UE is able to decode MIB and SIB but UE is not initiating RACH request

5G NR
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1

Hi Experts,

I am seeing an Issue with Private 5G SA network.

UE is able to decode MIB and SIB but UE is not initiating RACH request.

Admin note: this post was updated with image below.

SIB1
SIB1915×1600 105 KB

2

Adding to my previous description,

UE used for test SAMSUNG Galaxy S22, Model name SM-S901E/DS

we are able to initiate RACH request from our Smartjac SIM card to other Networks like Jio, AIRTEL and can see RACH reject as expected.

However when we are trying for RACH on our private GNB configured with Band N78 and SSB Frequency configured as 647232 we do not see RACH getting initiated, when manually scanned network from UE for available networks we can see our GNB network as well and In QXDM logs we can see MIB and SIB with our GNB PCI, MCC, MNC

4

Most likely S criteria is not satisfied.
Check for rsrp reported in qxdm and calculate s-criteria from values obtained in sib1 by UE.

5

Hi @Dhananjay_kumar

S-criteria result shows success but still facing same issue,

05:14:51.410182	[0xB970]	NR5G ML1 Searcher Idle S Criteria
Ml1Version {
   Major.Minor Version = 2
   4
}
nr5g_ml1_srch_idle_s_criteria_check_log_s_V0x20004 {
   System Time {
      Slot Number = 0
      SubFrame Number = 3
      System Frame Number = 460
      SCS = 30KHZ
   }
   NR ARFCN = 647232
   Phy Cell ID = 1
   Serving SSB Index = 0
   Q Rx Level Min = -120 dBm
   Q RX Level Min Offset = NP
   P Max = 23 dBm
   Max UE TX Power = 23 dBm
   Qoffset Temp = 0 dB
   Cell Quality RSRP = -83.88 dBm
   S Rx Level = 36 dB
   Q Qual Min Present = 1
   Q Qual Min = -17 dB
   Q Qualmin Offset = 0 dB
   S Qual = 7 dB
   Cell Quality RSRQ = -10.37 dBm
   Result = SUCCESS
}
7

Which TDD pattern and PRACH config index are you using?

8

PRACH config index is 156.

TDD UL DL configuration common with pattern 1 and pattern 2.

9

Okay.

Could you try manually selecting your network on your mobile device?

Alternatively, you can adjust the SSB-PBCH power and the Rx-Lev Min values.

10

Most likely S criteria is not satisfied.

11

We are manually trying to select the network, but from the QXDM logs on the UE side, we see that the RACH attempt is not being initiated.

PBCH power is -17 dBm, and the RxLevMin is set to -60 dBm

What parameters should be considered for initiating a RACH attempt?

12

You can compare the MIB and SIB1 of your network with those of other networks to identify any differences.

Generally, PBCH power should be kept as low as possible, and RxLev as high as possible.

13

Ok sure.

14

Is this happening consistently or only in certain locations?

In QXDM, did you observe anything in packet B889 (NR5G MAC RACH Trigger)?

15

This issue is consistently observed with our gNodeB network, where the UE is not triggering the RACH attempt

16

You mean you’ve also checked on different cells, and the observation is the same?

17

We only have one cell active with our gNB and are observing this behavior.

When we attempt RACH on other networks like Airtel or Jio, we can at least see the RACH trigger and reject as expected.

18

Has the rsrp-ThresholdSSB parameter been configured?

Check in SIB1, and if it is configured, what is the value?

19

Yes, it is configured to 40.

20

Value looks fine.

21

Are you using DDDSUUDDDD?

What is the PRACH confirmation index, SSBperRO and CBpreamblesperSSB?

22

PRACH Configuration index is 156.

SSB per RO and CB preamble per ssb one: n8.

I am not sure what is DDDSUUDDDD?