• Title/Summary/Keyword: Time synchronization

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Clock Synchronization for Multi-Static Radar Under Non-Line-of-Sight System Using Robust Least M-Estimation (로버스트한 최소 M-추정기법을 이용한 비가시선 상의 멀티스태틱 레이더 클락 동기 기술 연구)

  • Shin, Hyuk-Soo;Yeo, Kwang-Goo;Joeng, Myung-Deuk;Yang, Hoongee;Jung, Yongsik;Chung, Wonzoo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.37C no.10
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    • pp.1004-1010
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    • 2012
  • In this paper, we propose the algorithm which considers applying recently proposed clock synchronization techniques with quite high accuracy in a few wireless sensor networks researches to time synchronization algorithm for multi-static radar system and especially overcomes the limitation of previous theory, cannot be applied between nodes in non-line of sight (NLOS). Proposed scheme estimates clock skew and clock offset using recursive robust least M-estimator with information of time stamp observations. And we improve the performance of algorithm by tracking and suppressing the time delays difference caused by NLOS system. Futhermore, this paper derive the mean square error (MSE) to present the performance of the proposed estimator and comparative analysis with previous methods.

Timeline Synchronization of Multiple Videos Based on Waveform (소리 파형을 이용한 다수 동영상간 시간축 동기화 기법)

  • Kim, Shin;Yoon, Kyoungro
    • Journal of Broadcast Engineering
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    • v.23 no.2
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    • pp.197-205
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    • 2018
  • Panoramic image is one of the technologies that are commonly used today. However, technical difficulties still exist in panoramic video production. Without a special camera such as a 360-degree camera, making panoramic video becomes more difficult. In order to make a panoramic video, it is necessary to synchronize the timeline of multiple videos shot at multiple locations. However, the timeline synchronization method using the internal clock of the camera may cause an error due to the difference of the internal hardware. In order to solve this problem, timeline synchronization between multiple videos using visual information or auditory information has been studied. However, there is a problem in accuracy and processing time when using video information, and there is a problem in that, when using audio information, there is no synchronization when there is sensitivity to noise or there is no melody. Therefore, in this paper, we propose a timeline synchronization method between multiple video using audio waveform. It shows higher synchronization accuracy and temporal efficiency than the video information based time synchronization method.

Hybrid MAC Protocol Design for an Underwater Acoustic Network (수중음향통신망을 위한 하이브리드 MAC 프로토콜 설계)

  • Park, Jong-Won;Ko, Hak-Lim;Cho, A-Ra;Yun, Chang-Ho;Choi, Young-Chol;Lim, Yong-Kon
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.13 no.10
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    • pp.2088-2096
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    • 2009
  • This paper deals with hybrid MAC protocol design for underwater acoustic networks. The proposed MAC protocol has the cluster structure with a master node and slave nodes, and the hybrid network structure that combines a contention free period based on TDMA(Time Division Multiple Access) with a contention period. The suggested MAC protocol has a beacon packet for supervising network, a guard period between time slots for packet collision, time tag for estimation of propagation delay with a master node, the time synchronization of nodes, entering and leaving of network, and the communication method among nodes. In this paper, we adapt the proposed hybrid MAC protocol to AUV network, that is the representative mobile device of underwater acoustic network, and verify this protocol is applicable in real underwater acoustic network environment.

The Comparison of RBS and TDP for the Sensor Networks Synchronization

  • Lee, Hyo-Jung;Kim, Byung-Chul;Kwon, Young-Mi
    • Journal of Information Processing Systems
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    • v.1 no.1 s.1
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    • pp.70-74
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    • 2005
  • Sensor networks have emerged as an interesting and important research area in the last few years. These networks require that time be synchronized more precisely than in traditional Internet applications. In this paper, we compared and analyzed the performance of the RBS and TDP mechanisms in the view of the number of generated messages and the synchronization accuracy. The reason that we chose be RBS ad the TDP mechanism to be compared is because the RES is an innovative method to achieve the high accurate synchronization. And TDP is a new method taking over the NTP method which has been used widely in the Internet. We simulated the performance of two methods assuming the IEEE 802.11 CSMA/CA MAC. As for the number of nodes in the sensor networks, two situations of 25 (for the small size network) and 100 (for the large size network) nodes are used. In the aspect of the number of messages generated for the synchronization, TDP is far better than RBS. But, the synchronization accuracy of RBS is far higher than that of TDP. We cm conclude that in a small size sensor networks requiring very high accuracy, such as an application of very high speed objects tracking in a confined space, the RBS is more proper than TDP even though the RBS may generate more traffic than TDP. But, in a wide range sensor networks with a large number of nodes, TDP is more realistic though the accuracy is somewhat worse than RBS because RBS may make so many synchronization messages, and then consume more energies at each node. So, two mechanisms may be used selectively according to the required environments, without saying that the one method is always better than the other.

Analysis of Comparisons of Estimations and Measurements of Loran Signal's Propagation Delay due to Irregular Terrain (Loran 신호의 지형에 의한 전파 지연 예측 및 실측 비교 분석)

  • Yu, Dong-Hui
    • Journal of the Institute of Convergence Signal Processing
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    • v.12 no.2
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    • pp.107-112
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    • 2011
  • Several developed countries have been developing their own satellite navigation systems, such as Europe's Galileo, China's BEIDOU, and Japan's QZSS, to cope with clock errors and signal vulnerabilities of GPS. In addition, modernization of Loran, eLoran, for GPS backup has been conducted. In Korea, a dependent navigation system has been required and for GPS backup, the need for utilization of time synchronization infrastructure through the modernization of Loran has been raised. Loran signal uses 100Khz groundwave. A significant factor limiting the ranging accuracy of the Loran signal is the ASF arising from the fact that the groundwave signal is likely to propagate over paths of varying conductivity and topography. Thus, an ASF compensation method is very important for Loran and eLoran navigation. This paper introduces the propagation delay model and then compares and analyzes the estimations from the propagation delay model and measured ASFs.

