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Digital Backend and Recorder for VLBI

Digital Backend and Recorder for VLBI. Shep Doeleman MIT Haystack Observatory Charlottesville, August 6-7 2009. New 4Gb/s VLBI System. Digital Recorder (Mark5). Digital Backend (DBE). Current 4Gb/s system: 1 DBE + 2 x Mark5B+ Total cost ~$65K (media not included).

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Digital Backend and Recorder for VLBI

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  1. Digital Backend and Recorder for VLBI Shep Doeleman MIT Haystack Observatory Charlottesville, August 6-7 2009

  2. New 4Gb/s VLBI System Digital Recorder (Mark5) Digital Backend (DBE) • Current 4Gb/s system: 1 DBE + 2 x Mark5B+ • Total cost ~$65K (media not included). • DBE1: 2 x 480MHz input, 2-bit sampling, VSI output • DBE2: same with 10GbE output, extension to 8Gb/s • Mark5C: 4Gb/s over 10GbE.

  3. DBE1 DSP Flow: CASPER iBOB • 16 channels (32MHz each) processed, but one lost due to aliasing. • New algorithm: SSB mix prior to FFT – allows recovery of 16th channel with slightly higher computational cost.

  4. 16MHz vs 32MHz Channels8 vs 4 filter taps 16MHz Channel 4 taps 32MHz Channel 8 taps

  5. ROACH 1 Board UC Berkeley, S. Africa, NRAO

  6. RDBE DSP Flow: ROACH1

  7. Mark 5 Data Acquisition System(Mark 5A/B/B+/C all look the same)

  8. PATA & SATA: $/GB vs. time courtesy Walter Brisken; data based on pricewatch.com monitoring

  9. Mark 5C Characteristics • Mark 5C specification developed jointly by Haystack & NRAO;comments solicited from global community in early 2007 • 4096 Mbps max data rate to two standard Mark 5 disk modules • 10GigE data interface • A “dumb” Ethernet packet recorder (accepts OSI Layer 2 or higher) • Not VLBI specific • Data source is responsible for data formatting and Ethernet packet creation • Expect most applications will create VDIF-compliant data streams • Record through real-time hardware 10GigE interface • Playback of Mark 5C will be through host computer accessed as standard Linux files using FUSE • Natural for software correlators

  10. Data Packetizing

  11. Evolving Mark 5C Functionality

  12. Burst Mode (16Gb/s)

  13. Possible Future Directions • Higher data rates (8-16 Gbps) • New module connector with many high-speed serial data streams • Suitable connector has been identified • Would not be backwards compatible with current modules • Move to 16 or more 2.5” SATA disk drives in current module geometry • Data rates to >=8Gbps with single module; >=16Gbps with two modules • Possibility to use solid-state disk drives for higher reliability (currently too expensive, but prices dropping rapidly) • Possible data interface upgrades • Multiple 10GigE interfaces • 100GigE

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