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Description:
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Given a certain transmission frequency , Shannon spatial sampling limit de¯nes
an upper bound for the antenna element spacing . Beyond this bound , the exceeded
ambiguity avoids correct estimation of the signal parameters (i .e . , array manifold
crossing ) . This spacing limit is inversely proportional to the frequency of transmis -
sion . Therefore , to meet a wider spectral support , the element spacing should be
decreased . However , practical implementations of closely spaced elements result in a
detrimental increase in electromagnetic mutual couplings among the sensors . Further -
more , decreasing the spacing reduces the array angle resolution . In this dissertation ,
the problem of Direction of Arrival (DOA ) estimation of broadband sources is ad -
dressed when the element spacing of a Uniform Array Antenna (ULA ) is inordinate .
It is illustrated that one can resolve the aliasing ambiguity by utilizing the frequency
diversity of the broadband sources . An algorithm , based on Maximum Likelihood
Estimator (MLE ) , is proposed to estimate the transmitted data signal and the DOA
of each source . In the sequel , a subspace -based algorithm is developed and the prob -
lem of order estimation is discussed . The adopted signaling framework assumes a
subband hopping transmission in order to resolve the problem of source associations
and system identi¯cation . The proposed algorithms relax the stringent maximum
element -spacing constraint of the arrays pertinent to the upper -bound of frequency
transmission and suggest that , under some mild constraints , the element spacing can be conveniently increased . An approximate expression for the estimation error has
also been developed to gauge the behavior of the proposed algorithms . Through con -
¯rmatory simulation , it is shown that the performance gain of the proposed setup
is potentially signi¯cant , speci¯cally when the transmitters are closely spaced and
under low Signal to Noise Ratio (SNR ) , which makes it applicable to license -free
communication . |