• Title/Summary/Keyword: message synchronization

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SBAS SIGNAL SYNCHRONIZATION

  • Kim, Gang-Ho;Kim, Do-Yoon;Lee, Taik-Jin;Kee, Changdon
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • v.1
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    • pp.309-314
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    • 2006
  • In general DGPS system, the correction message is transferred to users by wireless modem. To cover wide area, many DGPS station should be needed. And DGPS users must have a wireless modem that is not necessary in standalone GPS. But SBAS users don't need a wireless modem to receive DGPS corrections because SBAS correction message is transmitted from the GEO satellite by L1 frequency band. SBAS signal is generated in the GUS(Geo Uplink Subsystem) and uplink to the GEO satellite. This uplink transmission process causes two problems that are not existed in GPS. The one is a time delay in the uplink signal. The other is an ionospheric problem on uplink signal, code delay and carrier phase advance. These two problems cause ranging error to user. Another critical ranging error factor is clock synchronization. SBAS reference clock must be synchronized with GPS clock for an accurate ranging service. The time delay can be removed by close loop control. We propose uplink ionospheric error correcting algorithm for C/A code and carrier. As a result, the ranging accuracy increased high. To synchronize SBAS reference clock with GPS clock, I reviewed synchronization algorithm. And I modified it because the algorithm didn't consider doppler that caused by satellites' dynamics. SBAS reference clock synchronized with GPS clock in high accuracy by modified algorithm. We think that this paper will contribute to basic research for constructing satellite based DGPS system.

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Intermedia Synchronization Protocol for Continuous Media Using MPEG-4 in Mobile Distributed Systems

  • Dominguez, Eduardo Lopez;Hernandez, Saul Eduardo Pomares;Gil, Pilar Gomez;Calleja, Jorge De La;Benitez, Antonio;Marin-Hernandez, Antonio
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.6 no.6
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    • pp.1689-1706
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    • 2012
  • The preservation of temporal dependencies among a group of processes that exchange continuous media at runtime is a key issue for emerging mobile distributed systems (MDS), such as monitoring of biosignals and interactive multiuser games. Although several works are oriented to satisfy temporal dependencies, most of them are not suitable for MDSs. In general, an MDS is characterized by the absence of global references (e.g. shared memory and wall clock), host mobility, limited processing and storage capabilities in mobile hosts, and limited bandwidth on wireless communication channels. This paper proposes an asymmetric synchronization protocol to be used at runtime in an MDS without using a common reference. One main aspect of our synchronization protocol is that it translates temporal constraints to causal dependencies of the continuous media data as seen by the mobile hosts. We simulate the protocol by considering a cellular network environment and by using MPEG-4 encoders. The simulation results show that our protocol is effective in reducing the synchronization error. In addition, the protocol is efficient in terms of processing and storage costs at the mobile devices, as well as in the overhead attached per message across the wired and wireless channels.

Clock Synchronization in Wireless Embedded Applications (무선 임베디드 환경에서의 시간 동기화)

  • No, Jin-Hong;Hong, Young-Sik
    • Journal of KIISE:Information Networking
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    • v.32 no.6
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    • pp.668-675
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    • 2005
  • With the proliferation of wireless network and the advances of the embedded systems, the traditional distributed systems begin to include the wireless embedded systems. Clock synchronization in the distributed systems is one of the major issues that should be considered for diverse Purposes including synchronization, ordering, and consistency. Many clock synchronization algorithms have been proposed over the years. Since clock synchronization in wireless embedded systems should consider the low bandwidth of a network and the poor resources of a system, most traditional algorithms cannot be applied directly. We propose a clock synchronization algorithm in wireless embedded systems, extending IEEE 802.11 standard. The proposed algorithm can not only achieve high precision by loosening constraints and utilizing the characteristics of wireless broadcast but also provide continuous time synchronization by tolerating the message losses. In master/slave structure the master broadcasts the time information and the stave computes the clock skew and the drift to estimate the synchronized time of the master. The experiment results show that the achieved standard deviation by the Proposed scheme is within the bound of about 200 microseconds.

Resolving the Funneling Effect in the Node Mobility Management of Infrastructure-based Mobile Ad Hoc Networks (인프라구조 기반 이동 애드혹 네트워크의 이동성 관리에서 깔때기 효과의 해결 방안)

  • Lee, Sung-Uk;Ngo, Chi-Trung;Kim, Je-Wook;Oh, Hoon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.12A
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    • pp.984-993
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    • 2011
  • In this paper, we present a new method for efficient mobility management in infrastructure-based ad hoc networks. This type of network inherently takes the tree topology model in which an Internet gateway (IG) becomes a root. Accordingly, the nodes near the IG process get much more number of messages, thereby causing a bottleneck phenomenon that degrades network performance. This problem is known as a funneling effect. We present a method to maximize message aggregation in which the nodes in the networks form tree topology and perform skewed time synchronization according to the depths of the nodes during the tree construction process. We proved by resorting to simulation that the funneling effect is alleviated and network performance is improved greatly.

