• Title/Summary/Keyword: cyclic correlation

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Blind OFDM Synchronization Algorithm using Cyclic Correlation (순환상관(Cyclic Correlation)을 이용한 OFDM 시스템에서의 블라인드 동기 알고리즘)

  • Park Byungjoon;Ko Eunseok;Kang Changeon;Hong Daesik
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.30 no.1C
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    • pp.92-98
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    • 2005
  • In this paper, blind synchronization algorithm is developed for estimating jointly timing and frequency offset of OFDM system. The proposed estimator exploits the second-order cyclostationarity of received signals, and then uses the information of symbol timing and carrier frequency offset appeared in the cyclic correlation. As a bling estimator, the information of impulse response of channel and training symbols are not required. The performance of the proposed method is consistent in spite of channel conditions in mean squre error sense, and simulation results prove it. For more accurate estimaion, the method that averages cyclic correlation is applied. In this case, the performance of averaging method is better.

Link Scheduling Method Based on CAZAC Sequence for Device-to-Device Communication (D2D 통신 시스템을 위한 CAZAC 시퀀스 기반 링크 스케줄링 기법)

  • Kang, Wipil;Hwang, Won-Jun;Choi, Hyung-Jin
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.38A no.4
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    • pp.325-336
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    • 2013
  • FlashLinQ, one of the typical D2D communication systems developed by Qualcomm, considers a single-tone communication based distributed channel-aware link scheduling method to realize the link scheduling process with low control overheads. However, considering the frequency selective fading effect of practical multi-path channel, the single-tone based SIR estimation causes a critical scheduling error problem because the received single-tone signal has quite different channel gain at each sub-carrier location. In order to overcome this problem, we propose a novel link scheduling method based on CAZAC (Constant Amplitude Zero Auto-Correlation) sequence for D2D communication system. In the proposed method, each link has a unique offset value set for the generation of CAZAC sequences. CAZAC sequences with the cyclic offsets are transmitted using multiple sub-blocks in the entire bandwidth, and then each device can obtain nearly full-band SIR using a good cyclic cross-correlation property of CAZAC sequence.

The blocking channel to reduce the performance decrease using the low correlation with cyclic delay scheme in LED-ID system (LED-ID 시스템에서 채널 차단에 따른 성능 열화를 줄이기 위한 저 상관 순환 지연 기법)

  • Lee, Kyu-Jin;Kim, Gui-Jung
    • Journal of Digital Convergence
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    • v.13 no.10
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    • pp.319-325
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    • 2015
  • We proposed the blocking channel to reduce the performance decrease using the low correlation with cyclic delay scheme in LED-ID system. LED-ID is based on the visible light to transmit the data. However, It is occurred the block channel by structure or environment of indoor for light of straightness. LED-ID system is degraded the performance by the block channel as loss of data, and burst error. To solve the block channel, the proposed system is overcome the burst error by low correlation among data, which is able to obtain the maximize time diversity gain to improve the performance of BER by cyclic delay scheme. The BER performance is evaluated by computer simulation according to channel parameter. The simulation results shows that proposed system gives much better performance than conventional system and constant cyclic delay scheme system.

Blind symbol timing offset estimation for offset-QPSK modulated signals

  • Kumar, Sushant;Majhi, Sudhan
    • ETRI Journal
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    • v.42 no.3
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    • pp.324-332
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    • 2020
  • In this paper, a blind symbol timing offset (STO) estimation method is proposed for offset quadrature phase-shift keying (OQPSK) modulated signals, which also works for other linearly modulated signals (LMS) such as binary-PSK, QPSK, 𝜋/4-QPSK, and minimum-shift keying. There are various methods available for blind STO estimation of LMS; however, none work in the case of OQPSK modulated signals. The popular cyclic correlation method fails to estimate STO for OQPSK signals, as the offset present between the in-phase (I) and quadrature (Q) components causes the cyclic peak to disappear at the symbol rate frequency. In the proposed method, a set of close and approximate offsets is used to compensate the offset between the I and Q components of the received OQPSK signal. The STO in the time domain is represented as a phase in the cyclic frequency domain. The STO is therefore calculated by obtaining the phase of the cyclic peak at the symbol rate frequency. The method is validated through extensive theoretical study, simulation, and testbed implementation. The proposed estimation method exhibits robust performance in the presence of unknown carrier phase offset and frequency offset.

