Research Of Adaptive Filtering Algorithm And Application In VoIP System

With the development of technology,people's demand on the requirement for the quality of communication services is increasing,among that including noise elimination.As the most popular noise cancellation module,the adaptive filtering theory was first proposed by Widrow and Hoff in 1960.It has been widely used in many fields such as communication,radar,vehicle system,medicine and so on.In recent years,due to the rise of virtual operators,all kinds of Vo IP software emerge in an endless stream,has broken the limit of original operators.People's views on various types of VoIP software is mixed,the voice quality of communication has became an important standard for people to choose a VoIP software.Therefore,a good ability to eliminate noise is an important test for VoIP software.The present LMS algorithm has the contradiction between convergence speed and steady-state error.When the step-size factor is too large,so the convergence speed is fast,but the error is larger.When the step factor is too small,the convergence rate will be slow,but the error is stable.To solve this problem,this paper proposes a variable step-size LMS algorithm based on DCT.The algorithm combines the advantages of the variable step-size algorithm based on Lorentzian function,realizes the change of step-size in the algorithm by introducing the Lorentzian function,establishes a nonlinear function relationship between step-size and error,makes the step factor dynamic change.At the same time incorporate the idea of domain transform,through the DCT to achieve further improvement of convergence speed,making full use of the decorrelation ability of DCT and the fast convergence ability of Lorentzian function.The completed contents of this paper are as follows:(1)This paper studies the principle and general framework of adaptive filtering technology.Analyze and simulate the fixed step LMS algorithm and variable step-size LMS algorithm,then by comparing the performance of the algorithms,can obtain the advantages and disadvantages of the algorithms.(2)Through the study of discrete cosine transform to further understand the principle of transform domain LMS algorithm.By comparing the discrete cosine transform and discrete Fourier transform,can analyze the advantages of the two transforms.(3)Through integrating the idea of variable step-size LMS algorithm with the idea of transform domain LMS algorithm,can get a new variable step-size LMS algorithm based on DCT by combining the advantages of the two ideas.Simulate and analyze the proposed algorithm,and test the superiority by the experiment of the actual speech signal.(4)This paper designs a kind of VoIP software based on iOS,and analyzes how to achieve the software.Through applying the new algorithm to the VoIP software so that can add noise cancellation module to improve the quality of voice service,and then test the system.