• Journal of information and communication convergence engineering
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• 제19권3호
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• pp.131-135
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• 2021

The interference between closely placed co-coverage satellites was analyzed. In general, a satellite network may use different orthogonal polarizations and frequencies to increase the throughput of a satellite. However, when orthogonal linear polarization (horizontal polarization and vertical polarization) or orthogonal circular polarization (left-handed circular polarization and right-handed circular polarization) is used, the signal from one polarization sense to another may be coupled, resulting in cross-polarization interference. This signal-coupling arises due to the finite value of the cross-polarization discrimination of the earth station. In this study, field equations were used to analyze the interference between adjacent satellites using co-frequency. The level of interference was compared to that when two adjacent satellites used the same polarization. The simulation results show that the interference mainly depends on the off-axis co-polar pattern and the cross-polar pattern of the earth station antenna.

• 한국정보통신학회논문지
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• 제18권6호
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• pp.1255-1261
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• 2014

본 논문에서는 계절별 국내 해상 DGPS 기준국 신호의 전파 특성을 측정하고 기후 및 계절에 따른 서비스 영역을 분석한다. 해상 DGPS 기준국을 중심으로 내륙 서비스 영역에서 수신 신호의 전계 강도와 신호대 잡음비를 측정 분석한다. 산악지형과 대지 도전율이 낮은 안테나 사이트를 갖는 기준국을 제외한 해상 DGPS 기준국의 내륙 서비스 영역은 서비스 영역 대비 68 %이상의 양호한 서비스 영역을 제공하고 있다. 계절에 따른 안정된 서비스 영역을 갖기 위해서는 양호한 대지 도전율을 갖는 안테나 사이트와 보다 높은 안테나 효율을 갖는 해상 DGPS 기준국 설치 및 운영이 필요하다. 아울러 내륙 기준국과의 이중 서비스 영역 제공으로 전파 경로상의 장애물로 인한 불안정한 서비스 영역을 해소할 수 있다.

• 한국항행학회논문지
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• 제25권5호
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• pp.390-396
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• 2021

본 연구에서는 해양수산부가 2016년 실행 계획을 발표한 전자어구 실명제를 실현할 수 있는 어구 자동식별 모니터링 시스템에서 통신 거리를 늘릴 수 있는 해상 중계기 설계와 제작에 대해 보고한다. 해상 중계기는 중계기를 구성하는 서비스 안테나와 링크 안테나 사이의 되먹임 신호에 의한 발진을 제거할 수 있는 ICS (interference cancellation system) 방식의 RF 중계기로 설계 제작하였다. ICS RF 중계기 설계에 있어 링크 안테나와 서비스 안테나 간 이격을 30 dB 확보하였다. 시험을 통한 검증 결과 ICS RF 중계기의 출력 신호 일부가 입력으로 되먹임되는 신호 레벨이 중계기 이득보다 15 dB 이상 낮을 때 발진에 의해 발생하는 EVM(error vector magnitude)이 성능 기준인 6%보다 낮게 얻어지는 것을 확인하였다. 본 연구를 통해 개발된 ICS RF 중계기를 어구 자동식별 모니터링 시스템 등의 해상 IoT 네트워크에 적용하면 서비스 영역이 늘어날 것으로 기대된다.

• International Journal of Railway
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• 제9권2호
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• pp.36-40
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• 2016

TETRA communication system is very versatile system which can transmit voice + data and packet data optimized. Direct mode operation permits to connect between mobiles when mobile stain is out of coverage of networks. It can be more secure communication channel for railway signaling systems. Railway signaling systems use many of wayside signal equipment, which require many maintenance efforts and budget. Many railway authorities want to reduce and replace the wayside equipment. Radio based signaling systems are one of candidate for replacing the conventional signaling systems. The radio based signaling systems can replace track circuit and wayside signal. The radio systems permit to connect between control centers and trains. The radio systems have to ensure high quality of the connectivity more or equal to the existed track circuits. We studied the application of TETRA systems for railway radio systems for bridging between train control centers and trains. We provide an operation scenario for radio based train control system to ensure the safety require to the existed trains control system and satisfied the existed operational availability. We showed the data transmission speed, maximum bit error rate, and data coding for the radio-based signal system using TETRA systems.

