Re: [802.3_EPOC] short term ad hoc committee on mulitple modulation profiles until January interim
Hal,
I agree with your observations.
I'll try to dig up some scatter plots of SNR vs receive level for example modes. They show that most but not all low SNR modems have low signal level. I don't think it is such a surprise that gateways also have a distribution with several dB improvement. The drop from the tap to the gateway and the position along the line and DC still vary the same as a STB feed. And gateway devices are not on the outside of the house, they are inside the home and are part of a splitter network. They are intended be right off the first splitter and not have a long in home cable run. But there can be cases where another substantial length of cable may be needed, apartments, duplexes, unique home designs. In the future, we will rely on more self installs and gateways that integrate WiFi and need to be located in particular locations for coverage but that variability is not reflected in this MTA data. These are all professionally installed without WiFi.
When designing for 4K-QAM we could/should operate at higher levels than 256-QAM just as analog runs 6 dB above 256-QAM and 64-QAM runs at 6 dB below, lower the receiver noise figure, improve the modulator MER. All these and others, including improving or eliminating the analog optics will help get more devices to 4K-QAM. In some cases these changes will tighten distributions but in others they will reveal variations that previously were masked.
Dave Urban
On Dec 5, 2012, at 10:47 AM, "Hal Roberts" <Hal.Roberts@xxxxxxxxx<mailto:Hal.Roberts@xxxxxxxxx>> wrote:
All,
Some observations based on Dave Urban’s presentation of downstream SNR field data. The purpose is to check if: A) I’ve understood the data properly and B) to see if there are some points we have consensus on (recognizing we only got partway through the presentation):
1. Impact of Analog Optics: It is often stated that the data we should be analyzing should subtract the impact of the analog optics, since this will not be present in some EPoC scenarios. Observation: The impact of the analog optics is negligible. The optics sets a baseline of about 42dB SNR for digital channels. However the problematic channels have noise that is 10dB worse than the optical baseline. Eliminating the optical noise will only improve the SNR of a 30dB modem by a fraction of a decibel. Therefore elimination of the analog optics will not substantially alter the problem or solution space. The higher SNR channels will, however, improve by elimination of the analog optics.
2. Source of Low SNR Modems: These are generally correlated to modems with low received signal power (RSSI) due to long in-home cable runs or high split ratios. Observation: However this leads to the following mystery when examining the Gateway Data……..
3. Gateway Data - Impact of Locating Modem at Home Entry Point: Locating the modem here would seem to solve both low signal problems as well as reduce in-home ingress. Surprisingly, locating the modem here has a relatively negligible affect with only a 2dB shift in average SNR and a ½ dB reduced Standard Deviation. Observation: How do we reconcile #2 and #3?
4. General Conclusion: The only potential way of eliminating the low SNR outliers is to reduce those modems experiencing a low signal (eliminating the analog optics will not do it). Therefore, locating the CNU at the entrance to the home where the signal level should be close to 0dBmV (and any in-home ingress at lower levels) would seem to be the way to do this. However, current data shows this is not the case. The only possibilities to explain this seem to be: A) Low signal is not the cause of low SNR or B) the ‘gateway’ location mysteriously still experiences low signal strength even though it is not behind a long cable run or high loss splitters.
Do I have the observations correct?
It would be interesting to see the SNR of the ‘gateway’ located modems paired to received signal levels to get a correlation between low SNR and low RSSI.
Hal
From: Salinger, Jorge [mailto:Jorge_Salinger@xxxxxxxxxxxxxxxxx]
Sent: Monday, December 03, 2012 7:40 AM
To: STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx<mailto:STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_EPOC] short term ad hoc committee on mulitple modulation profiles until January interim
Dear IEEE P802.3bn members,
Expanding on Mark's Email, attached below, during the last IEEE EPoC F2F meeting we had a lot of discussion regarding multiple modulation and coding schemes (M-MCS) for EPoC. However, the time available was not sufficient to express all views an opinions, both pros and cons. Given the interest in the topic, and the desire to make a decision on whether to use M-MCS or not for EPoC rather soon, there was consensus on creating a short-lived ad-hoc for the purpose of discussing the potential benefits and draw-backs of M-MCS in EPoC. To that end, this ad-hoc will be a forum to discuss the merits and draw-backs of M-MCS for EPoC, and to try to arrive to a recommendation on whether M-MCS should be used or not in EPoC for the next EPoC F2F meeting. While we may discuss approaches for implementing M-MCS for EPoC to facilitate the discussion on its merits or draw-backs, it is not the purpose of this ad-hoc to arrive to a recommendation on how M-MCS would be implemented even if it is deemed appropriate to use it.
