[Sea-sa] SLS reply: Notes on VCM, DVB-S2, and SCCC

Wed Apr 7 15:36:56 UTC 2021

Gian Paolo,
Thanks for the thoughtful response to my questions. I would like to clarify my references to CCSDS 415, which I intended to use as an example of something other than CCSDS 401.0, more than as an explicit target RF & Mod standard.

Until CCSDS introduced VCM, it was simple and appropriate to align the CCSDS Sync and Channel Coding (S&CC) and RF & Mod Recommended Standards with the S&CC Sublayer and Physical Layer (respectively) of the CCSDS layered model. The

Conveniently, in the case of CCSDS 401, both the modulation and RF aspects of the space Physical Layer are addressed, so that any protocol profile that places a non-VCM S&CC on top of 401 does indeed address everything, including the RF requirements needed to produce (as called in CCSDS 231.0) "Modulated Radio Waveforms".

However, in the case of VCM Type 1* (i.e., SCCC-style VCM), contrary to the depiction of the VCM protocols corresponding to the full CCSDS Physical Layer, the recommendations do not address the RF aspects of the Physical Layer. As you confirmed below, CCSDS 401.0 is normatively cited only with respect to the modulation definitions. CCSDS 131.2 and 431.1 are mute on RF requirements.
[*I am uncertain about whether this claim also applies to VCM Type 2 (i.e., DVB-S2-style VCM). If the DVB-S2 specifications define all of the RF aspects and those RF aspects are appropriate to civil space applications, then this is NOT an issue for Type 2 VCM. ]

My use of 415 as a "straw man" alternative was perhaps not the best example. But what I was attempting to address is that, at least for Type 1 VCM, there is no indication of the requirements or expectations regarding RF. I am not an "RF person", so perhaps the answer is so obvious to any practitioner in the field that is not necessary to "state the obvious". However, from my past protocol work I am used to writing statements about  requirements on "the underlying layer", and from my SLE/CSTS work I am used to specifying the requirements on the underlying production process. It seems strange to me to just leave the RF aspects unaddressed (even by reference) in documents that are nominally supposed to address them.

Finally, here are two more observations that I forgot to include in my earlier email:

1)     CCSDS 131.2-B-1 (Flexible Advanced Coding ... ) specifies that transfer frames be pseudo-randomized before the ASMs are attached to create CADUs. CADUs are the appropriate term because pseudo-randomization is applied to the frames.

CCSDS 431.1-B-1 (VCM Protocol) splits the functionality into "SMTF Stream Generation" and "VCM Protocol", but only the VCM Protocol is normatively addressed. SMTF Stream Generation is only discussed informatively (in section 3.1 - DISCUSSION), where it is described as simply being the attachment of ASMs directly to the transfer frames to create appropriately-named SMTFs. In the case of Type 1 VCM using SCCC codes, this ignores the pseudo-randomization requirement of CCSDS 131.2-B-1. Is that randomization requirement no longer in effect? If it is in effect, CCSDS 431.1-B-1 should be updated to address it. Would the randomization requirement apply to only Type 1 VCM using SCCC, or to Type 1 VCM using TM codes as well?

2)     The list of Managed Parameters in CCSDS 431.1 (VCM Protocol) specifies five managed parameters, CCSDS 131.2-B-1 (SCCC) specifies seven managed parameters, and CCSDS 131.3-B-1 (CCSDS SLP over DVB-S2) specifies twelve managed parameters. If CCSDS 431.1 encompasses CCSDS 131.2-B-1 and CCSDS 131.3-B-1, it seems as though its list of managed parameters should include more parameters from those other "component" Blue Books (e.g., Baseband pulse shaping roll-off factor and Scrambling code number?).

Thanks again for your consideration of my questions and observations.

