<span style=" font-size:10pt;font-family:sans-serif">Dear Peter,</span>
<br><span style=" font-size:10pt;font-family:sans-serif">
I must say that I am quite puzzled by this mail.</span>
<br><span style=" font-size:10pt;font-family:sans-serif">I still need to
digest all the aspects of your message, however I can ensure that SLS (with
proper coordination) will try to provide some punctual technical comments
on the individual items.</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">Here, after a
check with SLS colleagues, I want to comment on your statement about the
</span><span style=" font-size:11pt;font-family:Calibri">“3-layer sandwich”
</span><span style=" font-size:10pt;font-family:sans-serif">.</span>
<br><span style=" font-size:10pt;font-family:sans-serif">Indeed that sandwich
is not so big as you claim.</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">Actually all the
following documents</span>
<br><a href=https://public.ccsds.org/Pubs/131x2b1e1.pdf><span style=" font-size:10pt;color:blue;font-family:sans-serif">https://public.ccsds.org/Pubs/131x2b1e1.pdf</span></a>
<br><a href=https://public.ccsds.org/Pubs/131x3b1.pdf><span style=" font-size:10pt;color:blue;font-family:sans-serif">https://public.ccsds.org/Pubs/131x3b1.pdf</span></a>
<br><a href=https://public.ccsds.org/Pubs/431x0b1.pdf><span style=" font-size:10pt;color:blue;font-family:sans-serif">https://public.ccsds.org/Pubs/431x0b1.pdf</span></a>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">clearly state
that "This Recommended Standard covers the functions of both the Synchronization
and Channel Coding Sublayer and the Physical Layer"; i.e. the layers
combined are two (or let's say 1 and half as one layer and one sublayer
are combined).</span>
<br><span style=" font-size:10pt;font-family:sans-serif">They all also
show this (even with some minor differences) in their "Figure 2-1:
Relationship with OSI Layers" showing together the</span>
<br><span style=" font-size:10pt;font-family:sans-serif">1) Synchronization
and Channel Coding Sublayer that provides methods of synchronization and
channel coding for transferring Transfer Frames over a space link and the
</span>
<br><span style=" font-size:10pt;font-family:sans-serif">2) Physical Layer
that provides the RF and modulation methods for transferring a stream of
bits over a space link in a single direction</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">For reference
the three figures are attached as snapshots.</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">Best regards</span>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">Gian Paolo </span>
<br>
<br>
<br><img src=cid:_1_0A24B7500A24B4E400649293C125868D style="border:0px solid;"><img src=cid:_1_0A24B9580A24B4E400649293C125868D style="border:0px solid;"><span style=" font-size:10pt;font-family:sans-serif"> </span><img src=cid:_1_0A24BBA40A24B4E400649293C125868D style="border:0px solid;">
<br>
<br>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">From:
</span><span style=" font-size:9pt;font-family:sans-serif">"Shames,
Peter M\(US 312B\) via SEA-SA" <sea-sa@mailman.ccsds.org></span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">To:
</span><span style=" font-size:9pt;font-family:sans-serif">"SEA-SA"
<sea-sa@mailman.ccsds.org></span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Date:
</span><span style=" font-size:9pt;font-family:sans-serif">02-03-21
23:37</span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Subject:
</span><span style=" font-size:9pt;font-family:sans-serif">[Sea-sa]
Background materials for today's SEA-SA SCCS-ARD discussion</span>
<br><span style=" font-size:9pt;color:#5f5f5f;font-family:sans-serif">Sent
by: </span><span style=" font-size:9pt;font-family:sans-serif">"SEA-SA"
<sea-sa-bounces@mailman.ccsds.org></span>
<br>
<hr noshade>
<br>
<br><span style=" font-size:10pt;font-family:sans-serif">[attachment "431x1b0_CESG_Approval.pdf"
deleted by Gian Paolo Calzolari/esoc/ESA] </span>
<br>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri">Dear SCCS-ARD
sub-team,</span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri">During
today’s SEA-SA SCCS-ARD discussion we spent quite a period of time discussing
the challenges in create a reasonably compact, and also accurate, table
that reflects the currently documented set of configurations that are made
available by the suite of space data link, coding, synchronization, modulation,
RF (and optical), and physical layer signaling standards. There are
many situations where there is no one, simple, statement, or even set of
statements, that can be made. We have had to resort to a tabular
presentation, Table 6-8 in Sec 6 on protocols, to address this.
