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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