[opendtv] Re: LG launches 6th gen ATSC digital TV broadcast receiver chipset
- From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 23 Apr 2007 16:09:41 -0400
John Shutt wrote:
> I seemed to have taken away from the R-S presentation given to our SBE
chapter last fall that AVSB monkeyed around with the Trellis encoder and R/S
error correction to create "pseudo" training sequences.
> As that requires that the data interleaver and a deterministic R/S reset
be under the control of the modulator, AVSB would "break" all existing
encoders
anyway.
A-VSB really is a composite of two proposals. One part of the proposal is
to put prescribed reference sequences (SRS) of up to twenty bytes following
a 6-byte deterministic trellis reset (DTR), all put into an adaptation field
following a 2-byte adaptation field header in accordance with MPEG-2
protocol.
The other part is to use turbo coding of a serial form that includes the 2/3
trellis coding as one of the component convolutional codes. This allows
turbo coding to be done at half the code rate of ordinary 8VSB, rather than
one third that code rate. This is per se a damned good thought IMO, but
Samsung also puts the turbo coding into the adaption fields of MPEG-2
compliant data packets.
I think the Samsung serial turbo code will be used, but will be packed into
data segments differently than currently proposed. As I think John Wilkie
observed, PSIP is not fully MPEG-2 compliant; and some other utility signals
do not provide for adaptation fields.
SRS is used to help auto-regressive adaptive equalization under dynamic
multipath conditions, providing Wiener type feedback to help out Kalman type
feedback. It is probably better to use Doug McDonald's DFT methods for
adaptive equalization, which rely on self correlation of blocks of a few
thousand 8 VSB symbols and skip the SRS. This also boosts effective code
rate.
Al Limberg
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