Position validation
In one implementation, a method includes receiving versions of a message from a first satellite-based receiver and a second satellite-based receiver that both received a radio frequency (“RF”) transmission of the message, the message comprising a self-reported position of a transmitter of the message. The method also includes determining a time difference between a first arrival time of the RF transmission of the message at the first satellite-based receiver and a second arrival time of the RF transmission of the message at the second satellite-based receiver. The method further includes determining a measure of the likelihood that the self-reported position of the transmitter is valid based on the time difference between the first and second arrival times. The method still further includes transmitting an indication of the measure of the likelihood that the self-reported position is valid.
1. A method comprising:
receiving, on a first beam of a satellite-based receiver having multiple beams, a radio frequency (“RF”) transmission comprising a message, the message comprising a self-reported position of a transmitter of the RF transmission;
determining a first set of beams of the satellite-based receiver expected to receive the RF transmission based on the self-reported position of the transmitter and a beam radiation pattern for beams of the satellite-based receiver;
determining a second set of beams of the satellite-based receiver that received the RF transmission;
determining a measure of the likelihood that the self-reported position of the transmitter is valid based on results of comparing the first set of beams of the satellite-based receiver expected to receive the RF transmission and the second set of beams of the satellite-based receiver that received the RF transmission; and
transmitting an indication of the likelihood that the self-reported position is valid.
2. The method of claim 1 , wherein the beam radiation pattern defines an expected gain for each of individual beams of the satellite-based receiver with respect to a coverage area including the self-reported position of the transmitter.
3. The method of claim 2 , wherein determining a first set of beams of the satellite-based receiver expected to receive the RF transmission comprises:
determining a likelihood of each of individual beams of the satellite-based receiver receiving the RF transmission based on the expected gain of each beam with respect to the coverage area including the self-reported position of the transmitter.
4. The method of claim 2 , wherein the transmitter is hosted on an in-flight aircraft.
5. The method of claim 4 , wherein the message is an automatic dependent surveillance-broadcast (“ADS-B”) message transmitted by the transmitter on the aircraft.
6. The method of claim 2 , wherein determining the measure of the likelihood that the self-reported position of the transmitter is valid comprises determining that at least a threshold percentage of the first set of beams of the satellite-based receiver expected to receive the RF transmission received the RF transmission, and wherein the transmitting comprises transmitting an indication that the self-reported position is valid.
7. The method of claim 3 , wherein the indication of the measure of the likelihood that the self-reported position of the transmitter is valid is determined based on a state machine that is updated after the message is received.
8. The method of claim 3 , wherein the transmitter is hosted on an aircraft and transmits automatic dependent surveillance-broadcast (“ADS-B”) messages.
9. The method of claim 1 , wherein determining the measure of the likelihood that the self-reported position of the transmitter is valid comprises determining that at least a threshold percentage of the first set of beams of the satellite-based receiver expected to receive the RF transmission received the RF transmission, and wherein the transmitting comprises transmitting an indication that the self-reported position is valid.
10. The method of claim 9 , wherein the beam radiation pattern defines an expected gain for each of individual beams of the satellite-based receiver with respect to a coverage area including the self-reported position of the transmitter.
11. The method of claim 1 , wherein the indication of the measure of the likelihood that the self-reported position of the transmitter is valid is determined based on a state machine that is updated after the message is received.
12. The method of claim 11 , wherein the beam radiation pattern defines an expected gain for each of individual beams of the satellite-based receiver with respect to a coverage area including the self-reported position of the transmitter.
13. The method of claim 9 , wherein determining the measure of the likelihood that the self-reported position of the transmitter is valid comprises determining that at least a threshold percentage of the first set of beams of the satellite-based receiver expected to receive the RF transmission received the RF transmission, and wherein the transmitting comprises transmitting an indication that the self-reported position is valid.
14. The method of claim 1 , wherein the transmitter is hosted on an aircraft and transmits automatic dependent surveillance-broadcast (“ADS-B”) messages.
15. The method of claim 14 , wherein determining the measure of the likelihood that the self-reported position of the transmitter is valid comprises determining that at least a threshold percentage of the first set of beams of the satellite-based receiver expected to receive the RF transmission received the RF transmission, and wherein the transmitting comprises transmitting an indication that the self-reported position is valid.
16. The method of claim 1 , wherein the satellite-based receiver is hosted on a satellite that is part of a satellite constellation, wherein the transmitter is out of range of other satellites in the satellite constellation, and wherein the measure of the likelihood that the self-reported position of the transmitter is valid is used to validate self-reported position data transmitted by the transmitter after previous self-reported position data was validated using time difference of arrival (“TDOA”) based on differences in times of arrival of RF transmissions transmitted by the transmitter at two or more satellites of the satellite constellation.
17. The method of claim 16 , wherein the beam radiation pattern defines an expected gain for each of individual beams of the satellite-based receiver with respect to a coverage area including the self-reported position of the transmitter.
18. The method of claim 16 , wherein determining the measure of the likelihood that the self-reported position of the transmitter is valid comprises determining that at least a threshold percentage of the first set of beams of the satellite-based receiver expected to receive the RF transmission received the RF transmission, and wherein the transmitting comprises transmitting an indication that the self-reported position is valid.