Multipath interference signal identification method for satellite navigation system based on two-dimensional focusing analysis

Abstract

The present invention relates to a method for identifying multipath interference signals in a satellite navigation system based on two-dimensional focusing analysis, and belongs to the field of global navigation satellite system (GNSS) positioning technology. Specifically, it relates to an adaptive identification method for multipath interference signals in a satellite navigation system. First, two-dimensional focusing imaging is performed on the direct wave data; then, the position of the multipath interference is found in the direct wave imaging result, and the angle of the multipath signal source is calculated based on the position where the multipath interference is focused, so as to achieve high-precision identification of the multipath interference signal. This invention solves the problem that multipath signals are difficult to accurately identify in a navigation satellite positioning system, effectively reduces the system ranging error, reduces the amount of computational complexity of the system processing, improves positioning accuracy, and has practical application value.

Description

Technical Field

[0001] The present invention relates to a method for identifying multipath interference signals of a satellite navigation system based on two-dimensional focusing analysis, belongs to the field of global navigation satellite system (GNSS) positioning technology, and specifically relates to an adaptive identification method for multipath interference signals of a satellite navigation system. Background Art

[0002] The Global Navigation Satellite System (GNSS) uses signals transmitted from multiple satellites orbiting the Earth to determine the receiver's position, velocity, and precise time. GNSS positioning requires signals from at least four satellites to determine its coordinates. In open outdoor environments, terminals can receive sufficient satellite signals for high-precision positioning. However, because GNSS signals are electromagnetic, they can be reflected by objects like buildings and mountains in urban and mountainous environments, causing multipath interference and hindering high-precision positioning.

[0003] Signals transmitted by GNSS satellites can be reflected by objects near the antenna before reaching the receiving antenna. When multiple propagation paths occur, multipath interference occurs, seriously affecting the system's positioning accuracy and reliability. Multipath interference is a significant source of error in GNSS positioning. Compared to direct wave signals, multipath signals have a longer path, resulting in a phase lag. Their amplitude also changes during reflection or scattering, reducing the receiver's ranging accuracy.

[0004] There are three common methods for suppressing multipath signals: filtering in the frequency domain, time domain, and spatial domain. Frequency domain filtering achieves this by filtering out certain unnecessary frequency components in the frequency domain. Time domain filtering treats multipath signals as delayed versions of a reference signal and filters out these delayed components based on certain criteria. Spatial domain filtering uses a shaped beam to pass the desired signal or signals in the desired direction while suppressing interference from unwanted directions. Spatial domain filtering requires estimating and calculating the direction of multipath signal interference. However, traditional direction-of-arrival (DOA) estimation algorithms are computationally intensive and suffer from significant multipath signal identification errors, which degrades measurement accuracy. Summary of the Invention

[0005] In view of this, the present invention proposes a satellite navigation system multipath interference signal identification method based on two-dimensional focusing analysis. The method mainly constructs a multipath interference model, uses the direct wave signal for two-dimensional focusing, determines the position of the multipath interference in the imaging image, and then calculates the arrival direction of the multipath interference signal to achieve high-precision identification of the multipath interference signal. First, the direct wave signal is used for two-dimensional focusing to find the response position of the multipath interference signal in the imaging image, and then the angle of the multipath signal arriving at the receiving antenna is calculated according to the position of the interference signal, thereby realizing adaptive identification of the multipath signal.

[0006] The present invention is achieved through the following technical solutions.

[0007] A method for identifying multipath interference signals of a satellite navigation system based on two-dimensional focusing analysis, the method comprising the following steps:

[0008] Step 1: Use a receiving antenna to collect the navigation signal to obtain direct wave data, and record the relative geometric position of the receiving antenna and the ground;

[0009] Step 2: Using the direct wave data collected in step 1 and the recorded relative geometric position of the receiving antenna and the ground, perform two-dimensional focused imaging to obtain a direct wave image;

[0010] Step 3: Identify the multipath signal in the direct wave image obtained in step 2 and record the interference position of the multipath signal;

[0011] Step 4: Calculate the angle at which the multipath signal reaches the receiving antenna based on the interference position of the multipath signal recorded in step 3, and complete the identification of the satellite navigation system multipath interference signal based on two-dimensional focusing analysis.

