CCM versus VCM


Ernst Lobsiger
 

Dear SR1 users

EUMETSAT describes HVS-2 on tranponder T2 as using CCM while we all
know transponder T1 uses VCM to send at the same time BAS + HVS-1.
EUMETSAT also says that CCM is easier to receive (less demanding)
so that potentially cheaper DVB-S2 equippment can be used for reception
of HVS-2 and future HVS-3, HVS-4 that all will use CCM only.

CCM versus VCM is singnaled in first byte of MATYPE in the BBHEADER (see page 17 of pdf).

https://www.etsi.org/deliver/etsi_en/302300_302399/302307/01.02.01_60/en_302307v010201p.pdf

Actually VCM is signaled as ACM in bit 4 counting from 0 to the left.
I patched the TBE-6909X driver to write out MATYPE info at startup.

I GET (first byte of) MATYPE=194 FOR BOTH EUMETCAST TRANSPONDERS T1 AND T2.
Decimal 194 has a dual system representation of  1 1 0 0 0 0 1 0 meaning:

- Packetized Transport Stream
- MIS yes
- ACM (VCM) yes
- ISSYI not active
- NPD not active
- RO (RollOff) 20%

So what kind of CCM and simpler DVB-S2 receivers is EUMETSAT talking about?

The SR1 has AFAIK an Rx Status page where it displays Link Adaption ACM/CCM.
If you receive HVS-2 with your SR1, what does the Link Adaption field show?


Best Regards,
Ernst


David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺
 

On 31/05/2021 17:10, Ernst Lobsiger via groups.io wrote:
The SR1 has AFAIK an Rx Status page where it displays Link Adaption ACM/CCM.
If you receive HVS-2 with your SR1, what does the Link Adaption field show?
Best Regards,
Ernst
Ernst,

I hope the information is here. I see both ACM and CCM.....

Cheers,
David
--
SatSignal Software - Quality software for you
Web: https://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv


nrd545@...
 

Hello Ernst,
please see attached screenshot of my SR1 status page receiving HVS-2.
Hope this helps.



Best regards
Wolfgang Boehmer
***************

Am 31.05.2021 um 18:10 schrieb Ernst Lobsiger via groups.io:


Dear SR1 users

EUMETSAT describes HVS-2 on tranponder T2 as using CCM while we all
know transponder T1 uses VCM to send at the same time BAS + HVS-1.
EUMETSAT also says that CCM is easier to receive (less demanding)
so that potentially cheaper DVB-S2 equippment can be used for reception
of HVS-2 and future HVS-3, HVS-4 that all will use CCM only.

CCM versus VCM is singnaled in first byte of MATYPE in the BBHEADER (see page 17 of pdf).

https://www.etsi.org/deliver/etsi_en/302300_302399/302307/01.02.01_60/en_302307v010201p.pdf

Actually VCM is signaled as ACM in bit 4 counting from 0 to the left.
I patched the TBE-6909X driver to write out MATYPE info at startup.

I GET (first byte of) MATYPE=194 FOR BOTH EUMETCAST TRANSPONDERS T1 AND T2.
Decimal 194 has a dual system representation of  1 1 0 0 0 0 1 0 meaning:

- Packetized Transport Stream
- MIS yes
- ACM (VCM) yes
- ISSYI not active
- NPD not active
- RO (RollOff) 20%

So what kind of CCM and simpler DVB-S2 receivers is EUMETSAT talking about?

The SR1 has AFAIK an Rx Status page where it displays Link Adaption ACM/CCM.
If you receive HVS-2 with your SR1, what does the Link Adaption field show?


Best Regards,
Ernst

Mit freundlichen Grüßen
Best Regards

Wolfgang Böhmer

No trees were harmed with the sending of this message,
just billions of electrons – terribly confused!