To that end, and after considering multiple options for timeslots for this meeting, we will hold an initial discussion tomorrow, Tuesday, at 9:30 AM ET. I tried to pick this timeslot with 2 criteria in mind: a. that the meeting not overlap with existing EPoC or DOCSIS 3.1 activities, and b. that it be possible for the widest range of participants as possible. I think that the a. criteria is met with this timeslot, but it is very difficult to pick a timeslot that meets the b. criteria for everyone (in particular, I know that this timeslot is pretty early in the West coast).
During this initial meeting we will review objectives and then start with a presentation on the benefits of M-MCS based on data collected by Comcast. Subsequent meetings will include additional presentations on the benefits of M-MCS, and presentations on the draw-backs of M-MCS and/or complications from its implementation.
Please see a meeting invitation following this Email. Please let me know should you not receive that meeting invitation.
Thanks!
Jorge
From: Mark Laubach <laubach@xxxxxxxxxxxx<mailto:laubach@xxxxxxxxxxxx>>
Reply-To: Mark Laubach <laubach@xxxxxxxxxxxx<mailto:laubach@xxxxxxxxxxxx>>
Date: Monday, November 19, 2012 6:26 PM
To: EPoC Task Force <STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx<mailto:STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx>>
Subject: [802.3_EPOC] short term ad hoc committee on mulitple modulation profiles until January interim
Dear IEEE P802.3bn members,
At the meeting last week, it was mutually desired by everyone to have more discussion time on the topic of multiple modulation profiles as there was not enough time at the meeting for everyone to fully share their views. The following ad hoc is charted until the January P802.3bn interim meeting in Phoenix, AZ:
Name: Multiple Modulation Profiles
Chair: Jorge Salinger
Until: January 2013 P802.3bn Interim meeting
Focus: facilitate discussion and information sharing on multiple modulation profiles
For everyone having a holiday this week, please have a happy one!
Cheers,
Mark Laubach, Chair
IEEE P802.3bn EPoC PHY Task Force
Broadband Communications Group
Broadcom Corporation
1351 Redwood Way
Petaluma, CA, 94954
<image002.png>
Tel: +1.707.792.9093
Cell: +1.650.996.2219
________________________________
From: Mark Laubach <laubach@xxxxxxxxxxxx<mailto:laubach@xxxxxxxxxxxx>>
Reply-To: Mark Laubach <laubach@xxxxxxxxxxxx<mailto:laubach@xxxxxxxxxxxx>>
Date: Monday, November 19, 2012 6:26 PM
To: EPoC Task Force <STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx<mailto:STDS-802-3-EPOC@xxxxxxxxxxxxxxxxx>>
Subject: [802.3_EPOC] short term ad hoc committee on mulitple modulation profiles until January interim
Dear IEEE P802.3bn members,
At the meeting last week, it was mutually desired by everyone to have more discussion time on the topic of multiple modulation profiles as there was not enough time at the meeting for everyone to fully share their views. The following ad hoc is charted until the January P802.3bn interim meeting in Phoenix, AZ:
Name: Multiple Modulation Profiles
Chair: Jorge Salinger
Until: January 2013 P802.3bn Interim meeting
Focus: facilitate discussion and information sharing on multiple modulation profiles
For everyone having a holiday this week, please have a happy one!
Cheers,
Mark Laubach, Chair
IEEE P802.3bn EPoC PHY Task Force
Broadband Communications Group
Broadcom Corporation
1351 Redwood Way
Petaluma, CA, 94954
<image003.jpg>
Tel: +1.707.792.9093
Cell: +1.650.996.2219
________________________________
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________________________________
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________________________________
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