Interference Avoidance Using Fractional Fourier Transform in Transform Domain Communication System

The method of fractional Fourier transform (FRFT) is introduced to transform domain communication system (TDCS) for signal transforming in the paper after theoretical analysis. The method yields optimal basis function (BF) by FRFT with optimal transform angle. The TDCS using the proposed method has wider usable spectrum, stronger robustness and better ability of anti non-stationary jamming than using usual methods, such as Fourier Transform (FT), auto regressive (AR), wavelet transform (WT), etc. The main simulation results are given as follows. First, the bit error rate (BER) P_b is close to theoretical bound of no jamming no matter in single tone or in linear chirp interference. Second, the interference-to-signal ratio (J/E) is at least 12 dB more than that of direct spread spectrum system (DSSS) under the same BER if the spectrum hopping-to-signal ratio is 1:20 in chirp plus hopping interfering. Third, the E_b/N_O (when estimation difference is 90% between transmitter and receiver) is about 3.5 dB or about 0.5 dB (when estimation difference is 10% between transmitter and receiver) more than that of theoretical result when no estimation difference under P_b =10².