Best regards,
John

From: Gian.Paolo.Calzolari at esa.int [mailto:Gian.Paolo.Calzolari at esa.int]
Sent: Tuesday, April 6, 2021 6:43 PM
To: John Pietras <john.pietras at gst.com>
Cc: sea-sa at mailman.ccsds.org; Jon Hamkins <jon.hamkins at jpl.nasa.gov>; Dudal Clement <Clement.Dudal at cnes.fr>; Lee, Dennis K (332G) <dennis.k.lee at jpl.nasa.gov>; Enrico.Vassallo at esa.int; Gilles.Moury at cnes.fr; Andrews, Kenneth S(332B) <Kenneth.S.Andrews at jpl.nasa.gov>; Massimo.Bertinelli at esa.int; Andrea.Modenini at esa.int
Subject: SLS reply: [Sea-sa] Notes on VCM, DVB-S2, and SCCC

John,
        after some coordination  with other SLS representatives, please find here below mixed in your text (marked in bold red  and starting with >>>).

Further clarifications may follow.

Best regards

Gian Paolo

PS Please consider that Monday 6 April was a Public Holiday in most of Europe.

From:        "John Pietras" <john.pietras at gst.com<mailto:john.pietras at gst.com>>
To:        "sea-sa at mailman.ccsds.org<mailto:sea-sa at mailman.ccsds.org>" <sea-sa at mailman.ccsds.org<mailto:sea-sa at mailman.ccsds.org>>
Date:        31-03-21 17:53
Subject:        [Sea-sa] Notes on VCM, DVB-S2, and SCCC
Sent by:        "SEA-SA" <sea-sa-bounces at mailman.ccsds.org<mailto:sea-sa-bounces at mailman.ccsds.org>>
________________________________

SEA-SAWG colleagues ---

I've been wading through the Flexible Advanced Coding and Modulation Scheme for High Rate Telemetry Applications Blue Book (CCSDS 131.2-B-1, March 2012, hereinafter referred to as SCCC [for Serial Concatenated Convolutional Code]), CCSDS Space Link Protocols Over ETSI DVB-S2 Standard (CCSDS 131.3-B-1, March 2013, hereinafter simply referred to as CCSDS/DVB-S2), and Variable Code Modulation Protocol (CCSDS 431.1-B-1, February 2021) and comments from reviewers of the ARD table 6-8, trying to understand the relationships among these various VCM schemes.

This email recaps my observations and the questions that my reading has raised. Ultimately my concern is to be able to represent this area correctly (albeit abstractly) in the SCCS-ARD. I would very much appreciate any feedback about the correctness of my interpretations.

>>> SLS do appreciate do appreciate your concern to correctly represent this.

A.     SCCC (CCSDS 131.2-B-1, March 2012)

The SCCC protocol stack diagram  (figure 2-1) indicates the it covers the CCSDS Sync and Channel Coding Sublayer and the Physical Layer:

[cid:image001.gif at 01D72B93.AD6986C0]

An introductory paragraph that precedes this diagram states "The Synchronization and Channel Coding Sublayer provides methods of

synchronization and channel coding for transferring Transfer Frames over a space link while the Physical Layer provides the RF and modulation methods for transferring a stream of bits over a space link in a single direction."

However, the SCCC specification addresses only some aspects of the Physical Layer -  specification of the five modulation schemes to be used as part of SCCC:

1)     QPSK (specified by cross reference to the appropriate definition in CCSDS 401.0):

2)     8PSK

3)     16APSK

4)     32APSK

5)     64APSK

and coding rates.

