• Title, Summary, Keyword: Software correlator

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Development of Software Correlator for KJJVC (한일공동VLBI상관기를 위한 소프트웨어 상관기의 개발)

  • Yeom, J.H.;Oh, S.J.;Roh, D.G.;Kang, Y.W.;Park, S.Y.;Lee, C.H.;Chung, H.S.
    • 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).

A NEW HARDWARE CORRELATOR IN KOREA: PERFORMANCE EVALUATION USING KVN OBSERVATIONS

  • Lee, Sang-Sung;Oh, Chung Sik;Roh, Duk-Gyoo;Oh, Se-Jin;Kim, Jongsoo;Yeom, Jae-Hwan;Kim, Hyo Ryoung;Jung, Dong-Gyu;Byun, Do-Young;Jung, Taehyun;Kawaguchi, Noriyuki;Shibata, Katsunori M.;Wajima, Kiyoaki
    • Journal of The Korean Astronomical Society
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    • v.48 no.2
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    • pp.125-137
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    • 2015
  • We report results of the performance evaluation of a new hardware correlator in Korea, the Daejeon correlator, developed by the Korea Astronomy and Space Science Institute (KASI) and the National Astronomical Observatory of Japan (NAOJ). We conduct Very Long Baseline Interferometry (VLBI) observations at 22 GHz with the Korean VLBI Network (KVN) in Korea and the VLBI Exploration of Radio Astrometry (VERA) in Japan, and correlated the aquired data with the Daejeon correlator. For evaluating the performance of the new hardware correlator, we compare the correlation outputs from the Daejeon correlator for KVN observations with those from a software correlator, the Distributed FX (DiFX). We investigate the correlated flux densities and brightness distributions of extragalactic compact radio sources. The comparison of the two correlator outputs shows that they are consistent with each other within < 8%, which is comparable with the amplitude calibration uncertainties of KVN observations at 22 GHz. We also find that the 8% difference in flux density is caused mainly by (a) the difference in the way of fringe phase tracking between the DiFX software correlator and the Daejeon hardware correlator, and (b) an unusual pattern (a double-layer pattern) of the amplitude correlation output from the Daejeon correlator. The visibility amplitude loss by the double-layer pattern is as small as 3%. We conclude that the new hardware correlator produces reasonable correlation outputs for continuum observations, which are consistent with the outputs from the DiFX software correlator.

Amplitude Correction Factors of KVN Observations Correlated by DiFX and Daejeon Correlators

  • Lee, Sang-Sung
    • The Bulletin of The Korean Astronomical Society
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    • v.40 no.1
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    • pp.54.1-54.1
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    • 2015
  • We report results of investigation of amplitude calibration for very long baseline interferometry (VLBI) observations with Korean VLBI Network (KVN). Amplitude correction factors are estimated based on comparison of KVN observations at 22 GHz correlated by Daejeon hardware correlator and DiFX software correlator in Korea Astronomy and Space Science Institue (KASI) with Very Long Baseline Array (VLBA) observations at 22 GHz by DiFX software correlator in National Radio Astronomy Observatory (NRAO). We used the observations for compact radio sources, 3C 454.3 and NRAO 512 which are almost unresolved for baselines in a range of 350-477 km. VLBA visibility data of the sources observed with similar baselines as KVN are selected, fringe-fitted, calibrated, and compared in their amplitudes. We found that visibility amplitudes of KVN observations should be corrected by factors of 1.14 and 1.40 when correlated by DiFX and Daejeon correlators, respectively. These correction factors are attributed to the combination of two steps of 2-bit quantization in KVN observing systems and characteristics of Daejeon correlator.

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A Study on Optimum Coding Method for Correlation Processing of Radio Astronomy (전파천문 상관처리를 위한 최적 코딩 방법에 관한 연구)

  • Shin, Jae-Sik;Oh, Se-Jin;Yeom, Jae-Hwan;Roh, Duk-Gyoo;Chung, Dong-Kyu;Oh, Chung-Sik;Hwang, Ju-Yeon;So, Yo-Hwan
    • 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.

Development of the software for high speed data transfer of the high-speed, large capacity data archive system for the storage of the correlation data from Korea-Japan Joint VLBI Correlator (KJJVC)

  • Park, Sun-Youp;Kang, Yong-Woo;Roh, Duk-Gyoo;Oh, Se-Jin;Yeom, Jae-Hwan;Sohn, Bong-Won;Yukitoshi, Kanya;Byun, Do-Young
    • Bulletin of the Korean Space Science Society
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    • pp.37.2-37.2
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    • 2008
  • Korea-Japan Joint VLBI Correlator (KJJVC), to be used for Korean VLBI Network (KVN) in Korea Astronomy & Space Science Institute (KASI), is a high-speed calculator that outputs the correlation results in the maximum speed of 1.4GB/sec.To receive and record this data keeping up with this speed and with no loss, the design of the software running on the data archive system for receving and recording the output data from the correlator is very important. But, the simple kind of programming using just single thread that receives data from network and records it by turns, can cause a bottleneck effect while processing high speed data and a probable data loss, and cannot utilize the merit of hardwares supporting multi core or hyper threading, or operating systems supporting these hardwares. In this talk we summarize the design of the data transfer software for KJJVC and high speed, large capacity data archive system using general socket programming and multi threading techniques, and the pre-BMT(Bench Marking Test) results from the tests of the storage product providers' proposals using this software.