A copy of this table is attached, along with the “cheat sheet” of notes
that encode the cells in this table.</span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri">Any standards
that are expected to come into being within the next 6-12 months, but that
are not yet final, are highlighted in yellow. We hope these are final
before we publish this document, but all of those dates are still rather
uncertain.</span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri">Note that
uplink is separate from downlink, that RF coding and modulation is separate
from optical coding and modulation, and that SCCC and DVB-S2 (which both
contain coding, modulation, and physical layer signaling in a single standard)
are separated from the “normal” CCSDS standards that break these into
three separate layers. The new Variable Coding and Modulation (VCM)
spec that is now in progress is also shown as a separate layer. This
VCM spec is related to the “bottom” parts of the DVB and SCCC specs,
but it is different from them in distinct ways. </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri">It became
clear during discussion that most of those on the call were unfamiliar
with the details and complexities represented in this table. Furthermore,
most are unfamiliar with the complexities inherent in the “3-layer sandwich”
that SCCC and DVB present, and with how they compare with the “normal”
CCSDS link layer, coding, synch, modulation, physical layer and RF stack.
I have attached a presentation that some of us constructed in order
to make sure that we understood what those relationships are. It
is named “SEA high rate comm issue 1Mar21” and is attached here. This
is a statement of the recent issues and also a set of diagrams comparing
these different protocol sets. It does not address optical comm.</span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri">It should
be noted that the “bottom” part of the DVB and SCCC specs includes a
specialized set of physical layer signaling mechanisms. These are
not present in normal CCSDS protocol stacks, where any choices that are
made for different coding, synchronization, and modulation combinations
are made “by management”. That phrase “by management” means that
the mission manages these choices manually, outside of the protocols themselves,
that the protocol layers contain no “signals” as to which choices were
made, and that any changes to the coding and modulation must be agreed
to and managed out of band, by pre-agreement. </span></p>
<p style="H/╝;■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style="H/╝;■"><span style=" font-size:11pt;font-family:Calibri">In the
DVB and SCCC, and in the new draft CCSDS VCM spec (CCSDS 431.1-b-1) which
is attached here as a CESG draft spec, a physical layer signaling mechanism
is introduced. VCM is defined as “<b>variable coded modulation,
VCM</b>: A method to adapt the transmission scheme to channel conditions
following a predetermined schedule. ”. This includes two separate
physical layer structures: 1) the “Pilot Symbols” and 2) the encoded
and modulated data symbols. The CCSDS 431.1 spec describes two different
VCM “types”. Type 1 uses the DVB-S2 VCM pilot symbol and data symbol
length approach, Type 2 uses the SCCC VCM pilot symbol and data symbol
length approach. These pilot symbols are, in both cases, just short
blocks of 7 bits, protected by a linear code and BPSK modulation (see attached
Table from Annex E). Five of these bits are used to identify one
of the 32 possible sets of code and modulation pairs that are applied to
the encoded and modulated symbols that follow the pilot. </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri">Where these
DVB Type 1, SCCC Type 2, and CCSDS Type 1 or 2 schemes differ is in the
length of the symbol strings and the sets of code/modulation pairs that
are allowed. </span></p>
<ul>
<li><span style=" font-size:11pt;font-family:Calibri">DVB-S2 has its own
set shown in Table 3-4. It allows different code rates, from 1 /
4 (0.25) up to 9 / 10 (0.9), different input lengths from 2992 up to 58112
bits, different modulations (QPSK, 8-PSK, 16 & 32-APSK) and its own
set of DVB-S2 codes that are patented. </span>
<li><span style=" font-size:11pt;font-family:Calibri">SCCC has its own
set shown in Table 3-3. It allows different code rates, from 0.36
up to 0.9, different input lengths from 5758 up to 43678 bits, the same
set of modulations (QPSK, 8-PSK, 16 & 32-APSK) and its own set of SCCC
codes that are patented. </span>
<li><span style=" font-size:11pt;font-family:Calibri">The CCSDS VCM has
its own set shown in Table 3-2. It allows different (CCSDS standard)
code rates, from 1 / 6 (0.16) up to 223/255 (0.875), different (CCSDS standard)
input lengths from 1748 up to 16384 bits, the same set of modulations plus
BPSK (BPSK, QPSK, 8-PSK, 16 & 32-APSK) and the standard LDPC codes.
