A GBAS anti-interference system based on array antenna

Abstract

The present invention provides a GBAS anti-interference system based on array antennas. Through two-way interaction between multiple array signal processing modules and a GBAS differential processing center, a constellation configuration that is more conducive to the performance of the GBAS system in an interference environment is screened out, thereby improving the ability of the GBAS system to continuously provide services in an interference environment.

Description

Technical Field

[0001] The invention belongs to the technical field of satellite navigation, and in particular relates to a GBAS anti-interference system based on array antennas. Background Art

[0002] The Ground Based Augmentation System (GBAS) is a satellite navigation local augmentation system that can be used to provide positioning and navigation services during the aircraft's precision approach, landing and ground taxiing phases. It consists of a ground base station system, an airborne system and a satellite navigation system. The ground base station system is used to capture GNSS satellite signals, and after differential processing, the correction signal is broadcast to the airborne system using a very high frequency data broadcasting device. The airborne device is a multi-mode receiver that receives satellite navigation signals and differential augmentation messages broadcast by ground equipment, performs differential positioning solutions and integrity warning judgment processing, and thus generates the guidance information required by the aircraft.

[0003] Navigation positioning requires 4 or more satellites, so the GBAS system also needs to process at least 4 satellites to provide differential message services. In an interference environment, the GNSS receiver may not be able to acquire a sufficient number of satellites. Therefore, array antenna technology can be used to automatically adjust the antenna pattern through spatial signal processing to form a null in the interference direction to achieve interference suppression, while forming a beam pointing in the direction of the desired satellite signal to obtain beam gain. The selection of different satellite combinations will affect the positioning performance. Satellites are usually selected based on their geometric layout relative to the GNSS receiver. A commonly used satellite selection method is the optimal geometric dilution of precision (GDOP) method. The smaller the GDOP value of a group of satellites, the more uniform the geometric distribution and the higher the positioning accuracy. However, the GDOP method only depends on the geometric distribution of satellites and does not consider the impact of interference on the quality of satellite signals. For the traditional array antenna anti-interference system, each GNSS receiver and the corresponding array antenna operate independently as a module and independently select the beam pointing satellite. The problem with this approach is that in an interference environment, the null position and depth of each array antenna in the GBAS ground station may be different, and the satellite combination of the beam pointing may also be different, resulting in the GBAS ground station being unable to integrate at least 4 effective satellites for differential message services. Summary of the invention

[0004] Therefore, the present invention provides a GBAS anti-interference system based on array antenna, including a differential processing center, an array signal processing module and M groups of GNSS receivers, wherein the array signal processing module includes M groups of array antennas and M groups of anti-interference modules, the differential processing center interacts with the array signal processing module, each group of anti-interference modules is respectively located between each group of array antennas and each group of GNSS receivers, the differential processing center has a two-way communication connection with each anti-interference module, and uses the array antenna pattern and the almanac to screen out the best constellation configuration under the interference environment, including:

[0005] Step 1: The array antenna receives the GNSS signal and the interference signal, and after being processed by the RF front end, transmits the digital intermediate frequency signal to the anti-interference module;

[0006] Step 2: In the anti-interference module, the adaptive nulling pattern matrix of each array antenna is generated and sent to the differential processing center. According to the satellite position information selected by the differential processing center, multiple anti-interference modules synchronously perform beam pointing on the selected satellite and then send the signal to the GNSS receiver.

[0007] Step 3: The GNSS receiver and differential processing center use the signal processed in step 2 to generate differential messages and broadcast them to users.

[0008] Furthermore, step 2 includes the following steps:

[0009] Step 2-1: In the anti-interference module, adaptive zeroing operations are performed respectively according to the received signals of the M groups of array antennas to generate M antenna pattern matrices and send them to the differential processing center;

[0010] Step 2-2: The differential processing center calculates the positions of all satellites within the visible range based on the calibrated M groups of array antenna coordinates, the pre-stored satellite almanac and the current time, and then calculates the optimal constellation configuration containing S satellites in combination with the array antenna pattern matrix in step 2-1, and sends the elevation angles and azimuth angles of these S satellites to the anti-interference module;

[0011] Step 2-3: Based on the given satellite position information, the M anti-interference modules perform beam pointing to the same S satellite positions, and generate nulls in their respective corresponding interference directions, and then send the module output signals to the GNSS receiver.

