A Study Of Multipath Channel Equalization Method Of Ionized Stratum

With the application and development of various new weapons in modern warfare, the radar which is limited by the earth curvature cannot satisfies the need of the detection of long-distance and super low altitude target, so all kinds of OTHRs become one of the important detection equipment all over the world. In addition, considering the characteristic of large-scale, long-distance detection, multi-target detection, stealth detection and super low altitude target detection etc. the OTHR which take advantage of electromagnetic wave being reflected by ionized stratum have already became the research focus in many countries.However, considering the high-frequency sky-wave OTHR utilizing the theory of backward refraction to detect the long-distance target, which adopts high-frequency electromagnetic wave and uses ionospheric medium as signal path, its performance will be influenced by external active jamming and passive jamming which introduced by non-stationary ionospheric medium and low-detection etc. In addition, electromagnetic wave multipath effect which caused by ionospheric medium channel will have a bad effect on the detection accuracy of radar. So there are important practical significance and practical value to improve the performance of radar detection by investigating multipath channel equalization method of sky-wave OTHR and eliminating or declining the signal contamination which caused by multipath effect.In this thesis, the influence caused by multipath effect during the application of high-frequency sky-wave OTHR on the performance of radar detection is studied. Initially, the influence caused by multipath effect on radar echo(distance, the Doppler frequency shift and Doppler broadening) is studied by analyzing the basic characteristic of ionized stratum or utilizing the propagation mode and the propagation characteristics of ionospheric propagation. After that, in order to restrain or decline the effect on radar echo caused by multipath effect, the channel estimation and equalization method which use channel convolution to cancel the interference is proposed. A multipath channel estimation method based on the training sequence and a channel equalization method using minimum mean square error criterion is used. The signal model of channel estimation and channel equalization is constructed for simulating the performance andeffect during the channel estimation and the channel equalization. Considering the higher sidelobe of the output signal after the channel equalization, the method of increasing mismatch filter is used to restrain the sidelobe and the weighted iterative least squares algorithm is used to tackle the parameters of mismatch filter, at the same time, the response and effect of the output signal is simulated after adding the mismatch filter during the channel equalization. Furthermore, a method of increasing the length of equalization filter to restrain the sidelobe is proposed and it is compared with the simulated result of the method utilizing mismatch filter. Considering the possible error during the multipath channel estimation, channel equalization and mismatch filter, the influence on the output signal in different parts such as the changes of channel equalization parameter, the changes of mismatch filter and the read error of multipath channel is simulated. So the proposed channel equalization can have an efficient effect on the practical project. Finally, the conclusion of this article and the direction of further research is put forward.In this thesis, the proposed method of multipath channel equalization can have a positive effect on declining the signal contamination of radar caused by multipath effect, it can also improve the performance of target detection of sky-wave OTHR and enhance the radar performance.