High Speed Floating-point Signal Processing Technologies Of Broadband Imaging Sonar

As the major detecting equipment which is irreplaceable in national product and security fields,imagimg sonar plays an important role in underwater target acquisition,location,imaging,life-saving,guarding and security areas.With the rapid development of imaging sonar technologies and electronic technologies,the signal processing has been changed from all-analog devices into digital beamforming,the working structure has been changed from mechanical single-beam scanning into electronic multi-beam imaging and the frequency from narrow band into broadband.With the extensions of application fields and working conditions,imaging sonar requires higher dynamic range and computational accuracy meanwhile smaller device volume.However,due to the relatively slower processing speed and more complicated structure,there is seldom researches can be seen in large scale floating-point processing algorithms and applications in underwater acoustics fields,especially in broadband imaging sonar fields.It is can be expected that broadband,floating-point,high speed and miniaturization will be the developing tendency of imaging sonar.Therefore,it is necessary to make advanced study in high speed floating-point signal processing technologies in order to provide suggestions on future design of broadband imaging sonar.After a review on technological development of narrow band imaging sonar,signal processing researches on broadband imaging sonar and traditional floating-point processing,this dissertation conducts academic research on multi-channel floating-point pulse compression,distributed floating-point fractional time-delay filtering and multi-channel floating-point beamforming on the background of broadband imaging sonar applications.Combined with matched filtering method,comparisons are made between single channel time-domain and frequency-domain pulse compression processed by DSP and FPGA respectively.Designs of frequency-domain multi-channel pulse compression always take more resources and require complicated controllers,therefore,are hardly to achieve.To solve these problems,a signal processing structure based on SOPC is raised.A multi-channel floating-point pulse compression system which can be flexibly configured and tailored is designed according to this structure.The major performances and critical parameters of the multi-channel floating-point pulse compression system are discussed and measured under different working configurations.To fulfill time-delay beamforming in higher precision,combined with fractional time-delay filter theory,coefficient designing algorithms adapted to FPGA are discussed and compared.Traditional Farrow fractional time-delay filter is analyzed,due to the problems in complexity and difficulty in improvement,a distributed floating-point time-delay filter based on distributed algorithm is raised.The key performance such as computational precision,dynamic range and resource usages under different configurations in time and space optimization are analyzed.To achieve high speed floating-point beamforming computation,defects of traditional floating-point multipliers and accumulators are studied.Several critical arithmetic units such as fast-shifting-tree,floating-point compressor and distributed floating-point accumulator are raised.Several kinds of multi-channel floating-point beamformers are designed,bind to distributed floating-point time-delay filer,key performance of the floating-point fractional time-delay beamformers are tested.Direct sector address generating and data buffering algorithms are discussed so that the digital signal processing structure of broadband imaging sonar is optimized and the speed is improved.Combined with floating-point multi-channel pulse compression system,distributed floating-point time-delay filter and multi-channel floating-point beamformer,a floating-point signal processing system of broadband imaging sonar is designed.Working principle and key performance are verified and measured by hardware tests and underwater experiments.