Reference beacon methods and apparatus for TDOA/FDOA geolocation

A method of determining bias error in a geolocation system, comprising:

• transmitting from a transmitter a reference beacon signal containing position information including at least one of a position of the transmitter at a time of fix and an estimate of the position of the transmitter at a time of transmission of the reference beacon signal;
• receiving the reference beacon signal at a plurality of collection platforms;
• determining a position measurement of the transmitter based on at least one of a time of arrival and a frequency of arrival of the reference beacon signal at the plurality of collection platforms;
• determining a first bias error based on the position measurement of the transmitter and the position information contained in the reference beacon signal;
• measuring a time of arrival of the reference beacon signal at each of the plurality of collection platforms;
• determining an expected difference between the times of arrival of the reference beacon signal at two of the plurality of collection platforms based on the position information contained in the reference beacon signal;
• and
• determining a timing bias error based on the measured times of arrival of the reference beacon signal at the two collection platforms and the expected difference between the times of arrival of the reference beacon signal at the two collection platforms.

A method of determining bias error in a geolocation system, comprising:

• transmitting from a transmitter a reference beacon signal containing position information including at least one of a position of the transmitter at a time of fix and an estimate of the position of the transmitter at a time of transmission of the reference beacon signal, wherein the reference beacon signal contains motion information relating to the transmitter;
• receiving the reference beacon signal at a plurality of collection platforms;
• determining a position measurement of the transmitter based on at least one of a time of arrival and a frequency of arrival of the reference beacon signal at the plurality of collection platforms;
• determining a first bias error based on the position measurement of the transmitter and the position information contained in the reference beacon signal;
• measuring a frequency of arrival of the reference beacon signal at each of the plurality of collection platforms;
• determining an expected frequency difference of arrival of the reference beacon signal at the plurality of collection platforms based on the motion information contained in the reference beacon signal;
• and
• determining a frequency bias error based on the measured frequency of arrival of the reference beacon signal at each of the plurality of collection platforms and the expected frequency difference of arrival of the reference beacon signal at the plurality of collection platforms.

A method of determining bias error in a geolocation system, comprising:

• transmitting from a transmitter a reference beacon signal containing position information including at least one of a position of the transmitter at a time of fix and an estimate of the position of the transmitter at a time of transmission of the reference beacon signal;
• receiving the reference beacon signal at a plurality of collection platforms;
• determing a position measurement of the transmitter based on at least one of a time of arrival and a frequency of arrival of the reference beacon signal at the plurality of collection platforms
• determining a first bias error based on the position measurement of the transmitter and the position information contained in the reference beacon signal;
• measuring a frequency of arrival of the reference beacon signal at each of the plurality of collection platforms;
• determining an expected frequency difference of arrival of the reference beacon signal at the plurality of collection platforms based on the position information contained in the reference beacon signal;
• and
• determining a frequency bias error based on the measured frequency of arrival of the reference beacon signal at each of the plurality of collection platforms and the expected frequency difference of arrival of the reference beacon signal at the plurality of collection platforms.