[opendtv] Re: WAS: --FCC OKs WiFi between TV channels
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 26 May 2004 10:37:48 -0400
Tom Barry wrote:
> So, are we all waiting for the 5'th generation Zenith boxes
> instead of the 4'th gen Linx boxes now?
No, why should we? The 5th gen Zenith appear to have a somewhat
wider range of echo tolerance possibly, but other than that,
they seem to be similar in performance to the Linx. But I've
not seen nearly as detailed test results for the Zenith
receivers.
The Brazil E results are virtually identical. Echo tolerance
might be +/- 50 usec vs +/- 38 usec, but even that apparent
difference is questionable, because the tolerance varies
according to echo strength. So you need more info to make
a valid comparison. Most likely, each one has its strengths
in slightly different conditions.
The Linx gets oustanding results in some other echo profiles,
such as Brazil C and D, where it requires only 13.3 and 12.6
dB of C/N with reacquisition (clearly using echo energy
contructively). I don't have the Zenith figures for
comparison.
Brazil C and D are less severe than Brazil E, in that the
second strongest signal path is attenuated by 0.1 dB compared
with the strongest path, and the other four echoes are even
weaker. Where Brazil E has three equally strong signals, with
1 usec spacing between each one.
Incidentally, the "generic" Rayleigh profile used in the ETSI
EN 300 744 simulation to derive the performance of COFDM
receivers is very clearly described in Annex B of the
document. Hard to make a very exact comparison with the
Brazil profiles, because the ensemble includes 20 total
signal paths of varying strength vs just 6 in most of the
Brazil profiles. But the important point is that the ETSI
document assumes only two of those paths to be strong, and
they are 0.065 dB different (10 * logbase10(0.407/0.401)
=3D 0.065 dB). So this profile is perhaps more comparable to
Brazil C or D than to Brazil E.
Bert
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