Digital Signal Processing Reference
In-Depth Information
what would happen if the signal received from a more distant transmitter
violates the guard interval is easily answered: it results in intersymbol in-
terference which becomes noticeable as noise in the receiver.
Tx3, RF1
Tx1, RF1
Tx5, RF1
Playout
center
Distance
Tx4, RF1
Tx2, RF1
Fig. 20.23.
DVB-T single-frequency network (SFN)
Table 20.16.
Guard interval lengths for 8K, 2K modes and transmitter distances
(8 MHz channel)
Mode
Symbol
duration
Μs
Guard
interval
ratio
Guard
interval
Μs
Transmitter
distance
km
2K
224
1/4
56
16.8
2K
224
1/8
28
8.4
2K
224
1/16
14
4.2
2K
224
1/32
7
2.1
8K
896
1/4
224
67.1
8K
896
1/8
112
33.6
8K
896
1/16
56
16.8
8K
896
1/32
28
8.4
Signals from transmitters at greater distances must simply be attennu-
ated sufficiently. The threshold for quasi error free operation is formed by
the same conditions as for pure noise. It is, therefore, of particular impor-
tance that the levels in a single-frequency network are calibrated correctly.
It is not the maximum transmitting power at every transmitting site which
is required but the correct one. Planning of the network requires topog-
raphical information.
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