Yixin Yang

Theoretical and Practical Solutions for High-Order Superdirectivity of Circular Sensor Arrays

An analytical and closed-form optimal solution expressed in elementary functions for superdirectivity of a circular sensor array is proposed in this paper. By utilizing the circulant property of the data covariance matrix for circular sensor arrays, such solutions are derived to accurately calculate the optimal beamforming vector, optimal beam pattern, corresponding directivity factor, and eigenbeams. Based on these solutions, it is proved that such array possesses several important properties which facilitate an eigenbeam decomposition and synthesis approach for practical implementations. Experiments conducted result in superdirective beams which contain zeroth- to fifth- and sixth-order eigenbeams. As a typical result, the superdirective beam which contains zeroth- to fifth-order eigenbeams has a 28° beamwidth and a 12-dB directivity index with a small circular array radius of 0.267 wavelength.

Adaptive design of FIR filter with applications in broadband beamforming

The design of FIR digital filter based on minimum mean square error criterion can be implemented via adaptive approach. An iterative algorithm is proposed in this paper to enhance the effectiveness of adaptive FIR digital filter design through adaptively obtaining optimum cost functions. This modified approach results in the best values of the cost function to reach a best fit between the FIR digital filter response and the design requirements. The adaptive design approach is used to get the weights of FIR filters in time domain broadband beamformers. An example of broadband beamforming for a 12-element arc array is illustrated to show the effectiveness of the iterative algorithm proposed in this paper.

Phase-Mode Circular Multi-channel Hydrophone with Super Directivity

A new model for the super directional circular multi-channel hydrophone based on the concept of phase-mode is presented in this paper. In this new model, the phase-mode strength calculated via boundary element method and the mode coefficients determined by desired directivity were used to obtain the directivity forming weights for each channel of the hydrophone. Therefore, the synthesized super directivity could be formed. The mathematical analysis of maximum directivity index for the phase-mode hydrophone is also presented. Computer simulations and water-tank experiments for the proposed hydrophone were carried out. The experimental results show that the phase-mode hydrophone owns a good super directivity, which is impossible for conventional methods using the same small-size hydrophone. For the low phase-mode order, the measured directivities are consist with the theoretical ones very well. For the cases of higher phase mode orders, the measured directivities are still much better compared with the conventional ones, although not match the theoretical ones perfectly due to the higher error sensitivity.

Optimum design on time domain wideband beamformer with constant beamwidth for sonar systems

In this paper, a new method is presented to design low-sidelobe wideband constant beamwidth beamformers (WCBB) in time domain, which alleviates the effect caused by array mismatch errors by applying the measured array models into the design procedure. A combination of FIR filters and digital delay lines is used in the beamformer structure to reduce the order of FIR filters. In FIR filter design, the semi-definite programming is utilized which is able to constrain both the mainlobe shapes and the sidelobe levels within the whole design frequency band. Results from lake experiments with a practical sonar system verified the effectiveness of the proposed method.

Robust target feature extraction based on modified cochlear filter analysis model

The performance of underwater target recognition systems depends on the consistency and adaptation of target feature in complex conditions during the training and testing stages. In this paper, we investigated the target feature extraction problems in a complex underwater environment and proposed a novel approach based on modified cochlear filter analysis model of the human auditory system. The frequency responses and distributions of the modified cochlear filter bank are similar to that of the basilar membrane in the cochlea. The fast forward and inverse transforms of modified cochlear filter bank are also presented for discrete-time signals to save the computational load. The experimental results using real ship radiated noise data verified that the modified cochlear filter analysis model is robust in background noise.

A new time-frequency rate distribution for multicomponent high-order PPS

A new time-frequency rate distribution (TFRD) referred to as Hybrid LPFT-LPD algorithm, which combines Local Polynomial Fourier Transform (LPFT) and L-phase distribution (LPD), is proposed in this paper. LPFT is a linear transform without outer cross-terms for multicomponent Polynomial Phase Signal (PPS) and LPD can suppress inner cross-terms for high-order PPS. Hybrid LPFT-LPD algorithm makes full use of the properties of these two methods, and a distribution without any cross-terms for multicomponent high-order PPS is obtained. The validity of the proposed method is demonstrated by computer simulations.

Beamforming for Circular Array Based on Mode Decomposition of Sound Field

A general mode decomposition beamformer for circular array is presented in this paper. In the proposed beamformer, the mode components of incoming wave are extracted via decomposing the sound field around the circular array. Then the synthesized beampattern is obtained by using the mode components and corresponding mode coefficients. The framework of the beamformer which we call it Mode Decomposition Beamformer (MDB for short) is presented. In the framework, the beamforming for the circular array is composed of three independent sections. Due to the mode decomposition for the sound field, we succeed in applying the linear array weights in the beamforming for circular array, such as Dolph-Chebshev weights, and we name the corresponding beamformer DC-MDB. The results of computer simulations and lake-experiments for a 24-element ring array indicate that the measured beampatterns obtained by MDB are consistent with the desired beampattern. So are the results of the DC-MDB case. Moreover, the obtained measured beampatterns are much better than the conventional beampatterns.

A new method for instantaneous frequency rate estimation of polynomial phase signal

In order to estimate the instantaneous frequency rate (IFR) of a polynomial phase signal (PPS) with arbitrary order, a new kind of transform referred to as L-phase distribution (LPD) is defined. The principle and realization procedure of this transform are given in detail. Furthermore, we propose an iterative IFR estimation algorithm, in which successive IFR estimates are obtained from the peak of the cross L-phase distribution (XLPD), and this new method can improve the accuracy of IFR estimation for a PPS in the presence of additive noise. The results of computer simulation demonstrate the validity of the proposed method.

Interference rejection for beamspace DOA estimation algorithms based on null-broadened beamformers

All beamspace DOA estimation algorithms are based on the beam outputs and the beamformers play an important role in providing high quality beam output data for further processing. We use null-broadened MVDR beamformers to apply to the element outputs. The broadened null can reject the interfering sources not only from a specific direction but from a specific spatial region as well. Performance of beamspace MUSIC using null broadened beamformers is studied via computer simulation for uniform linear array. The simulation results show that the proposed scheme has good spatial resolution than conventional beamspace DOA estimation algorithms.

Design broadband beamformers via interpolation techniques

A method for design of time domain broadband beamformers is proposed in this paper. It is based on applying the interpolation technique in fitting the expected FIR filter responses which are required to provide the amplitude and phase adjustment in each channel of the array. A uniform linear array and an arc array were studied as examples in this paper, and computer simulation results verified the effectiveness of the proposed method.