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It’s important to find an orthogonal set of transmitting waveforms of MIMO sonar, and the orthogonality of signal set has a direct affect on the detection efficiency of MIMO sonar. The frequency-hopped signal based on a Costas sequence has a nearly ideal range-Doppler ambiguity function, however, the different frequency-hopped signals constructed by different primitive elements of a finite field are not always orthogonal. A search method for primitive elements is proposed based on the finite field theory, and an optimal orthogonal set of transmitting waveforms is designed based on the primitive elements of safe primes. The simulated results show that a set of transmitting waveforms made from a safe prime, which is less than 1 000, has not only the best orthogonality but also the maximum number of signals. [ABSTRACT FROM AUTHOR]

The estimation of high-resolution and high-accurate direction-of-arrive (DOA) of underwater wideband acoustic sources in the cases of limited array aperture and lack of target feature information is Studied. Considering the independent statistical characteristics of underwater bandwidth acoustic sources, a stale coherence transform (SCT) method based on independent component analysis (ICA) is utilized to obtain DOA estimation. For the Gaussian distribution characteristics of additive noise, the wavelet denois-ing pre-processing is used to reduce the Gaussian components in the mixed signals. A spatial resampling method is proposed to fix the performance degraidation of SCT in low-frequency range. In the computer simulation and sea trial, the proposed algorithm has the advantages of higher resolution, fewer sensors, less dependence on the priori knowledge and better low-frequency performance compared with other traditional algorithms. The signal processing results confirm the feasibility and performance superiority of the proposed algorithm. [ABSTRACT FROM AUTHOR]