Can anyone give me an idea of my attenuation? is there a formula of working it out from both paths?
That's a good question, lockyatlrg! But maybe there isn't any one correct answer..
There are a few candidate formulas, some better than others..
A simple average could be calculated. It would be based on the sum of the attenuation calculations for the utilised frequency bands, and calculated separately for each direction. It wouldn't be very meaningful combining the attenuation figures for upstream and the downstream bands.
Alternatively, the attenuation could be apportioned according to the number of carriers in a given band and the bit loading for each carrier in that band. This metric would capture the impact of the attenuation on the quality of the connection.
The fact that the HG612 modem doesn't present an attenuation figure in its web interface could mean that Huawei hasn't got the answer either!
VDSL Band Status U0 U1 U2 U3 D1 D2 D3
------------------------------------------------------Line Attenuation(dB): 3.4 13.4 N/A N/A 7.8 16.6 N/A
Signal Attenuation(dB): 0.0 13.5 N/A N/A 7.8 16.6 N/A
EDIT: So we could combine the (downstream) Signal Attenuation (S/A) figures of D1 and D2, and divide the sum by 2.. And that gives us a single figure for Downstream S/A of 12.2dB
But if we sum the count of subcarriers per band, and using that count in the apportionment of the attenuation, we will obtain a different figure..
(Final) Band Plan
------------------------- U0 U1
US: (0,95) (696,1183) D1 D2
DS: (32,687) (1192,1627)
We see that frequency band D1 utilises 655 tones (or subcarriers) while 435 tones are utilised in band D2.
So the total count of subcarriers is 1090. And of those carriers some 60% are attenuated by 7.8dB (on average), while 40% of the subcarriers, those in the higher frequency band D2, are attenuated by 16.6dB.
Some very crude arithmetic gives us an average Signal Attenuation across both Downstream bands (D1 and D2) of (0.6*7.8) + (0.4*16.6) = 11.32dB
Not that different to the first calculation. Anyone still awake?
To make it more accurate, the bit depth for each carrier (the number of bits encoded in the subcarrier's QAM constellation) could be incorporated into the attenuation figure..
I won't try and work that out..
Edited by asbokid (Sat 10-Sep-11 21:45:05)