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Tingting
Please find my answers to your questions below.
> impacting on the 6T boundary decision. In the worst case, it wastes 6x synchronization time.
The symbol alignment is very fast and is a tiny portion of the start-up time, much, much less than 1%. So I don't see this as a significant factor.
> If PAM training using PAM3 blind equalization while data mode uses PAM5 partial response, will this work ok or not?
Yes, it does work. Blind equalization is very commonly used for PAM-3 modulation in multiple IEEE standards and has the advantage of simplicity.
> Will PAM2 make this simpler? 4B6B may be not the best coding, but I do not think additional coding for PAM2 will increase hardware complexity significantly.
I am not concerned about the hardware complexity, which I agree will be a small addition.
What I am concerned about, and what I believe most people who raised the same question for your presentation in Hamburg, is data correlation with PAM-2 training. Given that it is mandatory to support running disparity, there are only 48 possible PAM-2 codes
(out of 256). Your gave an example of using the 16 codes which have a very different frequency spectrum from the 256 codes used during data. Even using 32 codes, there is still a very significant problem with data correlation. So we then need a scheme (and
start-up time) to later switch from PAM-2 to PAM-3 and we have the risk that the equalizer and each cancellers are not correctly trained when we change to PAM-3. Furthermore strong correlation in the PAM-2 sequence will result in spurs in the power spectrum.
This is highly undesirable and runs the risk of creating EMC issues. Late changes were made in the 10BASE-T1L standard to eliminate correlation effects far less severe than would arise when using a PAM-2 sequence.
We had given serious consideration to the possibility of using PAM-2 but concluded that the complication of figuring out how to switch back to PAM-3 and verify that the equalizer and each cancellers are not correctly trained would negate any benefit and overall
we would be worse off.
> Less link up time is beneficial for the application.
First of all I don't believe PAM-2 will result in lower link up time and may result in longer linkup time or links that startup and then fail, which would be worse.
Secondly, lower link time is only an advantage if the application can benefit from it. We are proposing to target 100ms including Auto-Negotiation. This is the same as 100BASE-T1 and 1000BASE-T1. The system needs to be designed around the normal maximum time
to link which is comprised of the ANeg time plus the link_fail_inhibit time. A lower time to link is not an advantage as the system needs to be designed for the worst case. So unless we plan to further reduce the link_fail_inhibit time I don’t really see that
link time is a factor that needs to be considered.
Brian
From: zhangtingting (O) <zhangtingting59@xxxxxxxxxx>
Sent: Wednesday, September 25, 2024 04:13 To: Murray, Brian <Brian.Murray@xxxxxxxxxx> Subject: Concern on PMA training scheme
Hi Brian,
I wish we can achieve consensus on PMA training for the residual details so that we can make D1.0 possible in November. Regarding reusing 8B6T PAM3 for training mode, I have the following concern:
1. The advantage of simplifying hardware is obvious, but the training efficiency is low, considering the higher error impact on scrambler synchronization, consequently impacting on the 6T boundary decision. In the worst case, it wastes 6x synchronization
time.
2. If PAM training using PAM3 blind equalization while data mode uses PAM5 partial response, will this work ok or not? 8B6T with partial response is a good idea to achieve coding gain without FEC. We should think about a reliable training scheme with 8B6T
partial response taken into account. Otherwise, no benefit comparing it with the 8B6T for 100BASE-T4.
Will PAM2 make this simpler? 4B6B may be not the best coding, but I do not think additional coding for PAM2 will increase hardware complexity significantly. Less link up time is beneficial for the application.
Hear from you.
Best wishes,
Tingting
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