Multi-satellite multi-frequency precise point positioning precise message broadcasting method

Abstract

The application discloses a multi-satellite multi-frequency precise point positioning precise message broadcasting method, and the broadcasting method comprises the following steps: S1, using ephemeris parameters to characterize satellite ephemeris; S2, arranging basic ephemeris and navigation auxiliary information; S3, setting different information types and corresponding navigation information according to the requirement of information update frequency; S4, setting the message broadcasted by each satellite and the corresponding order according to the frequency of the satellite and the number of cooperative satellites; and S5, broadcasting the message. By adopting the method, the technical problem that the number of satellites is large, the amount of message data is large, and the communication efficiency of the message is low in the prior art can be solved, the broadcasting content of the precise message is simplified, the efficiency of the message broadcasting is improved, the amount of data broadcasted by a single satellite is reduced, and the effect that the ground user terminal collects the required message for positioning in a short time is ensured.

Description

Technical Field

[0001] This invention relates to the field of low-Earth orbit navigation satellite augmentation, and in particular to a method for broadcasting precise messages using multi-satellite, multi-frequency precision point positioning. Background Technology

[0002] With the continuous expansion and deepening of Global Navigation Satellite System (GNSS) applications in civilian and military fields, people have increasingly higher requirements for GNSS systems. These requirements not only include minimizing positioning time, improving positioning accuracy, and enhancing service quality in harsh environments, but also maximizing the use of other means to expand the system's application scope and provide backup service capabilities. Therefore, it is essential to conduct research and demonstration on navigation enhancement / backup systems. With the increasing popularity of various low-Earth orbit (LEO) constellations both domestically and internationally, their characteristics of low-altitude orbit with minimal attenuation, high speed, global coverage, and high-power communication signal transmission provide natural advantages for navigation enhancement. Using LEO satellites for navigation enhancement, backup, and even independent navigation services has become a hot topic of interest for academic and industrial communities both domestically and internationally.

[0003] Low-Earth orbit (LEO) navigation satellites enhance navigation performance through information enhancement and signal enhancement. Information enhancement improves the accuracy and reliability of navigation and positioning by correcting errors in the satellite navigation and positioning system. Information enhancement does not provide observations; it only provides information to eliminate GNSS system errors and improve navigation and positioning performance. To improve the positioning accuracy of navigation services, LEO satellites must broadcast their own precise orbits and clock biases, as well as those of medium- and high-Earth orbit (MEO) satellites. Simultaneously, to improve the integrity of navigation services, information such as system integrity also needs to be broadcast. Due to the large number of satellites and the large volume of message data, it is necessary to streamline the content of the precision messages broadcast while improving the efficiency of message broadcasting. This reduces the amount of data broadcast per satellite while ensuring that ground user terminals can collect the necessary positioning messages within a short time. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and propose a multi-satellite, multi-frequency, precise single-point positioning method for precise message broadcasting.

[0005] Therefore, the present invention adopts the following technical solution:

[0006] This invention proposes a method for broadcasting precise messages using multi-satellite multi-frequency precise single-point positioning. Each frame of the message is 1000 bits long and contains information type and navigation information. The information type is 6 bits long and the navigation information is 917 bits long. The message is designed in the form of data blocks with a fixed length. It is arranged according to the information type based on the information update frequency requirements, and each information type corresponds to a navigation information structure.

[0007] The broadcasting method includes the following steps:

[0008] S1. Characterize the satellite ephemeris using ephemeris parameters;

[0009] S2. Arrange the basic ephemeris and navigation aid information;

[0010] S3. Based on the information update frequency requirements, set different information types and their corresponding navigation information;

[0011] S4. Based on the satellite frequency and the number of cooperating satellites, set the message to be broadcast by each satellite and the corresponding order;

[0012] S5. Broadcast the aforementioned message.

