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Skinning the Multipath Cat

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Anonymous
May 12, 2005 10:42:08 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

Rack on AVSForum wrote today...

"Has anyone read anything about how the LGDT3303 performs its magic?
I know the Linx Casper chip was using some DSP magic (I think it was
some on-the-fly auto-correlation and digital filtering/signal shifting
to make the pilot and the echo waves interfere constructively) to get
their "5th generation" results, but I haven't read anything about how LG
is going about the process. It'd be interesting to know if there's more
than one way to skin the multipath cat."

The LGDT3303 is not what made the prototype tested last summer work. We
have tested two receivers now with this chip. One worked no better than
2+ generation receiver and the other is 4+ gen. That because the
manufacturer is getting tips from LG. It is the front end that makes the
difference and that may be too costly at the moment. Probably the same
problem with the Linx "Ghost".

There are many ways to "skin the multipath cat" for low cost and they
start with DMB-T, DMB-H, DBM-T, T-DMB and ISDB-T. The solution has been
around since 1998. We just don't have it in the US yet unless you talk
of Qualcomm, Crown Castle, XMRadio, Sirius, ENG, WiFi, WiMax, UWB and
any other modern RF use. All have COFDM in common.

Even the prototype we tested last summer that has everybody excited was
far from being in the same league with any COFDM system. The only way to
get such technology at the moment MAY be by buying one of the latest LG
DLP and one LG CRT HDTV. We will test a 52" LG DLP soon to see if indeed
they put their latest technology in it.

In the meantime Congress in the form of Chairman Barton are fixated in
getting cheap 8-VSB receivers subsidized. And we have the mandate that
has manufactures putting the cheapest 8-VSB receive tech into analog
sets and HD sets. They do not want to hear anything about multipath
issues or a receiver standard. Which in my opinion they should be
concentrating on since they were elected to look out for the taxpayers
interest.

As Chairman Barton said to me on Tuesday, "All the manufacturers are
telling him that there is NO problem with reception". And Motorola
chimed in that they have "perfect" receivers now.

What they should be doing is switching to a COFDM modulation and MPEG4
if anything but auction gold was on their mind. In essence they like CEA
head Shapiro have written OTA off and a dieing technology.

Bob Miller

More about : skinning multipath cat

Anonymous
May 13, 2005 1:05:08 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

Bob,

Not getting into the COFDM argument again, has the company that
produced the most recent LG 5th chip receiver prototype given up on
improving their design any further?

What is the chip number for the Motorola device that is supposed to be
perfect? Have you tested it?

IB
Anonymous
May 13, 2005 3:07:46 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

Bob,

You did not answer my questions. I asked you if the most recent
company to send you a receiver prototype using the new LG 5th chip has
given up on improving their design.

I asked about the new Motorola chip you refer to. I am unclear if you
meant to say that Motorola was in fact referring to the LG chip instead
of their own new design. Hard to imagine Motorola using an LG chip.

IB
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Anonymous
May 13, 2005 6:29:00 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

inkyblacks@yahoo.com wrote:
> Bob,
>
> Not getting into the COFDM argument again, has the company that
> produced the most recent LG 5th chip receiver prototype given up on
> improving their design any further?
>
> What is the chip number for the Motorola device that is supposed to be
> perfect? Have you tested it?
>
> IB
>
It is the same 5th gen chip, the LGDT3303. But that is not where the
solution lays. The problem is in the front end. I have a feeling as many
have told me over the years that the cost is the problem. Cost of the
correct front end for 8-VSB. Not a problem with COFDM. And that is where
the insurmountable problem may lay for Congress. Can they afford to
subsidize receivers if they cost too much. So what I see happening in DC
is they have closed their ears and covered their eyes to all talk of
receiver standard or any problem of reception so that they can buy the
cheapest receiver possible. One just like those now being installed in
TV sets to meet the mandate.

Congress knows and I am sure manufacturers are whispering in their ears
that the quality of the receiver doesn't matter because either the
integrated set will never be used with an antenna, 85% plus, or it will
be used by demographically challenged and non voters, the other 15%.

This is a cynical take on OTA being taken by Congress, the FCC and as
articulated over the last few days by the head of the CEA, Gary Shapiro.
Here is what he said before the ATSC on Tuesday (the bastards who stuck
us with 8-VSB). Gary Shapiro is one of the dumbest characters in this
whole disaster. It is hard to believe that he represents the CEA.

http://www.tvweek.com/news.cms?newsId=7825
"Thumbing his nose at broadcasters, Gary Shapiro, president and CEO of
the Consumer Electronics Association, characterized over-the-air TV as a
dying medium Tuesday and made a thinly veiled threat to pull his
organization out of the Advanced Television Systems Committee -- the
industry group charged with setting broadcast digital TV standards."

This has been his thinking as well as that of the former Chairman of the
FCC Powell. I believe many in Congress feel the same way. It is easy to
detect when you are one on one with the FCC. They think that OTA is dead
and not to make to much of a fuss over it. This thinking is prevalent in
DC and has been for many years. The fact that they are starting to say
it publicly is the only thing that is new. Congress and the FCC will
kill off OTA tomorrow if it was politically possible. 8-VSB is making it
more and more politically possible.

Even with the best front end for 8-VSB it will not compare with the
simplest COFDM receiver of 1999 or a $50 COFDM receiver of 2005.

Bob Miller
Anonymous
May 13, 2005 6:29:01 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

Bob Miller wrote:
>
> Cost of the
> correct front end for 8-VSB. Not a problem with COFDM.

Care to prove that there is a difference between the physics of a
receiver's front end for 8-VSB and COFDM?

We are talking RF, not digital, not data, especially not modulation. The
front end is all about matching levels and impedence.

--
Matthew

I'm a contractor. If you want an opinion, I'll sell you one.
Which one do you want?
Anonymous
May 13, 2005 10:23:43 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

inkyblacks@yahoo.com wrote:
> Bob,
>
> You did not answer my questions. I asked you if the most recent
> company to send you a receiver prototype using the new LG 5th chip has
> given up on improving their design.
>
> I asked about the new Motorola chip you refer to. I am unclear if you
> meant to say that Motorola was in fact referring to the LG chip instead
> of their own new design. Hard to imagine Motorola using an LG chip.
>
> IB
>
They have not given up.

