• Journal of Communications and Networks
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• v.9 no.2
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• pp.192-197
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• 2007

We analyze the performance of code division multiple access (CDMA) system with multicarrier (MC) that employs precoding in synchronous downlink channels. Even though considerable efforts are undergoing for frequency offset estimation and correction, it is inevitable for the system to bear the remaining frequency offset. Therefore it is important to predict accurately the system performance in the presence of the residual frequency offset. We obtain the bit error rate (BER) performance in terms of the number of users, the spreading factor, the number of sub-carriers, and frequency offset. We assume that the spreading factor is equal to the number of sub-carriers, although we can generalize the case. The simulation results show that the BER of MC-CDMA with precoding shows a performance that varies with frequency offset as well as system loading.

• Journal of Internet Computing and Services
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• v.23 no.3
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• pp.1-12
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• 2022

As the performance of Unmanned Aerial Vehicles (UAVs) are improving and the prices are lowering, it is expected that the use of UAVs will continuously grow in the future. It is important to always maintain control signal and video communication to operate remote UAVs stably, especially in military UAV operations, as unexpected jamming attacks can result in fatal UAV crashes. In this paper, to improve the network reliability and low latency when supporting UAV operations, the anti-jamming performance of Second generation Anti-jam Tactical UHF Radio for NATO (SATURN) networks is analyzed and enhanced by applying Forward Error Correction (FEC) and Minimum Shift Keying (MSK) modulation as well as Hamming code based multiple transmission techniques.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.8
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• pp.633-642
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• 2016

It is important for advanced active safety systems and autonomous driving cars to get the accurate estimates of the nearby vehicles in order to increase their safety and performance. This paper proposes a sensor fusion method for radar and vision sensors to accurately estimate the state of the preceding vehicles. In particular, we performed a study on compensating for the lateral state error on automotive radar sensors by using a vision sensor. The proposed method is based on the Interactive Multiple Model(IMM) algorithm, which stochastically integrates the multiple Kalman Filters with the multiple models depending on lateral-compensation mode and radar-single sensor mode. In addition, a Probabilistic Data Association Filter(PDAF) is utilized as a data association method to improve the reliability of the estimates under a cluttered radar environment. A two-step correction method is used in the Kalman filter, which efficiently associates both the radar and vision measurements into single state estimates. Finally, the proposed method is validated through off-line simulations using measurements obtained from a field test in an actual road environment.

• Journal of Radiation Protection and Research
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• v.26 no.4
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• pp.375-384
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• 2001

It is possible to count and perform quench correction on two ${\beta}$ -label samples so long as the maximum ${\beta}$-energies are sufficiently different. However, when 4he conventional technique is applied to the radioassay of a mixture of more than three nuclides, the reliability of the activities determined is considerably reduced, resulting from the large overlapping of liquid scintillation pulse height distributions of each nuclide. A technique that allows the activities of multiple ${\beta}$-labeled samples to be radioassayed was proposed by using the least square method. The technique was applied to mixture samples of $^3H,\;^{14}C,\;^{36}Cl$, and $^{90}Sr$. The analytical values were in good agreement with the reference values within 7% relative error.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.2 s.332
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• pp.23-30
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• 2005

This paper describes a DLL(delay locked loop)-based multi-clock generator having the lower active stand-by power as well as a fast relocking after re-activating the DLL. for low power and high speed VLSI chip. It enables a frequency multiplication using frequency multiplier scheme and produces output clocks with 50:50 duty-ratio regardless of the duty-ratio of system clock. Also, digital control scheme using DAC enables a fast relocking operation after exiting a standby-mode of the clock system which was obtained by storing analog locking information as digital codes in a register block. Also, for a clock multiplication, it has a feed-forward duty correction scheme using multiphase and phase mixing corrects a duty-error of system clock without requiring additional time. In this paper, the proposed DLL-based multi-clock generator can provides a synchronous clock to an external clock for I/O data communications and multiple clocks of slow and high speed operations for various IPs. The proposed DLL-based multi-clock generator was designed by the area of $1796{\mu}m\times654{\mu}m$ using $0.35-{\mu}m$ CMOS process and has $75MHz\~550MHz$ lock-range and maximum multiplication frequency of 800 MHz below 20psec static skew at 2.3v supply voltage.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.2
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• pp.199-208
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• 2014

