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? VLBI@home (Internet-based distributed computing

approach for VLBI correlator) Software baseband converter Summary

VLBI Systems developed at Kashima

K3 System

K4 (KSP) System

1983~Longitudinal RecorderOpen Reel TapesHardware Correlator

1990~Real-time e-VLBI with ATMOperational data rate: 256MbpsMax data rate: 2048MbpsHardware Correlator

K3 Correlator (Center)K3 Recorder (Right)

K4 Terminal

K4 Correlator

K5 System

K5 Data AcquisitionTerminal

2000~Real-time e-VLBI with IPPC based systemHard Disk DrivesSoftware Correlator

K5 Family : ConceptADS1000(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

Correlatorother DAS (Mark5)

Internet

PC-VSI Board (K5/VSI)(Supports VSI-H specifications) VSI

Device Name ADS-1000Sampling rate 1024/512MspsSample resolution 1/2bitExternal Reference 10MHz,1PPSOutput Data Format Starndard VSI-H formatSize/Weight 424 x 400 x 44mm / 5kg

Single channel VSI Data Acquisition System

Specifications of K5/VSI VLBI system

Multi-channel VSI Data Acquisition System

Device Name ADS-2000Number of input channels 16Sampling Rate 2,4,8,16,32,64MspsSample Resolution 2bitExternal Reference 10MHz,1PPSOutput Data Format Starndard VSI-H formatSize/Weight 482 x 550 x88mm / 12kgFunction P-Cal detection

VSI Data Capture Board (PC-VSI board)

Specifications of K5/VSI VLBI system

Device Name VSI2000-DIM

Continuous Capture Rate

2048Mbps1024Mbps512Mbps256Mbps

Input Interface Starndard VSI-H formatPCI interface PCI-X(64bit/66MHz)

VSI Data Recording System (PC-VSI board +RAID)

Device Name PC-VSIDisk Storage Interface Dual Fiber ChannelMax Recording Rate 2048MbpsHDD size 3TByte

Continuous Recording Time

3hours@2048Mbps6hours@1024Mbps12hours@512Mbps24hours@256Mbps

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.

RF-signal

Personal-ComputerPC-VSI Board(PCI-X)

Memory(1-4GByte) CPU Hard Disk

Drive(RAID)

VSI-H1-2Gbps

ADS-1000A/D sampler

(1Gsps/2bits)

DMA

Network transfer

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 …)

VLBI@home:Screensaver-type distributed correlator program runs during the idle time.

Control Server

Client

Client

XML XML

DataBase

Station 1

FTP

Station 2

FTP

FTP

Station 3

FTP

Schedule File

Obsinformation

WWWStatusinformation

VLBI@home -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 VLBI@home

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 VLBI@h

ome. Average processing speed:58.6Mbps (8 consumer PCs) UT1 – UTC estimation was completed 4hours and 30 minutes after the last obse

rvation in the session.

Westford(Mark5)

Kashima stationMark5→K5Conversion

File transfer File transfer

FTPServer

Client

Client

VLBI@home

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

IF signal IFDistributor

Image Rejection Mixer

Local signal

A/ D

Local signal

A/ D

Local signal

A/ D

..

..

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-signal

Personal-ComputerPC-VSI Board(PCI-X)

Memory(1-4GByte)

CPU(Software

BBC)Hard Disk

Drive(RAID)

VSI-H1-2Gbps

ADS-1000A/D sampler

(1Gsps/2bits)

DMA

Network transfer

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 signal 1024 or 512Mbps (1 or 2bit)

Baseband signal 1MHz ～ 64MHz (1,2,4,8 bit)

Number of taps 127 ～ 8191

Selectable baseband frequency Discrete (Not arbitrary frequency)

Frequency response of 4095- tap FIR bandpass filter

127 129 131 133 135

IF frequency (MHz)

Gai

n (d

B)

0

-10

-20

-30

-40

-50

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.