• International Journal of Computer Science & Network Security
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• 제22권3호
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• pp.382-388
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• 2022

Satellite communication for high altitude platform stations (HAPS) and low earth orbit (LEO) systems suffer from dust and sand (DU&SA) storms in the desert regions such as Saudi Arabia. These attenuations have a distorting effect on signal fidelity at high frequency of operations. This results signal to noise ratio (SNR) to dramatically decreasing and leads to wireless transmission error. The main focus in this paper is to propose common relations between HAPS and LEO for the atmospheric impairments affecting the satellite communication networks operating above Ku-band crossing the propagation path. A double phase three dimensional relationship for HAPS and LEO systems is then presented. The comparison model present the analysis of atmospheric attenuation with specific focus on sand and dust based on particular size, visibility, adding gaseous effects for different frequency, and propagation angle to provide system operations with a predicted vision of satellite parameters' values. Skillful decision and control system (SD&CS) is proposed to control applied parameters that lead to improve satellite network performance and to get the ultimate receiving wireless signal under bad weather condition.

• 대한방사선기술학회지:방사선기술과학
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• 제44권1호
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• pp.1-8
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• 2021

The purpose of this study was to analyze the effect of automatic exposure control (AEC) control factors in digital radiography systems based on the fine contrast images using coin phantoms. The AEC control factors were targeted at the range of dominent zone, sensitivity, and density. The dominent zone was divided into cases where a single coin was used to cover the field configuration, and cases where seven coins were used to cover the field configuration. The sensitivity was classified into three stages (200, 400, 800) and the density was classified into three stages (2.5, 0, 2.5). Image quality was evaluated by signal to noise ratio (SNR) and contrast to noise ratio (CNR). Then, the automatically exposed tube current was measured. As a result, the X-ray image of seven coins obtained a result value of about 1.2 times higher for SNR and 1.9 times higher for CNR than the X-ray image for one coin. The tube current was also about 1.6 times higher. In conclusion, In AEC, the higher the field configuration and dominent zone are matched and the higher the density, the lower the sensitivity, which increases the tube current and CNR, which increases the image quality. Therefore, it is judged that the appropriate setting of the range of dominent zone, sensitivity, and density of the control, which is the AEC control factor, could improve the fine contrast of images.

• JSTS:Journal of Semiconductor Technology and Science
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• 제10권4호
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• pp.282-291
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• 2010

This paper presents a full-CMOS transmitter and receiver for VDSL2 systems. The transmitter part consists of the low-pass filter, programmable gain amplifier (PGA) and 14-bit DAC. The receiver part consists of the low-pass filter, variable gain amplifier (VGA), and 13-bit ADC. The low pass filter and PGA are designed to support the variable data rate. The RC bank sharing architecture for the low pass filter has reduced the chip size significantly. And, the 80 Msps, high resolution DAC and ADC are integrated to guarantee the SNR. Also, the transmitter and receiver are designed to have a wide dynamic range and gain control range because the signal from the VDSL2 line is variable depending on the distance. The chip is implemented in 0.25 ${\mu}m$ CMOS technology and the die area is 5 mm $\times$ 5 mm. The spurious free dynamic range (SFDR) and SNR of the transmitter and receiver are 67.5 dB and 41 dB, respectively. The power consumption of the transmitter and receiver are 160 mW and 250 mW from the supply voltage of 2.5 V, respectively.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.1044-1053
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• 2010

Transmitting correct train control information is important in a train control system which demands safety. The train control information includes the maximum speed of trains, position of preceding trains, incline of tracks and curve sections etc. A radio frequency-communication based train control system is influenced by the noise and interference because the train control information is transmitted by wireless between a on-board system and wayside system. The radio frequency-communication based train control system is a mobile communication system due to moving trains. The inter symbol interference(ISI) occurs by the multipath fading in the mobile ommunication system. As signal-to-noise ratio(SNR) is decreased by the ISI, the train control information is not received correctly. In case of tunnel section, numerous reflected waves exist. Therefore, the power density of receiver is decreased by difference among the received times, magnitudes, phases through the multipath. So, the train suddenly is stopped by the fail-safe operation in the train control system on account of decreasing the power density of receiver. In this paper, a line of sight model-(Additive White Gaussian noise(AWGN) channel), rayleigh and rician fading model are presented. Probability density functions which are related to the SNR are derived from the models. The fading phenomenon severely occurs as a result of analyzing the probability density functions. So, the space diversity method is used in order to reduce the fading effect and it is demonstrated by using Matlab program.

