Differential Beidou transmission system based on measurement and control link

Abstract

The invention discloses a differential Beidou transmission system based on a measurement and control link. The ground end differential Beidou reference station preferentially processes information of Beidou satellites in the same sight range as the airborne end based on the Beidou satellite mask request information, generates corresponding differential Beidou reference information, and frames the differential Beidou reference information; the ground end measurement and control link module is used for sending the framed differential Beidou reference information to the airborne end measurement and control link module in a wireless communication mode; the Beidou satellite mask request module is used for receiving Beidou satellite mask request information from the airborne end measurement and control link module and forwarding the Beidou satellite mask request information to the ground end differential Beidou base station; the airborne end measurement and control link module is used for sending Beidou satellite mask request information from the airborne end differential Beidou module back to the ground end measurement and control link module; the differential Beidou module is used for receiving the framed differential Beidou reference information and forwarding the framed differential Beidou reference information to the airborne end differential Beidou module; the airborne end differential Beidou module is used for generating Beidou satellite mask request information; and the sub-positioning module is used for combining the framed differential Beidou reference information with Beidou satellite data received by the airborne end differential Beidou module, executing sub-positioning calculation and generating positioning information. According to the invention, the navigation precision and reliability of the unmanned aerial vehicle in various scenes can be enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of Beidou satellite navigation systems for unmanned aerial vehicles, and in particular relates to a differential Beidou transmission system based on a measurement and control link. Background Art

[0002] With the continuous advancement of domestic drone technology, the endurance and load capacity of these aircraft have been significantly enhanced, allowing them to carry more equipment and maintain longer operation time when performing various tasks. In order to achieve precise navigation, modern drones are generally equipped with advanced Beidou navigation systems. Through the positioning information provided by the system, drones can perform flight missions more accurately.

[0003] As an indispensable part of the UAV system, the measurement and control link establishes a two-way communication link between the ground control station and the UAV. This link not only transmits remote control signals and telemetry data, but also exchanges mission information. The measurement and control link of large UAVs usually includes multiple transmission channels, such as relay communication and satellite communication, to achieve unobstructed transmission.

[0004] In actual operation, the transmission of differential Beidou reference information of drones usually relies on V / UHF communication links. However, when the V / UHF line of sight conditions are poor or the link cannot be established, the drone cannot receive differential Beidou reference information, thus affecting the positioning accuracy. Summary of the invention

[0005] The purpose of the present invention is to provide a differential Beidou transmission system based on a measurement and control link. The present invention can enhance the navigation accuracy and reliability of unmanned aerial vehicles in various scenarios.

[0006] The technical solution of the present invention is: a differential Beidou transmission system based on a measurement and control link, comprising:

[0007] The ground-based differential Beidou reference station, based on the Beidou satellite mask request information, prioritizes the information of Beidou satellites in the same line of sight as the airborne terminal, generates corresponding differential Beidou reference information, and frames the differential Beidou reference information;

[0008] The ground-side measurement and control link module is used to send the framed differential Beidou reference information to the airborne measurement and control link module through wireless communication; it is used to receive the Beidou satellite mask request information from the airborne measurement and control link module and forward it to the ground-side differential Beidou reference station;

[0009] The airborne measurement and control link module is used to send the Beidou satellite mask request information from the airborne differential Beidou module back to the ground measurement and control link module; it is used to receive the framed differential Beidou reference information and forward it to the airborne differential Beidou module;

[0010] The airborne differential Beidou module is used to generate Beidou satellite mask request information; and to combine the framed differential Beidou reference information with the Beidou satellite data received by the airborne differential Beidou module itself, perform sub-positioning calculations, and generate positioning information.

[0011] In the aforementioned differential Beidou transmission system based on the measurement and control link, during data transmission, the satellite data of the Beidou satellite requested by the Beidou satellite mask request information and within the same line of sight as the airborne terminal has the highest priority and is broadcast first.

[0012] In the aforementioned differential Beidou transmission system based on the measurement and control link, the Beidou satellite mask request information is generated based on the satellite mask situation actually captured by the airborne differential Beidou module.

