Research On Sparse Array And Beamforming Algorithm For Phased Array Three-dimensional Imaging Sonar System

Phased array three-dimensional (3-D) imaging sonar system uses the phased array technology to generate more than ten thousands of beams simultaneously, it ensonifies the whole viewing volume with a single ping and results in a three-dimensional sonar image. Being capable of up to 20 updated per second, it can detect the underwate object in real-time. Based on the project of phased array 3-D imaging sonar system (No.2006AA09Z109) that is supported by the National High-Tech Research and Development Plan of China, this paper focuses on designing a two-dimensional sparse transducers array with a novel approximation for the delays of the digital near-field beamforming on a planar array and an optimized algorithm for underwater 3-D imaging sonar system. Based on the resolution of echo displacement vector, this paper proposes a new optimized algorithm for the 3-D imaging sonar beamforming in the frequency-domain. This paper also proposes one multi-FPGA (Field Programmable Gate Arrays) system for implementing beamforming algorithm of 3-D imaging sonar system in a parallel distributive processing method.In Chapter 1, the significance of this research work is presented together with a brief summary of the current research status. The research direction is also described.In Chapter 2, an optimized Simulated Annealing algorithm for thinning and weighting of large planar arrays is proposed. The optimized algorithm is aimed at designing a two-dimensional planar array using the fewest transducers with a fixed side-lobe peak and a fixed current taper ratio. The four extensions of the Simulated Annealing algorithm and the procedure for optimized Simulated Annealing algorithm are demonstrated. Two examples of the planar array are carried out to assess the efficiency of the optimized method.In Chapter 3, a novel approximation for the delays of the digital near-field beamforming based on a planar array is proposed and, an optimized algorithm for underwater 3-D imaging sonar system based on the novel approximation is described. Comparisons of the memory and the computational requirements between the optimized algorithm and the Direct Method beamforming are illustrated. Comparisons of the proposed approximation and the Fresnel approximation are also demonstrated. The optimization procedure of the proposed approximation will then ben presented.A new optimized algorithm for the 3-D imaging sonar beamforming in the frequency-domain based on the resolution of echo displacement vector is proposed in Chapter 4. The Matlab simulation results and the two data-paths for the proposed algorithm are presented. The memory and the computational requirements of the proposed data-paths are also analyzed. The paper validates that the proposed algorithm has the advantage in terms of reducing the memory requirements without sacrificing the system performance. Finally, the simulations for the two data-paths are carried out respectively on the FPGAs; the resource utilizations are listed.In Chapter 5, the multi-FPGA system architecture in parallel distributive processing method is implemented in a 3-D imaging sonar system for beamforming algorithm. The processing element of the system architecture is FPGA. The FPGAs is connected in user defined protocol using Low Voltage Differential Signaling (LVDS). The system has certain advantages such as low communication overhead and low requirement of hardware resource.3-D imaging sonar beamforming algorithm is implemented in the multi-stage parallel distributive processing method.The last chapter lists the new achievements of the whole research. The prospect of the future research is also described.