A method for concealing GPS device detection and localization

Abstract

The application discloses a detection and positioning method of hidden GPS equipment based on radio frequency information leakage. The GPS equipment generates specific electromagnetic radiation spectrum when receiving and processing satellite positioning signals, which can be regarded as the physical unclonable function of the equipment, independent of the use state of the equipment, and reflects the unique hardware characteristics of the equipment. In the embodiment, a wide-spectrum wireless signal catcher is constructed by using USRPX310 and a near-field probe to capture the electromagnetic radiation spectrum generated by the hidden GPS equipment and perform signal analysis. If a suspected GPS equipment is found, the system transmits an analog satellite positioning signal through the USRPX310 to induce the GPS equipment to generate stronger electromagnetic radiation to confirm the existence of the GPS equipment and enhance the detection distance. Finally, the user positions the hidden GPS equipment by moving the near-field probe.

Description

Technical Field

[0001] This invention mainly relates to the field of detection and positioning of hidden GPS devices. Based on the weak radio frequency information leakage when GPS devices are working, its radio frequency characteristics are analyzed, and GPS track recording devices hidden in hard-to-detect locations such as user vehicles, backpacks, and suitcases are detected and located. Background Technology

[0002] Currently, the commercial market lacks fully functional GPS device detectors. Most rely on placing the object to be detected (e.g., a vehicle) in an electromagnetically shielded room to observe whether a suspected GPS device is transmitting signals to a remote server. This signal transmission is primarily based on mobile cellular communication protocols such as 4G and 5G, exhibiting distinctive frequency characteristics. The detector only needs to detect whether a device within the shielded room is actively transmitting cellular signals to capture and locate a suspected GPS recording device. However, the construction cost of shielded rooms is high, thus limiting their application scenarios. Furthermore, GPS recording devices may have long periods of silence, during which they only record GPS location information without actively transmitting cellular signals to report data. Therefore, the object to be tested needs to remain stationary within the shielded room for an extended period to achieve good detection results. Summary of the Invention

[0003] This invention proposes a method for detecting and locating hidden GPS devices based on the leakage of radio frequency information from GPS devices. The implementation scheme involves using a USRP X310 and a near-field probe to build a broad-spectrum wireless signal capture device. During detection, the user holds the probe and scans the surrounding electromagnetic environment. The low-noise electromagnetic signal processed by the USRP X310 is transmitted to a laptop for further signal analysis. The system searches for the electromagnetic radiation spectrum generated by the GPS radio frequency circuitry when processing satellite-transmitted positioning signals, thereby determining whether a GPS device is suspected. To further enhance the detection range and confirm the presence of a GPS device, after identifying a suspected GPS device, the invention continues to use the USRP X310 to construct and transmit a simulated satellite positioning signal. This induces the GPS device's radio frequency circuitry to acquire a higher-amplitude "positioning signal," thereby generating stronger electromagnetic radiation, facilitating the confirmation and detection of hidden GPS devices. When using the system, the user only needs to hold the probe and scan the object under test. When the system detects a hidden GPS device within a 0.5m radius, an alarm sound will be emitted. When the user moves the probe closer to the concealed GPS device, the system will issue a more urgent alert and increase the volume. At this point, the user can carefully inspect the small area.

[0004] The detection approach of the GPS device in this invention is as follows:

[0005] (1) The hardware circuitry of a GPS device mainly includes an RF receiving circuit, a baseband signal processing circuit, a geographic location calculation circuit, and a cellular communication circuit. The RF receiving circuit is a crucial source of electromagnetic radiation signals. This circuit receives a 1575.42MHz satellite positioning signal via a GNSS antenna. After signal amplification, a mixer circuit reduces the frequency to an intermediate frequency of approximately 4MHz. In this process, the RF circuit uses a crystal oscillator as the clock signal reference source for the mixer; the crystal oscillator frequency is typically 26MHz or 13MHz. The oscillation circuit with the crystal oscillator undergoes near-field coupling with the intermediate frequency signal, generating electromagnetic radiation.

