Types Of 5G Beams: Broadcast & Traffic Beams - SSB, CSI-RS, PMI & SRS

In 5G, there are multiple types of beams that are used to transmit different types of information. For instance, we have broadcast beams and traffic beams.
The Broadcast beams are mainly the common channel beams that are used to transmit SSB. The same beams are also used for other broadcast channels like CSI resources.
Then we have traffic beams which are mostly based on PMI or SRS. If the PMI based beams are used then those beams depend on CSI resources and configuration as the UE decodes the CSI resources to generate CSI feedback which carries the PMIs. If the SRS based beams are used then those depend on the UE’s uplink coverage and the gNB uses the SRS to estimate the optimal beam candidate for the UE. In a nutshell,

  • SSB Beams are Broadcast Type beams and cover larger areas.
  • PMI based Beams are more focused and narrower. They are Traffic Type Beams.
  • SRS Based Beams can be even more focused and they are also Traffic Type Beams.

YouTube (video): :point_right: Types Of 5G Beams: Broadcast & Traffic Beams - SSB, CSI-RS, PMI & SRS - YouTube


Dear Ali Khalid,
thanks for your video!
We recently discovered that, Huawei product implement a randomized pattern which is static in terms of cell PCI MOD3, so if we look at left to right beam indexes they will be positioned differently for each cell with different PCI MOD3. Could you provide relevant official documents or reference materials that can explain the principle of this mechanism?
In addition, we found that in a case of 8-beams, beams 0-3 and beams 4-7 correspond to each other similarly. We think this is related to the antenna array of the base station, and it may be caused by the similarity of the two beams in the same horizontal direction caused by the vertical two-layer polarization. We would appreciate it if you could explain it.

Experts, what difference between:

  • SSB Beams
  • Refined Beams (CSI Beam)
  • PMI-Beams

SSB beams are for initial access.

Beamformed CSI RS i.e. you are transmitting CSI RS using beamforming.

For e.g., in our network Ericsson uses 32 port CSI-RS and uses only 1 CSI-RS beam i.e. CSI-RS transmission is not beamformed.

Whereas Nokia uses 8 port CSI-RS and they uses 4 beams for CSI RS transmission.

PMI beams are PDSCH beams used for cell edge UEs ( when the SRS SINR< threshold).

But which type is used?

Eigen vector that depends on srs only or GOB that depends on CSI or PMI?

PMI beams are also called GoB or Codebook based CSI-RS beam.

SRS based beams are also called Eigen based beamforming or Reciprocity based beamforming.

Ok, but for PMI, we have two methods of beams:

  • First is csi-rs beams (4 beam per ssb)

  • And second is pmi-beams (reach up to 256 beam)

So what method using?

And what is triggering for dynamic change?

If you enable SRS beamforming it is used, separated feature.

I think Sector and User Beam concept are for LTE.

For NR, same SSB used as Sector and User Beam.

What are your views?