[0013] In the aforementioned differential Beidou transmission system based on the measurement and control link, the number of frames used by the ground-side differential Beidou reference station is determined based on the bandwidth of the measurement and control link module allocated to the differential Beidou transmission system.

[0014] In the aforementioned differential Beidou transmission system based on the measurement and control link, the differential Beidou reference information after framing is sent in a transmission layer that is fixedly divided into 5 information frames; the transmission layer fixes the length of each information frame to 64 bytes, for a total of 320 bytes.

[0015] In the aforementioned differential Beidou transmission system based on the measurement and control link, the first information frame in the transmission layer carries the location parameters, time information, satellite mask for selection, signal mask and unit mask of the ground-end differential Beidou reference station.

[0016] In the aforementioned differential Beidou transmission system based on the measurement and control link, the first information frame of the transmission layer also carries the observed satellite data and signal data if there is spare space.

[0017] In the aforementioned differential Beidou transmission system based on the measurement and control link, the structure of the information frame is as follows:

[0018] Guide word: used to mark the beginning of data transmission;

[0019] Total frame number: the sum of all non-empty frames. When an empty frame is transmitted, the total frame number is 0.

[0020] Frame number: the Nth non-empty frame in a certain epoch, N≤5, the frame number is 0 when an empty frame is transmitted;

[0021] Presentation layer message data: used to transmit satellite ephemeris data; the presentation layer message data is divided into three parts: message header, satellite data and signal data;

[0022] Checksum: used to detect errors during data transmission.

[0023] In the aforementioned differential Beidou transmission system based on the measurement and control link, the method for sending the differential Beidou reference information after framing is as follows:

[0024] When there is no satellite signal: 5 empty frames are sent continuously, and the presentation layer message data of each frame only contains the message header, and the rest is filled with "0";

[0025] When the number of valid satellites is 1 to 2: send 1 data frame and 4 empty frames;

[0026] When the number of valid satellites is 3 to 6: send 2 data frames and 3 empty frames;

[0027] When the number of valid satellites is 7 to 10: send 3 data frames and 2 empty frames;

[0028] When the number of valid satellites is 11 to 14: send 4 data frames and 1 empty frame;

[0029] When the number of valid satellites is 15 to 18: send 5 data frames continuously.

[0030] In the aforementioned differential Beidou transmission system based on the measurement and control link, when the information frame containing the presentation layer message data is the first frame, the message header includes the position parameters and epoch time of the differential Beidou reference station on the ground side.

[0031] The advantages of the present invention are:

[0032] 1. According to different communication bandwidths and satellite environments, the present invention provides a differential Beidou transmission system that can transmit differential Beidou reference information through a UAV measurement and control link, which can enhance the navigation accuracy and reliability of UAVs in various scenarios.

[0033] 2. Aiming at the limitation in the prior art that "when the V / UHF line-of-sight condition is poor or the link cannot be established, the UAV cannot receive the differential Beidou reference information", the present invention proposes a differential Beidou transmission system based on the existing measurement and control link, solving the signal transmission problem under non-line-of-sight conditions. Since the present invention also overcomes the technical difficulty of "due to the bandwidth limitation of the measurement and control link", it realizes efficient narrowband transmission and ensures that the differential Beidou reference information can be reliably transmitted even under limited bandwidth.

[0034] 3. The present invention designs an implementation architecture for UAVs based on narrowband transmission of differential Beidou reference information. By improving the data structure of the transmission layer and its internal representation layer, the transmission efficiency is improved, thereby effectively improving the reliability and available range of UAV differential Beidou positioning.

[0035] 4. High-precision positioning: Based on the improved transmission means, the differential Beidou system of the present invention still realizes precise differential positioning through the traditional differential Beidou RTK (real-time dynamic differential) technology, effectively ensuring that the positioning accuracy is not affected.

[0036] 5. Significant cost-effectiveness: The present invention uses a measurement and control link to transmit differential Beidou data, eliminating the need to install additional airborne and ground differential radio stations on the UAV, thereby reducing the overall equipment cost.

[0037] 6. Enhanced communication robustness: With the diversified characteristics of the measurement and control link, anti-interference ability and wide coverage, the present invention effectively overcomes the problems of traditional differential radio stations being susceptible to interference and signal blocking limitations, ensuring a more reliable communication link.

