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<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2>Greg,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2>Indeed compression is being used on the uplink when data
rate / pass duration are not sufficient to upload a work plan (for example). On
our LEO earth observation spacecrafts, we often use what we call "macrocommands"
to actually encode the daily work plan so that it can be uploaded in one single
pass at 2 or 4 kbps. This macrocommand syntax is a way of compressing work plans
or sequences of commands by encoding with one single macrocommand a complete
Operational Control Procedure. This type of compression is of course highly
mission dependent and cannot be subject to standardization. Nevertheless, it is
very efficient.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2>On the contrary, a generic standard lossless compression
for S/C uploads could be envisaged derived from a mainstream universal lossless
compression algorithm like LZ (deflate RFC). This approach is interesting
if a single algorithm (with reasonable decoding complexity) provides
significant and consistent performances (2:1 compression ratio on average
at least) for a wide range of uploads types (work plans, software uploads, FPGA
configuration uploads, parameter tables uploads (e.g. star catalogues),
...).</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2>The first step would be to assemble a set of representative
uploads covering the whole range of type of traffic on TC links, and then
perform performance test with LZ. This initial step is necessary to decide on
agency interest for such a TC compression CCSDS standard.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2>Discussion with MHDC WG before next meeting could be
beneficial to assess their capability to support this first step, and to gather
their technical opinion on the opportunity/feasibility of such a
standardization.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2>Best regards,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=991551815-30062010><FONT face=Arial
color=#0000ff size=2>Gilles</FONT></SPAN></DIV>
<DIV><FONT face=Arial color=#0000ff size=2></FONT> </DIV><!-- Converted from text/rtf format -->
<P><SPAN lang=fr><FONT face=Arial size=2>Gilles MOURY</FONT></SPAN> <BR><SPAN
lang=fr><FONT face=Arial size=2>CNES Toulouse</FONT></SPAN> </P>
<DIV> </DIV><BR>
<DIV class=OutlookMessageHeader lang=fr dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>De :</B> sls-ngu-bounces@mailman.ccsds.org
[mailto:sls-ngu-bounces@mailman.ccsds.org] <B>De la part de</B> Kazz, Greg J
(313B)<BR><B>Envoyé :</B> mardi 29 juin 2010 00:57<BR><B>À :</B>
sls-ngu@mailman.ccsds.org; sls-hru@mailman.ccsds.org<BR><B>Cc :</B>
Gian.Paolo.Calzolari@esa.int<BR><B>Objet :</B> [Sls-ngu] Consideration of
data compression as a topic for discussion in NGU meeting<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=WordSection1>
<P class=MsoNormal>All,<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Please let me know if you would be interested in having a
discussion on the use of data compression as a technique towards conserving
bandwidth on the uplink.<o:p></o:p></P>
<P class=MsoNormal>In other words, do you think compression is likely to be a
big payoff and manageable, and worthy of inclusion in a CCSDS NGU standard, etc.
?<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>A current example of using compression on the uplink is the
NASA Mars Science Laboratory Project which is tentatively planning to use one of
the Lempel Ziv (LZ) encoders for compressing flight software loads.
<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Data compression could be another technique that the NGU WG
should consider for standardization for NGU applications. Considering that the
CCSDS Convolutional Code can approximately provide about a 5 db gain, and the
LDPC about 7 db. if we can get 3+ db from compression it might be a
worthwhile contender for consideration.<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>So this additional work could manifest itself by involving
agency collaboration on studying the various compression candidates for use on
the uplink. If that is the case, then NGU would need support from the MHDC WG in
supporting such a study.<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Some of the question we could consider asking ourselves
are:<o:p></o:p></P>
<P class=MsoNormal> <o:p></o:p></P>
<P class=MsoNormal>(1) Can we come up with uplink data sets that are good
examples of the type of uplink data that requires compression and that
compresses well?<o:p></o:p></P>
<P class=MsoNormal>(2) How much improvement might we get from different
variations of compression algorithms on the data types that are worth studying
?<o:p></o:p></P>
<P class=MsoNormal>(3) Have we convinced ourselves that the NGU data volume
problem is significant enough in the first place to warrant compression
?<o:p></o:p></P>
<P class=MsoNormal>(4) Is 2:1 lossless compression our goal ?<o:p></o:p></P>
<P class=MsoNormal>(5) What are the candidate compression algorithms and what
are the metrics to judge them by ?<o:p></o:p></P>
<P class=MsoNormal>(6) I don't know how much interest there is from other CCSDS
member agencies on this topic <SPAN
style="FONT-FAMILY: 'Times New Roman','serif'">–</SPAN> please let me
know.<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>If I get positive feedback from member agencies on this
survey, then I will pass this along to the MHDC WG to see if we can start up an
email dialog with them before the London meeting and also schedule some time in
London if necessary to meet with them.<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Best regards,<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Greg Kazz<o:p></o:p></P>
<P class=MsoNormal>Chairman CCSDS NGU WG
<o:p></o:p></P></DIV></BODY></HTML>