• Journal of Communications and Networks
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• 제18권5호
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• pp.677-687
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• 2016

Multi-way relay networks (MWRNs) allow multiple users to exchange information with each other through a single relay terminal. MWRNs are often incorporated with capacity achieving lattice codes to enable the benefits of high-rate signal constellations to be extracted. In this paper, we analytically characterize the symbol error rate (SER) performance of a functional decode and forward (FDF) MWRN in the presence of channel estimation errors. Considering M-ary quadrature amplitude modulation (QAM) with square constellations as an important special case of lattice codes, we obtain asymptotic expressions for the average SER for a user in FDF MWRN. The accuracy of the analysis at high signal-to-noise ratio is validated by comparison with the simulation results. The analysis shows that when a user decodes other users with better channel conditions than itself, the decoding user experiences better error performance. The analytical results allow system designers to accurately assess the non-trivial impact of channel estimation errors and the users' channel conditions on the SER performance of a FDF MWRN with M-QAM modulation.

• 전기학회논문지
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• 제61권4호
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• pp.612-616
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• 2012

This paper presents an active current regulator for LED driver IC. The proposed driver circuit is consists of DC-DC converter for supplying constant DC voltage to LED, active current regulator for compensating channel-to-channel current error from LED strings and feedback circuit for controlling duty ratio of the converter. The proposed active current regulator senses current of LED channels by equalizing both $V_{DS}$ and $V_{GS}$ at LED current control transistor. Because the proposed circuit directly measures the LED channel current without a sensing resistor and regulates all channel with same regulation loop, the power consumption and the current error are much small compared with previous works. The measured maximum efficiency of overall LED driver IC is approximately 94% and current error of LED channel-to-channel is under ${\pm}1.3%$. The proposed LED driver IC is fabricated Dongbu 0.35um BCD process.

• 지식경영연구
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• 제17권3호
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• pp.45-64
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• 2016

As the digital retail environement becomes prevalent, consumers are given greater opportunities to make purchases across physical and digital boundaries. Prior research emphasizes that the attractiveness of the digital or online channel is relatively determined by spatial specifics of physical locations. The overall market trend combined with prior research suggests that understanding spatial specifics becomes a key to managing both offline and online sales performance together. In this study, we focus on geographic variation in sales performance through offline and online channels and aim to investigate the channel-level sales difference between central and subsidiary areas. To this end, we obtain sales data of skincare and makeup products from a leading cosmetic company. Next, we examine spatial autocorrelations in data and then employ the spatial error models to study the effects of spatial specifics. The empirical findings are as follows. First, there are significant differences in category-specific and channel-level sales between central and subsidiary areas. Second, Moran's I statistics demonstrate the spatial autocorrelations of each variable. Third, spatial error models outperform simple regression models with lower AIC values. Finally, spatial specifics play a greater role in understanding online sales in subsidiary areas whereas they exert greater influence on offline sales in central areas. We believe our study advances the related theory and knowledge of multi-channel retailing and also contributes practically to location-dependent multi-channel strategies and sales data analytics.

• 한국산학기술학회논문지
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• 제12권2호
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• pp.895-900
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• 2011

기존의 이동 통신시스템에서 사용하는 변조방식의 단점을 개선하기 위하여, 본 논문에서는 채널의 환경이 변함에 따라 적응적으로 변조방식을 변화시킴으로써 채널의 처리율을 향상시킬 수 있는 적응변조방식을 사용한 채널 예측 방법을 제안한다. 제안된 방식은 요구되는 채널의 비트 에러율에 따라 부호율을 결정하기 위해 채널 특성을 실시간으로 측정하여 채널의 비트 에러율이 증가하면 부호율을 감소시켜 최대 처리율을 유지하도록 하는 방법을 사용하며, Matlab을 이용한 시뮬레이션을 통하여 제안된 방식의 성능을 분석하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(4)
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• pp.13-16
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• 2001

In the Dedicated Short Range Communication (DSRC) system channel, a large number of bit errors occur because of Additive White Gaussian Noise (AWGN) and fading. When an image data is transmitted under the condition, reconstructed image quality is significantly degraded. In this paper, as an alternative to the error correcting code and/or automatic repeat request scheme, we propose an error recovery scheme for image data transmission. We first analyze how transmission errors in the DSRC system channel degrade image quality. Then, in order to improve image quality, we propose error resilient and concealment schemes for still image transmission using DCT-based fixed length coding, hamming code, cyclic redundancy check, and interleaver. Finally, we show its performance by an experiment.

