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

4-June-07 P1901_PRO_016_r0
3.5.3 Bit conversion
The binary word u = (uz´, uz´-1,… u1) determines two binary words v’=(v’z´-y,…,v ’ 0) and w’=( w’y-1,…,w’0),
which are used to look up two constellations points in the encoder constellation table. As a first step, v and w
are obtained from u, as shown in Figure 14. Finally, v’ and w’ are obtained from v and w. For the usual case of
x≥2 and y≥2, z´=z=x+y-1, and v´=v and w´=w contain x and y bits respectively. For the special cases when
x=0 and y≥2, z´=z+2=y+1, v´=v=(v1,v0) and w´=w=(wy-1,…,w0), when y=0 and x≥2, z´=z+2=x+1,
w´=v=(v1,v0) and v´=w=(wx-1,…,w0), when x=1 and y≥2, z´=z+1=y, v´=v=(v1) and w´=w=(wy-1,…,w0), when
y=1 and x≥2, z´=z+1=x, w´=v=(v1) and v´=w=(wx-1,…,w0) and when x=1 and y=1, z´=z+2=3, v´=(w1) and
w´=(w0).
The bits (u3, u2, u1) determine (v1,v0) and (w1,w0) according to following figure:
u z´
u z´-1
u z´-y+3
u z´-y+2
u z´-y+1
u 4
u 3
u 2
u 1
Convolutional
Encoder
v1=u1⊕u3 v0=u3 w1=u0⊕u1⊕u2⊕u3 w0=u2⊕u3 Submission page 53 UPA-OPERA
u 2
u 1
u 0
Figure 14 Conversion of u to v and w
The convolutional encoder shown in Figure 14 is a systematic encoder as shown in Figure 15. At the beginning
of the encoding of each subcarrier group (1536 or 192 when HURTO mode is active), the convolutional encoder
state is initialized to (0,0,0,0). No special operation to terminate the code is performed.
w y-1
w y-2
w 2
v z´-y
v z´-y-1
v 2
v 1
v 0
w 1
w 0