Earticle

Coastal surveillance and harbour defence are the most complex and challenging opera- tional issues for modern navy in the current turbulent global political climate. In most of the coastal surveillance and harbour defence systems, long sea-bed arrays consisting of hundreds of pressure sensors are deployed along the coastal belt to capture the low frequency compo- nents emanating from the sub-surface targets. Deployment of these sensor-arrays along with its associated signal conditioning hardware at the ocean-bed is a challenging task. The output of the sensor-array is to be conditioned and then digitized using multi-bit analog to digital converters (ADC). Further, the digitized channel data are required to be send to a base station through a radio frequency link. In this paper, we propose a compressively sampled (CS) architecture of acoustic vector sensor (AVS) array, to estimate the direction of arrival (DoA) of multiple acoustic sources, in a range independent shallow ocean using a one-dimensional search without prior knowledge of the ranges and the depths of the sources. We extend the high resolution angular spectral estimators MUSIC, MVDR and subspace in- tersection method (SIM) to suit the compressively sampled AVS array architecture operating in a shallow ocean environment. This architecture promises a signicant reduction in the number of sensors, analog signal conditioning hardware, data rate or bandwidth, the number of snapshots and the software complexity, leading to easy installation and maintenance.

본 논문에서는 음향벡터 선배열 센서 기반에서의 광대역 적응빔형성기법을 다룬다. 적응 빔형성을 위하여 안정적인 공분산행렬추정은 매우 중요한 문제이다. 기존의 코히어런트 신호부공간기반의 적응 빔형성기법은 초점조정행렬(focusing matrix) 추정으로 인해 방위각 추정에 오차가 발생하며 또한 공분산행렬 추정을 위하여 많은 데이터 단편을 필요로 한다. 방위각 추정오차 및 공분산 행렬 추정시 필요한 데이터 단편의 수 문제를 완화하기 위하여 음압센서 선배열에 적용된 조향공분산 행렬 기법을 음향벡터 선배열 센서에 확장하여 적용한다. 그리고 부배열 기법을 통하여 공분산행렬의 차원을 줄임으로써 적은 수의 데이터 단편으로 안정적인 공분산행렬 추정이 가능하고 방위각 추정성능을 향상시킨다. 모의 실험을 통하여 기존의 코히어런트 신호 부공간 전처리 기반 광대역 빔형성기법과 제안한 기법의 방위각 추정 성능을 분석한다.

In this paper, a wideband adaptive beamforming approach for an acoustic vector sensor linear array is presented. It is a very important issue to estimate the stable covariance matrix for adaptive beamforming. In the conventional wideband adaptive beamforming based on coherent signal-subspace (CSS) processing, the error of bearing estimates is resulted from the focusing matrix estimation and the large number of data snapshot is necessary. To alleviate the estimation error and snapshot deficiency in estimating covariance matrix, the steered covariance matrix method in the pressure sensor is extended to the vector sensor array, and the subarray technique is incorporated. By this technique, more accurate azimuth estimates and a stable covariance matrix can be obtained with a small number of data snapshot. Through simulation, the azimuth estimation performance of the proposed beamforming method and a wideband adaptive beamforming based on CSS processing are assessed.