[opendtv] Re: Samsung Prototype ATSC Receiver Test Report

Frank Eory wrote:

> C'mon Al, T/2 equalizers are as old as the hills. I studied them in
college almost 2 decades ago and have built several in the intervening
years. Not all 8-VSB receivers use symbol-spaced equalizers, as we discussed
5 years ago in the ATSC ad-hoc group. So naturally, not all of them have
problems rejecting short-delay echoes. "Delay" never was and still is not a
real "problem" for equalizers in ATSC receivers -- delay, aka equalizer tap
spacing and total equalizer span, is just a matter of hardware...

The T/2 tap spacing is old, but the methods previously used for adjusting
the tap weights after data slicing (e.g. as described in Lee &
Messerschmidt) under-sampled the "feedback" concerning tap weight
adjustment. So, the performance advantages of T/2 equalizers over T
equalizers, as measured for fixed tap weights, are not realized.  The
deficiency shows up with short-delay echoes.

So, I believe USPAT 6,377,312 is instructive for most equalizer designers.

Al Limberg

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