Spin scanning direction finding and cross positioning method based on single unmanned aerial vehicle platform

Abstract

The invention discloses a spin scanning direction finding and cross positioning method based on a single unmanned aerial vehicle platform, and relates to a radio positioning technology. The method comprises the following steps: controlling an unmanned aerial vehicle carrying a directional antenna to hover at a first measurement point and spin around an axis, and synchronously acquiring received signal strength (RSSI) and a yaw angle; obtaining a first azimuth angle of the radiation source by detecting an RSSI peak value; then the unmanned aerial vehicle flies to a second measurement point to repeat the process to obtain a second azimuth angle; and finally, calculating the coordinates of the radiation source by using a cross positioning principle according to the coordinates and the azimuth angles of the measurement points. According to the invention, the antenna mechanical scanning is realized by using the spinning of the unmanned aerial vehicle, the single-station multi-point direction finding and positioning are realized by using extremely simple hardware (single antenna), and the method has the advantages of low cost, fast deployment and easy integration, and is suitable for fast searching and positioning of a ground fixed radiation source.

Description

Technical Field

[0001] This invention relates to the field of radio positioning and UAV application technology, specifically to a method for using a single UAV to drive a directional antenna to scan via spin motion, thereby achieving single-station multi-point direction finding and cross-locating radiation source targets. Background Technology

