PSD Masks and what they're for

Hi all,

I'm looking for a simple explanation that would clarify as to what exactly is a PSD mask used for when implementing a xDSL network.
From what I understand, PSD Masks are basically used to "mark" the frequencies (or bound them) to specific limits.
I'm sure I'm not quite there, but with a bit of help I'll finally be able to understand this.

New to the forum, so If I'm asking in the wrong area, please forgive me...

PSD means power spectral density to me.
A PSD mask ? Maybe to shield the line/equipment in question from crosstalk or REIN ?

I'm sure some clever [censored] will tell us shortly !

Something to do with the frequencies that are legal to use in different countries maybe? Not an acronym I've seen mentioned on this site before.

EDIT: Or could start with a google

Edited by ian72 (Thu 29-Dec-11 15:33:47)

Yes Power Spectral/Spectrum Density ... without going into detail about what it is and how it is calculated, you get a PSD figure for each frequency that is in use (for ADSL/VDSL/or anything else). These are plotted on a graph.

There is an Overlay MASK that sits on the graph and is the boundary figures for that particular technology and the transmissions cannot sit outside. the mask is defined to minimise transmission of interference or cross talk to other lines or services and may, for example have notches where other key transmissions opereate.

Use of a PSD mask with the chip set in the DSLAM brings in Dynamic Spectrum Management and allows continual adjustment of power levels at different frequencies to maximise throughput and minimise interference.

..... Crikey ! I winged it, what do I win ?

In reply to a post by Zarjaz:

..... Crikey ! I winged it, what do I win ?

An appointment to sort out my Infinity connection!

Often helps to say *why* you're asking.

For example, ANFP might be relevant to the answer.

Or might not.

Who knows?

The idea - when applied to VDSL from the cabinet - is to reduce the power in the frequency bands also used by ADSL to about the same level that the ADSL signals which have travelled from the exchange have when they reach the cabinet.

If you don't do this the ADSL lines get swamped by crosstalk in the cabinet from the VDSL signal which originated just metres away and would therefore at a much higher amplitude if not for power spectrum management.

Thus each cabinet will have a different mask (in practice one of a set of pre-determined profiles rather than totally unique to each cab) depending on its distance from the exchange,

That is one specific application.

There are also masks for ADSL, ADSL Max, ADSL2 &c

and away from xDSL they are used in many other RF based systems.

That is one specific application.

Nod - which is why I said "when applied to VDSL from the cabinet" - this is an xDSL forum after all .

Your explanation was perfect - I just thought an example might help people to understand a practical application.