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2 Transport aspects

Table 10-10 – Values of vectoring feedback control parameters

Parameter Mandatory values for FTU-R to support

Vectored bands: N_band 1, 2, 3,...,8
Vectored bands: Full range from "Index of the lowest supported downstream data-bearing
Index of subcarriers subcarrier" to "Index of the highest supported downstream data-bearing subcarrier"
as indicated in Table 6-1 for the supported profile(s)
F_sub 1, 2, 4, 8
F_block 1, 2 and 4
B_min 2, … , 17
B_max B_min, … , 17
L_w 0, 1, … , 10
Padding 1 (enable); with F_block = 1, 2 or 4
0 (disable) only with F_block = 2 or 4
Rounding 1 (enable); 0 (disable)

In case of reporting of DFT output samples, the valid values for the VCE to configure and the mandatory
values for the FTU-R to support are: F_block = 1, L_w = 10, 6, 4, and padding = 1 (see Table 10-9). B_min
and B_max do not apply.

For each vectored band assigned by the FTU-O for vectoring feedback reporting, the FTU-R shall report the
VF samples for all subcarriers with indices X = X_L + n × F_sub, where n gets all integer values 0, 1, 2, … for
which X_L ≤ X ≤ X_H and with X_L and X_H respectively, the indices of the lowest frequency and the highest
frequency subcarriers of the vectored band. VF samples of other subcarriers shall not be reported.
10.3.2.3.2 Grouping of VF samples

10.3.2.3.2.1 Grouping of VF samples in case of error samples reporting
In case of reporting of error samples, the FTU-R shall group VF samples into blocks. Valid block sizes for the
parameter F_block are defined in Table 10-10. For each block, the FTU-R shall calculate parameters B_M
and B_L. The parameters B_M and B_L represent the highest and the lowest bit indices of the reported VF
sample, in assumption that bit index is counted from the LSB to the MSB, starting from 0. If rounding=1,
and B_L>0 then the content of the bit with index B_L-1 (the MSB that is not reported) shall be examined. If
the content of this bit is "1", the binary value of the reported bits shall be incremented by 1. In case the
increment causes representation overflow (can be examined by the sign bit B_M) then the increment shall
be cancelled and the original contents shall be reported (see Figure 10-21).

Figure 10-19 depicts the example of F_block=1, B_min=2, B_max=10, L_w=4, and padding=1. Two registers
each (B_max+L_w) bits wide contain a VF sample component in the bits labelled from B_max (VF sample
MSB) down to zero (VF sample LSB), while the L_w – 1 = 3 remaining bits of each register are set to zero
and labelled with a negative bit index –1 down to 1 – L_w = –3. For each component in the block, only the
B_M – B_L + 1 bits with indices from B_M down to B_L inclusive are included in the vectoring feedback
report block (VFRB) format defined in clause 10.3.2.4.1. Parameters B_M and B_L shall be computed for
each block as described below. The FTU-R shall examine all VF sample components in each block and
determine for each component ec (ec = 1 to 2×F_block) a data-dependent scale parameter sec, defined to
be the sign bit index of the shortest two's complement representation of the component. For a component
value Vec, the scale parameter sec is:
(log ( )) + 1, > 0
2

= {0, = 0

(log (− )), < 0

2

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