Focal Plane Array Beamformer for the Expanded GMRT: Initial Implementation on ROACH Kaushal D. Buch Digital Backend Group, Giant Metrewave Radio Telescope, NCRA-TIFR, Pune, India kdbuch@gmrt.ncra.tifr.res.in
The GMRT Thirty 45-m dishes Max Baseline ~25km Min Baseline ~60m 14 antennas in a compact array 16 antennas in a Y-shaped array Freq: 150 MHz 1450 MHz Bandwidth: 400 MHz, 16K spectral channels Single pixel feeds Kaushal Buch Reference: http://www.ncra.tifr.res.in/ncra/newsevents/phiscc-2017-1/narendra_patra.pdf CASPER-2017, Caltech, USA 2 Kaushal Buch CASPER Meet 2013 2
The GMRT Central Square Antennas Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 3 Photo: B. Premkumar 3
The Expanded GMRT (egmrt) 30 new antennas at baselines less than 5 km. : need correlator and beamformer for 30 antennas Focal Plane Array (FPA) feeds with 30 beams on the sky : need a multi-beam beamformer Bandwidth: 300 MHz, 16384 spectral channels In prototype development stage Observing Frequencies L-band (1000 1450 MHz) 550 900 MHz Options being explored GMRT + FPA egmrt egmrt + FPA Reference: http://www.ncra.tifr.res.in/ncra/newsevents/phiscc-2017-1/narendra_patra.pdf Kaushal Buch CASPER-2017, Caltech, USA 4 Kaushal Buch CASPER Meet 2013 4
Requirements for egmrt FPA prototype Signal Transport through optical links from FPA to Beamformer Multi-element, multi-beam prototype beamformer (300 MHz, 16k spectral channels, 30-beam, 144-element) Algorithms for calibration and optimal beamforming Artist s Impression: Increased Field-of-View with FPA at the focus Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 5 5
FPA Beamformer Development ASTRON FPA Understanding and testing Low Frequency Array (LOFAR) FPA from ASTRON Computational and cost estimates Computat ional Estimates FPA Beamfo rmer Design Design & Implementation of multi-beam FPA beamformers Simulate the beam patterns, optimal weights Simulation Testing Develop the test setup and test the designs Kaushal Buch CASPER-2017, Caltech, USA Kaushal Buch CASPER Meet 2013 6 6
egmrt Narrowband & Wideband beamformers egmrt FPA Beamformer Narrowband (25-32MHz) Wideband (300 MHz) FPGAbased FPGA CPU-GPU Kaushal Buch CASPER-2017, Caltech, USA 7 Kaushal Buch CASPER Meet 2013 7
ASTRON Beamformer at GMRT 8*9 Vivaldi array (dual polarization) and beamformer built by ASTRON Netherlands (DIGESTIF version) Used for understanding FPAs and capability building Currently installed at the GMRT site 1.1 1.7 GHz, 80 MHz bandwidth Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 8 8
Prototype FPA beamformer Multi-element (fixed) beamforming Multiple beams(complex weights) Correlator(required but not all the time) Real-time data acquisition and processing Optimal beamforming and calibration Kaushal Buch CASPER-2017, Caltech, USA 9 Kaushal Buch CASPER Meet 2013 9
Compute & Data rate requirements Example of 2-element, 2-beam FPA beamformer Dominated by Multiply & Accumulate (MAC) Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 10 10
Wideband FPA Beamformer: Single Board 4-input, 300 MHz bandwidth, 256-channel FPA beamformer and correlator, ROACH-1 + iadc No coarse delay correction 4-bit real, 4-bit imaginary correlation Phase multiplication (18-bit real, 18-bit imaginary) Phase resolution: ~0.1 degree Data output: correlator(1 GbE) beam (10 GbE) coherent sum(8-bit) Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 11 11
Resource Utilization 100% 90% 80% 70% 60% 50% 40% 30% Logic On-chip memory Flip-Flop pair DSP Blocks 20% 10% 0% Single beam ROACH1 Two beam ROACH 1 Single beam ROACH2 Two beam ROACH 2 Three beam ROACH2 Four beam ROACH2 Comparison between ROACH-1 and ROACH-2 for 256-channel, 4-input, 300 MHz FPA beamformer Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 12 12
Wideband FPA Beamformer: Scalable Proposed Architecture 300 MHz, multi-beam, multi-input FPA beamformer Through Mux Final Beams are formed in the acquisition PC Beam: Coherent sum Correlator: FFT output Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 13 13
Narrowband FPA Beamformer Uses 64-input, 12-bit ADC from Techne Instruments Inc. connected to ROACH-1 board Processing in time division multiplexed fashion, FPGA clocked at 4x the ADC clock Narrowband multi-beam beamformer& correlator, 128-channel Rawvoltageon10GbEport:processinginsoftware Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 14 14
Narrowband FPA Beamformer Design Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 15 15
Narrowband Beamformer Setup Connecting RF cables to the ADC (below) 64-channel ADC connected with the ROACH-1 board (above) Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 16 16
Resource Utilization 90% 80% 70% 60% 50% 40% 30% Number of slices RAMB36 Slice LUT Flip-Flop pair DSP48E1s 20% 10% 0% FFT 256, 2 beams FFT 512, 2 beams FFT 1024, 2 beams FFT 2048, 2 beams FFT 256, 4 beams FFT 512, 4 beams FFT 1024, 4 beams FFT 2048, 4 beams 64-channel ADC+ROACH-1 based 16-input correlator and FPA beamformer (narrowband) Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 17 17
Testing beamformerswith the FPA Initial tests with CW signal and noise Tests carried using directional antenna in freespace test range Operate the ASTRON FPA beamformer in parallel to compare the results Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 18 18
Basic tests: Phase Correction Before Phase correction (left) After Phase correction (right) Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 19 19
Basic tests: Addition of beams Coherent beamforming using four elements single element (blue), two elements (cyan), three elements (black), four elements (red) Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 20 20
Narrowband beamformer Autocorrelation of 8 inputs Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 21 21
Free-space test range at GMRT Need better directivity (>25 db) about 10 degree beamwidth in 1.1 1.7 GHz range Use parabolic reflection as transmitting antenna Ways to reduce reflection from nearby objects Kaushal BuchBuch CASPER Meet 2013 USA Kaushal CASPER-2017, Caltech, 22 22
Summary Developing wide-band multi-beam multi-element FPA beamformer basic design done on ROACH-1, testing in progress Scalable architecture with offline correlation (or through reconfiguration of FPGA) and beamforming being developed Developing designs and testing narrowband FPA beamformer (in progress) FPGA, software option(cpu/gpu) also being developed Characterizing and testing the FPGA-based beamformers with the ASTRON FPA Determining the best architecture, platform and cost estimates for the prototype 300 MHz FPA beamformer ROACH-2, SNAP, SKARAB (?) (Inputs from the collaboration are welcome) Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 23 23
Future Plans Mount the FPA on 15m dish at NCRA campus (Pune) for tests 15m dish at NCRA Campus, Pune Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 24 24
Acknowledgements Current team members Atul Ghalame Siddhesh Hande Ajithkumar B. (Co-I, egmrt proposal) Jayaram Chengalur(Co-PI, egmrt proposal) Yashwant Gupta (Co-PI, egmrt proposal) Nissim Kanekar(PI, egmrt proposal) Past team members Bela Dixit Priya Hande GMRT groups Backend Group Computer Group Frontend & OFC group Mechanical, Electrical & Civil groups Kaushal Buch Buch CASPER-2017, Meet Caltech, 2013 USA 25 25
Thank You!