Ongoing e-VLBI Developments with K5 VLBI System Hiroshi Takeuchi, Tetsuro Kondo, Yasuhiro Koyama, and Moritaka Kimura Kashima Space Research Center/NICT

Outline What is K5 VLBI system? (Internet-based distributed computing approach for VLBI correlator) Software baseband converter Summary

VLBI Systems developed at Kashima K3 System K4 (KSP) System 1983~ Longitudinal Recorder Open Reel Tapes Hardware Correlator 1990~ Real-time e-VLBI with ATM Operational data rate: 256Mbps Max data rate: 2048Mbps Hardware Correlator K3 Correlator (Center) K3 Recorder (Right) K4 Terminal K4 Correlator K5 System K5 Data Acquisition Terminal 2000~ Real-time e-VLBI with IP PC based system Hard Disk Drives Software Correlator

K5 Family : Concept ADS1000 (1024Msample/sec 1ch 1bit or 2bits) ADS2000 (64Msample/ch·sec,16ch, 1bit or 2bits) IP-VLBI Board ( K5 or K5/VSSP ) (~16Msample/ch·sec, ~4ch, ~8bits) PC : Data Acquisition & Software Correlator VSI Correlator other DAS (Mark5) Internet PC-VSI Board (K5/VSI) (Supports VSI-H specifications) VSI

Single channel VSI Data Acquisition System Specifications of K5/VSI VLBI system Multi-channel VSI Data Acquisition System

VSI Data Capture Board (PC-VSI board) Specifications of K5/VSI VLBI system VSI Data Recording System (PC-VSI board +RAID)

Architecture of K5 data input module In K5 system, captured data is not directly recorded to HDD, but transferred to PC’s shared memory. So, multiple software applications can access the data simultaneously in real-time. Because of this function, various kinds of real-time operations are possible by writing PC software. Such as spectrometer, total power meter, oscilloscope, software correlator, p-cal detector, baseband converter, real-time data transfer, real-time recording, and so on.

Software correlator by distributed computing Merit of software method: No limitations on correlator parameters (number of lags, number of stations, integration time, FX or XF …) distributed correlator program runs during the idle time.

-Distributed correlator system over the Internet Procedures of distributed correlation process 1.A client PC queries the control server about the location of K5 data file to be processed. 2.The control server determines the files to be processed based on the information in the database server and sends back the URL of the files. 3.The client PC downloads indicated K5 files from the VLBI stations by FTP. 4.Correlate the received data. 5.Correlator results, client conditions, and network status are sent to the control server. 6.Control server stores the results to the database server. Processing conditions are updated and published to the Internet. Return to 1. SQL

Distributed computing method is effective only in the environment, where Network bit rate ＞ Data processing rate Current processing speed of software correlator(32 lags) : 15Mbps(Pentium4 3GHz) ・ Network between Institutes (Dedicated network) 1Gbps ～ 100Mbps ＞ 15Mbps → Effective ・ Network to the home (Public network) 1 ～ 10Mbps ＜ 15Mbps → Not Effective! Required network speed for Empirical rule, Guilder’s law, says, “Network bandwidth grows at least three times faster than computer power”.

Application ： Rapid UT1-UTC estimation (June 29,2004) After this session, Mark-5 data at Westford was transmitted to Kashima by FTP. Received Mark-5 data was converted to K5 format, and correlated with Average processing speed:58.6Mbps (8 consumer PCs) UT1 – UTC estimation was completed 4hours and 30 minutes after the last observation in the session.

Development of software baseband converter Analog BBC Multi-channel A/D samplers after image rejection mixers. Demerit: Gain and phase fluctuations caused by the variations of ambient temperatures. Conventional BBC(baseband converter) system Digital BBC(FPGA,ASIC) Digital baseband converters after a single-channel broadband A/D sampler. Demerit: Less flexibility for band selections. High development and maintenance cost.

Software BBC(SBBC) by K5/VSI system Merit: High flexibility, low cost, integrated to network transmission system and recording system. If sampling rate is lower than 2 Gbps, SBBC is realized by a current PC.

SBBC - Specifications and algorithm Lookup table method (Floating point) Written in assembly language Using vector operations(SSE2) and prefetch functions Multi-thread(8 threads) Current speed: By using a current PC(Xeon 3GHz), 2 baseband channels can be extracted in real-time from 1Gbps of IF signals. IF signal1024 or 512Mbps (1 or 2bit) Baseband signal 1MHz ～ 64MHz (1,2,4,8 bit) Number of taps 127 ～ 8191 Selectable baseband frequencyDiscrete (Not arbitrary frequency)

Test experiment using the SBBC April 18, 2004 Parkes(PC-EVN) – Kashima(K5, SBBC) At Kashima, 256-MHz of IF- signals were directly sampled and converted to 16-MHz of baseband signals by the software BBC system. It is easy to perform the experiments between different VLBI systems, because of the flexibility of the software method.

Summary K5 VLBI system is a low-cost and high-performance pc-based VLBI system. Because of the recent developments of consumer PCs, we can use software methods for the VLBI backend processes. For example, distributed software correlator and software BBCs.