[opendtv] Re: 20060616 Free Friday Fragments (Mark's Monday Memo)

John Shutt wrote:

> 
> Even with more frequent training signals, adapting for severe changes in 
> multipath is a recursive process that will span several training sequences. 


NO NO NO ... and if the training sequences are much closer
together than 1/24 sec, interpolating between them becomes 
much, much easier and less computationally intensive.

BIG HINT: you can not only extrapolate FORWARD from a 
training sequence, you can interpolate bewteen them (or even 
extrapolate backward!) if you wish.

Just remember RECURSIVE ONLY IF YOU WNAT RECURSIVE!.
Just because you were taught "recursive" in school does not 
mean it HAS to be recursive!

> And the amount of data payload you eat up in the extra sequences brings your 
> total to something lower than the 1999 Sinclair Baltimore tests used for 
> DVB-T, 

Not necessarily. Certainly if you use much 2-VSB that 
happens ... but of course the same thing happens to DVB-T in 
robust modes.



> 
> We would have been much better off switching to DVB-T in 1999, since we 
> would have ended up with as good or better multipath performance at a higher 
> data payload than A-VSB or E-VSB.
>

But at a SERIOUSLY increased power supply bill. DVB-T and 
other COFDM schemes are still inefficient due to pilots and
guard intervals. A-VSB and like schemes add "pilots" but 
don't need guard intervals.

Read my lips: guard intervals will eventually join the dodo. 
(And then, of course, COFDM will equal single carrier 
schemes ... there will be not much to choose between them.)

Doug McDonald

 
 
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