[0038] 7. Improved positioning capability: The present invention significantly enhances the precise positioning capability of the drone, whether in complex environments or facing various external challenges.

[0039] 8. Improved flight safety: Due to its reliability and accuracy, the present invention improves the overall safety level of UAV operations and reduces the risks caused by positioning errors.

[0040] 9. Enhanced environmental adaptability: The present invention has better adaptability to different environments and conditions, allowing the drone to perform tasks in more diverse occasions. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the system structure of the present invention;

[0042] Figure 2 A flow chart of the method for sending the system of the present invention;

[0043] Figure 3 Schematic diagram of information frame structure;

[0044] Figure 4 It is a schematic diagram of the data structure of the presentation layer message;

[0045] Figure 5 A schematic diagram of the information included in the message header in one case;

[0046] Figure 6 A schematic diagram of the information included in the message header in another case;

[0047] Figure 7 This is a schematic diagram of the satellite data structure;

[0048] Figure 8 This is a schematic diagram of the signal data structure. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0050] The features and illustrative embodiments of various aspects of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is by no means limited to any specific settings and methods proposed below, but covers any improvements, replacements and modifications of structures, methods, devices without departing from the spirit of the present invention. In the accompanying drawings and the following description, known structures and technologies are not shown to avoid unnecessary ambiguity in the present invention.

[0051] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other, and the embodiments can refer to and quote each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0052] Example 1. A differential Beidou transmission system based on a measurement and control link, see Figure 1-8 ,include:

[0053] The ground-based differential Beidou reference station, based on the Beidou satellite mask request information, prioritizes the information of Beidou satellites in the same line of sight as the airborne terminal, generates corresponding differential Beidou reference information, and frames the differential Beidou reference information;

[0054] The ground-side measurement and control link module is used to send the framed differential Beidou reference information to the airborne measurement and control link module through wireless communication; it is used to receive the Beidou satellite mask request information from the airborne measurement and control link module and forward it to the ground-side differential Beidou reference station;

[0055] The airborne measurement and control link module is used to send the Beidou satellite mask request information from the airborne differential Beidou module back to the ground measurement and control link module; it is used to receive the framed differential Beidou reference information and forward it to the airborne differential Beidou module;

[0056] The airborne differential Beidou module is used to generate Beidou satellite mask request information; and to combine the framed differential Beidou reference information with the Beidou satellite data received by the airborne differential Beidou module itself, perform sub-positioning calculations, and generate positioning information.

[0057] During data transmission, the satellite data of the Beidou satellites requested by the Beidou satellite mask request information and within the same line of sight as the airborne terminal have the highest priority and are broadcast first.

[0058] The aforementioned Beidou satellite mask request information is generated based on the satellite mask situation actually captured by the airborne differential Beidou module.

[0059] The number of frames used by the aforementioned ground-based differential Beidou reference station is determined based on the bandwidth of the measurement and control link module allocated to the differential Beidou transmission system.

[0060] The aforementioned framed differential Beidou reference information is sent at a transmission layer that is fixedly divided into 5 information frames; the transmission layer fixes the length of each information frame to 64 bytes, for a total of 320 bytes.

[0061] The first information frame in the aforementioned transmission layer carries the location parameters of the ground-side differential Beidou reference station, time information, satellite masks for selection, signal masks and unit masks.

[0062] The first information frame of the aforementioned transport layer also carries observed satellite data and signal data if there is free space.

[0063] The structure of the aforementioned information frame is as follows Figure 3 As shown:

[0064] Guide word: used to mark the beginning of data transmission;

[0065] Total frame number: the sum of all non-empty frames. When an empty frame is transmitted, the total frame number is 0.

[0066] Frame number: the Nth non-empty frame in a certain epoch, N≤5, the frame number is 0 when an empty frame is transmitted;

[0067] Presentation layer message data: used to transmit satellite ephemeris data; the presentation layer message data is divided into three parts: message header, satellite data and signal data;

[0068] Checksum: used to detect errors during data transmission.

