FDOA
Encyclopedia
Frequency difference of arrival (FDOA), also frequently called differential Doppler (DD), is a technique analogous to TDOA for estimating the location of a radio emitter based on observations from other points. (It can also be used for estimating one's own position based on observations of multiple emitters). TDOA and FDOA are sometimes used together to improve location accuracy and the resulting estimates are somewhat independent. By combining TDOA and FDOA measurements, instantaneous geolocation can be performed in two dimensions.
It differs from TDOA in that the FDOA observation points must be in relative motion with respect to each other and the emitter. This relative motion results in different doppler
shifts observations of the emitter at each location in general. The relative motion can be achieved by using airborne observations in aircraft, for example. The emitter location can then be estimated with knowledge of the observation points' location and vector velocities and the observed relative doppler shifts between pairs of locations.
A disadvantage of FDOA is that large amounts of data must be moved between observation points or to a central location to do the cross-correlation
that is necessary to estimate the doppler shift.
The accuracy of the location estimate is related to the bandwidth
of the emitter's signal, the signal-to-noise ratio
at each observation point, and the geometry and vector velocities of the emitter and the observation points.
It differs from TDOA in that the FDOA observation points must be in relative motion with respect to each other and the emitter. This relative motion results in different doppler
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
shifts observations of the emitter at each location in general. The relative motion can be achieved by using airborne observations in aircraft, for example. The emitter location can then be estimated with knowledge of the observation points' location and vector velocities and the observed relative doppler shifts between pairs of locations.
A disadvantage of FDOA is that large amounts of data must be moved between observation points or to a central location to do the cross-correlation
Cross-correlation
In signal processing, cross-correlation is a measure of similarity of two waveforms as a function of a time-lag applied to one of them. This is also known as a sliding dot product or sliding inner-product. It is commonly used for searching a long-duration signal for a shorter, known feature...
that is necessary to estimate the doppler shift.
The accuracy of the location estimate is related to the bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
of the emitter's signal, the signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
at each observation point, and the geometry and vector velocities of the emitter and the observation points.
Further reading
- Ho, K.C.; Chan, Y.T.; , "Geolocation of a known altitude object from TDOA and FDOA measurements," IEEE Transactions on Aerospace and Electronic Systems, vol.33, no.3, pp.770-783, July 1997. , IEEE XPlore.