• Title/Summary/Keyword: Time synchronization

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A Study on Cross-Layer Network Synchronization Architecture for TDMA-Based Mobile Ad-Hoc Networks (TDMA 기반 MANET을 위한 계층교차적 네트워크 동기 아키텍처 연구)

  • Seo, Myung-Hwan;Kim, Joung-Sik;Cho, Hyung-Weon;Jung, Sung-Hun;Park, Jong-Ho;Lee, Tae-Jin
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.37 no.8B
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    • pp.647-656
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    • 2012
  • TDMA MAC protocol in MANET requires precise network synchronization between nodes though network topology changes continuously due to node mobility and the effect of propagation environment. In this paper we propose in-band cross-layer network synchronization architecture for TDMA-based MANETs. In the proposed architecture TDMA MAC protocol and proactive routing protocol cooperate closely to rapidly detect network partition and merge caused by node mobility and to precisely maintain network synchronization. We also implement the proposed synchronization architecture in OPNET simulator and evaluate the performance of it in various simulation scenarios. Simulation results show that our architecture stably maintains network time synchronization in both network partition and merge situations.

Performance Analysis of Frame Synchronization and Structure Detection Utilizing Multiple Frames of the DVB-S2 Satellite Broadcasting System (다수개 프레임을 활용한 DVB-S2 위성방송 시스템의 프레임 동기 및 구조 검출 성능 분석)

  • Kim, Sang-Tae;Kang, Seok-Heon;Sung, Won-Jin
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.33 no.2A
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    • pp.139-147
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    • 2008
  • DVB-S2 (Digital Video Broadcasting-Satellite, Version 2) system transmits frames which adapt their structures based on the channel conditions, thus requiring simultaneous detection of the start of the Same (SoF) and the frame structure at the initial acquisition stage of the receiver. Also, a very low value of the minimum operating signal-to-noise ratio (SNR) for the acquisition necessitates a method utilizing multiple received frames to meet the required performance. In this paper, performance of joint time synchronization and frame structure detection methods using multiple DVB-S2 frames is evaluated by deriving the detection error probability. In particular, we evaluate the performance and complexity variations when the soft- and hard-decision values of the signal correlation output are used, present the synchronization parameters to optimize the performance, and verify the analysis results via computer simulations.

A Pseudo-Random Beamforming Technique for Time-Synchronized Mobile Base Stations with GPS Signal

  • Son, Woong;Jung, Bang Chul
    • Journal of Positioning, Navigation, and Timing
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    • v.7 no.2
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    • pp.53-59
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    • 2018
  • This paper proposes a pseudo-random beamforming technique for time-synchronized mobile base stations (BSs) for multi-cell downlink networks which have mobility. The base stations equipped with multi-antennas and mobile stations (MSs) are time-synchronized based on global positioning system (GPS) signals and generate a number of transmit beamforming matrix candidates according to the predetermined pseudo-random pattern. In addition, MSs generate receive beamforming vectors that correspond to the beam index number based on the minimum mean square error (MMSE) using transmit beamforming vectors that make up a number of transmit beamforming matrices and wireless channel matrices from BSs estimated via the reference signals (RS). Afterward, values of received signal-to-interference-plus-noise ratio (SINR) with regard to all transmit beamforming vectors are calculated, and the resulting values are then feedbacked to the BS of the same cells along with the beam index number. Each of the BSs calculates each of the sum-rates of the transmit beamforming matrix candidates based on the feedback information and then transmits the calculated results to the BS coordinator. After this, optimum transmit beamforming matrices, which can maximize a sum-rate of the entire cells, are selected at the BS coordinator and informed to the BSs. Finally, data signals are transmitted using them. The simulation results verified that a sum-rate of the entire cells was improved as the number of transmit beamforming matrix candidates increased. It was also found that if the received SINR values and beam index numbers are feedbacked opportunistically from each of the MSs to the BSs, not only nearly the same performance in sum-rate with that of applying existing feedback techniques could be achieved but also an amount of feedback was significantly reduced.

