Digital Signal Processing Reference
In-Depth Information
voting for each symbol and is then used for the demodulation. DBPSK
means that a zero is transmitted when the state of the TPS carriers changes
from one symbol to the next, and a one if the TPS carrier phase does not
change from one symbol to the next. The complete TPS information is
broadcast over 68 symbols and comprises 67 bits. This segment over 68
symbols is called a frame and the scattered pilots within this frame also
jump over the DVB-T channel from the start of the channel right to the end
of the channel.
Q
I
Fig. 20.5.
DBPSK modulated TPS carriers
17 of the 68 TPS bits are used for initialization and synchronization, 13
bits are error protection, 22 bits are used at present and 13 bits are reserved
for future applications. Table 20.1. explains how the TPS carriers are util-
ized.
Thus, the TPS carriers keep the receiver informed about:
•
Mode (2K, 8K)
•
Length of the guard interval (1/4, 1/8, 1/16, 1/32)
•
Type of modulation (QPSK, 16QAM, 64QAM)
•
Code rate (1/2, 2/3, 3/4, 5/6, 7/8)
•
Use of hierarchical coding
However, the receiver should have already determined the mode (2K,
8K) and the length of the guard interval which are thus actually meaning-
less as TPS information.
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