[opendtv] Re: PAL
- From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sat, 16 Dec 2006 10:38:29 -0500
Albert E. Manfredi wrote:
> The Chinese, in two of three training sequence options, seem to use a
partial repetition of the PN sequence. In one case, a 255 symbol sequence,
and in the other, a 511 symbol sequence, like the one in ATSC.
>"PN420 and PN945 are made up of a complete M-sequence of length 255 and
length 511, respectively and with their respective cyclical extensions as
pre-ambles and post-ambles, while PN595 is made up of the first 595 symbols
of an M-sequence of length 1023 and it has no cyclical characteristic."
>I'm not sure how this might be done, but if these extensions help, couldn't
we repurpose the three unused (as far as I know) PN63 sequences now in the
ATSC training segment? Would it help to create an extension to the PN511
sequence?
This has been proposed in the past, but has been stymied by the legacy
receiver concern. This is also why McDonald's repetitive PN1023 sequence
was not considered further.
After reflection I may have been too critical of the Chinese system design.
But their sequence 3 suggests that they are simply using the random
sequences as training signal for the Wiener method of adaptive equalization,
rather than as a basis for computing channnel impulse response by a DFT
method or by match filter.
Al
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