This paper considers the problem of direction-of-arrival (DOA) estimation ofcoherent signals on passive coprime arrays, where we resort to the fourth-ordercumulants of the received signal to explore more information. A fourth-ordercumulant matrix (FCM) is introduced for the coprime arrays. The specialstructure of the FCM is combined with the array configuration to resolve thecoherent signals. Since each sparse array of the coprime arrays is uniform, aseries of overlapping identical subarrays can be extracted. Using thisproperty, we propose a generalized spatial smoothing scheme applied to the FCM.From the smoothed FCM, the DOAs of both the coherent and independent signalscan be successfully estimated on the pseudo-spectrum generated by thefourth-order MUSIC algorithm. To overcome the problem of occasional false peakappearing on the pseudo-spectrum, we use a supplementary sparse array whoseinter-sensor spacing is coprime to that of either existing sparse array. Fromthe combined spectrum aided by the supplementary sensors, the false peaks areremoved while the true peaks remain. The effectiveness of the proposed methodsis demonstrated by simulation examples.
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