[0012] In step 1, the time for collecting the navigation signal using the receiving antenna is not less than 600 seconds;

[0013] In step 2, imaging is performed using the BP algorithm. The BP imaging steps are as follows: first, the imaging plane is gridded, then the navigation signal is pulse-compressed in the range direction, and then the distance from the satellite to each grid is calculated to achieve azimuth imaging, thereby obtaining a two-dimensional focused imaging result of the navigation signal;

[0014] In step 3, the direct wave response is extracted, the residual image amplitude is evaluated, and the location of the multipath interference is found;

[0015] In the fourth step, the parameter information of each multipath source is calculated by using the focus position of the multipath interference and the position of the direct wave antenna;

[0016] Assume that the location of a multipath signal interference is (x n ,y n ) is represented by the receiver position (x a ,y a ), and the angle between the antenna and the north direction is θ a , then the angle θ between the multipath signal interference and the true north direction is n Expressed as:

[0017]

[0018] The angle θ at which the multipath interference signal reaches the antenna i for:

[0019] θ i =θ n -θ a

[0020] Similarly, the angles at which other multipath signals in the image reach the receiving antenna can be calculated, thereby achieving high-precision adaptive identification of each multipath signal.

[0021] Beneficial effects

[0022] (1) The method of the present invention solves the problem of difficulty in accurately identifying multipath signals in navigation satellite positioning systems, effectively reduces system ranging errors, reduces the amount of system processing operations, improves positioning accuracy, and has practical application value;

[0023] (2) The present invention discloses a high-precision identification method for multipath interference signals in a satellite navigation system based on two-dimensional focusing analysis. First, two-dimensional focusing imaging is performed on the direct wave data. Then, the location of the multipath interference is found in the direct wave imaging result. Based on the location of the multipath interference focus, the angle of the multipath signal source is calculated to achieve high-precision identification of the multipath interference signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of navigation signal multipath interference configuration. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] Figure 1 This is a schematic diagram of multipath interference of navigation signals in this specific implementation method, specifically: the navigation satellite transmits a signal and is received by the receiver. The direct wave signal is the signal that is directly received, but the satellite signal may be reflected and diffracted by multiple obstacles in the scene before being received by the receiving antenna. Its phase will be delayed and the amplitude will be weakened. It will be superimposed with the direct wave signal to produce an error, causing multipath interference and affecting the performance of the navigation and positioning system.

[0027] After signal capture, demodulation and other processing, the signal received by the receiving antenna can be expressed as:

[0028]

[0029] Where, As(t-τ m )exp(j2πf d ) represents the received echo signal, where A represents the echo amplitude, s(t) is the satellite transmission signal, τ m and f d Respectively represent the time delay and Doppler frequency of the echo signal; Represents a multipath signal of the satellite, subscript i represents the i-th multipath signal in the multipath, W is the multipath number, ω i represents the gain of the i-th multipath, τ n is the time delay of the multipath signal; e s (t) is the noise of the echo channel.

[0030] In practical imaging, multipath signals cause interference. As multipath signals are received by the antenna, they produce multipath responses, degrading image quality. To address this issue, spatial filtering has been considered, creating narrow nulls in the receiving antenna pattern in the direction of arrival of the multipath signals to address multipath interference. However, multipath signals are complex and difficult to accurately identify, making it difficult to accurately estimate the direction of arrival of all multipath signals.

[0031] Based on this, the present invention addresses the problem that multipath interference in navigation positioning is difficult to accurately identify, and proposes a method for high-precision identification of multipath signals: first, the direct wave data is imaged; then the location of the multipath interference is found in the imaging result, and the angle at which the multipath signal reaches the antenna at this location is calculated based on the location; the antenna radiation pattern is adjusted according to the angle to suppress multipath interference.

[0032] Example

[0033] A method for high-precision identification of multipath signals, comprising the steps of:

[0034] Step 1: Direct wave data collection.

[0035] This embodiment built a navigation satellite signal receiving system in Changshu City, Jiangsu Province, using Beidou2_IGSO5 as the transmitting source, and conducted a data collection experiment on July 5, 2021. The experimental topology is as follows: Figure 1 As shown in the figure, the navigation signal is collected for a long time (not less than 600 seconds) and the position of the receiving antenna is recorded.

[0036] Step 2: Two-dimensional focusing of the navigation signal.

[0037] Perform two-dimensional focused imaging on the long-duration navigation signal collected in step 1. Select the ground as the projection plane and the receiving antenna position as the imaging plane origin. To achieve higher range resolution, synthesize the B2a and B2b frequencies of the BeiDou signal. Finally, use the BP algorithm for imaging. The BP imaging steps are as follows: first, grid the imaging plane, then perform range pulse compression on the navigation signal. Finally, calculate the distance from the satellite to each grid cell to achieve azimuth imaging, resulting in a two-dimensional focused imaging result for the navigation signal.

[0038] In this embodiment, the navigation signal is focused in two dimensions.

[0039] Step 3: Multipath signal identification.

