Broadband Related > Broadband Technology

Virtual noise?

<< < (6/6)

Weaver:
This is the best bit of that paper, TR-197. Even I can actually understand the following:

“6.3.9 Virtual Noise (VN)

6.3.9.1 Objective – basic variant

The Virtual Noise function defines a Noise Mask (either transmitter or receiver referred), frequency shaped, which at the receiver is converted into a shape that represents the expected noise on the line. This could be seen to have a similar effect to a frequency dependent Target Noise Margin.
Normally the crosstalk noise changes with frequency and VN can attempt to model such change. If the Target Noise Margin is configured only on the peak value it could be too limiting in case of high values of crosstalk noise.
This way the xDSL line is configured to withstand a noise level equal to the configured Virtual Noise Mask, hence decreasing the bitrate with the expectation of increased stability.”

It then goes on to say more (I’ll need to read the whole thing) about how this is mentioned in the standards.

Is a “noise mask” then just a function whose output is either an SNR allowance or an actual current measured SNR, not sure which, and whose argument is the tone/bin number/bin?

I have seen virtual noise mentioned in G.994.1 where it very briefly mentions a flag in the modem capabilities and settings data set. This is declared as on/off as to whether or not a modem can employ virtual noise mathematics or is going to do so currently. I can’t remember which it is, but it’s telling the other end about whether VN is going to be/might be used by the this-end modem.


Also, I found this Broadcom patent relating to virtual noise. I admit that I haven’t read it yet, but it looks interesting.

Navigation

[0] Message Index

[*] Previous page