Inter gNB HandOver using ZMQ + GRC

[aliasadi2001]

Hello everyone,

I recently attempted to implement inter-gNB handover in the srsRAN project and encountered some questions along the way. I followed the concept of inter-eNB S1 Handover from GRC and implemented the following scenario:

I ran two gNBs and one srsUE. Initially, the UE connects without issues, but when I modify the "const" value from 0 to 1, the UE disconnects and fails to smoothly connect to the next gNB, requiring a restart of the srsUE to re-establish the connection.

Below is my gNB configuration. I understand that I need to add more elements to the cu-cp section of the configuration file to enable the handover scenario, but I don’t have a sample configuration to correctly assign the values for activating handover.

gnb_id: 412
amf:
  addr: 10.53.1.2                  # The address or hostname of the AMF.
  bind_addr: 10.53.1.3             # A local IP that the gNB binds to for traffic from the AMF.

ru_sdr:
  device_driver: zmq                # The RF driver name.
  device_args: tx_port=tcp://127.0.0.1:2002,rx_port=tcp://127.0.0.1:2003,base_srate=11.52e6 # Optionally pass arguments to the selected RF driver.
  srate: 11.52                      # RF sample rate might need to be adjusted according to selected bandwidth.
  tx_gain: 75                       # Transmit gain of the RF might need to adjusted to the given situation.
  rx_gain: 75                       # Receive gain of the RF might need to adjusted to the given situation.

cell_cfg:
  dl_arfcn: 368500                  # ARFCN of the downlink carrier (center frequency).
  band: 3                           # The NR band.
  channel_bandwidth_MHz: 10         # Bandwith in MHz. Number of PRBs will be automatically derived.
  common_scs: 15                    # Subcarrier spacing in kHz used for data.
  plmn: "00101"                     # PLMN broadcasted by the gNB.
  tac: 7                            # Tracking area code (needs to match the core configuration).
  pdcch:
    common:
      ss0_index: 0                  # Set search space zero index to match srsUE capabilities
      coreset0_index: 6             # Set search CORESET Zero index to match srsUE capabilities
    dedicated:
      ss2_type: common              # Search Space type, has to be set to common
      dci_format_0_1_and_1_1: false # Set correct DCI format (fallback)
  prach:
    prach_config_index: 1           # Sets PRACH config to match what is expected by srsUE
    total_nof_ra_preambles: 64      # Sets number of available PRACH preambles
    nof_ssb_per_ro: 1               # Sets the number of SSBs per RACH occasion.
    nof_cb_preambles_per_ssb: 64    # Sets the number of contention based preambles per SSB.

cu_cp:
  inactivity_timer: 7200            # Sets the UE/PDU Session/DRB inactivity timer to 7200 seconds. Supported: [1 - 7200].

log:
  filename: /tmp/gnb.log            # Path of the log file.
  all_level: info                   # Logging level applied to all layers.
  hex_max_size: 0

pcap:
  mac_enable: false                 # Set to true to enable MAC-layer PCAPs.
  mac_filename: /tmp/gnb_mac.pcap   # Path where the MAC PCAP is stored.
  ngap_enable: false                # Set to true to enable NGAP PCAPs.
  ngap_filename: /tmp/gnb_ngap.pcap # Path where the NGAP PCAP is stored.
  e2ap_enable: true                 # Set to true to enable E2AP PCAPs.
  e2ap_filename: /tmp/gnb_e2ap.pcap # Path where the E2AP PCAP is stored.

e2:
  enable_du_e2: true                # Enable DU E2 agent (one for each DU instance)
  e2sm_kpm_enabled: true            # Enable KPM service module
  addr: 127.0.0.1                   # RIC IP address
  #bind_addr: 127.0.0.100           # A local IP that the E2 agent binds to for traffic from the RIC. ONLY required if running the RIC on a separate machine. 
  port: 36421                       # RIC port

metrics:
  rlc_json_enable: 1                # Enable RLC metrics reporting (need to deliver measurements to E2SM_KPM service model)
  rlc_report_period: 1000           # Set reporting period to 1s

It's worth mentioning that I successfully implemented a multi-gNB and multi-UE setup, where the UE connects to each gNB individually without any issues.

Any guidance or sample configurations would be appreciated!

[ismagom]

Hi @aliasadi2001, thanks for posting.

Inter-gNB HO is not supported in srsRAN Project.

Regards

[aliasadi2001]

Thank you for your guidance.

Actually, I am looking for a 5G handover solution that doesn't require USRP. Currently, the only available solution is inter-cell handover using USRP.

Is it possible to achieve inter-cell handover using ZMQ and GRC instead?

Best regards,

[pgawlowicz]

@aliasadi2001 It should be possible with AmarisoftUE. 5G srsUE does not support HO.

[aliasadi2001]

Thank You for your response
Best Regards

[Justin-Garey]

Is the 5G srsUE handover on the radar for something that might be implemented in the future or is it something that is not going to be considered for implementation?

[pgawlowicz]

@Justin-Garey currently, there are no plans for supporting HO in the 5G srsUE.