The "RF" aspects of the Physical Layer of a space link (frequency bands, polarization, etc., etc.) are not mentioned at all. So the protocol stack diagram is at least partially misrepresentative. There should be another "RF Physical sublayer" under the Flexible Advanced Coding and Modulation Scheme for High Rate Telemetry Applications "layer". But this raises another issue - what CCSDS Blue Books (or what parts of what CCSDS Blue Books) would constitute such an RF Physical sublayer? CCSDS 401.0 is referenced, but only with respect to the specification of QPSK modulation. Is it assumed that 401.0 supplies the underlying RF functions? CCSDS also has CCSDS 415.1 (Data Transmission and PN Ranging for 2 GHz CDMA Link via Data Relay Satellite) - is SCCC viable for use over 415.1 links? [Note - the SCCS-ARD does not include CCSDS 415.1 because it is currently used only for the NASA TDRSS-based Space Network. But the authors of the SCCC book should not ignore the implications for use of SCCC over something other than 401.0, and how to address such possible wider usage in the SCCC blue book.]

>>> Indeed 401.0-B ( https://public.ccsds.org/Pubs/401x0b31.pdf<https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpublic.ccsds.org%2FPubs%2F401x0b31.pdf&data=04%7C01%7Cjohn.pietras%40gst.com%7Cb7448a0473974ee7623808d8f94d6683%7C17917f83951e48839dd6b11685623b38%7C1%7C0%7C637533458127636936%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=YRis4GezmVt1wc%2B%2BRfwT0o45lsOdiinZC8qu8W0TuZo%3D&reserved=0> ) contains other regulations in addition to modulations. This is visible in section 1.4 DOCUMENT FORMAT. By convention those other conventions are never mentioned explicitly in the standards referring to 401.0-B. It is clear that modulations are not used ignoring the rest of the regulations and this is considered implicit and it has never given implementation problems.

>>> SCCC in NOT intended for use over 415.1 links. In fact, that book is not mentioned in SCCC.

Some other observations:

a)     The book - written in 2012 - normatively references only the TM and AOS space data link protocols. SCCC depends on the use of the Frame Error Control Field (as defined in the TM and AOS SDLPs) to perform Frame Validation. SCCC is also expected to be used to carry fixed-length USLP frames, so USLP (at least the specification of the FECF in the USLP frame) is normative on the SCCC. >>> SCCC is going to add USLP Frames and the normative references will be listed together with TM SDLP and AOS. Andrea Modeninini as book Editor is preparing the relevant draft.

b)     In section 2.3 (Internal Organization), the document describes the Sending End (section 2.3.1) using diagrams of the individual functions involved and the "stream format at different stages of process". However, the description of the Receiving End (2.3.2) consists of "At the receiving end, the Synchronization and Channel Coding Sublayer accepts a continuous and contiguous stream of physical channel symbols, performs functions selected for the mission, and delivers Transfer Frames to the Data Link Protocol Sublayer." Besides saying nothing about how this is done, this description is inconsistent with the declared scope of SCCC as performing functions in in the Physical Layer as well as the Synchronization and Channel Coding Sublayer. >>> In a few cases some remarks on the receiving side are mentioned when relevant, however, specification of receivers is not part of our standards. The output at the sending side shall be unique while at the receiving side several algorithm can be used to correctty process the received stream. This is valid for decoding, demodulation, decompression, decrypt, etc.  >>> However you are correct, the book will mention that also the receiving side performs functions in in the Physical Layer and in the Synchronization and Channel Coding Sublayer.

c)     Section 7.1.1 states "Frame synchronization is necessary for subsequent processing of the Transfer Frames. Furthermore, it is necessary for synchronization of the pseudo-random generator, if used (see section 8).} [italicization mine]. Section 8.1 states "The Pseudo-Randomizer defined in reference [1] is always required by SCCC". The "if used" qualifier in 7.1.1 seems superfluous since 8.1 says that it must be used, and could lead to misunderstanding that randomization might be optional.  >>> Andrea Modeninini as book Editor is preparing the relevant draft and will take of this editorial improvement.

d)     This is a nit-pick, but the acronyms "PSK", "QPSK", and "APSK" are never spelled out or listed in the acronym list. I already knew what "PSK" and "QPSK" stood for, but had to Google "APSK" to get "amplitude and phase shift keying".  >>> Andrea Modeninini as book Editor is preparing the relevant draft and will take of this editorial improvement together with Tom Gannett for completing the list of acronyms.

