A GNSS cascade adaptive multi-beamforming method

Abstract

The present invention relates to a GNSS cascade adaptive multi-beam forming method, belonging to the field of satellite navigation. The method of the present invention includes two major parts: whitening processing and beam forming, wherein the whitening processing completes interference suppression at the antenna end, and the beam forming completes the beam forming at the receiver end. The whitening processing includes autocorrelation matrix calculation, autocorrelation matrix square root calculation, square root inversion operation and data transformation processing; beam weighting includes weight transformation processing and beam weighting. Compared with the traditional GNSS beam forming method, this scheme can separate the anti-interference processing from the beam weighting, so that the antenna end anti-interference processing does not need the assistance of prior information such as satellite direction and antenna attitude, and the receiver end can easily achieve space, time and frequency three-dimensional integrated search and tracking; at the same time, the autocorrelation matrix square root inversion algorithm adopted in this scheme helps to improve the interference suppression degree of the autocorrelation matrix under odd conditions and improve the anti-interference stability of the system.

Description

Technical Field

[0001] The invention belongs to the field of satellite navigation, and in particular relates to a GNSS cascade adaptive multi-beam forming method. Background Art

[0002] The Global Navigation Satellite System (GNSS) is the mainstay of the current satellite navigation field. With the development of satellite navigation jamming technology in modern naval battlefields, the strong suppression jamming power against satellite navigation receiver antennas is becoming stronger and stronger. Traditional adaptive nulling antennas can only suppress suppression jamming but cannot increase signal power.

[0003] The conventional adaptive beamforming technology in the prior art couples anti-interference and beamforming into one, which makes it difficult to separate the two independent parts. The receiver is required to provide the anti-interference antenna with beamforming prior information, resulting in severe coupling between the receiver and the antenna.

[0004] Chinese invention patent 20151601963.1 discloses a method and device for anti-interference of a navigation receiver with a cascade structure, which includes an array antenna and an adaptive filtering processor, a two-stage cascade structure composed of an array antenna and an adaptive filtering processor, and an anti-interference method of cascading an adaptive spatial filtering processing module with multiple adaptive spatial or spatial-temporal filtering processing modules to avoid the influence of the selection of reference filling on the anti-interference performance of the system. The patented method can resist interference and thus ensure the positioning efficiency of the navigation receiver. By adopting polling processing and cascade processing, each antenna is selected one by one as a reference antenna for adaptive filtering processing. However, the polling adaptive filtering processing of this method requires adaptive filtering of each signal of the array, or the resource overhead is large or the real-time performance is poor, which is not conducive to engineering implementation, and the despreading and demodulation of the satellite navigation signal is located before beamforming, which cannot improve the sensitivity of loop tracking (key processing of despreading and demodulation), which is not conducive to the receiver to realize space, time and frequency three-dimensional integrated search and tracking, and cannot give play to the advantages of three-dimensional tracking. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a GNSS cascade adaptive multi-beam forming method. The method of the present invention does not require satellite direction and antenna attitude information assistance at the antenna end, and it is easy to integrate the wave velocity formation with the receiver capture tracking at the receiver end, so that the end can achieve space, time and frequency three-dimensional search and tracking. In addition, the autocorrelation square root inverse algorithm provided by the present invention is conducive to improving the singularity of the autocorrelation matrix under strong and weak interference, and improving the interference suppression of the system.

[0006] In order to achieve the above invention purpose, the technical solution adopted by the present invention is as follows:

[0007] A GNSS cascade adaptive multi-beam forming method, characterized in that the method includes two-stage processing, the first stage processing is array signal whitening processing to generate interference-free array signals; the second stage processing is beam weighting processing of the interference-free array signals;

[0008] The array signal whitening process generates an interference-free array signal, which includes the following steps:

[0009] The first step is to generate the autocorrelation matrix for the original array signal x = [x0, ..., x n ,...,x N-1 ] T (N is the number of array elements contained in the array) and perform autocorrelation operation to obtain its autocorrelation matrix R:

[0010] R=E[xx H ] (1)

[0011] In the above formula, the symbol E represents the calculation of mathematical expectation;

[0012] The second step is to decompose the autocorrelation matrix by square root. Use Cholesky to decompose the autocorrelation matrix R by square root so that R = LL H , where L is a lower triangular matrix with the following form:

[0013]

[0014] After the square root decomposition, the obtained triangular matrix is ​​convenient for matrix inversion calculation, and the calculation stability is improved, which is beneficial to improve the system's anti-interference ability under large difference interference power (autocorrelation matrix is ​​singular).

