• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1736-1738
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• 2016

In modern digital communication systems adapting high-order modulation and high performance channel code, log-likelihood ratios involving the repeated calculations of the logarithm of sum of exponential functions are necessary for demodulation and decoding. In this paper, the approximation methods called Min and MinC are applied to demodulation and decoding together and their complexity and joint performance are analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12A
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• pp.949-961
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• 2009

This paper analyses BER (Bit Error Rate) performance of 2-hop wireless communications networks with hybrid decode-and-forward (HDF) relays. The conventional HDF method is usually based on the receive signal-to-noise ratio (SNR) for the relay to decide whether to forward the decoded data in order to obviate the erroneous detection at the relay. In contrast, we propose a new solution of using log-likelihood ratio (LLR) as an efficient alternative to SNR. The approximate BER expressions of different HDF schemes are also derived and verified by Monte-Carlo simulations. In addition, we compute the optimum thresholds for HDF schemes. A variety of numerical results demonstrate that the new LLR-based HDF significantly outperforms the SNR-based HDF for any threshold level and relay location under flat Rayleigh fading channel plus AWGN (Additive White Gaussian Noise).

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.3
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• pp.127-133
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• 2009

In this study, dimensionless-cumulative rainfall curves were generated by multivariate Monte Carlo method. For generation of rainfall curve rainfall storms were divided and made into dimensionless type since it was required to remove the spatial and temporal variances as well as differences in rainfall data. The dimensionless rainfall curves were divided into 4 types, and log-ratio method was introduced to overcome the limitations that elements of dimensionless-cumulative rainfall curve should always be more than zero and the sum total should be one. Orthogonal transformation by Johnson system and the constrained non-normal multivariate Monte Carlo simulation were introduced to analyse the rainfall characteristics. The generative technique in stochastic rainfall variation using multivariate Monte Carlo method will contribute to the design and evaluation of hydrosystems and can use the establishment of the flood disaster prevention system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7C
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• pp.616-626
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• 2007

In spatially multiplexed MIMO systems that enable high data rate transmission over wireless communication channels, the spatial demultiplexing at the receiver is a challenging task, and various demultiplexing methods have been developed recently by many researchers. Among the previous methods, maximum likelihood detection with QR decomposition and M-algorithm (QRM-MM)), and sphere decoding (SD) schemes have been reported to achieve a (near) maximum likelihood (ML) performance. In this paper, we propose a novel signal detection method that achieves a near ML performance in a computationally efficient manner. The proposed method is demonstrated via a set of computer simulations that the proposed method achieves a near ML performance while requiring a complexity that is comparable to that of the conventional MMSE-OSIC. We also show that the log likelihood ratio (LLR) values for all bits are obtained without additional calculation but as byproduct in the proposed detection method, while in the previous QRM-MLD, SD, additional computation is necessary after the hard decision for LLR calculation.

• Journal of Broadcast Engineering
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• v.15 no.6
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• pp.742-748
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• 2010

Instead of using sphere decoding, list sphere decoding (LSD) has been introduced to increase the reliability of log-likelihood ratio (LLR) in recent soft decoding schemes employing iterative detection and decoding (IDD). Although LSD provides improved performance, it does not obtain complexity gain due to signal-to-noise ratio (SNR) increment as it detects large number of lattice points. Especially, its inefficient scenario arises when it has to search for lattice points which have small affect for obtaining LLR with high reliability. In this paper, we study an efficient algorithm to remove such lattice points, which results in complexity reduction based on radius optimization.

• The Journal of the Acoustical Society of Korea
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• v.36 no.4
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• pp.279-284
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• 2017

The localization of sources has a numerous number of applications. To estimate the position of sources, the relative time delay between two or more received signals for the direct signal must be determined. Although the GCC (Generalized Cross-Correlation) method is the most popular technique, an approach based on CCA (Canonical Correlation Analysis) was also proposed for the TDE (Time Delay Estimation). In this paper, we propose a new adaptive algorithm based on CCA in order to utilized the sparsity in the eigenvector of CCA based time delay estimator. The proposed algorithm uses the eigenvector corresponding to the maximum eigenvalue with log-sum regularization in order to utilize the sparsity in the eigenvector. We have performed simulations for several SNR(signal to noise ratio)s, showing that the new CCA based algorithm can estimate the time delays more accurately than the conventional CCA and GCC based TDE algorithms.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.12
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• pp.2534-2542
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• 2011

