• Journal of the Institute of Convergence Signal Processing
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• v.12 no.4
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• pp.322-332
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• 2011

In this paper, we introduce the 1st performance evaluation of VLBI Correlation Subsystem (VCS) main product, which is core system of Korea-Japan Joint VLBI Correlator (KJJVC). The main goal of the 1st performance evaluation of VCS main product is that the perfection of overall system will be enhanced after checking the unsolved part by performing the experiments towards various test items at the manufacturer before installation of field. The functional test was performed by including the overflow problem occurred in the FFT re-quantization module due to the insufficient of effective bit at the VCS trial product in this performance test of VCS main product. Through the performance test for VCS main product in the factory, the problem such as FFT re-quantization discovered at performance test of VCS trial product in 2008 was clearly solved and the important functions such as delay tracking, daly compensation, and frequency bining were added in this VCS main product. We also confirmed that the predicted correlation results (fringe) was obtained in the correlation test by using real astronomical observed data(wideband/narrow band).

• Journal of Astronomy and Space Sciences
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• v.26 no.4
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• pp.567-588
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• 2009

Korea-Japan Joint VLBI Correlator (KJJVC) is being developed by collaborating KASI (Korea Astronomy and Space Science Institute), Korea, and NAOJ(National Observatory of Japan), Japan. In early 2010, KJJVC will work in normal operation. In this study, we developed the software correlator which is based on VCS (VLBI Correlation Subsystem) hardware specification as the core component of KJJVC. The main specification of software correlator is 8 Gbps, 8192 output channels, and 262,144-points FFT (Fast Fourier Transform) function same as VCS. And the functional algorithm which is same as specification of VCS and arithmetic register are adopted in this software correlator. To verify the performance of developed software correlator, the correlation experiments were carried out using the spectral line and continuum sources which were observed by VERA (VLBI Exploration of Radio Astrometry), NAOJ. And the experimental results were compared to the output of Mitaka FX correlator by referring spectrum shape, phase rate, and fringe detection and so on. Through the experimental results, we confirmed that the correlation results of software correlator are the same as Mitaka FX correlator and verified the effectiveness of it. In future, we expect that the developed software correlator will be the possible software correlator of KVN (Korean VLBI Network) with KJJVC by introducing the correlation post-processing and modifying the user interface as like GUI (Graphic User Interface).

• 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.

• 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).

• Publications of The Korean Astronomical Society
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• v.27 no.1
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• pp.1-16
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• 2012

In this paper, we describe the installation of VLBI Correlation Subsystem (VCS) main product and its performance at the Korea-Japan Correlation Center (KJCC). The VCS main product was installed at KJCC in August 2009. For the overall performance evaluation of VCS, playbacks, Raw VLBI Data Buffer (RVDB) system, and Data Archive (DA) system were installed together. The VCS main product was connected between RVDB and DA, and the correlation results were put into the DA to confirm the normal operation of VCS 16 station mode configuration. The evaluation test was first performed with 4 station mode, same as the factory test of VCS main product. Based on the results of 4 station mode, the same evaluation test was conducted for 16 station mode of VCS. We found that the correlation results of VCS were almost similarly compared to those of the Mitaka FX Correlator. Through the test results, we confirmed that the problems such as spectrum errors, delay parameter processing module and field programmable gate array errors in antenna unit, which were generated at the factory test of VCS main product, were clearly solved. And we verified the performance and connectivity of VCS by obtaining the expected correlation results and we also confirmed that the performance of VCS was sufficient for real VLBI observation data in both 4 and 16 station modes.

• The Bulletin of The Korean Astronomical Society
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• v.34 no.2
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• pp.70.1-70.1
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• 2009

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.44.1-44.1
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• 2010

한국천문연구원에서는 2009년 1단계 한일공동VLBI상관기(Korea-Japan Joint VLBI Correlator, KJJVC)의 개발과 설치를 완료하였다. KJJVC는 한국우주전파관측망(Korean VLBI Network, KVN), KVN과 일본 내의 VLBI 관측망을 포함하는 한일공동VLBI관측망(Korea-Japan Joint VLBI Network, KJJVN), 그리고 한중일의 VLBI관측망인 동아시아 VLBI관측망(East Asian VLBI Network, EAVN)으로 관측한 VLBI 데이터를 상관처리할 수 있도록 설계 제작되었다. 그리고 고속재생기, 데이터 동기재생처리시스템(Raw VLBI Data Buffer, RVDB), VLBI상관서브시스템(VLBI Correlation Subsystem, VCS), 데이터 아카이브 시스템(Peta-scale Epoch Data Archive, PEDA)로 구성된다. 특히 일본국립천문대 VERA에서는 테이프 형태의 DIR2000 고속기록기를 사용하고 있는데, DIR2000의 제품단종으로 인해 이 데이터를 VCS에 재생하기 위해 DIR1000을 개량한 VERA2000 고속재생기를 개발하였다. 즉, VSI 형태의 데이터를 1Gbps 속도로 재생만 하기 위해 기존의 시스템을 개량하였으며, 2009년 10월에 VLBI상관기실에 설치되었다. 본 논문에서는 VERA2000 시스템의 구성 및 개발, 시험운영 등에 대해 간략히 소개하고자 한다.

