Transmitting Digital Television Signals by Satellite - DVB-S/S2 - Digital Video and Audio Broadcasting Technology - page 263

ever, to look for the two discrete points in the quadrant, decoding a further
bit for the low priority path in the process. In this case, 3 bits per symbol
are transmitted. There is also hierarchical modulation in DVB-T. After the
mapping, the signal passes through the physical layer framing and roll-off
filtering stages and is then converted into the modulation signal proper in
the IQ modulator. The roll-off factor is 0.20, 0.25 or 0.35.

Q

1010

1000

0010 0000

0110 0100

1100

1110

Code rates:
2/3, 3/4, 4/5,
5/6, 8/9, 9/10

I

0111

1111

0101

1101

0011

0001

1011

1001

Fig. 14.28. 16APSK

Q

01101

11101

01001
11001

01100

00101 00001

11100 00100

00000 01000

10101 10001

10100

Code rates:
¾, 4/5, 5/6,
8/9, 9/10

10000

11000

11110

I

10010

10110

10111 10011

01110

11010

00010

00110

00011

00111 01010

11111

11011

01111

01011

Fig. 14.29. 32 APSK

The error protection (Fig. 14.31.) consists of a BCH (Bose-Chaudhuri-
Hocquenghem) coder and an LDPC (low density parity check) encoder
followed by the bit interleaver. Possible code rates are 1/4 ... 9/10 and are