• Title/Summary/Keyword: Time Offset

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System Performance Improvement of IEEE 802.15.3a By Using Time Slot Synchronization In MAC Layer (UWB MAC의 Time Slot 동기를 통한 시스템 성능 개선)

  • Oh Dae-Gun;Chong Jong-Wha
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.43 no.3 s.345
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    • pp.84-94
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    • 2006
  • In this paper, we propose the algorithm to reduce guard time of UWB MAC time slot for throughput gain. In the proposed draft by multiband ofdm alliance (MBOA), Guard time of each medium access slot (MAS) is composed of shortest inter-frame space (SIFS) and MaxDrift which is the time caused by maximum frequency offset among devices. In this paper, to reduceguard time means that we nearly eliminate MaxDrift term from guard time. Each device of a piconet computes relative frequency offset from the device initiating piconet using periodically consecutive transferred beacon frames. Each device add or subtract the calculated relative frequency offset to the estimated each MAS starting point in order to synchronize with calculated MAS starting point of the device initiating piconet. According to verification of simulations, if the frequency offset estimator is implemented with 8 decimal bit, the ratio of the wasted time to Superframe is always less than 0.0001.

Carrier Frequency Offset Estimation Method for Single-Carrier MIMO Systems (단일 반송파 MIMO 시스템 기반의 PN 부호열을 이용한 반송파 주파수 오차 추정 기법)

  • Oh, Jong-Kyu;Kim, Joon-Tae
    • Journal of Broadcast Engineering
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    • v.17 no.5
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    • pp.864-875
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    • 2012
  • In this paper, we propose a carrier frequency offset estimation method for single-carrier MIMO systems. In the proposed method, phase rotated PN (Pseudo-Noise) sequences are transmitted to prevent a cancelling out of partial PN sequences. After removing a modulation of received PN sequences by multiplying of complex conjugated PN Sequences which are locally generated in receiver, a CFO (Carrier Frequency Offset) is accurately estimated by employing L&R method which is a kind of ML (Maximum Likelihood) estimation algorithm and uses multiple auto-correlatos. In addition, the frequency offset estimation scheme by using channel state information is proposed for accurate CFO estimation in time-varying Rayleigh channel. By performing computer simulations, MSE (Mean Square Error) performance of proposed method is almost same as MSE performance of SISO systems in AWGN channel. Moreover, MSE Performance of proposed method with using channel information is higher than MSE performances of SISO system and conventional method in time-varying Rayleigh channel.

An Improved Symbol Offset Estimation Technique in OFDM-based Wireless LANs (OFDM 기반 무선 LAN에서의 개선된 심볼옵셋 추정기법)

  • Jeon, Won-Gi;Cho, Yong-Soo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.27 no.1B
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    • pp.66-78
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    • 2002
  • In this paper, we propose a new symbol offset estimation technique for an orthogonal frequency-division multiplexing (OFDM)-based wireless LAN. When both inter-symbol interference (ISI) and inter-channel interference (ICI) do not exist in an OFDM symbol, symbol offsets cause circular shifts in the estimated channel impulse response (CIR) by the amount of symbol offset. Also, the power delay profile of a typical multipath wireless channel can be modeled by exponentially decaying function, and most energy of multipath channel is concentrated at the beginning part of the CIR. Based on these properties, the proposed symbol offset estimation technique estimates the CIR, which is circularly shifted by the amount of symbol offset, and then calculates the partial mean power from the estimated impulse response by using a moving window with a finite length. And, symbol offset can be estimated from the index of a moving window having the maximal partial mean power. The proposed technique can reduce noise effect in the process of the CIR estimation, and remove ISI and ICI using repetitive training symbol structure in time-domain for minimum training overhead. The performances of the proposed symbol offset estimation technique in typical indoor channels are demonstrated by computer simulation.

A Study on the Characteristics to working Condition of STD11 in Wire-Cut EDM (Wire-Cut EDM에서 가공조건에 따른 STD11의 가공특성에 관한 연구)

  • Lee, Hong-Gil;Kim, Won-Il;Lee, Yun-Kyung;Wang, Duk-Hyun;Kim, Jong-Up
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.4 no.3
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    • pp.5-12
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    • 2005
  • In wire discharge machining which is using STD 11 as die materials, the major factors of machining speed are discharge voltage, discharge current, and discharge time. All of the three factors give the effect. Increasing of the discharge pulse time gets groove width wider and it relatively increases surface roughness and clearance. If no load voltage is decreased, surface roughness is good but it decreases machining speed. If on time is increased, machining speed will get faster and clearance and offset value also get bigger.

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Aircraft Velocity and Altitude Estimation through Time Offset Calculation of KOMPSAT-3 Satellite (KOMPSAT-3 위성의 Time Offset 계산을 통한 항공기 속력 및 고도 추정)

  • Jung, Sejung;Shin, Hyeongil;Kim, Dohoon;Song, Ahram;Lee, Won Hee
    • Korean Journal of Remote Sensing
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    • v.38 no.6_4
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    • pp.1879-1887
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    • 2022
  • In this study, a method of estimating the velocity and altitude of aircrafts photographed in a KOMPSAT-3 satellite was proposed. In the proposed method, parallax effect, which is a time offset between bands due to the photographing method of the KOMPSAT-3 satellite, the structure of the sensor, and the movement of the satellite's orbit, was calculated, and in this process, trucks running on the highway were used. In addition, the actual direction and the direction by parallax effect of the aircraft were calculated using the coordinates of the aircraft in the image, and the attitude information of the KOMPSAT-3 satellite was calculated using metadata to estimate the velocity and altitude of the aircraft. The estimated value through the proposed method was compared with the actual value, automatic dependent surveillance-broadcast (ADS-B), and the error rate was calculated here. As a result, it was confirmed that the velocity and altitude error rate of large aircraft (I1, I3, S2) were lower than that of light aircraft (I2, S2), and the estimated velocity and altitude were relatively high in large aircraft using the proposed method.

