Analysis Of Anti-Interception Performance Of Weighted-Type Fractional Fourier Transform Signal

Weighted-type Fractional Fourier Transform(WFRFT) is a new form of definition, which is different from the Classic Fractional Fourier Transform(CFRFT), appeared later. WFRFT performed very well in optical applications when proposed at the beginning, and recently has been successfully introduced into communication field. In this paper, the anti-interception performance of WFRFT signals in digital comumuniation system is analyzed.Firstly, based on summerizing a variety of WFRFT's definitions and giving the system framework when WFRFT applied to communication system, the characteristics of WFRFT signals are annalyzed. The role of different transformation parameters, signal constellation can show some characteristics, like rotation, aliasing, Gaussian distribution and division. Each parameter can against the scan test of interceptor in certain degree, multi-parameter WFRFT(MP-WFRFT) has strongly anti-scan capability under overall consideration. In the case of unknown transformation parameters, only pay a certain price for signal to noise ratio(SNR), can non-purpose receiver get the same error rate characteristics as purpose receiver. These three aspects all indicate that WFRFT signals have some anti-inerception acpability.Secondly, the higher order cumulants(HOC) are selected as identfication means of this article by comparing a variety of commonly used modulation recognition methods. That is used to analyze single parameter 4-WFRFT(SP-4-WFRFT) signals. Simulation results show that, WFRFT has some impact on signal's HOC, and this kind of impact varies with transform order. Using identification methods based on HOC, which aiming at traditional modulated signals, to recognize WFRFT signal will not work out. These indicate that using WFRFT to process signals will greatly increase the difficulties of non-purpose receiver in detecting and demodulating signals, and reflect that WFRFT signals have rather good anti-inerception performance.Finally, according to the in-depth analysis of simulation data in previous chapter, an idea of hybrid carrier scheme recognition based on HOC is proposed. In the premise of simplifying conditions, the program with three fourth-order cumulants is given to recognize four modulated signals, that after SP-4-WFRFT. Moreover, verify the recognition performance of this program. Simulation results show that under the same conditions, the recognition ability of program varies as modulation type. SNR and transform order are all factors that affect recognition results, we can get higher correct recognition rate with high SNR and low transform order. But the above recognition idea can not be expended to multi-parameter case.