[Sls-rfm] [EXTERNAL] CCSDS RFM WG AI_20-01 (PN register convention)

Fri Jun 26 13:01:32 UTC 2020

Enrico,
               Yes, the 414.0-G-2 and 414.1-B-1 documents I mentioned are not ones that is affected by the proposal in SLS-CS_20-03 in the first place because they do not have polynomials, it just has the patterns of the components..  This is exactly the point we are trying to make.  Stating the pattern or showing a diagram of the generator shift register is unique, the polynomial is not.  The 414 books are the only ones we noticed that have no ambiguity since they do not have polynomials.  Hence our suggestion to not state polynomials in future CCSDS books, unless some standard is decided upon.
Victor

From: Enrico.Vassallo at esa.int <Enrico.Vassallo at esa.int>
Sent: Friday, June 26, 2020 8:09 AM
To: Sank, Victor J. (GSFC-567.0)[SCIENCE SYSTEMS AND APPLICATIONS INC] <victor.j.sank at nasa.gov>
Cc: Kazz, Greg J (JPL-312B)[Jet Propulsion Laboratory] <greg.j.kazz at jpl.nasa.gov>; Border, James S (JPL-335D)[Jet Propulsion Laboratory] <james.s.border at jpl.nasa.gov>; sls-rfm at mailman.ccsds.org
Subject: RE: [EXTERNAL] [Sls-rfm] CCSDS RFM WG AI_20-01 (PN register convention)

Victor,

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.

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.

The PN action is due next September, so we have time to discuss.

Cheers, Enrico

From:        "Sank, Victor J. (GSFC-567.0)[SCIENCE SYSTEMS AND APPLICATIONS INC]" <victor.j.sank at nasa.gov<mailto:victor.j.sank at nasa.gov>>
To:        "Enrico.Vassallo at esa.int<mailto:Enrico.Vassallo at esa.int>" <Enrico.Vassallo at esa.int<mailto:Enrico.Vassallo at esa.int>>, "sls-rfm at mailman.ccsds.org<mailto:sls-rfm at mailman.ccsds.org>" <sls-rfm at mailman.ccsds.org<mailto:sls-rfm at mailman.ccsds.org>>, "Border, James S (JPL-335D)[Jet Propulsion Laboratory]" <james.s.border at jpl.nasa.gov<mailto:james.s.border at jpl.nasa.gov>>
Cc:        "Kazz, Greg J (JPL-312B)[Jet Propulsion Laboratory]" <greg.j.kazz at jpl.nasa.gov<mailto:greg.j.kazz at jpl.nasa.gov>>
Date:        25/06/20 21:14
Subject:        RE: [EXTERNAL] [Sls-rfm] CCSDS RFM WG AI_20-01 (PN register convention)
________________________________

Enrico,

               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.

               In our CCSDS books we always show the generator diagram which is (unique) necessary and sufficient.

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).

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.

Thanks,

Victor

From: SLS-RFM <sls-rfm-bounces at mailman.ccsds.org<mailto:sls-rfm-bounces at mailman.ccsds.org>> On Behalf Of Enrico.Vassallo at esa.int<mailto:Enrico.Vassallo at esa.int>
Sent: Monday, June 22, 2020 5:32 AM
To: sls-rfm at mailman.ccsds.org<mailto:sls-rfm at mailman.ccsds.org>; Border, James S (JPL-335D)[Jet Propulsion Laboratory] <james.s.border at jpl.nasa.gov<mailto:james.s.border at jpl.nasa.gov>>
Cc: Kazz, Greg J (JPL-312B)[Jet Propulsion Laboratory] <greg.j.kazz at jpl.nasa.gov<mailto:greg.j.kazz at jpl.nasa.gov>>
Subject: [EXTERNAL] [Sls-rfm] CCSDS RFM WG AI_20-01 (PN register convention)

Dear All,

please find my response as both ESA representative in RFM WG and as RFM WG chair to the action item:

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

Input paper CS_20-03 recommends changes to the following RFM WG books:

1) 415.1-B-1, dated 2011

2) 415.1-G-1, dated 2013

3) 401.1-B REC 2.5.7B-white

Document CS_20-03 proposes to adopt the Matlab convention.
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).

Documents 1-2-3 are consistent.
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.
Document 1 (blue book) provides some explanation of the convention used in section 1.6.2.
Document 3 has two pictures in Annex A with no explanation while the polynomials are in the main body of the recommendation.

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.

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.

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.)

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.

Best Regards, Enrico

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