[0006] (2) By using the USRP X310 to construct a broad-spectrum electromagnetic signal capture device, electromagnetic radiation from radio frequency circuits can be captured to determine whether a suspected GPS device exists. In order to further confirm the detection results and enhance the detection range, this invention transmits a fake GPS signal with a strong amplitude through the USRP X310 to inject into the radio frequency circuit of the GPS device, thereby inducing an increase in the electromagnetic radiation intensity of the radio frequency circuit.

[0007] (3) The user continuously searches for the possible location of the GPS device by moving the USRP X310 receiving probe. This invention is based on the electromagnetic radiation of the GPS device's radio frequency circuit to complete the detection task. Since GPS positioning signals have a standard protocol process and fixed frequency information, and the selection of crystal oscillators in commercial radio frequency circuits is relatively consistent (26M or 13M are the mainstream choices), the electromagnetic radiation of different GPS devices in the radio frequency circuit tends to be uniform. The detection system of this invention does not need to analyze the electromagnetic radiation characteristics of a specific GPS device, and can realize black box detection of GPS devices.

[0008] Technical solution

[0009] Preliminary judgment stage:

[0010] Step 1. After the device is powered on, use the built-in radio frequency signal receiver of the USRP X310 to connect to the near-field probe to collect GPS signals from the surrounding environment;

[0011] Step 2. Perform Fourier transform, noise reduction and smoothing on the received GPS signal, and then perform spectrum analysis to find and mark peak points in the spectrum graph;

[0012] Step 3. Check whether the frequency point corresponding to the peak value conforms to the known spectral characteristics generated by the near-field coupling between the GPS receiver module crystal oscillator and the intermediate frequency signal;

[0013] Step 4. Match the calculated frequency points with the preset electromagnetic radiation signal frequency feature library. If a certain number of consistent frequency points are found, it is preliminarily confirmed that a GPS device has been detected.

[0014] Confirmation phase:

[0015] Step 5. By injecting simulated GPS signals into the existing electromagnetic environment, the detected GPS devices are further confirmed, and the GPS devices that react are located and their status is detected.

[0016] Furthermore, in the above technical solution, we use an RF signal receiving device to collect RF signals in the environment to be tested. The operating frequency band of this device covers the range of 10-80 MHz.

[0017] Furthermore, the collected radio frequency signals are processed as follows: First, a Fast Fourier Transform (FFT) is performed to generate the original spectrum, then smoothing is performed to generate a denoised spectrum, and finally it is determined whether there are any GPS signal spectrum characteristics in the spectrum.

[0018] Furthermore, the collected radio frequency signals can be processed directly using Python.

[0019] Furthermore, our GPS signal spectrum feature library is a universal feature library because the electromagnetic radiation characteristics of different GPS devices in their radio frequency circuits tend to be uniform.

[0020] Furthermore, if the detected signal spectral characteristics are consistent with those in the GPS signal spectral characteristic database, or the deviation is within ±5%, we consider the two to be consistent.

[0021] This invention also provides a GPS detection system based on electromagnetic signals, comprising:

[0022] A signal receiving device used to collect radio frequency signals in the environment, with an operating frequency band covering 10-80 MHz;

[0023] The signal analysis module is used to perform fast Fourier transform on the signal collected by the signal receiving device to obtain the original spectrum of the radio frequency signal, and then perform noise reduction and smoothing processing to determine whether there are preset electromagnetic signal spectrum features in the spectrum.

[0024] The feature matching module is used to compare the spectral features obtained by the signal analysis module with a pre-built GPS signal spectral feature library.

[0025] The signal injection module is used to inject specific signals into the environment to verify the response of the GPS device or trigger its specific behavior;

[0026] The advantages of this invention are:

[0027] Highly efficient and accurate: This invention can accurately identify and recognize GPS devices through a two-stage judgment process (pre-judgment stage and confirmation stage). Simultaneously, by utilizing the peak values ​​at specific frequency points and the mapping relationship between the probe and the distance to the GPS device, the hidden location of the GPS device can be precisely pinpointed.

