• Progress in Superconductivity
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• 제10권1호
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• pp.1-5
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• 2008

Magnetocardiography (MCG) is a non-contact, non-invasive, and harmless diagnostic tool to detect the abnormal electrical conductivities of the heart caused by the various coronary artery disease or cardiac muscular disease. The purpose of this study is to identify whether MCG signals and MCG parameter values vary depending on the location of sensor assembly. It will be an important reference for the standard measurement. Four healthy male subjects (33.3$\pm$6.3 years) participated in this study. Basal recording was made at 20 mm apart from the chest surface. All subjects were requested to take a regular breathe while MCG was taken. The gap between the chest surface and the bottom of the sensor assembly was 20, 40, 60, and 80 mm. Recording was made using 64 channel MCG system (Axial type, first order gradiometer) developed by Korea Research Institute of Standards and Science (KRISS). After resting for two minutes in a supine position on the bed in magnetically shielded room, MCG were recorded for 30 s. As the sensor location is getting away from the chest surface signal, the amplitude of R and T wave peak decreases to 70% (at 40 mm gap), 50% (at 60 mm), and 37% (at 80 mm) of the reference strength measured (y = $1.3903e^{-0.0169x}$, $R^2$ = 0.99; where y=amplitude remained after reduction, x=distance between chest surface and sensor location). The regression equations may be used as a good reference to calculate how much strength will be decreased by the distance. In MCG parameters, most values of parameters were decreased as the gap was increased. As an example, the current moment at T-wave peak reduced to 52% (at 40 mm gap), 33% (at 60 mm), and 19% (at 80 mm). However, the difference caused by the gap could be reduced by considering the distance when the MCG parameters were calculated. The study results can be used as a useful reference to design the baseline and the sensor location.

• 대한전자공학회논문지
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• 제25권7호
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• pp.819-825
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• 1988

An 1-bit DPCM image coding method is presented. Our method is specially designed to reduce the slope overload which seems to be the major performance degradation factor in 1-bit DPCM. In the present algorithm, based on the classification of neighborhoods by its flatness, slope strength and direction, predictor and quantizer operate adaptively through switching action. Compared with some other methods by computer simulation, proposed method shows improved performance in image quality as well as in signal to noise ratio. This gain mainly comes from the reduced slope overload and seems large to compensate the increased complexity in prediction. As a post processing, Lee filter is used to reduce the granular noise subjectively annoying in flat region.

• 제어로봇시스템학회논문지
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• 제18권9호
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• pp.830-836
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• 2012

According to increasing the importance of underwater environments, the needs of UUV are growing. This paper represents the mechanism and algorithm of UUV docking system with 21-inch torpedo tubes for military submarines as a docking station. To improve the reliability of the docking, torpedo tubes launch a wired ROV and next the ROV combined with UUV is retrieved. For estimating the relative position between the ROV and UUV, in this paper, combining RF sensors and vision system is proposed. The RSSI method of RF sensors is used to estimate the distance and the optical image is combined for the directional information.

• Journal of Advanced Marine Engineering and Technology
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• 제37권8호
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• pp.932-938
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• 2013

최근 WLAN을 이용한 실내 위치인식 방법 중 하나인 Fingerprint 기법은 신호의 반사 및 굴절에 의한 페이딩 현상에 강인하여 많이 연구되고 있다. 그러나 이 방법은 신호의 수집과 데이터베이스와 측정된 신호의 비교 연산의 과정에서 요구되는 시간과 연산량이 많다. 본 논문에서는 연산량을 줄이기 위하여 제안한 변형된 데이터베이스를 기반으로 실시간으로 수집되는 신호의 선택적 연산을 이용한 WLAN 실내 위치인식 알고리즘을 제안한다. 제안한 알고리즘은 신호의 세기에 따른 선형보간과 문턱치를 통하여 데이터베이스의 구성 시간 및 크기를 줄이고, 실시간으로 측정되는 신호의 선택적 연산을 통해 연산량은 감소시키면서 위치정확도를 유지하였다. 실험결과 제안한 알고리즘은 실내 복도 환경에서 기존의 Fingerprint 기법 대비 정확도를 17.8% 향상시켰으며 연산량은 평균 46% 감소되는 것을 확인하였다.

