An Adaptive Eigen-Subspace Filtering Method for Interference Suppression in Wuhan Ionospheric Oblique Backscatter Sounding System

Wuhan ionospheric oblique backscatter sounding system (WIOBSS) is a low-power instrument for monitoring and researching the ionosphere. Unfortunately, as operate in the high-frequency (HF) band, its performance suffers from a lot of unwanted interferences, which can result in low signal-to-interference and noise ratios (SINRs) and low ionogram quality. In this letter, an analysis of the range-domain correlation of radio frequency interference (RFI) in WIOBSS is presented. Based on this, a novel eigen-subspace-based filtering approach for ionospheric oblique backscatter sounding is proposed. It slides the range domain sequence into the submatrix to construct the subspace and uses an improved source number estimation approach to divide the subspace according to the mode criterion. Then, the range bins with signals are projected into the eigen subspace to suppress RFI. Experimental results show that this method is still effective under limited snapshot conditions. It can improve the SINR by about 25 dB at some typical frequencies. Furthermore, the proposed method is more robust than the typical methods, while the SINR fluctuates violently.