In this paper, we show that performance can be improved by using multiple antennas in the conventional orthogonal code hopping multiplexing (OCHM) scheme, which was proposed for accommodating a larger number of users with low channel activities than the number of orthogonal codewords used in code division multiple access (CDMA)-based communication systems through downlink statistical multiplexing. First, we introduce two different types of OCHM systems together with orthogonal codeword allocation strategies, and then derive their mathematical expression for log-likelihood ratio (LLR) values according to the two different schemes. Next, when a turbo encoder based on the LLR computation is used, we evaluate performance on the frame error rate (FER) for the aformentioned OCHM system. For comparison, we also show performance for the existing symbol mapping method using multiple antennas, which was used in 3GPP standards. As a result, it is shown that our OCHM system with multiple antennas based on the proposed orthogonal codeword allocation strategy leads to performance gain over the conventional system---energy required to satisfy a target FER is significantly reduced.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.144-148
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• 2009

지구온난화로 인한 홍수빈도 및 강우강도의 증가로 홍수피해의 규모는 더욱 증가하고 있다. 그리고 방재대책도 발생한 피해에 대한 복구를 주된 정책으로 하던 소극적 자세에서 벗어나 과학적 공학적 접근을 통해 재해에 대응할 수 있는 기술을 개발하는 적극적 홍수방어 체계를 구축하고 있다. 또한, 설계빈도의 무조건적인 상향조정에 따른 확정론적인 방법에 의존하기 보다는 추계학적 방법을 도입한 수문량 확충 및 매개변수의 불확실성 분석이 필요성이 대두되고 있는 실정이다. 일반적으로 수공구조물의 설계 시에는 설계홍수량을 사용하는데 이는 홍수특성, 홍수발생빈도, 홍수발생 가능성 등을 수공구조물의 규모와 파괴 시 예상되는 피해 정도에 따라 요구되는 안전성을 함께 고려해 수공구조물의 설계기준으로 활용된다. 설계홍수량은 지속시간과 재현기간을 사전에 지정하여 빈도분석을 통해 설계강우량을 산정하고 이를 강우-유출 분석을 함으로써 산정된다. 설계강우량은 빈도분석을 위해 선택된 강우형태에 따른 수문학적 무작위성을 포함하고 있다. 따라서 시간적 변동을 고려한 적절한 강우양상 형태의 선택은 수문학적으로 안전한 수공구조물의 설계 및 평가에 매우 큰 영향을 미친다. 현재의 경우는 강우형태에 대한 선택이 경험에 의해 임의로 이루어지므로, 토목공학자는 여러 가지 발생 가능한 강우형태에 따른 시간적 분포에 대해 고려해야 한다. 본 연구에서는 Huff분위에 따른 무차원 누가 강우곡선을 이용해 강우변동양상 생성을 위한 제약조건을 log-ratio 변환을 이용해 극복하였으며, 결과의 통계 특성치를 Johnson 분포를 통해 표준정규분포로 변환시켰다. 무작위 변수 발생 후 강우양상별 표준정규값의 상관행렬을 이용하여 상관성이 있는 무작위변수로 변환하였다. 얻어진 상관성을 갖는 무작위변수는 log-ratio 역변환을 통해 상관성을 갖는 변수로 재변환해서 무차원화된 강우곡선을 얻을 수 있었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12C
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• pp.1044-1051
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• 2010

In this paper, we propose an efficient soft-output signal detection method for spatially multiplexed multiple input multiple output (MIMO) systems. The proposed method is based on the ordered successive interference cancellation (OSIC) algorithm, but it significantly improves the performance of the original OSIC algorithm by solving the error propagation problem. The proposed method combines this enhanced OSIC (ESIC) algorithm with a multiple ordering technique in a very efficient way. As a result, the log likelihood ratio (LLR) values can be computed by using a very small set of candidate symbol vectors. The proposed method has been implemented with a $0.13{\mu}m$ CMOS technology for a $4{\times}4$ 16-QAM MIMO system. The simulation and implementation results show that the proposed detector provides a very good solution in terms of performance and hardware complexity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12C
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• pp.1197-1207
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• 2009

Orthogonal Frequency Division Multiple Access (OFDMA) is widely used as a multiple access technique for next generation mobile communication systems, however, its main drawback is the high peak-to-average ratio (PAPR). Thus for the uplink case where the transmit power is strictly limited due to the battery life of mobile units, single carrier frequency division multiple access (SC-FDMA) with low PAPR is preferred to OFDMA method. In this paper, we propose a method to improve the performance of SC-FDMA using frequency domain MMSE equalization. The proposed improved log-likelihood ratio (LLR) generation method exploits both the diversity characteristic of channels and the reciprocity that is obtained from the received signals. The complexity of the proposed method is analyzed and its performance gain is demonstrated via a set of computer simulations.