SAGEM 3P@C

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,

8.33M,4.17M,2.08M

QAM16

25 dB

2.08M

 

 

 

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.

3P@C Installation Manual

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