[opendtv] Re: Qualcom OFDM networks with MediaFlo
- From: Bob Miller <bob@xxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 10 Nov 2004 17:36:18 -0500
Craig Birkmaier wrote:
>At 1:06 PM -0500 11/10/04, Manfredi, Albert E wrote:
>
>
>>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).
>>
>>
>
>here we go again...
>
>So I take it Bert was involved in the development of this system and
>knows that this was the original plan. If this is not the case,
>perhaps Bert can provide us with some evidence that this is what
>Qualcom was planning to do.
>
>
>
>>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.
>>
>>
>
>They are not using COFDM big sticks Bert.
>
>This was documented by both Bob and myself. Please do not confuse the
>use of really high powered transmitters (50KW to 1 MW) on really big
>sticks, with what Qualcom has announced. They may be "big sticks"
>compared to existing cellular networks, however they are just what
>yo0u would expect for a COFDM-based Single Frequency Network.
>
>
>
>>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.
>>
>>
>
>You obviously did not read the links I provided. These networks have
>been designed to work together to maximize the potential for both.
>The backbone structure for both networks uses the SAME IP packet
>structure. The servers provide this data in a form that is equally
>useful for both modulation schemes (i.e. the packets are the SAME).
>COFDM is simply a more efficient way to deliver this data to CDMA
>enabled appliances, especially as it relates to power consumption.
>
>
>
>>> 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.
>>
>>
>
>You missed it again Bert.
>
>The channels are 1.25 MHz. They can be used to deliver any kind of
>packet data including audio and video. But this has nothing to do
>with what I wrote.
>
>Spectral efficiency comes from the ability to use the best form of
>modulation AND network infrastructure for unicast AND multicast data.
>The high density of CDMA towers achieves two benefits:
>
>1. Efficient spectral re-use for unjicast transactions as the cell
>sizes are small and the power levels are very very low.
>
>2. The ability to provide reliable two-way connections from CDMA
>phones and appliances that transmit at even lower power levels than
>the cell towers.
>
>In simple English, you need many small cells for a two-way unicast network.
> in the original message is the poor spectral efficiency that results
>in any cellular data network, when many users are trying to download
>the same bits. To a limited extent Qualcom has addressed this on the
>CDMA network side by using IP multicasts to serve multiple users in
>the same cell; but this still ties up the CDMA network for an
>application that is better served via the COFDM network. Hence the
>decision to move to SFNs with larger cells to deliver one way data
>broadcast services.
>
>This approach moves most of the IP Multicast traffic OFF of the CDMA
>network, freeing up bandwidth for more unicast and phone
>transactions. The added benefit is that services delivered via the
>COFDM network can be designed with real interactivity using the "CDMA
>back channel." And then there is the added benefit of the lower power
>consumption of the COFDM receiver, which does not need to
>continuously transmit bits back to the CDMA network, as is the case
>with a unicast transaction.
>
>There is MUCH MORE to spectral efficiency Bert, than just the number
>of bits you can deliver per Hz.
>
>
>
>>> 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!
>>
>>
>
>You are the one who is being illogical and spreading disinformation Bert.
>
>Physics have nothing to do with this. What we are talking about is
>the relative power levels and tower heights needed for a REAL big
>stick system versus COFDM Single Frequency Networks. Do you really
>think that Qualcom is going to start building 1000-2000 foot towers
>Bert?
>
>PLEASE STOP spreading the fertilizer.
>
>
>
>>Tall towers and high power are essential for
>>efficient broadcast. Tall towers result in lower
>>propagation losses, and high power is needed for
>>range.
>>
>>
>
>DUH!
>
>We've been through all of this before Bert. COFDM SFNs use lower
>towers and lower power levels than the high power big sticks used by
>Broadcasters.
>
>Get over it.
>
>
>
>>They said nothing about using only buildings for
>>the big stick or big sticks. That was your
>>editorial addition.
>>
>>
>
>Nor did I. I did suggest that some of the cell sites may be on
>building rather than towers; this was not in any of the articles that
>Bob and I cited. I have no reason to believe that this will be the
>case, given the cost and difficulty in citing tall broadcast towers.
>
>One COULD speculate that Qualcom may try to do deals with TV
>broadcasters to put their COFDM transmitters on existing towers in
>return for delivering their content to the mobile audience.
>
>I did provided two references that verified the notion that these
>would be COFDM SFNs. You might want to look again at the link Bob
>provided which states:
>
>
>
>>Paul Jacobs, head of the unit that houses MediaFLO, said the FLO
>>OFDM-based technology uses high broadcast towers and high wattage to
>>cover a city with an average of 2-3 transmitters, using the former
>>analog TV spectrum in 700MHz, which should be vacated by 2007-8 as
>>the broadcasters shift into digital TV.
>>
>>
>
>
>
>>(In NYC, that might even work, just as regular
>>DTT towers do.)
>>
>>
>
>It does work, as Viacel and ABC have already proven in NYC.
>
>Regards
>Craig
>
I should mention that the Qualcomm plan is not nearly as far along as
their press releases suggest. Also the rules for the spectrum they are
using limit the power to 50 kW ERP. So it is impossible for them to be
considering MEGA Watt power levels. For example they talk of delivering
local content but with a country wide SFN that would be ridiculous and
if you don't have a country wide SFN you have to allow for a lot of area
where there would be no coverage between SFNs. So I don't think they
have thought it through totally.
It might be possible, however, to petition the FCC to allow higher power
levels in some areas. After all they do own channel 55 country wide.
Bob Miller
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