Transmitting Digital Television Signals by Satellite - DVB-S/S2 - Digital Video and Audio Broadcasting Technology - page 262

transport stream or of generic data streams. Following the mode and
stream adaptation blocks, the data are fed to the FEC encoding block.

Q

10

00

Code rates:
1/4, 1/3, 2/5;
1/2; 3/5, 2/3,
3/4, 4/5, 5/6,
8/9, 9/10

I

11

01

Fig. 14.26. Gray-coded QPSK, absolute mapping (like DVB-S)

Q

100

110

000

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

010

I

001

011

101

111

Fig. 14.27. Gray-coded 8PSK

In the downstream mapper, QPSK (Fig. 14.26.), 8PSK (Fig. 14.27.),
16APSK (Fig. 14.28.) or 32APSK (Fig. 14.29.) is then mapped. This is al-
ways absolute mapping, i.e. non-differential. Hierarchical modulation is a
special case. It is virtually backward compatible with the DVB-S standard,
making it possible to transmit a DVB-S stream and an additional DVB-S2
stream. In the hierarchical modulation mode (Fig. 14.30.), the constellation
can be interpreted in two different ways.
The quadrant can be interpreted as a constellation point, gaining 2 bits
for the high priority path conforming to DVB-S. It is also possible, how-