Motorola was talking in general terms. The guy who spoke up knew nothing
as I later found out when speaking with him. He didn't even recognize
the term multipath.

Bob Miller
May 14, 2005 2:07:09 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

<inkyblacks@yahoo.com> wrote in message
news:1115957108.390615.95510@g49g2000cwa.googlegroups.com...
> Bob,
>
> Not getting into the COFDM argument again, has the company that
> produced the most recent LG 5th chip receiver prototype given up on
> improving their design any further?
>
> What is the chip number for the Motorola device that is supposed to be
> perfect? Have you tested it?
>
> IB
>

Bob apparently has _zero_ broadcasting engineering knowledge. As a matter
of fact, he actually posted awhile ago that changing antennas will not make
any difference in reception issues.

IMO, he's the last person in this NG you should be asking advise from.
Anonymous
May 14, 2005 9:48:49 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

Most implementations of Wi-Fi in multi-path prone environments rely on
diversity antenna deployment to decrease signal drop-outs. This is helpful
but I work for a sizable WiFi manufacturer and have a team that has done
well over 3000 Wi-Fi deployments in a wide array of commercial environments
and we do have sites where multi-path continues to plague performance
despite using dual diversity (both mobile and AP have diversity antennae),
those sites work VERY poorly without diversity installed on at least the
fixed end. COFDM is not a cure all for this common RF issue by any means.

Bob K.


"Bob Miller" <robmx@earthlink.net> wrote in message
news:4sNge.289$DK.160@newsread3.news.pas.earthlink.net...
> Rack on AVSForum wrote today...
>
> "Has anyone read anything about how the LGDT3303 performs its magic?
> I know the Linx Casper chip was using some DSP magic (I think it was
> some on-the-fly auto-correlation and digital filtering/signal shifting
> to make the pilot and the echo waves interfere constructively) to get
> their "5th generation" results, but I haven't read anything about how LG
> is going about the process. It'd be interesting to know if there's more
> than one way to skin the multipath cat."
>
> The LGDT3303 is not what made the prototype tested last summer work. We
> have tested two receivers now with this chip. One worked no better than
> 2+ generation receiver and the other is 4+ gen. That because the
> manufacturer is getting tips from LG. It is the front end that makes the
> difference and that may be too costly at the moment. Probably the same
> problem with the Linx "Ghost".
>
> There are many ways to "skin the multipath cat" for low cost and they
> start with DMB-T, DMB-H, DBM-T, T-DMB and ISDB-T. The solution has been
> around since 1998. We just don't have it in the US yet unless you talk
> of Qualcomm, Crown Castle, XMRadio, Sirius, ENG, WiFi, WiMax, UWB and
> any other modern RF use. All have COFDM in common.
>
> Even the prototype we tested last summer that has everybody excited was
> far from being in the same league with any COFDM system. The only way to
> get such technology at the moment MAY be by buying one of the latest LG
> DLP and one LG CRT HDTV. We will test a 52" LG DLP soon to see if indeed
> they put their latest technology in it.
>
> In the meantime Congress in the form of Chairman Barton are fixated in
> getting cheap 8-VSB receivers subsidized. And we have the mandate that
> has manufactures putting the cheapest 8-VSB receive tech into analog
> sets and HD sets. They do not want to hear anything about multipath
> issues or a receiver standard. Which in my opinion they should be
> concentrating on since they were elected to look out for the taxpayers
> interest.
>
> As Chairman Barton said to me on Tuesday, "All the manufacturers are
> telling him that there is NO problem with reception". And Motorola
> chimed in that they have "perfect" receivers now.
>
> What they should be doing is switching to a COFDM modulation and MPEG4
> if anything but auction gold was on their mind. In essence they like CEA
> head Shapiro have written OTA off and a dieing technology.
>
> Bob Miller
Anonymous
May 15, 2005 4:39:38 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

bobukcat wrote:
> Most implementations of Wi-Fi in multi-path prone environments rely on
> diversity antenna deployment to decrease signal drop-outs. This is helpful
> but I work for a sizable WiFi manufacturer and have a team that has done
> well over 3000 Wi-Fi deployments in a wide array of commercial environments
> and we do have sites where multi-path continues to plague performance
> despite using dual diversity (both mobile and AP have diversity antennae),
> those sites work VERY poorly without diversity installed on at least the
> fixed end. COFDM is not a cure all for this common RF issue by any means.
>
> Bob K.

Are you talking about 802.11b, a or g or all three? 80211.b is not
COFDM. And WiFi is not the same as using DVB-T with its different
settings in a 700 MHz space for one way broadcast.

The real proof of COFDM's capability comes in the real world using it as
intended. Our video...

www.viacel.com/bob.wmv

is the real world and shows both diversity and non diversity. The screen
on the seat back is diversity the other two are not.

This is a real world test with a transmitter at 100 Watts in what has to
be the worst RF environment there is, Manhattan. COFDM is the cure for
multipath both static and dynamic when broadcasting in 700 MHz. Is it
perfect? No but it is being improved all the time as witnessed by the
ISDB-T and DMB-T modulations using COFDM and improvements in DVB-T and
DVB-H.

This video doesn't even show how much better COFDM would be if we were
using an SFN, diversity on the transmit side. We were using a single
transmitter. We could have been using six transmitters around Manhattan.
But it is easy to see that a single transmitter with non diversity
reception works very well with DVB-T. And the Chinese say their DMB-T is
far better than DVB-T mobile which means it is better fixed as well.

There is still time for the US to change modulations. Few 8-VSB
receivers have been sold. And we would also benefit by going to MPEG4 at
the same time which does a far better job of handling HD or multiple HD
programs in a single channel or even 1080P.

Otherwise the US will be stuck with the worst DTV modulation in the
world far behind the technology of Japan, France, Germany , the UK and
many others.

We started with HD because we were terrified of being beaten by the
Japanese. Now we will find ourselves with the worst system. Doesn't make
sense.

