Abstract:
The problem of locating a signal source, or an emitter, has many civilian and military applications, such as communication regulations enforcement, military reconnaissance, and search-and-rescue operations. Many of the most widely used emitter location methods rely on the accurate and robust estimation of the differential time delay,
or time-difference-of-arrival (TDOA), and the differential Doppler shift, or frequency-
difference-of-arrival (FDOA), between signal replicas arriving at two spatially separated
receivers. There are many conventional methods for estimating TDOA and/or FDOA.
However, these methods are unable to produce unbiased TDOA and FDOA estimates
when multiple emitters are located spatially close to each other. In many cases, the
spatial proximity at which the conventional methods fail is still unacceptably large for
precision emitter location applications. This problem is made even more diffcult when
separating signals from multiple emitters that share the same regions of the spectrum
at the same time.
When spatially close emitters overlap spectrally and temporally, robust TDOA and
FDOA estimation is diffcult, and accurate emitter location not only requires both estimation of TDOA, or FDOA, or both jointly, but also the estimation of a signal parameter
that can be used to separate the signal-of-interest (SOI) from a signal(s)-not-of-interest
(SNOI) that are both within the receiver's field of view. The signal separation pa-
rameter selected depends on the type of signal modulation. In this thesis, the signals
of interest are bauded signals. The separation methodology for such signals is cyclo-
stationarity with parameterization by cyclic frequency. Based on this assumption, a
new three-dimensional joint estimation method for TDOA, FDOA, and cyclic frequency
parameters, called alpha cross ambiguity function (alpha-CAF), has been developed to ex-
ploit signal modulations with cyclostationary properties. By exploiting cyclostationarity,
alppha-CAF can produce separate unbiased TDOA and FDOA estimates that will in turn
yield reliable geolocation estimates for precision emitter location applications even when
severe interference causes conventional methods to fail. In this thesis the alpha-CAF param-
eter estimation (TDOA, FDOA, Cyclic Frequency) algorithm is introduced along with a
complete analysis of its performance compared to conventional estimators. A connection
is also made between the alpha-CAF algorithm and the additional steps needed to perform
an emitter location technique.