Analysis of GPS Galileo Time Offset Effects on Positioning (GPS Galileo Time Offset (GGTO)의 항법해 영향 분석)

  • Joo, Jung-Min;Cho, Jeong-Ho;Heo, Moon-Beom
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.37C no.12
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    • pp.1310-1317
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    • 2012
  • The Global Navigation Satellite System (GNSS) like US Global Positioning System (GPS) and EU Galileo are based on providing precise time and frequency synchronized ranging signals. Because of the exploitation of very precise timing signals these GNSS are used to provide both navigation and time distribution services. Moreover, because the positioning accuracy will improve as more satellites become available, we should expect that a combination of Galileo and GPS will provide better performance than those of both systems separately. However, Galileo will not use the same time reference as GPS and thus, a time difference arises - the GPS-Galileo Time Offset (GGTO). The navigation solution calculated by receivers using signals from both navigation systems will consequently contain a supplementary error if the GGTO is not accounted for. In this paper, we compared GPS Time (GPST) with Galileo Sytem Time (GST) and analyzed the effects of GGTO on positioning accuracy by simulation test. And then we also analyzed the characteristics of two representative GGTO correction methods such as the navigation message based method at system level and the estimation method at user level and propose the conceptual design of the novel correction method being capable of preventing previous method's problems.

Comparison of AT1- and Kalman Filter-Based Ensemble Time Scale Algorithms

  • Lee, Ho Seong;Kwon, Taeg Yong;Lee, Young Kyu;Yang, Sung-hoon;Yu, Dai-Hyuk;Park, Sang Eon;Heo, Myoung-Sun
    • Journal of Positioning, Navigation, and Timing
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    • v.10 no.3
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    • pp.197-206
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    • 2021
  • We compared two typical ensemble time scale algorithms; AT1 and Kalman filter. Four commercial atomic clocks composed of two hydrogen masers and two cesium atomic clocks provided measurement data to the algorithms. The allocation of relative weights to the clocks is important to generate a stable ensemble time. A 30 day-average-weight model, which was obtained from the average Allan variance of each clock, was applied to the AT1 algorithm. For the reduced Kalman filter (Kred) algorithm, we gave the same weights to the two hydrogen masers. We also compared the frequency stabilities of the outcome from the algorithms when the frequency offsets and/or the frequency drift offsets estimated by the algorithms were corrected or not corrected by the KRISS-made primary frequency standard, KRISS-F1. We found that the Kred algorithm is more effective to generate a stable ensemble time scale in the long-term, and the algorithm also generates much enhanced short-term stability when the frequency offset is used for the calculation of the Allan deviation instead of the phase offset.

A Study of Effects on GPS and GLONASS Time offset according to leap seconds in GNSSS time transfer (GNSS 시각 전송에서 윤초 적용 여부에 따른 GPS 시각과 GLONASS 시각의 오프셋 영향 연구)

  • Yu, Dong-Hui;Lee, Young-Kyu;Yang, Sung-Hoon;Lee, Chang-Bok
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.18 no.11
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    • pp.2628-2633
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    • 2014
  • BIPM(International Bureau of Weights and Measures) uses GPS Time Transfer technique for UTC(Universal Time Coordinated). Recently, since GLONASS constellation started the service, studies on GLONASS time transfer and combination of GPS and GLONASS time transfer have been conducted. This paper introduces GNSS time, UTC and leap seconds and proposes the time offset results for applicability of leap seconds in GLONASS time transfer.

An Internet Time Synchronization Model using Dynamic Linear Model (동적선형모델을 적용한 인터넷 시각동기 모델)

  • Yu, Dong-Hui;Hwang, So-Young;Kim, Yong-Ho
    • The KIPS Transactions:PartC
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    • v.10C no.6
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    • pp.711-716
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    • 2003
  • We propose a new Interet time synchronization model using danamic linear model and introduce the characteristics of internet transmission delays. SNTP(Simple Network Time Protocol) has been widely used as a time synchronization method on the Internet. While SNTP provides a very simple usage, SNTP may not provide the stable services, since SNTP does not consider the several essential error factors. In order to overcome the instabitily of SNTP, we analyze the process of time estimation of SNTP and find the difference between forward transmission delay and backward transmission delay operates the main error on the estimation of an time offset.

An offset compensation scheme for rail-to-rail CMOS op-amps (Rail-to-Rail CMOS 증폭회로의 옵셋 보상 방법)

  • 이경일;오원석;김정규;박종태;유종근
    • Proceedings of the IEEK Conference
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    • 1998.06a
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    • pp.859-862
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    • 1998
  • An offset compensation scheme for rail-to-rail CMOS op-amps with complementary input stages is presented. Two auxiliary amplifiers are used to compensate for the offsets of NMOS and PMOS differnetial input stages, and ping-pong control is employed for continuous-time operation. Simulation and measurements resutls show that offsets are reduced about 20 times by this scheme.

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