• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.6 no.1 s.12
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• pp.47-57
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• 2007

In this paper, optimal parameters of a hopping pilot beacon are analyzed in a CDMA mobile cellular network. The hopping pilot beacon is used for inter-frequency handoff. It can reduce the number of pilot beacons needed for the inter-frequency handoff by transmitting neighbor frequency pilots periodically through a pilot beacon. The optimal parameters for transmission time and period of the hopping pilot bacon are derived by mathematical approach. It is highly recommended that the optimal values for the hopping pilot beacon under various operation environments.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.7
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• pp.165-168
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• 2015

In this paper, we analyze a SFBC-OFDM(Space Frequency Block Code-Orthogonal Frequency Division Multiplexing) system with antenna selection method using pilot symbols. An antenna selection criterion is based on channel coefficients estimated from pilot symbols. At each frequency, the channel coefficients is arranged and the best is selected, and then data is sent to those antenna with the best coefficients. Also, The coding and diversity gain of the proposed system are analyzed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.341-344
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• 2004

This paper presents results of test for combustion vibration in the pilot furnace for fossil power plant under combustion test. We measured static pressure variation in the pilot furnace together with air and fuel flow. From test results, it shows that vibration magnitude is affected by air and fuel flow. Also, a finite element analysis using a commercial S/W is performed to calculate acoustic mode of the pilot furnace. These results show that dominant frequency occurred is related to acoustic natural frequency of furnace. After this, it needs to be studied the relation between dominant frequency of combustion vibration and air flow rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8C
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• pp.613-616
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• 2008

In this paper, a fine residual frequency offset estimation scheme is proposed for multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) systems. The basic idea of our approach is based on the fact that two adjacent OFDM symbols carry the identical information in the MB-OFDM UWB system, thus removing the need of pilot symbols. The mean square error of the synchronization scheme is evaluated and simulation results are used to verify the effectiveness of the proposed estimator. When compared to the pilot-aided conventional estimator, the proposed estimator has a lower estimation error.

• Journal of the Korea Society of Computer and Information
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• v.23 no.1
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• pp.1-7
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• 2018

The Korean Air Force FA-50 aircraft currently operating in the Air Force is using Ultra High Frequency (UHF) frequency communications for navigation communications with ground control stations or other aircraft. The pilot communicates by changing frequency at any time during flight, and performs communication by directly inputting from the Integrated Up-Front Controller installed in the cockpit. The frequency is designated as secret, and the pilot receives the task with the frequency channel number (001~xxx) and finds the frequency of the channel in the list of 4,000 frequency channels and inputs it manually. This reduces the safety and convenience of pilots' operations and exposes them to hazards that may occur especially during night flight missions. In this paper, we propose a function to embed the frequency corresponding to the frequency channel list in IMDC, the aircraft mission computer, and to automatically change the frequency when the pilot only inputs the channel number.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.12
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• pp.3055-3070
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• 2013

This paper proposes an improved carrier frequency offset (CFO) and sampling frequency offset (SFO) estimation scheme for orthogonal frequency division multiplexing (OFDM) based broadcasting system with cyclic delay diversity (CDD) antenna. By exploiting a periodic nature of channel transfer function, cyclic delay and pilot pattern with a maximum channel power are carefully chosen, which helps to enable a robust estimation of CFO and SFO against the frequency selectivity of the channel. As a performance measure, a closed-form expression for the achievable mean square error of the proposed scheme is derived and is verified through simulations using the parameters of the digital radio mondiale standard. The comparison results show that the proposed frequency estimator is shown to benefit from properly selected delay parameter and pilot pattern, with a performance better than the existing estimator.

• Restorative Dentistry and Endodontics
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• v.43 no.4
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• pp.41.1-41.7
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• 2018

Objectives: The purpose of the present study was to compare the mean preparation times and frequency with which Reciproc and Reciproc Blue instruments reached the full working length in mandibular molars, with or without glide path preparation. Materials and Methods: Previously untreated mesiobuccal and mesiolingual canals with completely formed apices were randomly divided into 6 groups (n = 50) depending on the usage of Reciproc (RC; VDW), Reciproc Blue (RC Blue; VDW), C-Pilot (CP; VDW), and R-Pilot (RP; VDW) files: RC, RC Blue, RC + C-Pilot (RC-CP), RC-Blue + C-Pilot (RC Blue-CP), RC+R-Pilot (RC-RP), and RC Blue + R-Pilot (RC Blue-RP). A glide path was prepared using the hand-operated C-Pilot or the machine-operated R-Pilot instruments, respectively. The ${\chi}^2$ test, analysis of variance, and the Tukey post hoc test were used for statistical comparisons. Results: No statistically significant differences were observed in the distribution of the frequency of reaching the full working length in the RC (94%), RC Blue (88%), RC-CP (94%), RC Blue-CP (90%), RC-RP (96%), and RC Blue-RP (92%) groups (p > 0.05). Conclusions: Preparation of a glide path did not have a significant effect on reaching the full working length using these systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9A
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• pp.858-866
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• 2005

This paper proposes the method of frequency synchronization using the spectrum correlation in ATSC terrestrial DTV system. If the spectrum around pilot is severely distorted by multipath or mobile reception environment, the conventional algorithm using the pilot signal makes the estimation error of the frequency offset. Because the proposed algorithm acquires frequency synchronization using the correlation between the received specalm and the standard spectrum without the use of pilot, the proposed method can acquire frequency synchronization faster and more accurate than conventional algorithm. And this paper proposes new method for ATSC frequency synchronization without the use of pilot.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.4
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• pp.399-407
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• 2010

SC-FDMA system uses DFT-spreading method for reducing the PAPR of OFDM signal, which improves the power efficiency. Block type pilot is used in SC-FDMA system. However, there are ICI due to the inevitable phase noise and frequency offset that can be generated from the Doppler frequency and inaccuracy between the transceiver oscillators. This ICI definitely degrades the BER performance. To overcome this problem and estimate the channel efficiently, we like to propose ICI compensation algorithm for the SC-FDMA system with comb type pilot. SLM method is additionally included for the PAPR reduction when pilot is assigned in comb type. Finally, it is confirmed that the ICI due to the phase noise and frequency offset is efficiently compensated by the suggested algorithm.

• Journal of electromagnetic engineering and science
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• v.7 no.4
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• pp.195-200
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• 2007

Doubly-selective channel estimator for orthogonal frequency division multiplexing(OFDM) systems is proposed in this paper. Based on the generalized complex exponential basis expansion model(GCE-BEM), we describe the time-variant channel with time-invariant coefficients over multiple OFDM blocks. The time variation of the channel destroys the orthogonality between subcarriers, and the resulting channel matrix in the frequency domain is no longer diagonal, but the main interference comes from the near subcarriers. Based on this, we propose a channel estimator with low pilot ratio. We first develop a least-square(LS) estimator under the assumption that only the maximum Doppler frequency and the channel order are known at the receiver, and then verify that the correlation matrix of inter-channel interference(ICI) is a scaled identity matrix based on which we derive an optimal pilot insertion scheme for the LS estimator in the sense of minimum mean square error. The proposed estimator has the advantages of low pilot ratio and robustness against inter-carrier interference.