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

Fri Jun 26 12:08:46 UTC 2020

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>
To:     "Enrico.Vassallo at esa.int" <Enrico.Vassallo at esa.int>, 
"sls-rfm at mailman.ccsds.org" <sls-rfm at mailman.ccsds.org>, "Border, James S 
(JPL-335D)[Jet Propulsion Laboratory]" <james.s.border at jpl.nasa.gov>
Cc:     "Kazz, Greg J (JPL-312B)[Jet Propulsion Laboratory]" 
<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> On Behalf Of 
Enrico.Vassallo at esa.int
Sent: Monday, June 22, 2020 5:32 AM
To: sls-rfm at mailman.ccsds.org; Border, James S (JPL-335D)[Jet Propulsion 
Laboratory] <james.s.border at jpl.nasa.gov>
Cc: Kazz, Greg J (JPL-312B)[Jet Propulsion Laboratory] 
<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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