Bob Miller
>
>
> "Bob Miller" <robmx@earthlink.net> wrote in message
> news:4sNge.289$DK.160@newsread3.news.pas.earthlink.net...
>
>>Rack on AVSForum wrote today...
>>
>>"Has anyone read anything about how the LGDT3303 performs its magic?
>>I know the Linx Casper chip was using some DSP magic (I think it was
>>some on-the-fly auto-correlation and digital filtering/signal shifting
>>to make the pilot and the echo waves interfere constructively) to get
>>their "5th generation" results, but I haven't read anything about how LG
>>is going about the process. It'd be interesting to know if there's more
>>than one way to skin the multipath cat."
>>
>>The LGDT3303 is not what made the prototype tested last summer work. We
>>have tested two receivers now with this chip. One worked no better than
>>2+ generation receiver and the other is 4+ gen. That because the
>>manufacturer is getting tips from LG. It is the front end that makes the
>>difference and that may be too costly at the moment. Probably the same
>>problem with the Linx "Ghost".
>>
>>There are many ways to "skin the multipath cat" for low cost and they
>>start with DMB-T, DMB-H, DBM-T, T-DMB and ISDB-T. The solution has been
>>around since 1998. We just don't have it in the US yet unless you talk
>>of Qualcomm, Crown Castle, XMRadio, Sirius, ENG, WiFi, WiMax, UWB and
>>any other modern RF use. All have COFDM in common.
>>
>>Even the prototype we tested last summer that has everybody excited was
>>far from being in the same league with any COFDM system. The only way to
>>get such technology at the moment MAY be by buying one of the latest LG
>>DLP and one LG CRT HDTV. We will test a 52" LG DLP soon to see if indeed
>>they put their latest technology in it.
>>
>>In the meantime Congress in the form of Chairman Barton are fixated in
>>getting cheap 8-VSB receivers subsidized. And we have the mandate that
>>has manufactures putting the cheapest 8-VSB receive tech into analog
>>sets and HD sets. They do not want to hear anything about multipath
>>issues or a receiver standard. Which in my opinion they should be
>>concentrating on since they were elected to look out for the taxpayers
>>interest.
>>
>>As Chairman Barton said to me on Tuesday, "All the manufacturers are
>>telling him that there is NO problem with reception". And Motorola
>>chimed in that they have "perfect" receivers now.
>>
>>What they should be doing is switching to a COFDM modulation and MPEG4
>>if anything but auction gold was on their mind. In essence they like CEA
>>head Shapiro have written OTA off and a dieing technology.
>>
>>Bob Miller
>
>
>
May 15, 2005 4:39:39 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

"Bob Miller" <robmx@earthlink.net> wrote in message
news:eTwhe.749$Lc1.500@newsread3.news.pas.earthlink.net...
> bobukcat wrote:
>> Most implementations of Wi-Fi in multi-path prone environments rely on
>> diversity antenna deployment to decrease signal drop-outs. This is
>> helpful
>> but I work for a sizable WiFi manufacturer and have a team that has done
>> well over 3000 Wi-Fi deployments in a wide array of commercial
>> environments
>> and we do have sites where multi-path continues to plague performance
>> despite using dual diversity (both mobile and AP have diversity
>> antennae),
>> those sites work VERY poorly without diversity installed on at least the
>> fixed end. COFDM is not a cure all for this common RF issue by any means.
>>
>> Bob K.
>
> Are you talking about 802.11b, a or g or all three? 80211.b is not COFDM.
> And WiFi is not the same as using DVB-T with its different settings in a
> 700 MHz space for one way broadcast.
>
> The real proof of COFDM's capability comes in the real world using it as
> intended. Our video...
>
> www.viacel.com/bob.wmv


"Ever feel like banging your head against the wall? Now's your chance
without the concussion."

http://baronbobgifts.com/headbanger.htm
Anonymous
May 15, 2005 4:22:59 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

Bob Miller wrote:
> It is the same 5th gen chip, the LGDT3303. But that is not where the
> solution lays. The problem is in the front end.


Do you know what the front-end difference is? Typically a front-end is
simply an amplification stage, ideally low noise with high signal
handling capability, used to isolate the antenna input from the
receiver. It sets the basic lower and upper signal handling limitations
and it may also employ AGC control. Other then striving for the "ideal"
front end, is there any unique front-end qualities that the "real" 5th
gen receiver employees?
Anonymous
May 15, 2005 8:49:59 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <DaHhe.215527$cg1.209969@bgtnsc04-news.ops.worldnet.att.net>,
numeric <numeric@att.net> writes:
>
>
> Bob Miller wrote:
>> It is the same 5th gen chip, the LGDT3303. But that is not where the
>> solution lays. The problem is in the front end.
>
>
> Do you know what the front-end difference is? Typically a front-end is
> simply an amplification stage, ideally low noise with high signal
> handling capability, used to isolate the antenna input from the
> receiver. It sets the basic lower and upper signal handling limitations
> and it may also employ AGC control. Other then striving for the "ideal"
> front end, is there any unique front-end qualities that the "real" 5th
> gen receiver employees?
>
Not answering your specific question, but there are some issues that
are missing in your (mostly complete) list of front end criteria. Here
is a list off the top of my head (not in order of importance):

1. NF at match
Just preamp -- 0.5dB is practical. With filters and careful
design, perhaps 3dB or so. Frankly, I suspect that a total NF
of 1dB is possible, but would definitely require front end stages
that are capable of very high signal handling.
2. NF over wide input impedance ranges (needed due to antenna.)
Noise resistance (Rn/50) of about 0.1 is easy with current components,
some can do 0.01 or 0.02. This provides an idea of the sensitivity
noise on input due to impedance mismatch. Previous generation components
had much higher noise resistance and therefore noise was very sensitive
to mismatch. (Current generation components can be chosen for noise
to be relatively insensitive to bias point also.)
3. P1dB (output power near saturation) -- 10-20dBm aren't impossible with LN.
4. 3rd order intermod performance (I/O IM3.) >30dBm isn't impossible.
5. Return loss (at least 10dB over 50-800MHz.) Achievable with above specs
given good PHEMT technology. (HP 54143.) It isn't too hard to achieve
15dB or better, with perhaps a few bumps.
6. I/O Isolation -- single stage, at least 15-20dB given typical negative
feedback. With multi-stage, you can do alot better. With some compromise
in power handling/distortion or using circulators/isolators, you can
do ALOT better.
7. Front end gain should be limited -- so that subsequent mixer and other
portions aren't overloaded. It is now easy to attain very high power
output in frontend, but subsequent stages are still problematical. Perhaps
it is good to avoid simple mixers that inject an oscillator into a
conventional nonlinear gain stage, but use more performant balanced
mixers AT LEAST like using quad diode, and perhaps using balanced FET
schemes... With a probable 10dB mixer noise figure, there is tension
between desiring more than 10dB of total front end gain (to start swamping
the mixer noise) and avoiding pushing the circuit into nonlinearity.
8. If AGC might be needed, perhaps PIN diodes are better than using variable
operating point (gm)?

