Netherlands Institute for Radio Astronomy 1 APERTIF beamformer and correlator requirements Laurens Bakker

2 APERTIF system  Focal Plane Arrays for 12 of 14 Westerbork 25 m dishes  7*8 (or 8*9) dual polarized Vivaldi arrays  25 beams, 300 MHz bandwidth, full Stokes  Aeff/Tsys > 100 m 2 /K (N tel =14  a =0.75 T sys =50 K)  Frequency range: 1000 – 1750 MHz Current system architecture

3 Beamformer requirements  56 or 72 dual polarization elements per telescope  Polarizations can be treated independently in beamformer  ADC sampling speed 800MHz, 8 bit  LVDS connection between ADC and Uniboard required  Synchronization between all elements required  16 ADCs (or more) per Uniboard  Subbands <1MHz required  25 beams per polarization, all elements of 1 polarization used for all beams of this polarization (for now)  Weights don’t have to be updated very often ( in principle only once during 12 hour measurement)

4 Determining weights  Full covariance matrix for every subband required  Both on and off source  Not required at the same time as the beamformer, is a separate measurement  Not required to be determined for every subband at the same time  Only required once for every beam that needs to be made for a 12 hours measurement

5 Beamformer processing requirements Assume 4 Uniboards for 1 polarization of 1 telescope(64 elements):  Filterbank: 64*400MHz*(2*16+2*9)=1280GMAC/s  Beamformer:64*25*300MHz*4=1920GMAC/s  Total:3200GMAC/s  Per Uniboard: 800GMAC/s ->~100GMAC/s FPGA  Memory requirements: limited, only for FFT coefficients and beamforming weights  Interconnect between these boards required  120Gb/s output datarate (240Gb/s for both polarizations)  to correlator, max 2km distance  Total beamforming processing all telescopes:3200*12*2=76800GMAC/s

6 Correlator requirements (preliminary) Requirements as a whole  Full stokes -> both polarizations needed in correlator  Total input data rate 2880Gbps (12 telescopes, 240Gbps each)  Visibilities (25*24*(24+1))/2=7500  Number of input subbands: 384, MHz/subband  X-subband width: 6.1kHz (X-subbands:128)  Total nof X-subbands:  Integration time: 1-10s  Output data rate: 1-10Gb/s  24*25*300MHz*(4*8+2*8)+4*7500*300MHz=17640GMAC/s  Correlator can be treated as many independent correlators

7 APERTIF timeline  2010Q1:  operational Uniboard with 4 receivers (800MHz, 8bit), fft and beamformer on 4 elements implemented  2010Q4:  4 Uniboards in a backplane structure, 64 receivers and fft and full beamformer across all elements implemented