Page 707 - 5G Basics - Core Network Aspects

Transport aspects 2

NOTE 1 – The estimate of the electrical length at each frequency should be sufficiently accurate to avoid spectrum
management problems while minimizing performance loss. Specification of the accuracy of the kl0 estimate by the
FTU-R is for further study.
NOTE 2 – Other methods for electrical length estimation are for further study and may be specified as a mandatory
capability in a future amendment.
The FTU-O may override the kl0 value estimated by the FTU-R with its own value of kl0. If in the DPU-MIB a
forced kl0 is configured (UPBOKLF = 1), the FTU-O shall override the kl0 with the DPU-MIB value of UPBOKL.

7.3.1.4.2.2 Computation of UPBOMASK
If the reference electrical length kl  0 , the UPBOMASK at any frequency f of the ITU-T G.9701
0 _ REF
frequency band shall be calculated as:

UPBOMASK(kl0, f) = UPBOPSD(f) + LOSS(kl0, f) [dBm/Hz]
where:

LOSS(kl0, f) = kl0 f [dB], and

UPBOPSD(f) = –a –b f [dBm/Hz],

with f expressed in MHz.
The values of a, b are determined by the DPU-MIB configuration parameters UPBOPSD.
The UPBOPSD(f) is a function of frequency but it is independent of the length and type of the loop.

If the reference electrical length kl  0 , the UPBOMASK at any frequency f of the ITU-T G.9701
0 _ REF
frequency band shall be calculated as:
• for ( .1 8  kl  kl 0 _ REF ):
0
 kl 
UPBOMASK   UPBOPSDf  ( f )  10 log  0 _ REF    LOSS kl ,  f [dBm/Hz]
10 
0
 kl 0 
• for ( kl  8 . 1 ):
0
 kl 
UPBOMASK   UPBOPSDf  ( f )  10 log  0 _ REF    LOSS  8.1  f , [dBm/Hz]
10 
 8 . 1 
• for ( kl  kl ):
0 0 _ REF
UPBOMASK   UPBOPSDf  ( f )  LOSS kl , f  [dBm/Hz]
0
with f expressed in MHz.

The value of kl is determined by the DPU-MIB configuration parameter UPBOKLREF.
0 _ REF
These values shall be provided to the FTU-R during the initialization (in the O-SIGNATURE message, see
clause 12.3.3.2). Further, the updated value of kl0 is provided to the FTU-R in the O-UPDATE message
(see clause 12.3.3.2).

UPBOMASK shall be equal to the LIMITMASKus when UPBO is turned off.
NOTE 1 – For sufficiently short loops, by the nature of FEXT coupling, FEXT is rapidly decreasing as the loop length
decreases. Accordingly, as the electrical length kl0 of the loop is below 1.8, no further increase in power back-off is
needed. Therefore, for lines with kl0 < 1.8, the FTU-R performs UPBO using kl0 = 1.8. An electrical length of 1.8
corresponds to, for example, a 0.4 mm loop about 70 m long.
NOTE 2 – In case of upstream vectoring, the operator may provision or allow for values of a and b corresponding to
higher upstream PSDs up to the limit established by PSDMASKus, because upstream FEXT is reduced through crosstalk
cancellation. After UPBO has been applied (during the initialization), the FTU-R may further adjust its transmit PSD

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