• 한국항공우주학회지
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• 제50권6호
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• pp.401-412
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• 2022

본 연구에서는 한반도에 대해 준 실시간 감시정찰을 수행하기 위한 여러 종류의 위성군 설계 기법들의 장단점을 조사하였다. 또한 지상 궤적 반복궤도 위성군과 워커 위성군을 이용하여 가용한 위성의 수, 궤도면 수 및 위상차에 대해 조합 가능한 모든 경우에서 위성군을 설계하고, 광학 위성과 합성개구레이더(SAR) 위성의 탑재체 제한조건을 반영하여 성능을 분석하였다. 평균 재방문 주기가 30분 이내로 준 실시간 한반도 감시정찰에 적합한 위성군의 특성을 제시하였다. 본 연구는 한반도 지역을 감시·정찰하기 위한 위성군 설계에 대한 전략을 수립하는 데 중요한 자료를 제공할 수 있으며, 나아가 초소형 위성군 운용을 위한 우주전력 구축에 대한 가이드라인을 제시하는 데 기여할 것이다.

• 한국통신학회논문지
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• 제32권2A호
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• pp.195-202
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• 2007

A differential space-frequency block code - orthogonal frequency division multiplexing (SFBC-OFDM) scheme as a multiple-input multiple-output (MIMO) transmission technique for next-generation digital multimedia broadcasting (DMB) is proposed in this paper. A linear decoding method for differential SFBC, which performs comparably to the ML decoding method, is derived for the cases of two or four transmit antennas. A simple table lookup method is proposed to improve the efficiency of the encoding/decoding process of DSFBC for the case of non-constant modulus constellations. A DMB MIMO channel model, developed by extending the 3GPP MIMO model to fit DMB environments, is used to compare BER performances of differential space block code schemes for various channel environments. Simulation results show that the differential SFBC-16QAM scheme using either four transmit antennas with one receive antenna or two transmit antennas with two receive antennas achieves a performance gain of 12dB than that of the conventional DQPSK scheme, even with a data rate twice faster.

• ETRI Journal
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• 제27권3호
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• pp.257-266
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• 2005

Many multi-modulus blind equalization algorithms (MMA) have been presented in the past to overcome the undesirable high misadjustment exhibited by the well-known constant modulus algorithm. Some of these MMA schemes, specifically tailored for quadrature amplitude modulation (QAM) constellations, have also been proved to fix the phase offset error without needing any rotator at the end of the equalizer stage. In this paper, a new multi-modulus algorithm is presented for QAM signals. The contribution lies in the technique to incorporate the sliced symbols (outcomes of decision device) in the multi-modulus-based weight adaptation process. The convergence characteristics of the proposed sliced multi-modulus algorithm (S-MMA) is demonstrated by way of simulations, and it is shown that it gives better steady-state performance in terms of residual inter-symbol interference and symbol-error rate. It has also been shown that the proposed algorithm exhibits lesser steady-state misadjustment compared to the best reported MMA.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(1)
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• pp.240-243
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• 2000

In this paper, new Multi-Modulus blind Equalizer Algorithms for QAM signal set is propsed and analyzed and its performance is evaluated. The MMA algorithm combines the benifits of RCA and CMA. A new Dual-mode blind Algorithms for QAM signal set is derived. The concept of this algorithms is based on the Dual-Mode algorithm and the MMA algorithm. In order to analyze and evaluate the performance of new MMA algorithms, computer simulation are performed for the nonsquare QAM signal constellations. Form the simulation results, we can verify that new MMA algorithms converges very fast comparing to conventional MMA algorithm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권6호
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• pp.2446-2462
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• 2016

In this paper, a frequency domain Expectation-Maximization (EM)-based channel estimation algorithm for Space Time Block Coded-Orthogonal Frequency Division Multiplexing (STBC-OFDM) systems is investigated to support higher data rate applications in wireless communications. The computational complexity of the frequency domain EM-based channel estimation is increased when higher order constellations are used because of the ascending size of the search set space. Thus, a search set reduction algorithm is proposed to decrease the complexity without sacrificing the system performance. The performance results of the proposed algorithm is obtained in terms of Bit Error Rate (BER) and Mean Square Error (MSE) for 16QAM and 64QAM modulation schemes.