[0013] Furthermore, the ephemeris parameters are characterized using 18 parameters, denoted as... , ,in, For ephemeris reference time, These are the basic orbital parameters, also known as the reference ephemeris, representing only the satellite's orbital parameters at the reference time. They are, in order: the semi-major axis orbit at the observation time and the orbit at the reference time. Difference, orbital eccentricity, orbital inclination, and right ascension of the ascending node at the observation time and reference time The difference, the argument of perigee, the mean perigee at reference time, the rate of change of the semi-major axis of the orbit, and the rate of change of the mean angle correction of the orbit; The long-term perturbation parameters of the orbit are, in order: the rate of change of orbital inclination, the rate of change of right ascension of the ascending node, and the correction for the mean angular velocity of the orbit. The short-term perturbation parameters of the track are, in order: the amplitude corrected by the cosine harmonic term of the ascending node angular distance, the amplitude corrected by the sine harmonic term of the ascending node angular distance, the amplitude corrected by the cosine harmonic term of the track half-axis, the amplitude corrected by the sine harmonic term of the track half-axis, the amplitude corrected by the cosine harmonic term of the track inclination, and the amplitude corrected by the sine harmonic term of the track inclination.

[0014] Furthermore, the first 555 bits of the navigation information are used to broadcast basic navigation information, and the last 362 bits are used to broadcast navigation assistance information. The navigation assistance information broadcast is different for different information types.

[0015] Furthermore, the basic navigation information includes satellite PRN, message data version number, global integrity status, ephemeris parameters, clock bias parameters, and group delay correction parameters. The navigation assistance information includes ionospheric delay correction model parameters, satellite yaw angle, BDT-UTC time synchronization parameters, BDT-GNSS time synchronization parameters, simplified almanac, and satellite health status spatial signal accuracy index.

[0016] Furthermore, in step S5, a multi-satellite, multi-frequency collaborative method is adopted for broadcasting. Specifically, at least two satellites are used, namely Satellite 1 and other satellites, for broadcasting.

[0017] Furthermore, the broadcasting method is as follows: for the satellite ephemeris, clock bias, and simplified almanac that need to be broadcast, half of them are broadcast on the first frequency point of Satellite 1, and the rest are broadcast on the second frequency point of Satellite 1; other satellites broadcast satellite ephemeris, clock bias, and simplified almanac on their first and second frequency points, but in a different order than the satellites.

[0018] Furthermore, the message broadcasting order between Satellite 1 and other satellites can be dynamically adjusted depending on the number of satellites.

[0019] The present invention has the following beneficial effects:

[0020] (1) Less data volume: Based on the characteristics of low-orbit satellite navigation systems, without affecting navigation performance, parameters such as "ionospheric delay correction model parameters" and "EOP parameters" in traditional medium and high orbit satellite messages have been removed, greatly reducing the amount of precision message data.

[0021] (2) The ephemeris is characterized by 18 parameters. Compared with medium and high orbit satellites, low orbit satellites are affected by the Earth's non-spherical gravity and atmospheric drag, and their orbital perturbations are more complex. More precise models are needed to approximate the orbit. This invention uses 18 parameters to characterize the ephemeris of low orbit satellites, which has the advantages of high accuracy and strong extrapolation ability.

[0022] (3) The order of information broadcasting can be flexibly adjusted: the order of broadcasting different information types can be adjusted. Without changing the software and hardware, it can be flexibly adjusted according to the number of cooperating satellites and the user's positioning time requirements.

[0023] (4) High broadcasting efficiency: The system adopts a multi-satellite and multi-frequency collaborative method to broadcast messages. Different broadcasting sequences can be configured between frequencies to coordinate broadcasting and ensure that users receive all messages as soon as possible. The time for user terminals to collect all the messages required for positioning is reduced to at least 25% to 50% of the original time. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the basic CNAV frame structure in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the CNAV information type 10 arrangement format in an embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram of the CNAV information type 11 arrangement format in an embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram of dual-satellite dual-frequency coordinated broadcasting in an embodiment of the present invention. Detailed Implementation

[0028] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be fully described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0030] This patent eliminates the "ionospheric delay correction model parameters," "simplified almanac," "EOP parameters," and "BGTO parameters" found in traditional medium- and high-orbit satellite messages, significantly reducing the amount of precise message data. It uses 18 parameters to characterize the ephemeris of low-orbit satellites, offering advantages such as high accuracy and strong extrapolation capabilities. The broadcast order of different information types is adjustable, allowing for flexible adjustments based on the number of cooperating satellites and user positioning time requirements without changing the software or hardware. Coordinated broadcasting through different inter-frequency and inter-satellite configurations ensures users receive all messages as quickly as possible. The time required for user terminals to collect all the messages needed for positioning is greatly reduced.

