Re: Is the BBC deliberately degrading FM?

DAB sounds worse than FM wrote:


You are comparing apples to oranges. If you use multiple parallel
links, the bandwidth is there sum, as used in Shannon's theorem,
which is what matters. You can't do otherwise ... it's the laws of
physics. Shannon's law is a consequence of the Second Law of
Thermodynamics. You MUST multiply the bandwidth by the number
of channels to compare transmission efficiency. Note that
you could use multiple VSB channels and the same fudge
would apply.


In the MIMO literature they refer to the overall capacity, they do not divide by the minimum number of antennas at each end. The whole purpose of MIMO is to increase the overall capacity, so they're hardly going to want to use the normalised figure, are they?

For example, someone designing a system where they know how many antennas are going to be used is going to use the overall capacity value, not the normalised capacity value, because they want to see how much data they can squeeze through in total, not how much they can squeeze through per antenna.

Sorry, but you're just looking for excuses because you said that OFDM "IS inarguably inefficient", when in fact OFDM is nothing of the sort,


You use "OFDM". No, "OFDM" without the pilot carriers and without guard bands
is not inefficient. COFDM without pilot carriers and without guard band
has identical average power efficiency to 8-VSB with the same error correct
level and no pilot carrier. Note that that is AVERAGE power level, which
is what goes into Shannon's Law. COFDM **IS* less efficient than 8-VSB
when considering "wall plug" power compared to ATSC, because of the higher
peak/average power ratio.

I originally said "DVB-T COFDM" and that's what I mean. What is inefficient
is the use of pilot carriers and guard band. DBV-T style COFDM is inarguably
inefficient compared to 8-VSB. It requires more power to deliver the same
number of bits per second per Hz. And that includes the 10% power inefficiency
due to the (unnecessary) carrier in the US ATSC 8-VSB.

Using multiple antennas does not change that ... if you use DVB-T on
one set of antennas and ATSC 8-VSB on that same set, the efficiency
ratio remains the same.

Doug McDonald
.

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