• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.93-96
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• 2005

We propose a computationally efficient sphere decoding (SD) algorithm with smart radius control (SRC). As a baseline algorithm for SD, we consider the modified Schnorr-Euchner (SE) algorithm [1] (hereafter, called as the MSE algorithm). In principle, the radius after zero-forcing decision feedback equalization (ZF-DFE) estimation can be reduced further if we select a new lattice vector closer to the received signal vector than the lattice vector corresponding to the ZF-DFE estimate does. In our case, we obtain such a better lattice vector by performing a sequence of alternating one-dimensional searches, starting from the ZF-DFE estimate. We then develop a novel SRC algorithm that adopts adaptively the additional radius reduction process according to the estimated signal-to-noise-power ratio (SNR) after ZF-DFE estimation. In addition, we analyze the effect of detection ordering on the complexity for SD. Column-norm ordering of the channel matrix and optimal ordering [1] are considered here. From our analyses, we see that SRC can reduce greatly the complexity for SD and the degree of complexity reduction gets significant as the SNR decreases, irrespective of detection ordering schemes used.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.7A
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• pp.623-631
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• 2010

In this paper, various of pilot-assisted channel estimation techniques for 3GPP LTE downlink are tested under multipath Rayleigh fading channel. At first, the conventional channel estimation techniques are applied with linear zero-forcing (ZF) equalizer, such as one dimensional least square (1-D LS) linear interpolation, two dimensional (2-D) wiener filter, the time and frequency dimension separate wiener filter and maximum likelihood estimator (MLE). Considering the practical implementation, we proposed two channel estimation techniques by combining time-dimension wiener filter and MLE in two manners, which showed a good tradeoff between system performance and complexity when comparing with conventional techniques. The nonlinear decision feedback equalizer (DFE) which can show a better performance than linear ZF equalizer is also implemented for mitigating inter-carrier interference (ICI) in our system. The complexity of these algorithms are calculated in terms of the number of complex multiplications (CMs) and the performances are evaluated by showing the bit error rate (BER).

• Korean Journal of Remote Sensing
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• v.33 no.2
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• pp.249-255
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• 2017

Antarctica isimportant area in order to understand climate change. In addition, this area is complex region where indicate warming and cooling trend according to previous studies. Therefore, it is necessary to understand the long-term variability of Antarctic energy budget. Net radiation, one of energy budget factor, is affected by albedo, and albedo cause negative radiative forcing. It is necessary to analyze a relationship between albedo and net radiation in order to analyze relationship between two factors in Antarctic climate changes and ice-albedo feedback. In thisstudy, we calculated net radiation using satellite data and performed an analysis of long-term variability of net radiation over Antarctica. In addition we analyzed correlation between albedo. As a results, net radiation indicates a negative value in land and positive value in ocean during study periods. As an annual changes, oceanic trend indicates an opposed to albedo. Time series pattern of net radiation is symmetrical with albedo. Correlation between the two factors indicate a negative correlation of -0.73 in the land and -0.32 in the ocean.

• Journal of the Korean earth science society
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• v.32 no.2
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• pp.239-247
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• 2011

The United Nations Framework Convention on Climate Change and the corresponding national low-carbon policy should be grounded on the scientific understanding of climate sensitivity to the increase in CO2 concentration. This is, however, precluded by the fact that current estimates of the climate sensitivity highly vary. To understand the scientific background, limitations, and prospects of the climate sensitivity study, this paper reviews, as objectively as possible, the most recent results on the sensitivity issue. Theoretically, the climate sensitivity hinges on climate feedbacks from various atmospheric and surface physical processes. Especially cloud and sea-ice processes associated with shortwave radiation are known to have largest uncertainty, resulting in an inaccurate estimation of climate sensitivity. For this reason, recent observational studies using satellite data suggest sensitivity lower than or similar to those estimated by climate models (2-5 K per doubled CO2).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4C
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• pp.351-363
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• 2006

The 8-VSB modulation, the transmission standard for the terrestrial digital television(DTV) of the Advanced Television Systems Committee(ATSC), suffers from multipath fading because it conveys information on the amplitude. To solve this problem, decision feedback equalizers(DFE's) have been commonly used in terrestrial DTV receivers. However, under severe channels, such as a 0 dB ghost channel or a single frequency network (SFN) channel, the DFE shows unstable convergence due to the error propagation caused by decision errors. Instead of unstable time-domain DFE schemes, by proposing a frequency-domain direct-inversion equalization method, we try to guarantee stable equalization and achieve low symbol error rates. To secure the existence of a channel inverse, channel-matched filtering and noncausal filtering are carried out prior to equalization. Simulation results show that the proposed method performs much better than existing DFE schemes in terms of both the stability and the symbol error rate.

• The KIPS Transactions:PartA
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• v.12A no.2 s.92
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• pp.181-190
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• 2005

The development of web-based distance education surroundings is steadily achieving. However the studying on the learning effect of learners is still weak against development of educational media itself. At present, most of the distance education system is showing limits in the evaluation of the learning effect because the teaming evaluation depends on mid or final-term exams by on-line or off-line. There is a strong point that the distance education is free from space and time. One of present weak points is limitation of evaluating learner's attitude which can estimate learning effects. Earnest teaming attitude at distance education is important factor for improving the learning effects. In this paper, we propose a model for improving the teaming effects by forcing real-time evaluation and returning feedback to learners at the cyber lectures. The developed experimental system is verified its possibilities.