• Journal of the Korea Society of Computer and Information
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• v.22 no.3
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• pp.1-8
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• 2017

In this paper, we propose a new hybrid wear leveling technique for NAND Flash memory, called Time-Aware Wear Leveling (TAWL). Our proposal prolongs the lifetime of NAND Flash memory by using dynamic wear leveling technique which considers the wear level of hot blocks as well as static wear leveling technique which considers the wear level of the whole blocks. TAWL also reduces the overhead of garbage collection by separating hot data and cold data using update frequency rate. We showed that TAWL enhanced the lifetime of NAND flash memory up to 220% compared with previous wear leveling techniques and our technique also reduced the number of copy operations of garbage collections by separating hot and cold data up to 45%.

• Proceedings of the Korea Multimedia Society Conference
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• 2000.04a
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• pp.449-452
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• 2000

This paper proposes a new, adaptive Dead Reckoning model, called Dynamic Dead Reckoning , for Distributed Interactive Simulation and humanoid avatar systems. The proposed model can overcome the weak points of traditional Dead Reckoning caused by a fixed threshold and strong dependency on rotation event. This paper introduces new criteria for update message filtering , named as Update lifetime. The Dynamic Dead Reckoning keeps the balance between extrapolation fidelity and filtering performance by two component models, Variable Threshold Mechanism and Rotation Event model. The experimental results show that the proposed model can lower the increment rate of update traffic to the increase of rotation frequency without any significant loss of accuracy.

• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.321-324
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• 1997

In this paper, Active Noise Control(ANC) algorithm is proposed based on the estimated frequency estimator of the reference signal. The conventional feedforward ANC algorithms should measure the reference and use it to calculate the gradient of the squared error and filter coefficients. For ANC systems applied to aircrafts and passenger ships, engines from which reference signal is usually measured is so far from seats where main part of controller is placed that the scheme might be difficult to implement or very costly. Feedback ANC algorithm which doesn't need to measure the reference uses the error signal to update the filter and is sensitive to unexpected transient noise like a sneeze, clapping of hands and so on The proposed algorithm estimates frequencies of the desired signal in real time using adaptive notch filter. New frequency estimation algorithm is proposed with the improved convergence rate, threshold SNR and computational simplicity. Reference is not measured but created with the estimated frequencies. It has strong similarity to the conventional feedback control because reference is made from error signal. Enhanced error signal is used to update the controller for better performance under the measurement noise and impact noise. The proposed ANC algorithm is compared with the conventional feedback control.

• ETRI Journal
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• v.29 no.5
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• pp.596-606
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• 2007

It is well known that an OFDM receiver is vulnerable to synchronization errors. Despite fine estimations used in the initial acquisition, there are still residual synchronization errors. Though these errors are very small, they severely degrade the bit error rate (BER) performance. In this paper, we propose a residual error elimination scheme for the digital OFDM baseband receiver aiming to improve the overall BER performance. Three improvements on existing schemes are made: a pilot-aided recursive algorithm for joint estimation of the residual carrier frequency and sampling time offsets; a delay-based timing error correction technique, which smoothly adjusts the incoming data stream without resampling disturbance; and a decision-directed channel gain update algorithm based on recursive least-squares criterion, which offers faster convergence and smaller error than the least-mean-squares algorithms. Simulation results show that the proposed scheme works well in the multipath channel, and its performance is close to that of an OFDM system with perfect synchronization parameters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6C
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• pp.611-618
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• 2009

Recently, an indoor location-aware technology has been focused on as a key technology for context awareness in ubiquitous computing environments. The conventional Cricket system was designed with a non-centralized architecture, which has advantages in terms of user privacy, deployment, scalability, decentralized administration, network heterogeneity, and low cost. In this paper, an indoor location system based on TDOA between RF and ultrasound signals is designed, which improves the Cricket system. A 2.4GHz frequency is employed for transmitting RF messages, which is in an ISM band. The beaconing frequency is doubled to enhance the channel utilization rate. The ultrasonic pulse duration is optimized to increase the coverage of ultrasonic signals. The function of calculating location coordinates is embedded in a listener. The location-update rate and location accuracy are also improved.

