5G Terminal Radio Capability Matching and Paging Assistance Information

In 5G (NR) systems, due to the large amount of data in terminal (UE) radio capability information, only the basic content is usually transmitted to the relevant core network units during the access registration phase; when the core network queries other related functions of the terminal (such as VoNR support), it will match its radio (support) capabilities with the radio network (paging is required when the terminal is in idle state); the specific process is as follows:

I. Radio Capability Matching Request: If the AMF needs more information about UE radio capability support to set the IMS VoPS session support indication (see Section 5.16.3), the AMF can send a UE Radio Capability Matching Request message to the NG-RAN. This process is typically used during the registration process or when the AMF has not yet received the voice support matching indication (as part of the 5GMM context); where:

• During the registration process, if the AMF has not yet obtained the UE's radio capabilities and if the RAT where the UE is located requires the establishment of an AN security context before retrieving radio capabilities, the AMF needs to provide a security context to the 5G-AN according to the "Initial Context Establishment" procedure defined in TS 38.413 [34] before sending the UE Radio Capability Matching Request message.

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II.Paging Assistance Information is information related to the user equipment (UE) radio in the 5G system, used to assist the radio access network (RAN) in efficient paging. Paging assistance information includes:

2.1 UE Radio Capability Information: The UE radio capability information used for paging includes information derived from the UE radio capability information of the next-generation radio access network (NG-RAN) node (such as frequency band support information);

• The AMF (Automatic Management Function) stores this information and needs to understand its content. Since the AMF only prompts the NG-RAN to retrieve and upload UE radio capability information (i.e., UE radio capability information) to the AMF in very few cases (e.g., during initial registration), and the AMF may be connected to multiple NG-RAN radio access technologies (RATs), the NG-RAN is responsible for ensuring that the UE radio capability information used for paging (derived by the NG-RAN node) includes all NG-RAN RAT information supported by the UE in that PLMN.

To assist the NG-RAN in completing this task, the AMF, as described in TS 38.413 [34], provides its stored UE paging radio capability information in each NG-AP initial context setup request message sent to the NG-RAN.

• During AMF reselection, the terminal (UE) paging radio capability information is maintained in the core network and stored in the UCMF along with the radio capability information associated with the UE radio capability ID.

2.2 Paging Recommended Cell and RAN Node Information

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• Based on the information sent by the NG-RAN, the AMF uses this information when paging the UE to help determine which NG-RAN nodes to page and provides recommended cell information to each RAN node to optimize the paging success rate while minimizing the signaling load on the radio path.
• The RAN provides this information during N2 release.