The problem with the above (and other specs), is that such performance requires
the use of transistors that cost approx $2.00 each, and perhaps two might
be desirable to meet all of the above specs (the I/O isolation while still
supporting very low distortion at high -- >10dBm output power.)

With the above, I'd suspect that many of the so-called 'multipath' problems
would disappear. In my own experience, when properly matching the indoor
antenna, and managing the signal levels, my UHF DTV reception has become
very solid when compared with an 'out of the box' conventional front end with
a direct antenna connection through 10feet of coax.

John
May 15, 2005 8:50:00 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

John, Bob, et al,

There has been no mention of phase response in the RF amplifier passband,
nor has there been mention of gain uniformity. I would think that both could
have a direct impact on multipath processing in the subsequent stages.

Smarty



"John S. Dyson" <toor@iquest.net> wrote in message
news:D 67ujn$2onf$1@news.iquest.net...
> In article <DaHhe.215527$cg1.209969@bgtnsc04-news.ops.worldnet.att.net>,
> numeric <numeric@att.net> writes:
>>
>>
>> Bob Miller wrote:
>>> It is the same 5th gen chip, the LGDT3303. But that is not where the
>>> solution lays. The problem is in the front end.
>>
>>
>> Do you know what the front-end difference is? Typically a front-end is
>> simply an amplification stage, ideally low noise with high signal
>> handling capability, used to isolate the antenna input from the
>> receiver. It sets the basic lower and upper signal handling limitations
>> and it may also employ AGC control. Other then striving for the "ideal"
>> front end, is there any unique front-end qualities that the "real" 5th
>> gen receiver employees?
>>
> Not answering your specific question, but there are some issues that
> are missing in your (mostly complete) list of front end criteria. Here
> is a list off the top of my head (not in order of importance):
>
> 1. NF at match
> Just preamp -- 0.5dB is practical. With filters and careful
> design, perhaps 3dB or so. Frankly, I suspect that a total NF
> of 1dB is possible, but would definitely require front end stages
> that are capable of very high signal handling.
> 2. NF over wide input impedance ranges (needed due to antenna.)
> Noise resistance (Rn/50) of about 0.1 is easy with current components,
> some can do 0.01 or 0.02. This provides an idea of the sensitivity
> noise on input due to impedance mismatch. Previous generation
> components
> had much higher noise resistance and therefore noise was very sensitive
> to mismatch. (Current generation components can be chosen for noise
> to be relatively insensitive to bias point also.)
> 3. P1dB (output power near saturation) -- 10-20dBm aren't impossible with
> LN.
> 4. 3rd order intermod performance (I/O IM3.) >30dBm isn't impossible.
> 5. Return loss (at least 10dB over 50-800MHz.) Achievable with above
> specs
> given good PHEMT technology. (HP 54143.) It isn't too hard to achieve
> 15dB or better, with perhaps a few bumps.
> 6. I/O Isolation -- single stage, at least 15-20dB given typical negative
> feedback. With multi-stage, you can do alot better. With some
> compromise
> in power handling/distortion or using circulators/isolators, you can
> do ALOT better.
> 7. Front end gain should be limited -- so that subsequent mixer and other
> portions aren't overloaded. It is now easy to attain very high power
> output in frontend, but subsequent stages are still problematical.
> Perhaps
> it is good to avoid simple mixers that inject an oscillator into a
> conventional nonlinear gain stage, but use more performant balanced
> mixers AT LEAST like using quad diode, and perhaps using balanced FET
> schemes... With a probable 10dB mixer noise figure, there is tension
> between desiring more than 10dB of total front end gain (to start
> swamping
> the mixer noise) and avoiding pushing the circuit into nonlinearity.
> 8. If AGC might be needed, perhaps PIN diodes are better than using
> variable
> operating point (gm)?
>
> The problem with the above (and other specs), is that such performance
> requires
> the use of transistors that cost approx $2.00 each, and perhaps two might
> be desirable to meet all of the above specs (the I/O isolation while still
> supporting very low distortion at high -- >10dBm output power.)
>
> With the above, I'd suspect that many of the so-called 'multipath'
> problems
> would disappear. In my own experience, when properly matching the indoor
> antenna, and managing the signal levels, my UHF DTV reception has become
> very solid when compared with an 'out of the box' conventional front end
> with
> a direct antenna connection through 10feet of coax.
>
> John
Anonymous
May 16, 2005 1:28:13 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <oomdnTXML73OLBrfRVn-3Q@adelphia.com>,
"Smarty" <nobody@nobody.com> writes:
> John, Bob, et al,
>
> There has been no mention of phase response in the RF amplifier passband,
> nor has there been mention of gain uniformity. I would think that both could
> have a direct impact on multipath processing in the subsequent stages.
>
For a relatively wideband preamp, there really shouldn't be too bad a phase
response/gain uniformity problem. For a narrowband IF, that is a different
story. Doing a single stage 10-15dB gain pHEMT over a 50-800MHz bandwidth
should be very feasable.

Since the topic was 'front end', that would tend to imply a relatively wideband
thingie with gradual skirts.

John
May 16, 2005 1:50:26 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

Thanks for the reply John. For the wideband example you have cited, which is
a likely approach to a tuner front-end, I agree that a design with
relatively flat bandpass and gentle roll off is achievable and unlikely to
substantially impact multipath performance.