• Journal of Communications and Networks
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• v.7 no.3
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• pp.248-257
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• 2005

In this paper, we develop design procedures for carrier tracking loop for orthogonal frequency division multiplexing (OFDM) systems or other systems of blocked data. In such communication systems, phase error measurements are made infrequent enough to invalidate the traditional loop design methodology which is based on analog loop design. We analyze the degradation in the OFDM schemes caused by the tracking loop and show how the performance is dependent on the rms phase error, where we distinguished between the effect of the variance in the average phase over the symbol and the effect of the phase change over the symbol. We derive the optimal tracking loop including optional delay in the loop caused by processing time. Our solution is general and includes arbitrary phase noise apd additive noise spectrums. In order to guarantee a well behaved solution, we have to check the design against margin constraints subject to uncertainties. In case the optimal loop does not meet the required margin constraints subjected to uncertainties, it is shown how to apply a method taken from control theory to find a controller. Alternatively, if we restrict the solution to first or second order loops, we give a simple loop design procedure which may be sufficient in many cases. Extensions of the method are shown for using both pilot symbols and data symbols in the OFDM receiver for phase tracking. We compare our results to other methods commonly used in OFDM receivers and we show that a large improvement can be gained.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.5
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• pp.791-798
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• 2015

It has been grown interests of the convergence technologies about communication systems and vehicular industry. Vehicular communications enable a number of infotainment applications to serve cars under high mobility environments. To achieve this goal, a robust and accurate channel estimation scheme is of great importance. This paper proposes an enhanced Decision-Directed channel estimation scheme called PTAU(Pilot Tone Aided Update) for IEEE 802.11p in vehicular communication environment. Existing approaches which use subsequent data symbols to estimate channel response in time domain will lead to the error propagation. In this paper, we use the pilot subcarriers to get initial channel response, then utilize the correlation characteristics to update channel response in frequency domain. Finally, Analysis and simulation results reveal that the proposed scheme outperforms in bit error rate(BER), significantly improve the performance of the estimation.

• Journal of Satellite, Information and Communications
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• v.10 no.1
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• pp.29-32
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• 2015

It has been a big trend of the convergence technologies about communication systems and vehicular industry to improve safety and convenience. To achieve a number of infotainment vehicular applications, vehicles should transmit information with high reliability. A robust and accurate channel estimation scheme is of great importance to achieve the goal. In this paper, we present a novel enhanced decision-directed channel estimation scheme called FADP (Frequency Averaging Data Pilot) for dynamic time-varying vehicular channels in IEEE 802.11p. We use linear averaging filtering in frequency domain, and utilize the correlation characteristic of the channels between the adjacent two data symbols, update the CR in time domain to get more accuracy. Finally, analysis and simulation results reveal that compared with exist schemes, the proposed scheme has a good performance in mean square error (MSE) and bit error rate (BER).

• International Journal of Internet, Broadcasting and Communication
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• v.14 no.3
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• pp.69-78
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• 2022

In this paper, we propose the new technique adopting power control to MIMO(multi-input multi-output)-OFDMA(orthogonal frequency division multiplexing Access) system with multi-beamformer. The proposed power controlling algorithm for MIMO-OFDMA allocates the transmitting power of each subcarrier based on the CSI(channel state information) and the interference signal. CSI is feedback from base station to mobile station to decide the transmitting power of each subcarrier. Through the proposed technique, we can control iteratively the transmitting power and update the weight of beamformer simultaneously. Therefore, the SNIR of each subcarrier become to converge the target SNIR and the beam is formed toward the desired direction. And the performance of MIMO-OFDMA system with the proposed approach is very improved. The improvement in bit error rate is investigated through computer simulation of a MIMO-OFDMA system with the proposed approach.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.491-500
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• 2020

The present study proposes a time domain model for the Vortex-induced Vibration (VIV) simulation of a catenary riser under the combination of the current and oscillatory flow induced by vessel motion. In this model, the hydrodynamic force of VIV comprises excitation force, hydrodynamic damping and added mass, which are taken as functions of the non-dimensional frequency and amplitude ratio. The non-dimensional frequency is related with the response frequency, natural frequency, lock-in range and the fluid velocity. The relatively oscillatory flow induced by vessel motion is taken into account in the fluid velocity. Considering that the added mass coefficient and the non-dimensional frequency can affect each other, an iterative analysis is conducted at each time step to update the added mass coefficient and the natural frequency. This model is in detail validated against the published test models. The results show that the model can reasonably reflect the effect of the added mass coefficient on the VIV, and can well predict the riser's VIV under stationary and oscillatory flow induced by vessel motion. Based on the model, this study carries out the VIV simulation of a catenary riser with harmonic vessel motion. By analyzing the bending moment near the touchdown point, it is found that under the combination of the ocean current and oscillatory flow the vessel motion may decrease the VIV response, while increase the excited frequencies. In addition, the decreasing rate of the VIV under vessel surge is larger than that under vessel heave at small vessel motion velocity, while the situation becomes opposite at large vessel motion velocity.