[0015] The third step is to calculate the inverse square root matrix of the autocorrelation so that LL -1 =I.

[0016] The fourth step is data transformation processing, using the autocorrelation square root inverse matrix L -1 Convert the original array signal x into a new array signal z, which is mathematically described as:

[0017] z=L -H x (3)

[0018] The beam weighting of the interference-free array signal comprises the following steps:

[0019] The fifth step is weight transformation processing, using the autocorrelation square root inverse matrix L -1 For the original beam weight vector set {a0,...,a m ,...,a M-1} to obtain a new beam weight vector set {b0,...,b m ,...,bM-1}, where M is the number of beams. The weight vector of each new beam is calculated as follows:

[0020] b m =L -H a m (4)

[0021] Step 6: Beam synthesis: Use the new weight vector set {b0,...,b m ,...,b M-1} is weighted to obtain the beam signal set {y0,...,y m ,...,y M-1}, the calculation method of each beam signal is as follows:

[0022]

[0023] In a GNSS cascade adaptive multi-beam forming method of the present invention, the method comprises two-stage processing of whitening processing and beam forming, wherein the whitening processing is to filter out interference signals in array signals, and the beam forming processing is to enhance satellite signals.

[0024] In a GNSS cascade adaptive multi-beam forming method of the present invention, the inversion of the autocorrelation matrix in the first step adopts a matrix square root decomposition method to reduce the calculation accuracy in the case of matrix singularity and enhance the anti-interference capability of the system.

[0025] In a GNSS cascade adaptive multi-beam forming method of the present invention, anti-interference processing is placed at the antenna end, and beam forming is placed at the receiver end. The antenna end does not need antenna attitude and satellite direction beam weight parameters, thereby reducing the coupling between the antenna and the receiver.

[0026] Based on the above technical solution, the patent of this invention has the following technical advantages compared with the prior art:

[0027] 1. Since the GNSS cascade adaptive multi-beam forming method of the present invention adopts anti-interference processing (array signal whitening) and beam weighted cascade architecture, the whitening processing is located at the antenna end and the beam forming processing is located at the receiver end, interference suppression can be achieved at the antenna end without external assistance, and the receiver end can easily complete three-dimensional integrated capture and tracking of space (beam forming), time and frequency.

[0028] 2. The GNSS cascade adaptive multi-beam forming method of the present invention adopts an autocorrelation square root decomposition algorithm, which can invert the autocorrelation square root matrix instead of directly inverting the autocorrelation matrix, thereby enhancing the interference suppression degree in the case of singular autocorrelation matrix and improving system stability.

[0029] 3. The GNSS cascade adaptive multi-beam forming method of the present invention can improve the loop tracking sensitivity in demodulation and despreading because the beam weighting processing is located before the signal demodulation and despreading. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is an overall implementation block diagram of a GNSS cascade adaptive multi-beam forming method of the present invention.

[0031] Figure 2 It is a schematic diagram of a whitening process flow in a GNSS cascade adaptive multi-beam forming method of the present invention.

[0032] Figure 3 It is a schematic diagram of the beam weighting principle in a GNSS cascade adaptive multi-beam forming method of the present invention.

[0033] Figure 4 It is a square root decomposition whitening processing interference suppression performance diagram in a GNSS cascade adaptive multi-beam forming method of the present invention.

[0034] Figure 5 The invention discloses a beam tracking gain curve in a GNSS cascade adaptive multi-beam forming method. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments, in order to more clearly understand the content of the patent application of the present invention, but the implementation mode of the present invention is not limited thereto, and the protection scope of the patent of the present invention cannot be limited thereto.