[0002] In tasks such as spectrum management, emergency search and rescue (locating emergency beacons), and tracing the source of illegal radio signals, rapid and accurate location of unknown radiation sources is crucial. Traditional mainstream technologies include multi-station time difference of arrival / frequency difference positioning and single-station array direction finding positioning. The former requires the deployment of receiving stations in multiple locations, resulting in a complex system, high cost, and slow deployment; the latter, although single-station, typically relies on expensive multi-antenna arrays and complex digital beamforming processing equipment, whose size, power consumption, and cost are unsuitable for miniaturized, low-cost UAV platforms. As a highly mobile aerial platform, unmanned aerial vehicles (UAVs) provide an ideal vehicle for flexible and rapid radiation source localization. However, most existing UAV-based localization schemes still rely on multiple physical antennas or require signals with cooperative characteristics (such as known modulation formats). Therefore, there is an urgent need for a lightweight radiation source localization method with extremely simple hardware configuration, suitable for small single UAV platforms. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a spin-scanning direction finding and cross-positioning method based on a single UAV platform. This method utilizes only a conventional directional antenna and the UAV's own rotation capability to achieve accurate direction finding through mechanical scanning, and then combines this with the UAV's positional movement for geometric intersection positioning, thus achieving reliable positioning with a minimal hardware configuration. To achieve the above objectives, the present invention adopts the following technical solution: a spin-scanning direction finding and cross-positioning method based on a single UAV platform, executed by a UAV platform equipped with a directional antenna, an RF signal acquisition unit, a navigation and attitude measurement unit, and a main control and processing unit, comprising the following steps: First, the UAV is controlled to fly to a first measurement point and hover. Then, the UAV is controlled to spin around its vertical axis (yaw axis) at a constant angular velocity. This motion drives the directional antenna to perform a mechanical scan in the horizontal plane. During this process, Received Signal Strength Indicator (RSSI) data from the RF signal acquisition unit and real-time yaw angle data from the navigation and attitude measurement unit are simultaneously and at high speed acquired. Next, based on the data acquired within one or more complete spin cycles, the correspondence between RSSI and yaw angle is analyzed, and the peak point of RSSI is detected. The real-time yaw angle corresponding to this peak point indicates that the antenna's main lobe maximum gain direction is aligned with the radiation source at this time, thereby obtaining the first azimuth angle measurement value of the radiation source at the first measurement point. Then, the UAV is controlled to fly to at least one second measurement point, and the above spin scanning and peak detection steps are repeated to obtain the second azimuth angle measurement value. Finally, based on the precise geographic coordinates of each measurement point and the corresponding azimuth measurement values, the estimated geographic coordinates of the radiation source are calculated using the direction finding cross-positioning geometry principle. Preferably, the horizontal 3dB beamwidth of the directional antenna is between 20 and 40 degrees, and more preferably 30 degrees. This beamwidth provides good azimuth resolution while ensuring sufficient signal acquisition probability and scanning efficiency. Preferably, during the direction finding process, the RSSI data is smoothed and filtered to suppress noise, and a peak detection algorithm is used to accurately determine the yaw angle corresponding to the peak value. Preferably, in the positioning solution step, the least squares estimation algorithm is used to handle the situation where multiple azimuth lines do not intersect at the same point due to the direction finding error. The optimal solution is obtained by minimizing the sum of squares of the vertical distances from the target estimated point to all azimuth lines, thereby improving the positioning robustness. Preferably, when selecting measurement points, the azimuth lines of the radiation source measured by the UAV at the two measurement points should be intentionally made to have a large angle of intersection, close to 90 degrees, in order to optimize the geometrical precision factor (GDOP) and thus obtain higher positioning accuracy. Preferably, the UAV is controlled to spin at a constant angular velocity of 3 degrees / second to 12 degrees / second. This speed range can achieve a balance between ensuring sufficient data acquisition and avoiding significant dynamic errors caused by excessive rotation. The present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, is used to control an unmanned aerial vehicle platform to implement the above-described method. Beneficial effects Compared with the prior art, the present invention has the following significant advantages: The hardware configuration is extremely simple, and the cost is significantly reduced: the core direction finding function relies only on a single ordinary directional antenna and the basic motion capability of the drone, completely eliminating the need for expensive and complex multi-antenna arrays and digital beamforming systems, which greatly reduces the hardware cost, weight and power consumption of the system. The principle is clear and intuitive, and it is easy to implement in engineering: the controllable spin of the UAV is converted into the mechanical scanning of the antenna, and the direction finding is performed by detecting the peak signal strength. The principle is simple and clear, the related data processing algorithm has low complexity, and it is easy to implement and integrate on embedded systems. Fully leverage the mobility of a single platform: The traditional multi-station direction finding task is cleverly transformed into a serialized direction finding task of a single mobile platform at different locations and times. The flexibility and mobility of UAVs solve the contradiction that a single station cannot directly locate, and achieve rapid deployment and response. The positioning accuracy is practical and reliable: By selecting an antenna with a suitable beamwidth, high-precision position / attitude measurement, and a reasonable geometric layout of measurement points, this method can stably achieve meter-level positioning accuracy, which fully meets the accuracy requirements of actual scenarios such as emergency search and investigation of illegal signals. Attached Figure Description Figure 1 This is a top view schematic diagram illustrating the basic principle of the method of the present invention. Figure 2 This is a typical waveform diagram showing the variation of Received Signal Strength (RSSI) with the yaw angle of a UAV during spin scanning. Figure 3 This is a schematic diagram of the geometric relationship for cross-location based on two measurement points. Figure 4 This is a flowchart illustrating the overall implementation of the method of the present invention. To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. See Figure 1 This illustrates the basic principle of the method of the present invention. The radiation source T to be located is located on the ground. A UAV equipped with a directional antenna first flies to position P1 and hovers. The UAV begins to spin around its vertical axis, and the antenna beam (shown as a fan shape) rotates accordingly. The received signal is strongest when the main axis of the beam is aligned with the radiation source T. By measuring the nose direction (yaw angle ψ1) of the UAV at this peak moment, the azimuth line L1 pointing from point P1 to the radiation source T can be obtained. Subsequently, the UAV moves to position P2 and repeats the spin scanning process to obtain a second azimuth line L2. The intersection of L1 and L2 is the estimated position of the radiation source T. See Figure 2The simulation curve shows the variation of the received signal strength RSSI with the yaw angle ψ during one uniform spin of a UAV at a measurement point. The curve exhibits a clear single-peak characteristic. The peak point can be determined by using a peak detection algorithm (finding local maxima), and the corresponding yaw angle ψ_peak is the azimuth angle θ of the radiation source measured at that measurement point (θ = ψ_peak). See Figure 3 This section describes the mathematical model for the positioning calculation. Let the coordinates of measurement point P1 be (x1, y1), and the measured azimuth angle of the radiation source be θ1 (measured clockwise with true north as the reference); let the coordinates of measurement point P2 be (x2, y2), and the measured azimuth angle be θ2. The equations of the two azimuth lines can be expressed as: cot(θ1) * (x - x1) - (y - y1) = 0, cot(θ2) * (x - x2) - (y - y2) = 0. Theoretically, solving this system of equations yields the target coordinates (x, y). In practice, due to the existence of direction-finding errors, the two lines may not intersect. In this case, a least-squares cost function can be constructed, and the solution that minimizes the sum of the squared distances from the target point (x_t, y_t) to the two lines can be found as the optimal estimate. See Figure 4This document demonstrates the complete implementation process of the method of this invention, with the following specific steps: Step 1: Task initialization and planning. Determine the frequency band to be searched and plan at least two direction finding hovering points P1, P2, …, Pn. During planning, try to make the two consecutive measurement points form a favorable triangular geometric configuration with the estimated target area. Step 2: Fly to the first measurement point and hover. Control the UAV to fly autonomously or under control to the first planned point P1 and enter a stable hovering state. Step 3: Perform spin scan and data acquisition. Control the UAV to start spinning around the axis at a preset constant angular velocity (6° / second). At the same time, the main control and processing unit synchronously acquire RSSI data streams from the RF front end and yaw angle data streams from the integrated navigation system. Step 4: Single-point azimuth angle calculation. After completing at least one full rotation scan, stop spinning. Filter and smooth the acquired RSSI data, and then execute the peak detection algorithm to determine the precise yaw angle corresponding to the RSSI peak value, denoted as θ1. Multiple rotations of data can be collected and averaged to improve accuracy. Step 5: Move to the next measurement point. Control the drone to fly to the next planned point P2. Step 6: Repeat direction finding. Repeat steps 3 and 4 at point P2 to calculate the azimuth angle θ2. Step 7: Determine if the number of measurement points meets the requirement. If at least two different azimuth angle measurements have been obtained, proceed to the next step; otherwise, return to step 5 to continue to the new measurement point. Step 8: Positioning calculation. Based on the coordinates {(xi, yi)} of all measurement points {Pi} and the corresponding azimuth angle measurements {θi}, use the least squares estimation method to calculate the geographic coordinates (x_t, y_t) of the radiation source. Step 9: Output and visualization. Output the positioning results, including coordinate estimates, possible error ellipse or circular probability error (CEP), and visualize them on the map interface.