[0031] The main steps in using this patent include:

[0032] (1) The satellite ephemeris is characterized according to the 18 parameters proposed in this patent;

[0033] (2) Arrange the basic ephemeris and navigation aid information;

[0034] (3) Set different information types and their corresponding navigation information according to the information update frequency requirements;

[0035] (4) Based on the satellite frequency and the number of cooperating satellites, set the message broadcast by each satellite and the corresponding order;

[0036] (5) Broadcast the telegram.

[0037] In some embodiments, the technical solution of the present invention is:

[0038] From the perspective of data source, messages broadcast by low-Earth orbit (LEO) satellites can be divided into LEO satellite messages themselves and messages from medium- and high-Earth orbit (MEO) satellite navigation systems. From the perspective of real-time performance, they can be divided into real-time information and non-real-time information. The information content and data length of the precision message designed in this invention are shown in Table 1:

[0039] Table 1. Contents and Data Length of Precision Messages

[0040]

[0041] Unlike medium and high orbit satellites, low orbit satellites are subject to greater non-spherical gravity and atmospheric drag from the Earth, resulting in more complex orbital perturbations. This requires more precise models to approximate the orbit. This invention uses 18 parameters to characterize the ephemeris of low orbit satellites.

[0042]

[0043] in:

[0044] (1) For ephemeris reference time

[0045] (2) These are the basic orbital parameters, also known as the reference ephemeris, representing only the satellite's orbital parameters at the reference time. They are, in order: the semi-major axis orbit at the observation time and the orbit at the reference time. Difference, orbital eccentricity, orbital inclination, and right ascension of the ascending node at the observation time and reference time The difference, the argument of perigee, the mean perigee at reference time, the rate of change of the semi-major axis of the orbit, and the rate of change of the mean angle correction of the orbit;

[0046] (3) The long-term perturbation parameters of the orbit are, in order: the rate of change of orbital inclination, the rate of change of right ascension of the ascending node, and the correction for the mean angular velocity of the orbit.

[0047] (4) The short-term (T / 2) perturbation parameters of the track are, in order: the amplitude corrected by the cosine harmonic term of the ascending node angle distance, the amplitude corrected by the sine harmonic term of the ascending node angle distance, the amplitude corrected by the cosine harmonic term of the track half-axis, the amplitude corrected by the sine harmonic term of the track half-axis, the amplitude corrected by the cosine harmonic term of the track inclination, and the amplitude corrected by the sine harmonic term of the track inclination.

[0048] Navigation message structure

[0049] As required, each frame of the broadcast message is 1000 bits long, tentatively using the Turbo (1 / 2) encoding scheme, with each frame containing 2000 symbol bits, a symbol rate of 2000 sps, and a broadcast cycle of 1 second. The basic frame structure definition is as follows: Figure 1 As shown:

[0050] Before encoding, the original information frame is 1000 bits long, containing fixed information (59 bits), including the synchronization header (Pre), the broadcast satellite number (PRN), the information type (MesType), and the system time (WN and SOW). The information frame ends with a checksum (CRC) (24 bits). The navigation information (917 bits) can be arranged according to the required message type, with a maximum of 63 information types that can be defined.

[0051] The first 24 symbol bits of each message frame are the frame synchronization header (Pre), with a value of 0xE24DE8, i.e., 111000100100110111101000, and the most significant bit is sent first.

[0052] Each message frame is 988 bits long before error correction coding, including the PRN number (10 bits), information type (6 bits), integer cycle count (WN, 13 bits), week-second count (SOW, 18 bits), navigation information (917 bits), and cyclic redundancy check (CRC, 24 bits). These flags and lengths are consistent with the BeiDou Navigation Satellite System by default for unified ground receiver design and can be modified. The PRN number, information type, integer cycle count, week-second count, and navigation information all participate in the cyclic redundancy check calculation.

[0053] Navigation information is designed in the form of data blocks with fixed lengths, and arranged according to information type based on the required information update frequency.

[0054] The basic navigation information in the navigation information data block includes: satellite PRN, message data version number, global integrity status, ephemeris parameters, clock error parameters, group delay correction parameters, etc., with a length of 551 bits.