Smarty

"John S. Dyson" <toor@iquest.net> wrote in message
news:D 68etd$2tgc$1@news.iquest.net...
> In article <oomdnTXML73OLBrfRVn-3Q@adelphia.com>,
> "Smarty" <nobody@nobody.com> writes:
>> John, Bob, et al,
>>
>> There has been no mention of phase response in the RF amplifier passband,
>> nor has there been mention of gain uniformity. I would think that both
>> could
>> have a direct impact on multipath processing in the subsequent stages.
>>
> For a relatively wideband preamp, there really shouldn't be too bad a
> phase
> response/gain uniformity problem. For a narrowband IF, that is a
> different
> story. Doing a single stage 10-15dB gain pHEMT over a 50-800MHz bandwidth
> should be very feasable.
>
> Since the topic was 'front end', that would tend to imply a relatively
> wideband
> thingie with gradual skirts.
>
> John
Anonymous
May 16, 2005 4:27:00 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

I'm talking about primarily G/B, and I'll note that YOU are the one who
mentioned Wi-Fi as proof of COFDM's capabilities - I pointed out the
problems with it to see if you would be willing to admit that .llb - which
is the "Wi-Fi" 95% of people have experience with (if any) - isn't COFDM
even though you neglected to mention it when touting it as proof that the
"reliable" data transmission schemes use it.

Bob K.


"Bob Miller" <robmx@earthlink.net> wrote in message
news:eTwhe.749$Lc1.500@newsread3.news.pas.earthlink.net...
> bobukcat wrote:
> > Most implementations of Wi-Fi in multi-path prone environments rely on
> > diversity antenna deployment to decrease signal drop-outs. This is
helpful
> > but I work for a sizable WiFi manufacturer and have a team that has done
> > well over 3000 Wi-Fi deployments in a wide array of commercial
environments
> > and we do have sites where multi-path continues to plague performance
> > despite using dual diversity (both mobile and AP have diversity
antennae),
> > those sites work VERY poorly without diversity installed on at least the
> > fixed end. COFDM is not a cure all for this common RF issue by any
means.
> >
> > Bob K.
>
> Are you talking about 802.11b, a or g or all three? 80211.b is not
> COFDM. And WiFi is not the same as using DVB-T with its different
> settings in a 700 MHz space for one way broadcast.
>
> The real proof of COFDM's capability comes in the real world using it as
> intended. Our video...
>
> www.viacel.com/bob.wmv
>
> is the real world and shows both diversity and non diversity. The screen
> on the seat back is diversity the other two are not.
>
> This is a real world test with a transmitter at 100 Watts in what has to
> be the worst RF environment there is, Manhattan. COFDM is the cure for
> multipath both static and dynamic when broadcasting in 700 MHz. Is it
> perfect? No but it is being improved all the time as witnessed by the
> ISDB-T and DMB-T modulations using COFDM and improvements in DVB-T and
> DVB-H.
>
> This video doesn't even show how much better COFDM would be if we were
> using an SFN, diversity on the transmit side. We were using a single
> transmitter. We could have been using six transmitters around Manhattan.
> But it is easy to see that a single transmitter with non diversity
> reception works very well with DVB-T. And the Chinese say their DMB-T is
> far better than DVB-T mobile which means it is better fixed as well.
>
> There is still time for the US to change modulations. Few 8-VSB
> receivers have been sold. And we would also benefit by going to MPEG4 at
> the same time which does a far better job of handling HD or multiple HD
> programs in a single channel or even 1080P.
>
> Otherwise the US will be stuck with the worst DTV modulation in the
> world far behind the technology of Japan, France, Germany , the UK and
> many others.
>
> We started with HD because we were terrified of being beaten by the
> Japanese. Now we will find ourselves with the worst system. Doesn't make
> sense.
>
> Bob Miller
> >
> >
> > "Bob Miller" <robmx@earthlink.net> wrote in message
> > news:4sNge.289$DK.160@newsread3.news.pas.earthlink.net...
> >
> >>Rack on AVSForum wrote today...
> >>
> >>"Has anyone read anything about how the LGDT3303 performs its magic?
> >>I know the Linx Casper chip was using some DSP magic (I think it was
> >>some on-the-fly auto-correlation and digital filtering/signal shifting
> >>to make the pilot and the echo waves interfere constructively) to get
> >>their "5th generation" results, but I haven't read anything about how LG
> >>is going about the process. It'd be interesting to know if there's more
> >>than one way to skin the multipath cat."
> >>
> >>The LGDT3303 is not what made the prototype tested last summer work. We
> >>have tested two receivers now with this chip. One worked no better than
> >>2+ generation receiver and the other is 4+ gen. That because the
> >>manufacturer is getting tips from LG. It is the front end that makes the
> >>difference and that may be too costly at the moment. Probably the same
> >>problem with the Linx "Ghost".
> >>
> >>There are many ways to "skin the multipath cat" for low cost and they
> >>start with DMB-T, DMB-H, DBM-T, T-DMB and ISDB-T. The solution has been
> >>around since 1998. We just don't have it in the US yet unless you talk
> >>of Qualcomm, Crown Castle, XMRadio, Sirius, ENG, WiFi, WiMax, UWB and
> >>any other modern RF use. All have COFDM in common.
> >>
> >>Even the prototype we tested last summer that has everybody excited was
> >>far from being in the same league with any COFDM system. The only way to
> >>get such technology at the moment MAY be by buying one of the latest LG
> >>DLP and one LG CRT HDTV. We will test a 52" LG DLP soon to see if indeed
> >>they put their latest technology in it.
> >>
> >>In the meantime Congress in the form of Chairman Barton are fixated in
> >>getting cheap 8-VSB receivers subsidized. And we have the mandate that
> >>has manufactures putting the cheapest 8-VSB receive tech into analog
> >>sets and HD sets. They do not want to hear anything about multipath
> >>issues or a receiver standard. Which in my opinion they should be
> >>concentrating on since they were elected to look out for the taxpayers
> >>interest.
> >>
> >>As Chairman Barton said to me on Tuesday, "All the manufacturers are
> >>telling him that there is NO problem with reception". And Motorola
> >>chimed in that they have "perfect" receivers now.
> >>
> >>What they should be doing is switching to a COFDM modulation and MPEG4
> >>if anything but auction gold was on their mind. In essence they like CEA
> >>head Shapiro have written OTA off and a dieing technology.
> >>
> >>Bob Miller
> >
> >
> >
Anonymous
May 17, 2005 1:34:34 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

Normally when I mention WiFi as an example of a COFDM I specify a, g. I
didn't this time by mistake.

