Neighbouring cells reports

[improperaffo]

Dear all,
we have been trying out the handover feature. We are able to trigger it with the ho <serving pci> <rnti> <target pci> command when using a USRP, but when moving to the measurement based handover, we encountered some difficulties.

We have tried setting the report_configs: for ncells: both to periodical and event_triggered. Yet, looking at the CU logs, we observe only one or two measurement reports for the neighbour cell right after the user connects, after that the phone only reports measurement for the cell it is connected to.
First one or two measurement reports:

2024-09-04T08:53:03.279847 [RRC     ] [D] ue=0 c-rnti=0x4601: Containerized measurementReport: [
  {
    "UL-DCCH-Message": {
      "message": {
        "c1": {
          "measurementReport": {
            "criticalExtensions": {
              "measurementReport": {
                "measResults": {
                  "measId": 1,
                  "measResultServingMOList": [
                    {
                      "servCellId": 0,
                      "measResultServingCell": {
                        "physCellId": 1,
                        "measResult": {
                          "cellResults": {
                            "resultsSSB-Cell": {
                              "rsrp": 51,
                              "rsrq": 65,
                              "sinr": 83
                            }
                          },
                          "rsIndexResults": {
                            "resultsSSB-Indexes": [
                              {
                                "ssb-Index": 0,
                                "ssb-Results": {
                                  "rsrp": 51,
                                  "rsrq": 65,
                                  "sinr": 83
                                }
                              }
                            ]
                          }
                        }
                      }
                    }
                  ],
                  "measResultNeighCells": {
                    "measResultListNR": [
                      {
                        "physCellId": 2,
                        "measResult": {
                          "cellResults": {
                            "resultsSSB-Cell": {
                              "rsrp": 40,
                              "rsrq": 63,
                              "sinr": 54
                            }
                          },
                          "rsIndexResults": {
                            "resultsSSB-Indexes": [
                              {
                                "ssb-Index": 0,
                                "ssb-Results": {
                                  "rsrp": 40,
                                  "rsrq": 63,
                                  "sinr": 54
                                }
                              }
                            ]
                          }
                        }
                      }
                    ]
                  }
                }
              }
            }
          }
        }
      }
    }
  }
]

All the remaining measurement reports:

 2024-09-04T08:53:03.555412 [RRC     ] [D] ue=0 c-rnti=0x4601: Containerized measurementReport: [
  {
    "UL-DCCH-Message": {
      "message": {
        "c1": {
          "measurementReport": {
            "criticalExtensions": {
              "measurementReport": {
                "measResults": {
                  "measId": 1,
                  "measResultServingMOList": [
                    {
                      "servCellId": 0,
                      "measResultServingCell": {
                        "physCellId": 1,
                        "measResult": {
                          "cellResults": {
                            "resultsSSB-Cell": {
                              "rsrp": 49,
                              "rsrq": 65,
                              "sinr": 73
                            }
                          },
                          "rsIndexResults": {
                            "resultsSSB-Indexes": [
                              {
                                "ssb-Index": 0,
                                "ssb-Results": {
                                  "rsrp": 48,
                                  "rsrq": 65,
                                  "sinr": 73
                                }
                              }
                            ]
                          }
                        }
                      }
                    }
                  ]
                }
              }
            }
          }
        }
      }
    }
  }

Our CU mobility config (we have tried setting report_configs: to 2 and 3):

mobility:
    trigger_handover_from_measurements: true
    cells:
      - nr_cell_id: 0x2130
        periodic_report_cfg_id: 1
        ncells:
          - nr_cell_id: 0x2131
            report_configs: [ 2, 3 ]
      - nr_cell_id: 0x2131
        periodic_report_cfg_id: 1
        ncells:
          - nr_cell_id: 0x2130
            report_configs: [ 2, 3 ]
    report_configs:
      - report_cfg_id: 1
        report_type: periodical
        report_interval_ms: 480
      - report_cfg_id: 2
        report_type: event_triggered
        a3_report_type: rsrp
        a3_offset_db: 2
        a3_hysteresis_db: 0
        a3_time_to_trigger_ms: 100
      - report_cfg_id: 3
        report_type: periodical
        report_interval_ms: 480

Complete CU logs in debug mode

What could be the reason? We tested various different phones, but we were never able to get measurements from neighbouring cells.
Thanks

[pgawlowicz]

Could you check the behaviour if you set the following:

    cells:
      - nr_cell_id: 0x2130
        periodic_report_cfg_id: 1
        ncells:
          - nr_cell_id: 0x2131
            report_configs: [ 1 ]  --> change to 1 
      - nr_cell_id: 0x2131
        periodic_report_cfg_id: 1
        ncells:
          - nr_cell_id: 0x2130
            report_configs: [ 1 ]  --> change to 1 

and also:

    cells:
      - nr_cell_id: 0x2130
        periodic_report_cfg_id: 1
        ncells:
          - nr_cell_id: 0x2131
            report_configs: [ 1, 2 ]  --> change to 1,2 
      - nr_cell_id: 0x2131
        periodic_report_cfg_id: 1
        ncells:
          - nr_cell_id: 0x2130
            report_configs: [ 1, 2 ]  --> change to 1,2

[pgawlowicz]

is there any difference depending on the serving cell? i.e. whether the UE is attached to cell1 or cell2?

[pgawlowicz]

Could you connect both USRPs to the same external reference clock?

[improperaffo]

We did not observe any difference changing serving cell
And we currently do not have an external clock. Do you think that could be the problem?

[pgawlowicz]

The configs you have shared are correct.
So I believe that running two cells using B210s operating with their own internal clocks (not very good ones) might be the main cause of the experienced issues. The cells are expected to operate at the same frequency, but due to different CFOs, they are not exactly at the same frequency. Therefore, while being synchronized to the serving cell, the UE cannot detect the other cell.

[yc541]

@pgawlowicz
I was trying to replicate this with 2 B205mini and an external clock (Octoclock).

I can see the similar behaviour of the absence of neighbour cell report. The cu/du configurations and logs are attached. Can you spot anything wrong with the configurations?

Many thanks.

HO_logs.zip

[pgawlowicz]

Which phone do you use as UE?

[yc541]

The phone is a Google Pixel 6

[pgawlowicz]

@yc541 any update on this issue?

[BGarcs]

Hello @improperaffo,
Were you able to solve this problem?

In my case I am trying to make the Handover work by having a TX/RX pair 22 meters away from the other pair and the handover is only performed when I am completely out of the coverage range of the serving cell. This generates that in the “overlap” area of the two generated cells there is no “competition” for which cell is the best for the UE.

I would appreciate if someone could help me to solve this, as I have been trying changing the gains in both RUs and I have not been able to reach a consistent configuration.

Regards and thank you very much!