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Advanced Widefield Imager Development for Transient Event Monitoring Using Scalable FPGA and GPU Designs

This project details the design and implementation of a cutting-edge widefield imager capable of large-field, short-time resolution imaging for detecting transient astronomical events. Utilizing a scalable FPGA-based correlator and a GPU imaging processing backend, the system allows for rapid sky surveys and efficient data handling. Early prototypes have been developed, including the SEPCAM and LASI instruments, focusing on transient event analysis and offering a new perspective on sky-wide imaging. Potential applications include deepening our understanding of fast transient phenomena in the cosmos.

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Advanced Widefield Imager Development for Transient Event Monitoring Using Scalable FPGA and GPU Designs

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  1. Single Station Correlator(UNI)

  2. A Widefield Imager Science: • Large field, short time resolution imaging for transient events. • Daily/Weekly sky survey Engineering: • Scalable FPGA based correlator design • GPU image processing backend • Prototype for large-N EoR arrays and SKA-Low Names: • SEPCAM (SEPnetCAMera) • LASI (LOFAR All Sky Imager) • UNI (UnNamed Imager) • …

  3. Instrument Overview RSP GPU Imaging Node Post-Processing/Storage Server FX Correlator x24 GPU Imaging Node RSP Real Time Imager ANT 0 CH 0 FFT Cornerturn (192 Antennas x 1024 Channels) CMAC LOFAR HBA x192 ANT 192 CH 1023 FFT CMAC

  4. Correlator Specifications • FPGA Based (UniBoard) • 96 dual-pol HBA antennas • →18624 baselines • 4 bit correlation • 15-30 MHz Bandwidth • 1024 FFT Channels • Integration times ~10 ms • Minimal modification to LOFAR station

  5. UniBoard • Developed at ASTRON • 8 × AlteraStratix IV 40nm FPGA, type EP4SGX230KF40C2, 1288 multipliers, 1517 pins • One front node → all back nodes mesh • 14 layers • 8 × 2 DDR3 modules • 4 × 4 10GbE links in • 4 × 4 8-bit LVDS out • Estimated maximum power consumption 280 W

  6. Correlator Design UniBoard EQ/4b Quant XAUI TX LVDS Mesh LVDS Mesh Cornerturn FN1 BN1 Mux FN2 BN2 Vacc Low Band FFT 192 antpol X Engines Vacc Xeng Out FN3 BN3 48 antpol X Engine Xeng Out Back Node FPGA 48 antpols/BN 4 BNs CLK @ 4 x Data CLK Front Node FPGA 256 Channels/FN 4 FNs CLK @ 4 x Data CLK • Daterates: • Input @ 25 MHz BW: 76.8 Gbps • Output: 141 MB per integration • Processing: • 6984 MACs @ 200 MHz: 1.4 TMACs • At 25 MHz BW complete correlation possible with 1 UniBoard

  7. ring AP0 RCU data RCU ctrl serdes Inter board interface (IBI) AP1 BP LCU CEP AP2 Inter board interface (IBI) serdes AP3 ring RSP Interface • Current RSP Design: • Connected to adjacent RSP boards • via a 4 lane(2.5 Gbps per lane) XAUI interface • Utilizing: • Beamlets: 195312.5 Hz × 248 × 4 × 24b = 4.65 Gbps • Crosslets: 195312.5 Hz × 96 × 4 × 18b = 1.35 Gbps • Overhead: 0.025 Gbps • Total: 6.025 Gbps • Modified RSP Firmware Design: • Signal Channel correlator dropped, utilize 2 lanes for • the beam ring and 2 for UNI. Requires a passive connector • to split/combine XAUI CX-4 interface • Utilizing: • Beamlets: 195312.5 Hz × 248 × 4 × 24b = 4.65 Gbps • Overhead: 0.025 Gbps • Total: 4.675 Gbps RSP Board RCU data RCU ctrl RCU data RCU ctrl RCU data RCU ctrl CX-4 XAUI Connector

  8. Firmware Design Options 12b Voltage samples1 • 12.5 MHz BW/ XAUI Lane • Simplest firmware modification 8b Voltage samples (quant) 1 • 18.75 MHz BW/ XAUI Lane • Maximize BW/ XAUI lane, require EQ control interface 1Limited band selection 18b Subband samples2 • 8.5 MHz BW/ XAUI Lane • Simpler firmware modification 8b Subband samples (quant) 2 • 18.75 MHz BW/ XAUI Lane • Maximize BW/ XAUI lane, require EQ control interface 2Selectable band, quantization required

  9. Fast Transient Imaging • Channelized data is independent and is easily parallelized, GPUs offer a good solution • Short timescale images can be crude, thus traditional imaging steps can be simplified/ignored • But short timescale images must be formed faster then the integration time, the wide field of view also introduces a number of challenges. GPU phase φ0 grid/w-proj fft clean phase φ1 grid/w-proj fft clean RFI calib facet Compare Threshold FX phase φn grid/w-proj fft clean Storage Prev. Image Array Model 1 s Image Antenna Model 10 s image Sky Model Detections

  10. Widefield Sky Survey • Longer timescale transient events • New viewable sky survey every few days • Take advantage of the fast transient pipeline by using the post RFI, calibrated data • Perform secondary integration/data compression • Follow a more traditional imaging pipeline • Analysis will focus on rare, bright, transient events which occur on timescales of minutes to days

  11. Where we are at Firmware: • Main modules (FIR,FFT,X Engine) currently being written • LOFAR RSP modifications and passive XAUI splitter done by ASTRON UniBoard: • First round of boards(7) have been produced and shipped to institutes Imaging: • Collaborators working on GPU imaging pipeline • Widefield imaging techniques in development on prototype array in Medicina Related: • AARTFAAC (Super Terp Correlator, ASTRON/U Amsterdam)

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