</span>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p></ul><span style=" font-size:11pt;font-family:Calibri">You
can see that these are similar, and that the modulation set largely overlaps,
but they are different. In all cases specialized equipment will be
needed in the RF front ends to handle the pilot symbols and the continually
changing coding and modulation . The other difference is that the
CCSDS VCM expects to signal a pre-planned set of code & modulation
changes, but the SCCC and DVB-S2 also include adaptive coding and modulation
(ACM), which uses signals sent back from the receiver to the sender. To
quote from SCCC, CCSDS 131x2b1d1, Sec 3.2.7:</span>
<p style=";■"><span style=" font-size:12pt;color:#424282;font-family:TimesNewRomanPSMT">NOTE
– </span></p>
<p style=";■"><span style=" font-size:12pt;color:#424282;font-family:TimesNewRomanPSMT">Changes
of the value of the information block size </span><span style=" font-size:12pt;color:#424282"><i>K
</i></span><span style=" font-size:12pt;color:#424282;font-family:TimesNewRomanPSMT">are
done by a system to adjust the modulation and coding schemes. This is achieved
through, e.g., one of the following approaches: the ground receiver provides
the signal quality estimation (or prediction) through a feedback channel
(e.g., via telecommand) or the change of modulation and coding schemes
is pre-scheduled for each satellite pass based on geometrical information
(elevation angle). </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri">So the
SCCC may use a feedback loop, but no specific protocol appears to be specified
for this. The DVB-S2 standard, as adapted for CCSDS, makes essentially
the same statement. The full ETSI DVB-S2 spec, however, defines
an actual feedback protocol that is, in my opinion, only of use over a
near Earth (or at least a “local”) communications path where the RTLT
is sufficiently short to allow requests for data rate changes to
be responded to. This is not appropriate for use in deep space where
the RTLT may be measures in 10’s of minutes or tens of hours. They
also bring substantial added complexity which, in the general case, may
not be worth the added cost of engineering, testing, etc unless the mission
is a) in a near Earth orbit, and b) can make use of available commercial
parts.</span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri">As I suggested
during the webex, I think we must treat the following groups of standards
separately, because to do otherwise will overly complicate the core of
the CCSDS standard suite, that I estimate meets 95% of the users.</span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:10pt;font-family:sans-serif">1.
</span><span style=" font-size:11pt;font-family:Calibri">The
“CCSDS standard” suite of link layer, coding, synchronization, modulation,
and RF standards</span></p>
<p style=";■"><span style=" font-size:10pt;font-family:sans-serif">2.
</span><span style=" font-size:11pt;font-family:Calibri">A
subsection on the Optical coding and modulation standards that slot in
underneath the normal link layer protocols, along with a brief description</span></p>
<p style=";■"><span style=" font-size:10pt;font-family:sans-serif">3.
</span><span style=" font-size:11pt;font-family:Calibri">A
separate subsection on the VCM and the associated SCCC and DVB-S2 “omnibus”
standards that replace the standard CCSDS coding, synchronization, modulation
and add physical layer signaling.</span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri">If anyone
has issues with this approach please bring them up now. I think this
is the only sensible way to handle this issue of these very different approaches
to the lower layer protocols.</span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri">Thanks,
Peter</span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span></p>
<p style=";■"><span style=" font-size:11pt;font-family:Calibri"> </span><tt><span style=" font-size:10pt">_______________________________________________<br>
SEA-SA mailing list<br>
SEA-SA@mailman.ccsds.org<br>
</span></tt><a href="https://mailman.ccsds.org/cgi-bin/mailman/listinfo/sea-sa"><tt><span style=" font-size:10pt">https://mailman.ccsds.org/cgi-bin/mailman/listinfo/sea-sa</span></tt></a><tt><span style=" font-size:10pt"><br>
</span></tt></p>
<br><span style=" font-size:10pt;font-family:sans-serif">[attachment "SEA
High Rate comm issue 1Mar21.pptx" deleted by Gian Paolo Calzolari/esoc/ESA]
[attachment "CCSDS 431 VCM protocol layers.pdf" deleted by Gian
Paolo Calzolari/esoc/ESA] [attachment "CCSDS 431 VCM pilot pattern.pdf"
deleted by Gian Paolo Calzolari/esoc/ESA] [attachment "CCSDS 431 DVB
SCCC pilot approaches.pdf" deleted by Gian Paolo Calzolari/esoc/ESA]
[attachment "SCCS-ARD Table 6-8 Notes 1Mar21.pdf" deleted by
Gian Paolo Calzolari/esoc/ESA] [attachment "SCCS-ARD Table 6-8 proto
layer options.pdf" deleted by Gian Paolo Calzolari/esoc/ESA] </span>
<br>
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