• Journal of the Institute of Convergence Signal Processing
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• v.15 no.2
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• pp.55-63
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• 2014

In this paper, we introduce the performance evaluation of data archive system for saving correlation result of Daejeon correlator with high-data rate. Daejeon correlator supports various correlation modes, but the speed of correlation result is affected by correlator according to the integration time in each mode. Maximum data rate of Daejeon correlator is 1.4GB/s in case of C1 mode with 25.6ms integration time. In this research, the performance evaluation of the proposed data archive system is conducted for saving correlation results connected with 4 10GbE optical cable with VCS (VLBI Correlation Subsystem), which is the core system of Daejeon correlator. For the experiments, the data archive system for 2 benders was selected and benchmark test was performed. In this paper, the developed data generation program of VCS correlation result file for benchmark test and evaluation results are described.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.25.2-25.2
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• 2009

한국천문연구원 한국우주전파관측망(Korean VLBI Network, KVN)에서 도입하여 시험운용중인 VLBI 상관서브시스템(VLBI Correlation Subsystem, VCS)은 한일공동 VLBI 상관기(Korea-Japan Joint VLBI Correlator, KJJVC)의 핵심 장비로서, 최대 16 관측국의 관측국 당 최대 8Gbps의 데이터를 처리할 수 있는 상관처리장치이다. VCS의 상관처리 결과는 총 4회선의 10GbE 광케이블을 통하여 UDP 프로토콜로 출력된다. 이 상관처리 결과는 광케이블 하나당 8개씩 총 32개의 상관 처리 블록(correlation block)으로 구성되며, 최대 출력속도는 1.4 GBytes/sec이다. 이 출력은 초고속 대용량 자료저장 시스템(Peta-scale Epoch Data Archive, PEDA)을 이용하여 저장하고 후속 자료처리를 위해 가공된다. PEDA는 총 4대의 고성능 자료 전송 및 저장 서버(writing server) 및 대용량 하드디스크 어레이로 구성된다. 상관처리 과정에 맞추어 PEDA의 writing 서버를 연계하여 제어하는 자료 전송 및 저장 제어 소프트웨어를 개발하였다. 이 소프트웨어는 핵심이 되는 전송 및 저장 프로세서와 이를 제어하는 제어프로세서로 구성된다. 전송 및 저장 프로세서는 개개의 상관 처리 블록에 대한 전송과 저장을 전담한다. 제어 프로세서는 총 32개의 상관 처리 블록을 처리하기 위하여 전송 및 저장 프로세스를 32개를 실행하고 각각의 상관 처리 블록에 해당하는 개별파라미터를 전달하는 전체적인 제어를 담당한다. 이 연구에서는 이 자료전송 및 저장 제어 소프트웨어의 설계 구성과 테스트 내용을 소개한다.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.45.2-45.2
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• 2010

한국천문연구원은 한국우주전파관측망(Korean VLBI Network, KVN)에서 시험 운영 중인 한일공동VLBI상관기(Korea-Japan VLBI Correlator, KJJVC)의 핵심인 VLBI상관 서브시스템(VLBI Correlation Subsystem, VCS)을 제어하기 위해 CCS(Correlation Control Software)를 개발하였다. CCS는 명령어의 문법 검사를 하고, VCS와 TCP/IP 소켓으로 통신하여 명령어와 응답(reply)을 주고받으며, VCS의 실시간 요청에 대응하여 입력 지연 파라미터(delay parameter)를 자동으로 전달하는 소프트웨어이다. CCS는 사용자의 명령어를 local UNX FIFO를 통하여, 명령줄(Command Line)로 전달받고, 이러한 명령어들의 조합을 쉘 스크립트로 묶는 형태로 구성 되어있다. 그러나, 이렇게 명령어의 조합을 직접 편집하여 구성할 때, 입력할 명령어나 지연 파라미터의 구성이 복잡해지면, 스크립트에 필요한 명령이 문법에 맞지 않게 사용되거나, 일부 명령어가 누락될 수 있는 위험이 있다. 이러한 오류를 차단하고 작업 효율을 높이기 위하여, 상관 처리의 전체 운용 및 제어를 통합적으로 할 수 있는 사용자 인터페이스가 필요하다. 이를 위하여 KJJVC의 운용 및 제어를 위한 GUI를 설계하고 제작하였다. 개발된 GUI는 Python 언어를 기반으로 하는 wxPython 패키지를 사용하였으며, 사용자(Operator)가 명령어 문법이나 순서를 확인할 필요 없이, 관측 정보와 관측국 정보, 기록 매체 정보만 가지고 손쉽게 명령어의 조합을 생성해 주며, 시스템 초기화와 각종 정보의 입력이 직관적으로 이루어질 수 있도록 해 준다. 본 연구에서는 개발된 GUI의 설계 및 개발 과정과 시험운영에 대해 소개한다.