• 한국통신학회논문지
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• 제27권7B호
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• pp.686-694
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• 2002

본 논문에서는 DS-CDMA 환경 하에서 일반적인 그룹형 간섭제거기(Groupwise Canceller) 중 초기단을 개선시킨 그룹형 간섭제거기(Improved initial-stage Grouping Interference Canceller)의 개선된 정렬기법을 소개한다. 비선형 간섭제거기 중 초기단을 개선시킨 그룹형 간섭제거기(IGIC)는 입력된 신호를 그룹으로 나누어 정렬기법을 통해 초기단 성능을 개선시킨 간섭제거기이다. 그러나, 이 시스템은 정렬기법에 의해서 각 그룹에 할당되는 사용자수가 항상 동일하기 때문에 동일 그룹내에서 신호세력의 차이가 생길 수 있다. 이 경우, 동일 그룹내에 작은 신호들은 큰 신호들로부터 많은 다중접속간섭의 영향을 받는다. 이와 같은 다중접속간섭의 영향을 줄이기 위해 본 논문에서는 개선된 정렬기법을 사용하여 각 그룹에 할당되는 신호들이 비슷한 신호전력분포를 가지도록 하였다. 따라서, 그룹내의 신호세력 차이를 줄여 다중접속간섭의 영향이 감소되었다. 성능 분석은 전력제어를 하였을 때와 하지 않았을 때를 다른 비선형 간섭제거기와 비교하여 분석하였다.

• 한국항해항만학회지
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• 제46권6호
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• pp.517-524
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• 2022

본 논문은 X-밴드 항해용(선박용) 레이더를 이용한 파랑 계측시, 강설 및 강수에 의한 레이더 신호 변화 및 파랑 계측 저해 요소를 분석한다. 사용된 자료는 속초해수욕장 행정지원센터에 설치된 레이더를 활용하였으며, 비교 검증에 필요한 기상자료는 기상청과 국립해양조사원의 공공자료를 사용하였다. 기상청 공공자료는 레이더로부터 약 7km 떨어진 속초기상대에서 측정한 자료이며, 국립해양조사원 공공자료는 레이더로부터 약 3km 떨어진 해양관측부이에서 계측된다. 지금까지 강우나 강설에 의한 레이더 신호 변화는 경험적으로 전해졌을 뿐, 실제 기상데이터와 비교하여 분석한 사례는 전무하다. 이에 본 논문에서는 기상청의 강수, 강설 자료, CCTV, 레이더 신호를 시계열에서 종합적으로 분석하였다. 그 결과 강설 및 강우에 따라 레이더에서 계측된 파고의 경우 실제 파고 대비 감소되는 것을 확인하였으며, 거리에 따른 레이더 신호강도의 감소 현상도 확인되었다. 본 논문은 강설 및 강우에 따라 레이더의 신호강도 감소 현상을 다각적으로 분석한 것에 그 의의가 있다.

• 제어로봇시스템학회논문지
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• 제20권7호
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• pp.774-781
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• 2014

This paper presents a fingerprint database construction method for WLAN RSSI (Received Signal Strength Indicator)-based indoor positioning. When RSSI is used for indoor positioning, the fingerprint method can achieve more accurate positioning than trilateration and centroid methods. However, a FD (Fingerprint Database) must be constructed before positioning. This step is a very laborious process. To reduce the drawbacks of the fingerprint method, a radio propagation model-based FD construction method is presented. In this method, an FD can be constructed by a simulator. Experimental results show that the constructed FD-based positioning has a 3.17m (CEP) error. In this paper, a spatial correlation method is presented to estimate the NLOS(Non-Line of Sight) error included in the FD constructed by a simulator. As a result, the NLOS error of the FD is reduced and the performance of the error compensated FD-based positioning is improved. The experimental results show that the enhanced FD-based positioning has a 2.58m (CEP) error that is a reasonable performance for indoor LBS (Location Based Service).

