eVLBI using a software correlator Nico Kruithof on

e-VLBI using a software correlator Nico Kruithof, on behalf of the FABRIC team. Joint Institute for VLBI in Europe (JIVE) The Netherlands

Introduction • • • Radio astronomy VLBI and e-VLBI EXPRe. S project Correlation Software correlator Conclusions April 18 th, 2007 e-VLBI using a software correlator 2

Radio and optical 408 Mhz optical 1. 4 Ghz April 18 th, 2007 e-VLBI using a software correlator 3

Larger dish: higher resolution Resolution: λ / b Sensitivity: b 2 λ = wavelength b = diameter telescope Arecibo: D = 305 m April 18 th, 2007 e-VLBI using a software correlator 4

Westerbork/Very Large Array April 18 th, 2007 e-VLBI using a software correlator 5

Even higher resolution: VLBI April 18 th, 2007 e-VLBI using a software correlator 6

Highest resolution: space VLBI April 18 th, 2007 e-VLBI using a software correlator 7

Aperture Synthesis Imaging • A technique that uses a number of telescopes to simulate a much larger one. A larger dish, real or simulated, improves image clarity and brightness. This requires coordination between the telescopes and a supercomputer. Consider the examples displaying aperture size, aperture distribution and image quality. April 18 th, 2007 e-VLBI using a software correlator 8

Aperture Synthesis Imaging April 18 th, 2007 e-VLBI using a software correlator 9

Introduction What is EXPRe. S? • EXPRe. S = Express Production Real-time e-VLBI Service • Three year project, started March 2006, funded by the European Commission (DG-INFSO), Sixth Framework Programme, Contract #026642 • Objective: to create a distributed, large-scale astronomical instrument of continental and inter-continental dimensions • Means: high-speed communication networks operating in realtime and connecting some of the largest and most sensitive radio telescopes on the planet • Current status: • 6 -station fringes at 256 Mbps • 3 -station 512 Mbps fringes April 18 th, 2007 e-VLBI using a software correlator 10

Introduction Participating EXPRe. S Telescopes April 18 th, 2007 e-VLBI using a software correlator 11

Why bother • Target of Opportunity - unscheduled observations triggered by sudden astronomical events. This capability will become much more important when LOFAR comes online • Adaptive Observing - Use e-VLBI as a finder experiment Or, e-VLBI sessions a few days apart, adapt schedules for later observations based on results (rapid results on large sample, focus in detail on best candidates) • Automatic Observing - small number of telescopes observing for extended periods doing spectral line observations of large galactic samples • Operational Reliability - Test data quality during observation • Interface with other real-time arrays – e-MERLIN, LOFAR, SKA. . Also function as SKA-pathfinder • Bandwidth no longer limited by magnetic media: 10 Gbps technology already becoming mainstream • Because we can… April 18 th, 2007 e-VLBI using a software correlator 12

Network EXPRe. S Network Diagram April 18 th, 2007 e-VLBI using a software correlator 13

Data Flow Past Today Results Today Soon Today April 18 th, 2007 e-VLBI using a software correlator 14

Introduction Hardware correlator April 18 th, 2007 e-VLBI using a software correlator 15

FABRIC Future Array of Broadband Radio-telescopes on Internet Computing • Will need a new correlator for > 1 Gb/s • Current EVN Mk 4 based on 16 x 1 Gb/s • Implemented on 1024 special chips • Develop a next generation correlator using standard CPUs • Current EVN Mk 4 processor equivalent 40 T-ops (2 bit) • LOFAR Blue. Gene ≈ 27 Tflops • 32 station x 4 Gb/s ⇒ 640 T-ops • And requirement to route 32 x 32 4 Gb/s input stream • Possible solution: distribute the computing • SCARIe – Software Correlator Architecture Research and Implementation for e-VLBI April 18 th, 2007 e-VLBI using a software correlator 16

Pros and cons. Software correlator Hardware correlator • High flexibility • Tracking of spacecrafts • Research on masers • Superior computing power • Ability to share resources • More efficient use of computing resources (Lower energy consumption) • Lower cost to develop What about hybrid forms? April 18 th, 2007 e-VLBI using a software correlator 17

Software correlator Telescopes Input nodes Time slicing Correlator nodes Sorting and merging Output node Grid April 18 th, 2007 e-VLBI using a software correlator 18

Software correlation on a grid April 18 th, 2007 e-VLBI using a software correlator 19

Input node • Reads data • directly from telescopes • replayed from files • Extracts time stamps from the data stream • Sends time slices to the correlate nodes (1 or 2 bits). Single input controller Input node Multiple output controller April 18 th, 2007 e-VLBI using a software correlator 20

Correlator node • Receives the 1 or 2 bit signal • Performs the correlation • Delay signals • Correlate • Sends the correlation product to the output node Multiple input controller Correlator node Single output controller April 18 th, 2007 e-VLBI using a software correlator 21

Output node • Receives the output from the correlator nodes • Sorts the slices • Writes the output to disk for further processing Multiple input controller Output node Single output controller April 18 th, 2007 e-VLBI using a software correlator 22

Manager node & Log node • Handles the entire correlation process • Initialises the nodes • Delegates time slices to the correlator nodes Manager node • Receives log messages from all nodes Log node April 18 th, 2007 e-VLBI using a software correlator 23

Correlation results April 18 th, 2007 e-VLBI using a software correlator 24

Preliminary results 4 AMD dual cores, 2 GHz 8 Gb memory Data stored locally on disk April 18 th, 2007 e-VLBI using a software correlator 25

Conclusions • EXPRe. S makes real-time e-VLBI operationally possible • The first results from the software correlator seem promising April 18 th, 2007 e-VLBI using a software correlator 26

Questions/Answers • Contact information Nico Kruithof JIVE Kruithof@jive. nl • Additional Information http: //expres-eu. org/ http: //www. jive. nl/ • [note: only one “s”] EXPRe. S is made possible through the support of the European Commission (DG-INFSO), Sixth Framework Programme, Contract #026642 April 18 th, 2007 e-VLBI using a software correlator 27

HTML output April 18 th, 2007 e-VLBI using a software correlator 28