Claims

1. A spin-scanning direction finding and cross-positioning method based on a single unmanned aerial vehicle (UAV) platform, characterized in that, The process is executed by an unmanned aerial vehicle (UAV) platform equipped with a directional antenna, a radio frequency signal acquisition unit, a navigation and attitude measurement unit, and a main control and processing unit, including the following steps: S1: Control the UAV to fly to the first measurement point and hover; S2: Control the UAV to spin around its vertical axis at a constant angular velocity, driving its onboard directional antenna to perform a horizontal mechanical scan, and simultaneously acquire Received Signal Strength Indicator (RSSI) data and the UAV's real-time yaw angle data; S3: Based on the correspondence between RSSI data and yaw angle data acquired within one or more spin cycles, detect the peak value of RSSI and record the real-time yaw angle corresponding to the peak value as the first azimuth angle measurement value of the radiation source at the first measurement point; S4: Control the UAV to fly to at least one second measurement point, repeat steps S2-S3, and obtain the second azimuth angle measurement value of the radiation source at the second measurement point; S5: Based on the geographical coordinates of the first measurement point and at least one second measurement point, and the corresponding first and second azimuth angle measurement values, calculate the estimated geographical coordinates of the radiation source based on the principle of direction finding cross-positioning.

2. The method according to claim 1, characterized in that, In step S3, the RSSI data is processed by smoothing filter, and the yaw angle corresponding to the peak is determined by peak detection of the RSSI-yaw angle curve, or by peak moment detection of the RSSI curve changing over time and matching it with the synchronously recorded yaw angle timestamp.

3. The method according to claim 1, characterized in that, In step S5, the solution uses the least squares estimation method to minimize the sum of squares of the vertical distances from the radiation source coordinate estimation point to each azimuth line determined by the coordinates of the measurement point and the azimuth measurement value.

4. The method according to claim 1, characterized in that, In steps S1 and S4, the selection of the first measurement point and the second measurement point is such that the included angle between the azimuth lines measured by the two is close to 90 degrees.

5. The method according to claim 1, characterized in that, The directional antenna on the UAV has a horizontal 3dB beamwidth of 20 to 40 degrees.

6. The method according to claim 5, characterized in that, The horizontal 3dB beamwidth of the directional antenna is 30 degrees.

7. The method according to claim 1, characterized in that, In step S2, the UAV is controlled to spin at a constant angular velocity of 3 degrees / second to 12 degrees / second.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by the processor, the program is used to control the unmanned aerial vehicle platform to implement the method as described in any one of claims 1 to 7.

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