Research On Underwater Ranging And Localization Based On Least Square Method In Multipath Enviroment

In the ocean there is amount of treasure,so many countries spare no efforts for the development of marine resources in recent years.Driven by demand,more attention is paid to the study of underwater positioning.With the underwater acoustic communication being the only long dis tance wireless communication means,underwater positioning based on underwater acoustic communication becomes one hot spot of academic research.Underwater acoustic channel has the several transmission characteristics,such as environmental noise,transmi ssion loss and multiple paths effect,etc.As the sea water is a kind of heterogeneous medium,the signal that first arrives or has the strongest amplitude is often not the useful one.All these problems bring obstacles for underwater positioning,positioning in the complex water environments becomes a problem to be solved in underwater acoustic communication.This research uses the measurement of acoustic signal transmission time between sender and receiving terminal to estimate the distance between two points.But due to that the seawater is not uniform and mixed with a lot of impurities and granular objects,the spread of sound waves in a shallow sea will occur all kinds of scattering and reflection,affected by the surface and bottom of the sea at the same time.So that the received signal is a collection of emission signal transmitted by multiple paths.The traditional positioning method use signal transmission time of the first arrived signal or amplitude of the strongest signal to estimate the location of the object.However,due to the speed of sound wave transmission,underwater is influenced by factors such as pressure,temperature and salinity,which causes the speed of sound waves along a curve is faster than the speed of sound waves along the stra ight line,the sound waves along a curve are likely to be earlier than sound waves along a straight line to reach the receiver.In addition,the phenomenon of surface wave focusing makes sound waves signal amplitude after surface reflection stronger than t he amplitude of the direct path.So,distance estimation using traditional methods has some errors.In this research,the underwater ranging and positioning error sources are analyzed based on full analysis of the domestic and foreign literature.In terms of distance measurement,this research considers the multiple paths interference with time delay.In this paper,a cost factor is added for each cost function in the least squares method,which is used to estimate the direct path transmission delay.After get the time delay,the distance estimation is completed using primitive array and the least squares curve fitting method.In terms of positioning,this paper improves least-square method using Newton iteration,in which position is estimated using the least squares estimate of the position as the initial value of Newton iteration.Finally,in terms of distance measuring and positioning precision of simulation,the simulation results show that the optimization of the least squares method compared with the traditional positioning method is improved on the precision,even in complex underwater environment.