What is the correlation between the beam and layer in 5G?

Hi Experts.

What is the correlation between the beam and layer in 5G?

  • When transferring I or 2 layers, there is a one-to-one mapping between the number of layers and the number of polarisations. ln this case, a beam can be generated by each polarisation to support the transmission of the 2 layers. When transferring more than 2 layers, it becomes necessary to use more than a single beam per polarisation. In these cases, the Codebook Mode does not have any impact and both modes apply the same selection procedure

  • Figure 399 illustrates the general concept of using multiple beams to support higher order MIMO. This means that multiple layers are transmitted by each polarisation but those layers are separated spatially by using different beams. These beams are pointing in different directions so the UE has to rely upon reflections and scattering to ensure that all layers can be received. The number of beams required is given by: ROUNDUP (Reported Rank I 2)

Source of above statement: 5G-NR-in-Bullets, page 483

Crosspolar beams means it have vertical and horizontal polarization.

So 1 cross polar beam can transmit 2 layer of data.

One layer with vertical other with horizontal. It will not interfere with each other.

Now for more than 2 layer, we need one more cross polar beam.

It would be transmitting in different direction so UE can use it only if its reflection is received at UE with sufficient energy.

Hence for higher order MIMO, multipth singals are required.

That means No of Beams = No of Layers / 2. Is it correct?

For 64T64R, maximum 64 cross polar beam is possible?

No, it is not correct.

Think that max 16 PDSCH layers is possible for MU-MIMO.

From UE perspective it looks correct.
But from antenna perspective its not correct.
Agree @RFSpecialist ?

If UE is served with 4 layers, it’s receiving 2 beams.

But not like mMIMO antenna radiating only 2 beams.

You will never have so many paired UE to transmit 64 beams.

And number of T and R have nothing to do with number of beams.