• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.7
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• pp.1-7
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• 2010

In this paper, we use the maximum-likelihood detection by the estimation of trellis targets on the 16-level cell NAND flash memory. This mechanism has a performance gain by using a maximum-likelihood detector. The NAND flash memory channel is a memory channel because of the coupling effect. Thus, we use the known data arrays to finding the targets of trellis. The maximum-likelihood detection by proposed scheme performs better than the threshold detection on the 16-level cell NAND flash memory channel.

• Journal of Positioning, Navigation, and Timing
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• v.5 no.3
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• pp.109-118
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• 2016

The present paper proposes a method that can estimate a roll rate of spinning vehicles utilizing GPS receivers. The proposed method analyzes a relation between received signal and correlation value and utilizes a phenomenon that received signal power that changes according to a signal incident direction affects a correlation value. That is, a roll-rate estimation method using zero crossing detection method for correlation value, which has sinusoidal periodicity according to rotations of vehicles, is proposed. A correlation value in real environments experiences a jitter so that the proposed method includes a pre-processing filter and detection threshold setting way is also considered to reduce the effect of received signal power. In order to verify the operation of the proposed method and analyze the performance, a signal generator and software-defined receiver (SDR) are designed. The signal generator generates intermediate frequency (IF) signal by taking the rotation of vehicles, antenna gain, and signal power into consideration, and a correlation value is acquired by taking the generated IF signals into consideration. Using the generated correlation value, the operation of the proposed roll rate estimation method is verified and the performance is analyzed.

• The Journal of the Acoustical Society of Korea
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• v.20 no.3
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• pp.42-47
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• 2001

This paper improves the performance of VAD (Voice Activity Detector) in G.723.1 Annex A 6.3kbps/5.3kbps dual rate speech coder, which is developed for Internet Phone and videoconferencing. The VAD decision is based on a three-level energy threshold. We evaluates for processing time, speech quality, and bit rate. The processing time is reduced due to the accuracy of VAD decision on the silence period. On subjective quality test there is almost no difference compared with the G.723.1. In order to measure the bit rate we count the active speech frame (VAD=1) and we can reduce more bit rate as silence periods are shown.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.3
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• pp.283-289
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• 2015

In this paper, a GNSS interference detection algorithm based on an adaptive fading Kalman filter is proposed to detect a spoofing signal which is one of the threatening GNSS intentional interferences. To detect and mitigate the spoofing signal, the fading factor of the filter is used as a detection parameter. For simulation, the effect of the spoofing signal is modeled by the ramp type bias error of the pseudorange to emulate a smart spoofer and the change of the fading factor value according to ramp type bias error is quantitatively analyzed. In addition, the detection threshold is established to detect the spoofing signal by analyzing the change of the error covariance and the effect of spoofing is mitigated by controlling the Kalman gain of the filter. To verify the performance analysis of the proposed algorithm, various simulations are implemented. Through the results of simulations, we confirmed that the proposed algorithm works well.

• Korean Journal of Optics and Photonics
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• v.5 no.2
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• pp.286-290
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• 1994

Lasing characteristics of an Er-doped fiber laser have been investigated at various conditions of resonator reflectivities and pump powers. Variation of the laser wavelength with various mirror reflectivities has been compared with the theoretical analysis based on absorption, gain spectra, and resonator parameters. The maximum slope efficiency of 38% was obtained with the resonator's mirror reflectivities of 100% and 4% on both sides, and the threshold powers were varied from 7.8 mW to 5.6 mW, and lasing wavelengths were varied $1.532\mum to 1.563\mum and 1.558 \mum to 1.570 \mum$ for 6 and 15.8 mlong Er-doped fiber, respectively, as the resonator reflectivities were changed from 0.0016 to 0.9.to 0.9.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.2
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• pp.26-38
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• 1994

