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A 4Gb/s Digital VLBI Backend. Sheperd Doeleman MIT Haystack Observatory On behalf of RDBE the collaboration. VLBI. VLBI data rates up by only x4 since 1980’s: recording and data formatting are the bottlenecks. SNR~(BW) 0.5 *(Diam) 2 Solution: move to COTS and industry trends.
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A 4Gb/s Digital VLBI Backend Sheperd Doeleman MIT Haystack Observatory On behalf of RDBE the collaboration
VLBI • VLBI data rates up by only x4 since 1980’s: recording and data formatting are the bottlenecks. • SNR~(BW)0.5 *(Diam)2 • Solution: move to COTS and industry trends. • Recording vs eVLBI
Collaboration NRAO: Steve Durand, Jon Romney, Craig Walker, George Peck, Mike Revnell, Walter Brisken, Miguel Guerr, Matt Luce MIT Haystack: Alan Hinton, Arthur Niell, Alan Whitney, Shep Doeleman, Mikael Taveniku, Alan Rogers, Chester Ruszczyk, Russ Mcwhirter CASPER: Dan Werthimer KAT: Alan Langman (ex)
A Short History of the VLBI DBE • In 2004-2006, MIT Haystack and CASPER group jointly develop 4Gb/s VLBI DBE using iBOB. • Aggregate data rate 32x sustainable VLBA rates. • Combined with 2 Mark5B+ HD recorders: full 4Gb/s system.
Prototype 4Gb/s System DBE: iADC + iBOB Mark5B+: 2Gb/s using VSI link. • Total system cost ~$65K • Portable Current modes: 15 channels, each 32MHz, 2-bit = 1920Mb/s 15 channels, each 16MHz, 2-bit = 960Mb/s
A Short History of the VLBI DBE • In 2005/2006, MIT Haystack and CASPER group jointly develop 4Gb/s VLBI DBE using iBOB. • Aggregate data rate 32x sustainable VLBA rates. • Combined with 2 Mark5B+ HD recorders: full 4Gb/s system. • Planned upgrades: • VLBA: to 4Gb/s - wildly cost-effective major upgrade of National facility instrument. • (sub)mm VLBI: output to 10GbE NIC cards for Burst Mode recording to maximize SNR in short atmospheric coherence times. • Geodetic VLBI: wideband sampling of ionosphere to improve geodesy accuracy to ~1mm, and enabling use of smaller dishes. • New collaboration to produce robust 4Gb/s DBE: NRAO, CASPER, Haystack, KAT
Hardware Layout 1 PPS Mark5C Recorder GPS Timing Module Mk5B or VDIF H-Maser 5/10MHz 4 Gb/s RDBE ROACH V5SX95T DSP and Formatting PFB or DDC Up to 4 IFs From Rx
PFB DSP Flow V5SX95T FPGA Julian Clk 1024MHz 256MHz Clk ADC 8-bit 2 chan Mk5B Format Header Gen 32 Ch 2-bit Quant- ization Interp Filter BiPlex FFT 512MHz IF FIR FIR 10Gb Ethernet Digital Gains --------- State Counts GPS 1 PPS Phase Cal Input Power Level To AGC 4Gb/s Switched Tsys Mk5C Each 512 MHz IF split into 16 channels, each 32 MHz.
Sweep Through PFB Channels 10GbE data output processed in MATLAB
Single PFB Channel Broadband noise input.
DDC DSP Flow V5SX95T FPGA Julian Clk 1024MHz 256MHz Clk ADC 8-bit 2 chan Mk5B Format Header Gen 32 Ch n-bit Quant- ization NRAO DDC 512MHz IF 10Gb Ethernet Digital Gains --------- State Counts GPS 1 PPS Phase Cal Input Power Level To AGC 4Gb/s Switched Tsys DDC’s: 62.5kHz - 128 MHz, tunable over full IF range. Goal to replicate current VLBA BBC capability. Mk5C
RDBE Software Architecture Commands in VSI-S format.
Summary • Status: • DSP chain for PFB complete, each block tested, now working to meet timing. • Mark5C passed 2Gb/s tests and 4Gb/s expected in ~2-3 months. • Remaining modules: phase cal, Tsys, Total power for ALC, DDC. • First version of software/command set complete. • Implementation Timeline: • 8Gb/s Geodetic wideband observations Spring 2010. • 8Gb/s 230/345GHz VLBI of SgrA*/M87 Spring 2011. • 2Gb/s VLBA system mid-2010. 4 Gb/s capability by 2011. • Impact: • RDBE+Mark5C 4Gb/s perfect match to current VLBA IF system, allowing optimal sensitivity for broad range of science. • RDBE meets all Geodetic requirements for use of 12m dishes. • RDBE’s in parallel match IF BW of ALMA Band 6,7 Rx: 4-12GHz. • Provides framework for ALMA VLBI backend.
