[opendtv] Re: Charles Rhodes on unlicensed devices and white spaces
- From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 8 Aug 2007 17:44:06 -0400
I over-simplified the analysis, since a multi-carrier receiver presumably
limits the bandwidth associated with each carrier in the OFDM filter. This
improves SNR for the individual carriers. But random noise power increases
square root of two with doubling of bandwidth, so SNR for a single carrier
should still be superior, I think.
Al
----- Original Message -----
From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Wednesday, August 08, 2007 3:15 PM
Subject: [opendtv] Re: Charles Rhodes on unlicensed devices and white spaces
> You are thinking about co-channel interference, John. I think the primary
> concern is with third-order intermodulation with strong adjacent signals
in
> a supposedly vacant channel. This raises more hell with a multi-carrier
> signal than with a single-carrier signal. Noise contribution is the same,
> but desired signal strength is less. Single-carrier modulation has better
> SNR, as reported for other wide-band noise, it would seem to me.
>
> Al
>
> ----- Original Message -----
> From: "johnwillkie" <johnwillkie@xxxxxxxxxxxxx>
> To: <opendtv@xxxxxxxxxxxxx>
> Sent: Wednesday, August 08, 2007 2:10 PM
> Subject: [opendtv] Re: Charles Rhodes on unlicensed devices and white
spaces
>
>
> > It would depend on the impairment, no?
> >
> > However, for most impairments, which are transitory and usually involve
a
> > portion of a channel, a multicarrier system would seem to minimize
> > interference compared to a 'monolithic' carrier system.
> >
> > (There are more than a few published studies on this topic.)
> >
> > John Willkie
> >
> > -----Mensaje original-----
> > De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx]
En
> > nombre de Craig Birkmaier
> > Enviado el: Wednesday, August 08, 2007 6:35 AM
> > Para: opendtv@xxxxxxxxxxxxx
> > Asunto: [opendtv] Re: Charles Rhodes on unlicensed devices and white
> spaces
> >
> > At 5:20 PM -0400 8/7/07, Manfredi, Albert E wrote:
> > >http://www.tvtechnology.com/pages/s.0072/t.7434.html
> > >
> > >Needless to say, he's against them. He favors repacking the DTT
spectrum
> > >to accommodate these devices in a band of their own. He also doesn't
> > >have anything good to say about the possibility that these devices can
> > >adequately detect an open channel.
> > >
> > >My thought on this was, if a consumer-grade device is good enough to
> > >detect a very weak signal, which has to be well below -85 dBm, why
> > >wouldn't TV tuner manufacturers use such a tuner to improve TV
> > >reception?
> >
> > There are many questions raised here. Once again the tuner front end
> > seems to be the area where things get messy.
> >
> > A generic question here. Is a multi-carrier modulation system
> > susceptible to the same interference issues, or does the use of
> > multiple carriers help to mitigate the interference issues?
> >
> > >
> > >One interesting stat he gives is that OTA signal strengths under -68
dBm
> > >(what the FCC calls weak) occur in 84 percent of DTT coverage area.
> > >(Note by area, not population.)
> >
> > Why should this be any different than it has been for NTSC?
> > Obviiously the big sticks can't cover everything. This is the primary
> > reason that there are thousands of TV translators around the country,
> > trying to extend coverage to remote areas.
> >
> > At some point one must ask what is the proper "mesh" of services to
> > deliver digital entertainment services to everyone? Clearly
> > terrestrial RF cannot reach everyone, although it may be feasible to
> > reach 95% or more with the right infrastructure. But it seems far
> > more reasonable to use satellite to fill in the gaps.
> >
> > There is also the issue of where the white spaces spectrum is in the
> > highest demand. In general this will NOT be the remote areas, but
> > rather, the urban areas where DTV signal strength should be
> > relatively high. There is considerable interest in using the white
> > spaces for rural broadband services, but this may be accommodated
> > using properly designed services on channels that are adequately
> > separated to prevent interference.
> >
> > Regards
> > Craig
> >
> >
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