[0028] Versatility: Our feature library is built around the common features of most GPS devices, thus enabling it to identify the majority of GPS devices on the market. Furthermore, if a new GPS device is discovered, our system can be updated accordingly to stay synchronized with the latest technologies. Attached Figure Description

[0029] Figure 1 This is a structural block diagram of the hidden GPS device detection and positioning method of the present invention.

[0030] Figure 2 Schematic diagram of GPS device operation

[0031] Figure 3 This is the original spectrum diagram of the electromagnetic radiation signal collected from the GPS device.

[0032] Figure 4 The spectrum diagram of the electromagnetic radiation signal from the collected GPS device after denoising.

[0033] Figure 5 This is a schematic diagram of peak detection on the denoised spectral data. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings.

[0035] like Figure 1 As shown, the system mainly consists of a signal receiving module, a signal processing module, a feature library matching module, and an analog signal injection module.

[0036] Preliminary judgment stage:

[0037] Step 1: The signal receiving module begins operation. First, the user powers on the USRP X310 device. The device's built-in RF signal receiver connects to the near-field probe, and the signal receiving module then begins operation. This module continuously collects electromagnetic signals in the 10-80MHz range and transmits them to a host computer running signal analysis software.

[0038] Step 2: The collected signals are processed by the signal processing module. This module first performs a Fast Fourier Transform (FFT) on the signal to generate the original spectrum, then performs denoising and smoothing to obtain a clean spectrum, and finds and marks peak points in the spectrum.

[0039] Step 3: The system determines whether the signal might be a GPS signal by judging whether the peak point matches the known spectral characteristics generated by the near-field coupling between the GPS receiver module crystal oscillator and the intermediate frequency signal. For example... Figure 2 As shown, the frequency of the crystal oscillator in a GPS device is generally 26MHz or 13MHz, and the intermediate frequency signal is generally around 4MHz. Therefore, we need to determine whether the frequency f(electromagnetic) corresponding to the existing peak satisfies f(electromagnetic) = k · f(crystal oscillator) ± l · f(intermediate frequency), k ∈ N+, l ∈ N. If this condition is met, the system will enter the confirmation phase; if not, the user can continue to move the probe to scan other areas.

[0040] Confirmation phase:

[0041] Step 4: The feature matching module matches the frequency points calculated in Step 3 with a preset electromagnetic radiation signal frequency feature library. If a certain number of matching frequency points are found, it is preliminarily confirmed that a GPS device has been detected.

[0042] Step 5: The analog signal injection module generates an analog GPS signal and injects it into the existing electromagnetic environment. If the peak value change of a specific frequency point detected exceeds the set empirical threshold α, the presence of a GPS device in the environment is finally confirmed.

[0043] Step 6: Once the user confirms the presence of a GPS device in the environment, they can locate and pinpoint its location by moving the near-field probe. At this point, the higher the peak value of a specific frequency detected, the louder the alarm will be; the user can infer the device's location based on the alarm's intensity.

[0044] The hidden GPS device detection and positioning method of this invention possesses two major advantages: high efficiency and accuracy, and versatility. Through two judgment steps—a pre-judgment stage and a confirmation stage—the system can accurately identify and recognize GPS devices. Utilizing the mapping relationship between peak values ​​at specific frequencies and the distance between the probe and the GPS device, the system can precisely pinpoint the location of hidden GPS devices. Furthermore, our constructed electromagnetic radiation signal frequency feature library is based on characteristics shared by most GPS devices, thus enabling the identification of most GPS devices on the market. When new GPS devices emerge, our system can also be updated accordingly, keeping pace with the latest technology. This efficient and versatile method undoubtedly greatly improves the detection and positioning capabilities of GPS devices, providing a new solution to prevent the misuse of GPS devices.

