• 방송공학회논문지
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• 제16권6호
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• pp.1026-1035
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• 2011

본 논문은 기존 블록 터보 부호의 SISO(Soft-input Soft-output) 기반 반복 복호 알고리즘의 일반화 및 활용에 대한 연구를 다루고 있다. R. M. Pyndiah는 AWGN 채널(Additive White Gaussian Noise Channel)에서 2차원 Linear Block Code(선형 블록 부호, LBC) 결합으로 구성된 Product 부호의 SISO 반복 복호 방식을 제안했으며, 이를 블록 터보 부호라 하였다. 블록 터보 부호의 SISO 복호방식은 SIHO(Soft-input Hard-output) 복호 방식인 Chase 알고리즘의 부호 판정을 기반으로 연판정 정보를 생성 후 전달하여 반복적인 복호를 수행한다. 블록 터보 부호는 AWGN 채널에서 높은 Code-rate(부호율)의 Product 부호에 대해 적은 SISO 복호 반복만으로도 샤논 한계에 근접하는 우수한 성능을 보여준다. 본 논문에서는 BPSK(Binary Phase Shift Keying) 변조와 AWGN 채널 전송을 가정한 기존 블록 터보 부호 복호 알고리즘을 채널 출력의 LLR(Log-likelihood Ratio)에 기반한 알고리즘으로 일반화하고, LDPC(Low-density Parity Check) 부호와 블록 터보 부호의 직렬 결합 구조에서 일반화된 알고리즘 활용 예를 제시한다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(1)
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• pp.273-276
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• 2001

In this thesis we propose symbol-based decoding for turbo codes which is used SOVA as a decoding algorithm. The proposed turbo codes that is interleaved on symbol-by-symbol basis and inputted as n-bit symbols to the decoder. This method makes that the stages of the original trellis are merged together and the trellis depth is reduced by 1/n. We research turbo codes with symbol size n=2 in this paper and its performance.

• Journal of Communications and Networks
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• 제6권3호
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• pp.203-208
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• 2004

A combined precoding and turbo decoding strategy for multi-path frequency-selective fading channels is presented. The precoder and multi-path fading channel are jointly modeled as a finite-state probabilistic channel to provide the multi-stage turbo decoder with its statistics information. Both a priori and a posteriori probabilities are used in the metric computation to improve the system performance. Structures of the combined turbo-encoder, interleaver, and precoder in the transmitter and two-stage turbo decoder in the receiver are described. Performance of the proposed scheme in fixed, Rician and Rayleigh multi-path fading channels are evaluated by simulation. The results indicate that the combined precoding and two-stage turbo decoding strategy provides a considerable performance improvement while maintaining the same inner structure of a conventional turbo decoder.

• Journal of electromagnetic engineering and science
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• 제6권3호
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• pp.147-154
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• 2006

In this paper, we propose and present implementation results of a high-speed turbo decoding algorithm. The latency caused by (de) interleaving and iterative decoding in a conventional maximum a posteriori(MAP) turbo decoder can be dramatically reduced with the proposed design. The source of the latency reduction is come from the combination of the radix-4, dual-path processing, parallel decoding, and rearly-stop algorithms. This reduced latency enables the use of the turbo decoder as a forward error correction scheme in real-time wireless communication services. The proposed scheme results in a slight degradation in bit-error rate(BER) performance for large block sizes because the effective interleaver size in a radix-4 implementation is reduced to half, relative to the conventional method. Fixed on the parameters of N=212, iteration=3, 8-states, 3 iterations, and QPSK modulation scheme, we designed the adaptive high-speed turbo decoder using the Xilinx chip (VIRTEX2P (XC2VP30-5FG676)) with the speed of 17.78 Mb/s. From the results, we confirmed that the decoding speed of the proposed decoder is faster than conventional algorithms by 8 times.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(1)
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• pp.213-216
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• 2001

In this paper, the performance of an OFDM/CDMA system with turbo coding is analyzed and simulated in a multipath fading channel. Bit error probability is derived fDr a Rayleigh fading channel. In an OFDM/CDMA system, an OFDM and a CDMA techniques are combined to exploit the advantages of both techniques. For decoding of turbo code, MAP decoding algorithm is employed. From the simulation results. it is demonstrated that turbo coding offers considerable coding gain with reasonable encoding/decoding complexity. Also, it is shown that the BER performance is substantially improved by increasing the interleaver length for a fixed code rate and the increasing number of iterations used in the decoding process. The results in the paper can be applied to the design of OFDM-based CDMA system.