• Journal of Communications and Networks
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• 제5권2호
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• pp.174-183
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• 2003

Space-Time (ST) codes are known to provide high transmission rates, diversity and coding gains. In this paper, a tight upper bound on the error probability of ST codes over rapid fading channels is presented. Moreover, ST codes suitable for rapid fading channels are presented. These codes are designed using the QPSK and 16-QAM signal constellations. The proposed codes are based on two different encoding schemes. The first scheme uses a single trellis encoder, whereas the second scheme uses the I-Q encoding technique. Code design is achieved via partitioning the signal space such that the design criteria are maximized. As a solution for the decoding problem of I-Q ST codes, the paper introduces a low-complexity decoding algorithm. Results show that the I-Q ST codes using the proposed decoding algorithm outperform singleencoder ST codes with equal complexity. The proposed codes are tested over fading channels with different interleaving conditions, where it is shown that the new codes are robust under such imperfect interleaving conditions.

• 대한전자공학회논문지
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• 제27권12호
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• pp.1792-1799
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• 1990

Two cases of block coded phase/frequncy modulations are investigated. minimum Euclidean distances are calculated as the function of modulation index h and rotation angle \ulcorner in the cases of 2-FSK/4-PSK and 2-FSK/8-PSK. Method of signal set partitioning is described, especially for the case of 2-FSK/8-PSK. The results are compared with S.I. Sayegh's work and shown better performance. For example, with simple parity check and repetition codes, we can get coding gain of 3 dB in the case of 2-FSK/4-PSK with block length n=4. We get 5.33 dB in the case of 2-FSK/8-PSK with n=4. And it is believed that we can get higher coding gain with proper combinations of block code and n-FSK/m-PSK type channel signal constellations.

• Journal of information and communication convergence engineering
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• 제16권1호
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• pp.6-11
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• 2018

It is important to find the random estimation points in wireless sensor network. A link quality indicator (LQI) is part of a network management service that is suitable for a ZigBee network and can be used for localization. The current quality of the received signal is referred as LQI. It is a technique to demodulate the received signal by accumulating the magnitude of the error between ideal constellations and the received signal. This proposed model accepts any number of random estimation point in the network and calculated its nearest anchor centroid node pair. Coordinates of the LQI sphere are calculated from the pair and are added iteratively to the initially estimated point. With the help of the LQI and weighted centroid localization, the proposed system finds the position of target node more accurately than the existing system by solving the problems related to higher error in terms of the distance and the deployment of nodes.

• 대한전자공학회논문지TC
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• 제49권8호
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• pp.65-69
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• 2012

회전 변환된 정사각 QAM 신호 성좌를 클리핑하여 좌표 축 인터리브 된 직교 설계(Coordinate Interleaved Orthogonal Design; CIOD)에 적용되는 낮은 최대 전력 대비 평균 전력 비(Peak-to-Average-Power Ratio; PAPR)을 가지는 신호 성좌를 설계한다. 본 논문에서 제안하는 신호 성좌는 기존의 회전 변환된 정사각 QAM 신호 성좌에 비해 매우 낮은 PAPR을 가질 뿐 아니라, 기존의 신호 성좌와 거의 동일한 비트 오율(Bit Error Rate; BER) 성능을 가진다.

• ETRI Journal
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• 제34권4호
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• pp.617-620
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• 2012

The denoising mapping with the closest-neighbor clustering (CNC) method in denoise-and-forward two-way relay channels is studied. Specifically, the symmetry of the constellations in source terminals A and B is utilized to reduce the complexity of the CNC method. The specific case considered first to illustrate how the constellation symmetry works in the CNC method is the quadrature phase-shift keying constellation in A and B and the single-antenna deployment in all terminals. This case study shows that an enormous complexity reduction can be achieved. Next, the result is extended to multiple-antenna scenarios and square quadrature amplitude modulations.