| 摘要 |
Methods and apparatus for providing integrity alert information include embedding the integrity alert message in a longer message stream that is broadcast to a receiver in order to meet a predetermined time to alert. In one particular embodiment, the receiver is a GPS receiver, the longer message is a navigation signal, and the integrity alert message is a 50 bit word containing an updated user range accuracy index. Advanced GPS users recognize the embedded integrity alert message by its message ID, pass a parity check on the integrity alert message and use the updated user range accuracy index in subsequent signal processing. Legacy GPS users fail parity on the integrity alert message and discard the message. The impact on legacy users is negligible since the infrequent alerts will only occasionally cause data to be discarded.
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