Research On Blind Synchronization Of FSK Signals With Frequency Selective Fading In Short Wave Channel

Shortwave communication is an important way to achieve long-distance data transmission in military communications.Blind synchronization of burst signals in shortwave channels is a difficult technical problem in non-cooperative communication.Based on the standard MIL-STD-188-141 B Appendix A,this paper studies the key technologies in the design of the brust FSK signal blind receiving system in the shortwave fading channel and channel parameter estimation algorithm.Based on the theoretical analysis,this paper designs a synchronization system scheme which has already been tested by matlab simulation and actual data from short wave channel.According to the US military standard MIL-STD-188-141 B Appendix A of the second-generation short-wave communication protocol,this paper studies the key technologies and some channel parameter estimation algorithms in blind synchronization system of burst Frequency Shift Keying signals from frequency selective fading channel.Based on an in-depth understanding of the working principle and data structure of the second-generation automatic link establishment system,a complete synchronization scheme for non-partners was designed and proven in practical applications.This research is of great significance in the field of short-wave non-cooperative communication.The first chapter of this paper briefly introduces the shortwave channel and the research background of the subject.The second chapter of this paper first analyzes the multipath delay and selective fading in short-wave channels,and combines the channel characteristics to perform Watterson modeling.Then the concepts of short burst signal,blind processing and diversity reception are explained.Finally,the related content of signal transmission process and word structure in 2G-ALE protocol are introduced.The traditional correlation peak capture method is not suitable for blind signal processing,so this paper mainly compares and researches the energy-entropy ratio-based and differential correlation-based capture methods proposed in recent years.Based on the study of the principles of two detection methods and the analysis of algorithm characteristics,the author proposes a joint decision detection using data from multiple channels and Discrete Short Time Fourier Transform(DSTFT)in short-wave channels.Utilizing time-frequency characteristics of FSK signals and combining data from multiple channels to jointly extract the diversity gain and achieve blind signal identification.This method can greatly improve the detection performance,thereby improving the initial synchronization performance.In order to eliminate the time difference between diversity signals,multiple signal synchronization is required.Due to the weak anti-fading ability of traditional matching methods and the effect of noise amplification,the author proposes a delay estimation method based on short-wave diversity signals,which can simultaneously estimate the relative time delays between multiple signals and multipath delay of short-wave channels.This method uses partial matching filtering and majority voting,which can effectively improve the anti-fading ability of the algorithm and better adapt to the transmission characteristics of short-wave channels.This chapter also studies the coarse synchronization algorithm of the signal,and proposes a coarse synchronization method based on decoding search.The algorithm takes advantage of the strong correlation between the signals within the coding length.It estimates the signal position through the sliding observation window and decoding.Through simulation verification,when coarse synchronization is performed on the basis of signal presence detection,the algorithm can achieve a balance between complexity and performance,and still maintain good synchronization performance in scenarios requiring high accuracy and low signal-to-noise.Chapter 5 of this paper studies the symbol synchronization and fine synchronization techniques of burst signals.Traditional timing loops have problems such as time extension and high complexity.This paper proposes two blind timing algorithms based on signal frequency domain energy peaks and decoding feedback.The former uses the characteristics of the frequency domain characteristics of the FSK signal to change with the symbol timing position,and does not need to send prior information such as the signal frequency point to achieve symbol synchronization,and the latter performs symbol timing based on the impact of timing errors on the decoding result.Considering that the result of the decoding of coarse synchronization can be directly used for symbol timing,after performance simulation verification,the method based on decoding feedback is finally selected for symbol timing.Sampling-level signal fine synchronization is a difficult point of the synchronization scheme.The author proposed a fine synchronization method based on the energy matrix and error steps,and also made a 2/3 majority voting of improvements.Simulations show that the performance of the improved fine synchronization method has greatly increased..The blind synchronization scheme designed in this paper can adapt to the low signal-to-noise ratio communication conditions of the short-wave channel,and shows good anti-interference and anti-fading characteristics.The algorithm is implemented on the C++ development platform after simulation and verification of actual data.Chapter 6 briefly summarizes the work done,and looks forward to the next research directions.