Although the Emergency Alert System (EAS) is a mature service is the United States, in territories that have adopted DVB standards, systems have not been implemented to alert the public of impending natural disasters. The original DVB-T standard incorporated a means of signaling to receivers using the DVB-SI, so it is possible for DVB-T receivers to automatically respond to the service information. At the upcoming BroadcastAsia2010 show in Singapore, June 15-18, the DVB Project will demonstrate an Emergency Warning System (EWS) for DVB-T transmission using data carried in the service information.
Every DVB-T demodulator can be configured by the modulator. This facility can be used to switch the receiver to a more robust transmission scheme during an emergency. For example, 64-QAM used for normal TV broadcast could be switched to QPSK.
In the event of towers and transmitters being lost, it would be useful to extend the reception area of the remaining facilities; this switch to more robust modulation can achieve just that.
DVB supports audible announcements, and the service information enables the switching of the receiver from a normal program to the announcement. It is even possible via proxy services to switch multiplexes to the one carrying the announcement using the announcement flag in the adaptation field of the transport stream packets.
This scheme is designed for audio announcements, but, ideally, visual warning should also be carried. It is possible to construct a scheme whereby the announcement is accompanied by a visual message and inserted into the video stream during an announcement. In that way, the emergency warning message could reach those with sensory impairment.
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