Ernst Lobsiger
 

On Mon, May 31, 2021 at 11:48 AM, <nrd545@...> wrote:
Hello Ernst,
please see attached screenshot of my SR1 status page receiving HVS-2.
Hope this helps.
David and Wolfgang,

thanks for your confirmation. It seems CCM on HVS-2 is only what EUMETSAT *thinks* it does.
It's also set in the SR1 configuration but status shows what's really going on is VCM. It looks like
The HVS-2 TS is VCM but with one MODCOD only. But this might ask for full VCM capability of
the receiver?!  Then " ...less demanding on the DVB device specification" is just fake news??

Regards,
Ernst


<CITE TD15>
  VCM will only be used when more than one service is operated at a transponder,
  i.e. on transponder 1. On all additional transponders the CCM mode (Constant Coding
  and Modulation) will be used which is less demanding on the DVB device specification.
</CITE TD15>




David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺
 

On 31/05/2021 20:53, Ernst Lobsiger via groups.io wrote:
David and Wolfgang,
thanks for your confirmation. It seems CCM on HVS-2 is only what EUMETSAT *thinks* it does.
It's also set in the SR1 configuration but status shows what's really going on is VCM. It looks like
The HVS-2 TS is VCM but with one MODCOD only. But this might ask for full VCM capability of
the receiver?!  Then " ...less demanding on the DVB device specification" is just fake news??
Regards,
Ernst
Yes, it seems like that, although given that one service pair require VCM, having both (all in future?) transponders set to VCM allows flexibility in the event of transponder change. Actually, "transponders" may be the wrong word, as I think the transponders simply retransmit the RF signal which is uplinked to them, they don't decode to a bit stream and re-modulate. Hence it's the setting on the ground equipment which may control this.

I don't know how this works physically. Are there two separate bitstreams from EUMETSAT (one BS, one HVS-1) and the kit (at the uplink station?) produces one uplink bitstream, or rather, one RF stream for uplinking?

Clever stuff!

Cheers,
David
--
SatSignal Software - Quality software for you
Web: https://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv


Ernst Lobsiger
 

On Mon, May 31, 2021 at 10:18 PM, David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺 wrote:
Hence it's the setting on the ground equipment which may control this.
David,

yes this must be a question of how the UPLINK formats the data stream. With CCM all frames
have the same MODCOD. So the DVB-S2 receiver has to determine (or to be told) that only once.
With VCM different frames can have different MODCODS. BAS and HVS-1 frames can be intermixed
but the DVB-S2 receiver must determine the MODCOD for every single frame to decode the data.
VCM is signaled as ACM in the first MATYPE byte as explained. The only difference between
VCM and ACM is that under ACM you have some sort or return path where the receiver can tell
the sender about current SNR etc. so that the sender can always use the MODCOD that allows
for the highest possible data rate. But that's only useful for point to point connections.

EUMETSAT seems to be convinced that they send HVS-2 as CCM. But the UPLINK is probably run
by a third party. There is a small possibility that the SR1 disregards the ACM bit in MATYPE
for reception if you configure HVS-2 as CCM. But the SR1 certainly knows it is ACM as it
displays that in the status page. The TBS drivers, as far as I understand those, analize the
data stream and discover all the stuff set in MATYPE. So they prepare for VCM on HVS-2 and
must determine the same MODCOD for every single frame. That's at least my understanding :-\.


Best Regards,
Ernst


CrazyCat
 

Real CCM must be without dummy frames. So both Eumetcast transponders VCM (data frames + dummy frames)


Ernst Lobsiger
 

On Tue, Jun 1, 2021 at 06:11 AM, CrazyCat wrote:
Real CCM must be without dummy frames. So both Eumetcast transponders VCM (data frames + dummy frames)
Thanks for that CrazyCat !

IIRC the ACM bit 0 on HVS-2 MATYPE was already there when we fixed the ECP3 stuff for the TBS-6903. I have contacted EUMETSAT for a clarification.

Best regards,
Ernst