Research On Accurate Parameter Estimation Methods For Complex Underwater Acoustic Channel

Spread spectrum communication is the commonly used communication system in the underwater acoustic communication system.The underwater channel parameter estimation technology based on direct spread spectrum sequence is the key point to realize high precision positioning and low bit error rate in underwater communication receiver system.However,compared with terrestrial radio channel,underwater acoustic channel is more complex.Especially in shallow water channel,a large number of multi-path interference become the key factor to affect the estimation accuracy of parameters in underwater acoustic channel.In addition,in multi-user quasi-synchronization CDMA communication systems,the signals of different users arrive at the receiver at almost the same time.With the limitation of the code length,it is difficult to achieve good orthogonality between users by correlation,thus forming multi-user interference at the receiver.Therefore,it is helpful to improve the performance of underwater positioning and communication receiver by studying how to estimate the channel parameters accurately,especially the channel parameters of direct path in these complex channel scenarios.At present,the widely used underwater receiver algorithm is the matching filter method.For multipath channels,the delay resolution of the matching filter algorithm is limited by the Rayleigh limit.The commonly used time-domain super-resolution MUSIC algorithm cannot estimate the amplitude of the multi-path and cannot calculate the channel parameters within a single shot.In this paper,the idea of decorrelation algorithm and the covariance matrix correction method are introduced into the frequency-domain MUSIC algorithm,and a single shot high-precision channel parameter estimation algorithm with the amplitude estimation capability is investigated.The disadvantage that the ordinary time-domain MUSIC algorithm cannot calculate the parameters in a single shot is effectively overcome.At the same time,the amplitude estimation method combined with the frequency-domain super-resolution time delay estimation algorithm is also presented.Other subspace algorithms,such as the ESPRIT and the Min-Norm algorithms,are also studied in this paper.The performance of the proposed method is verified by simulation and pool experiments.For the quasi-synchronization CDMA system,the receiver receives the transmitted signals of multiple users almost synchronously.If the matching filter algorithm is used toprocess each user's signal individually,the multi-user interference is treated as noise.The processing gain of single user is greatly reduced,and it is difficult to achieve high precision parameter estimation performance.However,the theoretically optimal algorithm(ML)and the suboptimal approximate maximum likelihood algorithm(AML)are too complicated to be applied due to the computational complexity.In this paper,the DEMA algorithm based on parallel interference cancellation is studied.The high precision parameter estimation of multi-user channel is realized while the computational complexity is considered,and its performance is verified by simulation and pool experiments.Finally,this paper makes a comparison of various receiver algorithms in complex underwater acoustic channels,gives the applicable range of the algorithm and the channel parameter estimation performance in the actual underwater channel,and evaluates its computational complexity and robustness.