组合chirp信号在水下声基站定位信号冲突避免中的应用研究

Application of combined chirp signal in collision avoidance of underwater acoustic station positioning signals

在水下声基站定位中,各基站发出的定位信号由于多途效应等因素影响,容易在用户终端产生信号碰撞接入现象,由此引发的信号丢失或接入阻塞是影响声基站定位应用的制约因素.通过信号结构设计减轻冲突影响是声基站定位研究的主要途径.经典的信号结构主要是以sine和cosine为载波的定位信号,但不适用于水声信道.因此提出通过合理设计组合斜率线性调频(chirp)信号,并将其作为各声基站的定位信号以提高基站定位系统的抗冲突、抗碰撞能力.为提高组合斜率chirp信号在声基站定位信号冲突碰撞应用中的检测效率,提出了一种基于混频变斜率分数阶傅里叶变换的快速检测方法.该方法能将组合斜率信号变斜率为对称三角波,并通过快速分数傅里叶变换实现基于斜率检测的多用户分离,从而提高解算的效率.理论推导和仿真实验均表明,利用该方法能较好地检测出声基站定位信号,估算定位时延差,降低多址干扰,提高定位信号检测性能.

In underwater acoustic base station positioning,the positioning signal sent by each base station is affected by multi-path effect and so on,so it is easy to generate signal collision access phenomenon in the user terminal.The resulting signal loss or access blocking is a limiting factor in the application of acoustic base station positioning.Through signal structure design to reduce the impact of conflict is the main way of the acoustic base station positioning.Classical signal structure is mainly sine and cosine as a carrier of positioning signals.However,the dual dispersion characteristics of the underwater acoustic channel will lead to the selective fading of the signal in time and frequency domain,which will affect the stability of the single frequency carrier spread spectrum signal.Therefore,sine and cosine as the carrier of positioning signal does not apply to the underwater acoustic channel.In this paper,through the rational design of combined slope of the linear frequency modulation（chirp）signal,and as a positioning signal of each base station to improve anti-collision ability of location system.In order to improve the detection efficiency of chirp signal in the application of signal collision in acoustic base station,this paper proposes a rapid detection method based on Fractional Fourier Transform of mixed variable slope.This method can change the slope of the combined slope signal to symmetric triangular wave signal,so that a fixed detection slope can be configured for each base station positioning signal,and through the fast fractional fourier transform for multi-user separation based on slope detection,so as to improve the efficiency of the solution.The theoretical derivation and simulation experiments show that this method can better detect the positioning signal of the acoustic base station,estimate the location time delay difference,reduce the multiple access interference,and improve the performance of positioning signal detection.