# An Anti-Interference Method Based on Energy Residual Searching in GNSS Positioning Applications
## 1 Introduction  
With the increasing number of applications utilizing global navigation satellite systems (GNSS), demand for reliable navigation and timing has significantly increased, encompassing critical fields such as transportation, energy systems, telecommunications, and emergency response. Previously, GNSS were predominantly employed for static geodetic measurements. However, their functionality has evolved to include dynamic measurements across various domains, such as land, marine (hydrographic), and aerial navigation. This transition highlights the expanding role of GNSS in meeting the diverse demands of modern navigation and positioning needs. The GNSS signals used in most satellite navigation systems [1] are typically designed with a direct-sequence spread spectrum (DSSS) scheme, which provides inherent resistance to electromagnetic interference. However, due to the significant distance between navigation satellites and receivers, the received GNSS signal strength is usually very weak by the time it reaches Earth. This low signal strength makes GNSS signals highly susceptible to interference from complex electromagnetic environments [1; 2; 3], as illustrated in Figure 1, especially around power facilities. Sources of such interference include, but are not limited to, power line harmonics, switching electromagnetic interference, and electromagnetic radiation from the power equipment itself. These interference sources can degrade GNSS signal quality, potentially causing errors in positioning and timing calculations, which, in turn, can impact the safety and reliability of power systems. Therefore, the development and the application of effective anti-interference algorithms to enhance GNSS signal reception andprocessing in power scenarios are crucial for ensuring the safe operation of power facilities and improving the management efficiency of energy systems. Among the various types of interference, linear frequency modulation (LFM) interference [3; 4; 5] is a common and typical form of broadband non-stationary interference widely employed to disrupt navigation signals. Compared to other types of interference, LFM interference has several notable characteristics [4]: firstly, the equipment required to generate this type of interference is relatively simple and low-cost, making it a frequently used method of interference; secondly, the frequency of LFM interference varies linearly with time, endowing it with powerful interference capabilities, which makes it difficult for conventional GNSS receivers to detect and suppress. This threat is particularly pronounced in power-related environments, where the electromagnetic conditions are complex and variable, exacerbating the impact of LFM interference on GNSS signals. It should be noted that while this study primarily focuses on anti-LFM interference in power environments, the proposed anti-interference method is versatile and can be applied beyond power scenarios. Countermeasures against LFM interference include techniques such as adaptive notch filtering [6; 7; 8; 9], time-frequency analysis [10], and array antenna methods [11; 12]. Time-frequency analysis, in particular, is widely applied, due to its ability to process signals simultaneously in the time and frequency domains, capturing the non-stationary characteristics of the interference signal. Compared with other methods, time-frequency analysis provides more detailed information on the interference, aiding in the precise localization and identification of interfering signals. Commonly used time-frequency analysis techniques include short-time Fourier transform (STFT), wavelet transform, and the Wigner-Ville distribution, all of which have been extensively employed for detecting and mitigating LFM interference. However, traditional time-frequency analysis techniques also have certain limitations. STFT, for example, cannot simultaneously achieve high time and frequency resolution, due to its fixed window size.