<span style=" font-size:10pt;font-family:sans-serif">Victor,</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">I must say that
I do not understand your proposal. The document you mention is not one
that is affected by the proposal in SLS-CS_20-03 in the first place.</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">Anyway, I think
we should proceed with agency review of REC 2.5.7B assuming I do not get
other comments today. I would use the version just sent out by Jim, having
just encapsulated the latest inclusion in a note since this is not normative
as suggested by our beloved AD.</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">The PN action
is due next September, so we have time to discuss.</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">Cheers, Enrico</span>
<br>
<br>
<br>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">From:
</span><span style=" font-size:9pt;font-family:sans-serif">"Sank,
Victor J. (GSFC-567.0)[SCIENCE SYSTEMS AND APPLICATIONS INC]" <victor.j.sank@nasa.gov></span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">To:
</span><span style=" font-size:9pt;font-family:sans-serif">"Enrico.Vassallo@esa.int"
<Enrico.Vassallo@esa.int>, "sls-rfm@mailman.ccsds.org"
<sls-rfm@mailman.ccsds.org>, "Border, James S (JPL-335D)[Jet
Propulsion Laboratory]" <james.s.border@jpl.nasa.gov></span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Cc:
</span><span style=" font-size:9pt;font-family:sans-serif">"Kazz,
Greg J (JPL-312B)[Jet Propulsion Laboratory]" <greg.j.kazz@jpl.nasa.gov></span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Date:
</span><span style=" font-size:9pt;font-family:sans-serif">25/06/20
21:14</span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Subject:
</span><span style=" font-size:9pt;font-family:sans-serif">RE:
[EXTERNAL] [Sls-rfm] CCSDS RFM WG AI_20-01 (PN register convention)</span>
<br>
<hr noshade>
<br>
<br>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;color:#004080;font-family:Calibri">Enrico,</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;color:#004080;font-family:Calibri">
I have a very simple solution
to the issue of PN generator diagrams and the associated polynomial. Do
not state the polynomial in CCSDS documents. </span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;color:#004080;font-family:Calibri">
In our CCSDS books we always
show the generator diagram which is (unique) necessary and sufficient.
</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;color:#004080;font-family:Calibri">We
can avoid the editing issue by not changing the existing books but going
forward, let’s not publish the ambiguous polynomial. At least one
of our books shows the generator diagram and never states a polynomial
(414.1-B).</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;color:#004080;font-family:Calibri"> </span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;color:#004080;font-family:Calibri">The
generator shift register diagram (Fibonacci, Galois, Gold) produces a unique
pattern and in a specific direction of flow. The polynomial is ambiguous.
For maximal patterns there are two polynomials that produce patterns
with the same statistic but when represented as a bit pattern, the bit
flow is in opposite directions. When doing abstract algebra, this
may not matter. When used in communications, it does matter. For
example a communications de-randomizer must flow in the same direction
at the randomizer. In the case where a pattern is truncated, using
the same starting point, the statistics will be different depending on
the flow direction. </span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;color:#004080;font-family:Calibri">Thanks,</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;color:#004080;font-family:Calibri">Victor</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;color:#004080;font-family:Calibri"> </span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:11pt;font-family:Calibri"><b>From:</b>
SLS-RFM <sls-rfm-bounces@mailman.ccsds.org> <b>On Behalf Of </b>Enrico.Vassallo@esa.int<b><br>
Sent:</b> Monday, June 22, 2020 5:32 AM<b><br>
To:</b> sls-rfm@mailman.ccsds.org; Border, James S (JPL-335D)[Jet Propulsion
Laboratory] <james.s.border@jpl.nasa.gov><b><br>
Cc:</b> Kazz, Greg J (JPL-312B)[Jet Propulsion Laboratory] <greg.j.kazz@jpl.nasa.gov><b><br>
Subject:</b> [EXTERNAL] [Sls-rfm] CCSDS RFM WG AI_20-01 (PN register convention)</span></p>
<p style="margin-top:0px;margin-Bottom:0px"><span style=" font-size:12pt;font-family:Times New Roman"> </span></p>
<p style="margin-top:0px;margin-Bottom:240px"><span style=" font-size:10pt;font-family:Arial">Dear
All,</span><span style=" font-size:12pt;font-family:Times New Roman"> <br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
please find my response <b>as both ESA representative in RFM WG and as
RFM WG chair</b> to the action item:</span><span style=" font-size:12pt;font-family:Times New Roman">
<br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
AI_20-01 Report about the PN register proposal
in CS_20-03, the possible need to have a similar standard representation
and, in case, the preferred way forward</span><span style=" font-size:12pt;font-family:Times New Roman">
<br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
Input paper CS_20-03 recommends changes to the following RFM WG books:
</span><span style=" font-size:12pt;font-family:Times New Roman"><br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
1) 415.1-B-1, dated 2011</span><span style=" font-size:12pt;font-family:Times New Roman">
<br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
2) 415.1-G-1, dated 2013</span><span style=" font-size:12pt;font-family:Times New Roman">
<br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
3) 401.1-B REC 2.5.7B-white</span><span style=" font-size:12pt;font-family:Times New Roman">
<br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
Document CS_20-03 proposes to adopt the Matlab convention. <br>
Main differences between what's in documents 1-3 and the proposal in CS_20-03
is the fact that in the pictures the output register is numbered N in 1-3
as opposed to 0 in the proposal; additionally, the first register is numbered
1 (zero is not used in 1-3).</span><span style=" font-size:12pt;font-family:Times New Roman">
<br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
Documents 1-2-3 are consistent. <br>
Document 2 (green book) provides in page 3-3 a detailed explanation of
the convention used, addresses different conventions in literature, and
links the drawing of the picture with resulting equations and polynomials.
This info is in sections 3.4 to 3.8.</span><span style=" font-size:12pt;font-family:Times New Roman">
</span><span style=" font-size:10pt;font-family:Arial"><br>
Document 1 (blue book) provides some explanation of the convention used
in section 1.6.2.</span><span style=" font-size:12pt;font-family:Times New Roman">
</span><span style=" font-size:10pt;font-family:Arial"><br>
Document 3 has two pictures in Annex A with no explanation while the polynomials
are in the main body of the recommendation. </span><span style=" font-size:12pt;font-family:Times New Roman"><br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
Documents 1-2 were mainly NASA's (GFSC) inputs aimed at extending the SNIP
agreement (latest version from 1998) between ESA, NASA and NASDA (now JAXA)
for which the latest version dates November 1998 to encompass more CCSDS
agencies.</span><span style=" font-size:12pt;font-family:Times New Roman">
<br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
The change request in CS_20-03 would entail editing the following number
of pictures: 5 (doc 1) + 10 (doc 2) + 2 doc (3) = 17 in addition to adjusting
the related text.</span><span style=" font-size:12pt;font-family:Times New Roman">
<br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
Given that documents 1 and 2 have been used for almost a decade with no
report of implementation mistakes by ESA equipment developers, and the
changes in CS_20-03 would result in full disagreement with the SNIP document,
it is proposed NOT to adopt the Matlab convention for the RFM WG books.
However, concerning the draft DDOR recommendation 2.5.7B under development,
some explanation could be added as done in 1 (or even in 2.)</span><span style=" font-size:12pt;font-family:Times New Roman">
<br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
It is possible that other WGs of the SLS area may prefer a different approach
for their books but as long as the recommendations of the same WG are consistent,
I do not see this as an issue.</span><span style=" font-size:12pt;font-family:Times New Roman">
<br>
</span><span style=" font-size:10pt;font-family:Arial"><br>
Best Regards, Enrico </span></p>
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