[0012] Further, the step 2-2 includes calculating the optimal constellation configuration:

[0013] Step 2-2-1: Based on the M groups of antenna pattern matrices Y1~Y M , after synthesis, the antenna pattern matrix Y is obtained. The synthesis method is as follows: for each elevation angle and azimuth , array gain of Y ;

[0014] Step 2-2-2: Calculate the positions of all N satellites within the visible range based on the calibrated geometric center coordinates of the M groups of array antenna coordinates, the pre-stored satellite almanac and the current time, and then generate A constellation configuration containing S visible satellites;

[0015] Step 2-2-3: Select One of the constellation configurations;

[0016] Step 2-2-4: According to the antenna pattern matrix Y, obtain the array gain g corresponding to the orientation of the S satellites i (i=1, 2, ...S), construct the weight factor w(g i ), and obtain the weight matrix W=diag(w(g1),w(g2),…w(g S ));

[0017] Step 2-2-5: Construct the observation matrix A based on the elevation and azimuth angles of the S satellites, then the weighted geometric precision factor ;

[0018] Step 2-2-6: Repeat steps 2-2-3 to 2-2-5 for The WGDOP is calculated for each of the constellation configurations, and a group of satellites with the smallest WGDOP value is selected as the selected optimal constellation configuration.

[0019] Furthermore, it includes a reverse differential verification module, in which each base station simulates the airborne equipment, uses the broadcasted telegrams for reverse differential positioning, and compares them with the calibrated coordinates. If the position deviation exceeds the threshold, it means that the reliability of the measurement result of the base station is low, and the base station is not used for GBAS solution. If the remaining available base stations are less than 2, GBAS stops broadcasting telegrams.

[0020] Furthermore, the value range of the number of satellites S varies according to the number of array antenna elements X: 4≤S≤X-2.

[0021] The beneficial effects of the present invention are:

[0022] 1) Taking into account the impact of satellite geometric distribution and interference, a better constellation configuration under interference environment is selected.

[0023] 2) The differential processing center interacts with multiple array signal processing modules to avoid the problem that GBAS cannot synthesize at least 4 effective satellites for differential message services due to differences in satellite selection configurations of each base station in an interference environment. This enhances the ability of GBAS ground stations to continue to provide services in an interference environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0025] Figure 1 This is a diagram of the structure of conventional GBAS;

[0026] Figure 2 Anti-interference GBAS data processing flow chart provided for an example of the present invention;

[0027] Figure 3 The composition diagram of the anti-interference GBAS module provided by the example of the present invention;

[0028] Figure 4 This is an example diagram of the array antenna pattern in an interference environment. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings:

[0030] The present invention provides a GBAS anti-interference system based on array antenna, referring to Figure 3 , including a differential processing center, an array signal processing module and M groups of GNSS receivers, the array signal processing module includes M groups of array antennas and M groups of anti-interference modules, the differential processing center interacts with the array signal processing module, each group of anti-interference modules is respectively located between each group of array antennas and each group of GNSS receivers, the differential processing center has a two-way communication connection with each anti-interference module, and uses the array antenna radiation pattern and the almanac to screen out the best constellation configuration in the interference environment.

[0031] GBAS principle diagram under interference environment Figure 1 As shown in the figure, each base station consists of a group of array antennas, an anti-interference module and a GNSS receiver. Each base station receives multiple satellite signals and interference signals. In the figure, the interference signal is in the same direction as the signal of one of the satellites. If the satellite signal participates in GBAS operation, it may affect the performance of GBAS. Therefore, it is necessary to reduce the weight of the satellite in the configuration selection according to the interference size.

[0032] The above system works by adopting the following steps:

[0033] Step 1: The array antenna receives the GNSS signal and the interference signal, and after being processed by the RF front end, transmits the digital intermediate frequency signal to the anti-interference module;

[0034] Step 2: In the anti-interference module, the adaptive nulling pattern matrix of each array antenna is generated and sent to the differential processing center. Based on the satellite position information selected by the differential processing center, multiple anti-interference modules synchronously perform beam pointing on the selected satellite and then send the signal to the GNSS receiver.

[0035] Step 2 includes the following steps:

[0036] Step 2-1: In the anti-interference module, adaptive zeroing operations are performed according to the received signals of the M groups of array antennas to generate M antenna pattern matrices and send them to the differential processing center.

[0037] Step 2-2: The differential processing center calculates the positions of all satellites within the visible range based on the calibrated M groups of array antenna coordinates, the pre-stored satellite almanac and the current time, and then calculates the optimal constellation configuration containing S satellites in combination with the array antenna pattern matrix in step 2-1, and sends the elevation and azimuth angles of these S satellites to the anti-interference module.

