When 5G is used as gnb and 4G is used as ue, the two cannot be connected. Is an external clock necessary? If no external clock is needed, how to modify the configuration file? Look forward to your reply. Thank you about srsran_project HOT 6 CLOSED

The gNB in srsRAN_Project is 5G-SA only, which means that only UE with 5G-SA capabilities can attach to that gNB. A 4G-only UE will not.

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According to https://docs.srsran.com/projects/project/en/latest/tutorials/source/srsUE/source/index.html's Over - the - air Setup part of the image, It's true that srsUE uses 4G, so why can't it connect?Is an external clock necessary?

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srsUE from the srsRAN_4G project is capable of both, 4G and 5G. To attach to gNB from srsRAN_Project, it uses its 5G capabilities.

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See https://docs.srsran.com/projects/project/en/latest/tutorials/source/srsUE/source/index.html#introduction

srsRAN Project is a 5G CU/DU solution and does not include a UE application. However, srsRAN 4G does include a prototype 5G UE (srsUE) which can be used for testing. This application note shows how to create an end-to-end fully open-source 5G network with srsUE, the srsRAN Project gNodeB and Open5GS 5G core network.

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So do we need an external clock or not? If not, how should the configuration file be modified?

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It is not strictly required.
To test without external clock, just replace/omit the lines that state to use external clock, e.g.:

gnb.yaml

...
  clock:                                                        # Specify the clock source used by the RF.
  sync:                                                         # Specify the sync source used by the RF.
...

ue.conf

...
device_name = uhd
time_adv_nsamples = 300
...

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