| 摘要 |
FM-based emergency alert systems and methods are very reliable, intrude only minimally on program material, leave battery life unchanged, and do not add to the cost of embedding FM reception in portable electronic devices such as cellular handsets. For compatibility with intermittently operating, low-energy-consumption FM receivers in cell phones, an alerting signal spanning at least the wake-up period of the FM receiver is transmitted prior to data transmission. The receiver may wake up at a rate of a few tenths of a hertz to a few hertz. Various modulation schemes may be used for the transmitted signal. After a sufficient amount of incoming signal is detected, an alarm or data relating to an emergency situation may be received. A plurality of transmitters may be used to transmit the signal redundantly.
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