• Journal of Astronomy and Space Sciences
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• v.27 no.2
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• pp.173-180
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• 2010

As a preparatory study for Global Positioning System-Very Long Baseline Interferometry (GPS-VLBI) hybrid system, we examined if VLBI type observation of the GPS signal is realizable through a test experiment. The test experiment was performed between Kashima and Koganei, Japan, with 110 km baseline. The GPS L1 and L2 signals were received by commercial GPS antennas, down-converted to video-band signals by specially developed GPS down converters, and then sampled by VLBI samplers. The sampled GPS data were recorded as ordinary VLBI data by VLBI recorders. The sampling frequency was 64 MHz and the observation time was 1 minute. The recorded data were correlated by a VLBI correlator. From correlation results, we simultaneously obtained correlation fringes from all 8 satellites above a cut-off elevation which was set to 15 degree. 87.5% of L1 fringes and 12.5% of L2 fringes acquired the Signal to Noise Ratios which are sufficient to achieve the group delay precision of 0.1nsec that is typical in current geodetic VLBI. This result shows that VLBI type observation of GPS satellites will be readily realized in future GPS-VLBI hybrid system.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2005.11a
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• pp.531-534
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• 2005

한국천문연구원에서는 한국우주전파관측망(Korean VLBI Network: KVN)을 위한 전파영상합성기(상관기) 개발을 진행하고 있다. 전파관측 VLBI 시스템 중 상관기(Correlater) 시스템의 한 구성요소로서 데이터 입력 부분에 각 관측 사이트의 데이터를 사전 처리하는 Station Unit(SU)이 있다. VLBI 시스템에서, 디지털화된 데이터의 다중채널은 테이프 또는 하드디스크에 다중트랙 형태로 인코딩된다. 이 SU의 주요기능은 다중트랙으로부터 인코딩된 데이터를 디코딩하고, 마치 기록되지 않은 것과 같이 채널기반의 샘플 스트림으로 이 데이터를 복원하는 것이다. 이 기능을 원활하게 수행하기 위해서, SU는 논리적으로 재생기 시스템과 함께 시스템이 통합될 필요가 있다. 본 논문에서는 전파 천문 VLBI 시스템 중 SU의 기능과 구조에 대해 고찰하고자 한다.

• Korean Journal of Optics and Photonics
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• v.2 no.2
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• pp.83-88
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• 1991

Studies on space-invariant pattern recognition have been carried out from various approaches. Pattern recognition system using SDF filter, from weighted linear summation of tranining images, has been the focus of research since its first appearence. In this thesis, off-axis pSDF spatial matched filter has been constructed by combining angular multiplexing of off-axis reference plane wave with pSDF filter made from pseudo-inverse algorithm, and transformed to phase only filter. From observation of the correlation responses in the correlation plane, it is shown that proposed off-axis pSDF spatial matched filter is available to pattern classification and can be used for optical correlator.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.12
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• pp.1065-1072
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• 2014

We developed a GPS digital signal processing FPGA IP, SIGP-1001 to replace the obsolete GP2021 device, which has been used for many space-borne GPS receivers. From a series of tests, we verified that SIGP-1001 has equivalent performance to the GP2021 device under the same operating condition and concluded that SIGP-1001 can replace the GP2021 device. The reliability of a GPS receiver can be improved by using a space-grade FPGA with SIGP-1001 instead of the GP2021 device and its performance is expected to be improved by increasing the number of search channels.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.641-643
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• 2015

VLBI experiments have been conducted by radio telescopes in the East Asia VLBI Network (EAVN) in which 14 telescopes in China, Japan, and Korea participated. One of the aims of the EAVN is to obtain higher angular resolution that is provided by the 6,000 km baseline between China and Japan and better sensitivity by adding large telescopes. Data were recorded at 1 a Gbps recording rate at all stations and processed on the Korea-Japan Joint VLBI Correlator (KJJVC) at the Korea-Japan Correlation Center (KJCC) after experiments. Fringes were obtained from these experiments conducted at 8 GHz and 22 GHz and post-correlation data analysis of the experiments is undergoing. The outcomes of these experiments open the possibility of conducting EAVN observations with global VLBI networks. In this presentation, the recent status of these experiments and future prospects are presented.