Bob Miller

bobukcat wrote:
> I'm talking about primarily G/B, and I'll note that YOU are the one who mentioned Wi-Fi as proof of COFDM's capabilities - I pointed out the
> problems with it to see if you would be willing to admit that .llb - which is the "Wi-Fi" 95% of people have experience with (if any) - isn't COFDM
> even though you neglected to mention it when touting it as proof that the "reliable" data transmission schemes use it.
>
> Bob K.
>
>
> "Bob Miller" <robmx@earthlink.net> wrote in message
> news:eTwhe.749$Lc1.500@newsread3.news.pas.earthlink.net...
>
>>bobukcat wrote:
>>
>>>Most implementations of Wi-Fi in multi-path prone environments rely on
>>>diversity antenna deployment to decrease signal drop-outs. This is
>
> helpful
>
>>>but I work for a sizable WiFi manufacturer and have a team that has done
>>>well over 3000 Wi-Fi deployments in a wide array of commercial
>
> environments
>
>>>and we do have sites where multi-path continues to plague performance
>>>despite using dual diversity (both mobile and AP have diversity
>
> antennae),
>
>>>those sites work VERY poorly without diversity installed on at least the
>>>fixed end. COFDM is not a cure all for this common RF issue by any
>
> means.
>
>>>Bob K.
>>
>>Are you talking about 802.11b, a or g or all three? 80211.b is not
>>COFDM. And WiFi is not the same as using DVB-T with its different
>>settings in a 700 MHz space for one way broadcast.
>>
>>The real proof of COFDM's capability comes in the real world using it as
>>intended. Our video...
>>
>>www.viacel.com/bob.wmv
>>
>>is the real world and shows both diversity and non diversity. The screen
>>on the seat back is diversity the other two are not.
>>
>>This is a real world test with a transmitter at 100 Watts in what has to
>>be the worst RF environment there is, Manhattan. COFDM is the cure for
>>multipath both static and dynamic when broadcasting in 700 MHz. Is it
>>perfect? No but it is being improved all the time as witnessed by the
>>ISDB-T and DMB-T modulations using COFDM and improvements in DVB-T and
>>DVB-H.
>>
>>This video doesn't even show how much better COFDM would be if we were
>>using an SFN, diversity on the transmit side. We were using a single
>>transmitter. We could have been using six transmitters around Manhattan.
>>But it is easy to see that a single transmitter with non diversity
>>reception works very well with DVB-T. And the Chinese say their DMB-T is
>>far better than DVB-T mobile which means it is better fixed as well.
>>
>>There is still time for the US to change modulations. Few 8-VSB
>>receivers have been sold. And we would also benefit by going to MPEG4 at
>>the same time which does a far better job of handling HD or multiple HD
>>programs in a single channel or even 1080P.
>>
>>Otherwise the US will be stuck with the worst DTV modulation in the
>>world far behind the technology of Japan, France, Germany , the UK and
>>many others.
>>
>>We started with HD because we were terrified of being beaten by the
>>Japanese. Now we will find ourselves with the worst system. Doesn't make
>>sense.
>>
>>Bob Miller
>>
>>>
>>>"Bob Miller" <robmx@earthlink.net> wrote in message
>>>news:4sNge.289$DK.160@newsread3.news.pas.earthlink.net...
>>>
>>>
>>>>Rack on AVSForum wrote today...
>>>>
>>>>"Has anyone read anything about how the LGDT3303 performs its magic?
>>>>I know the Linx Casper chip was using some DSP magic (I think it was
>>>>some on-the-fly auto-correlation and digital filtering/signal shifting
>>>>to make the pilot and the echo waves interfere constructively) to get
>>>>their "5th generation" results, but I haven't read anything about how LG
>>>>is going about the process. It'd be interesting to know if there's more
>>>>than one way to skin the multipath cat."
>>>>
>>>>The LGDT3303 is not what made the prototype tested last summer work. We
>>>>have tested two receivers now with this chip. One worked no better than
>>>>2+ generation receiver and the other is 4+ gen. That because the
>>>>manufacturer is getting tips from LG. It is the front end that makes the
>>>>difference and that may be too costly at the moment. Probably the same
>>>>problem with the Linx "Ghost".
>>>>
>>>>There are many ways to "skin the multipath cat" for low cost and they
>>>>start with DMB-T, DMB-H, DBM-T, T-DMB and ISDB-T. The solution has been
>>>>around since 1998. We just don't have it in the US yet unless you talk
>>>>of Qualcomm, Crown Castle, XMRadio, Sirius, ENG, WiFi, WiMax, UWB and
>>>>any other modern RF use. All have COFDM in common.
>>>>
>>>>Even the prototype we tested last summer that has everybody excited was
>>>>far from being in the same league with any COFDM system. The only way to
>>>>get such technology at the moment MAY be by buying one of the latest LG
>>>>DLP and one LG CRT HDTV. We will test a 52" LG DLP soon to see if indeed
>>>>they put their latest technology in it.
>>>>
>>>>In the meantime Congress in the form of Chairman Barton are fixated in
>>>>getting cheap 8-VSB receivers subsidized. And we have the mandate that
>>>>has manufactures putting the cheapest 8-VSB receive tech into analog
>>>>sets and HD sets. They do not want to hear anything about multipath
>>>>issues or a receiver standard. Which in my opinion they should be
>>>>concentrating on since they were elected to look out for the taxpayers
>>>>interest.
>>>>
>>>>As Chairman Barton said to me on Tuesday, "All the manufacturers are
>>>>telling him that there is NO problem with reception". And Motorola
>>>>chimed in that they have "perfect" receivers now.
>>>>
>>>>What they should be doing is switching to a COFDM modulation and MPEG4
>>>>if anything but auction gold was on their mind. In essence they like CEA
>>>>head Shapiro have written OTA off and a dieing technology.
>>>>
>>>>Bob Miller
>>>
>>>
>>>
>
>
Anonymous
May 17, 2005 1:40:53 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

Look at this. IB
----------------------------------------------------------------------
http://www.engadget.com/entry/1234000500042416/

The Clicker: Single Frequency Networks and OTA HDTV
Posted May 5, 2005, 4:20 PM ET by Peter Rojas
Related entries: Displays, HDTV, Home Entertainment

Every Thursday Stephen Speicher contributes The Clicker, a weekly
column on television and technology:


One look at the eye-popping picture and you were hooked. The
window-like effect dazzled you. You all but drooled over the rock-solid
picture. There's no snow. There's no ghosting. The resolution is to
die for. You saw the light and its name was High-Definition. There's
only one problem: you can't seem to pull in a reliable OTA
(over-the-air) signal.