[0055] The navigation information data block contains navigation aid information including code deviation, phase deviation, satellite attitude, BDT-UTC time synchronization parameters, BDT-GNSS time synchronization (BGTO) parameters, simplified almanac (full network), etc.

[0056] MesType (6 bits) can define up to 63 message types. Currently, two valid message types are defined: 10 and 11. The format is as follows: Figure 2 and Figure 3 .

[0057] Table 2. Content of Two Information Broadcasts

[0058]

[0059] The broadcast order of information types can be dynamically adjusted. Each time a user receiver receives a navigation message, it identifies the information type according to MesType.

[0060] Navigation message broadcasting order

[0061] According to the defined 10 and 11 information types, each low-Earth orbit satellite needs to broadcast the following information: its basic navigation information and 10 GNSS satellite messages (10 is the typical value for a low-Earth orbit satellite to be visible to medium and high-Earth orbit satellites).

[0062] The frame period is 1 second, and every 10 seconds it can broadcast basic navigation information from this satellite plus navigation messages from 9 other navigation systems. Currently, the format and definition of the basic navigation message from this satellite are consistent with those of GNSS navigation messages, and it is broadcast in the first 555 bits of the "navigation information" section of each frame. The last 362 bits of the "navigation information" section of each frame are used to broadcast other navigation auxiliary information from this satellite.

[0063] 10 and 11 can be configured with a broadcast cycle of N seconds. This configuration does not affect the number of satellites broadcasting basic navigation information, but only the broadcast frequency of other navigation auxiliary information in this system. It can be dynamically adjusted according to the broadcast requirements of various auxiliary information. BDT-UTC time synchronization parameters, BDT-GNSS time deviation parameters, and simplified almanac are parameters of this system. The parameters for broadcasting low-Earth orbit satellites across the entire network are the same. Different broadcast timing sequences can be configured between frequencies to coordinate broadcasting and ensure that users receive all information as quickly as possible.

[0064] Based on a 10-second broadcast cycle, the basic navigation messages of this satellite and nine other satellites are broadcast (polling broadcast, with the same priority). The broadcast cycle analysis of various messages is assumed to be performed according to the information broadcast sequence of 11, 10, 11, 11, 11, 10, 11, 11, 11.

[0065] Table 3. Repetition cycle of various types of telegram information (single satellite, single branch)

[0066]

[0067] Multi-satellite and multi-frequency collaborative broadcasting method

[0068] The statistical results in Table 3 show that the repetition period of the simplified almanac is approximately 20 seconds. By employing inter-frequency coordination, the repetition period is shortened to half that of a single-satellite, single-branch system, which can meet the 10-second broadcast requirement. Figure 4 .

[0069] Taking an almanac as an example, the broadcast of simplified almanacs across the entire network is interconnected, with simplified almanacs from all valid satellites being broadcast in a cyclical manner. For instance, on the ground, simplified almanacs for satellites 2, 4, 5, 6, 7, 8, 9, and 10 are listed. Satellite 1 frequency point A broadcasts simplified almanacs for satellites 2, 4, 5, 6, 7, 8, 9, and 10; Satellite 1 frequency point B broadcasts simplified almanacs for satellites 6, 5, 4, 2, 10, 9, 8, and 7, and so on, in a cyclical manner.

[0070] Therefore, the time for a user to receive a complete set of simplified almanacs can be reduced to half, approximately 10 seconds. Similarly, this method can be used when broadcasting navigation messages from other systems, reducing the time for users to receive navigation messages from medium- and high-orbit systems to half that of single-satellite single-path systems, or it can be used for broadcasting messages from systems other than BeiDou, such as GPS and Galileo.

[0071] Low-Earth orbit (LEO) navigation satellites serve as positioning sources, broadcasting their own messages. Simultaneously, as enhancements to medium- and high-Earth orbit (MEO) navigation systems, they also need to broadcast MEO messages. LEO satellites are subject to greater influence from Earth's non-spherical gravity and atmospheric drag, resulting in more complex orbital perturbations. An 18-parameter characterization method is used to represent the satellite ephemeris. Navigation information data is divided into basic navigation information and navigation assistance information, and a flexible and adjustable message arrangement method is designed to meet the real-time requirements of different information broadcasting types. Due to the large number of LEO navigation constellations, and the need for navigation satellites to broadcast messages from GPS, BeiDou, and other MEO navigation satellites, a multi-satellite, multi-frequency system broadcasting strategy is designed. This reduces the amount of data broadcast per satellite while ensuring that user terminals can collect all the necessary messages for positioning within 10 seconds, significantly shortening the initial positioning time.