[0036] like Figure 1 As shown, the present invention is a GNSS cascade adaptive multi-beam forming method, the purpose of which is to separate anti-interference processing from beam weighting, so that the anti-interference processing at the antenna end does not need the assistance of prior information such as satellite direction and antenna attitude, and the receiver end can easily achieve three-dimensional search and tracking in space, time and frequency; at the same time, the array signal whitening processing is completed by inverting the autocorrelation square root matrix, which helps to improve the interference suppression degree of the autocorrelation matrix under odd conditions and improve the anti-interference stability of the system.

[0037] The whole method of the present invention is cascaded into two parts: (1) array signal whitening processing (anti-interference processing), and (2) beam weighting. The anti-interference processing is located at the antenna end, and the beam weighting is located at the receiver end, and the two communicate through optical fiber. The antenna end is only responsible for anti-interference processing, and does not need the assistance of beam prior information, forming an independent system. The beam weighting is located at the receiver end, which is easy to integrate with the capture and tracking processing at the receiver end to achieve three-dimensional joint capture and tracking.

[0038] Taking the GPS L1 signal as an example, the RF signal received by the array antenna (n=0…6,7-element array) includes interference, signal and noise, frequency 1575.42MHz, bandwidth 2.04MHz, signal power range is -135~120dBm, noise power is -107dBm, and interference power is 70~100dB stronger than signal power. Since the signal power is submerged in the noise, the antenna end cannot extract any information of the satellite signal before capture and tracking. If beam forming is to be performed at the antenna end, external assistance must be obtained to obtain beam weight parameters, so the antenna end is not an independent autonomous system. To address this problem, this design only completes anti-interference processing at the antenna end, and places beam weighting processing that requires external assistance at the receiver end. The receiver end has a signal extraction function, which makes it easy to obtain beam parameters such as satellite direction. At the same time, beam weighting is integrated with capture and tracking, which can enhance capture and tracking performance.

[0039] First, the L1 RF signal received by the antenna (n=0…6) is converted into a 15.42MHz intermediate frequency signal through the RF module (n=0…6). Then, the intermediate frequency signal enters the anti-interference processing module for digital-to-analog conversion, orthogonal down-conversion and whitening processing, and is transformed into an interference-free zero intermediate frequency signal z n (n=0...6), wherein the interference-free zero intermediate frequency signal carrier frequency is 0 MHz and is a complex signal. Finally, the 7-channel digital signals are converted into optical signals through the electro-optical conversion module and sent to the receiver.

[0040] Whitening processing in array signal processing is as follows Figure 2 As described above, it consists of six parts: data storage, cholesy decomposition, lower triangular matrix inversion, delay matching and whitening processing.

[0041] The zero intermediate frequency signal output by the orthogonal down-conversion is expressed as:

[0042]

[0043] Where n is the array number, m is the satellite number, s represents the signal, j represents the interference, k is the sampling point number, T s represents the sampling period, θ m represents the satellite elevation angle, represents the satellite azimuth, and σ represents the noise standard deviation.

[0044] During the implementation process, the following steps were taken:

[0045] The first step is to cache the input signal and store K beats of intermediate frequency data to form an intermediate frequency data vector set, which is expressed as:

[0046] {x0,...,x k ,...,x K-1} (8)

[0047] The second step is to calculate the autocorrelation matrix R according to the intermediate frequency vector set. The calculation method is as follows:

[0048]

[0049] This department is an engineering approach to data expectation calculation.

[0050] The third step is to use the Cholesy method to diagonalize the autocorrelation matrix R and obtain:

[0051] R=LL H (2)

[0052] Where L is a lower triangular matrix, that is, the square root matrix of R.

[0053] Step 4: Invert the lower triangular matrix L to obtain L -1 .

[0054] Step 5: Use L -1 Whiten the original array signal x to obtain the interference-free array signal z. The calculation method is as follows:

[0055] z=L -H x (3)

[0056] At this point, the interference-free zero-IF array signal z is obtained, which is converted into an optical signal through electro-optical conversion and sent to the receiver.

[0057] The receiver recovers the interference-free zero-IF array signal z through the optoelectronic converter and completes the beam weighting processing according to the specific requirements of capture and tracking, such as Figure 3 , the beam weighting operation shown is:

[0058]

[0059] The direction of the satellite signal can be obtained by calculating the satellite ephemeris, or by obtaining the satellite angle information through three-dimensional tracking. In general, its expression is:

[0060]

[0061] Among them, [x n ,y n ,z n ] is the coordinate data of the antenna array element, θ m and Represent the satellite pitch and azimuth respectively.