Oh sure, cable is an alternative for many. However, over the years,
you've been spoiled; you're hooked on your PVR. And, as a
connoisseur of PVRs, you understand that the cable companies offer
anemic light-weight versions. You demand more. You're not happy
unless you've got your TiVo or your MCE (Microsoft Media Center
Edition). You've even been known to utter the phrase, "They'll
have to rip my TiVo out of my cold dead hands." Worse yet, you meant
it - LITERALLY.

Fear not - all hope is not lost. Despite previous attempts to scale
your house with antenna in hand only to be denied a clean signal, there
are two reasons to still have hope: a) Single-Frequency Networks and b)
5th generation receivers.

Since the beginning of broadcasting nearly all stations have followed
the same steps when it comes to transmitting their signals: a) do your
best to locate the tower in the middle b) build the tower high and c)
add power. The problem is that, in some regions, this method just
doesn't cut it. Natural terrain presents issues as do man-made
buildings. Signals bounce around or, worse yet, fly right over your
head. If State College, Pennsylvania's WPSX is a harbinger of things
to come, the answer to your woes just might be Single-Frequency
networks (SFNs).

More commonly discussed within the context of Europe's COFDM, SFNs
are beginning to show signs that they might just work with America's
8-VSB modulation scheme also.

So what are SFNs?

Simply stated, single-frequency networks are when a broadcaster uses
multiple transmitters to send the same signal over the same frequency.
The idea is that in certain geographically-difficult areas broadcasters
will have much better success if they can fill coverage voids by
utilizing smaller, usually-less-powerful satellite towers in addition
to their main tower.

It sounds like a simple idea, but, as always, the devil is in the
details. Unlike the repeater towers that are sometimes used in western
states (AKA translators), SFNs aren't simply receiving the signal,
error-correcting, and retransmitting on a different frequency. That is
an extremely inefficient use of the spectrum.

So what are they doing?

There are two main methods of creating a single-frequency network. The
first is through the use of on channel boosters. On channel boosters
quickly receive the OTA signal from the main tower and retransmit the
signal on the same frequency. The problem is that there is no error
correction. So, any errors in reception are simply retransmitted along
with the slight echo caused by the booster itself. On channel boosters
are also limited in their placement as they need reliable reception
from the main tower.

So, when WPSX took the plunge into SFNs, it opted for option two,
distributed transmission. Working with the New Jersey-based Merrill
Weiss Group, WPSX has created one of nation's most
technologically-advanced broadcasting systems.

With distributed transmission, the signal is delivered to each of its
transmitters via fixed channels (land-based delivery). Then through the
use of GPS-based reference clocks at each tower (for both time and
frequency), the signals are synced so each can emit a perfect copy of
both signal and symbol data. The result is a group of towers working in
harmony.

So why isn't this done more often (at all)?

No matter how synchronized the output from the towers may be, there
will always be some amount of multi-path to deal with, and until
recently receiver hardware wasn't equipped to handle anything but
very minor levels of multi-path. Multi-path? Yes, multi-path is the
result of your receiver seeing the same signal more than once. This can
be caused by a variety of things. For instance, in a crowded downtown
area the signal can bounce off buildings many times before it hits your
antenna. The problem occurs when some copies of the data arrive more
quickly than others. This, in effect, can jam your receiver.

The same effect occurs within SFNs. Because waves from different towers
have the potential to reach your antenna at different times, a
receiver's ability to handle multi-path is paramount to its success.

With that said, LG has continued to make great strides in their ability
to handle multi-path issues. Through the use of techniques such as
adaptive equalizing they have even begun to turn a negative into a
positive. First generation tuners had a multi-path window of -3 to +10
us. Fifth generation tuners have increased that window to -50 to +50.
As always bigger numbers are way better.

So, if you're like me, unable to receive a signal despite near-heroic
efforts. Have hope; there's technology out there that might just help
one day.

But for now - we wait.
Anonymous
May 17, 2005 11:19:42 AM

Archived from groups: alt.tv.tech.hdtv (More info?)

On 16 May 2005 21:40:53 -0700, "inkyblacks@yahoo.com"
<inkyblacks@yahoo.com> wrote:

>

Big snip... nothing to read.. just speculation..

SFN's have a problem with the signals canceling each other out,
because the signals arrive at the consumers location in varying
degrees of phase. It requires very careful planning, and placement
of transmission towers.. An unlikely event to occur in many of the
US's larger metropolitan areas..


Next.. is the commercial and operational aspects.

The FCC limits ownership of TV stations.. so that the networks own no
more than 35% of the potential viewers.. the rest are independent..
Each station provides their own advertising content and programming
during non prime time hours.


Third.. The existing HDTV/8VSB system using on-interfering
channels works well beyond initial expectations. The virtual channel
reassignment capability has no problem remapping DTV broadcasts to the
old NTSC channel assignments.

Those factors among several others preclude SFN's from being a
viable choice for the US..
Anonymous
May 17, 2005 9:39:31 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

I will believe SFN networks working with 8-VSB when I see it.

And why are we waiting? Why have we been waiting for seven years? What
do we gain by trying to make this 8-VSB turkey of a modulation work when
the rest of the world has a number of infinitely better modulations?

