• 제어로봇시스템학회논문지
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• 제19권2호
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• pp.125-130
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• 2013

Compared to OWR (One-Way Ranging) method that requires precise network time synchronization, TWR (Two-Way Ranging) method has advantages in building an indoor WPAN (Wireless Personal Area Network) location system with lower cost. However, clock offsets of nodes in WPAN system should be eliminated or compensated to improve location accuracy of the TWR method. Because conventional clock offset elimination methods requires multiple TWR transactions to reduce clock offset, they produce network traffic burden instead. This paper presents a clock offset estimation method that can reduce clock offset error with a single TWR transaction. After relative clock offsets of sensor nodes are estimated, clock offsets of mobile tags are estimated using a single TWR communication. Simulation results show that location accuracy of the proposed method is almost similar to the conventional clock offset elimination method, while its network traffic is about a half of the conventional method.

• 제어로봇시스템학회논문지
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• 제21권7호
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• pp.669-676
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• 2015

In this paper, we described the simulation results of the phase offset performance of a clock in holdover mode which was normally operated in GPS Disciplined Oscillator (GPSDO). In the TIE model, we included the time error term caused by environmental temperature variation because one of the most important parameters of clock phase error is the frequency offset and drift caused by the variation of temperature. For the simulation, we employed Maximum Time Interval Error (MTIE) for the performance evaluation when the frequency offset and drift are estimated by using an Unbiased Finite Impulse Response (UFIR) filter with ladder algorithm. We assumed that the noise in the GPS measurement is white Gaussian with zero mean and 1 ns standard deviation, and temperature linearly varies with a slope of $1{^{\circ}C}$ per hour. From the simulation results, the followings were observed. First, with the estimation error of temperature of less than 3 % and the temperature compensation period of less than 900 seconds, the requirement of CDMA2000 phase synchronization under 10 us could be achieved for more than 40,000 seconds holdover time if we employ an OCXO (Oven Controlled Crystal Oscillator) clock. Second, in order to achieve the requirement of LTE-TDD under 1.5 us for more than 10,000 seconds holdover time, below 3 % estimation error and 500 seconds should be retained if a Rubidium clock is adopted.

• 방송공학회논문지
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• 제19권3호
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• pp.355-361
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• 2014

본 논문에서는 HEVC(high efficiency video coding)의 루프내 필터 중 하나인 SAO (sample adaptive offset) 기술을 고속화하는 방법을 제안한다. 기존의 SAO는 원 영상과 복원된 영상 간의 오차를 최소화하기 위한 오프셋 값을 각 CTB마다 계산한다. 최적의 오프셋 값 결정을 위해 오프셋 값 후보군 내의 모든 오프셋 값을 검사한 후, 율-왜곡 비용 값을 최소화하는 오프셋 값을 선택한다. 따라서 SAO는 HEVC 부호기에서 상당한 양의 복잡도를 차지한다. 제안한 방법에서는 오프셋 값의 통계적 특성을 고려해 사용 빈도가 낮은 밴드를 결정하고, 사용 빈도가 낮은 밴드에 포함되는 오프셋 값을 처리하지 않는다. 또한, 오프셋 값 결정 단계에서 후보군 내의 모든 오프셋 값 대신 일부 오프셋 값만 검사한다. 실험 결과를 통해 제안한 방법이 큰 부호화 효율 감소 없이 약 8.15%의 부호화 시간을 감소시키는 것을 확인했다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 Ⅳ
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• pp.1739-1742
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• 2003

본 논문에서는 입력영상의 휘도 신호에 Neyman-pearson Test를 이용하여 descramble error를 효과적으로 보정하는 기법을 제안한다. 아날로그 회로의 오차와 noise 의 영향으로 scramble 된 라인의 오프셋 값을 정확히 보상하지 못할 경우에 발생하는 descramble error를 scrambler/ descrambler 의 기기별 차이에 관계없이, 또한 scrambler 와 descrambler로부터 어떠한 정보 없이 descramble 시에 발생한 error 의 offset 값과 scramble 된 라인을 검출하여 보상하는 방법을 논하였다.