Claims

1. A method for detecting and locating hidden GPS devices Step 1: Power on the USRP X310 device and use the built-in RF signal receiver to connect to the near-field probe to collect GPS signals from the surrounding environment; Step 2: Perform Fourier transform, denoising, and smoothing on the received GPS signal, then perform spectrum analysis to find and mark peak points in the spectrum. Step 3: Detect whether the frequency point corresponding to the peak value conforms to the known spectral characteristics generated by the near-field coupling between the GPS receiver module crystal oscillator and the intermediate frequency signal; Step 4: Match the calculated frequency points with the preset GPS signal frequency feature library. If a certain number of consistent frequency points are found, it is preliminarily confirmed that a GPS device has been detected. Step 5: Use simulated GPS signals to inject into the existing electromagnetic environment to further confirm the detection of GPS devices, and locate and detect the status of the GPS devices that produce a response.

2. The method for detecting and locating hidden GPS devices according to claim 1, characterized in that, Step 1: Collect electromagnetic signals generated by the GPS device in operation using a radio frequency signal receiver. The operating frequency band of the radio frequency signal receiver should cover 10-80 MHz.

3. The method for detecting and locating hidden GPS devices according to claim 1, characterized in that, Step 2 involves performing a Fast Fourier Transform (FFT) on the acquired GPS signal to generate the original spectrum, followed by smoothing to generate a denoised spectrum, and finally determining whether there are specific frequency peaks in the spectrum.

4. The method for detecting and locating hidden GPS devices according to claim 1, characterized in that, Step 3 judge the existing peak corresponding to the frequency point f 电磁 whether f 电磁 = k · f 晶振 ± l · f 中频 , where f 电磁 is the frequency of the collected electromagnetic signal, f 晶振 is the crystal frequency of the GPS receiver module, f 中频 is the intermediate frequency reference signal frequency of the GPS receiver module, and k and l are positive integers and natural numbers, respectively.

5. The method for detecting and locating hidden GPS devices according to claim 1, characterized in that, The GPS signal frequency feature library mentioned in step 4 is a general feature database because the electromagnetic radiation of different GPS devices in their radio frequency circuits tends to be uniform.

6. The method for detecting and locating hidden GPS devices according to claim 1, characterized in that, If the calculated peak frequency is equal to the frequency in the GPS signal frequency feature library, or if the deviation is within ±5%, then we consider the two frequencies to be consistent.

7. The method for detecting and locating hidden GPS devices according to claim 1, characterized in that, The simulated GPS signal generation module can simulate the signals of various GPS devices in terms of frequency and inject them into the original electromagnetic environment. An empirical threshold α is set. If the peak value change of a detected specific frequency point exceeds the threshold α, the presence of a GPS device in the environment is finally confirmed. In addition, we found that the closer to the GPS device, the higher the peak value of a specific frequency point. Based on this finding, we set up an alarm. The higher the detected peak value, the louder the alarm sound. Users can find and lock the location of the GPS device by moving the near-field probe according to the loudness of the alarm sound.

8. A concealed GPS device detection and positioning system, characterized in that, include: The signal receiving module is used to collect radio frequency signals in the environment, and its operating frequency band needs to cover 10-80 MHz; The signal processing module performs a Fast Fourier Transform (FFT) on the signal acquired by the signal receiving module to obtain the original electromagnetic signal spectrum. It then performs smoothing processing, marks the peaks in the spectrum, and determines whether a signal conforming to f(x) exists. 电磁 = k · f 晶振 ± l · f 中频 The frequency points, where f 电磁 It is the frequency of the acquired electromagnetic signal, f. 晶振 It is the crystal oscillator frequency of the GPS receiver module, f 中频 This is the intermediate frequency reference signal frequency of the GPS receiver module, where k and l are positive integers and natural numbers, respectively. The feature matching module is used to compare specific frequency points obtained by the signal processing module with a pre-built radio frequency signal feature library of GPS devices. The analog signal injection module is used to generate analog GPS signals and inject them into the existing electromagnetic environment. If the peak value change of a specific frequency point detected exceeds the set empirical threshold α, the presence of a GPS device in the environment is finally confirmed. The alarm module allows users to locate and pinpoint the GPS device's position by moving the near-field probe after confirming the presence of a GPS device in the environment. The higher the peak value of a specific frequency point detected, the louder the alarm sound. Users can locate and pinpoint the GPS device's position by moving the near-field probe based on the alarm sound level.

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