The Research On Time Delay Estimation Of Multi-channel Spread Spectrum Signal And DSP Implementation

The transponder is an important unit in the underwater acoustic positioning system.In this paper,the delay estimation algorithm of multi-channel spread-spectrum signals and DSP implementation in the transponder are mainly studied.In response to the requirements of multiple transponders working simultaneously and the characteristics of the underwater acoustic channel,a spread-spectrum signal is selected as the query response signal,and a multi-channel spread-spectrum signal detection requirement is designed.A step-wise correlation algorithm is designed and its calculation result is based on FFT.The fast correlation algorithm is equivalent,and has the advantages of small calculation amount and small storage space overhead.The paper first analyzes the characteristics of the required pseudo-random sequence according to the design requirements of the query response signal.The simulation compares the above-mentioned required sequence set size,non-periodic cross-correlation and non-periodic auto-correlation properties of each order sequence.The method of symbol phase optimization and sequence set optimization is adopted to further reduce the maximum edge value of the auto-correlation function and the maximum value of the cross-correlation function.Secondly,the spectrum and correlation performance of the spread spectrum signal under different signal parameters are simulated and analyzed.The effects of noise,multipath,multiple access interference,and Doppler on the correlation of spread spectrum signals in underwater acoustic channels under different signal parameters are compared and analyzed.Then it introduces the principle of direct correlation method and fast correlation algorithm based on FFT,and analyzes the theoretical calculation amount and storage resources required by the algorithm.Based on the binary structure of BPSK-modulated spread-spectrum signals,a step-wise correlation algorithm for equivalent direct correlation output envelope is derived.When detecting multi-channel underwater acoustic spread-spectrum signals,the storage space is greatly saved,and the amount of calculation is reduced.The structure is simpler and smaller,suitable for parallel operation of the device,and has the advantages of convenient Doppler compensation.Then,the algorithm implementation and optimization ideas of step-related algorithms on the DSP platform are designed.Aiming at the architecture of the DSP,focusing on optimizing the data storage and accumulation of the symbol values of the expansion steps,the algorithm implementation efficiency is improved.Finally,the decision thresholds such as the amplitude,peak point and width of the correlation peaks,as well as the specific implementation method of delay estimation are discussed.Finally,the algorithm is implemented by DSP system,and the hardware platform and system software are designed.Finally,the system power consumption,data acquisition function,step-related algorithms and response functions were tested and verified in a laboratory environment.The verification results show that the system can use step-wise correlation algorithms to achieve the functions of detection,delay estimation and response of spread spectrum signals.