• 전기전자학회논문지
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• 제22권4호
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• pp.1109-1114
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• 2018

뇌파(Electroencephalogram, EEG)는 외부 자극 때문에 발생하는 뇌 활동을 연구하기 위해 사용되는 도구로 두피에 전극을 부착하여 기록한다. 이 과정에서 잡파(artifact)가 혼입되어 신호를 왜곡시키기 쉬워 이를 제거하기 위한 후처리가 필수적이다. 잡파 제거를 위해 널리 사용되는 방법으로 독립성분분석(Independent Component Analysis, ICA)이 존재한다. 이 방법은 성능은 우수하나 뇌파 정보를 일부 손실시키는 단점이 있다. 본 논문에서는 이러한 문제점을 보완하기 위해 시선 추적 센서(Eyetracker)를 통해 얻은 눈 깜빡임 정보를 이용하여 필터 적용 범위를 제한함으로써 뇌파 정보 손실을 줄이는 방법을 제안한다. 이후 신호 대 잡음 비(Signal to Noise Ratio, SNR), 스펙트럼 일관성(Spectral Coherence, SC) 등의 정량화 방법을 이용하여 기존의 방법과 제안하는 방법의 결과를 비교하였다.

• ETRI Journal
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• 제44권5호
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• pp.715-732
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• 2022

Despite the successful launch of Advanced Television Systems Committee (ATSC) 3.0 broadcasting worldwide, broadcasters are facing obstacles in constructing void-less large-scale single-frequency networks (SFNs). The bottleneck is the absence of decent on-channel repeater (OCR) solutions necessary for SFNs. In the real world, OCRs suffer from the maleficent feedback interference (FI) problem, which overwhelms the desired input signal. Moreover, the undesired multipaths between studio-linked transmitters and the OCR deteriorate the forward signals' quality as well. These problems crucially restrict the feasibility of conventional OCR systems, arousing the strong need for cost-worthy advanced OCR solutions. This paper presents an ATSC 3.0-specific solution of advanced OCR that solves the FI problem and refines the input signal. To this end, the FI canceler and channel equalizer functionalities are carefully implemented into the OCR system. The presented OCR system is designed to be fully compliant with the ATSC 3.0 specifications and performs a fast and efficient signal processing by exploiting the specific frame structure. The real product of ATSC 3.0 OCR is fabricated as well, and its feasibility is verified via field and laboratory experiments. The implemented solution is installed at a commercial on-air site and shown to provide substantial coverage gain in practice.

• 한국인터넷방송통신학회논문지
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• 제10권5호
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• pp.69-75
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• 2010

새로운 휴대 이동 방송 방식인 고품질 지상파 DMB(Advanced T-DMB)시스템은 계층변조 방식을 이용하여 기존 T-DMB와 역호환성을 유지하면서 동일한 주파수 대역폭에서 전송률을 최대 2배로 높이기 위해 개발되었다. 이러한 고품질 지상파 DMB 시스템은 T-DMB의 DQPSK 변조신호에 새로운 변조가 적용된 BPSK 또는 QPSK 신호를 향상 계층으로 중첩하여 전송함으로써 기존 T-DMB의 고품질화를 실현한다. AT-DMB의 향상계층에 새로 추가되는 신호는 T-DMB와 역호환성 유지 및 방송권역 축소를 최소화하기 위해 크기가 충분히 작아야하는데, 추가되는 크기가 작은 신호는 전송채널에 존재하는 페이딩에 의해 쉽게 왜곡될 수 있다. 따라서 본 논문에서는 새로 추가되는 신호에는 오류정정 성능이 우수한 이중이진터보 (turbo) 부호를 적용하여 채널왜곡을 보상하고, 컴퓨터 시뮬레이션을 통해 이의 적용가능성을 분석하였다.

