Terrestrial Transmission of Digital Television Signals (DVB-T) - Digital Video and Audio Broadcasting Technology - page 372

In many cases, however, network planning is relatively simple since
mostly only small regional single-frequency networks with only very few
transmitters are set up.

Table 20.17. Guard interval lengths for 8K, 2K modes and transmitter distances
(7 MHz channel)

Mode Symbol

duration
Μs

Guard
interval
ratio

Guard
interval
Μs

Transmitter
distance
km

2K 256 1/4 64 19.2

2K 256 1/8 32 9.6

2K 256 1/16 16 4.8

2K 256 1/32 8 2.4

8K 1024 1/4 256 76.7

8K 1024 1/8 128 38.4

8K 1024 1/16 64 19.2

8K 1024 1/32 32 9.6

Table 20.18. Guard interval lengths for 8K, 2K modes and transmitter distances
(6 MHz channel)

Mode Symbol

duration
Μs

Guard
interval

Guard
interval
Μs

Transmitter
distance
km

2K 299 1/4 75 22.4

2K 299 1/8 37 11.2

2K 299 1/16 19 5.6

2K 299 1/32 9 2.8

8K 1195 1/4 299 89.5

8K 1195 1/8 149 44.8

8K 1195 1/16 75 22.4

8K 1195 1/32 37 11.2

The velocity of light is c = 299792458 m/s which results in a signal de-
lay per kilometer transmitter distance of t 1km = 1000 m/c = 3.336 Μs. Since
in the 8K mode, the guard interval is longer in absolute terms, it is mainly
this mode which is provided for single frequency operation.
Long guard intervals are provided for single frequency networks. Me-
dium-length guard intervals are used in regional networks. The short guard
intervals, finally, are provided for local networks or used outside of single
frequency networks.