Abstract
High-frequency surface wave radar (HF SWR) plays an important role in marine stereoscopic monitoring system. Nevertheless, the congestion of external radio frequency interference (RFI) in HF band degrades its performance seriously. In this article, two novel fractional Fourier transform (FRFT)-based RFI suppression approaches are proposed. One is based on the orthogonal projection of sequences from fractional Fourier domain, and the other is based on singular value decomposition (SVD) of Hankel matrix of sequences from fractional inverse-Fourier domain. Simulation and experimental data collected by HF SWR from Wuhan University were used to test the effectiveness as well as the application condition of the proposed RFI suppression algorithms. The FRFT-based orthogonal projection algorithm is practicable for suppressing stationary RFI with unvaried carrier frequency, while the FRFT-based SVD algorithm is applicable equally for mitigating nonstationary RFI with time-varying carrier frequency or occasional duration time. The processing results may provide useful guidelines for interference suppression of HF SWR, and inspiring the further application of the FRFT-based methods for signal processing.
Highlights
High-frequency surface wave radar (HF SWR) has the advantage of real-time monitoring over the horizon, and is widely applied for oceanographic parameters extraction [1,2,3] and the detection of surface vessels and low-altitude flying targets [4]
External radio frequency interference (RFI) was converted into a bunch of strips across all range bins; the interference mainly existed in −0.83 Hz, −0.43 Hz, −0.03 Hz, 0.36 Hz, and 0.76
Some conclusions are as follows: External RFI can be recognized as the combination of a finite number of single-frequency components
Summary
High-frequency surface wave radar (HF SWR) has the advantage of real-time monitoring over the horizon, and is widely applied for oceanographic parameters (such as current vectors, wind direction, and wave field) extraction [1,2,3] and the detection of surface vessels and low-altitude flying targets [4]. External RFI is composed of natural disturbances such as lighting strikes and human-induced interferences. Due to the disappearing of D layer and the joining of F1-F2 layer in the ionosphere during nighttime, human-induced RFI utilizing sky wave propagation, such as short-wave communication and broadcasting signal, shows an obvious increase in HF band [5,6]. External RFI is composed of a finite number of single-frequency signals, and can be divided into stationary and nonstationary [13]. The carrier frequency of External RFI is composed of a finite number of single-frequency signals, and can be divided into stationary RFI was unaltered or limited to a narrow bandwidth that was negligible. “stationary” and “nonstationary” refer to the carrier frequency of variation nonstationary varied obviously between adjacent sweep periods
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