When dealing with mobile Early Warning Systems, most countries select the cell broadcast technology. The cell broadcast service architecture is described in the 3GPP standard 23.041. It is supported over 2G, 3G, 4G and 5G networks in a similar manner. With a single CBC (Cell Broadcast Center) serving all these networks, the broadcast service’s functionality does not change when roaming from one network to another.
Cell Broadcast is defined by the European Telecommunications Standards Institute (ETSI) and is incorporated into the GSM 3GPP standards. It is a location-based mobile network service that mass-delivers text or binary messages to citizens’ mobile phones, within the range of a single cell to the entire network.
Cell broadcast messages undergo a series of steps involving the following components:
CBE (Cell Broadcast Entity) – this is where the Cell Broadcast message originates, dictating the message text, its destination, and the message scheduling.
CBC (Cell Broadcast Center) — this entity connects to the mobile operator’s core network. The CBC manages the transmission of messages received from the CBE and routes them to the target cells, through the RAN controllers (see below), by implementing the various required interfaces.
RAN (Radio Access Network) Controller — the entity in the operator’s radio network that manages a group of cells. The RAN controller distributes the cell broadcast message to the target cells. BSC, RNC, MME and AMF are the RAN Controllers for 2G, 3G, 4G and 5G, respectively.
Cell Antenna – the component that wirelessly sends the cell broadcast message to mobile devices.
End-user device – the end-user’s equipment, generally a mobile phone, that complies with the cell broadcast protocol, thereby receiving and presenting the cell broadcast message on the device. The Cell broadcast message may appear in different ways, depending on the specific protocol and the specific mobile device.
In emergency situations, everyone tries to make a call or text, which may jam the network. Since the CBC connects directly to the RAN, the emergency alerts can still go through, even when the network is congested, and are sent out simultaneously to all mobile devices that are latched to the cells in a designated area.
This point-to-area approach allows the area to be fully “blanketed” without the need for users to confirm receipt of the message, thereby keeping the users privacy.
A Cell Broadcast message page has a limit of 93 characters and up to 15 pages. Each page uses the same message identifier (indicating the source of the message), and an identical serial number. This way, the recipient’s mobile device can identify and ignore broadcasts of messages already received.