How beamforming is done is separate concept.
It can be digital or analogue.
See:
My question is very simple: how gNodeB use all antenna elements and still point the beam in 2 directions, not one?
Please see the below course, It has excellent basics about Wireless communications and how MIMO works.
Thanks I will watch the videos although I am sure there’s too much math inside.
To point 2 beams in 2 directions is very easy if you use half of the elements to steer one beam in one direction and the other half of elements to steer the other beam. But using all antenna elements to steer 2 beams in 2 distinct directions in the same time ( as explained in the book)sounds impossible to me.
There is a Concept called Antenna Polarization that is used in Beamforming, please check that.
I am aware about +45 and -45 polarization.
Yet to do 4x4 DL MIMO one need 2 beams, each beam having a +45 and -45 polzarization stream.
@samohiuddin, this is my post and it is one case of MIMO.
In the book it is explained another case of MIMO that I am asking questions about.
It was a good post.
Yes there is a lot of math involved, I did complete most of the course took me some time though
Ahhh, I see I got this question now.
The Author is talking about MU-MIMO with each UE receiving 2x2 MIMO.
This is absolutely possible, I have worked on this feature.
Nope, in highlighted phrase in yellow it is about 4x4 DL MIMO.
4x4 DL MIMO for single UE, using all antenna elements yet 2 beams need to point in 2 distinct directions.
Oh, got it.
Then UE will need to be camped on two SSB beams?
I think those are dedicated user beams i.e PDSCH ones, not cell beams like SSB.
I think I understand the text in book now.
In its example, basically antenna array is 8 elements (4 +45 + 4 -45).
Author is suggesting that 1st UE is being served 4x4 layer using 4 +45 polarization and 2nd UE being served 4x4 using 4x -45 polarization.
I had long discussion on similar topic with a colleague long time ago and we sort of agreed that +45/-45 polarization of 1 antenna element actually points in same direction.
This book is suggesting otherwise.
I cannot confirm this.
I think i found the answer in Sharetechnote (@Jaeku_Ryu) page that each stream of MIMO is generated by a sub-array and not by all antenna elements.
Please see attached picture and the link here:
https://www.sharetechnote.com/html/5G/5G_CSI_RS_Codebook.html
Hope this clarify all the doubts.
So if there are 8 streams for 8x8 DL MIMO there will be 4 subarrays generating them each subarray having a +45 and a -45.
Don’t know what was written in that book and I am not trying further to understand…
Hi @RFSpecialist.
If we have 128 AE (64 T64R) ie 64 (+45) and 64 (-45) then considering case of dual stream.
I think all 128 AE will use for steam generation ie 64 for one steam and 64 for second stream.
How to decide which AE to used out of 128?
I also think the same that for 2x2 DL MIMO layers will be 2 streams one +45 from 64 AE and another -45 from 64 AE.
I don’t know what priprietary algos decide which AE to be used for that but I think it has to do with N1, N2, O1and O2 numbers and number of CSI-RS ports as written on sharetechnote page.
Yes same apply for 5G NR active antenna as well.
