Page 766 - 5G Basics - Core Network Aspects
P. 766

2                                                 Transport aspects


            where NRMC = floor(LRMC/8). The number of padding bits added after the user data bytes shall be equal to the
            difference between the number of data bits modulated over user data tones (LDR) and the number of user
            data bits (8 × BDR) with BDR=floor(LDR/8). Figure 10-3 (on the bottom) shows the RMC symbol structure.
            The content of the padding bits is vendor discretionary. The values of LD, LR, and LDR shall accommodate
            actual bit loading and trellis overhead, as defined in clause 10.2.1.3.
            The order of the data extracted per symbol is presented in Figure 10-3 (shaded area shows padding bits).
            For normal data frames, the symbol encoder shall first extract BD bytes from the incoming data frame and
            then add (LD − 8×BD) padding bits. For RMC data frames, the symbol encoder shall first extract NRMC bytes
            from the incoming data frame and add (LRMC − 8×NRMC) padding bits, and then it shall extract BDR more bytes
            from the incoming data frame and add (LDR − 8×BDR) padding bits; the total number of bits LR = LRMC + LDR
            and the total number of bytes BR = NRMC + BDR.



























                                    Figure 10-3 – Order of bit extraction from data frame

            10.2.1.2   Tone ordering
            During the initialization, the receive FTU shall calculate the number of bits and the relative gains to be used
            for  every  subcarrier  in  the  MEDLEY  set  during  data  symbols  and  RMC  symbols  (either MEDLEYus  or
            MEDLEYds, depending on the transmission direction), as well as the order in which subcarriers are assigned
            bits (i.e., the tone ordering). The number of subcarriers in MEDLEYus and MEDLEYds is denoted by NSCus
            and NSCds, respectively.
            In addition, the receive FTU shall select the subcarriers used to encode the RMC during the RMC symbols.
            The selected RMC tone set is denoted by RTSus and RTSds for upstream and downstream, respectively. The
            number of subcarriers in the RMC tone set is denoted NSCRds and NSCRus for the downstream and upstream
            directions, respectively. The tones from the RMC tone set are exclusively for RMC and shall not carry any
            DTU  bits.  No  subcarriers  of  the  RMC  tone  set  shall  be  loaded  with  1-bit  for  RMC  symbols  or  for  data
            symbols in the NOI in order to use the same re-ordered tone table for data symbols in the NOI and RMC
            symbols. The RMC tone set may be modified in showtime through OLR. The FTU shall calculate the number
            of bits and the relative gains to be used for every subcarrier in the RMC tone set during RMC symbols and
            shall  send  them  back  to  the  transmit  FTU  during  initialization.  The  bits  and  gains  used  to  encode  the
            subcarriers not belonging to the RTS shall be the same for RMC and data symbols in the NOI.

            The pairs of bits and relative gains used for data symbols are defined in ascending order of frequency or
            subcarrier index i as a bit allocation table b and gain table g containing, respectively, bi and gi values for all
            subcarrier indices i that belong to the MEDLEY set. The bit allocation table b shall include an even number
            of 1-bit subcarriers (NCONEBIT).
            The tone ordering table t is defined as the sequence {tk} in which subcarriers from the MEDLEY set shall be
            assigned  bits.  Each  value  tk  (for  k  =  1  to  k  =  NSCus  for  the  upstream  tones,  k  =  1  to  k = NSCds  for  the


            756
   761   762   763   764   765   766   767   768   769   770   771