面向OFDM系统的高精度窄带干扰抑制算法

A frequency-domain NBI suppression algorithm for OFDM systems with high precision and minimum spectrum leakage is proposed to solve the problem that the spectrum leakage of narrowband interference (NBI) seriously affects the bit error rate (BER) of orthogonal frequency division multiplexing (OFDM) systems. Firstly, the quantitative relationship between the fractional factor of the NBI frequency and the spectrum leakage is derived using the fast Fourier transform (FFT). It is concluded that the NBI spectrum leakage energy is less than 0.01% of the total energy when the fractional factor is less than 0.005. Secondly, interference alignment is achieved by multiplying the received signal by the frequency shift matrix in time domain and the interference suppression is achieved by zeroing the aligned interference signal in frequency domain. It is proved that the residual NBI spectrum leakage is only related to the estimation error of the fractional factor but independent of the fractional factor. Finally, a high-precision fractional factor estimation is obtained based on the range of rough positioning of interference frequency by FFT and on refining of the range using Chirp-Z transform. A high-precision fractional factor estimation with an estimated error less than 0.005 and uniform distribution is obtained. Simulation results show that the BER performance improvement of the proposed algorithm for OFDM systems is similar to that of the notch filter interference suppression algorithm. When the fractional factor is 0.5 and the BER is 10^-4, the signal to noise ratio (SNR) of the proposed algorithm, the notch filter interference suppression algorithm and the table-lookup interference suppression algorithm are 4.5, 4.5 and 6 dB, respectively.