[0072] In the description of this specification, references to terms such as "an embodiment" and "example" refer to specific features, structures, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms are not necessarily intended to refer to corresponding embodiments or examples in a suitable manner.

[0073] It must be pointed out that the above description of the embodiments is not intended to limit the invention but only to help understand the core idea of ​​the invention. For those skilled in the art, any improvements to the invention and equivalent alternatives made to the invention without departing from the principle of the invention are also within the scope of protection of the claims of the invention.

Claims

1. A method for broadcasting precision messages using multi-satellite, multi-frequency, precise single-point positioning, characterized in that: Each frame of the message is 1000 bits long and contains information type and navigation information. The information type is 6 bits long and the navigation information is 917 bits long. The message is designed in the form of data blocks with a fixed length. The data blocks are arranged according to the information type based on the information update frequency requirements. Each information type corresponds to a navigation information structure. The broadcasting method includes the following steps: S1. Characterize the satellite ephemeris using ephemeris parameters; S2. Arrange the basic ephemeris and navigation aid information; S3. Based on the information update frequency requirements, set different information types and their corresponding navigation information; S4. Based on the satellite frequency and the number of cooperating satellites, set the message to be broadcast by each satellite and the corresponding order; S5. Broadcast the aforementioned message; The ephemeris parameters are characterized using 18 parameters, denoted as , ,in, For ephemeris reference time, These are the basic orbital parameters, also known as the reference ephemeris, representing only the satellite's orbital parameters at the reference time. They are, in order: the semi-major axis orbit at the observation time and the orbit at the reference time. Difference, orbital eccentricity, orbital inclination, and right ascension of the ascending node at the observation time and reference time The difference, the argument of perigee, the mean perigee at reference time, the rate of change of the semi-major axis of the orbit, and the rate of change of the mean angle correction of the orbit; The long-term perturbation parameters of the orbit are, in order: the rate of change of orbital inclination, the rate of change of right ascension of the ascending node, and the correction for the mean angular velocity of the orbit. The short-term perturbation parameters of the track are, in order: the amplitude corrected by the cosine harmonic term of the ascending node angular distance, the amplitude corrected by the sine harmonic term of the ascending node angular distance, the amplitude corrected by the cosine harmonic term of the track half-axis, the amplitude corrected by the sine harmonic term of the track half-axis, the amplitude corrected by the cosine harmonic term of the track inclination, and the amplitude corrected by the sine harmonic term of the track inclination.

2. The method according to claim 1, characterized in that, The first 555 bits of the navigation information are used to broadcast basic navigation information, and the last 362 bits are used to broadcast navigation assistance information. The navigation assistance information broadcast is different for different information types.

3. The method according to claim 2, characterized in that, The basic navigation information includes satellite PRN, message data version number, global integrity status, ephemeris parameters, clock bias parameters, and group delay correction parameters. The navigation aid information includes ionospheric delay correction model parameters, satellite yaw angle, BDT-UTC time synchronization parameters, BDT-GNSS time synchronization parameters, simplified almanac, and satellite health status spatial signal accuracy index.

4. The method according to claim 1, characterized in that, In step S5, a multi-satellite, multi-frequency collaborative method is used for broadcasting. Specifically, at least two satellites are used, namely Satellite 1 and other satellites, for broadcasting.

5. The method according to claim 4, characterized in that, The broadcasting method is as follows: for the satellite ephemeris, clock bias and simplified almanac that need to be broadcast, half of them are broadcast on the first frequency of satellite one, and the rest are broadcast on the second frequency of satellite one. Other satellites broadcast satellite ephemeris, clock bias, and simplified almanacs on their first and second frequencies, but in a different order than Satellite 1.

6. The method according to claim 5, characterized in that, Depending on the number of satellites, the order in which Satellite 1 and other satellites broadcast messages can be dynamically adjusted.

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