A Packet Collision Avoidance Technique in IEEE1609.4 Based Time Synchronization Multi-channel Environment (IEEE1609.4 기반 시간 동기 멀티채널 환경에서의 패킷 충돌 회피 기법)

  • Jin, Seong-Keun;Lim, Ki-Taeg;Shin, Dae-Kyo;Yoon, Sang-Hun;Jung, Han-Gyun
    • Journal of IKEEE
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    • v.19 no.3
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    • pp.385-391
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    • 2015
  • In this paper, we analyze the communication performance in a time synchronous multi-channel environment and deal with a packet collision avoidance technique to improve it based on IEEE1609.4 for increasing the efficiency of the control channel IEEE802.11p WAVE communication system. In previous works, they tried to solve this problem by message scheduling method on application layer software or changing the value of the random back-off optionally Contention Window. In this paper, we propose a method for adjusting the Channel Guard Interval for packet collision avoidance. The performance was evaluated by the actual vehicle test. The result was confirmed performance over 90% PDR(Packet Delivery Ratio).

Correlation Analysis of Event Logs for System Fault Detection (시스템 결함 분석을 위한 이벤트 로그 연관성에 관한 연구)

  • Park, Ju-Won;Kim, Eunhye;Yeom, Jaekeun;Kim, Sungho
    • Journal of the Society of Korea Industrial and Systems Engineering
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    • v.39 no.2
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    • pp.129-137
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    • 2016
  • To identify the cause of the error and maintain the health of system, an administrator usually analyzes event log data since it contains useful information to infer the cause of the error. However, because today's systems are huge and complex, it is almost impossible for administrators to manually analyze event log files to identify the cause of an error. In particular, as OpenStack, which is being widely used as cloud management system, operates with various service modules being linked to multiple servers, it is hard to access each node and analyze event log messages for each service module in the case of an error. For this, in this paper, we propose a novel message-based log analysis method that enables the administrator to find the cause of an error quickly. Specifically, the proposed method 1) consolidates event log data generated from system level and application service level, 2) clusters the consolidated data based on messages, and 3) analyzes interrelations among message groups in order to promptly identify the cause of a system error. This study has great significance in the following three aspects. First, the root cause of the error can be identified by collecting event logs of both system level and application service level and analyzing interrelations among the logs. Second, administrators do not need to classify messages for training since unsupervised learning of event log messages is applied. Third, using Dynamic Time Warping, an algorithm for measuring similarity of dynamic patterns over time increases accuracy of analysis on patterns generated from distributed system in which time synchronization is not exactly consistent.

Development of Integrated eLoran/GNSS Receiver and Performance Test Result (eLoran/GNSS 통합 수신기 개발 및 성능시험 결과)

  • Kim, Jeong-been;Yu, Je Hyun;Park, Il Kyu;Son, Seok Bo;Kim, Young-Baek
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • 2019.11a
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    • pp.73-74
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    • 2019
  • We are developing a receiver that integrates eLoran and GNSS for navigation. The receiver shows similar performance to LORADD receiver in single navigation using Loran-C. In the case of GNSS navigation, the receiver uses GPS and GLONASS or GPS and BDS, so it has better navigation performance than the LORADD receiver using only GPS. Therefore, it is possible to expect better performance than the LORADD receiver in the integrated navigation which can complete the time synchronization between the chains later and obtaion the TOA. Loran data channel decoding function is implemented for eLoran navigation and the function of eliminating error factors such as interference is being implemented.

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A Standard Time Management Scheme in the Internet of Things (사물인터넷에서 표준 시각 관리 방안)

  • Hwang, Soyoung
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.22 no.6
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    • pp.929-934
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    • 2018
  • The Internet of Things (IoT) is the network of devices embedded with electronics, software, sensors, actuators, and connectivity which enables these objects to connect and exchange data without any human intervention. The importance of time information is increased in order to impose order on scattered sensor data streams, resolving conflicts through time stamp information and so on. Time information and time synchronization are critical building blocks in the IoT. They allow devices to share a consistent notion of time and it is easier to build efficient and robust collaborative services. This paper proposes a standard time management scheme in the Internet of Things. Many IoT applications involve collection and forwarding of event data. It is useful to know when an event occurs for the purposes of triggering an action. In order to verify the feasibility of the proposed scheme, it is implemented and evaluated in the Arduino development environment.

Speech Quality Measure for VoIP Using Wavelet Based Bark Coherence Function (웨이블렛 기반 바크 코히어런스 함수를 이용한 VoIP 음질평가)

  • 박상욱;박영철;윤대희
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.27 no.4A
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    • pp.310-315
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    • 2002
  • The Bark Coherence Function (BCF) defies a coherence function within perceptual domain as a new cognition module, robust to linear distortions due to the analog interface of digital mobile system. Our previous experiments have shown the superiority of BCF over current measures. In this paper, a new BCF suitable for VoIP is developed. The unproved BCF is based on the wavelet series expansion that provides good frequency resolution while keeping good time locality. The proposed Wavelet based Bark Coherence function (WBCF) is robust to variable delay often observed in packet-based telephony such as Voice over Internet Protocol (VoIP). We also show that the refinement of time synchronization after signal decomposition can improve the performance of the WBCF. The regression analysis was performed with VoIP speech data. The correlation coefficients and the standard error of estimates computed using the WBCF showed noticeable improvement over the Perceptual Speech Quality Measure (PSQM) that is recommended by ITU-T.