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First Flight: Successful Use of a High Rate LDPC Code With High Data Rate in a Restricted Band

Spring Technical Meeting, Portsmouth, VA 05/03-07/2010. Spring Technical Meeting, Bordeaux, Fr 04/15-18/2013. First Flight: Successful Use of a High Rate LDPC Code With High Data Rate in a Restricted Band. H. Garon, V. Sank, W. Fong NASA/GSFC. “Successful Use of a High Rate LDPC…”

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First Flight: Successful Use of a High Rate LDPC Code With High Data Rate in a Restricted Band

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  1. Spring Technical Meeting, Portsmouth, VA 05/03-07/2010 Spring Technical Meeting, Bordeaux, Fr 04/15-18/2013 First Flight: Successful Use of a High Rate LDPC Code With High Data Rate in a Restricted Band H. Garon, V. Sank, W. Fong NASA/GSFC “Successful Use of a High Rate LDPC…” SLS-C&S 16 April 2013 01 of 11

  2. Statement of the Problem Imposed Requirement: LDCM Characteristic: Restriction: Limited contact time Sun-synchronous polar orbit (16 day repeat cycle at nominally 705 km) with a finite number of ground stations Imaging mission with high data rate of 384 Mbps in 375 MHz X band. Requires low coding overhead. CFDP with 1 G Byte file size but using CFDP class where entire file is re- transmitted if there is an error. EESS X band Abuts DSN X band Limited time/capacity to repeat transmissions and large file size drives BER < 10-12 Sensors generate data at high data rate Limited onboard storage (4 Tbits) Bandwidth limited to 375 MHz Band pass filtering aboard S/C to achieve PSFD at DSN Power Spectral Flux Density restriction at Deep Space Network antennas “Successful Use of a High Rate LDPC…” SLS-C&S 16 April 2013 02 of 11

  3. Selection of Codec • Unlike DSN, expect excess signal margin operationally • S/C science data rate, and limited storage capacity forces high RF data rate. • High Data Rate in restricted bandwidth channel, forces high rate code (384 Mbps => 440 Msps) • Large file and low retransmission, requires BER < 10-12 • High data rate restricts Complexity of encoder • while decoder important, it is on the ground • Absence of BER floor LDPC 7/8 chosen even though there was no flight heritage. “Successful Use of a High Rate LDPC…” SLS-C&S 16 April 2013 03 of 11

  4. Will it work?(Establishing link viability prior to flight) • Questions … • Flight experience for LDPC 7/8? Receiver/Decoder availability? • Assuming LDPC 7/8 is used, what is the impact on truncating the transmission spectrum to less than 375/440 in order to meet spectral emission requirements? • Similarly, impact of radiated spectrum asymmetrical about carrier? • The spectrum truncation is accompanied by significant phase distortion. Can we properly compensate for that distortion on the ground? • Can we achieve a BER < 10-12 ? Absolute requirement to build both end-to-end simulation and hardware emulation in order to gain confidence in flight application. “Successful Use of a High Rate LDPC…” SLS-C&S 16 April 2013 04 of 11

  5. End-to-End Simulation Using Mathworks Matlab/Simulink “Successful Use of a High Rate LDPC…” SLS-C&S 16 April 2013 05 of 11

  6. End-to-End Emulation Using Test Bench “Successful Use of a High Rate LDPC…” SLS-C&S 16 April 2013 06 of 11

  7. Key to hardware emulationCustom bandpass filter designed using simulation to replicate distortion introduced aboard spacecraft “Successful Use of a High Rate LDPC…” SLS-C&S 16 April 2013 07 of 11

  8. Emulation Spectrum Compared To Flight Actual on orbit LDCM spectrum Original emulation of LDCM spectrum “Successful Use of a High Rate LDPC…” SLS-C&S 16 April 2013 08 of 11

  9. Mission Events • 2/11/13 Launch • 2/14/13 X-band SSOH files have been successfully received at both Gilmore Creek and Sioux Falls ground stations.  • The Svalbard ground station corrected a configuration setting so they should be able to receive X-band files on future contacts.  There was a problem with getting S-Band SSOH back from Svalbard . The X-Band mission data from Svalbard uses a different link and is unaffected. • 3/17/13 OLI & TIRS activation • 3/21/13 Released its first X band images of Earth • 3/25/13 X-band downlink with International Collaborators • 3/27/13 LDCM hit a 400 scenes/day milestone All with the rate 7/8 LDPC code. “Successful Use of a High Rate LDPC…” SLS-C&S 16 April 2013 09 of 11

  10. Conclusion: • Demonstrated in flight • A viable 440 Msps link with BER < 10-12 and implementation loss less than 2 dB (including ground station loss) despite an asymmetrical spectrum truncation to 375 MHz, • Commercial off-the-shelf availability of • Flight encoder chips qualified to Level 1 (GEO environment at 1 Gbps) along with • Commercial hardware using sliced data frame, now proven. • Multiple vendors offering FPGA cores and high data rate receivers with LDPC decoder (Zodiac, RT Logic, Avtec, …) (both sliced and not sliced) • Successful cooperation within CCSDS to standardize the codec. Now we can say that not only does it look good, but the rate 7/8 LDPC code works well in practice. “Successful Use of a High Rate LDPC…” SLS-C&S 16 April 2013 10 of 11

  11. The Real Conclusion, an Error Free Image http://www.nasa.gov/images/content/736042main_onion-skin-still-detail.jpg “Successful Use of a High Rate LDPC…” SLS-C&S 16 April 2013 11 of 11

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