Next Generation Workshop

Chinese VLBI Software Correlator Development and its Applications

Zheng Weimin, Yang Yan, Zhang Dong, Chen Zhong, Shu Fengchun, Zhang Xiuzhong

Shanghai Astronomical Observatory, Chinese Academy of Sciences

2006,06,28

1. First Chinese software correlator: Satellite Fringe Searcher2. CVN prototype software correlator3. Quasi-realtime software correlator for Chinese Lunar project 4. Future plan5. Conclusions

OutlineOutline

1.1. Satellite Fringe Searcher Satellite Fringe Searcher --First Chinese VLBI software correlator--First Chinese VLBI software correlator

Experiment of track a geostationary satellite, 2003

CVN (Chinese VLBI Network) harddisk record/playback system(By Shanghai Observatory)

2-station hardware correlator could not find fringe?

Attempt the software method

CVNCVN Geography, 2003Geography, 2003

KUNMIN - SESHAN25 1920.

URUMQI - KUNMIN 2477.

URUMQI - SESHAN25 3249.

Satellite Observations

CVN harddisk systemCVN harddisk systemRecord terminalRecord terminal

CVN system:

A VLBI harddisk system based on PC/Linux

Satellite Fringe Searcher Satellite Fringe Searcher

1 baseline, 1 IF correlator Hybrid architecture: XF and FX Specially for satellite downlink telemetry(TM) sig

nals fringe search & correlation Function:VLBI correlation and post-correlation

Produce delay and DOD (Differential One-Way Doppler )—delayrate

Characteristic:

Does NOT need a priori correlation delay model Matlab version

Satellite Fringe SearcherSatellite Fringe Searcher InterfaceInterface

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-200

0

200

400

600SH-UR 1365060000000, Fr=991.6818¡À0.002764t+-0.37449

Time

Pha

se (

circ

le)

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-4

-2

0

2

4

Time

Pha

se (

rad)

-2000 -1500 -1000 -500 0 500 1000 1500 20000

0.1

0.2

0.3

0.4

Delayrate=991.6992(Hz)

Cor

rela

tion

Am

plitu

de=

0.26

181

1.5 2 2.5 3 3.5

x 105

-20

-10

0

10

20

30

40

Frequency

Pow

er S

pect

rum

Mag

nitu

de (

dB)

Peak freq=263037.1094Hz(SH), Time=1365060000000(UTC)

1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4

x 105

-30

-20

-10

0

10

20

30

Frequency

Pow

er S

pect

rum

Mag

nitu

de (

dB)

Peak freq=264028.7912, Dopple freq shift=991.6818Hz(UR)

1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4

x 105

20

40

60

80

Cro

ss S

pect

rum

Pha

se (

Deg

ree)

Fr=-3.2941e-007f+0.23935,Time=1365060000000(UTC), Trk=10, sigma=3, Threshold value=-20

1.5 2 2.5 3 3.5

x 105

-2

0

2

4

Cro

ss S

pect

rum

Pha

se (

rad)Iteration=2, Lag=-1392, delay=2.5e-006(s), Total Delay=-0.00696032941¡À1.4751e-009(s)

1.5 2 2.5 3 3.5

x 105

-50

0

50

FrequencyCro

ss S

pect

rum

Mag

nitu

de (

dB)

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.540

50

60

70Fr=-0.074884t+0.17116,Trk=10,sigma=3,Time=1365060000000(UTC),Total Delay Rate=991.60691¡À0.0035106Hz

Time(s)

Pha

se (D

egre

e)

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50.5

1

1.5

Time(s)

Pha

se (r

ad)

-200 -150 -100 -50 0 50 100 150 2000

2

4

6x 10

-11

Delayrate(Hz)

Cor

rela

tion

Am

plitu

de=4

.007

5e-0

11 Delayrate=-0.079688Hz

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

x 105

0

0.2

0.4

0.6

0.8

1

SH

-UR

Lag

delay=1

-1 -0.5 0 0.5 1

x 10-3

0

50

100

150

200

250

300

350

Delay(s)

Cor

rela

tion

Am

plitu

de=

327.

1703

delay=2.5e-006(s)

Satellite Fringe Searcher ApplicationsSatellite Fringe Searcher Applications1. Fringe check through satellite telemetry(TM) signals Station performance check Self-developed formatter check

2. Hardware correlator model guider and checker Produce Delay & Delay rate of satellite, more accurate than the

prior model

3. Study the satellite orbit determination method by VLBI

CVN 3-station tracked satellite TC-1

2004,7,27~29

Satellite Orbit: 550km perigee, 78000km apogee, 28.5 degree inclination

Data processed by SFS correlator

Chinese first satellite orbit determination experiment using VLBI.