[0062] Figure 4It is the GNSS cascade adaptive multi-beamforming method that gives this scheme adaptive beamforming performance. In the figure, for the 7-element central circle array, the array element is omnidirectional gain, the signal is located at 45°, the strong interference is located at 10°, the weak interference is located at 85°, and the strong interference is 60dB stronger than the weak interference. Under the same interference condition, the system is simulated using the autocorrelation matrix inversion algorithm and the autocorrelation square root inversion algorithm respectively. The dotted line in the figure is the autocorrelation matrix inversion method, and the solid line is the autocorrelation square root inversion method. Due to the large difference in power between strong and weak interference, the autocorrelation matrix is ​​singular. If the inverse of the autocorrelation matrix is ​​directly used to whiten the array signal, the weak interference suppression will be reduced and the suppression angle will deviate (as shown by the dotted line in the figure). Using the autocorrelation square root inverse matrix for whitening can significantly improve the weak interference suppression performance (as shown by the solid line in the figure). Figure 5 This is the beam gain tracking curve. Because the satellite is not aligned at the beginning of the tracking stage, the gain is 0dB. After the space-time-frequency three-dimensional tracking is locked, the beam is aligned with the satellite and the gain increases to the theoretical value.

[0063] Undoubtedly, the GNSS cascade adaptive multi-beam forming method of the present invention includes other implementation methods besides the above embodiments and is not limited to the above limitations. In summary, the protection scope of the present invention also includes other obvious changes and substitutions for those skilled in the art.

Claims

1. A GNSS cascade adaptive multi-beam forming method, characterized in that: The method includes two-stage processing, the first stage of which is array signal whitening processing to generate interference-free array signals; the second stage of which is beam weighting processing of the interference-free array signals; The array signal whitening process generates an interference-free array signal, which includes the following steps: The first step is to generate the autocorrelation matrix for the original array signal x = [x0, ..., x n ,...,x N-1 ] T , N is the number of arrays contained in the array. Perform autocorrelation operation to obtain its autocorrelation matrix R: R=E[xx H ](1); In the above formula, the symbol E represents the calculation of mathematical expectation; The second step is to decompose the autocorrelation matrix by square root. Cholesky is used to decompose the autocorrelation matrix R by square root: R=LL H (2) Where L is a lower triangular matrix; The third step is to calculate the inverse square root matrix of the autocorrelation so that LL -1 =I; The fourth step is data transformation processing, using the autocorrelation square root inverse matrix L -1 Convert the original array signal x into a new array signal z, which is mathematically described as: z=L -H x(3); The beam weighting of the interference-free array signal comprises the following steps: The fifth step is weight transformation processing, using the autocorrelation square root inverse matrix L -1 For the original beam weight vector set {a0,...,a m ,...,a M-1 } to obtain a new beam weight vector set {b0,...,b m ,...,b M-1 }, where M is the number of beams, and the weight vector of each new beam is calculated as follows: b m =L -H a m (4); Step 6: Beam synthesis: Use the new weight vector set {b0,...,b m ,...,b M-1 } is weighted to obtain the beam signal set {y0,...,y m ,...,y M-1 }, the calculation method of each beam signal is as follows:

2. A GNSS cascade adaptive multi-beam forming method according to claim 1, characterized in that: The method comprises two-stage processing of whitening processing and beamforming, wherein the whitening processing is located at the antenna end to filter out interference signals in array signals, and the beamforming processing is located at the receiver end to enhance satellite signals.

3. The GNSS cascade adaptive multi-beam forming method according to claim 1, characterized in that: The whitening process in the first step adopts the inversion method of the autocorrelation square root matrix to enhance the interference suppression degree when the autocorrelation matrix is ​​singular.

4. The GNSS cascade adaptive multi-beam forming method according to claim 1, characterized in that: The beam weighting process in the second step is located before signal demodulation and despreading to improve the loop tracking sensitivity in demodulation and despreading.

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