• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.05a
• /
• pp.30-35
• /
• 2007

Various acoustic tests were carried out to investigate the acoustic performance of diesel engine exhaust silencers. In order to consider flow effects, test equipment composed of fan, duct and silencer was set up. Using the test equipment, insertion loss tests were carried out to improve the performance in the low-frequency ranges. Through a series of tests, the fact that array resonators may be effective in the low-frequency noise has been verified. Consequently, the hybrid-type silencer which is the combination of reflective silencer with array resonators and conventional absorptive silencer were proposed and its high acoustic performance in the low-frequency range has also been verified.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.66 no.1
• /
• pp.48-52
• /
• 2017

This paper proposes a hybrid algorithm of space-time block coding and space-frequency block coding using alternate time switch. The traditional alternate time-switched space-time or space-frequency block coding technique for orthogonal frequency division multiplexing system does not provide a good performance with a variety of communication environments. This hybrid algorithm has searched good performance ranges in various environments in view points of mobile speed and doppler frequency. In this paper, we investigate better performance ranges for two algorithms, suggest a hybrid algorithm for dynamically changing communication environments, propose a structure for transmitter and receiver, and show that its performance is better than the traditional algorithm by simulations.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.16 no.6
• /
• pp.819-827
• /
• 2013

Compared to legacy frequency hopping communications, future radio communications are required the secure and high data rate, ad-hoc network communication. In this paper, we have designed the network communication structure on the frequency hopping mode, and analyzed the performance of synchronization on the frequency hopping network radio systems. The design results are shown the initial sync. phase of approximately 9 hops and the traffic packet phase of approximately 30 hops. Also, we have simulated the performance on the communication conditions which are carrier bandwidth of 50kHz, user data rate of 64kbps and OQPSK modulation scheme in AWGN. In the simulation, we analyzed the correlation and the performance of synchronization success. The result of simulation show 99% probability for synchronization success at $E_b/N_o$ -4dB.

• Journal of Korean society of Dental Hygiene
• /
• v.10 no.3
• /
• pp.503-512
• /
• 2010

Objectives : In this study, in order to provide basic data for more efficient and systematic clinical practice training by recognizing the need of effective and standardized operation of clinical practice accomplished in clinical fields belonging to the curriculum of dental hygiene department, grasping, investigating, and analyzing satisfaction degree of the clinical practice through student's frequency of observation practice and performance practice. Methods : A survey was conducted against 208 students in the 3rd grade of 4 dental hygiene departments located in Jeonbuk province. Results : As results, it was found that for the observation practice frequency according to clinical practice term by universities, the basic clinical practice was higher in A, B, and D university and that the correction and practice was higher in D university. For the performance practice frequency, it was found that basic care practice was higher in B and D university, oral medicine practice, preventive dentistry practice, and periodontal practice were higher in A and C university, pediatric dentistry practice was higher in B and C university, prosthetic dentistry practice was higher in A, B, and C university, and oral surgery practice was higher in B university. It was identified that satisfaction was higher in the basic care practice, the preventive dentistry practice, and the periodontal practice in the range of clinical practice, and the A and C university receiving higher score in the performance practice frequency got higher score in the oral medicine practice, the preventive dentistry practice, and the periodontal practice. Conclusions : As the basic care practice items in the clinical practice area which got relatively higher score in observation practice, performance practice, and satisfaction degree of the dental hygiene trainee are basic and essential works that they will perform the most frequently, it is considered that integrated clinical practice training including the intramural practice course is required.

• Journal of international Conference on Electrical Machines and Systems
• /
• v.3 no.2
• /
• pp.229-234
• /
• 2014

In this paper, a design problem of the flywheel energy storage system controller using genetic algorithm (GA) is investigated for a frequency control of the wind diesel hybrid power generation system in an isolated power system. In order to select parameters of the FESS controller, two performance indexes are used. We evaluated a frequency control effect for the wind diesel hybrid power system according to change of the weighted values of a performance index. To verify performance of the FESS controller according to the weighted value of the performance index, the frequency domain analysis using a singular value bode diagram and the dynamic simulations for various weighted values of performance index were performed. To verify control performance of the designed FESS controller, the eigenvalue analysis and the dynamic simulations were performed. The control characteristics with the two designed FESS controller were compared with that of the conventional pitch controller. The simulation results showed that the FESS controller provided better dynamic responses in comparison with the conventional controller.

