| At present,all countries in the world use spectrum by unified division or auction,which leads to a very low utilization rate of spectrum resources.Cognitive radio technology is the good solution to this difficult problem,cognitive radio system through the perception of wireless power,system loss,interference types and other spectral characteristics,and realtime adjustment of their own parameters,so as to make reasonable use of spectrum resources to improve the purpose of spectrum utilization.VHF wave frequency band is an important frequency band in wireless communication of private network,which shows great difference in spectrum characteristics in the transmission process of radio waves.Meanwhile,available spectrum resources are complex and changeable in electronic countermeasures.In practical application,spectrum characteristics and spectrum cooperative perception are the primary problems to be solved for the efficient transmission of VHF waves.Based on the cognitive radio theory,this paper analyzes the spectrum characteristics of the VHF wave channel and the spectrum perception algorithm in detail.Meanwhile,aiming at the multi-node transmission of VHF wave,a collaborative perception distributed transmission protocol is proposed,and finally a reconfigurable waveform is designed.The main contents are as follows:(1)The research status of VHF wave transmission based on cognitive theory at domestic and overseas is briefly described.The spectral characteristics of the frequency band are studied.The relationship between multi-path delay and spectral characteristics is analyzed by combining the measured channel data.Meanwhile,the system loss of VHF wave frequency band is analyzed and the system loss difference curve is given by an example.This paper studies the spectrum characteristics in the environment of electronic countermeasures and expounds the application of spectrum sensing technology in the communication environment of VHF wave electronic countermeasures.(2)In this paper,the frequency spectrum perception quantization of VHF wave is proposed,and the spectrum characteristics of VHF wave channel are expounded from the dimensions of SNR,bit error rate,packet loss rate and interference type.The measurement relation between the Euclidean distance and SNR in continuous phase modulation,the characteristic of signal error code and the spectral performance of ultrashort wave signal in Gaussian noise and Rayleigh fading channel are proposed.Aiming at the influence of different interference sources on signal transmission to different degrees,the spectrum detection method of interference channel in electronic countermeasures is presented.Simulation and test results show that this method can effectively characterize the spectrum quality of channel in electronic countermeasures and different topography environments,thus providing theoretical basis for the distributed chain construction of ultrashort waves(3)According to the requirements of long distance transmission of VHF wave transmission and channel optimization,this paper propose the single-node spectrum sensing protocol and multi-node cooperative spectrum sensing protocol,which are respectively applied to point-to-point mode and broadcast mode transmission,and the spectrum cooperative sensing protocol of VHF wave channel is given.By using this method,we can find the appropriate guarantee the suitable frequency and the communication distance effectively.(4)According to the VHF wave channel spectrum characteristics and spectrum cooperative perceive agreement,by selecting reasonable modulation and coding method,this paper designed the cognitive system reconfigurable VHF waveform.The anti-interface ability of the free spectrum search and reconfigurable frequency-hopping mode was verified at national key laboratory of science and technology on communication of the UESTC and the results and analysis are given. |
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