• 한국전자파학회논문지
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• 제17권9호
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• pp.795-803
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• 2006

본 논문에서는 Ka 대역 초고속 위성 방송 시스템에서 강우 감쇠에 대처하면서 가입자에게 지속적으로 방송을 제공하기 위해 unequal error protection(UEP) 방식을 이용한 계층적 부호화 방식에 대한 연구를 하였다. 신호의 중요도에 따라 변조 방식 및 채널 코딩 방식을 달리하는 time sharing 방식과 달리 하나의 변조 방식을 이용하여 성상도 위치에서 신호의 중요도에 따라 신호간의 최소 거리를 다르게 배치하는 UEP 방식에 대한 구조 및 성능을 분석하였으며, 성능 분석을 토대로 최적의 방식을 제시하였다.

• Journal of information and communication convergence engineering
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• 제2권4호
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• pp.214-218
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• 2004

In this paper, we have analyzed TCP performance over wireless correlated fading links with and without Snoop protocol. For a given value of the packet error rate, TCP performance without Snoop protocol is degraded as the fading is getting fast (i.e. the user moves fast). When Snoop protocol is introduced in the base station, TCP performance is enhanced in most wireless environments. Especially the performance enhancement derived from using Snoop protocol is large in fast fading channel. This is because packet errors become random and sporadic in fast fading channel and these random packet errors (mostly single packet errors) can be compensated efficiently by Snoop protocol's local packet retransmissions. But Snoop protocol can't give a large performance improvement in slow fading environments where long bursts of packet errors occur. Concerning to packet error rate, Snoop protocol results in the highest performance enhancement in the channel with mid-high values of packet error rate. This means Snoop protocol cannot fully fulfill its ability under too low or too high packet error rate environments.

• 전자공학회논문지A
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• 제32A권9호
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• pp.1177-1183
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• 1995

This paper proposes a new modulation scheme of $\pi$/4-DQPSK with stepped phase for a frequency selective fading channel. In the proposed modulation scheme, the phase of transmitted signal is shifted in the mid of a symbol duration in order to reduce the effect of multipath delay spread. It reduces the irreducible error of $\pi$/4-DQPSK over a frequency selective fading channel. It is shown that $\pi$/4-DQPSK with stepped phase achieves smaller average bit error probability than regular $\pi$/4- DQPSK by simulation. The former achieves much smaller average bit error probability than the latter for small TEX>${\tau}/T_{s}$.

• 전자공학회논문지A
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• 제28A권1호
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• pp.1-7
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• 1991

Degradation of communication quality is due to transmission error rather than quantization noise when DPCM signal is transmitted over a heavily noise channel. The communication quality can be improved by employing an error correcting code to the DPCM signal transmission over such a channel. We considered both quantization noise and transmission error simultaneously in evaluating the signal to noise ratio. To efficiently improve the signal to noise ratio, we analyze the unequal symbol error probability of convolutional code, and encoded to more protect significant symbols from channel errors than least ones, so that the signal to noise ratio is improved. We derived related formulas and also made computer simulations.

• 한국항행학회논문지
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• 제18권1호
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• pp.74-77
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• 2014

본 논문은 사물 지능 통신 환경에서 미디어 다중 채널을 위한 오류 제어에 대해서 제안하였다. 이 시스템은 사물 지능 통신 환경 멀티미디어 컴퓨터 협력 작업을 위한 소프트웨어 복구에 적합하다. 이것은 세션의 진행 과정 중 세션의 미디어 서비스 인스턴스가 비정상적으로 종료되는 경우에 세션의 진행을 중단할 수 있지만 허용하는 한 미디어 서비스 인스턴스를 재 활성화 시켜 사용자에 대한 보호를 하는 경우에 필요하다. 본 논문은 규칙-기반 DEVS 모델링과 시뮬레이션 기법을 사용하면서 사물 지능 통신 기반 컴퓨팅 공동 환경의 오류 복구 시스템의 성능 분석을 설명한다.