Kinematics-augmented position validation

1. A method comprising:

receiving a number of instances of a message from a corresponding number of satellite-based receivers that each received a radio frequency (“RF”) transmission of an instance of the message, the message comprising a self-reported position of a transmitter of the message;

determining the number of satellite-based receivers that received an instance of the message;

selecting a validation technique, from a plurality of validation techniques, for validating the self-reported position of the transmitter of the message based on the number of satellite-based receivers that received an instance of the message;

determining a measure of the likelihood that the self-reported position of the transmitter is valid using the selected validation technique; and

transmitting an indication of the measure of the likelihood that the self-reported position is valid.

2. The method of claim 1 , wherein selecting a validation technique for validating the self-reported position of the transmitter of the message based on the number of satellite-based receivers that received an instance of the message includes selecting, if the number of satellite-based receivers that received an instance of the message is two or more, a TDOA-based validation technique that estimates the current position of the transmitter based on times at which the satellite-based receivers that received an instance of the message received the RF transmissions of the instances of the message.

3. The method of claim 1 , wherein determining the measure of the likelihood that the self-reported position of the transmitter is valid using the selected validation technique includes determining the measure of the likelihood that the self-reported position of the transmitter is valid based on a second measure of the likelihood that a previous self-reported position of the transmitter is valid.

4. The method of claim 3 , wherein determining the measure of the likelihood that the self-reported position of the transmitter is valid using the selected validation technique includes determining the measure of the likelihood that the self-reported position of the transmitter is valid based on a length of time since the previous self-reported position of the transmitter.

5. The method of claim 1 , wherein the transmitter is hosted on an in-flight aircraft.

6. The method of claim 1 , wherein the message is an automatic dependent surveillance-broadcast (“ADS-B”) message transmitted by a transmitter on the aircraft.

7. The method of claim 1 , wherein:

determining that a total number of satellite-based receivers that received an instance of the message is one, and

the validation technique estimates the current position of the transmitter based on prior position information for the transmitter.

8. The method of claim 7 , wherein selecting a validation technique for validating the self-reported position of the transmitter of the message based on the number of satellite-based receivers that received an instance of the message includes:

determining that the number of satellite-based receivers that received an instance of the message is one, and

selecting the validation technique as a consequence of having determined that the number of satellite-based receivers that received an instance of the message is one; and

determining a measure of the likelihood that the self-reported position of the transmitter is valid using the selected validation technique includes determining a measure of the likelihood that the self-reported position of the transmitter is valid using the validation technique based on a previous position of the transmitter at a previous time, a previous speed of the transmitter at the previous time, a previous bearing of the transmitter at the previous time, and a time at which the transmitter transmitted the RF transmission of the message.

9. A method comprising:

receiving an instance of a current message from a satellite-based receiver that received a radio frequency (“RF”) transmission of the current message, the current message comprising a self-reported position of a transmitter of the message;

estimating, based on a previous message transmitted by the transmitter at a previous time, a current position of the transmitter based on a previous position of the transmitter at the previous time, a previous speed of the transmitter at the previous time, a previous bearing of the transmitter at the previous time, and a current time at which the transmitter transmitted the RF transmission of the current message;

determining a measure of the likelihood that the self-reported position of the transmitter is valid based on a distance between the estimated current position of the transmitter and the self-reported position of the transmitter; and

transmitting an indication of the measure of the likelihood that the self-reported position is valid.

10. The method of claim 9 , wherein estimating the current position of the transmitter includes estimating a distance travelled by the transmitter between the current time and the previous time based on the previous speed of the transmitter at the previous time and the time between the current time and the previous time.

11. The method of claim 10 , wherein estimating the current position of the transmitter based on the previous position of the transmitter at the previous time, the previous speed of the transmitter at the previous time, the previous bearing of the transmitter at the previous time, and the current time at which the transmitter transmitted the RF transmission of the current message includes estimating the current position of the transmitter based on the estimated distance travelled by the transmitter between the current time and the previous time.

12. The method of claim 11 , wherein estimating the current position of the transmitter includes using Vincenty's formula to estimate the current position of the transmitter based on the previous position of the transmitter at the previous time, the previous bearing of the transmitter at the previous time, and the estimated distance travelled by the transmitter between the current time and the previous time.

13. The method of claim 9 , wherein the transmitter is hosted on an in-flight aircraft.

14. The method of claim 9 , wherein the message is an automatic dependent surveillance-broadcast (“ADS-B”) message transmitted by the transmitter on the aircraft.

15. A system comprising:

one or more processors; and

a memory coupled to the processors comprising instructions executable by the processors, the processors being operable when executing the instructions to:

receive a number of instances of a message from a corresponding number of satellite-based receivers that each received a radio frequency (“RF”) transmission of an instance of the message, the message comprising a self-reported position of a transmitter of the message;

determine the number of satellite-based receivers that received an instance of the message;

select a validation technique, from a plurality of validation techniques, for validating the self-reported position of the transmitter of the message based on the number of satellite-based receivers that received an instance of the message;

determine a measure of the likelihood that the self-reported position of the transmitter is valid using the selected validation technique; and

transmit an indication of the measure of the likelihood that the self-reported position is valid.

16. The system of claim 15 , wherein the processors are further operable when executing the instructions to:

update a validation state for the transmitter based on the determined measure of the likelihood that the self-reported position of the transmitter is valid; and

transmit an indication of the measure of the likelihood that the self-reported position is valid based on the updated validation state for the transmitter.

17. The system of claim 15 , wherein the processors are further operable when executing the instructions to select a TDOA-based validation technique that estimates the current position of the transmitter based on times at which the satellite-based receivers that received an instance of the message received the RF transmissions of the instances of the message if the number of satellite-based receivers that received an instance of the message is two or more.

18. The system of claim 15 , wherein the processors are further operable when executing the instructions to determine the measure of the likelihood that the self-reported position of the transmitter is valid based on a second measure of the likelihood that a previous self-reported position of the transmitter is valid.

19. The system of claim 18 , wherein the processors are further operable when executing the instructions to determine the measure of the likelihood that the self-reported position of the transmitter is valid based on a length of time since the previous self-reported position of the transmitter.

20. The system of claim 15 , wherein the processors are further operable when executing the instructions to:

select the validation technique as a consequence of having determined that the number of satellite-based receivers that received an instance of the message is one;

determine a measure of the likelihood that the self-reported position of the transmitter is valid using the validation technique based on a previous position of the transmitter at a previous time, a previous speed of the transmitter at the previous time, a previous bearing of the transmitter at the previous time, and a time at which the transmitter transmitted the RF transmission of the message.

21. The system of claim 15 , wherein the message is an automatic dependent surveillance-broadcast (“ADS-B”) message transmitted by a transmitter on the aircraft.