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The FDOA between the adjacent AIS signals can be expressed as
where [DELTA]T = [[[DELTA][t.sub.1], [DELTA][t.sub.2], ...,[DELTA][t.sub.N]].sup.T] is the TDOA measurement vector obtained by synchronization technique and [DELTA]F = [[[DELTA][f.sub.r1], [DELTA][f.sub.r2], ..., [DELTA][f.sub.rN]].sup.T] is the FDOA measurement vector.
Figure 1 shows the locations of an emitter and two FDOA receiving stations.
Now we can write the equation for E1, the standard deviation (1[sigma]) error of the offset (in kin) of the erroneous isofreq curve from the true isofreq that passes through the emitter, where F is the transmitted frequency in Hz, and [DELTA]F is the 1[alpha] error of the FDOA measurement (in Hz).
Time difference of arrival (TDOA) and frequency difference of arrival (FDOA) are precision emitter-location approaches, which were discussed in previous "EW 101" columns (see "Precision Emitter-Location Techniques," ]ED, December 2002, p.
The accuracy with which TDOA and FDOA systems calculate emitter locations is usually stated in terms of the circularerror probable (CEP) (see "Emitter Location--Conversion of ACA Errors to Location Errors" JED, March 2003, p.
Frequency difference of arrival (FDOA) is one of the techniques for achieving precision emitter location.
With a third moving receiver, we have three measurement baselines, each of which can collect FDOA data and calculate isofreqs.
Two techniques are typically used for precision emitter location: time difference of arrival (TDOA) and frequency difference of arrival (FDOA).
Next month, we'll continue our coverage of precision emitter location with FDOA and combined TDOA/FDOA approaches.
The two passive techniques available for precision emitter location are time difference of arrival (TDOA) and frequency difference of arrival (FDOA).
Also like TDOA, FDOA can be implemented on a single platform or multiple platforms.
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- FDO RAM
- FDP Avulsion