Blind Detection And Blind Parameter Estimation Of High Frequency FH Signals Based On Array Signal Processing

Wireless communication is one of the most important measures in modern warfare. Especially in command of the moving object, it is even the only means of communication. But this kind of open emission and reception system in High frequency(HF) communication has to face two challenges: firstly, natural interference from atmospherics and industry; secondly, tracing, blocking and multipath interference from enemy. For HF communications, improving its performance and enhancing its anti-interference capabilities have become an important topic of innovation and development, and frequency-hopping(FH) communications technology will be timely. Because of its high anti-jamming capability, low intercept probability and secrecy, etc., Frequency Hopping (FH) communication has been widely used in military field and become one of the most effective measures to improve the anti-jamming capability.To meet the need of communication reconnaissance and countermeasures, FH signal detection and parameter estimation, as the base of signal separation, interference, monitoring and deceiving, has become the focus of the research. Therefore, it is useful to research the topic of FH signal blind detection and blind parameter estimation. And it is very difficult, this is because: 1) The environment of high frequency communication with fixed frequency signal, noise, interference and many kinds of burst signal make it difficult to detect FH signal; 2) Because carrier frequency of FH signal hops in pseudorandom form, it is more difficult to FH signal detection and parameter estimatimation than fixed frequency signals; 3) If the baseband signal is voice modulated by Single Side-Band (SSB), the discontinuity of voice will lead to the similar discontinuity of the received energy, which will increase the difficulty of analysis, etc.In this thesis, we focus on the problem of shortwave FH signal blind detection and blind parameter estimation based on array signal processing. That is, without enough apriori information, estimating the number of FH signals and their parameters, including dwell-time, hop-rate, hop-time, direction of arriving(DOA) , frequency-set and hop-bandwidth by making the most of time-domain, frequency-domain and spatial-domain information.The main job and contribution of this paper are as follows:Based on narrowband signal processing, we propose a new method for FH signal blind detection and blind parameter estimation. Firstly, compute the cross-correlation function(CCF) of FH signals from multichannels, then we get the cross power spectral density matrix(CSDM); Secondly, select the hops of FH signals from the CSDM via processing and analyzing the CSDM, meanwhile reduce the influence coming from noise, fixed frequency signal and other interferences; Lastly, estimating the DOA of every hop and according to the DOA, we can separate the hops, get the number of FH signals and their parameters. Propose a new method for designing the threshold in FH signal detection. This method makes it easy to get the threshold by theoretic computing and it can extremely reduce the interference of non-FH signals.Based on broadband signal processing, we propose a new method for FH signal blind detection and blind parameter estimation. Firstly, get the DOA of the signals by wideband spatial spectrum estimation; secondly, separate the signals by spatial filtering using wideband beamformer; Lastly, we propose two methods for FH signal blind detection and blind parameter estimation, one is for several constant hop-rate FH signals whose dwell-time are different and another is for a single FH signal whose hop-rate is alterable.By employing spatial interpolation in broadband signal beamforming, it can reduce the number of antenna elements and corresponding RF modules, A/D converters, etc. It can also eliminate the mutual coupling between antenna elements while getting the narrower main beamwidth and lower sidelobe level.Design and realization of the high-frequency reconnoitering system bringing together broadband signal searching, broadband signal direction finding, frequency-hopping signal searching, narrowband signal direction finding, and narrowband signal analysis,etc. The system has been put to use and the field test shows that the presented system outperforms traditional high-frequency reconnoitering receiver.The technical routes and methods proposed in the thesis are not only theoretically meaningful but also are great valuable in HF communication coutermeasures. Some of the methods have been applied to a HF reconnoitering system and the result of the field is fairly well.