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An Efficient Correlation Scheme for the GPS Software Receiver

  • Lim, Deok-Won;Cho, Deuk-Jae;Park, Chan-Sik;Lee, Sang-Jeong
    • 제어로봇시스템학회:학술대회논문집
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    • pp.1216-1221
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    • 2005
  • The GPS software receiver based on the SDR(Software Defined Radio) technology provides the ability to easily adopt other signal processing algorithms without changing or modifying the hardware of the GPS receiver. However, it is difficult to implement the GPS software receiver using a commercial processor because of heavy computation load for processing the GPS signals in real time. This paper proposes an efficient GPS signal processing scheme and correlator structure to reduce the computation load for processing the GPS signal in the GPS software receiver, which uses a patterned look-up table method to generate the correlation value between the GPS signals and the replica signals. In this paper, it is explained that the computation load of the proposed scheme is much smaller than that of the previous GPS signal processing scheme. Finally, the processing time of the proposed scheme is compared with that of the previous scheme, and the improvement is shown from the viewpoint of the computation load.

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AMPLITUDE CORRECTION FACTORS OF KOREAN VLBI NETWORK OBSERVATIONS

  • LEE, SANG-SUNG;BYUN, DO-YOUNG;OH, CHUNG SIK;KIM, HYO RYOUNG;KIM, JONGSOO;JUNG, TAEHYUN;OH, SE-JIN;ROH, DUK-GYOO;JUNG, DONG-KYU;YEOM, JAE-HWAN
    • Journal of The Korean Astronomical Society
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    • v.48 no.5
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    • pp.229-236
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    • 2015
  • We report results of investigation of amplitude calibration for very long baseline interferometry (VLBI) observations with Korean VLBI Network (KVN). Amplitude correction factors are estimated based on comparison of KVN observations at 22 GHz correlated by Daejeon hardware correlator and DiFX software correlator in Korea Astronomy and Space Science Institute (KASI) with Very Long Baseline Array (VLBA) observations at 22 GHz by DiFX software correlator in National Radio Astronomy Observatory (NRAO). We used the observations for compact radio sources, 3C 454.3, NRAO 512, OJ 287, BL Lac, 3C 279, 1633+382, and 1510–089, which are almost unresolved for baselines in a range of 350-477 km. Visibility data of the sources obtained with similar baselines at KVN and VLBA are selected, fringe-fitted, calibrated, and compared for their amplitudes. We find that visibility amplitudes of KVN observations should be corrected by factors of 1.10 and 1.35 when correlated by DiFX and Daejeon correlators, respectively. These correction factors are attributed to the combination of two steps of 2-bit quantization in KVN observing systems and characteristics of Daejeon correlator.

Development and Evaluation of Global Fringe Search Software for the Preprocess of Daejoen Correlator (대전 상관기의 전처리를 위한 광역 프린지 탐색 소프트웨어 개발 및 시험)

  • Oh, Se-Jin;Roh, Duk-Gyoo;Yun, Young-Joo;Yeom, Jae-Hwan;Oh, Chung-Sik;Kurayama, Tomoharu;Chung, Dong-Kyu;Jung, Jin-Seung
    • Journal of the Institute of Convergence Signal Processing
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    • v.15 no.4
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    • pp.176-182
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    • 2014
  • This paper introduces the development of global fringe search (GFS) software for preprocessing of Daejeon Correlator. In case of the VLBI observation, a observer conducts the observation for the reference sources with strong and point-like radio stars on schedule in order to confirm the well-observedness of the radio source by the radio telescope. The correlator performs the correlation for the reference sources to detect the fringe completely. We developed the GFS software by calculating the precise delay time between each observatory based on specific observatory. Then, this software calculates the precise delay time by using the delay model (correlator model) of reference source and information of time offset between the Hydrogen Maser frequency standard and GPS (Global Positioning System) clock located in each observatory through the correlation preprocessing. In order to confirm the performance of the developed software, experiments were carried out for the reference sources and target sources observed by the KaVA (KVN and VERA Array). Experimental results show that the GFS software has effectively good performance by finding the precise delay time offset according to the comparison between the compensated delay time offset and one without compensation.

SMALL-SCALE GIGABIT VLBI OBSERVATION SYSTEM USING PC (PC를 이용한 소규모 기가비트 VLBI 관측시스템)

  • Oh, Se-Jin;Roh, Duk-Gyoo;Kim, Kwang-Dong;Chung, Hyun-Soo;Je, Do-Heung;Wi, Seog-Oh;Han, Seog-Tae;Kim, Hyun-Goo
    • Publications of The Korean Astronomical Society
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    • v.20 no.1
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    • pp.125-134
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    • 2005
  • In this paper, we propose a small-scale Gigabit VLBI observing system for the Korean VLBI Network (KVN) under construction. The system consists of high-speed sampler, IP-VLBI board, PC-VSI board, and software correlator. Radio signal received by receiver is sampled by high-speed sample. at 1 Gsps (Gigabit sample per second) rate with 2 bits quantization. The digitized signal is recorded in PC and the software correlator does the cross correlation. IP-VLBI board will be used for the geodesy VLBI observation, while PC-VSI board is for the astronomical VLBI observation. The PC-VSI board adopts the VSI-H (VLBI Standard Interface Hardware). The proposed system is based on commercial PCs and therefore can be built inexpensively.