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On the Fly LOFARStation Correlator

André W. Gunst

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LOFAR System Overview

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LOFAR Station Locations

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Remote Station Architecture

120-240 MHz

30-80 MHz

Optional10- … MHz

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Receiver Bands

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Key Numbers

Description Unity

160 MHz 200 MHz

Subband width 156 195 kHz

Number of beamlets 206 165

Value for fs of

Description Value Unity

# subbands 512

Max. number of beams (B = 4 MHz) 8

Min. number of beams (B = 32 MHz) 1

A/D converter resolution 12 bit

Sample frequency 200 / 160 MHz

Number of polarizations 2

Output word width (complex) 16+16 bit

Aggregate output bandwidth 32 MHz

Output data rate 2048 Mbit/s

Transient buffer storage period 1 s

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Top Level Digital Processing Functions

InputFiltering

Station Beam Forming

Station CrossCorrelation

TransientData

Forwarding

CEP

LCU

RCU

TBBTDS

sync

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Digital Filter Bank

Sample rate max. 200 MHz Number of taps: 16384 Number of subbands: 512

100f (MHz)

P

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CentralBeamformer

,,,Filter

BEAMFORMER

Filter Filter Filter

~192 receiver units

8 Gbit/s 8 Gbit/s

8 Gbit/s8 Gbit/s

200 Gbit/s

RCUsRCUsRCUsRCUs

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CentralBeamformer

Add

,,,Filter

BEAMFORMER

beamformer

Filter

beamformer

Filter

beamformer

Filter

beamformer

2 Gbit/s

2 Gbit/s 2 Gbit/s

2 Gbit/s

50 Gbit/s

RCUsRCUsRCUsRCUs

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,,,

Filterbeamformer

Filterbeamformer

Filterbeamformer

Filterbeamformer

2 Gbit/s 2 Gbit/s 2 Gbit/s

2 Gbit/s

RCUs RCUs RCUs

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Beams Versus Bandwidth Exchange

FB00

FB01

FB95

BF00

BF01

BF128

N

M

M = 165 (200 MHz mode)M = 205 (160 MHz mode)

N = 96

beamlet

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Remote Station Architecture

Receiver

Filter

Beamformer

Buffer

Receiver

Filter

Beamformer

Buffer

Receiver

Filter

Beamformer

Buffer

Receiver

Filter

Beamformer

Buffer

10 GbE

1 GbE

Used for 1 beam & station cross correlation

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Station Correlator Applications

Station analogue hardware calibration (based on the full cross correlation matrix)

RFI detection System health management

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Overall Ring Structure

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+

Correlator

Beamlets

Beam former

Antenna data (all subbands)

Antenna data(1 subband)

Ring

10

:215

10

:191

Beamlets

Antennas

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Board Architecture

AP 1

AP 3

AP 2

AP 4

BP

RSPRCU 1X

RCU 1Y

RCU 2X

RCU 2Y

RCU 3X

RCU 3Y

RCU 4X

RCU 4Y

RSP in

RSP out

LCU

WAN

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Station Correlator Scenarios

Real-time correlation of 1 subband (2 subbands possible) Full band correlation with update rates of about 9 minutes Odd or even subband correlation with update rates of

about 4 minutes Everything in between

Full flexibility in selection of the subbands

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Correlator Characteristics Summary (1)

Full dual polarized cross correlator (PFX) # Signal paths correlated: 192 (96 antennas) Instantaneous bandwidth 2*195 = 391 kHz Number of multiplier bits: 18 (set by RFI) 144 multipliers per station necessary @ 200 MHz for correlator Station processing: 1.8 Tmul/s (1.6% procent used for correlator)

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Correlator Characteristics Summary (2)

Integration time: 1 s Used technology: 90 ns FPGA technology Design is scalable, but at some point the ring bandwidth

will limit (@ 216 antennas) Subbands can be selected from a full 100 MHz band

In total 77 stations/correlators in the field

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Remote Station Hardware Numbers

96 dual pole low band antennas 96 dual pole high band tiles 192 receiver boards 24 dig. signal processing boards with 5 FPGAs each 12 transient buffer boards 6 backplanes 6 clock boards

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Remote Station Numbers

Input data rate: ~ 460 Gbps Output data rate: ~ 2 Gbps Processing capacity: ~ 1.8 Tmul/s Storage capacity: 96 Gbyte

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Remote Station Implementation

Clo

ck

Receiver

Filter

Beamformer

Buffer

Receiver

Filter

Beamformer

Receiver

Filter

Beamformer

Receiver

Filter

Beamformer

Buffer

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Remote Station Cabinets

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Concluding Remarks

Other way of thinking: instead of bringing all antenna data traditionally to one point the antenna data is send to each other and locally processed

Architecture optimized for beam forming used for a distributed correlator

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The End