# An Emergency Alert Broadcast Based on the Convergence of 5G and ATSC 3.0
## 2 Conventional Works
### 5G CBS Protocol  
5G cellular systems consist of user equipment (UE), radio access network (RAN), and core network (CN). Among the system components, the UE indicates a cellular phone, and the RAN includes multiple base stations. The CN adopts the service based architecture (SBA) [29], which offers high flexibility and scalability. Therefore, 5G cellular systems can offer various services including enhanced mobile broadband (eMBB), ultra-reliable low latency communication (URLLC), and massive machine type communications (mMTC) [32]. In addition to those services, 5G cellular systems offer the CBS for emergency alert broadcast. Figure 1 illustrates the network architecture for the 5G CBS. The network architecture consists of alerting authority, cell broadcast entity (CBE), cell broadcast center function (CBCF), access and mobility function (AMF), RAN, and UE. In Figure 1, a central or a local government may act as the alerting authority. In Figure 1, CBCF and AMF belong to the 5G core network (CN). When an emergency occurs, the alerting authority sends emergency message and location information (of emergency areas) to the CBE as shown in Figure 1. The CBE acts as a gateway between network operator and alerting authority. Therefore, the CBE receives the emergency message from the alerting authority, and relays the message to the CBCF, which the network operator administrates. Then, the CBCF transforms the emergency message format into the CBS message format, which is specified by the 3 GPP standard [12]. After the transformation, the CBCF sends the CBS message to the AMF. The AMF are interfaced to multiple RANs. Using the location information and tracking area information (TAI), the AMF selects the base stations for the emergency areas in the RANs. Then, the AMF sends the CBS message to the identified base stations. In Figure 1, the CBS message is transferred from CBCF to base station (RAN) via wired channels. Figure 2 illustrates the network protocols for the CBS message transfer from CBCF to base station (RAN) [12]. As shown in Figure 2, the interface between CBCF and AMF relies on TCP/IP. The interface between AMF and base station (RAN) utilizes stream control transmission protocol (SCTP) and IP. In Figure 2, the back-end of the base station (RAN) is connected to the AMF via a wired channel. However, the front-end of the base station is interfaced to the UEs (cellular phones) of Figure 1 via a wireless channel. Figure 3 illustrates the radio protocol for the wireless channel of the base station, which is used for the CBS message broadcast to all cellular phones in a cell. In Figure 3, the radio resource control (RRC) is responsible for the CBS paging and the CBS message broadcast [33]. If the base station receives a CBS message, the RRC of Figure 3 sends the paging message to all cellular users in a cell via the layer 2 and the layer 1. As indicated in Figure 3, the layer 2 includes packet data convergence protocol (PDCP), radio link control (RLC), and medium access control (MAC) sublayers. In Figure 3, the layer 1 indicates the physical layer (PHY). Among the interface channels between the sublayers, paging control channel (PCCH), paging channel (PCH), and physical downlink shared channel (PDSCH) are used for the paging broadcast in Figure 3. As stated earlier, the paging message enables the idle-state cellular phones to receive the CBS message. After the paging broadcast, the RRC sends the CBS message (SIB 8) to all cellular phones in a cell via layer 2 and layer 1 in Figure 3. For the CBS message  
Figure 1: The network architecture for the 5G CBS. broadcast, the CBS message is embedded into the system information block (SIB) 8 [33]. Among the interface channels between the sublayers, broadcast control channel (BCCH), downlink shared channel (DL-SCH), and PDSCH are used for the CBS message (SIB 8) broadcast in Figure 3. The SIBs are usually utilized for the broadcast of control information (such as cell selection information) to all cellular phones in a cell. Therefore, the SIBs carry small-sized information.