Code division multiple access (CDMA) is one of the promising medium access control (MAC) schemes for underwater acoustic sensor networks because of its robustness against frequency-selective fading and high frequency-reuse efficiency. As a way of performance evaluation, sea or lake experiment has been employed along with computer simulation.. In this study, we design the underwater CDMA forward-link transceiver and evaluate the feasibility aginst harsh underwater acoustic channel in water-tank first. Then, based on the water-tank experiment results, we improved the transceiver and showed the improvements in a lake experiment. A pseudo random noise code acquisition process is added for phase error correction before decoding the user data by means of a Walsh code in the receiver. Interleaving and convolutional channel coding scheme are also used for performance improvement. Experimental results show that the multiplexed data is recovered by means of demultiplexing at receivers with error-free in case of two users while with less than 15% bit error rate in case of three and four users.

• The Transactions of the Korea Information Processing Society
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• v.3 no.5
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• pp.1273-1280
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• 1996

In order perform high accuracy recognition of text recognition systems, the recognized text must be processed through a post-processing stage using contextual information. We present a system that combines multiple knowledge sources to post-process the output of an optical character recognition(OCR) system. The multiple knowledge sources include characteristics of word, wrongly recognized types of Hangul characters, and Hangul word learning In this paper, the wrongly recognized characters which are made by OCR systems are collected and analyzed. We imput a Korean dictionary with approximately 15 0,000 words, and Korean language texts of Korean elementary/middle/high school. We found that only 10.7% words in Korean language texts of Korean elementary/middle /high school were used in a Korean dictionary. And we classified error types of Korean character recognition with OCR systems. For Hangul word learning, we utilized indexes of texts. With these multiple knowledge sources, we could predict a proper word in large candidate words.

• The Journal of the Acoustical Society of Korea
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• v.36 no.1
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• pp.39-48
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• 2017

CDMA (Code Division Multiple Access) is promising medium access control schemes for underwater acoustic sensor networks because of its robustness against frequency-selective fading and high frequency-reuse efficiency. In this paper, we design diversity schemes of underwater CDMA transceiver for the forward and reverse links. User data are multiplexed by Walsh code and a pseudo random noise code acquisition process is added for phase error correction before decoding the user data at the receiver. Then, the diversity reception using equal gain combining and maximal ratio combining is performed in order to minimize performance degradation caused by rich multipath fading of underwater acoustic channel. We evaluated the performance of diversity transceiver through lake experiment, which was performed at Lake Kyungcheon, Mungyeong city using two transmitters and two receivers placed 460 m apart at an average depth of 40 m. The lake experiment results show that user data are recovered with error-free in both of the forward and reverse links.

• The Journal of the Korea Contents Association
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• v.9 no.8
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• pp.91-98
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• 2009

This paper presents a solution to error avalanche of deciphering where radio noise brings random bit errors in encrypted image data under ubiquitous environment. The image capturing module is to be made comprising data compression and encryption features to reduce data traffic volume and to protect privacy. Block cipher algorithms may experience error avalanche: multiple pixel defects due to single bit error in an encrypted message. The new fault tolerant scheme addresses error avalanche effect exploiting a three-dimensional data shuffling process, which disperses error bits on many frames resulting in sparsely isolated errors. Averaging or majority voting with neighboring pixels can tolerate prominent pixel defects without increase in data volume due to error correction. This scheme has 33% lower data traffic load with respect to the conventional Hamming code based approach.

• Journal of Korea Port Economic Association
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• v.24 no.1
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• pp.1-10
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• 2008

This paper analyses the dynamic causal relationship between vessel export and economic growth using annual data over the period from 1977 to 2006. Tests for ADF unit-roots, the dynamic vector using Johansen's multiple cointegration procedure, dynamic vector error correction model and impulse response function are presented. The findings of the Granger test suggest that vessel export Granger-causes economic growth in the short-run and economic growth Granger-causes exports in the short and long-run. The empirical results of impulse-response analysis show that the vessel export to a shock in real GDP responds positively and the real GDP responds positively to the shocks in vessel export. Also, the results indicate that the impact of vessel export shock on the real GDP is short-lived.