• International Journal of Aeronautical and Space Sciences
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• 제10권1호
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• pp.75-82
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• 2009

In this parer, we propose a new way of improving DGNSS service using combination of multiple SBAS information. Because SBAS uses Geostationary Earth Orbit (GEO) satellites, it has very large coverage but it can be unavailable in urban canyon because of visibility problem. R. Chen solved this problem by creating Virtual Reference Stations (VRS) using the SBAS signal [1]. VRS converts SBAS signal to RTCM signals corresponding its location, and broadcast the converted RTCM signals over the wireless internet. This method can solve the visibility problem cost effectively. Furthermore it can solve DGNSS coverage problem by creating just a transmitter instead of a reference station. Developing above method, this paper proposes the methods that integrate two or more SEAS signals into one RTCM signal and broadcast it. In Korea, MSAS signal is available even though it is not officially certified for Korean users. As a Korean own SBAS-like system, there is the internet-based KWTB (Korean WADGPS Test Bed) which we developed and released at ION GNSS 2006. As a result, virtually two different SBAS corrections are available in Korea. In this paper, we propose the integration methods for these two independent SBAS corrections and present the test results using the actual measurements from the two systems. We present the detailed algorithm for these two methods and analyze the features and performances of them. To verify the proposed methods, we conduct the experiment using the logged SBAS corrections from the two systems and the RINEX data logged at Dokdo monitoring station in Korea. The preliminary test results showed the improved performance compared to the results from two independent systems, which shows the potential of our proposed methods. In the future, the newly developed SBASs will be available and the places which can access the multiple SBAS signals will increase. At that time, the integration or combination methods of two or more SBASs will become more important. Our proposed methods can be one of the useful solutions for that. As an additional research, we need to extend this research to the system level integration such as the concept of the decentralized W ADGPS.

• IEIE Transactions on Smart Processing and Computing
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• 제6권2호
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• pp.109-116
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• 2017

In this paper, we propose an Internet of Things (IoT) platform for ocean observation buoys. The proposed system consists of various sensor modules, a gateway, and a remote monitoring site. In order to integrate sensor modules with various communications interfaces, we propose a controller area network (CAN)-based sensor data packet and a protocol for the gateway. The proposed scheme supports the registration and management of sensor modules so as to make it easier for the buoy system to manage various sensor modules. Also, in order to extend communication coverage between ocean observation buoys and the monitoring site, we implement a multi-hop relay network based on a mesh network that can provide greater communication coverage than conventional buoy systems. In addition, we verify the operation of the implemented multi-hop relay network by measuring the received signal strength indication between buoy nodes and by observing the collected data from the deployed buoy systems via our monitoring site.

• 센서학회지
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• 제19권1호
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• pp.1-7
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• 2010

Electrostatic capacitance measurement method in a fine hose was proposed, in which two ring-type electrodes were disposed on the hose in the direction of fluid flow instead of the conventional face-to-face electrodes. With the proposed electrode structure, we realized a Ringer's solution exhaustion detector for an IV(invasive vein) injection set. On a 4 mm-diameter hose of IV set, we disposed two ring-type electrodes of 10 mm width at a distance of 5 mm each other and obtained 0.72 pF and 2.51 pF for air and 10 % dextrose Ringer's solution in the hose, respectively. The capacitance between the two electrodes varied with the hose-wraparound coverage of electrode as well as the width of electrode and the distance between the electrodes. For hose-wraparound electrode coverage of 75 %, the capacitance varied from 0.62 pF to 1.98 pF with the Ringer's solution level between the two electrodes. A charge amplifier converted the capacitance. variation into electric signal and a comparator was used to detect whether Ringer's solution was exhausted or not. The result was delivered to a host using a RF transmitter with 320 MHz carrier frequency.