We demonstrate a repeatless transmission of 2.5 Gbps digital signal over 98 km opticla filbers using optical transmitter and optcial receiver which are designed and implemented using commercially available devices. The optical transmitter is realized by using a distributed feedback(DFB) laser. Temperature of the laser is thermoelectrically stabilized and the output optical power is also stabilized by using negative feedback. The output power of the transmitter is 0 dBm. The optical receiver consists of an InGaAs avalanche photodiode, a preamplifier. an automatic gain control amplifier, and a clock/data regenerator. We find an optimum decision threshold that gives the best receiver sensitivity form the measured V curve. The best sensitivity is -35.5dBm( BER-1*10S010T, PRBS=2S023T -1 ) and the overload power is -9 dBm. Finally, we achieve error free optical transmission with 98 km optical fibers. The exinction ration penalty of 2 dB. the chromatic dispersion penalty of 1 dB, and the total power penalty of 3.0 dB are measured. These results satisfy CCITT recommendation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.2
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• pp.61-74
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• 2014

In recent years, development of femtocells are receiving considerable attention towards increasing the network coverage, capacity, and improvement in the quality of service for users. In 3GPP LTE-Advanced (LTE-A) system, to efficiently utilize the bandwidth, femtocell and macro cell uses the same frequency band, but this deployment poses a technical challenge of cross-tier interference to macro users. In this paper, the novel quality of service based fractional power control (QoS-FPC) scheme under the heterogeneous networks environment is proposed, which considers the users priority and QoS-requirements during the power allocation. The proposed QoS-FPC scheme has two focal points: firs, it protects the macrocell users uplink communication by limiting the cross-tier interference at eNB below a given threshold, and second, it ensures the optimization of femtocell users power allocation at each power adjustment phase. Performance gain is demonstrated with extensive system-level simulations to show that the proposed QoS-FPC scheme significantly decreases the cross-tier intereference and improves the overall users throughput.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.2
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• pp.837-856
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• 2016

Underwater image enhancement has received considerable attention in last decades, due to the nature of poor visibility and low contrast of underwater images. In this paper, we propose a new automatic underwater image enhancement algorithm, which combines nonsubsampled contourlet transform (NSCT) domain enhancement techniques with the mechanism of the human visual system (HVS). We apply the multiscale retinex algorithm based on the HVS into NSCT domain in order to eliminate the non-uniform illumination, and adopt the threshold denoising technique to suppress underwater noise. Our proposed algorithm incorporates the luminance masking and contrast masking characteristics of the HVS into NSCT domain to yield the new HVS-based NSCT. Moreover, we define two nonlinear mapping functions. The first one is used to manipulate the HVS-based NSCT contrast coefficients to enhance the edges. The second one is a gain function which modifies the lowpass subband coefficients to adjust the global dynamic range. As a result, our algorithm can achieve contrast enhancement, image denoising and edge sharpening automatically and simultaneously. Experimental results illustrate that our proposed algorithm has better enhancement performance than state-of-the-art algorithms both in subjective evaluation and quantitative assessment. In addition, our algorithm can automatically achieve underwater image enhancement without any parameter tuning.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.6
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• pp.514-520
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• 2002

In this paper, the study of a design and fabrication of the receiver MMIC mixer for L-band application is described. The mixer is composed of active LO and RF balun to integrate on a chip and applied a newly proposed bias circuit to compensate the process variations of active devices. The conversion gain of the mixer is -14 dB, IIP3 is approximately 4 dBm and port-to-port isolation is over 25 dB. The newly proposed bias circuit is composed of a few FETs and resistors, and can compensate the variation of the threshold voltage by the process variations, temperature changes and etc. The designed chip size is $1.4\;mm{\times}1.4\;mm$.

• Korean Journal of Optics and Photonics
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• v.6 no.4
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• pp.282-287
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• 1995

We have studied the characteristics of a cw Ti:sapphire laser pumped by an Ar-ion laser. Ti:sapphire is one of the most attractive materials for the generation of ultra-short pulses because of its very broad gain bandwidth. We used a 4.1 mm thick, 0.15 wt. % $Ti^{3+}$ -doped, Brewster-angled Ti:sapphire crystal and made a folded cavity to create a strong focusing mode. The folding angle of the cavity was adjusted to $15.4^{\circ}$ to compensate for the astigmatism from the Brewster-angled Ti:sapphire crystal. 5 WAr-ion laser was used as a pumping source. We observed that the Ti:sapphire cw output power was sensitively changed with respect to the condition of the folded cavity. The threshold pumping power was 2 Wand the slope efficiency was 16% when an output coupler of 10% transmission was used. The maximum output power was more than 450 mW at 5 W pumping. mping.