Page 767 - 5G Basics - Core Network Aspects

Transport aspects 2

downstream tones) equals to the index of the subcarrier to be assigned bits. Constellation mapping shall
start from the subcarrier with index i = t1 and end on the subcarrier with index i = tNSC (for example,
t75 = 160 means that the subcarrier with index 160 is the 75th subcarrier to be assigned bits). The tone
ordering table t shall be created and exchanged during the initialization (see clause 12.3.4.2) and shall
remain unchanged until the next initialization. The same tone ordering table shall be used for both NOI and
DOI.
The pairs of bits and relative gains used on the RMC tone set during RMC symbols are defined in ascending
order of frequency as a bit allocation table br and gain table gr containing, respectively, bri and gri values
for all subcarrier indices i that belong to the RMC tone set. The gri value shall be the same value as the gi
value used for data symbol in the NOI at the same subcarrier index. The bit allocation table br shall not
include 1-bit subcarriers.
Following reception of the tables b, g and t, and the RMC tone set, both the transmit and the receive FTUs
shall calculate a re-ordered bit allocation table b' and a pre-ordered tone table t1 from the original tables b
and t. The pre-ordered tone table t1 for the RMC symbol and the data symbols in the NOI shall be
constructed by moving in front of the original table all the values corresponding to the tones of the RMC
tone set using the same relative order as in table t. For data symbols in the DOI, the pre-ordered tone table
t1 shall be identical to the original table t.
From the pre-ordered tone table t1, the transmitter shall calculate the re-ordered tone table t'. The
re-ordering of table t1 shall be performed by the transmit PMD function. The re-ordered tone table t' shall
be generated according to the following rules:
• Indices of all subcarriers supporting 0 bits or two or more bits appear first in t', in the same order
as in table t1.

• Indices of all subcarriers supporting 1 bit appear last in table t', in the same order as in table t1.
If the bit allocation does not include any 1-bit subcarriers, the re-ordered tone table t' is identical to the
pre-ordered tone table t1.
The (even number of) 1-bit subcarriers shall be paired to form 2-dimensional constellation points as input
to the trellis encoder. The pairing shall be in the order that the 1-bit subcarriers appear in the pre-ordered
tone ordering table t1.

The table b' shall be generated by re-ordering the entries of table b according to the following rules:
• The first NCONEBIT/2 entries of b' shall be 0, where NCONEBIT (by definition, even) is the number
of subcarriers supporting 1 bit.
• The next entries of b' shall be 0, corresponding to all subcarriers that support 0 bits, in order
determined by the new tone table t'.
• The next entries of b' shall be non-zero, corresponding to the subcarriers that support two or more
bits. These entries shall be in order determined by the new tone table t' in conjunction with the bit
allocation table b.
• The last NCONEBIT/2 entries of b' correspond to the paired 1-bit constellations (i.e., two bits per
entry).
The total number of bits L' associated with bit-loading tables b and b' is the same:

L'  b '  b
 i  i
Calculation of tables b' and t' from the original tables b and t by subcarrier pairing and bit re-ordering
processes described above is shown below.
/*** CONSTRUCT THE TONE RE-ORDERING TABLE ***/
/*
Tone ordering table is denoted as array 't', pre-ordered tone table is
denoted as array 't1', tone re-ordering
table is denoted as array 'tp'. The indices to these arrays are
denoted as 't_index', 't1_idx' and 'tp_index', respectively.

757