I see from the CCSDS Framework that an update to this document is underway. Perhaps these comments will be useful  to the C&S WG.

B.     CCSDS/DVB-S2 (CCSDS 131.3-B-1, March 2013)

The following figure is presented in the Blue Book to relate the functions defined in the CCSDS/DVB-S2 Blue Book to the OIS and CCSDS layered models:

[cid:image002.gif at 01D72B93.AD6986C0]

Other than the relatively-simple "CADU Stream Generation" sublayer, the great majority of the functionality of this book is specified by reference to the DVB-S2 specification that was in effect as of the time of specification of this Recommended Standard, which is given in the normative References as

[1]  Digital Video Broadcasting (DVB); Second Generation Framing Structure, ChannelCoding and Modulation Systems for Broadcasting, Interactive Services, News Gathering and other Broadband Satellite Applications. ETSI EN 302 307 V1.2.1 (2009-08). Sophia-Antipolis: ETSI, 2009.

NOTE - ETSI standards are available for free download at http://www.etsi.org<https://nam12.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.etsi.org%2F&data=04%7C01%7Cjohn.pietras%40gst.com%7Cb7448a0473974ee7623808d8f94d6683%7C17917f83951e48839dd6b11685623b38%7C1%7C0%7C637533458127646928%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=oqb1o%2B%2Bt6s6tGyfPS7cejjQbirekhC7ACYOhbu9426Q%3D&reserved=0>.

In attempting to use the link to obtain a copy of the document, I searched on the document number (ETSI EN 302 307 V1.2.1). There was no document with this number available, but three with variations on the number:

-        DVB-S2: ETSI EN 302 307 V1.3.1 (2013-03),

-        DVB-S2, Part1, DVB-S2: ETSI EN 302 307-1 V1.4.1 (2014-11), and

-        DVB-S2, Part2, DVB-S2 Extensions: ETSI EN 302 307-2 V1.2.1 (2020-08).

My interpretation is that the Part 1 (2014) and Part 2 (2020) versions are replacements for the 2008 and 2013 DVB-S2 (no parts) version and update (respectively), although the documents don't say that in so many words. Without a better understanding of the applicable technologies, I am unable to determine (or even guess) which Parts (1, 2, or both) are applicable to the use of DVB-S2 for the encoding and transmission of CCSDS SDLP frames. >>> CNES has prepared an updated document that should start soon Agency Review.  The CMC Approval versuon still refernces ETSI EN 302 307 V1.2.1. I think that the standard is really intended for use with V1.2.1 and not with later versions.

I am unable to say for certain, but it also appears that neither the Part 1 nor the Part 2 specifications address complete set of RF requirements to a level similar to that found in CCSDS 401.0. If my impression is correct in this respect, as with the SCCC book it is somewhat incorrect to imply that the DVB-S2 specifications address all aspects of the Physical Layer, as is implied by Figure 2-1 (copied above). Again, should there be some "RF Physical sublayer" under the DVD-S2 transmission sublayer? And if so, are some subset of functions defined in CCSDS 401.0 assumed to satisfy the requirements for that RF Physical sublayer? What about DVB-S2 "over" CCSDS 415.1 links?

>>> Please consider the SCCC reply above for 401.0-B.

C.     VCM Protocol (CCSDS 431.1-B-1, February 2021)

Figure 2-1 of the VCM Protocol Blue Book is:

[cid:image003.gif at 01D72B93.AD6986C0]

Note that the "SMTF Stream Generation" function/sublayer is exactly the same as the "CADU Stream Generation" function/sublayer of the CCSDS/DVB-S2 Blue Book: "SMTF" is the more-appropriate term for a transfer frame that is pre-pended with an ASM, whereas "CADU" in general allows the possibility of intermediate encoding being applied before the ASM.  >>> C&S WG may consider using a uniform term. Andrea & Ken may consider thois point of discussion.

