Ping;Kim, Soo-Young
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.6A
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    • pp.577-586
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    • 2011
  • Modem digital communication systems are required to use forward error correction (FEC) codes to combat inevitable channel impairment. Turbo codes or low density parity check (LDPC) codes, using iterative decoding with soft decision detection (SDD) information, are the most common examples. The excellent performance of these codes should be conditioned on accurate estimation of soft decision detection information. In order to use FEC codes with iterative decoding for Multi-Input Multi-Output (MIMO) system, reliable soft decision channel gain should be provided. In this paper, we investigate efficient SDD methods for turbo-coded MIMO system, and derive the corresponding formulas of SDD for various MIMO detection schemes. We present simulation results of the derived SDD schemes for turbo-coded MIMO systems, and show that the presented results almost approximate to maximum likelihood detection performance with much less computational load.

EM Algorithm for Designing Soft-Decision Binary Error Correction Codes of MLC NAND Flash Memory (멀티 레벨 낸드 플래시 메모리용 연판정 복호를 수행하는 이진 ECC 설계를 위한 EM 알고리즘)

  • Kim, Sung-Rae;Shin, Dong-Joon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.39A no.3
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    • pp.127-139
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    • 2014
  • In this paper, we present two signal processing techniques for designing binary error correction codes for Multi-Level Cell(MLC) NAND flash memory. MLC NAND flash memory saves the non-binary symbol at each cell and shows asymmetric channel LLR l-density which makes it difficult to design soft-decision binary error correction codes such as LDPC codes and Polar codes. Therefore, we apply density mirroring and EM algorithm for approximating the MLC NAND flash memory channel to the binary-input memoryless channel. The density mirroring processes channel LLRs to satisfy roughly all-zero codeword assumption, and then EM algorithm is applied to l-density after density mirroring for approximating it to mixture of symmetric Gaussian densities. These two signal processing techniques make it possible to use conventional code design algorithms, such as density evolution and EXIT chart, for MLC NAND flash memory channel.

Soft Detection using QR Decomposition for Coded MIMO System (부호화된 MIMO 시스템에서 QR 분해를 이용한 효율적인 연판정 검출)

  • Zhang, Meixiang;Kim, Soo-Young
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.37 no.7A
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    • pp.535-544
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    • 2012
  • Multi-Input Multi-Output (MIMO) transmission is now considered as one of essential techniques enabling high rate data transmissions in wireless communication systems. In addition, severe channel impairments in wireless systems should be compensated by using highly efficient forward error correction (FEC) codes. Turbo codes or low density parity check (LDPC) codes, using iterative decoding with soft decision detection information (SDDI), are the most common examples. The excellent performance of these codes should be conditioned on accurate estimation of SDDI from the MIMO detection process. In this paper, we propose a soft MIMO detection scheme using QR decomposition of channel matrices as an efficient means to provide accurate SDDI to the iterative decoder. The proposed method employed a two sequential soft MIMO detection process in order to reduce computational complexity. Compared to the soft ZF method calculating the direct inverse of the channel matrix, the complexity of the proposed method can be further reduced as the number of antennas is increased, without any performance degradation.

Performance Analysis of a Bit Mapper of the Dual-Polarized MIMO DVB-T2 System (이중 편파 MIMO를 쓰는 DVB-T2 시스템의 비트 매퍼 성능 분석)

  • Kang, In-Woong;Kim, Youngmin;Seo, Jae Hyun;Kim, Heung Mook;Kim, Hyoung-Nam
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.38A no.9
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    • pp.817-825
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    • 2013
  • The UHDTV system, which provides realistic service with ultra-high definite video and multi-channel audio, has been studied as a next generation broadcasting service. Since the conventional digital terrestrial transmission system is not capable to cover the increased transmission data rate of the UHDTV service, there are great necessity of researches about increase of data rate. Accordingly, the researches has been studied to increase the transmission data rate of the DVB-T2 system using dual-polarized MIMO technique and high order modulation. In order to optimize the MIMO DVB-T2 system where irregular LDPC codes are used, it is necessary to study the design of the bit mapper that matches the LDPC code and QAM symbols in MIMO channel. However, the research related to the design of the bit mapper has been limited to the SISO system. Therefore, this paper defines a new parameter that indicates the VND distribution of MIMO DVB-T2 system and performs the performance analysis according to the parameter which will be helpful for designing a MIMO bit mapper.

Distributed Video Coding based on Adaptive Block Quantization Using Received Motion Vectors (수신된 움직임 벡터를 이용한 적응적 블록 양자화 기반 분산 비디오 코딩 방법)

  • Min, Kyung-Yeon;Park, Sea-Nae;Nam, Jung-Hak;Sim, Dong-Gyu;Kim, Sang-Hyo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.35 no.2C
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    • pp.172-181
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    • 2010
  • In this paper, we propose an adaptive block quantization method. The propose method perfrect reconstructs side information without high complexity in the encoder side, as transmitting motion vectors from a decoder to an encoder side. Also, at the encoder side, residual signals between reconstructed side information and original frame are adaptively quantized to minimize parity bits to be transmitted to the decoder. The proposed method can effectively allocate bits based on bit error rate of side information. Also, we can achieved bit-saving by transmission of parity bits based on the error correction ability of the LDPC channel decoder, because we can know bit error rate and positions of error bit in encoder side. Experimental results show that the proposed algorithm achieves bit-saving by around 66% and delay of feedback channel, compared with the convntional algorithm.

Unequal Power MIMO SM Scheme for Different Modulation Orders (다른 변조 차수를 위한 비균등 전력을 이용한 MIMO SM 기법)

  • Seo, Jae Hyun;Kim, Heung Mook;Kim, Hong Jung;Jung, Tae Jin
    • Proceedings of the Korean Society of Broadcast Engineers Conference
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    • 2012.07a
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    • pp.181-182
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    • 2012
  • 본 논문에서는 DVB-NGH 시스템에서 수직-수평 편파 안테나를 이용한 $2{\times}2$ MIMO SM 기법 중 두 안테나에 서로 다른 변조 차수를 가진 신호를 전송할 경우 비균등 전력을 이용하여 수신 성능을 향상시키는 기법을 제안한다. 이를 위해 기존의 MIMO SM 구조와 비교해 서로 다른 변조 차수를 가진 신호에 비균등 전력을 포함하는 송수신 시스템의 구조를 도입하였다. 전산실험 결과 LDPC 부호율이 각각 4/9, 2/3에서 비트오류율이 $10^{-4}$의 조건에서 0.2, 0.5 dB의 성능 향상이 있음을 확인할 수 있다.

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A Cooperative Communication System using Cross-Layer Coding Method base on Hybrid-ARQ (Cross-Layer 부호기법을 이용한 Hybrid-ARQ 기반의 협력통신 시스템 연구)

  • Park, Tae-Doo;Kim, Min-Hyuk;Kim, Chul-Seung;Jung, Ji-Won
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.35 no.11C
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    • pp.889-895
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    • 2010
  • MIMO system generally requires more than one antenna at the communication device. However, many wireless devices are limited by size, cost or hardware complexity to one antenna. To overcome such restrictions, we used a new technique, called cooperative communication. We propose a new cooperative transmission strategy system using cross-layer coding method base on H-ARQ for optimal communication. Proposed cooperative H-ARQ system that can improve the above problems and can get the better performance. In proposed cooperative system with H-ARQ method, if the received signal from source node is satisfied by the destination preferentially, the destination transmit ACK message to both relay node and source node, and then recovers the received signal. In addition, if ARQ message indicates NACK message, relay node operates selective retransmission. Based on the simulation results in aspect to BER performance and throughput, the proposed method which combined cooperative system with H-ARQ based on cross-layer coding can improve spectral efficiency reliability of system compared with that of general one by one system.

Transform domain Wyner-Ziv Coding based on the frequency-adaptive channel noise modeling (주파수 적응 채널 잡음 모델링에 기반한 변환영역 Wyner-Ziv 부호화 방법)

  • Kim, Byung-Hee;Ko, Bong-Hyuck;Jeon, Byeung-Woo
    • Journal of Broadcast Engineering
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    • v.14 no.2
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    • pp.144-153
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    • 2009
  • Recently, as the necessity of a light-weighted video encoding technique has been rising for applications such as UCC(User Created Contents) or Multiview Video, Distributed Video Coding(DVC) where a decoder, not an encoder, performs the motion estimation/compensation taking most of computational complexity has been vigorously investigated. Wyner-Ziv coding reconstructs an image by eliminating the noise on side information which is decoder-side prediction of original image using channel code. Generally the side information of Wyner-Ziv coding is generated by using frame interpolation between key frames. The channel code such as Turbo code or LDPC code which shows a performance close to the Shannon's limit is employed. The noise model of Wyner-Ziv coding for channel decoding is called Virtual Channel Noise and is generally modeled by Laplacian or Gaussian distribution. In this paper, we propose a Wyner-Ziv coding method based on the frequency-adaptive channel noise modeling in transform domain. The experimental results with various sequences prove that the proposed method makes the channel noise model more accurate compared to the conventional scheme, resulting in improvement of the rate-distortion performance by up to 0.52dB.