Enhancing the Usability of the Commercial Mobile Alert System

The U.S. Department of Homeland Security initiated the Commercial Mobile Alert System (CMAS) to inform the general public of emergencies. CMAS utilizes the commercial telecommunications infrastructure to broadcast emergency alert text messages to mobile users in an area affected by an emergency. Because CMAS uses cell broadcast service, the smallest area that CMAS can broadcast messages is a cell site, which is usually quite large for local emergencies. This paper proposes an enhancement that uses CMAS as a transport protocol to distribute local emergency alerts to areas smaller than a cell site. The paper also conducts an investigation of the Common Alerting Protocol (CAP), the current emergency protocol standard, and suggests an enhancement to the CAP message structure for CMAS emergency alerts. The viability of the approach is demonstrated using a prototype implementation, which simulates broadcasts of emergency alerts to confined areas such as a city block or an apartment complex.