Cell Broadcast


Cell Broadcast is a method of sending messages to multiple mobile telephone users in a defined area at the same time. It is defined by the ETSI’s GSM committee and 3GPP and is part of the 2G, 3G, 4G LTE and 5G standards. It is also known as Short Message Service-Cell Broadcast.
Unlike Short Message Service-Point to Point, Cell Broadcast is a one-to-many geo-targeted and geo-fenced messaging service.

History

Cell Broadcast messaging was first demonstrated in Paris in 1997. Some mobile operators used Cell Broadcast for communicating the area code of the antenna cell to the mobile user, for nationwide or citywide alerting, weather reports, mass messaging, location-based news, etc. Cell broadcast has been widely deployed since 2008 by major Asian, US, Canadian, South American and European network operators. Not all operators have the Cell Broadcast messaging function activated in their network yet, but most of the currently used handsets support cell broadcast.

Service

One Cell Broadcast message can reach a large number of telephones at once. Cell Broadcast messages are directed to radio cells, rather than to a specific telephone. The latest generation of Cell Broadcast Systems can send to the whole mobile network in less than 10 seconds, reaching millions of mobile subscribers at the same time. A Cell Broadcast message is an unconfirmed push service, meaning that the originators of the messages do not know who has received the message, allowing for services based on anonymity. Cell Broadcast is compliant with the latest EU General Data Protection Regulation as mobile phone numbers are not required by CB. The originator of the Cell Broadcast message can request the success rate of a message. In such a case the Cell Broadcast System will respond with the number of addressed cells and the number of cells that have broadcast the Cell broadcast message.

Technology

The maximum length of a cell broadcast message is 1395 characters. The CB message parameters contain the broadcasting schedule. If the start-time is left open, the CBC system will assume an immediate start, which will be the case for Public Warning messages. If the end-time is left open, the message will be repeated indefinitely. A subsequent cancel message shall be used to stop this message. The repetition rate can be set between 2 seconds and to values beyond 30 minutes. Each repeated CB message will have the same message identifier, and the same serial number. Using this information, the mobile telephone is able to identify and ignore broadcasts of already received messages.
A Cell Broadcast message page is composed of 82 octets, which, using the default character set, can encode 93 characters. Up to 15 of these pages may be concatenated to form a Cell Broadcast message.
A Cell Broadcast Centre, a system which is the source of SMS-CB, is connected to a Base Station Controller in GSM networks, to a Radio Network Controller in UMTS networks, to a Mobility Management Entity in LTE networks or to a core Access and Mobility management Function in 5G networks.
The technical implementation of the cell broadcast service is described in the 3GPP specification TS 23.041
A CBC sends CB messages, a list of cells where messages are to be broadcast, and the requested repetition rate and number of times they shall be broadcast to the BSC/RNC/MME/AMF. The BSC's/RNC's/MME/AMF responsibility is to deliver the CB messages to the base station, NodeBs, ENodeBs and gNodeBs which handle the requested cells.

Emergency communication system

Cell Broadcast is not affected by traffic load; therefore, it is very suitable during a disaster when load spikes of data, regular SMS and voice calls usage tend to significantly congest mobile networks, as multiple events have shown.
Wireless Emergency Alerts and Government alerts using Cell Broadcast are supported in all models of mobile telephones. Smart phones have a configuration menu that offer opt-out capabilities for certain public warning severity levels.
Broadcast messages are used in most countries to send emergency alerts, using as input a CAP message as specified by OASIS or Wireless Emergency Alerts C-interface protocol, which has been specified jointly by the Alliance for Telecommunications Industry Solutions and the Telecommunications Industry Association.
Advantages of using Cell Broadcast for Public warning are:
A point of criticism in the past on Cell Broadcast was that there was no uniform user experience on all mobile devices in a country.
This limitation is since 2012 no longer present. In case a national civil defence organisation is adopting one of the Wireless Emergency Alerts standards, WEA - formerly known as CMAS in North America, EU-Alert in Europe, LAT-Alert in South America, Earthquake Tsunami Warning System in Japan, each subscriber in that country either making use of the home network or is roaming automatically makes use of the embedded Public warning Cell Broadcast feature present in every Android and IOS mobile device.
In countries that have selected Cell Broadcast to transmit public warning messages, up to 99% of the handsets receive the cell broadcast message reaching between 85-95% of the entire population as not all people have a mobile phone within seconds after the government authorities have submitted the message see as examples Emergency Mobile Alert, Wireless Emergency Alerts and NL-Alert.

Public warning implementations

Many countries have implemented location-based alert systems based on cell broadcast. The alert messages to the population, already broadcast by various media, are relayed over the mobile network using cell broadcast.
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The following countries have selected Cell Broadcast to use for their national public warning system but are currently in the process of implementing.
The government of the United Kingdom established a project to evaluate options for a National Alerting Service in 2013, conducted trials in 2014. The project stopped in 2015. In 2018 the Cabinet Office commissioned a discovery report to assess the state of UK networks, review international developments with mobile alerting and the steps required to implement a service in the UK. In 2019, The Environment Agency together with Fujitsu, the Mobile Operator EE and the University of Hull explored the potential use of Cell Broadcast as an alerting channel for severe flooding. In January 2019 a Cell Broadcast message was successfully sent from the Flood Warning System over the 4G network in EE's test lab to a number of mobile devices. During 2019 the Environment Agency commissioned a survey to assess public responses to the use of Cell Broadcast messages and in November 2019 a workshop was held at the University of Hull to assess behavioural responses to Cell Broadcast messages. The results of this workshop were made available publicly.

Footnotes