• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.70.2-70.2
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• 2013

한국천문연구원은 일본국립천문대와 한일공동으로 개발한 한일공동VLBI상관기(KJJVC)의 VLBI 관측자들에게 연구결과를 제공할 수 있는 정상운영을 2013년부터 수행하였다. 한일상관센터(KJCC)에서는 평균 8시간정도 관측한 VLBI 관측자료의 상관처리에 소요되는 시간은 약 2주 정도이며, 데이터 분석가의 확인을 거친 후 담당 PI에게 상관결과를 전달하고 있다. 현재 상관처리는 다양한 관측모드 중에서 연구관측에서 많은 비중으로 차지하고 있는 C5(16MHz 대역폭에 16stream) 모드를 지원하고 있으며, 2013년도에 여러 연구자들의 요구에 대응하기 위해 Wideband(512MHz 대역폭), C1(256MHz 대역폭, 1stream), C2(128MHz 대역폭, 2stream) 모드를 지원할 수 있도록 시스템의 성능을 개선할 예정이다. 또한 일본국립천문대에서는 자기테이프를 사용하고 있는 VERA 관측망에 대해 관측자료의 복사시간 단축, 운영효율을 향상시키기 위해 하드디스크를 채용한 OCTADISK 시스템을 개발하였으며, 한일상관센터에도 동기재생처리장치에 장착된 2대의 OCTADDB를 OCTADISK로 수정작업을 추진하였다. 본 보고에서는 이상에 기술한 것과 같이 한일상관센터의 운영현황과 향후 계획에 대해 자세히 기술한다.

• 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.

• Publications of The Korean Astronomical Society
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• v.23 no.2
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• pp.73-90
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• 2008

A software simulator is developed for verifying the VLBI Correlation Subsystem (VCS) trial product hardware. This software simulator includes the delay tracking, fringe rotation, bit-jump, FFT analysis, re-quantization, and auto/cross-correlation functions so as to confirm the function of the VCS trial product hardware. To verify the effectiveness of the developed software simulator, we carried out experiments using the simulation data which is a mixed signal with white noise and tone signal generated by software. We confirmed that the performance of this software simulator is similar as that of the hardware system. In case of spectral analysis and re-quantization experiment, a serious problem of the VCS hardware, which is not enough for expressing the data stream of FFT results specified in VCS hardware specification, was found by this software simulator. Through the experiments, the performance of software simulator was verified to be efficient. In future, we will improve and modify the function of software simulator to be used as a software correlator of Korea-Japan Joint VLBI Correlator (KJJVC).

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.75.4-76
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• 2015

우리는 동아시아 각국(대한민국, 중국, 일본)의 VLBI관측망을 통합하고 구성될 동아시아 VLBI 관측망(East Asia VLBI Network; EAVN)의 초기 검증 작업을 진행하고 있다. EAVN은 2 ~ 129 GHz로 관측이 가능하는데, 주로 6.7, 8, 22, 43 GHz로의 관측을 상정하고 있다. 또한 최대 기선장은 약 5,000 km으로 공간분해능은 약 0.3 mas(43 GHz로의 관측의 경우)가 된다. 높은 공간분해능과 고감도의 특징을 활용하고 저광도 활동성은하핵이나 우리 은하의 메이저 천체 등의 연구에 대해서 위력을 나타낼 수가 있다. 우리는 EAVN 시험관측, 상관처리, 자료처리의 실행, 및 그것들을 통한 EAVN 운영의 검증을 하는 EAVN Tiger Team을 2013년에 조직하고 현재까지에 8 GHz 및 22 GHz로 8회의 VLBI 시험관측을 실행하였다. 상관처리는 주로 한국천문연구원에서 운영하고 있는 한일 공동상관기(KJJVC)와 상하이천문대의 소프트웨어 상관기(DiFX)로 실행되어 있다. 현재까지에 8 GHz 및 22 GHz 쌍방에서 프린지검출에 성공하고 있고, 올해는 영상합성을 포함한 과학적인 관측을 진행할 예정이다. 이 발표에서는 EAVN의 개요와 과학목표, 시험관측 현황과 결과, 및 앞으로의 운영 계획 등을 소개하겠다.

• Publications of The Korean Astronomical Society
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• v.24 no.1
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• pp.65-81
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• 2009

We present the performance test results of VLBI Correlation Subsystem (VCS) trial product which was being developed for 1 year from August 2007. It is a core component of Korea-Japan Joint VLBI Correlator (KJJVC). The aim for developing VCS trial product is to improve the performance of VCS main product to reduce the efforts and cost, and to solve the design problems by performing the preliminary test of the manufactured trial product. The function of VCS trial product is that it is able to process the 2 stations-1 baseline, 8 Gbps/station speed, 1.2 Gbps output speed with FX-type. VCS trial product consists of Read Data Control Board (RDC), Fourier Transform Board (FTB), and Correlation and Accumulation Board (CAB). Almost main functions are integrated in the FTB and CAB board. In order to confirm the performance of VCS trial product functions, the spectral analysis, delay compensation and correlation processing experiments were carried out by using simulation and real observation data. We found that the overflow problem of re-quantization after FFT processing was occurred in the delay compensation experiment. We confirmed that this problem was caused by valid bit-expression of the re-quantized data. To solve this problem, the novel method will be applied to VCS main product. The effectiveness of VCS trial product has been verified through the preliminary experimental results, but the overflow problem was occurred.

• Journal of the Institute of Convergence Signal Processing
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• v.16 no.4
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• pp.139-148
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• 2015

In this paper, the optimum coding method is proposed by using open library in order to improve the performance of a software correlator developed for Korea-Japan Joint VLBI Correlator(KJJVC). The correlation system for VLBI observing system is generally implemented with hardware using ASIC or FPGA because the computational quantity is increased geometrically according to the participated observatory number. However, the software correlation system is recently constructed at a massive server such as a cluster using software according to the development of computing power. Since VLBI correlator implemented with hardware is able to conduct data processing with real-time or quasi real-time compared with mostly observational time, software correlation has to perform optimal data processing in coding work so as to have the same performance as that of the hardware. Therefore, in this paper, the experimental comparison was conducted by open-source based fftw library released in FFT processing stage, which is the most important part of the correlator system for performing optimum coding work in software development phase, such as general method using fftw library or methods using SSE(Streaming SIMD Extensions), shared memory, or OpenMP, and method using merged techniques listed above. Through the experimental results, the proposed optimum coding method for improving the performance of developed software correlator using fftw library, shared memory and OpenMP is effectively confirmed by reducing correlation time compared with conventional method.