Page 796 - 5G Basics - Core Network Aspects

2 Transport aspects

represent modulo 16 the sequence number of the VF block it precedes as an unsigned integer, in
assumption that the first block in the vectored band has the number 0.

In case F_block = 1, a Block_ID shall not be inserted.
NOTE – The VCE can identify VBB in the received VFRB by its VBB_ID and then compute the number of VF blocks,
N_block(vb), in the VBB-vb as described in clause 10.3.2.3.2, since all the vectoring feedback control parameters are
known to the VCE. The length of the VF block is computed using the parameters (B_M, B_L) of the VF sample and the
block size F_block. The first reported sample of the first VF block in the vectored band is for the subcarrier with index
X_L (which is always even).
10.3.2.4.2 Format of the VF block

The representation for a VF block containing F_block VF samples (2×F_block VF sample components of
F_block subcarriers) shall include an EXP field (4 bits), and a vectoring feedback field (variable length), see
Figure 10-24. The vectoring feedback field includes F_block sub-fields, each carrying a complex VF sample
of a subcarrier which is assigned for reporting during the vectoring feedback report configuration (see
clause 10.3.3.2).

In case of reporting of error samples, for each VF sample component (r_x, r_y), the compressed
representation, as defined in clause 10.3.2.3.2.1, includes only those bits of the VF sample component with
indices B_L through B_M, using the convention that the MSB of the compressed representation of the
component has index B_max and the LSB of the compressed representation of the component has index
B_min. Accordingly, the total number of bits in the vectoring feedback field of a block of VF samples in
compressed representation shall be 2×F_block×(B_M – B_L + 1).

When a VF block contains error samples, the EXP fields shall include parameter B_M decreased by 2 and
represented as a 4-bit unsigned integer, in the range from 0 to 15 representing B_M values in the range
from 2 to 17. NOTE – The parameter B_L is not reported as it can be calculated by the VCE from the
vectoring feedback control parameters (see equations 10-1 and 10-2) and the value of the reported B_M
parameter.

In case of reporting of DFT output samples, each VF sample component (f_x, f_y), shall be calculated
corresponding to the definition of DFT output samples (see clause 10.3.2.2). The total number of bits in the
vectoring feedback field of a block of VF samples in compressed representation shall be 2×F_block×
(B_M – B_L + 1) = 2×F_block×L_w.
When a VF block contains DFT samples, the EXP fields shall include parameter B_M represented as a 4-bit
unsigned integer, in the range from 0 to 15.
The format of the VF block is presented in Figure 10-24. All parameters and VF samples shall be mapped
with the MSB at the left side and LSB to the right side so that the MSB is transmitted first (i.e., the first
transmitted bit is the MSB of the EXP field). The VF samples in a VF block may not be aligned with byte
boundaries as demonstrated in Figure 10-24.

VF samples in the vectoring feedback field shall be mapped in ascending order of subcarrier index from left
to right. In case of error samples, for each VF sample, the r_x (real) component shall be mapped left from
the r_y (imaginary) component. In case of DFT output samples, the f_x (real) component shall be mapped
left from the f_y (imaginary) component.

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