Bob Miller

inkyblacks@yahoo.com wrote:
> Look at this. IB
> ----------------------------------------------------------------------
> http://www.engadget.com/entry/1234000500042416/
>
> The Clicker: Single Frequency Networks and OTA HDTV
> Posted May 5, 2005, 4:20 PM ET by Peter Rojas
> Related entries: Displays, HDTV, Home Entertainment
>
> Every Thursday Stephen Speicher contributes The Clicker, a weekly
> column on television and technology:
>
>
> One look at the eye-popping picture and you were hooked. The
> window-like effect dazzled you. You all but drooled over the rock-solid
> picture. There's no snow. There's no ghosting. The resolution is to
> die for. You saw the light and its name was High-Definition. There's
> only one problem: you can't seem to pull in a reliable OTA
> (over-the-air) signal.
>
> Oh sure, cable is an alternative for many. However, over the years,
> you've been spoiled; you're hooked on your PVR. And, as a
> connoisseur of PVRs, you understand that the cable companies offer
> anemic light-weight versions. You demand more. You're not happy
> unless you've got your TiVo or your MCE (Microsoft Media Center
> Edition). You've even been known to utter the phrase, "They'll
> have to rip my TiVo out of my cold dead hands." Worse yet, you meant
> it - LITERALLY.
>
> Fear not - all hope is not lost. Despite previous attempts to scale
> your house with antenna in hand only to be denied a clean signal, there
> are two reasons to still have hope: a) Single-Frequency Networks and b)
> 5th generation receivers.
>
> Since the beginning of broadcasting nearly all stations have followed
> the same steps when it comes to transmitting their signals: a) do your
> best to locate the tower in the middle b) build the tower high and c)
> add power. The problem is that, in some regions, this method just
> doesn't cut it. Natural terrain presents issues as do man-made
> buildings. Signals bounce around or, worse yet, fly right over your
> head. If State College, Pennsylvania's WPSX is a harbinger of things
> to come, the answer to your woes just might be Single-Frequency
> networks (SFNs).
>
> More commonly discussed within the context of Europe's COFDM, SFNs
> are beginning to show signs that they might just work with America's
> 8-VSB modulation scheme also.
>
> So what are SFNs?
>
> Simply stated, single-frequency networks are when a broadcaster uses
> multiple transmitters to send the same signal over the same frequency.
> The idea is that in certain geographically-difficult areas broadcasters
> will have much better success if they can fill coverage voids by
> utilizing smaller, usually-less-powerful satellite towers in addition
> to their main tower.
>
> It sounds like a simple idea, but, as always, the devil is in the
> details. Unlike the repeater towers that are sometimes used in western
> states (AKA translators), SFNs aren't simply receiving the signal,
> error-correcting, and retransmitting on a different frequency. That is
> an extremely inefficient use of the spectrum.
>
> So what are they doing?
>
> There are two main methods of creating a single-frequency network. The
> first is through the use of on channel boosters. On channel boosters
> quickly receive the OTA signal from the main tower and retransmit the
> signal on the same frequency. The problem is that there is no error
> correction. So, any errors in reception are simply retransmitted along
> with the slight echo caused by the booster itself. On channel boosters
> are also limited in their placement as they need reliable reception
> from the main tower.
>
> So, when WPSX took the plunge into SFNs, it opted for option two,
> distributed transmission. Working with the New Jersey-based Merrill
> Weiss Group, WPSX has created one of nation's most
> technologically-advanced broadcasting systems.
>
> With distributed transmission, the signal is delivered to each of its
> transmitters via fixed channels (land-based delivery). Then through the
> use of GPS-based reference clocks at each tower (for both time and
> frequency), the signals are synced so each can emit a perfect copy of
> both signal and symbol data. The result is a group of towers working in
> harmony.
>
> So why isn't this done more often (at all)?
>
> No matter how synchronized the output from the towers may be, there
> will always be some amount of multi-path to deal with, and until
> recently receiver hardware wasn't equipped to handle anything but
> very minor levels of multi-path. Multi-path? Yes, multi-path is the
> result of your receiver seeing the same signal more than once. This can
> be caused by a variety of things. For instance, in a crowded downtown
> area the signal can bounce off buildings many times before it hits your
> antenna. The problem occurs when some copies of the data arrive more
> quickly than others. This, in effect, can jam your receiver.
>
> The same effect occurs within SFNs. Because waves from different towers
> have the potential to reach your antenna at different times, a
> receiver's ability to handle multi-path is paramount to its success.
>
> With that said, LG has continued to make great strides in their ability
> to handle multi-path issues. Through the use of techniques such as
> adaptive equalizing they have even begun to turn a negative into a
> positive. First generation tuners had a multi-path window of -3 to +10
> us. Fifth generation tuners have increased that window to -50 to +50.
> As always bigger numbers are way better.
>
> So, if you're like me, unable to receive a signal despite near-heroic
> efforts. Have hope; there's technology out there that might just help
> one day.
>
> But for now - we wait.
>
Anonymous
May 17, 2005 9:45:19 PM

Archived from groups: alt.tv.tech.hdtv (More info?)

Tim Keating wrote:
> On 16 May 2005 21:40:53 -0700, "inkyblacks@yahoo.com"
> <inkyblacks@yahoo.com> wrote:
>
>
>
> Big snip... nothing to read.. just speculation..
>
> SFN's have a problem with the signals canceling each other out,
> because the signals arrive at the consumers location in varying
> degrees of phase. It requires very careful planning, and placement
> of transmission towers.. An unlikely event to occur in many of the
> US's larger metropolitan areas..

An SFN worked fine with COFDM in NYC.
>
>
> Next.. is the commercial and operational aspects.
>
> The FCC limits ownership of TV stations.. so that the networks own no more than 35% of the potential viewers.. the rest are independent..
> Each station provides their own advertising content and programming during non prime time hours.

Don't understand this item.
>
>
> Third.. The existing HDTV/8VSB system using on-interfering channels works well beyond initial expectations. The virtual channel
> reassignment capability has no problem remapping DTV broadcasts to the old NTSC channel assignments.

If I understand this one your saying that the current system doesn't
need SFN's because it works so well? Why then is the FCC working on
allowing SFN's?
>
> Those factors among several others preclude SFN's from being a
> viable choice for the US..

SFN's will be deployed using COFDM in the US by Qualcomm and Crown
Castle for starters.

Bob Miller
!