5G RACH attempts failure issue in 5G n78 band Standalone

5G NR
#1

Hi,

in our testing 5G Standalone n78 band for SCS30 KHz and 100 MHz bandwidth used, One one single cell radiating only for testing

Get
MIB,SIB1, 5GS MM [5gNR] - Registration request,UL-CCCH [5gNR] - rrcSetupRequest are getting passed

after that getting failure message in RACH

NR5G MAC RACH Trigger	CONNECTION_REQUEST
NR5G MAC RACH Attempt	FAILURE_MSG2_RA_TIMER_EXP	
NR5G MAC RACH Attempt	FAILURE_MSG2_RAPID_MISMATCH

What will be reason?

#2

NR5G MAC RACH Attempt FAILURE_MSG2_RA_TIMER_EXP: this is because UE is under poor RF condition;check RSRP from Log.

In case there is good coverage ,then need to check UE software issue.

#3

Hi,

CHecked with 2 mobile phone same issue observed

cell_quality_rsrp : -86.500000
cell_quality_rsrq : -10.507813
SINr: 15 to 20

#4

how about link adaptation ,its enable?

whats model of both mobile

#5

what is value of Maximum number of preamble transmission

#6

PRACH
transmit_power : -6
pathloss : 67
mtpl : 23
rach_attempt : 2
min_power : -38

#7

i am rx prach min power -38 dbm is that OK

#8

PRACH power = Min{mtpl, *PRACH target power * + (rach_attempt – 1) × prach Power Ramp + pathloss}

PRACH power = Min{23, *PRACH target power * + (2 – 1) × prach Power Ramp + 67}

We assume that power Ramp =1

in above case min_power : -38 ========> PRACH target power -105 dbm

in your case UE send Prach preamble with less power .

can you check configuration of PRACH target power & prach Power Ramp & Maximum number of preamble transmission

#9 
<rach-ConfigCommon>
                <setup>
                  <rach-ConfigGeneric>
                    <prach-ConfigurationIndex>70</prach-ConfigurationIndex>
                    <msg1-FDM>
                      <one/>
                    </msg1-FDM>
                    <msg1-FrequencyStart>4</msg1-FrequencyStart>
                    <zeroCorrelationZoneConfig>7</zeroCorrelationZoneConfig>
                    <preambleReceivedTargetPower>-90</preambleReceivedTargetPower>
                    <preambleTransMax>
                      <n8/>
                    </preambleTransMax>
                    <powerRampingStep>
                      <dB6/>
                    </powerRampingStep>
                    <ra-ResponseWindow>
                      <sl8/>
                    </ra-ResponseWindow>
                  </rach-ConfigGeneric>
                  <ssb-perRACH-OccasionAndCB-PreamblesPerSSB>
                    <one>
                      <n64/>
                    </one>
                  </ssb-perRACH-OccasionAndCB-PreamblesPerSSB>
                  <groupBconfigured>
                    <ra-Msg3SizeGroupA>
                      <b56/>
                    </ra-Msg3SizeGroupA>
                    <messagePowerOffsetGroupB>
                      <dB0/>
                    </messagePowerOffsetGroupB>
                    <numberOfRA-PreamblesGroupA>48</numberOfRA-PreamblesGroupA>
                  </groupBconfigured>
                  <ra-ContentionResolutionTimer>
                    <sf40/>
                  </ra-ContentionResolutionTimer>
                  <prach-RootSequenceIndex>
                    <l139>129</l139>
                  </prach-RootSequenceIndex>
                  <msg1-SubcarrierSpacing>
                    <kHz30/>
                  </msg1-SubcarrierSpacing>
                  <restrictedSetConfig>
                    <unrestrictedSet/>
                  </restrictedSetConfig>
                </setup>
              </rach-ConfigCommon> 

prach_data
        resource_allocation : 4
        zc_root_seq : 67
        preamble_format : 5
        symbol_offset : 0
        numerology : 30KHZ (1)
        prach_number : 0
        zc_cyclic_shift : 91


3530	2021-12-14 13:23:12.059154	Qc. 5G-NR[Chipset]	______[0xB88A] NR5G MAC RACH Attempt	FAILURE_MSG2_RA_TIMER_EXP	
[ 2021  Dec  14    13:23:12.059154 ]  [0xB88A] NR5G MAC RACH Attempt  

Chipset timestamp: 2021-09-28 08:48:00.159348, CFN : 96
Dual Mode Index : 0
SIM Index : 1
Version : 131079
Major.Minor Version : 2.7
  log_fields_change
  log_fields_change_bmask : 0x0000
  sub_id : 0
  header
    num_records : 1
  num_attempt : 1
  ssb_id : 0
  csi_rs_id : 0
  carrier_id : 0
  rach_result : FAILURE_MSG2_RA_TIMER_EXP (1)
  contention_type : CONT_DL_MCE (1)
  rach_msg_bitmask : 0x01
      rach_msg1 (0x01)
    msg1_scs : 30KHz (3)
    ul_bwp_scs : 30KHz (1)
  rach_msg1
    system_time
      frame : 321
      sub_frame : 9
      slot : 1
      scs_value : 1
    symbol_start : 0
    prach_config : 70
    preamble_format : 5
    preamble_format : FORMAT_A1 (5)
    ra_id : 37
    fdm : 0
    uroot : 67
    cyclic_shift_v : 91
    ra_rnti : 267
    rar_window_start_sfn
      frame : 322
      sub_frame : 2
      slot : 0
      scs_value : 1
    rar_window_end_sfn
      frame : 322
      sub_frame : 6
      slot : 0
      scs_value : 1
    backoff_duration : 0
#10

Wrong preamble detection check the clock source.