• 대한방사선기술학회지:방사선기술과학
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• 제38권3호
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• pp.205-211
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• 2015

복부 전후 방향 검사 시 automatic exposure control (AEC) mode에서 조사시간을 제한하지 않고 검사를 하는 방법 (non-time limit, NTL) 과 조사시간을 제한하고 검사하는 방법 (time limit, TL)에 대해서 영상 품질 평가인 신호 대 잡음비 (signal to noise ratio, SNR), 대조도 대 잡음비 (contrast to ratio, CNR)를 측정하여 TL 방법과 NTL방법을 비교 평가하고자 하였다. 실험 기기는 XGEO GC 80 (Samsung, Korea), Unfors ThinX RAD (Unfors, Sweden), Rando Phantom (alderson research laboratories, USA)과 $5.5{\times}9{\times}0.1cm^3$ 크기의 차폐재를 사용하였으며, AEC mode에서 전리함 (ionization chamber)를 상단 2 개만 작동하도록 설정하고 관전압은 80 kVp로 설정하였다. TL 방법의 경우에는 조사시간을 51 msec로 제한하였으며, 전리함에 차폐재를 부착하지 않은 상태와 부착한 상태에서 NTL AEC mode와 TL AEC mode의 영상을 획득하였다. 또한 'Image J"를 이용하여 영상 평가방법인 SNR과 CNR로 평가하였다. 결론적으로 차폐재를 부착했을 때 NTL AEC mode가 다른 실험 방법보다 선량이 최대 130.7% 최소 80%까지 증가한 결과 값을 보였으며, TL AEC mode는 NTL AEC mode보다 mAs와 피폭선량에서 각 각 43.8%, 44.4% 감소한 값을 보였다. 통계적으로는 SNR과 CNR은 유의한 차이를 보이지 않았다($p{\geq}0.05$). 그러므로, 본 연구에서는 BMI 지수가 높은 환자나 수술 후 인체 내에 금속물질이 있는 환자를 검사할 경우에는 TL AEC mode가 유효한 검사법이라고 사료된다.

• 디지털융복합연구
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• 제11권5호
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• pp.285-290
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• 2013

유성음원과 무성음원을 사용하는 멀티펄스 음성부호화 방식에 있어서, 대표구간의 멀티펄스를 사용하는 경우에 유성음의 합성음성파형에서 일그러짐이 나타난다. 이것은 대표구간의 멀티펄스를 피치구간마다 복원하는 과정에서 재생 음성신호가 정규화되는 것이 원인으로 작용한다. 이것을 해결하기위하여 본 논문에서는 피치구간마다 멀티펄스의 위치를 보정하는 방법(PC-MPC)을 제시하였으며, 기존의 MPC와 멀티펄스 위치를 보정한 PC-MPC의 $SNR_{seg}$를 평가한 결과, PC-MPC의 남자음성에서 0.4dB, 여자음성에서 0.5dB 개선된 것을 확인할 수 있었다. 결국, MPC에 비해 PC-MPC의 $SNR_{seg}$가 개선되어 음성파형의 일그러짐을 제어할 수 있었으며, 본 방법은 셀룰러폰이나 스마트폰과 같이 Low Bit Rate의 음원을 사용하여 음성신호를 부호화하는 방식에 활용할 수 있을 것으로 기대된다.

• 대한원격탐사학회지
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• 제33권2호
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• pp.159-169
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• 2017

위성용 전자광학탑재체는 제한된 소모전력 및 우주방사선과 같은 사용 환경에 의해 설계부터 특별한 요구사항을 가지고 있으며, 획득 영상의 품질은 주로 GSD (Ground Sampled Distance), 신호대잡음비(SNR, Signal to Noise Ratio), MTF (Modulation Transfer Function)에 따라 좌우된다. 영상센서의 출력신호에 포함된 잡음 감소를 통한 신호대잡음비 개선을 위하여, 센서에 추가된 프리픽셀(Pre-pixel) 및 다크픽셀(Dark-pixel)을 사용하여 CDS (Corrective Double Sampling) 방식을 통해 영상센서의 잡음 성분을 포함한 오프셋 신호(Offset Signal)를 제거하는 아날로그 신호처리(ASP, Analog Signal Processor) 방법을 제안한다. 또한 센서 제어시스템에서는 영상의 불균일성 처리를 위해 제어시스템의 출력 포트별 게인(Gain), 오프셋, 및 센서의 화소별 특성을 반영한 다양한 방식에 의한 보정 방법이 적용된다. 본 논문에서는 이상 설명한 여러 가지 잡음 개선방법을 시스템 설계 및 운영에 적용하여 위성탑재용 전자광학카메라의 신호대잡음비 향상 방법을 제안하고, 실험을 통해 검증한다.

