Transcript Slide 1
OSKAR: Simulating Station Beams for the SKA Aperture Array Fred Dulwich Ben Mort Stef Salvini wiki.oerc.ox.ac.uk/Oskar Combine delayed antenna signals. In the frequency domain: Geometric time delay = applying a phase factor (multiplicative weights) FFT Poor flexibility (compute now, throw away later). Can’t even use all the beams! Weighted sum (matrix-vector product) A vector of weights define a direction. Flexible: any beam / channel combination. Cost linear on number of channels x number of beams. Detectors Weights matrices: Vary much slower than the signal sample rate. May be computed off the signal path. Beams = “Trivial” parallelism. Beamforming weights Detectors Output beams Split the problem to be hierarchical and parallel. Station divided into tiles (can be logical). Dump as much unwanted data as we can early on. Station beams Tile beam Scope and Goals Scalable to large numbers of antennas (~105). Choice of number of beams and channels (limited by available processing power). Simulation of time-variable effects. Design MPI-parallel. Hierarchical. Modular. Portable. Frontend sets up: Sky Station Beams Simulator Frontend Run on desktop (cross-platform) Graphical interface Data exchange XML parameter files Beam checkpoints Backend Run on cluster Parallel (MPI) computational engine Beam forming (end-to-end simulation) mode: Sky model. Multiple beams per level. Time-dependence. Investigate processing hierarchy, algorithms and performance. Beam pattern mode: Snapshot (no time dependency). Constant weights (single beam). Sweep a test source around. Investigate beam shaping, effects of array configuration, antenna response. 80 x 80 degrees: Tile beam at zenith. Station beam at (45, 87) degrees. Tile beam Zenith Station beam Zenith: 100% amp. Zenith (45, 87) deg: ~75% amp. Station beams Tile beams (Some) Next Steps: Other beamforming methods: Null-steering Multiple (> 2) levels Simulation of ionospheric corruptions. Connection to interferometer simulations. Summary OSKAR: Simulates frequency-domain digital beamforming for an SKA station. Hierarchical, matrix-vector strategy. Parallel, modular framework. Open source. Available at http://www.oerc.ox.ac.uk/research/oskar