Qam wrong?

[Viper-t]

Hi can someone tell me if my qam is wrong please?. My upload qam is always 64 as is everyone's I have 1 channel 32qam and 2 at 16qam I think 64 symbols is more data than 16 no? 

Upstream channels

Channel Frequency (Hz) Power (dBmV) Symbol Rate (ksps) Modulation Channel ID

1	43100000	41.3	5120 KSym/sec	32QAM	2
2	30100000	40.8	5120 KSym/sec	16QAM	4
3	36600000	41	5120 KSym/sec	16QAM	3
4	49600000	41.5	5120 KSym/sec	64QAM	1
5	23600000	40	5120 KSym/sec	64QAM	5

[gitty]

It goes like this: 53.4 MHz is the center of the first active subcarrier. 53.45 MHz is the center of the following subcarrier (50 kHz spacing). Etc.

[Sephiroth]

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@gitty wrote:
It goes like this: 53.4 MHz is the center of the first active subcarrier. 53.45 MHz is the center of the following subcarrier (50 kHz spacing). Etc.

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Ah - what about the bandwidth as distinct from the sub-carrier range?

[Viper-t]

Thank you for your knowledge you are always a very helpful member of the community and I appreciate your help. Does the channel width effect my qam levels as per my picture my qam keeps dropping to 16 and 32 instead of 64. Also I have 5, 3.0 channels with 1, 3.1 I thought it was supposed to be 4 bonded with 1, 3.1?

Regards

[Sephiroth]

Thank you for your kind words. I'll repeat that I'm not 100% sure of what I said in my earlier post. The maths of DOCSIS 3.1 is complex; its sub-carriers could easily admit a bandwidth other than a round 10MHz because the sub-carrier division, as gitty has pointed out, is demarcated in kHz.

But, if it is off-centre, then the upstream can misbehave and the VM end (the CMTS) may try to compensate by lowering the QAM level. This reduces the data density giving it a chance to "miss the potholes".

I do hope that real experts who live this stuff at VM can definitively state whether I've set a false hare running.

The DOCSIS 3.1 upstream channel is configured so that it can bond with the "slower" DOCSIS 3.0 channels. The six upstream channels provide better contention levels than 4. I don't know VM's plan for D3.1 , which can provide far better speeds and is more noise tolerant than D3.0.

[gitty]

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@Sephiroth wrote:
But, if it is off-centre

I'm not sure what you mean by that.

About the width... It's reported to be 10.8 MHz. The active subcarrier count is reported to be 220, though, which results in a width of 11 MHz (220 * 50 kHz).

[Viper-t]

Many thanks for your swift responce. It is interesting as more stuff is added to make things better are actually making it worse at the minute. I hope it's fixed soon as I don't want to complain all the time it's driving me mad, I just want a working service in 2022. There seems to be far more problems nowadays than just a few years ago with older technologies, why is these new things added if its not helping customers Internet, dont they test before doing so or at least know how to make it right.

[Sephiroth]

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@gitty wrote:

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@Sephiroth wrote:
But, if it is off-centre

I'm not sure what you mean by that.

About the width... It's reported to be 10.8 MHz. The active subcarrier count is reported to be 220, though, which results in a width of 11 MHz (220 * 50 kHz).

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Yeah bad terminology on my part (off-centre).  My point is that 10.8MHz bandwidth doesn't stack up against the count*spacing calculation and I'm mooting that the OP's upstream problems are contributed to by this discrepancy.  

[gitty]

It can be explained by the size of a minislot. There are 8 subcarriers in a minislot when the subcarrier spacing is 50 kHz. That gives you 27 minislots (216 subcarriers). Only full minislots can be used, so there are four subcarriers left, which go in the unused pool.

27 minislots * 8 subcarriers/minislot * 50 kHz = 10.8 MHz

[Sephiroth]

Got it. Thanks. That was the gap in my D3.1 knowledge. So my advice to the OP can be disregarded.

[Viper-t]

Hi so does anyone have advice on what to do next I've never had problems with upstream and qam, only since adding the new 3.1 and extra 3.0 channel recently. The problem is I have recieved a few messages from vm saying we have discovered a problem and that I would need an engineer. When the engineer arrives he asks me what the problem is, and I have nothing to tell him except they said I have a problem and need an engineer. Both engineers have said qam problems is back at head office cabinet fine I have a little noise but not alot so he tells me. Do I make a complaint or cisas or I can contact some directors as the lutz sculler route is hit or miss and yome consuming ive been advised. My service is not fit for purpose at the minute and should be compensated for. I just won a case for terrible customer service and lies caught on audio, I'm astonished I now have new problems days after case is closed. Can't they just give me a working Internet I hate complaining and wasting a lot of my time chasing a service I pay for. I had no problems till I got the volt package none, it was fine. Regards