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Transport aspects                                              2


            10.1.2.1   Vectoring interfaces

            Vectoring interfaces ε(k,n) and η(k,n) presented in Figure 10-1 (for downstream direction) and clarified in
            detail in Figure 10-16 are between the precoder and VCE and post-canceller and VCE, respectively. The
            primitives at vectoring interfaces provide the VCE with the signals necessary to perform channel estimation.
            The VCE, via vectoring interfaces, provides channel matrix coefficients to the precoder (via ε(k,n) interface,
            see  Figure  10-16)  and  to  the  post-canceller  (via η(k,n)  interface),  and  TIGA  settings  to  the  FTU-O  for
            communication to the FTU-R. Both vectoring interfaces are vendor discretionary.

            10.2    Symbol encoder
            This  clause  describes the data  symbol,  initialization symbol  and  pilot  symbol encoders of  the PMD (see
            Figure 10-1).
            10.2.1  Data symbol encoder
            The data symbol encoder provides the following functions:
            –       Bytes to bits padding;
            –       Tone ordering;
            –       Trellis coding;
            –       Constellation mapping;
            –       Constellation point scaling.

            The tone ordering and trellis coding shall be performed differently for data symbols and RMC symbols, as
            defined in clauses 10.2.1.2 and 10.2.1.3, respectively. The functional model of the data symbol encoder is
            defined in Figure 10-2.




























                                  Figure 10-2 – Functional model of the data symbol encoder
            10.2.1.1   Bytes to bits padding

            The data frames crossing the  interface from the PMS-TC include an integer number of bytes. Bits shall be
            extracted LSB first from the bytes received. Bit padding shall be used if the number of bits loaded onto one
            symbol is not an integer multiple of eight.

            For data symbols, up to seven padding bits shall be appended to the end of the data frame prior to the
            symbol encoding. The number of padding bits shall be equal to the difference between the number of data
            bits modulated over the symbol (LD) and the size of the data frame in bits (8 × BD), where BD=floor(LD/8).
            Figure 10-3 (on the top) shows the data symbol structure.
            For RMC symbols, padding bits shall be appended separately to the RMC part and the user data part of the
            data frame. The number of padding bits added after the RMC data shall be equal to the difference between
            the number of data bits modulated on RMC tones (LRMC) and the size of the RMC frame in bits (8 × NRMC),


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