# A Novel GNSS Interference Detection Method Based on Smoothed Pseudo-Wigner-Hough Transform
## 1 Introduction  
Complex electromagnetic environments affect satellite navigation applications. Although Global Navigation Satellite Systems (GNSS) are designed with a level of immunity from signal interference through the adoption of the direct-sequence spread spectrum (DSSS) scheme in signal design, the power of the received GNSS signal at the receiver antenna is very low [1]. Hence, unintentional or intentional disturbing signals have the potential to significantly degrade receiver performance [2, 3]. Therefore, the problem of GNSS interference detection has become a major issue for researchers, industry and relevant governmental entities [4]. One of the most serious threats to GNSS receivers is radio frequency interference (RFI). This is because of the ease and simplicity of generating intentionally interfering signals using low-cost jamming devices. These jammers can radiate powerful and disruptive disturbing signals into the GNSS frequencies part of the L-band. The jammers usuallyemit mono- or multi-component nonstationary disturbing signals assumed to exhibit time-varying frequency characteristics. In addition, each GNSS interfering signal component is usually explained by a type of frequency or amplitude modulation. For example, linear frequency modulation (LFM) interference (i.e., linear chirp or sweep interference) is a relatively common and typical broadband nonstationary interference, which has the potential to seriously affect the performance of a GNSS receiver [2; 3]. Moreover, unintentional GNSS interfering signals can result from faulty electronics (i.e., RFI sources co-existing with the GNSS signals), which are typically caused by the nonlinearities in the radio transmitters producing harmonics in the GNSS frequency bands. An example of unintentional interference is a continuous-wave RF signal originating from Digital Video Broadcast Terrestrial (DVB-T) services, which could present a serious threat to GNSS signals [5]. The linear frequency modulation or continuous-wave interference property usually results in a highly localizable power in the time-frequency (TF) plane. Therefore, time-frequency representations (TFRs) can be used in GNSS interference detection techniques [6; 7; 8; 9; 10; 11; 12; 13; 14]. It is known that the spectrogram has the unavoidable time-frequency resolution trade-off problem in accordance with the uncertainty principle, which shows impoverished time-frequency concentration properties [6; 8; 9; 10; 11]. Thus, the Wigner-Ville distribution (WVD) approach can be adopted in interference detection for GNSS receivers to overcome the time-frequency resolution limitation with the spectrogram technique [6; 8; 9; 10; 11]. Although the Wigner-Ville distribution approach can provide a near-optimal time-frequency resolution property among the time-frequency analysis-based techniques, it presents the serious and unacceptable cross interfering term problem resulting from the mutual interaction between different components of the corresponding signal [6; 8; 9; 10; 11]. In order to mitigate this problem, a type of kernel function can be adopted in [PERSON]'s class [15]. For example, the Choi-Williams transform (CWT) has been suggested to attenuate the influence of the cross-interfering term when detecting GNSS interfering signals [8]. In addition, reassignment methods have been proposed for the improvement of the time-frequency localization properties of the time-frequency analyses adopted in GNSS interference detection [9; 10; 16]. From another perspective, Wigner-Ville distribution transforms the analyzed signal into a time-frequency energy distribution in the time-frequency plane, whose shape depends on the frequency modulation law impressed on the analyzed signal [16]. When dealing with the sweep interference present in the received GNSS signal, a time-frequency distribution can be obtained with its energy focused on a straight line in the time-frequency domain by adopting Wigner-Ville distribution.