• 한국인터넷방송통신학회논문지
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• 제19권5호
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• pp.55-62
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• 2019

본 논문에서는 K 사용자 MIMO 간섭 채널을 고려하였으며, 정보와 전력을 동시에 전송하는 SWIPT 시스템을 위한 송수신기 설계 방법에 대해서 다룬다. 그리고, 정보 수신 장치와 전력 수확 장치가 같은 수신기에 존재하는 SWIPT 시스템을 고려한다. 제안하는 방식에서는 신호대 누수 잡음비 (SLNR)를 비용 함수로 사용하고, 수확 전력에 대한 임계값을 만족하도록 송수신기를 설계한다. 즉, 수확 전력에 대한 제약 조건 하에서, SLNR을 최대화시키도록 송신단 프리코딩 벡터, 수신단 검파기 벡터, 전력 분배 상수를 동시에 설계한다. 컴퓨터 모의실험을 통하여, 제안하는 기법과 기존 기법의 신호 대 간섭 잡음비 (SINR) 성능을 비교하였다. 사용자 수, 송신 안테나 개수, 수신 안테나 개수 간의 특별한 제약 조건을 만족하는 경우, 제안하는 기법은 낮은 SNR에서 기존 기법보다 우수한 SINR 성능을 나타낸다는 것을 보였다. 또한, 특별한 제약 조건을 만족하지 못하는 경우에는, 제안 기법이 모든 SNR 범위에 대해서 기존 기법보다 더 우수한 성능을 나타낸다는 것을 보였다.

• International Journal of Railway
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• 제3권2호
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• pp.39-45
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• 2010

The RF-CBTC (Radio Frequency-Communication Based Train Control) System is a communication system in railroad systems. The communication method of RF-CBTC system is the wireless between the wayside device and on-board device. The wayside device collects its location and speed from each train and transmits the distance from the forwarding train to the speed-limit position to it. The on-board device controlling device controls the speed optimum for the train. In the case of the RF-CBTC system used in Korea, transmission frequency is 2.4 [GHz]. It is the range of ISM(Industrial Scientific and Medical equipment) band and transmission of voice and data is performed by CDMA (Code Division Multiple Access) method. So noises are made in the AWGN (Additive White Gaussian Noise) and fading environment. Currently, the SNR (Signal to Noise Ratio) is about 20 [dB], so due to bit errors made by noises, transmission of reliable information to the train is not easy. Also, in the case that two tracks are put to a single direction, it is needed that two trains transmit reliable voice and data to a wayside device. But, by noises, it is not easy that just a train transmits reliable information. In this paper, we estimated the BER (Bit Error Rate) related to the SNR of voice and data transmission in the environment such as AWGN and fading from the RF-CBTC system using the CDMA method. Also, we supposed the SNR which is required to meet the BER standard for voice and data transmission. By increasing the processing gain that is a ratio of chip transmission to voice and data transmission, we made possible voice and data transmission from maximally two trains to a wayside device, and demonstrated it by using Matlab program.

• 대한방사선기술학회지:방사선기술과학
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• 제42권1호
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• pp.19-24
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• 2019

For general radiological examinations, even in the same area and the same test, the test conditions must be set differently according to the patient. However, since it is impossible to consider the body shape and conditions of patients every time in medical institutions where various patients visit, the tests are conducted by setting the AEC which automatically sets the test conditions. AEC is most commonly used in chest radiography. Therefore, the purpose of this study is to propose the improvement plans for using AEC by measuring the exposure dose and evaluating the image quality according to whether the AEC is used or not, and to provide basic data for AEC research. In the present study, images were acquired while varying tube voltage and test distance according to the use of AEC in chest radiography. The radiation dose was measured by placing the dosimeter in front of the chest phantom, and the CNR and SNR of acquired images were analyzed using Image J. The t-test was conducted for the statistical analysis and the significance was determined at the level of 95%(p<.05). As a result of this study, in the inspection distance (100cm, 140cm, 180cm) according to the use of AEC, high doses were observed when the AEC was used and there was statistically significant difference(p<.05). In the t-test to determine the difference between CNR and SNR depending on whether AEC was used or not, there was no significant difference according to the use of AEC(p>.05). Therefore, when performing chest radiography, if the radiologist establishes the appropriate examination conditions and conducts the examination by not just relying solely on AEC, it may be possible to reduce unnecessary radiation exposure to the patient.