Sagem 4450E - Manual (Page 175)

SAGEM 3P@C
3P@C Installation Manual
Page 12-18 Reproduction and communication in any form prohibited without the written permission of
SAGEM SA
The line length determines the attenuation and delay of transmission, which is the most important factor to
determine the VDSL transmission distance. In practice, other possible factors should be combined for
consideration. The following only lists the experience value for reference:
In the environment of cells, the 0.4mm cable can be used for commissioning 1km/ symmetry/12.5M;
In the central office, the 0.32mm cable can be used for commissioning 1km/non-symmetry/downstream 4.17M
and upstream 1.56M.
„ Insulation resistance
Usually, the insulation resistance between the insulation wire and the ground, and between shielded insulation
wires should not be less than 30M.
„ Crosstalk interference
Since the transmission distance of VDSL is shorter than ADSL, and the power is low, NEXT (Near End
Crosstalk) can be ignored, so the crosstalk interference mainly refers to FEXT (Far End Crosstalk). The PBO
(Power Backoff) of VDSL mechanism can automatically adjust the transmission power according to the size of
SNR, thus making the crosstalk the smallest.
„ Line attenuation
The line transmission attenuation can result in the weakening of signals, thus communication cannot be
established or a large number of outburst error codes can occur in the transmission process. The main factor to
affect the attenuation is the cable length, core diameter and the quantity of pairs in the harness.
„ Pulse noise
The pulse noise refers to the outburst discrete pulse interference, it has a large amplitude and the duration is far
shorter than the time interval. The source of pulse noise may be the ringing signals of telephone and the human
electric sparks (Such as auto ignition, electric power), the power switching of large power (for example, the
telephone lines are paralleled with the electric power in the elevator well). The pulse noise is hard to be tested
because it occurs randomly, and at present, no specific index requirement is available. VDSL provides the
interleaving function, to effectively avoid some pulse noises, which can reach up to 300ms at most, while 90% of
the pulse noise can last for less than 200ms.
„ Idle channel noise
This is the background noise, a main parameter for calculating SNR.
The factor to affect VDSL connection rate is the attenuation of the transmission distance to the upstream high
frequency band. as shown in the table below:
Table 12-10 The minimum SNR value for the rates (for reference)
1.56M,1.04M 1.04 M QAM4 19 dB
12.5M,8.33M,4.17M,
2.08M 8.33M,4.17M,2.08M QAM16 25 dB
X 12.5 M QAM64 31 dB
Analyzing based on the above table, the low rate does not necessarily mean the low requirements for line
quality, but is determined by the QAM points. That’s why the connection of the symmetric 2.08M/2.08M is not so
stable as the non-symmetric 4.17M/1.56M (the default rate mode) in the poor condition of lines, because the
minimum SNR of the upstream 2.08M is 25dB, higher than 19dB of the upstream 1.56M.