[Sea-sa] Notes from 6 Apr 21 SEA-SA webex. SCCS-ARD subset discussion

Shames, Peter M (US 312B) peter.m.shames at jpl.nasa.gov
Tue Apr 6 22:10:50 UTC 2021

Dear SCCS-ARD subset,

During yesterday’s WebEx session we spent most of the time discussing the issue of how to handle, specifically in Sec 6 of the document, the issue of the added complexities introduced by the publication of the SCCC and DVB-S2 combined coding / modulation / VCM Blue Books and the more recent publication of the VCM Blue Book 431x0.  There has been a lot of side discussion with the SLS Area experts on the best way to represent these newer “combined layer” protocols, and a very complicated “Spaghetti” diagram was provided by them.  This diagram combines all of the “normal” layer by layer specs, application data structures (packets), space data links (all five of them, now including USLP), the three different “normal” coding and sync standards (TM, TC, Prox), and the RFM 401x0 book.

The attached PPT file has this updated spaghetti diagram (pg 4) and we spent quite some time discussing it.  It has the advantage of covering a lot of standards “territory”.  It has the disadvantages of both introducing a lot of complexity and hiding a lot of special cases that must be understood.  And it does not really address optical comm, ranging & D-DOR, or the complexities relating to just which of the many paths are allowed in different circumstances, nor which of the available modulations and physical layer frequencies may be used with the different directions (fwd, ret, cross), and, especially, which of the higher order modulations (HOM) from the various “VCM” options are applicable, and when.

After analyzing this diagram, and then doing a deep dive into these three “VCM” specs, John Pietras produced a new “integrated VCM” diagram.  This leverages some of the concepts newly introduced in the 431x0 Blue Book, which states:

The purpose of this Recommended Standard is to specify various combinations of coding and modulations in references [1], [2], [4], and [5], that can operate under the VCM protocol defined in references [2] and [4]. This enables, for example, some of the CCSDS recommended channel codes (reference [1]) and modulations (reference [5]) to be used with the CCSDS VCM protocol. The main applications are for space missions that need high data rate telemetry, or that operate in dynamic environments.

When VCM is used, the use is to follow this VCM Recommended Standard, which is compatible with references [2] and [3]. This Recommended Standard does not require all transmissions to use a VCM protocol. For example, CCSDS telemetry codes in reference [1] and the modulations in reference [5] may be used without a VCM protocol.
As such, this new VCM document effectively integrates all three of the optional VCM specs into one document.  This is convenient for us since we can choose to use the 431x0 document as the framework for describing this collection of related standards that support VCM, and it already does a decent job of describing how they fit together.  What it misses is an integrated diagram, but we think that John’s new diagram, pg 5 in the attached, does a great job of handling that.  Please review it and provide any needed feedback on this and other pages.

We are proposing to tackle this set of issues in the following way:

  1.  In the core of Sec 6 address the “normal” packet data, data link, coding, modulation, and physical (RF) layer flows
  2.  Cover these in Table 6-8 that addresses all of the complexities (at this ‘level’) with the necessary “if this then that, but not that” explanations
  3.  Provide a diagram (like pg 2 in the attached file) that shows these “normal” layered configurations and supports that discussion
  4.  Add a one-line reference in Table 6-8 that points to a subsection that explicitly addresses how optical comm fits in
  5.  Add a one-line reference in Table 6-8 that points to a subsection that explicitly addresses how the VCM protocol subset fits in
  6.  Provide diagrams (like pgs 3 & 5 in the attached file) that shows these VCM specific configurations and a page that supports the discussion of open questions, pg 6
  7.  Update the radiometric section to address issues with standard regen or PN ranging, telemetry ranging, and D-DOR
  8.  Provide a diagram (like pgs 7 in the attached file) that shows these specific ranging configurations and supports the discussion of open questions, pg 8
  9.  Consider how to handle the new Time Management WG efforts.  These might well be described in an adapted version of the pg 7 diagram that shows a Time Reference on the Spacecraft too, and describes the time exchange, correlation, and synchronization in that context.  Comments on this are solicited.

We want to call your attention, on pgs 6 & 8, to some open questions that have come up as we dug more deeply into all of this.   These questions will need to be explored in more depth since they appear to be disconnects between what is actually documented and what is needed for a fully interoperable, and cross supportable, set of specifications.

Lastly, we had a discussion about whether to have a set of working meetings in the next month or if we should just plan for a special overview meeting of the planned changes and their impacts on the documents that would specifically be aimed at the SLS and CSS areas, since they are most directly affected by the work we have done so far.  Feedback on this is also solicited, and we will make this request of those affected areas and WGs directly.

Thanks, Peter

From: John Pietras <john.pietras at gst.com>
Date: Monday, April 5, 2021 at 6:24 AM
To: Peter Shames <peter.m.shames at jpl.nasa.gov>
Subject: [EXTERNAL] Proposed updated spaghetti diagram

Hi, Peter. I don’t know if you will read this before this morning’s ARD session, but I’ve taken a stab at simplifying the spaghetti diagram to take advantage of the CCCSDS VCM Protocol BB being one at over-arches SCCC, DVB-S2, and “VCM TM S&CC”. I think this approach will let us more-easily abstract and sequester the VCM variants in the ADD. Of course I’ll explain more when in the session.

Talk to you soon.


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