Design and Implementation of IoT Platform-based Digital Twin Prototype (IoT 플랫폼 기반 디지털 트윈 프로토타입 설계 및 구현)

  • Kim, Jeehyeong;Choi, Wongi;Song, Minhwan;Lee, Sangshin
    • Journal of Broadcast Engineering
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    • v.26 no.4
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    • pp.356-367
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    • 2021
  • With the recent development of IoT and artificial intelligence technology, research and applications for optimization of real-world problems by collecting and analyzing data in real-time have increased in various fields such as manufacturing and smart city. Representatively, the digital twin platform that supports real-time synchronization in both directions with the virtual world digitized from the real world has been drawing attention. In this paper, we define a digital twin concept and propose a digital twin platform prototype that links real objects and predicted results from the virtual world in real-time by utilizing the oneM2M-based IoT platform. In addition, we implement an application that can predict accidents from object collisions in advance with the prototype. By performing predefined test cases, we present that the proposed digital twin platform could predict the crane's motion in advance, detect the collision risk, perform optimal controls, and that it can be applied in the real environment.

Estimation of GPS Holdover Performance with Ladder Algorithm Used for an UFIR Filter (UFIR 필터 Ladder 알고리즘 이용 GPS Holdover 성능 추정)

  • Lee, Young-kyu;Yang, Sung-hoon;Lee, Chang-bok;Heo, Moon-beom
    • Journal of Institute of Control, Robotics and Systems
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    • v.21 no.7
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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.

Development of the hybrid-type ultrasound speaker (하이브리드형 초음파 스피커 개발)

  • Lee, Hyoung-Sang;Kim, Bok-Kyu
    • The Journal of the Acoustical Society of Korea
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    • v.40 no.3
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    • pp.247-253
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    • 2021
  • Directional ultrasonic speakers that are used to hear sound only in a specific area have been continuously researched on various improvements in terms of sound quality and cost compared to general speakers. In this paper, we propose a DSP based hybrid-type ultrasonic speaker that can be heard at the same time as a general speaker in order to compensate for the sound in the low-band range, considering that it is difficult to hear the low-band sound below 500 Hz due to the sensor characteristics of the ultrasonic speaker. In the case of the system that is implemented by simply connecting a general speaker and an ultrasonic speaker, there are issues of high cost and difficulties of control as two amplifiers are used to playback ultrasonic and general sound sources. In addition, sound quality deteriorates due to the difference in playback time between ultrasonic and general sound sources. In order to improve issues of cost, control and sound quality, we developed hybrid-type ultrasonic speaker with a DSP based amplifier that can simultaneously playback by synchronizing the general sound source with the regenerated ultrasonic sound source, in addition to implement the existing CODEC functions such as Dynamic Range Control (DRC) and Equalizer (EQ).

A Distributed Wireless Local Area Network (WLAN) Access Scheme for Efficient WLAN Communication in Busy Train Stations (혼잡 철도 역사에서 효율적인 무선랜 통신을 위한 무선랜 분산 접속 방법)

  • Koh, Seoung-Chon;Choi, Kyu-Hyoung;Kim, Ronny Yongho
    • Journal of the Korean Society for Railway
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    • v.17 no.6
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    • pp.402-409
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    • 2014
  • Wireless local area network (WLAN) is a widely used wireless access method due to its easy usability and excellent performance. However, its performance degrades significantly as the number of users increases. In busy train stations, where the number of WLAN users are large and, more importantly the number of simultaneous packet transmission attempts is extremely large due to the time synchronization upon train arrival, the packet transmission delay problem is very severe and almost impossible for WLAN stations to initiate communication with WLAN networks. In this paper, a novel distributed WLAN access scheme for efficient WLAN communication in busy train stations is proposed. Using the proposed scheme, WLAN access delay can be significantly reduced under highly congested traffic environments. Therefore, a significant performance enhancement for the WLAN performance used in the Communication Based Train Control (CBTC) can be achieved.

