The Application Of Fractional Fourier Transform In Underwater Acoustic Location System

Underwater acoustic location systems have been focused more and more with the development of the underwater acoustic system. How to achieve location technology has been an important flied. This paper makes use of hyperboloid intersection algorithm to calculate the position of target, whatever linear and nonlinear we both need to acquire the distance between target and transducer arrays.This paper makes sure the distance by making use of fractional Fourier transform to acquire time delay. Fractional Fourier transform is an effective tansform manner to analyse linear frequency modulation signals. It can make the energy of linear frequency modulation signal gather. Making use of energy gathered, linear frequency modulation signal can be detected by fractional Fourier transform. The time measurement manner can be changed into frequency measurement manner by employing the only corresponding relation between the number of lacked points in time domain and the peak position in u-domain of a linear frequency modulation signal. The precision of this means is according to the corresponding relation between the peak position in u-domain and lacking points in time domain when the peak shifts first. To decrease the error and improve time measurement precision we need design the waveforms of transmitted signal by extending bandwidth and truncating a few points of transmitted signal. Truncated signal makes the peak position shift first susceptible. The performance of a single signal transformed by FRFT is excellent than matched filter.There are doppler frequency shift and multi-path in underwater acoustic environment, which have a great effect on frequency measurement manner. We make use of Notch filter which can follow up the cetren frequcy of single frequency signals to acauire doppler frequency shift and employ Rake receiver to descrete multi-path effection. Making use of Notch filter, we can compensate frequency shift. Making use of Rake receiver, we can improve SNR of output.Base on Matlab have achieved the simulating of time delay measurement, a single position and target trajectory tracked, we design and achieve digital signal processing software of fractional Fourier transform and time delay measurement on TMS320C6416. We have completed program optimization and the data transmission which is between L2 and SDRAM. We can achive the real-time character of FRFT.