[opendtv] Re-evaluating Rome's SFNs

From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
Date: Fri, 9 Jul 2010 18:50:50 -0500
The topic of spectrum efficiency resulting from the use of SFNs made me rethink 
Rome's current setup. Briefly, two transmitter sites, one way up 3100' above 
sea level, and the other Monte Mario, merely 456' altitude.

The two locations are used in SFN for the UHF channels (not for the VHF 
channels). And the GI is set to 1/4.

Now here's the deal. Monte Cavo, the second tallest of Alban hills immediately 
South of Rome, is so high that its transmitters essentially cover all of Rome 
and many other communities besides. Monte Mario, instead, is only useful for 
the northern parts of Rome. For instance, there are communities North of Rome 
that use Monte Cavo, not Monte Mario as one might think, just because the 
towers are so much higher.

But the transmitters used are low power, by our standards, so that SFN or no 
SFN, you need outdoor yagis pointed specifically at one or the other location 
to get reliable reception.

And the other piece of the puzzle is, this Rome SFN only applies to Rome. 
Transmitter locations in adjacent markets use different frequencies.

So here's a proposal to increase the spectral efficiency of this setup.

The GI of 1/4 is used to ensure that the two tower farms don't interfere. But 
the reason they might interfere is because this is a true SFN. Meaning, the ERP 
is close to the same from the two locations. (We're talking ERP in the 10s of 
KW only. Much like France.)

What if, instead, the ERP from Monte Cavo were increased by, say, 3 to 6 dB, 
and the Monte Mario location were converted into an on-channel gap filler? If 
the signal from Monte Mario were allowed to be more quickly overpowered from 
the Monte Cavo site, you wouldn't need that wasteful 1/4 GI. The GI could be 
reduced probably to 1/16 anyway, or even 1/32 as in France, and you'd gain 
almost 4 or more than 4 Mb/s of channel capacity, without reducing the C/N 
margin requirement. (8K, 64 QAM, 2/3 FEC is used in Italy.)

This should also help reduce the complaints about the Monte Mario site, right 
there in a residential neighborhood. Given that adjacent markets are used as 
interference buffers anyway, I think this demonstrates just the sort of 
balancing act that's involved with SFNs.

Bert
 
 
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[opendtv] Re-evaluating Rome's SFNs

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