DL Radio Transmission Technologies for WRAN Applications : Adaptive Sub-channel Allocation and Stationary Beamforming Algorithms for OFDMA CR System (WRAN 응용을 위한 하향링크 무선전송 방식 : OFDMA 상황인식 시스템에서의 적응 부채널 할당 및 고정 빔 형성 기법)

  • Kim Jung-Ju;Ko Sang-Jun;Chang Kyung-Hi
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.31 no.3A
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    • pp.291-303
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    • 2006
  • In this paper, we analyze functional requirements of the IEEE 802.22 WRAN, and propose a downlink 프레임 structure satisfying the requirements. The proposed downlink 프레임 structure maximizes e transmission efficiency by adopting the cognative radio to assign the sub-channel by reflecting the channel environment of WRAN. We also calculate the signalling overhead for both downlink and uplink, and analyze the performances of time synchronization, frequency synchronization and cell identification based on the 프리앰블 in downlink and suggest the channel estimation method tough 프리앰블 or pilot. As a final result, e stationary beamforming (SBF) algorithm with dynamic channel allocation(DCA) is proposed. The proposed OFDMA downlink 프레임 structure with channel adaptive sub-channel allocation for cognitive radio applications is verified to meet the requirements of IEEE 802.22 WRAN, by computer simulations.

Multi-Hop Clock Synchronization Based on Robust Reference Node Selection for Ship Ad-Hoc Network

  • Su, Xin;Hui, Bing;Chang, KyungHi
    • Journal of Communications and Networks
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    • v.18 no.1
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    • pp.65-74
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    • 2016
  • Ship ad-hoc network (SANET) extends the coverage of the maritime communication among ships with the reduced cost. To fulfill the growing demands of real-time services, the SANET requires an efficient clock time synchronization algorithm which has not been carefully investigated under the ad-hoc maritime environment. This is mainly because the conventional algorithms only suggest to decrease the beacon collision probability that diminishes the clock drift among the units. However, the SANET is a very large-scale network in terms of geographic scope, e.g., with 100 km coverage. The key factor to affect the synchronization performance is the signal propagation delay, which has not being carefully considered in the existing algorithms. Therefore, it requires a robust multi-hop synchronization algorithm to support the communication among hundreds of the ships under the maritime environment. The proposed algorithm has to face and overcome several challenges, i.e., physical clock, e.g., coordinated universal time (UTC)/global positioning system (GPS) unavailable due to the atrocious weather, network link stability, and large propagation delay in the SANET. In this paper, we propose a logical clock synchronization algorithm with multi-hop function for the SANET, namely multi-hop clock synchronization for SANET (MCSS). It works in an ad-hoc manner in case of no UTC/GPS being available, and the multi-hop function makes sure the link stability of the network. For the proposed MCSS, the synchronization time reference nodes (STRNs) are efficiently selected by considering the propagation delay, and the beacon collision can be decreased by the combination of adaptive timing synchronization procedure (ATSP) with the proposed STRN selection procedure. Based on the simulation results, we finalize the multi-hop frame structure of the SANET by considering the clock synchronization, where the physical layer parameters are contrived to meet the requirements of target applications.

Effect of System Instability Factors in a Bistatic MTI Radar Using Pulse Chasing Scan Method (펄스 체이싱 스캔 방식을 이용한 바이스태틱 MTI 레이더에서 시스템 불안정 요소들의 영향)

  • Yang, Jin-Mo;Han, Il-Tak;Lee, Yong-Suk;Lee, Min-Joon;Kim, Whan-Woo
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.22 no.3
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    • pp.299-311
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    • 2011
  • In this paper, we have identified the system instability factors in a bistatic radar system using pulse chasing and considered their effects on the bistatic receiver's MTI(Moving Target Indication) improvement performance. The pulse chasing is a scan method that searchs a restricted area on the transmit pulse-to-pulse basis and the MTI filter is a signal processing that separates a target from some kinds of interferences such as clutter using small number of transmit pulses. Ideal MTI processing performance, e.g., clutter attenuation and improvement, has been limited by the property of the clutter itself, however, the MTI performance in a proposed bistatic receiver configuration could be affected by the receiving beam pointing error during pulse chasing scanning. Also, for the bistatic receiver, we have defined other system instability factors, which result from the time synchronization error, COHO's phase error, the frequency/phase synchronization error, and have analyzed their effects on the system performance improvement.