Frequency difference of arrival (FDOA) or 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.
The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.
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.
In signal processing, cross-correlation is a measure of similarity of two series as a function of the displacement of one relative to the other. This is also known as a sliding dot product or sliding inner-product. It is commonly used for searching a long signal for a shorter, known feature. It has applications in pattern recognition, single particle analysis, electron tomography, averaging, cryptanalysis, and neurophysiology.
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.
In computing, bandwidth is the maximum rate of data transfer across a given path. Bandwidth may be characterized as network bandwidth, data bandwidth, or digital bandwidth.
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. SNR is defined as the ratio of signal power to the noise power, often expressed in decibels. A ratio higher than 1:1 indicates more signal than noise.
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. doi:10.1109/7.599239, IEEE XPlore.
In computing, a Digital Object Identifier or DOI is a persistent identifier or handle used to uniquely identify objects, standardized by the International Organization for Standardization (ISO). An implementation of the Handle System, DOIs are in wide use mainly to identify academic, professional, and government information, such as journal articles, research reports and data sets, and official publications though they also have been used to identify other types of information resources, such as commercial videos.
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