What happens if we configure less SSB power in SIB1?

Hello Experts.

What happens if we configure less SSB power in SIB1?

For example, let’s say actual SSS EPRE is -11 dBm, but in SIB1, I transmit ss-PBCH-BlockPower as -20 or -30 dBm.

It may affect the performance of the UE in terms of cell search, initial access, and coverage.


But i am looking for a detailed answer. This was kind of basic.

How can you set -20 in SIB1 while -11 for actual transmitting?

I can set the SIB1 parameter that conveys the tx power of SSB to whatever I want. I can set it to -20 dBm. Also, I can increase the power of my radio to any allowable value I want.

pls share the parameter name and lets see how you able to set sib1 power.

Hi @LordGm I am not talking about SIB1 power, I am talking about SSB Power. Parameter that carries this value in SIB1 is ss-PBCH-BlockPower

Bro, when you set ss-pbch-blockpower it is boosted by vendor in sib1 or rrcreconf like 3 or 6 db based on dlmimomode setting in the cell. I have never seen, minus ssbpbch power anywhere, only in FR2.
For instance if u set 11 dbm in sspbchpower in configuratiom and cell is configured 4x4 than you will see 14 dbm in SIB1. If you can share your vendor perhaps people can help you but very little information you are sharing.

UE estimates the path loss as ss-PBCH-BlockPower - RSRP

So if RSRP is -100 dbm and the ss-PBCH-BlockPower broadcasted as 10 then UE will assume PL = 110 dB and use it as a basis for calculating UL TX power

If in reality, the SSS EPRE is 20 not 10 then actual PL is 120 dB and hence UE is using 10 dB less in UL TX power than what is supposed tonand hence UL performance will be severaly degraded.

For RACH there is power RAMP so rach may be successful after multiple attempts but for PUSCH and PUCCH, UE will need closed loop power control to be able to function under these conditions

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Thanks, @O.B I was looking for a similar answer. My concern is that in indoor scenarios it doesn’t work as expected or like what you explained. I had to keep my ss-PBCH-BlockPower 20-30 dB less than the actual transmit power, for the UL to work. For example in one of the cases, my ss-PBCH-BlockPower parameter is -20 dBm and the actual transmit power is 24 dBm per antenna, this gives me perfect UL reception.
Is it purely because of reflections? Even if UE is transmitting at very low power gNB is receiving good power, since it is indoor so UEs are also not that far. How do we tune P0 nominal in this case and find out the right ss-PBCH-BlockPower?
@LordGm There is no other vendor. It is an in-house developed 5G gNB.

You are asking why you see different power at sib1 for sspbchpower than discussion goes over pathloss calculation. ::slight_smile: UE estimates PL based on ss-PBCH-BlockPower - RSRP and ss-PBCH-BlockPower sent to UE in SIB1 is depend on your antenna mode, 2x2 or 4x4.
Regarding your real question, seems you have UL issue as indoor (we would be happy if you clearly state your problem instead of asking different things), just set p0nominalpucch to low value and enable close loop power control. It is tdd or fdd? you see we have to ask so many questions because of the poor title. I will lock next time the post if you give few details…

@Sakshama_Ghoslya ss-PBCH-BlockPower should match SSS EPRE. Before tuning P0, you should check your UL RSSI and UL SINR. Make sure there is no UL interference (e.g. PIM) and the recieved power by gNB is expected as per P0 configuration