• ETRI Journal
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• 제25권1호
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• pp.1-8
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• 2003

This paper introduces an efficient iterative decoding method for high-dimensional block turbo codes. To improve the decoding performance, we modified the soft decision Viterbi decoding algorithm, which is a trellis-based method. The iteration number can be significantly reduced in the soft output decoding process by applying multiple usage of extrinsic reliability information from all available axes and appropriately normalizing them. Our simulation results reveal that the proposed decoding process needs only about 30% of the iterations required to obtain the same performance with the conventional method at a bit error rate range of $10^{-5}\;to\;10^{-6}$.

• 한국통신학회논문지
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• 제30권6C호
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• pp.442-449
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• 2005

최근 터보 부호에 비해서 구현시 복잡하지 않고, 높은 부호화율에서 거의 샤논 이론에 접근하는 Turbo Product Code(TPC)에 대해 관심이 고조되고 있다. 본 논문에서는 초고속 통신 시스템에 적용하기 위한 고속 TPC 복호를 위한 세가지의 알고리즘을 제안하는 바이다. 첫째로, 기존의 Turbo Product code 복호기에서 row과 column을 직렬로 복호를 하지 않고 복호 구조가 병렬로 동작하는 Turbo Product code 복호기를 제안한다. 둘째로 반복 중지 알고리즘을 제안하고 마지막으로, P-Parallel 알고리즘을 통해 P rows와 P columns을 병렬로 처리하여 복호한다. 모의 실험을 한 결과 기존의 방식에 비해 복호 지연이 줄어들고 성능면에서 직렬 방식과 거의 비슷한 성능이 나타난다. 또한 고속알고리즘을 바탕으로 VHDL모델링을 하였으며, 이를 timing 시뮬레이션 하여 메모리 요구량 및 복호 속도 향상도를 분석하였다.

• 한국통신학회논문지
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• 제25권3B호
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• pp.464-471
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• 2000

The number of quantization bits of the input signals $X_k$,$Y_k$ need to be optimally determined through the trade-off between the H/W complexity and the BER performance in Turbo codes applications. Also, an effective means to incorporate a channel reliability $L_c$ in the Log-MAP-based Turbo decoding is highly required. because it has a major effect on both the complexity and the performance. In this paper, a novel bit-shifting approach that substitutes for the multiplying is proposed so as to effectively incorporate. $L_c$ in Turbo decoding. The optimal number of quantization bits of $X_k$,$Y_k$ is investigated through Monte-Carlo simulations assuming that bit-shifting approach is adopted. In addition. The effects of an incorrect estimation of noise variance on the performance of Turbo codes is investigated. There is a confined range in which the effects of an incorrect estimation can be ignored.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 하계종합학술대회 논문집(1)
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• pp.39-42
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• 2004

Turbo codes, proposed by Berrou, that increase the interleaver size and the number of iteration have better than conventional convolutional codes, in case of BER performance. However, because turbo codes has been required much decoding delay to increase iteration number, it demands unnecessary iterative decoding. Therefore, in this paper, we propose iterative decoding stop criterion that uses the variance of absolute value of LLR. This algorithm can be reduced average iterative decoding number and had lossless performance of BER, because of decreasing unnecessary iterative decoding.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 추계종합학술대회 논문집
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• pp.175-178
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• 1998

In this paper, turbo codes with the DC-free trellis codes based on partition chain as constituent codes are presente. And efficient methods to design the DC-free turbo codes are introduced. An iterative decoding with the MAP algorithm is used for the decoding of the turbo codes designed by various methods. As results of simulations, the presented DC-free turbo codes show better error performances than the DC-free trellis codes.