• Journal of Communications and Networks
• /
• v.8 no.1
• /
• pp.38-48
• /
• 2006

A synchronous multicarrier (MC) code-division multiple access (CDMA) system using inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) for the downlink mobile communication system operating in a frequency selective Rayleigh fading channel is analyzed. Both carrier frequency offset and timing offset are considered in the analysis. Bit error rate performance of the system with both equal gain combining and maximum ratio combining are obtained. The performance is compared to that of the conventional system using correlation receiver. It is shown that when subcarrier number is large, the system using IFFT/FFT has nearly the same performance as the conventional one, while when the sub carrier number is small, the system using IFFT/FFT will suffer slightly worse performance in the presence of carrier frequency offset.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.1735-1740
• /
• 2000

The aim of this study is to analyze the sound insulation performance of windows depending on the sound source types and to propose the noise control method in the apartment house. The regions where apartment houses are constructed are varied in the dominant noise sources such as aircraft noise, railway noise and road traffic noise. For the experiment, nine noise sources including pink noise were selected and recorded, which was used in the experiment by reproducing. As a result of this study, the sound insulation performance of window was found that when the frequency contents of the noise were high level in all frequency bands the difference of sound insulation performance was negligible, but when the frequency contents were low level at particular frequency band the difference of sound insulation performance was shown very differently.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.30A no.9
• /
• pp.6-13
• /
• 1993

In is well-known that system performance in the high speed digital radio communication system is usually deteriorted due to the frequency selective fading distortion. In this paper, bit error rate(BER) performance by the reception phase error in cellular mobile communication systems is derived and analyzed. The system is modeled as a frequency selective fast Rayleigh fading channel corrupted by additive white gaussian noise(AWGN) and co-channel interference(CCI). Our numerical results show that for the 24KBaud(48Kb/s) $\pi$/4-DQPSK operated at carrier frequency 800 MHz and C/I<20 dB, the BER will be dominated by CCI if the vehicular speed is below 100 Km/h. The results show that performance, when reception phase error is below $\pi$/12, is deterioreted less than 3 dB, and that performance, when reception phase error is above $\pi$/12, is degraded over 3 dB.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.23 no.2
• /
• pp.139-146
• /
• 2018

This work puts forward a theoretical analysis on position estimation performance of interior permanent magnet synchronous motor (IPMSM) according to the injection frequency in carrier-based sensorless operation. The effects of spatial harmonics on inductance and voltage distortion due to the nonideal characteristics of IPMSM and inverter are examined as factors influencing the position estimation performance. Furthermore, the position estimation performance is analyzed by calculating the current at the switching instant in several operating conditions. In summary, the half switching frequency injection is more robust to the nonideal characteristics of IPMSM, especially with light load condition. The validity of the analysis is verified by the simulation and experimental results.

• Journal of Positioning, Navigation, and Timing
• /
• v.9 no.3
• /
• pp.207-214
• /
• 2020

In this paper, we implement linear-quadratic-Gaussian based vector tracking loop (LQG-VTL) instead of conventional extended Kalman filter based vector tracking loop (EKF-VTL). The LQG-VTL can improve the performance compared to the EKF-VTL by generating optimal control input at a specific performance index. Performance analysis is conducted through two factors, frequency thermal noise and frequency dynamic stress error, which determine total frequency tracking error. We derive the thermal noise and the dynamic stress error formula in the LQG-VTL. From frequency tracking error analysis, we can determine control gain matrix in the LQG controller and show that the frequency tracking error of the LQG-VTL is lower than that of the EKF-VTL in all C/N0 ranges. The simulation results show that the LQG-VTL improves performance by 30% in Doppler tracking, so the LQG-VTL can extend pre-integration time longer and track weaker signals than the EKF-VTL. Therefore, the LQG-VTL algorithm is more robust than the EKF-VTL in weak signal environments.