[0069] The method for sending the above-mentioned framed differential Beidou reference information is as follows:

[0070] When there is no satellite signal: 5 empty frames are sent continuously, and the presentation layer message data of each frame only contains the message header, and the rest is filled with "0"; that is: epoch (K) empty frame → epoch (K) empty frame → epoch (K) empty frame → epoch (K) empty frame → epoch (K) empty frame → epoch (K+1) empty frame → epoch (K+1) empty frame → epoch (K+1) empty frame → epoch (K+1) empty frame…

[0071] When the number of valid satellites is 1 to 2 stars: 1 data frame and 4 empty frames are sent; that is, when the Beidou original observation quantity does not exceed 2 stars, the Beidou message is sent in one frame, and the sending order is: epoch (K) frame 1→empty frame→empty frame→empty frame→empty frame→epoch (K+1) frame 1→empty frame→empty frame→empty frame→empty frame….

[0072] When the number of valid satellites is 3 to 6: send 2 data frames and 3 empty frames; that is: epoch (K) frame 1 → epoch (K) frame 2 → empty frame → empty frame → empty frame → epoch (K+1) frame 1 → epoch (K+1) frame 2 → empty frame → empty frame → empty frame…

[0073] When the number of valid satellites is 7 to 10: send 3 data frames and 2 empty frames; that is: epoch (K) frame 1 → epoch (K) frame 2 → epoch (K) frame 3 → empty frame → empty frame → epoch (K+1) frame 1 → epoch (K+1) frame 2 → epoch (K+1) frame 3 → empty frame → empty frame…

[0074] When the number of effective satellites is 11 to 14: send 4 data frames and 1 empty frame; that is: epoch (K) frame 1 → epoch (K) frame 2 → epoch (K) frame 3 → epoch (K) frame 4 → empty frame → epoch (K+1) frame 1 → epoch (K+1) frame 2 → epoch (K+1) frame 3 → epoch (K+1) frame 4 → empty frame…

[0075] When the number of effective satellites is 15 to 18: 5 frames containing data are sent continuously, namely: epoch (K) frame 1 → epoch (K) frame 2 → epoch (K) frame 3 → epoch (K) frame 4 → epoch (K) frame 5 → epoch (K+1) frame 1 → epoch (K+1) frame 2 → epoch (K+1) frame 3 → epoch (K+1) frame 4 → epoch (K+1) frame 5…

[0076] Among them, the maximum number of satellites in the differential Beidou reference information is 18. According to the transmission rules of 5-frame data, when there are 18 satellites, the number of satellites included in the 1st, 2nd, 3rd, 4th and 5th frames of data are 2, 4, 4, 4 and 4 respectively.

[0077] When the information frame containing the aforementioned presentation layer message data is the first frame, the message header includes the ground-side differential Beidou reference station position parameters and epoch time.

[0078] The remaining information frame of the aforementioned transport layer carries the remaining satellite masks, signal masks and unit masks, as well as the corresponding satellite data and signal data, so as to complete the subsequent positioning processing.

[0079] The presentation layer message data is divided into three parts: message header, satellite data and signal data, see Figure 4 ;

[0080] a) Message header

[0081] There are two cases for the presentation layer message header. In one case, the message data frame is the first frame, and the message header contains the reference station location parameters and epoch time. The corresponding message header length is 204 bits, such as Figure 5 shown.

[0082] Another case is that the message data is from the second frame to the fifth frame, then the message header does not contain the reference station location parameters and epoch time, and the corresponding message header length is 15 bits, such as Figure 6 shown.

[0083] b) Satellite data

[0084] Satellite data in the presentation layer is as follows Figure 7 shown.

[0085] Nsat refers to the total number of bits in the satellite mask (DF394) that are 1. Each data field is repeated Nsat times, and the data order is determined by the bit order of the satellite mask.

[0086] c) Signal data

[0087] Presentation layer signal data such as Figure 8 shown.

[0088] Ncell refers to the total number of bits in the cell mask (DF396) that are 1. Each data field is repeated Ncell times, and the data order is determined by the bit order of the cell mask.