Time Synchronization with Oceanic Movement Pattern in Underwater Wireless Networks (해수운동의 특성을 활용한 수중 무선 네트워크 시각 동기화)

  • Kim, Sungryul;Park, Seongjin;Yoo, Younghwan
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.38C no.5
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    • pp.486-496
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    • 2013
  • Time synchronization in underwater environment is challenging due to high propagation delay and mobility of sensor nodes. Previous researches do not consider practical issues affecting on the accuracy of time synchronization such as high-channel access delay and relative position between sensor nodes. Also, those protocols using bidirectional message exchange shorten the network lifetime and decrease the network throughput because numerous transmission, reception and unnecessary overhearing can be occurred. Therefore, in our research, we suggest enhanced time synchronization based on features of underwater environment. It controls the instant of transmission by exploiting the feature of an oceanic movement and node deployment. Moreover, the protocol uses more accurate time information by removing channel access delay from the timestamp. The proposed scheme is also practical on the underwater sensor network requiring low-power consumption because the scheme conducts time-synchronization with smaller transmission and reception compared with previous works. Finally, simulation results show that the proposed protocol deceases time error by 2.5ms and 0.56ms compared with TSHL and MU-Sync respectively, reducing energy consumption by 68.4%.

Reliable Time Synchronization Protocol in Sensor Networks (센서 네트워크에서 신뢰성 있는 시각 동기 프로토콜)

  • Hwang So-Young;Jung Yeon-Su;Baek Yun-Ju
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.31 no.3A
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    • pp.274-281
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    • 2006
  • Sensor network applications need synchronized time extremely such as object tracking, consistent state updates, duplicate detection, and temporal order delivery. This paper describes reliable time synchronization protocol (RTSP) for wireless sensor networks. In the proposed method, synchronization error is decreased by creating hierarchical tree with lower depth and reliability is improved by maintaining and updating information of candidate parent nodes. The RTSP reduces recovery time and communication overheads comparing to TPSN when there are topology changes owing to moving of nodes, running out of energy and physical crashes. Simulation results show that RTSP has about 20% better performance than TPSN in synchronization accuracy. And the number of message in the RTSP is $20%{\sim}60%$ lower than that in the TPSN when nodes are failed in the network. In case of different transmission range of nodes, the communication overhead in the RTSP is reduced up to 40% than that in the TPSN at the maximum.

A Proposal of Time Synchronization amongst Wireless Sensors for Ship Diagnosis and Maintenance Supporting (선박의 진단 및 정비를 위해 사용되는 무선 센서 간 효율적인 시간동기 알고리즘 제안)

  • Kim, Byoung-Kug
    • Journal of Advanced Navigation Technology
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    • v.24 no.4
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    • pp.267-272
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    • 2020
  • In order to monitor in large area of a ship without any concerns of spacial environments, there can be the use of many sensors that support wireless network technologies. Through the deployment of the wireless sensors and their autonomous network formations, the status of a ship can be easily monitored in real time. Moreover, if all the sensors are timely synchronized with each other, the locations and the moving directions of certain events can be estimated. Thus, the time synchronization amongst wireless sensors are crucial. In this paper, we propose an algorithm which supports reduced message transmissions between the sensors for synchronization.

Paper Duplication Method Supported by Task (태스크 기반 이중화 방안)

  • Lee, Jong-Chan;Park, Sang-Joon;Kang, Kwon-Il
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.27 no.1C
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    • pp.103-111
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    • 2002
  • In RNC of IMT-2000, main control processors such as ASP, ACP and OMP are responsible for call control function, and the high reliability and real-time property should be provided for it. So, the study of real-time fault-tolerant for it is needed. In this paper, we proposes an Task based duplication method, in which Tasks in active side operated on message unit and send the updated data to standby side after operation, log in the message to standby side for recovery during take-over. This scheme decreases the dual down and the complexity of synchronization procedure, and performs the synchronization more exactly because Tasks control the synchronization of system. This paper also proposes the fault detection and the fault handing method for effective implementation of Task based duplication. This scheme focus on increasing the fault detection rate and intercepting originally that fault data is send to standby side.

A feedback Scheme for Synchronization in a Distributed Multimedia (분산 멀티미디어 프리젠테이션 시스템에서 동기화를 위한 피드백 기법)

  • Choi, Sook-Young
    • The KIPS Transactions:PartB
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    • v.9B no.1
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    • pp.47-56
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    • 2002
  • In the distributed multimedia document system, media objects distributed over a computer network are retrieved from their sources and presented to users according to specified temporal relations. For effective presentation, synchronization has to be supported. Furthermore, since the presentation in the distributed environment is influenced by the network bandwidth and delay, they should be considered for synchronization. This paper proposes a distributed multimedia presentation system that performs presentation effectively in the distributed environment. And it also suggests a method to supports synchronization, in which, network situation and resources are monitored when media objects are transferred from servers to a client. Then a feedback message for the change of them is sent to the server so that the server might adjust the data sending rate to control synchronization. To monitor the situation of network, we use two methods together. One is to manage the level of the buffer by setting thresholds on a buffer and the other is to check the difference between the sending time of a packet from the server and the arrival time of the packet to the client.

A Study on the Ordered Multicast Protocols with Flow Control (흐름제어를 이용한 순서화 멀티캐스트 프로토콜에 관한 연구)

  • 박판우;이기현;조국현
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.17 no.10
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    • pp.1117-1130
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    • 1992
  • In this study, we propose a protocol for the communication between process groups required during message transfers. This is accomplished by an efficient process management of distributed systems connected by computer networks. For a single process group, a multicast protocol was proposed, which can control message flows while maintaining the order of messages sent or delivered. Through use of membership-related services, a member composing a process group may leave and join the current a membership anytime during execution. Moreover, message delivery can be delayed by using a logical vector time stamp. The functionality of the message delivery includes a virtual synchronization in response to a change in membership.

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