[opendtv] Berlin report
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 23 Aug 2004 18:37:18 -0400
The Berlin SFN DTT experience is described in this project
report (an update of a previous one, apparently):
http://www.mabb.de/bilder/Projektbericht_engl.pdf
Some interesting highlights:
1. Before the transition, 8.9 percent of households in
Berlin and Brandenburg states depended on OTA TV
distribution entirely. An additonal 5 percent used OTA
for second and third sets in the household.
2. The Berlin and Brandenburg states, a single TV market,
had 12 analog stations, which they replaced with 9 DTT
multiplexed channels.
3. The transition took place from 1/1/2002 through 8/4/2003.
It consisted of selectively shutting off analog transmitters
and replacing these with digital. The higher power analog
were shut off first, one by one, over time. The low power
analog were the last to go off the air.
4. The 9 DTT channels, some VHF some UHF, range in power
from a low of 25 KW for VHF, replacing 100 KW analog, to
a high of 200 KW UHF, replacing 100 KW to 1 MW analog
transmitters.
5. A company called T-Systems was contracted with designing
the SFN. It consists of two towers. "Two transmitter
stations were established in a single frequency network.
Further transmitter locations could improve reception, but
this would require considerable additional expenditure."
They use COFDM with 16-QAM and 2/3 convolutional FEC.
6. The coverage patterns they show are based on Ch 44, which
is a 170 KW UHF transmitter pair.
7. Commercial broadcasters paid no more for this transition
than they would have paid to remain on the air with analog.
So the transition was a joint commercial and publically
funded effort.
8. The price goal for DTT STBs was set at 200 Euro. This was
quickly met and even reduced.
9. Channel 44 reception was found to be about what had been
estimated. That is:
Indoor reception out to just under 14.5 miles from
pattern center.
"Outdoor antenna" reception to 26.4 miles of pattern
center.
"Rooftop antenna" reception to 58.2 miles of pattern
center.
I estimated these distances based on landmarks the report
provides in their coverage map. Below I'll estimate the
antenna heights these numbers suggest. Unfortunately, the
report does not provide this info.
10. Of the STBs sold, 60 percent went to OTA users, 26
percent to cable subscribers, and 14 percent to DBS
subscribers. The vast majority went to folks living in
the "indoor coverage" area, i.e. people living within
14.5 miles of pattern center.
11. In the analog days, 66 percent of OTA users were the
"over 50" demographic. Now, 60 percent of OTA users are
in the "under 50" demographic.
12. The experience in Spain and the UK convinced mabb that
a free service should be used to introduce DTT. But plans
for the future include portable and mobile reception, as
well as pay TV, including the possibility of interactive
TV based on MHP and DTT-H to handheld devices. For these
portable and mobile services, they expect integrated
receivers will be mandatory.
The transmitter antenna height estimation uses the ITU-R
model, the COFDM mode performance expectations, and an
estimated receiver sensitivity for COFDM of -80 dBm.
C/N margins required for COFDM in this mode are:
14.2 dB for Rayleigh fading
11.6 dB for Ricean
11.1 dB for Gaussian
Reception of a signal from a 170 KW ERP transmitter with
-80 dBm receiver sensitivity and unity gain Rx antenna
implies a max total path loss of 162.3 dB. But 14.2 dB
of margin is required, leaving 148.1 dB of loss due to
distance alone, for indoor reception.
From this, if the receiver antenna is at 6' height, I
conclude that the Tx antenna must be just under 800'.
The roof mounted antenna coverage is about 58.2 miles.
Assuming gaussian fading, signal loss due to distance
alone can be up to 151.2 dB. Assuming a 30' antenna
height at the receiver, the transmitter's antenna must
have been 657'.
Now the intermediate position, with "outdoor antenna,"
will be assumed to have 16' height and Ricean fading.
The range is 26.4 miles, and the transmitter antenna
results in 677' antenna height.
So in all cases, these two sticks appear to be fairly
tall. It would be nice to know the actual height.
Bert
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