[Ground-station] LTE transmit question (will help Neptune)

[Michelle Thompson]

Do you know about #LTE transmitters and can help with some questions?

I have what I hope is a simple question about space frequency block coding
(SFBC) implementation.

SFBC is a special case of space time block coding (STBC) in MIMO, where we
get a stream of transmitter samples that are supposed to go out the door
and on the air, and we use some tricks to get better reliability in
#multipath environments.

In STBC, we take two samples at a time, and transmit each of them on a
different antenna. This gives space diversity. We’ve sent out two samples
in one time step, so we have an extra time step. We fill this with special
copies of the two symbols. These copies help us a lot at the receiver. It’s
really neat and is called the Alamouti technique. OK, so two samples, two
time slots, two antennas.

Now, to get even more diversity gain, I am going to send the special copies
of the samples on a different subcarrier. That’s SFBC. Great. It makes
sense. But I now have an extra time slot “back again”. If I have a 10 MHz
channel originally, are these two subcarriers 5 and 5 MHz? Every place it’s
described simply mentions “N subcarriers to give frequency diversity” with
no guidance on what frequencies we’re talking about.

Do I split up my original transmit spectrum in traditional subcarrier
methods? Use new transmit filters? I’m assuming yes, but if there’s
something else that we do, please let me know. Now that we have two sample
sent in one time step, what do I do with the other time step? I think I
simply extend the four samples out to cover it, but this isn’t said
anywhere that I can find.

This is probably common knowledge to someone, and if that someone is
probably reading this, I just want to make sure that’s what is generally
done before I cook up hardware that doesn’t comply with the way SFBC is
generally done in LTE or other systems that use this transmitter diversity
technique.

1) how are subcarriers assigned in SFBC? Do I split the transmit bandwidth
and use traditional techniques?
2) do we extend the samples out in time because we now have frequency
diversity?

Thank you!
-Michelle Thompson
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