• Journal of Astronomy and Space Sciences
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• v.27 no.2
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• pp.107-116
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• 2010

We developed the playback control software for a high-speed playback system which is a component of the Korea-Japan Joint VLBI Correlator (KJJVC). The Mark5B system, which is a recorder and playback system used in the Korean VLBI Network (KVN), has two kinds of operation mode. That is to say, the station unit (SU) mode, which is for the present Mark4 system, and the VSI mode, which is for the new VLBI standard interface (VSI) system. The software for SU is already developed and widely used in the Mark4 type VLBI system, but the software for VSI has only been developed for recording. The new VLBI system is designed with a VSI interface for compatibility between different systems. Therefore, the playback control software development of the VSI mode is needed for KVN. In this work, we developed the playback control software of the Mark5B VSI mode. The developed playback control software consists of an application part for data playing back, a data input/output part for the VSI board, a module for the StreamStor RAID board, and a user interface part, including an observation time control part. To verify the performance of developed playback control software, the playback and correlation experiments were performed using the real observation data in Mark5B system and KJJVC. To check the observation time control, the data playback experiment was performed between the Mark5B and Raw VLBI Data Buffer (RVDB) systems. Through the experimental results, we confirmed the performance of developed playback control software in the Mark5B VSI mode.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.05a
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• pp.512-515
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• 2010

SIGINT(SIGnal INTelligence) includes several parameters intercepted by measurement and analysis of the RF(Radio frequency) signal from free space. One of the important parameters is frequency information. Expecially, in order to perform instantaneous frequency measurement of Radar and Missile seeker's RF signals, we use dedicated RF modules as a DFD(Digital Frequency Discriminator) to provide frequency information by measurement of the relative phase difference between signals via intended RF delay lines. It must measure and provide realtime based frequency information on short pulsed RF signal up to 100 nSec or less. This document proposes Ultra wideband DFD consisted of a RF input section of Wideband 4 channel RF delay line and correlator, a digital processing section to measure and provide frequency information from I/Q signal, and a frequency calibration section. Also, it will show design suitability based on test results measured under test condition of very short input pulse signals.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.8
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• pp.62-70
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• 1997

In this paper, we presetn a new method to display 3-D image modelled as a sum of 2-D sliced images by expanding the concept of the conventional 2-D optical correlator based on spatial matched filtr to the 3-D region. It is hsown that a arbitrary image can be constructed by an array of the correlation-peaks between pixel-to-pixel and propose the systhesis precedure of 3-D spatial-matched-fjilter using fresnel diffraction equation to display 3-D image in space. It is also shown that the quantization problem is severe when the systehsised filter function is displayed on the conventional LC-SLM. To overcome this problem, anonlinear quantizaton method using the sigmoid function is suggested, and this method can reduce the bias and the loss of high spatial-frequency information, and improve the diffraction efficiency. Finally, the suggested method is tested by computer simulation and then approved by some optical experiments with the conventional LC-SLM.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.431-434
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• 2006

현재 사용되는 디지털 신호처리 방식의 GPS(Global Positioning System) 수신기는 최소의 RF 블록만을 이용하여 모든 디지털 신호 처리를 소프트웨어로 수행하고 있다. 소프트웨어 GPS수신기의 장점으로는 디지털 신호처리 과정이 모두 소프트웨어로 구현되어 있기 때문에 새로운 구현 방식이나 알고리즘을 적용할 시, 하드웨어 변경은 필요가 없게 되고, 소프트웨어 재설계만으로 가능하다. GPS 수신기의 Tracking module 성능은 DLL discriminator function과 FLL discriminator function의 Algorithm에 의해서 영향을 받게 된다. DLL discriminator function algorithm에는 dot-product 와 normalized dot-product 방법 등이 있으며, FLL discriminator function algorithm에는 sign(dot)(cross)-product 와 cross-product 그리고 ATAN 방법이 있다. 이러한 discriminator function들은 algorithm에 따라 input error에 대한 discriminator의 출력 값을 일정한 범위에서의 차이를 나타내게 되면서 ranging accuracy에서 차이가 나타나게 된다. 본 논문에서는 Nordnav 소프트웨어 GPS 수신기를 이용하여 DLL discriminator algorithm과 FLL discriminator algorithm의 성능을 비교, 분석을 하고 Tracking accuracy, sensibility, 그리고 multipath rejection에 대해서 알아보고자 한다.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.07a
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• pp.221-221
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• 2004