User guide

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14 Troubleshooting
14.1 No SIB found
When running LTE UE simulator, before creating any UE or starting scenario, the first output
that should be displayed on the shell is "(ue) Cell 0: SIB found". This means that LTE UE
simulator has detected the eNodeB and can read the SIB. This is a prerequisite before running
any tests.
If this message is not displayed, here is a check list that can help to find the root cause:
• Check that LTE UE config file parameters match with eNodeB configuration: bandwidth,
dl earfcn, n antenna dl
• Check correct SDR card is being used (For PCIe SDR cards , check rf driver config file :
args: "dev0=/dev/sdr0").
• Check rx_gain value. Should be around 60dB in wireless connection or 0dB in wired
connection
• Check received signal strength with t spl command. See [t spl command], page 39, for
more details.
• Test in wireless condition instead of conducted one. This can help to verify that RF cabling
is not the culprit (see RF connection section for TF and RX gain impact)
If all checks above haven’t been enough to figure out why eNodeB signal is not detected, you
can also use the spectrum analyzer function embedded in the UE simulator to verify the LTE
signal quality received in downlink. See trx sdr.pdf documentation for more details.
14.2 SIB found but attach fails
When multiple UE mode is enabled, UE simulator may have difficulties to synchronize with
eNodeB signal. If such a case occurs, you should see that UE is able to receive SIBs but further
communications fails with bad CRC on physical layer.
This means that you should adjust the parameter global_timing_advance in your config-
uration file. The global_timing_advance parameter can be set automatically by using the
special value -1 (global_timing_advance:-1). If automatic mode is set, the UE simulator uses
the timing advance from the first received RAR for all UEs. This is the default behavior.
You can also manually adjust the timing advance for all UEs in case you still experience CRC
erros with automatic mode. You can check TA value on eNodeB side and set it to minus 1 in
UE
(global timing advance = TA[enb] - 1). if you are using simulator with Amarisoft eNodeB, you
can type t at eNodeB screen and look at PRACH traces.
Then, use ta value minus one as global_timing_advance.
PRACH: cell=01 seq=17 ta=2 snr=18.5 dB
PRACH: cell=01 seq=22 ta=2 snr=18.0 dB
PRACH: cell=01 seq=23 ta=2 snr=18.5 dB
PRACH: cell=01 seq=29 ta=3 snr=17.6 dB
In this example, adjust global_timing_advance to 1.
If you are using another eNodeB and you do not have access to eNodeB logs and information,
you can enable the PHY and MAC layer logs in UE simulator and look for ta value in MAC
traces
12:13:37.086 [MAC] - 0001 ta=13 ul_grant=128768 c_rnti=0x0047
In this example, you should set the global_timing_advance to 12.