[0089] Regarding the maximum number of bytes. According to the above detailed explanation of the transport layer and its internal presentation layer fields, the transport layer data length is:

[0090] Len1=8+6+24=38(bit)

[0091] Calculated based on the maximum capacity, the maximum number of satellites is 18, that is, Nsat = 18, and it also contains B1, B3 military code or civil code observations (military code and civil code do not exist at the same time), that is, Ncell = 36, which is transmitted in five valid information frames, of which the first frame only contains 2 satellites, and the data length is:

[0092] Len_frame(1)=Len1+204+18*2+44*4=454(bit)

[0093] Frames 2 to 5 contain 4 satellites, and the data length is:

[0094] Len_frame(2, 3, 4, 5)=Len1+15+18*4+44*8=477(bit)

[0095] The length of each data frame is fixed to 64 bytes. If the length of the above data frame is less than 64 bytes, 0 is added before the check word.

[0096] Example 2. A differential Beidou transmission system based on a measurement and control link, see Figure 1-8 , including: ground-side differential Beidou base station, ground-side measurement and control link module, airborne measurement and control link module, and airborne differential Beidou module.

[0097] Data is transmitted between the ground-end differential Beidou base station and the ground-end measurement and control link module through wired communication, data is transmitted between the airborne measurement and control link module and the airborne differential Beidou module through wired communication, and data is transmitted between the ground-end measurement and control link module and the airborne measurement and control link module through wireless communication.

[0098] The ground-side differential Beidou reference station is composed of a differential Beidou receiver and an antenna. Its main function is to capture and track Beidou satellite information, generate differential Beidou reference information, and frame the differential Beidou reference information. Subsequently, the framed information is passed to the ground-side measurement and control link system for further transmission and processing. In addition, the reference station can also prioritize the signals of Beidou satellites in the same line of sight as the airborne end according to the Beidou satellite mask request information sent by the airborne end of the drone, generate differential Beidou reference information and send it.

[0099] The ground-side measurement and control link module is composed of a ground-side transceiver and a ground-side antenna. Its main responsibility is to send the framed differential Beidou reference information to the airborne measurement and control link module through wireless communication. At the same time, the system is also responsible for receiving Beidou satellite mask request information from the airborne measurement and control link, and forwarding these signals to the ground-side differential Beidou reference station for processing;

[0100] The airborne measurement and control link module is composed of an airborne transceiver and a 3186-airborne antenna. It sends the Beidou satellite mask request information from the airborne differential Beidou module back to the ground measurement and control link module through the measurement and control link; at the same time, it receives the differential Beidou reference information uploaded from the ground end and passes it to the airborne differential Beidou module for processing.

[0101] The airborne differential Beidou module is composed of an airborne data processing device, an airborne differential Beidou receiver and an antenna. Its function is to receive the positioning signal sent by the Beidou satellite through the airborne differential Beidou receiver and the antenna, and send it to the airborne data processing device. The airborne data processing device generates Beidou satellite mask request information based on the collected ephemeris data and sends it to the airborne measurement and control link module. At the same time, the airborne data processing device receives the differential Beidou reference information transmitted by the measurement and control link system, combines this information with the Beidou satellite data received by the airborne differential Beidou receiver, performs sub-positioning calculations, and generates high-precision positioning information.

[0102] Furthermore, the BeiDou satellite mask request information is generated based on the satellite mask actually captured by the airborne differential BeiDou module. The main purpose of this differential BeiDou satellite mask request is to ensure that the airborne end can receive enough satellite signals within the common field of view with the ground-based differential BeiDou base station to optimize the accuracy and integrity of the positioning data.

[0103] Furthermore, the number of frames used by the ground-based differential BeiDou base station is determined by the measurement and control link bandwidth allocated to the differential BeiDou system. Usually, this number is between 4 and 6 frames.

[0104] Furthermore, the first frame in the transmission layer is mainly responsible for carrying the location parameters, time information, satellite masks, signal masks and unit masks for selection of the ground-side differential Beidou reference station, and will also include some observed satellite data and signal data if there is free space. The subsequent sub-frames are mainly responsible for carrying more satellite signal masks and unit masks, as well as their satellite data and signal data, in order to complete the subsequent positioning processing.