[0038] Step 2-2-1: Based on the M groups of antenna pattern matrices Y1~Y M , after synthesis, the antenna pattern matrix Y is obtained. The synthesis method is as follows: for each elevation angle and azimuth , array gain of Y .

[0039] Step 2-2-2: Calculate the positions of all N satellites within the visible range based on the calibrated geometric center coordinates of the M groups of array antenna coordinates, the pre-stored satellite almanac and the current time, and then generate The constellation configuration of the group contains S visible satellites.

[0040] Step 2-2-3: Select One of the groups in the constellation configuration.

[0041] Step 2-2-4: According to the antenna pattern matrix Y, obtain the array gain g corresponding to the orientation of the S satellites i (i=1, 2, ...S), construct the weight factor w(g i ), and obtain the weight matrix W=diag(w(g1),w(g2),…w(g S )).

[0042] Step 2-2-5: Construct the observation matrix A based on the elevation and azimuth angles of the S satellites, then the weighted geometric precision factor .

[0043] Step 2-2-6: Repeat steps 2-2-3 to 2-2-5 for The WGDOP is calculated for each of the constellation configurations, and a group of satellites with the smallest WGDOP value is selected as the selected optimal constellation configuration.

[0044] Step 2-3: Based on the given satellite position information, the M anti-interference modules perform beam pointing to the same S satellite positions, and generate nulls in their respective corresponding interference directions, and then send the module output signals to the GNSS receiver.

[0045] Step 3: The GNSS receiver and differential processing center use the signal processed in step 2 to generate differential messages and broadcast them to users.

[0046] The system also includes a reverse differential verification module. Each base station simulates the airborne equipment and uses the broadcast telegrams for reverse differential positioning and compares them with the calibration coordinates. If the position deviation exceeds the threshold, it means that the measurement result of the base station is of low credibility and the base station will not be used for GBAS solution. If the remaining available base stations are less than 2, GBAS stops broadcasting telegrams.

[0047] like Figure 2 As shown, the implementation steps in this embodiment are as follows:

[0048] S1: 4 groups of 7-element array antennas receive GNSS signals and interference signals, and after RF front-end processing such as down-conversion and analog-to-digital conversion, transmit the digital intermediate frequency signals to the anti-interference module.

[0049] S2: In the four anti-interference modules, adaptive zeroing operations are performed according to the received signals of the four groups of array antennas to generate four antenna pattern matrices. In this example, the power inversion method is used for zeroing.

[0050] S3: The antenna pattern matrices Y1, Y2, Y3, and Y4 generated by the four anti-interference modules are transmitted through information a (such as Figure 3 As shown in Figure 2, the antenna pattern matrix Y is obtained after integration. Figure 4 As shown in Figure 1, the antenna pattern matrix consists of three dimensions: elevation angle, azimuth angle, and array gain. The comprehensive method is to and azimuth , array gain of Y .

[0051] S4: Figure 2 As shown in the figure, the differential processing center calculates the positions of all N satellites within the visible range at the current time based on the calibrated geometric center coordinates of the four groups of array antennas, the pre-stored satellite almanac and the current time, and then generates The constellation configuration contains 4 visible satellites.

[0052] S5: Select One of the groups in the constellation configuration.

[0053] S6: According to the antenna pattern matrix Y, obtain the array gain g corresponding to the azimuth of the four satellites i (i=1, 2, 3, 4), construct the weight factor w(g i ), and obtain the weight matrix W=diag(w(g1),w(g2),w(g3),w(g4)).

[0054] S7: Construct the observation matrix A according to the elevation angles and azimuth angles of the four satellites. The observation matrix A is expressed as:

[0055] ;

[0056] in and are the elevation angle and azimuth angle of the nth (n=1, 2, 3, 4) satellite respectively. Then the weighted geometric precision factor is .

[0057] S8: Repeat steps 5 to 7. The WGDOP is calculated for each of the constellation configurations, and the group of satellites with the smallest WGDOP value is selected as the selected optimal constellation configuration.

[0058] S9: The azimuth and elevation angles of the satellites in the best constellation configuration are transmitted through information b (such as Figure 3 The anti-interference modules use the linear constrained minimum variance criterion (LCMV) to point the beams of the four satellites according to the given azimuth information, and generate nulls in the interference direction. Then, the output signals of the modules are sent to the GNSS receiver.

[0059] S10: The GNSS receiver captures, tracks, and demodulates the signal to obtain navigation satellite observation data, navigation messages, and other data. These data are then sent to the differential processing center to generate GBAS differential messages, which are then broadcast to users via the VDB transmitting antenna.

