[opendtv] Re: How About Portable ATSC Receivers?

  • From: Steve Jones <codesjones@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Fri, 01 Apr 2005 10:07:13 -0800

Ron,

Your comment is not quite correct "This will cause almost every ATSC
receiver to display a black screen and no audio".  The early receivers
did not use the VCT information for programing.  They only used the
PAT/PMTs this was because most manufactures used their core code base
from there DVB receiver product lines. The demand on the manufacturer
for supporting the guide information and compliance to the ATSC table
specification pushed forward and they started to process the MGT and VCT
for program information. This is were I have seen the problem manifest
it self into what you are seeing.  

The encoders are usually MPEG/DVB and do not have support for the full
ATSC tables(PSIP).  The broadcaster has some table generator to supply
the PSIP and these two devices require the broadcaster to manually enter
the program information into his table generator.  The information being
entered is the encoders descriptors, program numbers and PIDs.  This is
were most of the problems start.  The tables are muxed together and the
feed is transmitted.  Then the broadcaster has a drone receiver to see
that his signal is good.  This is usually that really old receiver I
told you about earlier, the one that only looks at the PAT and PMTs.
Surprise every thing looks good. The other problem is if the broadcaster
does a code update or worse the encoder crashes.  The chances of the
encoder coming backup with the same program numbers and pids is a 50/50
chance.  This will now leave the system in a disparity between the PSIP
and the encoder, as you are seeing.

With all this being said, and the chances of changing the PMT-to-VCT
duplication mistake in the ATSC spec. are never going to happen.  The
broadcasters need to push back on the vendors to prevent these
disparity's from happening and remove the human error factor.  I have
seen a few way's to handle this problem, but all have there flaws.  The
one that I think is the best is at the multiplexer.  The multiplexer has
taken on additional roles of compliance protector and live monitor.  It
is also the last in the chain that can manage the PSIP.  The
configuration of the mux as the protector would be to lock down the PIDs
and program numbers on the inputs from the encoders and block the
PAT/PMTs from the table generator and have the multiplexer re-generate
all the tables accordingly.  Logic Innovations has a mux that can do
this, and I am not sure if there are any others.

Something to think about,

Codejones


On Fri, 2005-04-01 at 03:23 -0800, Ron Economos wrote:
> Here's my favorite example of DTV apathy. I've
> dumped the Transport Stream from KFSF-DT below.
> KFSF-DT transmits from Sutro tower in San Francisco
> with 150 kW ERP. It's a TeleFutura affiliate.
> They have a great signal in Milpitas (tons better
> than the analog channel) and their SD video quality
> is really quite nice.
> 
> As you can see, the TVCT PID's are mismatched fromRon
> the PMT PID's. This will cause almost every ATSC
> receiver to display a black screen and no audio.
> It's been like this since January when they attempted
> to meet the 0x30 and above PID requirement.
> 
> I think it may be possible that this DTV station
> has zero viewers.
> 
> Ron
> 

 
 
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