• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.4
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• pp.380-387
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• 2015

Various forms of passive shock absorber have developed to supplement performance which is poorer than that of active shock absorber. It is called 'Hybrid Conventional Damper (HCD)'. Frequency sensing shock absorber that this study will cover belongs to the HCD. This study aims to demonstrate that performance of frequency sensing shock absorber is superior than that of passive shock absorber. Study process is as follows. Firstly, analysis models for both passive shock absorber and frequency sensing shock absorber are developed to secure reliability. Then, elements which cause difference of ride quality are found out through comparison of hysteresis characteristics. By comparison of frequency characteristic, furthermore, damping principle of frequency sensing shock absorber is understood. Also, it determines if the absorber performs well even though maximum excitation speed is changed. Finally, the study proves that performance of frequency sensing shock absorber is superior than that of passive shock absorber after comparing change of damping power in excitation condition that various frequencies are mixed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.5
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• pp.1270-1281
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• 1998

Frequency offset in an orthogonal frequency division multiplexing (OFDM) system is known to cause the inter-channel interference (ICI), amplitude and phase distortion of a received signal, resulting in a severe performance degradation of the total system. In this paper, we propose an improved pilot-based masimum likelihood frequency offset estimation technique, which uses the predefined sync-subchannels, and derive the error performance of the proposed frequency offset estimator analytically. The proposed technique improves the performance of the frequency offset estimator by adding up the frequency offset caused by coherent phase changes and averaging out the effect caused by random phase error. It is confirmed by computer simulations that the upper bound of error variance for the proposed frequency offset estimator analytically derived in this paper is correct, and that the proposed estimator has better performance than the previous ones in terms of error variance, tracking range, and time-varying characteristics of a channel.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.1
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• pp.47-53
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• 2012

In cellular geo-location systems, positioning performance is influenced by hearability of receivers. Hearability can be enhanced by using long integration at the receiver. When unknown residual frequency remains in baseband signals, however, the coherent integration loss increases as the residual frequency becomes larger. Consequently, length of coherent integration is determined by the residual frequency. By precise estimation and compensation of the residual frequency, integration length can be enlarged. This paper presents a residual frequency estimator for WiBro geo-location and analyzes its performance in multipath environment. By computer simulation, an optimal receiver structure to enhance the hearability of WiBro geo-location is proposed.

• Journal of Information Technology Applications and Management
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• v.13 no.4
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• pp.273-290
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• 2006

This study suggests a frequency matrix technique to predict personal credit rate more efficiently using incomplete data sets. At first this study test on multiple discriminant analysis and logistic regression analysis for predicting personal credit rate with incomplete data sets. Missing values are predicted with mean imputation method and regression imputation method here. An artificial neural network and frequency matrix technique are also tested on their performance in predicting personal credit rating. A data set of 8,234 customers in 2004 on personal credit information of Bank A are collected for the test. The performance of frequency matrix technique is compared with that of other methods. The results from the experiments show that the performance of frequency matrix technique is superior to that of all other models such as MDA-mean, Logit-mean, MDA-regression, Logit-regression, and artificial neural networks.

• Proceedings of the Acoustical Society of Korea Conference
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• 1985.10a
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• pp.87-94
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• 1985

In this paper, enhancement of speech corrupted by additive white or colored noise is stuided. The nuconstrained frequency-domain block least-mean-square (UFBLMS) adaptation algorithm and its frequency-weighted version are newly applied to speech enhancement. For enhancement of speech degraded by white noise, the performance of the UFBLMS algorithm is superior to the spectral subtraction method or Wiener filtering technique by more than 3 dB in segmented frequency-weighted signal-to-noise ratio(FWSNERSEG) when SNR of speech is in the range of 0 to 10 dB. As for enhancement of noisy speech corrupted by colored noise, the UFBLMS algorithm is superior to that of the spectral subtraction method by about 3 to 5 dB in FWSNRSEG. Also, it yields better performance by about 2 dB in FWSNR and FWSNRSEG than that of time-domain least-mean-square (TLMS) adaptive prediction filter(APF). In view of the computational complexity and performance improvement in speech quality and intelligibility, the frequency-weighted UFBLMS algorithm appears to yield the best performance among various algorithms in enhancing noisy speech corrupted by white or colored noise.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.6
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• pp.819-827
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• 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 the Korea Institute of Information and Communication Engineering
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• v.5 no.4
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• pp.684-691
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• 2001

In this paper, the BER performance of OFDM/M-ary PSK systems is analyzed with considering carrier-frequency offset and TCM technique, which encodes and modulations simultaneously, is adopted to OFDWM-ary PSK systems for compensation of performance degradation according to carrier-frequency offset. As a result of analysis, the error performance of OFDM/M-ary PSK systems is degraded as the frequency offset is increased. And the frequency offset should be below 0.025 in order to achieve $BER= 10^{-3}$ with $E_b/N_o$ of 10 dB. Especially, when the TCM technique is adopted to OFDM/M-ary PSK systems, the performance improvement of about 4 dB is obtained in terms of $E_b/N_o$.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.5
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• pp.2124-2143
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• 2016

In Long Term Evolution-Advanced (LTE-A) systems, Inter-cell Interference (ICI) is a prominent limiting factor that affects the performance of the systems, especially at the cell edges. Based on the literature, Fractional Frequency Reuse (FFR) methods are known as efficient interference management techniques. In this report, the proposed Dynamic Fractional Frequency Reuse (DFFR) technique improved the capacity and cell edge coverage performance by 70% compared to the Fractional Frequency Reuse (FFR) technique. In this study, an improved power allocation method was adopted into the DFFR technique to reach the goal of not only reducing the ICI mitigation at the cell edges, but also improving the overall capacity of the LTE-A systems. Hence, an improved water-filling algorithm was proposed, and its performance was compared with that of other methods that were considered. Through the simulation results and comparisons with other frequency reuse techniques, it was shown that the proposed method significantly improved the performance of the cell edge throughput by 42%, the capacity by 75%, and the coverage by 80%. Based on the analysis and numerical expressions, it was concluded that the proposed DFFR method provides significant performance improvements, especially for cell edge users.

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

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.299-304
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• 1993

A 1/4 car model(2 DOF system) is employed to evaluate the performance included a quadratic cost functional in frequency domain. The design procedure of feedback control to optimize the performance index results in a modified Linear-Quadratic-Gaussian problem and cultivates a quite simple control algorithm. Computer simulation result is shown that the LQG method using frequency shaped performance index is outstanding in ride comfort and its response converges to the steady state very rapidly in comparison with the known passive suspension, classical design methods LQR/ and LQG.