Research Of Underwater Positioning Signal Generator Based On Chaos

Chaotic signals have excellent properties such as inherent randomness,boundedness and sensitivity to small changes in initial conditions and have been widely used in the field of localization.After the chaotic signal is digitized,it will cause the decline of chaotic characteristics,such as shorter cycle,lower linear complexity and less correlation.At present,there are various ways to solve the problem of diminishing the chaotic characteristics of digital chaotic signals.By analyzing and comparing the advantages and disadvantages of various methods,this paper proposes a method of perturbing chaotic parameters to improve the characteristics of digital chaotic signals.Based on this,design of signal generator is completed.This paper analyzes several methods to solve the problem of diminishing the chaotic characteristics of digital chaotic signals,and then proposes an improved method based on Logistic mapping and chebyshev map to perturb the parameters of the system to improve the characteristics of digital chaotic signals.FPGA devices are used to develop digital circuits,simplifying the design process and implementing signal generators.Direct digital frequency synthesis design is divided into phase accumulator,waveform memory,digital-analog conversion,low-pass filter and other parts to achieve.The DDS output is generally a digital waveform,so the D/A converter and the low-pass filter are also needed to obtain the analog frequency signal.On this basis,the above hardware circuit is improved to reduce the quantization error and suppress the spurious.The effect of generating chaotic signal center frequency is 29.8KHz and amplitude is 8~12v.After the chaotic signal is generated by the hardware design,through analysis of its spectral characteristics,Lyapunov exponents,autocorrelation characteristics,and noise immunity,the signal has good chaotic characteristics and the characteristics of the chaotic signal are experimentally verified.Using the generalized correlation delay method to calculate the time delay difference to obtain the time difference,the sound wave propagation velocity in the water is about 1500m/s,so that the test distance can be obtained.The experiment shows that the positioning error is within 0.3%,which is better than the sequence before the improvement.From the experimental point of view,the chaotic characteristic of the signal is enhanced.