1. H. Garon, V. Sank, W. Fong NASA/GSFC
Spring Technical Meeting, Portsmouth, VA 05/03-07/2010
Spring Technical Meeting, Bordeaux, Fr /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 of 11

2. Statement of the Problem
LDCM Characteristic:
Imposed Requirement:
Restriction:
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 contact time
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 of 11

3. “Successful Use of a High Rate LDPC…”
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 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 < ?
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 of 11

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

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

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

9. “Successful Use of a High Rate LDPC…”
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 of 11

10. “Successful Use of a High Rate LDPC…”
Conclusion:
Demonstrated in flight
A viable 440 Msps link with BER < 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 of 11

11. “Successful Use of a High Rate LDPC…”
The Real Conclusion, an Error Free Image
“Successful Use of a High Rate LDPC…”
SLS-C&S 16 April of 11