[opendtv] Re: Qualcom OFDM networks with MediaFlo
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 10 Nov 2004 13:06:25 -0500
Craig Birkmaier wrote:
> Once again we have caught Bert shooting from the
> hip, at a target he missed by a mile.
Once again, lack of understanding of the subject
matter causes Craig to get all confused and to
hype up what is fairly straighforward.
First of all, I was quoting the original article,
posted by Bill Sheppard. That article had not
mentioned anything about COFDM.
As to this:
> What it IS, is a creative use of broadcast OFDM
> technology to ENHANCE the existing two-way CDMA
> infrastructure in a backward compatible way,
> delivering MANY of the services and benefits that
> I have been advocating via the "spectrum utility"
> concept.
The original concept was to transmit both one-way
TV and two-way cellular service using cdma2000.
The TV signals would use regular TV-like broadcast
towers. However, in order to allow for efficient
frequency reuse for the two-way cellular service,
the cellular service could not possibly also make
use of the big stick(s).
THEREFORE, replacing the CDMA big stick with a
COFDM big stick is easy enough to do, especially
when DVB-H already exists to make this an
efficient proposition for hand-helds.
So there's no "backward compatible" mumbo jumbo
involved here at all. It is just a way of
reapportioning the 700 MHz frequency band they
bought to provide the two services they want to
sell.
> Using CDMA unicast is highly inefficient, both
> in terms of spectral efficiency and power
> consumption,
Bull. CDMA is only less spectrally efficient than
COFDM *if* you use COFDM at 16-QAM or better.
That's because the CDMA downlink uses QPSK
(uplink BPSK). So you trade off robustness for bit
rate. But "highly inefficient" is clearly an
exaggeration. With CDMA, they might create
multiple channels with orthogonal spreading
codes. With COFDM, they might instead create
a single broadcast channel, and have receivers
tune into different subchannels of that one band.
> The physical infrastructure that Qualcom will
> use is virtually identical to that which I have
> been describing for COFDM-based SFNs for DTV.
> Transmission will come from "one or a small
> number of towers," potentially using tall
> buildings in urban areas.
Oh, PLEASE! Own up to having been spreading
illogical ideas nd misinformation, will you? The
infrastructure they are talking about is simply
big sticks, for the TV portion. Physics doesn't
care whether the tower is used for normal DTT or
for this mobile TV service, especially because
they are using the UHF band!
Tall towers and high power are essential for
efficient broadcast. Tall towers result in lower
propagation losses, and high power is needed for
range.
They said nothing about using only buildings for
the big stick or big sticks. That was your
editorial addition.
(In NYC, that might even work, just as regular
DTT towers do.)
Bert
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