Design and Simulation of a Linear Adaptive System to Eliminate the Effect of Single-frequency Jammer in Warplane Data Link

In this study a two-stage linear adaptive filtering is designed in order to remove the single-frequency Jammer from the broadband message signal. The result of this suggested approach is a system that despite the Doppler Effect, obtains the unknown interference in inputs automatically and removes it. The design of the adaptive system is based on a version of the interference signal, in which an unknown amount of Doppler shift occurred. The proposed system is implemented based on NLMS two linear adaptive filtering due to the low complexity of NLMS algorithm on the one hand and the possibility of practical implementation on the other hand. Given the parameter µ indicates the step size of the algorithm implementation, is a key factor in signal estimation based on adaptive filter. In the first step, the NLMS algorithm with a large step size and a variable behavior over time is used to initial estimates of the interference signal. Afterwards, the NLMS algorithm with a small step size is used as an approximation of the Wiener filter to correct the reference signal amplitude and the phase shift. The simulation of the proposed interference removal system has been done for the broadband QPSK signal which is mixed with strong interferences. The results have demonstrated that the proposed system has improved the QPSK broadband message signal, which affected by the single-frequency jammer as a strong interference factor, by 60 dB in SJR. Thus, despite a strong interference, the proposed system illustrates significant improvements in signal detection (bit error).