Indoor OTA UE Won't Attach

[Nick Accurso]

Hello,

I am working on conducting an experiment in the indoor OTA lab to gather throughput in a 5G network. I have the open5gs 5g core up and running, and the srsgNB attached. The gNB is operating with a dl_arfcn of 637666 (~3565 MHz) to coincide with my reserved frequencies. It connects with the core and its log files show it is working properly.

My problem is that the UE is not searching for the cell on the proper frequency, regardless of what I set for the dl_earfcn in the ue configuration file. It is always conducting its cell search on the default 1842.5 MHz. I have also tried directly setting the dl_freq in the configuration file, but it does not change its cell search. Here is what I observe in the UE's log file:

2025-09-09T23:52:13.668608 [UE     ] [I] Using binary ./srsue with arguments: ./ue_rf.conf
2025-09-09T23:52:13.711459 [UE     ] [I] Built in Release mode using commit ec29b0c1f on branch master.
2025-09-09T23:52:13.766227 [RF     ] [I] Configuring physical DL channel 0 with band-pass filter (0.0, 0.0)
2025-09-09T23:52:13.766227 [RF     ] [I] Configuring physical UL channel 0 with band-pass filter (0.0, 0.0)
2025-09-09T23:52:15.341878 [MAC    ] [I] [    0] Resetting MAC
2025-09-09T23:52:15.341884 [MAC    ] [I] [    0] Logical Channel Setup: LCID=0, LCG=0, priority=0, PBR=-1, BSD=50ms, bucket_size=0
2025-09-09T23:52:15.341887 [MAC    ] [I] [    0] Logical Channel Setup: LCID=1, LCG=0, priority=1, PBR=-1, BSD=50ms, bucket_size=0
2025-09-09T23:52:15.341894 [MAC    ] [I] [    0] Setting configuration
2025-09-09T23:52:15.341895 [MAC    ] [I] [    0] BSR:   Configured timer reTX 2560 ms
2025-09-09T23:52:15.341901 [RLC    ] [I] Added LTE radio bearer with LCID 0 in Transparent Mode
2025-09-09T23:52:15.341911 [USIM   ] [I] Read Home PLMN Id=00101
2025-09-09T23:52:15.348505 [RLC-NR ] [I] Added LTE radio bearer with LCID 0 in Transparent Mode
2025-09-09T23:52:15.348511 [MAC-NR ] [I] [    0] Logical Channel Setup: LCID=0, LCG=0, priority=0, PBR=0, BSD=0ms, bucket_size=0
2025-09-09T23:52:15.348518 [RRC    ] [I] using srand seed of 348517
2025-09-09T23:52:15.395712 [STCK   ] [I] Triggering NAS switch on
2025-09-09T23:52:15.395721 [NAS5G  ] [I] Switching on
2025-09-09T23:52:15.435509 [USIM   ] [I] Read Home PLMN Id=00101
2025-09-09T23:52:15.435510 [NAS5G  ] [I] Requesting IMSI attach (IMSI=001010123456789)
2025-09-09T23:52:15.435516 [NAS5G  ] [I] Sending Registration Request
2025-09-09T23:52:15.435517 [RRC-NR ] [I] Proc "Setup Request" - Initiation of Setup request procedure
2025-09-09T23:52:15.435517 [RRC-NR ] [I] Proc "Cell Selection" - Starting...
2025-09-09T23:52:15.435527 [PHY-SA ] [I] [    0] Cell Search: Going to IDLE
2025-09-09T23:52:15.435528 [PHY-SA ] [I] [    0] Tuning Rx channel 0 to 1842.50 MHz
2025-09-09T23:52:15.436857 [RF     ] [I] Mapping RF channel 0 (device=0, channel=0) to logical carrier 0 on f_rx=1842.5 MHz
2025-09-09T23:52:15.610812 [PHY-SA ] [I] [    0] Cell search: Setting SSB configuration srate=23.04 MHz; c-freq=1842.500 MHz; ss-freq=1842.050 MHz; scs=15kHz; pattern=A; duplex=fdd;
2025-09-09T23:52:15.611160 [PHY-SA ] [I] [    0] Cell Search: Running Cell search state
2025-09-09T23:52:15.627260 [RF     ] [I] Overflow
2025-09-09T23:52:15.643158 [RF     ] [I] Overflow
2025-09-09T23:52:15.659051 [RF     ] [I] Overflow
2025-09-09T23:52:15.675028 [RF     ] [I] Overflow

Any insight into why the cell search frequency isn't changing would be greatly appreciated.

Thank you,

Nick

[Dustin Maas]

Hi Nick,

1. As to why the UE is not tuning to the configured channel, I would first double-check that the UE process isn’t using a different configuration than the one you are editing.
2. srsue does not support TDD or 30 kHz SCS, so I wouldn’t expect anything to work if you are configuring the srsRAN gNB in TDD or with 30 kHz SCS.

In general, it is very hard to help without details about the profile, software versions, configuration files, command line arguments involved. Please always include a link to your running experiment as well.

Thanks,
Dustin

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