[0040] The response of the satellite signal in the imaging image is represented by the fuzzy function:

[0041]

[0042] Where P is the position of the target point, Q is the position of any target point nearby. λ is the carrier wavelength, and c is the speed of light. Φ TP , Φ RP are the unit vectors from the transmitter and receiver to the target point P. β is the bistatic angle, i.e. Φ TP and Φ RP The angle between them, Θ is the unit vector in the direction of the β angle bisector. ω E is the transmitter’s equivalent angular velocity, and Ξ is its equivalent direction of motion. p(~) and m(~) are the autocorrelation functions in the range and azimuth directions, respectively.

[0043] In this embodiment, the signal response can be extracted according to the above formula, and the noise level of the remaining image is estimated to be 190 dB. There are still some images with amplitudes higher than the noise. The responses 10 dB higher than the noise are all generated by multipath signals.

[0044] Step 4: Extracting multipath signal source parameters;

[0045] Assume that the position of a multipath interference signal is represented by (x n ,y n ) is represented by the receiver position (x a ,y a ), and the angle between the antenna and the north direction is θ a , then the angle θ between the multipath interference and the north direction is n Expressed as:

[0046]

[0047] Furthermore, the angle θ at which the multipath interference signal reaches the antenna is calculated. i for:

[0048] θ i =θ n -θ a (4)

[0049] Similarly, the angles at which other multipath signals in the image reach the receiving antenna can be calculated, thereby achieving high-precision adaptive identification of each multipath signal.

[0050] In this embodiment, there are three interferences caused by multipath signals, located at (430, 50), (478, 93), and (553, 164). The receiver is located at (0, 0), and the angle θ between the receiving antenna and due north is a =45°. According to equations (3) and (4), it can be calculated that the angles of the three multipath signals to the receiving antenna are 38.37°, 33.99°, and 28.48° respectively.

[0051] In summary, the present invention proposes an adaptive high-precision identification method for multipath interference signals of satellite navigation systems, which can accurately identify the sources of multipath interference signals, effectively reduce the system ranging error, reduce the amount of system processing operations, and improve positioning accuracy, and has practical application value.

[0052] The above specific embodiments merely illustrate the design principles of the present invention. The shapes and names of the components described herein may vary and are not limiting. Therefore, those skilled in the art may modify or substitute equivalents for the technical solutions described in the above embodiments. Such modifications and substitutions, without departing from the inventive spirit and technical solutions of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A method for identifying multipath interference signals in a satellite navigation system based on two-dimensional focusing analysis, characterized in that The steps of the method include: Step 1: Use a receiving antenna to collect the navigation signal to obtain direct wave data, and record the relative geometric position of the receiving antenna and the ground; Step 2: Using the direct wave data collected in step 1 and the recorded relative geometric position of the receiving antenna and the ground, perform two-dimensional focused imaging to obtain a direct wave image; Step 3: Identify the multipath interference signal in the direct wave image obtained in step 2 and record the position of the multipath interference signal; Step 4: Calculate the angle at which the multipath interference signal reaches the receiving antenna based on the position of the multipath interference signal recorded in step 3, thereby completing the identification of the multipath interference signal of the satellite navigation system based on two-dimensional focusing analysis; In step 4, the method for calculating the angle at which the multipath interference signal reaches the receiving antenna is: Assume the position of the multipath interference signal is (x n ,y n ), the receiver position is (x a ,y a ), the angle between the receiving antenna and the north direction is θ a , then the angle θ between the multipath interference signal and the north direction is n for: The angle θ at which the multipath interference signal reaches the receiving antenna i for: i i =θ n -θ a ; The BP algorithm is used for two-dimensional focusing imaging.

2. The method for identifying multipath interference signals in a satellite navigation system based on two-dimensional focusing analysis according to claim 1, characterized in that: In the step 1, the time for collecting the navigation signal using the receiving antenna is not less than 600 seconds.

3. The method for identifying multipath interference signals in a satellite navigation system based on two-dimensional focusing analysis according to claim 2, characterized in that: In the step 2, the specific method for performing two-dimensional focused imaging is: first, the imaging plane is gridded, then the navigation signal is pulse compressed in the range direction, and then the distance from the satellite to each grid is calculated to achieve azimuth imaging and obtain the two-dimensional focused imaging result of the navigation signal.

4. The method for identifying multipath interference signals in a satellite navigation system based on two-dimensional focusing analysis according to claim 3, wherein: In step three, the method for identifying the multipath signal in the direct wave image is: extracting the direct wave response, and then evaluating the residual image amplitude after extracting the direct wave response to find the position of the multipath interference signal.

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