# A Novel GNSS Interference Detection Method Based on Smoothed Pseudo-Wigner-Hough Transform
## 7 Discussion  
From the GNSS interference detection results obtained with the Hough transform-based techniques, the proposed smoothed pseudo-Wigner-Hough transform can be successfully used to detect the GNSS sweep interference since it deals with the cross-term problem effectively and shows much-improved energy aggregation property over the pseudo-Wigner-Hough transform and Wigner-Hough transform techniques. In contrast to the traditional Wigner-Hough transform-based technique [23], the GNSS interference detection performance obtained with the smoothed pseudo-Wigner-Hough transform method is at least double that of the Wigner-Hough transform-based technique, according to the zero Hough-transformed energy percentage criteria. In contrast to the pseudo-Wigner-Hough transform-based technique [24], for any JNR value of the GNSS interfering signal, the  
Figure 16: The zero Hough-transformed energy percentage metrics of the Hough transform based GNSS interference detection techniques.  
zero Hough-transformed energy percentage obtained with the smoothed pseudo-Wigner-Hough transform-based GNSS interference detection method is improved at least 20% compared with the pseudo-Wigner-Hough transform-based technique. Therefore, the smoothed pseudo-Wigner-Hough transform method has been proven to be superior to the Wigner-Hough transform and pseudo-Wigner-Hough transform techniques in the detection of sweep interference present in the received GNSS signal.  
Recently, the reassigned smoothed pseudo-Wigner-Ville distribution was combined with the Hough transform to detect GNSS interference [26]; and the rearranged wavelet-Hough transform was proposed to improve interference detection performance for GNSS receivers [16]. The reassignment algorithms implemented in the smoothed pseudo-Wigner-Ville distribution or wavelet transform cost heavy computational resources, which will cause problems in the real-time detection of GNSS interfering signals. These methods are more suitable for the anti-interference design of the FPGA-based GNSS receivers. In this paper, the smoothed pseudo-Wigner-Hough transform has been proposed in the GNSS interference detection with moderate computational complexity; this method presents better real-time performance in interference detection in comparison to the above two techniques, which is recommended for the anti-interference GNSS receiver even implemented on the low-cost software-defined radio platform.  
Due to the fact that Hough transform can be used to detect arbitrary shapes and recognize complex patterns [17; 18], and the nonlinear frequency modulation signal can be described by the high order polynomial function, hence, the nonlinear curve which represents the frequency modulation law for the nonlinear chirp signal can be detected and recognized using the Hough transform. Therefore, the developed Hough transform-based GNSS interference techniques are supposed to be valid and effective at dealing with nonlinear sweep interference present in the received GNSS signal. Although it is really difficult to detect the nonlinear chirp interfering signal, we will try to deal with this challenging problem of detecting nonlinear frequency modulated GNSS interference in our future research works.