Before a wireless end device (UE) can communicate it first selects the network it supports access to; in the 5G (NR) system the UE either selects a PLMN or an SNPN; its exactly how this is done.
Ⅰ. PLMN Selection When not operating in SNPN access mode, the terminal's (UE's) access (AS) in the wireless network shall report the available PLMNs and any associated CAG-IDs to the NAS upon NAS request or autonomously; whereas when operating in SNPN access mode, the AS shall report the available SNPNs to the NAS upon NAS request or autonomously. During this period, the terminal (UE) identifies the list of PLMNs in order of priority; a specific PLMN can also be selected automatically or manually; each PLMN in the PLMN identification list is identified by a “PLMN ID”. Depending on the system information broadcast by the network, a terminal (UE) may receive one or more PLMN IDs in a given cell; the result of the NAS implementation is the identifier of the selected PLMN. Typically at the request of the NAS, the terminal at the access (AS) layer shall search for available PLMNs and report them to the NAS.
Ⅱ.SNPN selection The end equipment (UE) using the private network can automatically or manually select a specific SNPN for its identification list during SNPN selection. each SNPN in the SNPN identification list is identified by an “SNPN ID”. In a system message on a broadcast channel, the UE can receive one or more “SNPN IDs” in a given cell and can choose to receive the associated HRNN. the result of the NAS implementation is the identifier of the selected SNPN.
Ⅲ.PLMN Selection in 5G The 5G terminal (UE) shall scan all RF channels in the supported NR bands for available PLMNs and CAGs according to its capability. on each carrier the terminal (UE) shall search for the strongest cell and read its system information in order to find out to which PLMN the cell belongs and the associated CAGs. for the operation of shared spectrum channel access the terminal (UE) can also read the system information of multiple strongest cells. The terminal (UE) can also read the system information of multiple strongest cells for shared spectrum channel access operations. If the UE can read one or more PLMN identifiers in the strongest cell or multiple strongest cells (in the case of shared spectrum channel access), it shall report each found PLMN as a high-quality PLMN (but without the RSRP value) and any associated CAG-ID to the NAS, provided the following high-quality criteria are met.
* For 5G (NR) cell terminals (UEs) the RSRP measurement shall be greater than or equal to -110 dBm; when PLMNs are found that do not satisfy the high quality criteria, but the UE is able to read their PLMN identifiers, these PLMNs will be reported to the NAS along with their corresponding RSRP values and any associated CAG-ID.The quality measurements that are reported by the UE to the NAS correspond to the quality measurements that are found in a each PLMN found in a cell.
* The terminal (UE) may stop searching for PLMNs based on a request from the NAS, or it may optimize the PLMN search using stored information (e.g., frequency) and optionally cell parameter information from previously received measurement control information elements.
Ⅳ.Once the PLMN has been selected, the terminal (UE) shall perform a cell selection process in order to select the appropriate cell to reside in that PLMN. To support manual CAG selection, the UE shall report to the NAS, upon request, the available CAG IDs and their Manual CAG Selection Allowed Indicator (e.g., broadcast), HRNN (e.g., broadcast), and PLMN.If the NAS has already selected a CAG and provided this selection to the AS, the UE shall search for an acceptable or suitable cell belonging to the selected CAG to be stationed.
Ⅴ.SNPN Selection in 5G At the request of the NAS, the terminal (UE) shall search for available SNPNs in random access (AS) only on NR cells and report them to the NAS. where:The terminal (UE) shall scan all RF channels in the NR band for available SNPNs according to its capability. on each carrier the terminal (UE) shall search for the strongest cell and read its system information to find out which SNPN the cell belongs to. find out which SNPN the cell belongs to. for shared spectrum channel access operation, the UE may also read the system information of multiple strongest cells. If the UE can read one or more SNPN identifiers in the strongest cell, it shall report each SNPN found to the NAS.For manual selection, the UE shall report available SNPN identifiers and their HRNNs (e.g., broadcasts) to the NAS upon the request of the NAS, and may stop the search for available SNPNs upon the request of the NAS. The search for SNPNs may be stopped based on the NAS request. the UE may optimize the SNPN search using stored information (e.g., frequency) and optionally cell parameter information from previously received measurement control information elements. Once the UE has selected an SNPN, a cell selection procedure shall be performed in order to select the appropriate cell for that SNPN to be stationed.
