5G Initial Network Access Procedure

5G Initial Access

5G Network Access Procedure

When a 5G device is switched on, depending on the device capability and stored information, it will attempt to select a suitable network.

Four Key Stages 5G Initial Access

  • PLMN and Network Selection
  • Cell Selection
  • RRC Setup
  • Registration

PLMN and Access Network Selection
The initial stage involved the device performing PLMN (Public Land Mobile Network) and access technology selection. This will utilize information on the USIM (Universal Subscriber Identity Module), as well as information of the device.

PLMN Selector with Access Technology List -

  • PLMN 1 / 5G-RAN
  • PLMN 1 / E-UTRAN (WB-S1 Mode)
  • PLMN 1 / UTRAN - PLMN 2 / 5G-RAN
  • PLMN 2 / E-UTRAN (WB-S1 Mode)
  • PLMN 3 / E-UTRAN (WB-S1 Mode)
    Listed in priority order

Note that there are various “lists” in the USIM which are able to provide a priority order of both PLMNs and RAT (Radio Access Technology).

Scanning
In order to determine the PLMN identity the device needs to obtain SI (System Information) from a cell. This will involve obtaining the SSB (Synchronization Signal Block) which will be transmitted from the cell based on the GSCN (Global Synchronization Channel Number) raster. Options are illustrated in Note that the GSCN has its own numbering scheme, as well as occurring on a NR-ARFCN (NR - Absolute Radio Frequency Channel Number).