The CVN Real Time Correlator

Zhang Xiuzhong, Chen Zhong

Shanghai Astronomical Observatory China4th e-VLBI Workshop

Sydney 2005.7

Outline :

VLBI Stations in China

The 5 station Real Time Correlator

Some results of Real Time Correlator

Mark5 connection

The Future plan

VLBI Stations in China

1 Gbps from station to Urmuqi

New station - 2006

A New Correlator

2006New station - 2006

Fiber in late 2005 – plan 1 Gbps

Main Specification of Chinese VLBI stations

Name Location Antenna diameter

(m)

Band

(GHz)

VLBI

Terminal

Network Connect

(Data Rate)

Available

Sheshan Near Shanghai

25 0.3, 1.6, 2.3, 5.0, 8.4, 22

VLBA, MKIV,S2,

MKV

No (1) 1987

Nanshan Near Urumqi

25 0.3, 1.6, 2.3, 5.0, 8.4, 22

MKIV, K4, MKV

2Mbps (2) 1994

Mobile VLBI

Kunming 3 2.3, 8.4 S2, MKIV 2Mbps (2) 1999

Kunming Kunming 40 2.3, 8.4 MKIV, MKV 2Mbps (2) 2006

Miyun Near Beijing

50 2.3, 8.4 MKIV, MKV No (2) 2006

(1) 100Mbps data rate network connect will be created before end of 2005

(2) 10Mbps data rate network connect will be upgrade before end of 2006

Nanshan (Urumqi) at sunrise

Seshan (Shanghai)

Main Characteristics :

1. 5 Stations

2. date rate： 0 - 256Msamples/s, 1 or 2 bits/sample

3. IFs: 8. (16 MHz / IF, may be expanded to 0.5GHz/IF)

4. Integration Time： 10 ms – 2 hours

5. data format: VLBA、MKIII、MKIV 、 VSI

6. data source ： Disk Array, Network

7. Functions： Fringe searcher, Phase Cal

8. Output: via net and disk files ( in FITS format)

CVN Real Time Correlator

Architecture of Correlator(Chinese Lunar Project)

MKV

MKV

MKV

MKV

MKV

PBD

PBD

PBD

PBD

PBD

PBI

PBI

PBI

PBI

PBI

FFT &

MAC

LTA(PC)

CCC(PC with 32 users RS232)

MCCSystem Clock, Start/Stop control

Cal Fringe & FSTC

PCAL

net

net

net

net

netRS232

RS232

RS232

RS232

7300A

7300A

7300A

7300A

7300A

7300A/RS232

5 Station8Ch

7300A

BENEFITS:

Fringe Finder

Phase Calibration

10Mbps data streamfrom network

256Mpbs data stream from Disk Array

Hard Disk Array Storage

RS232

2Bit,8Ch

RS232

Data Stream & PBI

PC/AD7300AMKV

MKV

MKV

MKV

MKV PC/AD7300A

PC/AD7300A

PC/AD7300A

PC/AD7300A

Ch0 ~ Ch8

32 Tracks

32 Tracks32 Tracks32 Tracks

32 Tracks

32 Tracks

32 Tracks

PBI&

CROSS STITCH

Control Unit RS232

CLK

Delay Control

Delay Control

Delay Control

Delay Control

Delay Control

NET

NET

NET

NET

NET

Diagram of PBIDISK

ARRAYFIFO IN

CROSS SWITCH

FIFO OUT64 bits deep

FAN OUT1:4, 1:2, 1:11 or 2 bits

PARITY & CRC Check

IRQCLK

DATATrack data

DATA

Valid IF data

Ready

IF data

Clock

MCU 131ms TIC

RS232

New Frame

EN_SYNC

IRQ = FIFO_IN_not_FULLReady = FIFO_OUT_not_empty * data_validy *SyncSync = New Frame * EN_Sync

FFT Module

Two Parameter 40-Bit Fixed PT Model

Generator/Sample rate

Two Parameter 20-Bit Fixed PT Model

Generator/Sample rate

20-Bit Ramp Generator/62.5ns

Fringe Stopping

16Bit/Sample

FFT16 Bit fix-point

1024 point

FSTCFractinalSampleTime

Correction

Delay Model

Data from PBI1~2Bit/ch5 Stations

WindowFunction

MAC

The Advantages• The correlator has fringe searcher and P-cal access function.

• The PC-based disk array(CVNHD) will be used as the playback system for correlator. There are maximal 4GB memory should be mounted in these PCs. The 4GB memory could take on a huge FIFO, to smooth the data stream from disk array and from network. The commercial PC board AD7300A is used in these PCs, as a high data rate interface between PC memory and playback interface. The data rate of interface is 10Mbps for real time correlation and 256Mbps for post correlation. The data streams are controled by playback interface.

• The FFT and MAC logics of one channel of 5 stations could be configured in one FPGA chip. Compared with old hardware correlator, this design could reduce many connect cables and will increase the system reliability.

Virtex-II FPGA chips

PBD(CVNHD)

Some Results of Real Time Correlator

The Fringe of the SH-UR

Baseline TC-1 observation with

Integration time of 4 seconds

The Fringe of the SH-UR

Baseline TC-1 observation

with Integration time of

62.5 ms

MKV Connection

• Transfer Mode ：MKV to PBD transfer through network MKV command : disk2net, in2net Net protocol : tcp/udp, tcp prefered

• PBD(CVNHD) Command : net2mem, mem2card Net protocol : tcp/udp, tcp prefered

MARK5A CVNHD

Network 10M/100Mbps

TCP/UDP

7300A

PBI

Transfer mode in Low rate Network Connection

• Mark5A Disk FIFO Mode(Need more tests)

A special ‘disk-FIFO’ mode use a Mark 5 scratch disk pack as the FIFO buffer in the case network transfer rates are slow. It is suitable for the low network transfer rate (10Mbps) for chinese Lunar Project .

• Make data in FIFO Disk Pack usable for playback after experiments is to be done in the future.

MKV – PBD – Correlator

Formater

SS Disk

I/O Board

Mark5A

AD 7300A Card

Disk2net

In2net

PBD

CVNHD

Correlator

Mark5A to PBD Transfer Through Network

Shared Memory

PBD Data Flow

Initial shared memory

Initial a socket to Mark5A

Save socket data to shared memory

Initial 7300A Card

Output data stored in shared memory to 7300A

Net2mem Mem2card

Shared Memory

Buffer[i] Empty?

Initial shared memory

Buffer[i] Full?

Yes Yes

Buffer[i+1] Buffer[i+1]

Waiting Singal Waiting Singal

No No

Test Results

• MK5 – PBD in 100Mbps network

Network transfer rate>50Mbps

peak rate~100Mbps

• MK5 – PBD – 7300A –PBI

A/D 7300A : TRIG_DO_CLK_10M_ACK, 32bits

Average speed 250kbps, controled by PBI

The Future plan

1. MKV connection via network

2. Network creation

3. System auto-operation software

developement

The network connect

Urumuqi

Kunming

Miyun

SheShan

City Network Connect

Real Time Corellator100Mbps/1G

35KM firbe Data Process Center in SHAO

Thank you