May 12, 2014
APL, DHS Science and Technology Work to Improve Wireless Emergency Alerts
In case of a chemical attack, major earthquake, or nuclear detonation, it’s important for government authorities to alert people as quickly as possible. They do so with Wireless Emergency Alerts (WEA)—short messages that can be broadcast to any “WEA-enabled” mobile device in a locally targeted area.
But what happens to the alerts if there’s a high level of cell broadcast traffic or massive infrastructure damage?
A service like WEA must be reliable and operational despite extreme conditions, but you can’t create an emergency to run a test. So APL recently crafted a model for the Department of Homeland Security Science and Technology Directorate to simulate the transmission of these alerts to mobile devices under extreme circumstances.
To virtually replicate an extreme circumstance, an Asymmetric Operations Sector team, led by Emre Gunduzhan, simulated increased amounts of background cell broadcast traffic on a cellular network and increased message loads to the Federal Emergency Management Agency’s servers that handle WEA messages. They also introduced very high levels of delays over the Internet, transmission errors due to interference and poor reception, and ongoing telephone calls that would prevent reception of alert messages.
“The main finding was that under normal operating conditions, WEA can alert the public with very small latencies—adequate for many types of alerts and warnings,” Gunduzhan said. “But under some extreme conditions, such as high levels of delay on the Internet, alert delivery latencies can approach a minute [long], which would not be acceptable for alerts such as earthquake warnings.”
From these simulations, the team recommended ways to improve the alerts. One idea: assign a higher priority for WEA messages than other types of cell broadcasts. Another is to use permanent secure channels over the Internet—particularly for alert originators dealing with earthquake and tornado warnings. A significant portion of delays were due to setting up these secure channels.
Gunduzhan explained that an adaptive algorithm to repeat broadcasts over the air is also recommended. This would minimize the alert reception delays without consuming excessive cellular bandwidth or draining cell phone batteries.
The simulations also found that high call volume in an area and poor cellular coverage are two independent conditions that can have significant impacts on reception and delay alerts by several minutes for a portion of the target population.
Gunduzhan said a related challenge is making sure that people have devices to receive the messages. According to a new RAND study, less than 45 percent of cell phones are WEA-capable, although that figure is estimated to exceed 95 percent by 2018.
Media contact: Gina Ellrich, 240-228-7796, Gina.Ellrich@jhuapl.edu