Re: An idea. Could diversity reception be useful for DAB(+).

"Richard Evans" <rp.evans@xxxxxxxxxxxxx> wrote in message
news:24173e64-fa97-4823-b656-b4de95aa11a8@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
(I'm reposting this via Google as my previous attempt seems to have
failed, sorry if it ended up posted twice)

This is something I've been thinking about a fair bit recently, and
I'm wondering whether it would actually work, and whether it would
actually make a significant difference.

Some new broadcast systems use more than one transmit antenna, but
only one receive antenna.


That's referred to as "transmit diversity", whereas "receive
diversity" is where you use multiple antennas at the receiver.


As far as I understand it, the idea is that
it is unlikely that the signals from all antennas will be in deep
fade
all at the same time.


Correct.


Hence deep fade events usually only affect part
of the transmission,


It's best to think about what's happening in the frequency domain
(i.e. what happens on a single subcarrier) rather than the time
domain. The theory is that the signals/multipaths from the different
transmitting antennas will be uncorrelated at the receiver, so the
probability that the signals from all of the transmitting antennas
will simultaneously be in a deep fade is reduced, and errors occur
when the signal strength on a subcarrier is low, so it reduced the BER
prior to error correction.

But transmit diversity schemes also use space-time coding techniques
to improve robustness, so it's not just about teh fact that there are
more antennas and more multipaths.


and so error correction can then restore the
original data stream.


It will reduce the post-error correction BER.


With DAB/DAB+ the transmission is simple differential modulation.
There is no channel estimation etc. Hence I don't see any reason why
you couldn't transmit on multiple antennas, with each antenna
carrying
some of the sub carriers. Hence less chance of the signal from all
antennas being faded at any one time.


Yes, but DAB and DAB+ couldn't incorporate a space-time coding
algorithm, because it would break the backward compatibility
requirement, so only a fraction of the gain from using transmit
diversity would be realised.


The big questions are, is this likely to work, and if so is it
likely
to make the transmission sufficiently more robust to make it worth
doing.


No, it won't happen because I don't think the gain from using transmit
diversity without using a space-time coding algorithm would be worth
the while doing it.



--
Steve - www.savefm.org - stop the BBC bullies switching off FM

www.digitalradiotech.co.uk - digital radio news & info

"It is the sheer volume of online audio content available via
internet-connected devices which terrifies the UK radio industry. I
believe that broadband-delivered radio will explode in the years to
come, offering very local, unregulated content, as well as opening a
window to the radio stations of the world." - from the Myers Report


.

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