• 한국통신학회논문지
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• 제25권10A호
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• pp.1473-1479
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• 2000

This paper presents the performance evaluation of an adaptive QAM scheme under flat and frequency selective fading channels for indoor wireless communication systems. The QAM modulation is combined with differential encoding and the demodulation process is carried out noncoherently. The adaptation is performed by varying the modulation level of QAM, depending upon received signal strength. The adaptation mechanism allows a 2- or 3-bit increase or decrease at a time, if the channel condition is considered to be significantly good or bad. Simulation results show that the average number of bits per symbol (ABPS) for each symbol block transmitted over a flat fading channel is higher than 5.0 and the BER performance is better than 10^-4 for a SNR value higher than 30 dB. For frequency selective fading channels, an oversampling technique in the receiver was employed. The BER performance obtained for frequency selective fading channels is better than 10^-4 with a SNR value of 40 dB and ABPS is found to be approximately 5.5. Therefore, this scheme is very useful in that it provides both very high bandwidth efficiency and acceptable performance with moderate SNR values over flat and frequency selective fading channels. In addition, this scheme provides reduced receiver complexity by way of noncoherent detection.

• 한국통신학회논문지
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• 제37권5A호
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• pp.339-347
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• 2012

최근에 실내 커버리지 확장 및 광대역 데이터 서비스를 위한 가정용 기지국인 펨토셀에 대한 연구가 활발하다. 펨토셀이 배치될 때, 기존에 있던 네트워크 상황 속에서 다양한 기술적인 문제들을 발생 시킬 수 있다. 본 논문에서는 OFDMA 시스템에서 펨토 - 매크로셀 간의 간섭 완화에 대하여 연구하였고, 동적인 하향링크 자원 관리 방법을 제안하였다. 펨토셀의 전송 파워를 매크로셀로부터 오는 신호의 세기에 기반을 두어서 선택하는 방법과 펨토셀 에게 할당 할 부반송파를 동적으로 관리하는 방식을 제안하였다. 이러한 방법으로 펨토셀과 매크로셀 사용자와의 간섭을 줄일 수 있다. 제안하는 방법은 수용율을 비롯한 여러 평가 지표로 성능을 검증하였다.

• Asian-Australasian Journal of Animal Sciences
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• 제29권1호
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• pp.149-156
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• 2016

In this experiment, we proposed and implemented a disease forecasting system using a received signal strength indication ZigBee-based wireless network with a 3-axis acceleration sensor to detect illness at an early stage by monitoring movement of experimentally infected weaned piglets. Twenty seven piglets were divided into control, Salmonella enteritidis (SE) infection, and Escherichia coli (EC) infection group, and their movements were monitored for five days using wireless sensor nodes on their backs. Data generated showed the 3-axis movement of piglets (X-axis: left and right direction, Y-axis: anteroposterior direction, and Z-axis: up and down direction) at five different time periods. Piglets in both infected groups had lower weight gain and feed intake, as well as higher feed conversion ratios than the control group (p<0.05). Infection with SE and EC resulted in reduced body temperature of the piglets at day 2, 4, and 5 (p<0.05). The early morning X-axis movement did not differ between groups; however, the Y-axis movement was higher in the EC group (day 1 and 2), and the Z-axis movement was higher in the EC (day 1) and SE group (day 4) during different experimental periods (p<0.05). The morning X and Y-axis movement did not differ between treatment groups. However, the Z-axis movement was higher in both infected groups at day 1 and lower at day 4 compared to the control (p<0.05). The midday X-axis movement was significantly lower in both infected groups (day 4 and 5) compared to the control (p<0.05), whereas the Y-axis movement did not differ. The Z-axis movement was highest in the SE group at day 1 and 2 and lower at day 4 and 5 (p<0.05). Evening X-axis movement was highest in the control group throughout the experimental period. During day 1 and 2, the Z-axis movement was higher in both of the infected groups; whereas it was lower in the SE group during day 3 and 4 (p<0.05). During day 1 and 2, the night X-axis movement was lower and the Z-axis movement was higher in the infected piglets (p<0.05). Overall, the movement of infected piglets was altered, and the acceleration sensor could be successfully employed for monitoring pig activity.