[0105] Furthermore, during the frame transmission process, the satellite data contained in the Beidou satellite mask request information will be broadcast first with the highest priority. Subsequently, the satellite data in each frame will be sorted and sent according to the numerical value of the satellite mask. The broadcasting order follows the natural number order starting from 1 (i.e. 1, 2, 3...). In addition, this order must correspond to the satellite mask listed in the first frame to maintain coherence and consistency.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the field can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A differential Beidou transmission system based on a measurement and control link, characterized in that: include: The ground-based differential Beidou reference station, based on the Beidou satellite mask request information, prioritizes the information of Beidou satellites in the same line of sight as the airborne end, generates corresponding differential Beidou reference information, and frames the differential Beidou reference information; The ground-side measurement and control link module is used to send the framed differential Beidou reference information to the airborne measurement and control link module through wireless communication; Used to receive Beidou satellite mask request information from the airborne measurement and control link module and forward it to the ground-based differential Beidou reference station; The airborne measurement and control link module is used to send the Beidou satellite mask request information from the airborne differential Beidou module back to the ground measurement and control link module; it is used to receive the framed differential Beidou reference information and forward it to the airborne differential Beidou module; The airborne differential Beidou module is used to generate Beidou satellite mask request information; and to combine the framed differential Beidou reference information with the Beidou satellite data received by the airborne differential Beidou module itself, perform sub-positioning calculations, and generate positioning information.

2. The differential Beidou transmission system based on the measurement and control link according to claim 1 is characterized in that: During data transmission, the satellite data of the Beidou satellites requested by the Beidou satellite mask request information and within the same line of sight as the airborne terminal have the highest priority and are broadcast first.

3. The differential Beidou transmission system based on the measurement and control link according to claim 1 is characterized in that: The Beidou satellite mask request information is generated based on the satellite mask situation actually captured by the airborne differential Beidou module.

4. The differential Beidou transmission system based on the measurement and control link according to claim 1 is characterized in that: The number of frames used by the ground-based differential Beidou reference station is determined based on the bandwidth of the measurement and control link module allocated to the differential Beidou transmission system.

5. The differential Beidou transmission system based on the measurement and control link according to claim 1 is characterized in that: After framing, the differential Beidou reference information is sent at the transport layer which is fixedly divided into 5 information frames; the transport layer fixes the length of each information frame to 64 bytes, for a total of 320 bytes.

6. The differential Beidou transmission system based on the measurement and control link according to claim 5 is characterized in that: The first information frame in the transport layer carries the location parameters of the ground-based differential Beidou reference station, time information, satellite mask for selection, signal mask and unit mask.

7. The differential Beidou transmission system based on the measurement and control link according to claim 6 is characterized in that: The first information frame of the transport layer also carries observed satellite data and signal data if there is free space.

8. The differential Beidou transmission system based on the measurement and control link according to claim 5, characterized in that: The structure of the information frame is as follows: Guide word: used to mark the beginning of data transmission; Total frame number: the sum of all non-empty frames. When an empty frame is transmitted, the total frame number is 0. Frame number: the Nth non-empty frame in a certain epoch, N≤5, the frame number is 0 when an empty frame is transmitted; Presentation layer message data: used to transmit satellite ephemeris data; the presentation layer message data is divided into three parts: message header, satellite data and signal data; Checksum: used to detect errors during data transmission.

9. The differential Beidou transmission system based on the measurement and control link according to claim 8, characterized in that: The method for sending differential Beidou reference information after framing is as follows: When there is no satellite signal: 5 empty frames are sent continuously, and the presentation layer message data of each frame only contains the message header, and the rest is filled with "0"; When the number of valid satellites is 1 to 2: send 1 data frame and 4 empty frames; When the number of valid satellites is 3 to 6: send 2 data frames and 3 empty frames; When the number of valid satellites is 7 to 10: send 3 data frames and 2 empty frames; When the number of valid satellites is 11 to 14: send 4 data frames and 1 empty frame; When the number of valid satellites is 15 to 18: send 5 data frames continuously.

10. The differential Beidou transmission system based on the measurement and control link according to claim 8, characterized in that: When the information frame containing the presentation layer message data is the first frame, the message header includes the position parameters and epoch time of the ground-side differential Beidou reference station.

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