4. e-VLBI experiment data correlating

Fringe checkFringe check

Fringe of satellite telemetry signals

Find the UR station local oscillator frequency shiftFind the UR station local oscillator frequency shift

Test formatterTest formatter

Delay jitter

Delay of satellite TC-1(launching phase)Delay of satellite TC-1(launching phase)

DOD of TC-1(launching phase)DOD of TC-1(launching phase)

Satellite Spin effect of the DODSatellite Spin effect of the DOD

Hardware correlator following the results of the Hardware correlator following the results of the software correlator results to get the fringessoftware correlator results to get the fringes

2003,5 e-VLBI data transmit experiment (FTP) of CVN

Sheshan Nanshan

Shanghai

Observatory

Urmuchi

乌

ISDN car

car

Internet

50Kb/s

2. CVN prototype software correlator2. CVN prototype software correlator

Purpose:

Process both quasar & satellite observation data

Debug tool for CVN hardware correlator Started from 2004 First version, Matlab on Windows OS Final version, c language on linux OS

SpecificationsSpecifications Architecture: FX 3 stations 1 IF ×32~4096 Channels / IF Data format:

Mark4 recorded by CVN harddisk system Output format: self-defined visibility & self-spectra Correlation speed:

5MSample/s/station, 1bit/Sample, 1024Channel/IF (one Pentium 4 PC, 3.2GHz)

Block Diagram of Block Diagram of CVN software correlatorCVN software correlator

“FX” correlator model and Signal transformation

ISTC Fringe

Stopping FFT FSTC

ISTC FFT FSTC

MAC SF12(ν ) SF11(ν ) SF22(ν )

Fringe

Stopping

CVN

harddisk

ISTC

CVN

harddisk

ISTC

CVN

harddisk

ISTC

ISTC: Integer Sample Time Correction

FFT: Fast Fourier Transform

FSTC: Fractural Sample Time Correlation

MAC: Multiply-accumulate

ApplicationsApplications In operation: 2004~2006 Study the VLBI usage in the Chinese Lunar exploration

project – Chang-E(CE-1)

Processed much CVN observation data, for the analysis of DELTA-DOR:

Chinese earth satellites :TC-1, etc. ESA SMART1 lunar spacecraft Processed the data of the Chinese first VLBI joint track

TC-1 experiment, March, 2005 Debug tool of the CVN hardware correlator (under

developing) Station fringe checker

SMART-1 O-C delay/delayrate coSMART-1 O-C delay/delayrate compared with ESA orbitmpared with ESA orbit

Delayrate

O-C

Baseline

SH-UR

SH-KM

UR-KM

Delay

O-C

Baseline

SH-UR

SH-KM

UR-KM

3. Chang-E software correlator for3. Chang-E software correlator forChinese Lunar projectChinese Lunar project

Chang-E lunar spacecraft will be launched in 2007 Chang-E software correlator design target: 2 working modes: Quasi-realtime, Non-realtime Satellite fringe search and PCAL (Phase Calibrati

on signal) abstraction abilities 4station, 8 IF Processing rate, 16Msps/station, quasi-realtime m

ode Backup of hardware correlator

CVN geography for CVN geography for Chinese lunar “Chang-E” projectChinese lunar “Chang-E” project

CVN Configuration, 2006CVN Configuration, 2006

• 4 stations:

2×25m + 50m + 40m• Fiber link between stations• VLBI center at Shanghai Observatory

CVN TopologyCVN Topology

Beijing

Quidway S6506R

VLBI center at Shanghai Observatory

Data Server

Firewall

Secpath100F

R

Network Administrator

Urumqi

RR

Kunming

R

Shanghai

Quidway NE20

Chang-E Software correlator Chang-E Software correlator systemsystem

Chang-E software correlator Chang-E software correlator system system

block diagramblock diagram

Station Shanghai

Station Urmuqi

Station Beijing

Station Kunming

Data receive & Synchronization

NFS

Fringe searcher

PCALCalibration

Correlator control &

configure file

Software correlator

OutputSatellite delay model

reconstruction

Postprocess & orbit

determination

Function: VLBI correlation, fringe search, PCAL abstraction

Software correlator working platformSoftware correlator working platform • Constructed by COTS component;

• Hardware platform:

SMP (Symmetrical Multi Processing) PC server:

HP585, Dawning4380

CPU:4 dual core AMD Opteron 875, 2.2GHz

• Software platform:

