Research On Anti-Interception Performa Nce Of Communication System Based On Weighted Fractional Fourier Transform

Fractional Fourier transform (FRFT) is a generation of the ordinary Fourier transform, which can simultaneously supply time and frequency domain information and has received much attention in signal processing field, having widely application prospects. Its definitions contain two types, classical and weighted. This paper sets 4-weighted FRFT as an example, researching anti-interception performance of communication system based on weighted fractional Fourier transform (WFRFT).Firstly, latest progress of WFRFT is summarized, and a feasible expression of discrete WFRFT is given following the structural form of discrete Fourier transform. Accordingly, a data communication system is designed based on WFRFT, the complexity of which only increases a little.Secondly, the characteristics of signals after WFRFT are analyzed. Different weighted coefficients have different phase shifts and the phase shifts would change a lot with the change of transform orders. The constellations of non-purpose receivers would rotate, scatter, fuse and even split when adopting the multi-parameter WFRFT. Different weighted coefficients have different modulus, which could mediate the proportion of time-frequency components. If non-purpose receivers don't utilize inverse transformation correspondingly, the equivalent SNR will has some decrease. These two respects above show anti-interception performance of this system.Finally, to get the quantitative analysis of anti-interception performance, the same modulation scheme classifications are adopted and the classification probabilities are compared between classical and weighted signals. The modulation classification type is high-order cumulants. From the simulation results, if WFRFT is used in classical data communication system, there will have two factors influencing the receiving of non-receivers. One is carrier characteristics. Different transform orders bring about different carrier characteristics. The other is the equivalent SNR decreasing of non-receivers. If non-purpose receivers don't utilize inverse transformation correspondingly and want the same classification performance as classical signals, the additional SNR will be paid out. The SNR cost is about 2~3dB when the transform order is 0.1.