Ab initio and Vibrational Predissociation Studies on Methylammonium-(Water)4 Complex: Evidence for Multiple Cyclic and Non-cyclic Hydrogen-bonded Structures

  • Kim, Kwang-Yon;Han, Woon-Hui;Cho, Ung-In;Lee, Yuan T.;Boo, Doo-Wan
    • Bulletin of the Korean Chemical Society
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    • v.27 no.12
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    • pp.2028-2036
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    • 2006
  • The combined ab initio and vibrational predissociation (VP) spectroscopic studies on methylammonium-$(water)_4$ complex aimed at understanding the hydration behavior of an amphiphilic ion core are described. The ab initio calculations predicted eleven low-energy isomers forming cyclic, tripod, chain, and caged structures, and their relative stabilities, total hydration energies and thermodynamic functions at 298 K and 150 K. The excellent correlation between the observed VP spectra and ab initio spectra for bonded N-H, bonded O-H and free O-H stretches suggested co-existence of five cyclic isomers and two non-cyclic isomers in ion beam at 150 K, consistent with the trends of calculated Gibbs free energies.

Cyclic fatigue resistance tests of Nickel-Titanium rotary files using simulated canal and weight loading conditions

  • Cho, Ok-In;Versluis, Antheunis;Cheung, Gary S.P.;Ha, Jung-Hong;Hur, Bock;Kim, Hyeon-Cheol
    • Restorative Dentistry and Endodontics
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    • v.38 no.1
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    • pp.31-35
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    • 2013
  • Objectives: This study compared the cyclic fatigue resistance of nickel-titanium (NiTi) files obtained in a conventional test using a simulated canal with a newly developed method that allows the application of constant fatigue load conditions. Materials and Methods: ProFile and K3 files of #25/.06, #30/.06, and #40/.04 were selected. Two types of testing devices were built to test their fatigue performance. The first (conventional) device prescribed curvature inside a simulated canal (C-test), the second new device exerted a constant load (L-test) whilst allowing any resulting curvature. Ten new instruments of each size and brand were tested with each device. The files were rotated until fracture and the number of cycles to failure (NCF) was determined. The NCF were subjected to one-way ANOVA and Duncan's post-hoc test for each method. Spearman's rank correlation coefficient was computed to examine any association between methods. Results: Spearman's rank correlation coefficient (${\rho}$ = -0.905) showed a significant negative correlation between methods. Groups with significant difference after the L-test divided into 4 clusters, whilst the C-test gave just 2 clusters. From the L-test, considering the negative correlation of NCF, K3 gave a significantly lower fatigue resistance than ProFile as in the C-test. K3 #30/.06 showed a lower fatigue resistance than K3 #25/.06, which was not found by the C-test. Variation in fatigue test methodology resulted in different cyclic fatigue resistance rankings for various NiTi files. Conclusions: The new methodology standardized the load during fatigue testing, allowing determination fatigue behavior under constant load conditions.

Correlation Between Fatigue Life of 2.2Ni-0.1Cr-0.5Mo Steel Accompanying Mean Stresses with Cyclic Strain Energy Density (평균응력을 동반하는 2.2Ni-lCr-0.5Mo강의 피로수명과 변형률에너지 밀도와의 상관관계)

  • Koh, Seung-Kee;Ha, Jeong-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.1
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    • pp.167-174
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    • 2003
  • Fatigue damage of 2.2Ni-1Cr-0.5Mo steel used fir high strength pressure tubes and vessels was evaluated using uniaxial specimens subjected to strain-controlled fatigue loading. Based on the fatigue test results from different strain ratios of -2. -i 0, 0.5, 0.75, the fatigue damage of the steel was represented by using a cyclic strain energy density. Mean stress relaxation depended on the magnitude of the applied strain amplitude. The high pressure vessel steel exhibited the cyclic softening behavior. Total strain energy density consisting of the plastic strain energy density and the elastic tensile strain energy density described fairly well the fatigue life of the steel, taking the mean stress effects into account. Compared to other fatigue damage parameters, fatigue life prediction by the cyclic strain energy density showed a good correlation with the experimental fatigue lift within a factor of 3.

