A Novel Amplitude Spectrum Formation Algorithm for FRFT-TDCS

For the problems of the traditional Transform Domain Communication System (TDCS) dealing with Multi-component Linear Frequency Modulation (MLFM) interference signals, we propose a novel amplitude spectrum formation algorithm for FRFT-TDCS (Transform Domain Communication System based on Fractional Fourier Transform) in this paper. The algorithm can achieve the maximum available bandwidth through an optimal transform order selection scheme. We firstly analyze the spectrum distribution characteristics of LFM interference signals with different transform orders in the FRFT domain, and quantify their energy bandspread and center position. Then the spectrum magnitude vector would be generated through the preset threshold, and the optimal transform order which can maximize the number of available spectrum subcarrier is chosen. We then derive the relationship between the system BER and autocorrelation function of the basis function through the CSK demodulation model. It proves that the system BER can be reduced by increasing the number of available spectrum subcarrier. Simulation results show that when dealing with MLFM interference signals, the proposed algorithm can find the optimal transform order, decrease the peak and mean value of the basis function, improve the system LPI and LPD performance, and reduce the system BER effectively.