# Machine Learning-Based Paging Enhancement in 5G Network
## 2 Background  
### 5G Paging  
In 5G systems, the number of gNodeBs is greater than that in 4G long-term evolution owing to 5G service characteristics such as hyper-connectivity and 5G new radio frequency band features. As shown in Figure 1, the AMF manages these gNodeBs, the TA, and the TA list including multiple TAs, which comprise several adjacent gNodeBs. The UE initially sends a registration request to the AMF and then receives a registration accept message and the TA list managed by the AMF. When the UE moves to a new TA that is not in the TA list, it performs registration with its AMF and receives a new TA list [5]. In general, when the UE is in the CM-connected state, the AMF knows the location information such as the gNodeB and cell information of the UE. If traffic data are transmitted to the UE, they may be directly transmitted to the UE via the connected channel of the radio resource. However, when the UE is in the CM-idle state, the AMF contains only the UE's last visited gNodeB, latest visited gNodeBs, and TA [6]. When the UE moves outside the current TA, the UE reports its TA change to the AMF via the mobility registration update procedure, which is periodically operated based on the periodic registration update timer received from the AMF in the registration procedure. Subsequently, the AMF stores a new TA in the latest visited TAs of the UE and updates the TA list [7]. Next, the AMF can notify the data transmission or initiate a voice call to the UE when it is ready for transmission to the UE in the CM-idle state. As shown in Figure 2, the AMF can initiate paging when it receives an N1N2 message transfer message from the SMF. The AMF verifies the connection status of the corresponding UE [8]. At this time, if the UE is in the CM-idle state, the AMF selects gNodeBs in which the UE is likely to exist and transmits paging signals to the gNodeBs based on the NGAP. Subsequently, these gNodeBs broadcast paging signals to all cells via a paging channel. Meanwhile, the UE monitors the wireless paging channel connected to the gNodeB. If the paging signal is identified, then the state is changed to the CM-connected state with the gNodeB; subsequently, the traffic data are transmitted from the user plane function to the UE [9]. Figure 1: Next generation application protocol (NGAP) paging of 5G system. Figure 2: Flow of 5G network-initiated paging. However, before performing paging to the UE, the AMF should decide the range of paging on the registered gNodeB, TA, and TA list. The paging profile configuration in Table 1 shows that it has various paging conditions to be assigned for the different UE service types. The configuration includes the paging range, number of paging attempts, and paging profile created by the UE service type. Figure 3 shows an example of the paging range profile. When No. 20 of the paging profile configuration in Table 1 is selected, the first paging message, based on the configuration, is sent up to three times to the last visited gNodeB. If no response is received from the gNodeB within a certain duration, then the same paging message is sent up to two times to the gNodeBs in the latest visited gNodeB list as the second attempt. Subsequently, the third paging attempt can be sent up to two times to all gNodeBs in the last visited TA when no response is obtained from the gNodeBs. As the last paging attempt, a paging message is sent up to two times to the gNodeBs of all TA lists. In other words, the number of paging attempts and the range of gNodeBs for paging are set in the AMF paging profile configuration [10]. Figure 4 shows an example of UE movement between gNodeBs and the typical paging range in an AMF. Based on the paging range order in Figure 3 and paging profile configuration No. 20 in Table 1, the first paging message is sent to gNodeB0, the second to gNodeB0, gNodeB3, gNodeB4, and gNodeB5, and the third to all gNodeBs from gNodeB0 to gNodeB5 in the TA.