Medium Access Control (MAC) and Physical Layer (PHY) - CISE

4-June-07 P1901_PRO_016_r0
Normal
Data
Frame
Frame after block
coding. msb is up.
Transmission order will be
top to bottom, msb first.
Figure 12 Adaptive mapping
Submission page 48 UPA-OPERA
BPS
Bits
Zero filling
if needed
BPS in the figure means the number of necessary data bits to fill an entire OFDM symbol with a certain bitloading.
A mathematical expression of this definition is shown in Equation 17. The last symbol shall be padded
with zeros before scrambling, if necessary, until an integer number of symbols is used.
3.5 TRELLIS CODED MODULATION (4D-TCM)
Once obtained a delimiter or data payload that will fill a integer number of OFDM symbols, a 16 state 4dimensional
truncated trellis code is used for error correction. This code will be applied over groups of 1536
subcarriers and reset each OFDM symbol, except in HURTO mode, where the 4D-TCM encoder will be reset
each 192 subcarriers out, or, in other words, each 288 bits in.
3.5.1 Bit Extraction
Data bits from both delimiters and data payload shall be extracted according to a bit-loading table bj, with
j=0…1535, righter bits first, in groups of z bits. In the case of HURTO mapping bj= 2 ∀j ∈ [0..1535]. Due to
the constellation expansion associated with coding and the 4-dimensional nature of the code, zi will be
calculated from a given pair (x,y) of two consecutive bj, where bj is the number of coded bits that subcarrier j
will transmit.
Due to the heavy impairments of the BPL channel, or regional regulations, some subcarriers can be set not to carry
any information. This case is denoted with a bit loading bj = 0 for such subcarriers. When the two consecutive
subcarriers x and y that form a symbol of the four dimensional code are set to zero, no bit extraction is performed,
and the following pair of subcarriers is taken into account. On the other hand, when only one of the two subcarriers