[0060] S11: The differential processing center performs reverse differential positioning on the four reference stations according to the GNSS data transmitted by the reference station and the differential message broadcast. The positioning results are compared with the calibration coordinates. If the position deviation exceeds the threshold, it means that the measurement result of the reference station is of low credibility and the reference station is not used for GBAS solution. If the remaining available reference stations are less than 2, GBAS stops broadcasting messages. The threshold is set by technicians in this field according to actual conditions.

[0061] The present invention provides a GBAS anti-interference system based on an array antenna, which takes into account the influence of satellite geometric distribution and interference, and selects a better constellation configuration under an interference environment.

[0062] The differential processing center interacts with multiple array signal processing modules to avoid the problem that GBAS cannot synthesize at least 4 effective satellites for differential message services due to differences in satellite selection configurations of each base station in an interference environment. This enhances the ability of GBAS ground stations to continue to provide services in an interference environment.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A GBAS anti-interference system based on array antenna, characterized in that: The invention comprises a differential processing center, an array signal processing module and M groups of GNSS receivers. The array signal processing module comprises M groups of array antennas and M groups of anti-interference modules. The differential processing center interacts with the array signal processing module. Each group of anti-interference modules is respectively located between each group of array antennas and each group of GNSS receivers. The differential processing center has a two-way communication connection with each anti-interference module. The array antenna pattern and the almanac are used to screen out the best constellation configuration under the interference environment, including: Step 1: The array antenna receives the GNSS signal and the interference signal, and after being processed by the RF front end, transmits the digital intermediate frequency signal to the anti-interference module; Step 2: In the anti-interference module, an adaptive nulling pattern matrix of each array antenna is generated respectively, and the matrix is ​​sent to the differential processing center; and according to the satellite position information selected by the differential processing center, multiple anti-interference modules synchronously perform beam pointing on the selected satellite, and then send the signal to the GNSS receiver, wherein step 2 includes: Step 2-1: In the anti-interference module, adaptive zeroing operations are performed respectively according to the received signals of the M groups of array antennas to generate M antenna pattern matrices and send them to the differential processing center; Step 2-2: The differential processing center calculates the positions of all satellites within the visible range based on the calibrated M groups of array antenna coordinates, the pre-stored satellite almanac and the current time, and then calculates the optimal constellation configuration containing S satellites in combination with the array antenna pattern matrix in step 2-1, and sends the elevation angles and azimuth angles of these S satellites to the anti-interference module, including: Step 2-2-1: Based on the M groups of antenna pattern matrices Y1~Y M , after synthesis, the antenna pattern matrix Y is obtained. The synthesis method is as follows: for each elevation angle and azimuth , array gain of Y ; Step 2-2-2: Calculate the positions of all N satellites within the visible range based on the calibrated geometric center coordinates of the M groups of array antenna coordinates, the pre-stored satellite almanac and the current time, and then generate A constellation configuration containing S visible satellites; Step 2-2-3: Select One of the constellation configurations; Step 2-2-4: According to the antenna pattern matrix Y, obtain the array gain g corresponding to the orientation of the S satellites i , where i = 1, 2, ... S, constructs the weight factor w(g i ), and obtain the weight matrix W=diag(w(g1),w(g2),…w(g S )); Step 2-2-5: Construct the observation matrix A based on the elevation and azimuth angles of the S satellites, then the weighted geometric precision factor ; Step 2-2-6: Repeat steps 2-2-3 to 2-2-5 for Calculate WGDOP for each constellation configuration, and select a group of satellites with the smallest WGDOP value as the selected optimal constellation configuration; Step 2-3: Based on the given satellite position information, the M anti-interference modules perform beam pointing to the same S satellite positions, and generate nulls in their respective corresponding interference directions, and then send the module output signals to the GNSS receiver; Step 3: The GNSS receiver and differential processing center use the signal processed in step 2 to generate differential messages and broadcast them to users.

2. The system according to claim 1, characterized in that: Including a reverse differential verification module, each base station simulates the airborne equipment, uses the broadcast telegrams for reverse differential positioning, and compares them with the calibration coordinates. If the position deviation exceeds the threshold, it means that the measurement result of the base station is of low credibility, and the base station will not be used for GBAS solution. If the remaining available base stations are less than 2, GBAS stops broadcasting telegrams.

3. The system according to claim 1, characterized in that: The value range of the number of satellites S varies according to the number of array antenna elements X: 4≤S≤X-2.

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