[opendtv] Berlin SFNs
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 22 Aug 2005 16:46:48 -0400
I found some info that I hadn't seen before, with respect
to details of the Berlin DTT SFNs.
The Berlin DTT system, if you remember, is a set of seven
8 MHz channels, each one transmitting 4 program streams.
And the report
http://www.mabb.de/bilder/Projektbericht_engl.pdf
explains that the SFNs consist of two transmitters, with
output power varying between the different channels, from
a low of 25 KW (VHF) to a high of 180 KW.
More info is given in
http://www.garv.de/dvb_t_programme.htm
It wasn't clear that the info would be here, because they
only say that program info is given at that URL. But in
fact they also show the towers, the power output, and
the COFDM modes used.
1. The power output given in the project report (the first
URL listed) is a total of the power outputs from each of
the two or three towers. In fact, three towers are used
for the two VHF channels and one of the UHF channels.
2. The main transmitter site at Alexanderplatz transmits
10 KW for each VHF channel, 120 KW for two of the UHF
channels, and 20 or 10 KW for the remaining three UHF
channels.
3. A second tower, SW of the main one, is used for all
channels. This one, Shaefersberg, transmits 5 KW for VHF,
50 KW for all but one UHF channels, and 20 KW for one UHF
channel.
4. The two VHF channels and one of the UHF channel also
use a third transmitter, west of the main one, at
Scholtzplatz. This one is 10 KW for each of the three
channels it supports. Turns out the max output for any
given channel is actually only 170 KW, not 180 KW, but
only 120 KW, at best, can really be counted for coverage
to the North and East. Which explains the pattern.
Since the Alexanderplatz and Schaefersberg towers are
roughly 10.6 miles apart as the crow flies, they could
not use 1/16 GI for this unsynchronized SFN. So they
dialed in 1/8 GI, good for 14 mile spacing, and with
16-QAM and 2/3 FEC they achieve 14.75 Mb/s in each 8 MHz
band. And the C/N margin required is 11.1 to 14.2 dB.
Bert
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