Yes, initial synchronization by PSS-SSS.
But only particular beams can we read by a particular UE depending on the position of it from the GNB. So if not all beams have high power at all times, then UE needs to wait for right time when it can get synchronised.
Am I correct in saying this timing of all ssb being tranmitted one after another is fixed to be 5 ms but repeated by default every 20ms?
Talking about FR1 TDD here.
The whole burst of SSB beams is set at max 5 msec.
When you say whole burst, still any one beam out of the burst is active at a time, right?
Yes.
It is well explained here by @Jaeku_Ryu:
http://sharetechnote.com/html/5G/5G_SS_Block.html
Idea is that based on scs and frequency UE always knows how many SSBs are and where are located so it can measure them.
Not actualy. Even by reading weaker beam, UE can get synchronised.
It just have to allign with subframe.frame timing and read PCI
If the idea of weaker beams comes here, does it not imply that all beams are active simultaneously?
UE measure the weaker beams but does not select them to send RACH.
It is only for purpose of selecting the highest RSRP.
When I say all beams, I mean all SSB beam.
No, not all.
I mean to say that, for example, there are 8 SSB beams in the sector.
UE lies in location of beam number 7.
So UE dont have to wait until beam 7 is transmitetd.
It can decode any beam, for example beam 3, provided it satisfied certain RSRP threhsold.
Yes, correct.
Okay, got your point, thanks!
So my understanding that gNB can have simultaneously active beams is wrong.
It has a single beam active at any time instant which it sweeps.
That is for idle mode indeed only one beam.
For connected mode it has several layers (PDSCH layers) transmitted in parallel; this is how MIMO spatial multiplexing works.
Otherwise how could gNB send 4x4 MIMO data in DL?
So for PDSCH there are multiple active beams?
When MIMO is activated like 2x2 or 4x4 yes
Also for MU-MIMO there are multiple beams.
For example Huawei can support 16 layers in DL that allows to simultaneously serve several UEs if they are enough spatially decorrelated.
As of today maximum an UE can support is 4x4 in DL.
There may be CPE with 8x8 DL MIMO but that is static situation most likely for FWA.
Is there a calculation of how long a beam stays at one SSb index before moving onto the next one?
An SSB lasts for 4 symbols
Can be calculated from sharetechnote explanation: