Page 776 - 5G Basics - Core Network Aspects
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2                                                 Transport aspects


            label corresponds to the uppermost branch for each state. The trellis diagram may be used when decoding
            the trellis code by the Viterbi algorithm.

            10.2.1.4   Constellation mapper
            The  constellation  mapper  maps  a  set  of  bits  to  a  constellation  point.  For  each  symbol,  L'  bits  shall  be
            extracted from the encoded data buffer (see Figure 10-5, reference point B) as defined in clause 10.2.1.4.1.
            The extracted bits shall be mapped to constellation points as defined in clause 10.2.1.4.2.
            10.2.1.4.1  Bit extraction

            The bit extraction mechanism described in this clause is applicable only for RMC symbols and data symbols
            (during showtime); for other types of symbols, see clause 10.2.2. Groups of bits shall be extracted from the
            incoming  data  frames  or  from  a  pseudo  random  binary  sequence  (PRBS)  generator  for  mapping  to
            individual  subcarriers,  based  on  the  subcarrier  order  defined  by  the  re-ordered  tone  table  t'  (see
            clause 10.2.1.2).

            For each subcarrier i of the MEDLEY set with bi > 0, the mapper shall extract b = bi bits from the data frame.
            The number of bits extracted for each subcarrier is determined by the original bit allocation table b. The set
            of b extracted bits shall be represented as a binary word (vb−1 vb−2 ... v1 v0), where the first bit extracted shall
            be v0,  the  LSB.  The  encoder  shall  select  a  point  (X,  Y)  from  the  constellation  based  on  the  b-bit  word
            (vb−1 vb−2 ... v1 v0) as defined in clause 10.2.1.4.2.

            For each subcarrier of the MEDLEY set with bi = 0 (monitored tones, pilot tones, and sub-carrier with gi=0,
            see Table 10-5), no bits shall be extracted from the data frame. Instead, for each of those subcarriers, the
            encoder shall extract b = 2 bits (v1 v0) from the PRBS generator, where the first bit extracted (LSB) shall be
            v0. For the pilot tone subcarrier(s), the bits extracted from the PRBS generator shall be overwritten by bits
            00 (i.e., the two bits from the PRBS generator are effectively ignored).
            The output bits dn of the PRBS generator shall be defined by:
                                             d n      1   for  n  1     to     n  23     and


                                             d n   d   n  18  d  3 2  n     for    n  23.

            The  PRBS  generator  shall  be  restarted  at  the  symbol  with  index  0  of  the  first  logical  frame  of  each
            superframe. The index n is incremented after each bit extraction from the PRBS generator. Upon the restart
            of the PRBS, d1 shall be the first bit extracted, followed by d2, d3, etc. For each symbol position of the NOI
            and DOI interval except the positions in the TA interval, the sync symbol position, and symbol positions
            outside of TBUDGET, the number of bits extracted from the PRBS generator shall be twice the number of
            subcarriers in the MEDLEY set with bi=0 that would be needed if the symbol position contains a data symbol
            or an RMC symbol with the respective bit loading table. No bits shall be extracted from the PRBS generator
            during sync symbols (see clause 10.2.2.1).

            For subcarriers that are not in the MEDLEY set (bi = 0 by definition), no bits shall be extracted from the
            encoded data buffer and no bits shall be extracted from the PRBS generator. Instead, the constellation
            mapper  may  select  a  vendor-discretionary  (X, Y)  point  (which  may  change  from  symbol  to  symbol  and
            which does not necessarily coincide with any of the constellation points defined in this Recommendation).
            10.2.1.4.2  Constellations

            The defined algorithmic constellation mapper shall be used to construct subcarrier quadrature amplitude
            modulation (QAM) constellations with a minimum number of bits equal to one and a maximum number of
            bits equal to 12, 13 or 14 (based on the "FTU-O maximum bit loading" and "FTU-R maximum bit loading"
            capability indicated during initialization in the O-MSG 1 and R-MSG 2 messages for the FTU-O and FTU-R,
            respectively.
            NOTE – Supporting a maximum bit loading of 13 or 14 may lead to increased power consumption at the transmitter or
            the receiver or both relative to supporting a maximum bit loading of 12.





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