Research On Key Techniques Of Signal Analysis For Narrowband Non-cooperative Communication

As one of the important research fields of modern communication systems,noncooperative signal processing involves many communication systems and has many application requirements.For example,in the field of wireless spectrum resource management,government departments will detect civilian communication systems to prevent the illegal use of limited spectrum resources and wireless interference.And in the field of military electronic countermeasures,non-cooperative signal processing is used in enemy intelligence information interception and communication electronic countermeasures etc.Based on the background and requirements of the project,this study focuses on the key technologies of narrow-band non-cooperative communication signal analysis.According to the information recovery process of the communication system,the research content was divided into three parts: non-cooperative signal feature extraction,noncooperative signal demodulation,and non-cooperative signal frame structure and channel coding recognition.Firstly,in the key features extraction of non-cooperative signals such as time and frequency characteristics and modulation characteristics,a comparison and analysis of commonly used non-cooperative signal time-frequency analysis methods is given.Then summarized existing modulation parameter identification techniques,and performed simulation analysis and comparison.At the same time,based on the existing modulation parameter identification methods,the shortcomings of low signal-to-noise ratio shortterm burst signal recognition performance are improved,and further combined with simulation analysis,a feasible method for common digital signal modulation types classification process scheme is given.Secondly,according to the demodulation process of non-cooperative signals,gave research on theoretical and technical methods of signal detection synchronization,carrier synchronization,and symbol synchronization.Considered short-term burst noncooperative signal demodulation,in terms of signal detection synchronization technology,this paper proposes a burst signal detection synchronization algorithm based on median filtering which has a better performance under low signal-to-noise ratio conditions,in terms of carrier synchronization technology,simulated and compared different frequency offset estimation algorithms.And based on the comparative analysis of simulations,in view of disadvantages of limited estimation range of these frequency offset estimation algorithms,an improved method of large range of estimated frequency interval division and precision estimation of inter-cell frequency offset is carried out for achieving carrier synchronization in the case of large frequency offsets.Then combined with the existing symbol synchronization technologies,the demodulation process framework of the shortterm burst non-cooperative signal is given and implemented by simulation,and completed the demodulation recovery of the short-term burst non-cooperative signal.Finally,for the problem of frame structure analysis and channel coding identification of non-cooperative signals,the technical principles and methods of frame synchronization and block codes,convolutional codes,scrambling codes,and interleaving identification are classified and summarized.Then,the frame synchronization of symbol data recovered from non cooperative demodulation of short-time burst signals is considered,through using symbol difference compound cyclic autocorrelation and accumulated frame filtering method,realized the recover data frame synchronization which have phase ambiguity.In terms of channel coding identification,the recognition principle of the existing recognition algorithm is given for the recognition of the mainstream deleted convolutional code,and then improved it.The improved deletion convolution code recognition algorithm has a lower recognition signal-to-noise threshold and a higher correct recognition rate than before the improvement.