Atacama Large Millimeter/submillimeter Array Expanded Very Large Array Robert C. Byrd Green Bank Telescope Very Long Baseline Array Digital Signal Processing A Green Bank Perspective John Ford Contributions from Scott Ransom, Paul Demorest and Jason Ray

Outline Digital Signal Processing Trends – Available Computing Power – Architectures Recent Developments at Green Bank – The Green Bank Ultimate Pulsar Processing Instrument (GUPPI) Future Developments – Continuous GUPPI Upgrades – New GBT Spectrometer – New Backends for the 20 Meter SkyNet Project – Phased Array Feed beamformers 2

DSP Trends – Computing Power 3

DSP Trends - Architecture Possible Architectures – Multi-core conventional CPUs – Graphical Processing Units (GPU) – Reconfigurable Computing Elements (FPGA based Processors) 4

Heterogeneous Computing A System consisting of two or more disparate types of computing elements Typically a mixture of the following – Traditional CPUs – Reconfigurable computing elements (FPGAs) – Graphical Processing Units Use – Reconfigurable computing elements for the fastest streaming fixed- point signal processing and data distribution – GPUs for fast floating-point and memory intensive operations – General Purpose CPUs for managing the systems, handling data, and for non-parallelizable parts of the computations 5

Pulsar Backends Search mode backends – Fast-dump spectrometer – Time resolution of 50 to 100 microseconds – Frequency resolution of 25 KHs to 1 MHz – Bandwidth more important than data quality Timing backends – Known pulsar period allows folding data – Coherent De-dispersion required – Very high time resolution, ~ 1 microsecond – Data quality is important 6

GUPPI Specifications Search Mode – Dual polarization, 8 bit real sampling, 800 MHz bandwidth inputs – Configurable signal processing 64 to 4096 spectral channels 100, 200, 400 and 800 MHz bandwidth – Configurable output rates and dump time 4, 8, or 16 bit outputs at ~50 microsecond dump time – Front end hardware capable of supporting Coherent De-dispersion modes Timing Mode – 800 MHz Coherent De-dispersion – 1 to 4 MHz channel widths, 8 bit sampling 7

GUPPI Hardware Configuration 8

GUPPI Block Diagram 9

GUPPI Signal Processing with CASPER 10

Complete GUPPI 11

Interstellar Dispersion 12

GUPPI Coherent De-dispersion Mode 13

Profile Comparison 14

Profile Comparison 15

Future Developments Continuous GUPPI enhancements – More bandwidth – New algorithms – Array receiver/ multi-beam support Multiple IF inputs Huge data handling requirements Huge computational load New GBT Spectrometer New Backends for Radio SkyNet Wide-band Phased Array Feed Beamformers Front-end signal processing 16

Development Systems 17

43m GUPPI with RFI package 18