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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Enrico,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> 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.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> In our CCSDS books we always show the generator diagram which is (unique) necessary and sufficient.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">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).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">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.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Victor<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> SLS-RFM <sls-rfm-bounces@mailman.ccsds.org>
<b>On Behalf Of </b>Enrico.Vassallo@esa.int<br>
<b>Sent:</b> Monday, June 22, 2020 5:32 AM<br>
<b>To:</b> sls-rfm@mailman.ccsds.org; Border, James S (JPL-335D)[Jet Propulsion Laboratory] <james.s.border@jpl.nasa.gov><br>
<b>Cc:</b> Kazz, Greg J (JPL-312B)[Jet Propulsion Laboratory] <greg.j.kazz@jpl.nasa.gov><br>
<b>Subject:</b> [EXTERNAL] [Sls-rfm] CCSDS RFM WG AI_20-01 (PN register convention)<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Dear All,</span>
<br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">please find my response
<b>as both ESA representative in RFM WG and as RFM WG chair</b> to the action item:</span>
<br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">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>
<br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">Input paper CS_20-03 recommends changes to the following RFM WG books:
</span><br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">1) 415.1-B-1, dated 2011</span>
<br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">2) 415.1-G-1, dated 2013</span>
<br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">3) 401.1-B REC 2.5.7B-white</span>
<br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">Document CS_20-03 proposes to adopt the Matlab convention.
</span><br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">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> <br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">Documents 1-2-3 are consistent.
</span><br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">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> <br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">Document 1 (blue book) provides some explanation of the convention used in section 1.6.2.</span>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">Document 3 has two pictures in Annex A with no explanation while the polynomials are in the main body of the recommendation.
</span><br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">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> <br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">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>
<br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">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>
<br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">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>
<br>
<br>
<span style="font-size:10.0pt;font-family:"Arial",sans-serif">Best Regards, Enrico
</span><o:p></o:p></p>
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