[opendtv] Cellular and SFN mix

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
  • Date: Thu, 15 Nov 2012 17:28:52 -0600

Since this topic seems to elicit vague and unworkable thoughts, here's the 
simple facts.

You can deploy a dense mesh of small sticks, and use different frequency 
channels in each one. You can use some of the freqs in a SFN, and others in 
cellular mode (where you have the checkerboard of different frequencies).

LTE can do this. LTE already has the signaling channels required for cellular 
handovers, in cellular mode, and it has the guard intervals adequate for SFNs.

But can you use the physically different small sticks as a way to differentiate 
ad transmissions, via "checkerboard" topology, when operating in SFN? No.

Why? Just think it through. At some point, you will inevitably have to transmit 
different ad content on two adjacent SFN towers. That's inevitable, and it will 
create interference zones.

As to broadcasters themselves building such an LTE infrastructure. The mesh of 
small sticks becomes dense. To achieve 3.1 b/s/Hz, in MBMS mode, which is close 
to 8T-VSB, requires 2 Km spacing between sticks (1.25 mi.).

http://www.ericsson.com/res/thecompany/docs/journal_conference_papers/wireless_access/p22-huschke.pdf

In the conclusions, "Our simulations show that MBMS has a spectral efficiency 
of 3.1b/s/Hz up to a cellular inter-site-distance of 2km."

Greater spacing results in less spectral efficiency. In one presentation passed 
around, it said 4 Km (2.5 mi) spacing for 1.5 b/s/Hz. I couldn't find that 
presentation, unfortunately.

So that means, hundreds of these small sticks, or over 1000, depending on the 
coverage your market needs. We also went through this in the past.

Bert

 
 
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  • » [opendtv] Cellular and SFN mix - Manfredi, Albert E