Research On Semi-blind Frequency Selection Technology Of Shor-wave Communication Based On CW Signal

Short-wave communication can achieve over-the-horizon communication of thousands of kilometers with the mechanism of ionospheric reflection of high-frequency(HF)electromagnetic waves,it is the basic means of long-distance communication,mobile communication and emergency communication in important departments such as military,diplomatic,meteorological,and transportation.However,the frequency band of HF communication is very narrow(3-30MHz),resulting in serious self-interference and mutual interference.On the other hand,the dynamic changes of communication channel windows in specific time and region with sunshine,meteorology and weather,leading to the inefficiency of traditional fixed channel division and serious waste of precious spectrum resources.For this reason,this thesis proposes a semi-blind frequency selection scheme combining passive reception with active detection based on cognitive software radio technology.Firstly,a priori frequency set is selected by multi-channel parallel reception technology;on this basis,bidirectional CW detection is carried out,and then the currently available communication channel is selected: On the one hand,it reduces the problems of high frequency occupancy,serious frequency pollution and high energy consumption caused by blind detection;On the other hand,it solves the problem of low frequency availability of passive receiving frequency selection,aiming at realizing dynamic tracking of HF skywave transmission channel and improving the access capability of HF communication channel.The main work is as follows:1.Passive frequency selection technology based on multi-channel parallel receiving technology.The short-wave broadband spectrum is divided into 3 kHz multi-channel,then the narrowband signals of each channel are processed by FFT processing for passive sensing interference energy.The energy threshold is set by the percentile method to determine the prior frequency set.The results of frequency selection with different thresholds are analyzed to verify the feasibility of the passive frequency selection algorithm.2.Bidirectional active channel detection technology based on CW signal.Aiming at the problem that the current CW telegraph signal recognition algorithm has poor detection and recognition performance under the background of high code rate and strong noise,an automatic recognition algorithm of high frequency CW telegraph signal based on Kalman filter is proposed.The simulation and actual communication environment are used to verify that the algorithm can effectively recognize CW telegraph signals under strong noise background.However,this algorithm has poor performance for non-stationary colored noise and needs further improvement.3.A short-wave semi-blind frequency selective system based on CW signal is designed.The system is tested in Chongqing University of Posts and Telecommunications,Shizhu County and Qijiang County,and the results of frequency selection are processed and analyzed,which verifies the feasibility and real-time of the scheme.However,for some time periods with complex propagation characteristics(between 21 and 22,and between 2 and 5),the performance is relatively poor.It is necessary to explore a new efficient communication technology and design and improve the frequency selection scheme.