Monitoring Copper Line Monitoring
Table 84: Graph Parameters
Channel Characteristics
Function Hlog(f) per sub-
channel
The channel characteristics function H(f) is the frequency response of the
channel, i.e., amplitude magnification at each frequency point, which can
be used for analyzing the physical copper loop condition, for example,
determining line quality and presence of bridge taps. Its magnitude values
are depicted in a logarithmic scale, Channel characteristics, Hlog(f).This
function yields valuable information about the physical condition of the
copper loop and its topology.
Quiet Line Noise PSD
QLN(f) per sub-channel
The quiet line noise PSD QLN(f) for a particular sub-carrier is the rms
(Root Mean Square) level of the noise present on the line, in absence of
ADSL signals. Quiet line noise provides a wideband spectral analysis
function. QLN(f) can be used for analyzing crosstalk or RF interference,
for example, spikes in a plot of this data would indicate interference
The signal-to-noise ratio SNR(f) for a particular sub-carrier is a real value
that represents the ratio between the received signal power and the received
noise power for that sub-carrier.
The SNR(f) data provides the user with information about the capacity of
the line. The signal-to-noise ratio can be used to derive the impact of
topology or spectral issues on a line. The interference combination of
Hlog(f), QLN(f) and SNR(f) can be used to troubleshoot why the data rate
is not able to reach the maximum in a given loop.
The Bit Loading provides the amount of bits transmitted per sub-carrier per
DSL frame. Sub carrier with higher SNR may transmit more bits (up to 15
bits).
Graph may be set according to Subcarrier Index or Tone Frequency (Khz)
Actual PSD Shape (verify if supported, I don’t think it’s supported today)
provides the transmitted PSD (Power Spectral Density) in dBm/Hz. The
actual PSD depends on multiple parameters such as used technology,
profile, spectral limitations (UPBO, DPBO, RFI notch etc.) loop length,
etc.
Gi provides the transmit gain used by the modem to equalize the SNR over
the sub-carriers. Gain values are -14.5 dB up to +2.5 dB (usually the values
are between -1.5dB and 1.5dB)
This graph provide both charts (SNR and Bit loading) together.
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