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

[Michelle Thompson]

Got the answer (Thank you Dr. Estevez) and will proceed with the rest of
the in-progress article about SFBC on Neptune.

These are not adding physical frequency diversity channels, but a
particular use of the existing subcarriers in the resource grid. The
nomenclature threw me.

-Michelle Thompson




On Sat, Feb 24, 2024 at 8:39 AM Michelle Thompson <
mountain.michelle at gmail.com> wrote:

> 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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