A multi-tone interference equivalence method for analyzing the impact of LFM interference on the BER of communications data link system
The Direct Spread Communications Data Link System (CDLS) bears strong Linear Frequency Modulation (LFM) interference from collocated radars, which makes it necessary to analyze the influence of the LFM interference on the performance of CDLS. LFM interference has both the characteristics of an instantaneously single-tone and cumulatively multi-tone signals. For this reason, the derivation of an analytic Bit Error Rates (BER) formulation is difficult. This paper presents a BER model that can transform calculation of the BER under LFM interference into the BER under equivalent multi-tone interference, and then derive the equivalence factor between the two. We conduct simulations to analyze the impact of the single-tone and multi-tone as well as LFM interference on the BER of CDLS. Then, we verify the equivalence relationship between LFM interference and multi-tone interference with different center frequencies and FM modulation coefficients. The simulation results show that the equivalence error is less than 2.5% when the BER is higher than 10−3, which is the typical case of CDLS. The LFM interference equivalence BER calculation method proposed in this paper can quantify the equivalence coefficient, and accurately reflect the influence of LFM interference on the BER of CDLS, which contributes to the research of effective analysis of the interference mechanism of CDLS.