Comparison of Dynamic Sorption and Hygroexpansion of Wood by Different Cyclic Hygrothermal Changing Effects

  • Yang, Tiantian;Ma, Erni
    • Journal of the Korean Wood Science and Technology
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    • v.44 no.2
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    • pp.191-203
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    • 2016
  • To investigate the dynamic sorptive and hygroexpansive behaviors of wood by different cyclic hygrothermal changing effects, poplar (populus euramericana Cv.) specimens, were exposed to dynamic sorption processes where relative humidity (RH) and temperature changed simultaneously in sinusoidal waves at 75-45% and $5-35^{\circ}C$ (condition A) and where RH changed sinusoidally at 75-45% but temperature was controlled at $20^{\circ}C$ (condition B), both for three cyclic periods of 1, 6, and 24 h. Moisture and dimensional changes measured during the cycling gave the following results: Moisture and transverse dimensional changes were generally sinusoidal. Moisture and dimensional amplitude increased with increasing cyclic period but all were lower for thicker specimens. The amplitude ratio of condition A to condition B ranged from 1.0 to 1.6 with the maximum value of 1.57 occurring at the shortest cyclic period, not as much as expected. T/R increased as cyclic period increased or specimen thickness decreased. T/R from condition B was weaker than that from condition A. Sorption and swelling hysteresis existed in both conditions. Sorption hysteresis was negatively related to cyclic period but in positive correlation with specimen thickness. Sorption hysteresis was found more obvious in condition B, while moisture sorption coefficient and humidity expansion coefficient showed the opposite results.

A Study on the Influence Factors for Liquefaction Based on the Disturbed State Concept (DSC 이론을 기초로 한 액상화 영향인자들에 관한 연구)

  • 박인준
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 1998.10a
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    • pp.361-368
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    • 1998
  • The purpose of this study is to find out the factors affacting liquefaction potential by using DSC(disturded state concept) method and to verify these results through cyclic shear test (truly triaxial test and cyclic triaxial) on saturated sandy soil. Based on this reserch, the DSC method predictions were found to provide satisfactory correlation with the cyclic shear test. And the relationship between the factors affecting liquefaction characteristics--relative density(Dr0 and initial effective confining pressure and physical properties of the saturated sand --ξD and Dc--is found. If the relative density and the initial effective confining pressure increase, the number of cyclic grows up. This means that Dc is incresed and ξD is decreased. Therefore, the liquefaction potential can be evaluated and the factors affacting liquefaction potential can be investigated by using on DSC method. Finally, it is shown that the DSC method can capture the liquefaction mechanism.

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Creep of stainless steel under heat flux cyclic loading (500-1000℃) with different mechanical preloads in a vacuum environment using 3D-DIC

  • Su, Yong;Pan, Zhiwei;Peng, Yongpei;Huang, Shenghong;Zhang, Qingchuan
    • Smart Structures and Systems
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    • v.24 no.6
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    • pp.759-768
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    • 2019
  • In nuclear fusion reactors, the key structural component (i.e., the plasma-facing component) undergoes high heat flux cyclic loading. To ensure the safety of fusion reactors, an experimental study on the temperature-induced creep of stainless steel under heat flux cyclic loading was performed in the present work. The strains were measured using a stereo digital image correlation technique (3D-DIC). The influence of the heat haze was eliminated, owing to the use of a vacuum environment. The specimen underwent heat flux cycles ($500^{\circ}C-1000^{\circ}C$) with different mechanical preloads (0 kN, 10 kN, 30 kN, and 50 kN). The results revealed that, for a relatively large preload (for example, 50 kN), a single temperature cycle can induce a residual strain of up to $15000{\mu}{\varepsilon}$.