Parameter Estimation Of LPI Radar Signal Based On FRFT

The low probability of intercept technology is a widespread use radar technology currently.LPI radars make reconnaissance receivers difficult to detect and identify the signal parametersthrough low power transmitter, large time and bandwidth product signals and complex signalmodulation means. Therefore, most of the traditional estimation methods are poor or even failureto the LPI radar signal processing. In this paper, on the basis of the analysis of the relationshipbetween LPI radar low interception performance and the target and radar characteristics, thespeed and range resolution and low interception features of four LPI radar signals are researchedfrom the time-frequency domain and fuzzy domain. A time and frequency analysis tool ofFractional Fourier Transform is introduced to analysis LPI radar signals. A signal parameterestimation algorithm based on FRFT of the LPI radar signal is In-depth studied and improved theproblem of computational complexity is too large in practical applications. The main work ofthis paper is as follows:1. The LPI radar is defined by low probability of intercept factor. The relationship betweenradar characteristics and intercept factor is detailed analysis and several achieving means of LPIradar is proposed. The radar signal waveform design is one of the important means to improveradar LPI characteristics, so this paper focuses on two conventional LPI radar signals and twocomposites modulation LPI radar signals, which are Linear FM signal, Polyphase Codes signaland Symmetrical triangular linear frequency modulation signal, Pseudo-random binary codingand linear frequency modulation signal. Simulation results verify the LPI performance of twocomposite modulation signals.2. A time-frequency analysis tool of Fractional Fourier Transform is studied. Threecommonly used definitions are given for its different application, and then a discrete fractionalFourier transform calculation method is proposed, which is widely used in digital signalprocessing. It is simple and intuitive and has a considerable amount of computation with FFT.LFM signal parameter estimation principle based on FRFT is studied and its detectionperformance is analyzed theoretically. In order to avoid the FRFT complex two-dimensionalsearch, an improved new algorithm based on the WVD slice and FRFT for LFM signalparameter estimation is proposed. The simulation results verify the effectiveness and efficiencyof the algorithm.3. To reduce the high complexity of two-dimensional search of FRFT estimation STLFMsignal parameters and different signal estimation algorithms have different adaptability to thesignal-to-noise ratio. Two different algorithms are proposed in high signal-to-noise ratio and lowsignal-to-noise ratio conditions. The signal is detected and chirp rate is estimated using the RATtransform in low signal-to-noise ratio. RAT only one-dimensional search in angle and reduce theamount of computation with fast algorithm. A new STLFM signal parameter estimationalgorithm based on the AF the slice is proposed in high signal-to-noise ratio. The algorithm candetect signal and estimate signal FM slope by only calculating a fuzzy function slice. Afterobtaining signal chirp rate estimation under different SNR condition, the FRFT optimal transform order is determined. Finally, the initial frequency, FM cycle and FM bandwidth ofSTLFM signal is estimated through twice FRFT. Simulation results show the effectiveness of thealgorithm.4. The PRBC-LFM signal FRFT expression is derived and the symmetry and monotonicityof the FRFT transform of Infinite and time limit LFM signal are analyzed. The FRFT modefunction of a symbol signal in the PRBC-LFM signal is symmetrical with peak point and is amonotonic function of the FRFT order. An initial rough and then fine search program is proposedtake advantage of this feature, greatly improving the searching efficiency. The parameters ofPRBC-LFM signal is estimated through the relation between the peaks’ distance and theparameters of the frequency modulation signal. Finally, the linear frequency modulation signalcan be reconstructed and multiplied with the conjugated signal in every code to remove thecarrier wave. The coding rule of the biphase coded signal can be identified through division thesign of the signal’s amplitude. Simulation results show that the algorithm in this paper canestimate the parameters of the PRBC-LFM signal effectively at low SNR.