Specifications

Watson SHDSL Router
Operating Manual
Watson-SHDSL-Router-Manual.doc
Version 1.1-07
3-14 Revision: 2012-02-15
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 operat-
ing on adjacent pairs bundled in the same cable.
With enabled power back-off the transmit power will be reduced adaptively in
function of the estimated 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 –
Estimated 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
pn is the calculated noise margin
pkoN is the signal to noise ratio calculated by the transceiver by analyzing
the error correction bits (Trellis bits) in the line code.
pkoM is the signal to noise ratio that gives a bit error rate of 10
-7
in pres-
ence of average white Gaussian noise. For TC-PAM16 the theoretical
value for pkoM is 27.7 dB.
Attenuation
The link attenuation is calculated by the modem assuming 0.4mm PE cable with-
out 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 atten-
uation 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 determin-
ing inadequate or bad cable pairs. They are available in the Web Based Man-
agement or in the Monitor with the “shdsl diagnostic” command.