Not expected result in constellation

[pablosreyero]

Hi,

I've been following the MIMO OFDM Transmissions over the CDL Channel Model tutorial, but I made a few changes that are listed below:

• I deployed 4 transmitting BSs and 1 UE, all of them equipped with only one antenna (downlink) instead of only 1 UT (equipped with 4 Tx antennas) and 1 BS.
• I replaced the cdl channel model with the Ray tracing module.

Everything else remained untouched, except for the obvious parameters and all the "1's" placed throughout the notebook making reference to the single UT. After changing all of this, I run my code, but I get a very high BER: 13% (approx), after noticing this, I represented both Tx and Rx constellations to compare them, and indeed, they are quite different. If I plot both Tx and Rx constellations on the 'out of the box' tutorial, I get pretty much the same constellation, but of course, with some added noise, due to channel effects. In order to get more insight on this matter, I printed all shapes, i.e., x.shape and x_hat.shape knowing that x_hat is supposed to have the following shape, [batch_size, num_tx, num_streams, num_data_symbols] as depicted here: Equalization. I get: [1, 4, 1, 432] but I've seen searching if num_streams is equivalent to num_streams_per_tx , but I didn't manage to find anything, so I guess it is the same. In that case, does the ResourceGrid class support multiple transmitters? I guess that it does, since one is able to specify num_tx but somehow I don't see it on the result.

Note that I assigned one stream per transmitter, since I only have one antenna per Bs (downlink) and I have 4 BSs, therefore, I should have 4 streams, but I just see one symbol on the constellation and not 4 as I should, unless there was another problem in another part of the code.

Now, what could be the problem to this issue?

Below, find my code as well as the obtained constellations from my code and the ones from the tutorial:

MIMO-OFDM-RT.zip

Thanks in advance,

Pablo.-