Regarding the VCM Protocol itself, the blue book specifies three sets of  "modes":

-        Modes that apply to CCSDS Turbo and LDPC encoding (a subset of, and as defined in, CCSDS 131.0-B). These are the "TM" codes;

-        Modes that apply to SCCC encoding. These modes are "consistent with the existing specification of codes, modulations, and VCM protocol given in references [2] [SCCC Blue Book] and [5] [CCSDS 401.0]"; and

-        Modes that apply to CCSDS DVB-S2 encoding.  These mode are "consistent with the existing specification of codes, modulations, and VCM protocol given in references [3] [CCSDS/DVB-S2], [4] [the 2014 version of DVB-S2: Part 2], and [5] [CCSDS 401.0]".

Type 2 VCM has a set of modes that apply to CCSDS Turbo and LDPC coding schemes (as defined in CCSDS 131.0-B) and a different set of codes for DVB-S2. The difference between Type 1 and

The VCM BB defines two VCM protocol "Types": Type 1 and Type 2. The two Types differ in the values for the parameters H (the length of the PLFRAME header, S (the number of codeword modulation symbols between pilot symbol blocks), and P (the number of modulation symbols present in each optional symbol block). Type 1 uses the H/S/P values that have already been defined in the SCCC Blue Book, and Type 2 uses the H/S/P values that have already been defined in the CCSDS/DVB-S2 Blue Book and the ETSI DVB-S2: Part 2 standard.

What the VCM Blue Book specifies uniquely is the use of TM Turbo and LDPC encoding, which is defined for both VCM Type 1 and VCM Type 2. However, the material regarding SCCC encoding and DVB-S2 encoding appears to me to be simply a restatement of existing material that is already normatively stated in the SCCC Blue Book, CCSDS/DVB-S2 Blue Book, and the ETSI DVB-S2: Part 2 standard. Is there is something that the VCM Protocol BB adds to the existing standards? >>>  The 431.1-B VCM standard does not alter the specification of the 131.2-B and 131.3-B VCM protocols. This means that a user of SCCC or DVB-S2 codes compliant with 131.2-B or 131.3-B will also comply with 431.1-B. The 431.1-B book puts the VCM protocol under a common umbrella to help explain how to use TM codes with either of the SCCC or DVB-S2 approaches to VCM. This has the side benefit of showing that there really is one common VCM approach in CCSDS..

The fact that the VCM Protocol book restates and in a sense co-opts the SCCC and CCSDS/DVB-S2 Blue Books can lead to ambiguity.

>>>  This situation is no different than the 401.0-B incorporating the definitions of the higher order modulations which are already described in 131.2-B and 131.3-B. They are the same, so there is no ambiguity.

When one refers to "CCSDS VCM", should that be interpreted as a blanket reference to "TM VCM", SCCC VCM, and DVB-S2 VCM, or do we want to continue to cull out the different flavors separately? For the purposes of the SCCS-ARD, we might want to just use "CCSDS VCM" to collectively refer to all flavors, with a single reference to CCSDS 431.1, and have a separate (simple, high-level) "discussion" of the components of that collective protocol. That will certainly make the tables in the ARD simpler. >>> Agreed. There really is only one approach to VCM in CCSDS. OK for SCCS-ARD to just use "CCSDS VCM" to collectively refer to all flavors. However referincg may better include all the books for those willing to look at the details .

Finally, as with the SCCC and CCSDS/DVB-S2 blue books, the VCM Protocol Blue Book does not address the RF aspects of the Physical Layer. The same questions apply about whether an RF Physical sublayer should be called out, whether and what aspects of CCSDS 401.0 meet the requirements for such a sublayer, and whether other space link physical layer specifications (such as CCSDS 415) can be used for VCM. >>> Please consider the SCCC reply above for 401.0-B.

Best regards,

John

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