Modeling And Equalization For Communication Channel Under Complex Electromagnetic Environment

With the rapid development of digital wireless communications, people’s requirement on the communication quality becomes higher and higher. A wireless communication environment has the characteristics of strong randomness and variability, the entire communication system is not only subject to the propagation path loss, but also affected by the shadow fading caused by various obstacles and the multipath fading caused by reflection and scattering, if there has a relative movement in the communication, the system will be affected by Doppler shift. Establish the correct channel model from the actual situation is the basic of the research of communication system and the key of the performance of communication system, it is an important research topic in digital communication.In the process of signal transmission, inter-symbol interference caused by multipath propagation severely reduces the quality of communication, how to eliminate or reduce the inter-symbol interference has been a matter of concern. Blind equalization technique has become a hot research topic in modern equalization technique, because it greatly improving the efficiency of communication by using only the information of the received signal in the channel equalization.In this paper, we researched channel modeling and equalization technique under the electromagnetic environment and finished the work as follows:(1) Introduce the basics of the communication channel and analyze the effects of large-scale fading and small-scale fading on signal transmission, after this, we research the typical channel model and establish the communication channel model by Jakes model which based on the theory of the sum of sine, at last,we verify the model by Matlab simulation.(2) Introduce the basic principles and related guidelines of blind equalization algorithm and analyze several common algorithms of Bussgang blind equalization algorithms, after this, we do some detailed research on constant modulus algorithm and analyze the influence of the parameters like step、noise and channel to constant modulus algorithm.(3) Discuss and analyze the shortcomings of constant modulus algorithm exist now, in order to solve the problems of constant modulus algorithm, for example, it cannot correct the phase deflection, the convergence speed is too slow and the steady-state error after convergence is too large, we modify the constant modulus algorithm through new cost function、 variable step-size and dual-mode algorithms,make the algorithm performance has been improved to some extent, at last, we propose a new dual-mode variable step constant modulus algorithm based on variable segment error function, this algorithm has faster convergence speed and smaller state residual error than traditional constant modulus algorithm.