• International Journal of Aeronautical and Space Sciences
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• 제18권1호
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• pp.154-164
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• 2017

This work conducts a validation study for the XH-59A helicopter using a rigid coaxial rotor system in order to establish the techniques of the conceptual design and performance analysis for the lift-offset compound rotorcraft. As a tool for conceptual design and performance analysis, NDARC (NASA Design and Analysis of Rotorcraft) is used for the present study. An assumed mission profile is considered for the conceptual design of the XH-59A. As a validation result of the design, the dimensions and weight of the XH-59A are appropriately designed when compared to the target values since the relative error is less than 0.5%. Then, performance analyses are conducted for the designed XH-59A model with and without auxiliary propulsion in hover and forward flight conditions. The present analyses show good validity since the prediction results compare well with both the flight test and previous analyses. Therefore, the techniques for the conceptual design and performance analysis of the lift-offset compound helicopter are overall considered to be appropriately established. In addition, this study investigates the influence of the lift-offset on the rotor effective lift-to-drag ratio of the XH-59A helicopter with auxiliary propulsion. As a result, the improvement of the rotor effective lift-to-drag ratio can be obtained by appropriately increasing the lift-offset in high-speed flight.

• 한국통신학회논문지
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• 제31권2A호
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• pp.103-109
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• 2006

OFDM 시스템은 전송단과 수신단의 발진기의 불일치로 인해 발생하는 주파수 오프셋의 영향에 민감하다는 단점을 가지고 있다. 주파수 오프셋은 정수 부분과 소수 부분으로 구분할 수 있다. 정수 부분 주파수 오프셋은 부반 송파 사이의 직교성에는 영향을 주지는 않지만, 수신된 데이터 심볼들 간에 순환성 천이를 일으켜 비트 오류 확률이 0.5가 되게 한다. 이 논문에서는 다중 경로 페이딩(multipath fading) 채널 환경에서 학습 심볼 하나 만을 요구하면서 최대 우도(Maximum Likelihood: ML) 함수를 이용한 새로운 정수 부분 주파수 오프셋 추정 방법을 제안한다. 제안한 방법이 학습 심볼의 수를 줄여 줄뿐만 아니라, 복잡성을 늘이지 않으면서 성능이 우수함을 모의 실험을 통해 보인다.

• 한국정보통신학회논문지
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• 제5권4호
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• pp.684-691
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• 2001

본 논문에서는 OFDM/M-ary PSK 시스템의 BER 성능을 반송파 주파수 오프셋을 고려하여 분석하였고, 부호화와 변조를 동시에 행할 수 있는 TCM 기법을 OFDM/M-ary PSK시스템에 적용하여 반송파 주파수 오프셋에 따른 성능 열화를 보상하였다. 성능 해석 결과, 주파수 오프셋이 커짐에 따라 OFDM/M-ary PSK 시스템의 성능이 열화 됨을 알 수 있었고, 10 dB의 Eb/No로 $BER= 10^{-3}$ 을 달성하기 위해서는 주파수 오프셋을 0.025이하로 제한해야 함을 알 수 있었다. 또한 음성 서비스 ($BER= 10^{-3}$)를 목표로 하는 경우 TCM 기법을 적용함으로써 약 4 dB의 성능 개선이 얻어짐을 알 수 있었다.

• Journal of electromagnetic engineering and science
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• 제8권3호
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• pp.134-137
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• 2008

This paper proposes a novel quadrature VCO(QVCO) based on direct back-gate second harmonic coupling. The QVCO directly couples the current sources of the conventional LC VCOs through the back-gate instead of front-gate to generate quadrature signals. By the second harmonic injection locking, the two LC VCOs can generate quadrature signals without using on-chip transformer, or stability problem that is inherent in the direct front-gate second harmonic coupling. The proposed QVCO is implemented in $0.18{\mu}m$ CMOS technology operating at 2 GHz with 5.0 mA core current consumption from 1.8 V power supply. The measured phase noise of the proposed QVCO is - 63 dBc/Hz at 10 kHz offset, -95 dBc/Hz at 100 kHz offset, and -116 dBc/Hz at 1 MHz offset from the 2 GHz output frequency, respectively. The calculated figure of merit(FOM) is about -174 dBc/Hz at 1 MHz offset. The measured image band rejection is 46 dB which corresponds to the phase error of $0.6^{\circ}$.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.239-240
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• 2008

A new frequency offset estimator using low cross-property of PN sequences is proposed in the orthogonal frequency division multiple access (OFDMA) uplink systems. Simulation results show that the proposed estimator improves the mean square error (MSE) performance compared to conventional estimator [2] where each user have both different timing offset and different frequency offset. In addition, the MSE performance is improved as the length of PN sequence increases.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2274-2279
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• 2008

This paper numerically investigates thermo-flow characteristics of offset strip fins to obtain a correlation of heat transfer and pressure drop. The flow is divided into three regimes, i.e. laminar, transition and turbulent. The predicted j and f values from the SST k-w turbulence model agree with previous correlations with the error less than 20% in transition and turbulent regimes. Prandtl number is varied from 0.5 to 40 and a correlation to predict heat transfer and pressure drop for offset strip fins is suggested.