Redhat Enterprise version

quasi-realtime modequasi-realtime mode

No. 1 PC server: Software correlator

No. 2 PC server: Fringe searcher & PCAL

for software correlator

No. 3 PC server: Fringe searcher & PCAL

for hardware correlator

Specifications Specifications

• 4 stations

• FX architecture

• 8 IF ×64~4096 Channels / IF

• Data format: Mark5

• Output format:self-defined

• Quasi realtime ability: Data input & output delay: < 4 minutes

• Correlating speed: 40Msps/station,4 station 1bit/Sample,1024Channel/IF (one PC server)

• portable, flexible, expandable to 10 stations

Running on one HP585 PC server

Testing data format: Mark5, 4IF/station, 4Msps/IF, 1bit/sample

10-station software correlator 10-station software correlator processing speed vs station numberprocessing speed vs station number

Non-realtime modeNon-realtime mode

3 PC servers constitute a 4-station software correlator pipeline:

speed: 120Msps/station,

8 IF ×64 Channels / IF

P1

S1 S2 S3 S4 S5 S6 S7

Data slice Playback No.1 data slice from all

station to No.1 software correlator

C1 No1 software correlator

process No.1 data slice

P5 Playback No.5 data slice from all

station to No.2 software correlator

Playback No.6 data slice from all

station to No.3 software correlator

C5 No2 software correlator

process No.5 data slice

C6 No3 software correlator

process No.6 data slice

P5

No.3 correlator No.1 correlator No.2 correlator

t

t S8

P2

C1

P3

C2

C1

C3

C2

C1

P4

C3

C2

P5

C3

C4

P6

C5

C4

P1

C6

C5

C4

P6

Applications(1)Applications(1)

Test the performance of the new CVN stations ( Beijing & Kunming) and help to debug station system

Get the first fringe of SH-BJ baseline, 2006,05,08 Get the first fringe of SH-KM baseline, 2006,05,15 Debug tool of hardware correlator

2006,05,08, First SH-BJ fringe of 2006,05,08, First SH-BJ fringe of geostationary satellitegeostationary satellite

2006,05,17, First SH-KM fringe of2006,05,17, First SH-KM fringe ofSMART1SMART1

BJ-KM

UR-KMUR-BJSH-UR

SH-KMSH-BJ

First 4-station fringes in quasi rear-time mode First 4-station fringes in quasi rear-time mode Source SMART1 Source SMART1 ，， 2006,05,172006,05,17

Applications(2)Applications(2)

Chinese first VLBI joint orbit determination experiment of SMART1 (lunar spacecraft),

2006,5,29~6,1 Chang-E software correlator successfully processed

all VLBI data

2-stage experiment: 1st stage: 4 days real-time observation of SMART1& quasar,

2006,5,29~6,1, 15 hours observation / day Observing mode: S-band, narrow band, 2 IF, 2MHz

bandwidth/IF, 1bit/sample Total data rate 8Mbps/station

Applications(3)Applications(3)

Successful test fast satellite fringe search and delay model reconstruction ability

Fringe searcher stop Fringe searcher open

Applications(4)Applications(4) 2nd experiment stage: 24 hours quasar & SMART1 observation, 2006,6,2.

1. Geodetic experiment, accurate position determination of Beijing & Kunming station

2. High accurate DELTA-DOR experiment

Observing mode: S+X band,wide band, 8IF, 8MHz bandwidth /IF, 1bit/sample

4096 channels/IF (SMART1) 64 channels/ IF(Quasar) Total data rate, 128Mbps/station Software correlator played an import role in this experimen

t

5-day orbit positioning O-C result5-day orbit positioning O-C result

Left:delay

Right:delay rate

2006,5,29~6,2

5,29 5,30 5,31

6,1 6,2

5-day angular positioning O-C 5-day angular positioning O-C resultresult

Up:Azimuth angle

Down:Pitching angle

2006,5,29~6,2

5,29 5,30 5,31

6,1 6,2

4. Future Plan4. Future Plan

Fulfill Chang-E software correlator

Accelerate correlation speed using new structure:

single PC server PC server cluster⇒

5. Conclusions5. Conclusions1. Software correlator validates its value in the lunar

spacecraft orbit determination.

2. Quite flexible and portable

3. Software correlator running on high performance SMP server (now) or small scale cluster(future) is very suitable for VLBI spacecraft navigation.

4. Software correlator working on large scale HPC will be a good candidate of the next generation high speed VLBI correlator for the radio astronomy and geodesy in the near future.

ConclusionsConclusions General commercial computer will promote software corr

elator

CMP & SMT CPU become popular.

Cluster make HPC more popular and cheaper

CMP: 　 Chip Multi － Processing

SMT: Simultaneous multithreading

Cell processor:theoretical rate about 250GFLOPS, supported by Linux, IBM/Sony/Toshiba

World first petaflops HPC “Braker” (2008), based on Linux-Opteron,

Cray/AMD (Announced 2006,6)

Thank you very much