Schmid SHDSL - Power Backoff; DSL Performance

Watson SHDSL Router
Operating Manual
Watson-SHDSL-Router-Manual.doc
Version 1.0-03
3.5.4 Power Backoff
The transmit power of the modem can be decreased by activating the power back-off mode. This
reduces interference to other transmission systems operating on adjacent pairs bundled in the
same cable.
With enabled power back-off the transmit power will be reduced adaptively in function of the esti-
mated cable attenuation:
Estimated Power Loss(*) Power Backoff
< 1 dB 6 dB
< 2 dB 5 dB
< 3 dB 4 dB
< 4 dB 3 dB
< 5 dB 2 dB
< 6 dB 1 dB
≥ 6 dB
no backoff
(*) Calculated as Tx Power – Esti-
mated Rx Power
Table 3-2: Power Backoff
3.5.5 DSL Performance
Watson SHDSL router provides information about the current Signal Quality and Attenuation of a
DSL link.
Signal Quality
The Signal Quality is the noise margin calculated by the modem:
SQ = SNR1 - SNR0
Where
SQ is the calculated noise margin
SNR1 is the signal to noise ratio calculated by the transceiver by analyzing the error correc-
tion bits (Trellis bits) in the line code.
SNR0 is the signal to noise ratio that gives a bit error rate of 10
-7
in presence of average
white Gaussian noise. For TC-PAM16 the theoretical value for SNR0 is 27.7 dB.
Attenuation
The link attenuation is calculated by the modem assuming 0.4mm PE cable without bridged taps
and measured at 150 kHz (for linerates of 200 kbit/s up to 1'992 kbit/s) or 200 kHz (for linerates of
2'056 kbit/s and above). This calculated attenuation may differ from the attenuation measured by
other equipment for other cable configurations (other cable diameter, splices, bridged taps).
Both Signal Quality and Attenuation are effective maintenance tools for determining inadequate or
bad cable pairs. They are available in the Web Based Management or in the Monitor with the
“shdsl diagnostic” command.
3-12 Revision: 2007-05-24