Beidou short message real estate co-seismic deformation transmission and GNSS (Global Navigation Satellite System) resolving method

Abstract

The invention discloses a Beidou short message real estate co-seismic deformation transmission and GNSS (Global Navigation Satellite System) resolving method, which belongs to the technical field of geophysics, is used for GNSS co-seismic deformation transmission and resolving, and comprises the following steps: a user side performs co-seismic deformation compression, executes information coding and information subpackage, obtains a short message and broadcasts an information subpackage; and the server side performs information sub-packet checking, information decoding, co-seismic deformation recovery and co-seismic deformation splicing integration. The resolving method comprises the steps that the server side collects SSR correction numbers, generates equivalent distance correction numbers of visible satellites of each BDS SMC broadcast epoch, and encodes the distance correction numbers; and the user side downloads the equivalent distance correction from the Beidou satellite, constructs a positioning model by using the original observation value, the broadcast ephemeris and the equivalent distance correction, and performs co-seismic deformation calculation. According to the invention, reliable transmission of the compressed co-seismic displacement is realized, and the risk of data packet loss in the transmission process of the Beidou short message can be avoided.

Description

Technical Field

[0001] The invention discloses a Beidou short message real estate co-seismic deformation transmission and GNSS solution method, belonging to the field of geophysical technology. Background Art

[0002] Seismic data transmission technology has undergone significant development. Early transmission relied primarily on wireless ultrashortwave, microwave, or spread-spectrum microwave radios. Because ultrashortwave and microwave transmission operate within line-of-sight distances, they require tall antennas to maintain direct line-of-sight distances and are susceptible to interference. With the advancement of communications technology, seismic data transmission technology has also continued to evolve. Currently, seismic data transmission primarily utilizes wired and wireless mobile communication networks. Wired communication networks include Asymmetric Digital Subscriber Line (ADSL), Digital Data Network (DDN), and Synchronous Digital Hybrid (SDH). ADSL is significantly affected by distance and line quality, with transmission distances typically limited to 3–5 km. DDN offers high transmission quality, low latency, and high communication speeds. However, due to high transmission costs and maintenance difficulties, the number of DDN network stations has gradually decreased in recent years. SDH, with its synchronous multiplexing, standard optical interfaces, and robust network management capabilities, has become the primary method for wired data transmission among network stations.

[0003] However, whether using wired or wireless mobile communication networks, after an earthquake, near-field network infrastructure may be damaged, rendering communication impossible. This can create challenges for seismic data transmission. For example, during an earthquake, signals from 20 network stations in a certain area were lost, including 14 wireless stations and 6 wired stations. Therefore, a communication method less susceptible to earthquake damage is necessary as a backup link for data transmission. Satellite communications clearly meet this requirement, but specialized communication satellites (such as Iridium and Inmarsat) are expensive (annual fees can reach tens of thousands of yuan), hindering widespread adoption. Beidou Short Message Communication Service (BDS SMC), a unique feature of the Beidou navigation and positioning system, enables two-way communication via GEO satellites without relying on a network. Therefore, earthquake monitoring stations can transmit critical information to earthquake monitoring centers using only a single set of short message communication equipment costing only a few thousand yuan. This provides a low-cost and highly reliable communication method for transmitting IGS RTS corrections and coseismic deformation data. However, while BDS SMC is a low-cost communication method unaffected by earthquakes, it suffers from bandwidth and frequency limitations, making it incapable of directly transmitting high-frequency GNSS / strong-motion seismometer coseismic deformation data. Furthermore, there is the risk of data loss during transmission. When seismic data transmission technology is unreliable, the accuracy of GNSS coseismic deformation solutions that rely on seismic data transmission is also reduced. Summary of the Invention

[0004] The purpose of the present invention is to provide a Beidou short message real estate co-seismic deformation transmission and GNSS solution method to solve the problem in the prior art that the Beidou short message co-seismic deformation transmission of real estate has low reliability, resulting in inaccurate GNSS co-seismic deformation solution of real estate.

[0005] The BeiDou short message real estate co-seismic deformation transmission method includes: a user end performs co-seismic deformation compression, executes information encoding and information packetization to obtain a short message, broadcasts information sub-packets, and uploads the short message to the BeiDou GEO satellite through the BDS SMC terminal of the user end; a server end downloads the short message from the BeiDou GEO satellite to the BDS SMC terminal of the server end, performs information sub-packet verification, information decoding, co-seismic deformation recovery, and co-seismic deformation splicing and integration.

[0006] The coseismic deformation compression involves dimensionless processing of the coseismic deformation and then rounding it off to the nearest integer: ; Where, Represents the rounding operator, is the GNSS co-seismic displacement time series, is the selected data resolution, is the rounded result; Calculate the integer co-seismic displacement epoch difference between two adjacent epochs Further compress the integral co-seismic displacement: ; Where, and Represents the current epoch and the previous epoch The integer co-seismic displacement value of ; The following conversion formula is used to convert the integer co-seismic displacement time series into an unsigned integer displacement time series: ; Where, is an integer unsigned integer coseismic deformation time series, is the minimum value of the integer co-seismic displacement epoch difference time series; The number of bits required to encode the co-seismic deformation time series of integer and unsigned integer is determined according to the following inequality: ; Where, is the maximum value of the coseismic deformation time series of integer unsigned integer, The number of bits required to binary encode the coseismic deformation time series of unsigned integer.

[0007] The information encoding includes, the encoding format includes a header file and a body file; The header file includes an 8-bit binary start tag, a message type, a message number, a first epoch time, a sampling interval, an epoch number, an initial co-seismic deformation value, an integer epoch differential co-seismic deformation value, and a bit number. The message type is used to distinguish data types. The message number is a unique identifier used to distinguish and sort messages. The first epoch time is determined by the time the information is received and is the number of milliseconds within the hour of transmission. The sampling interval is the time interval between consecutive observation epochs. The epoch number indicates the total number of epochs contained in the information. The initial co-seismic deformation value indicates the initial co-seismic deformation value of the first epoch in the north, east, and sky directions. The integer epoch differential co-seismic deformation value indicates the integer epoch differential co-seismic deformation value in the north, east, and sky directions. The bit number indicates the unsigned integer co-seismic deformation time series in the north, east, and sky directions. The volume file includes all epochs to be transmitted, arranged in the order of north, east and sky. value.

[0008] Information decoding includes, each epoch The value is used to calculate the corresponding The epoch difference value corresponding to the value: ; Where, for Corresponding ; From the first epoch in each direction value Start by accumulating Calculate the subsequent epochs value, will Multiply the value by , get the first BDS SMC decoded value of each epoch The coseismic deformation value of epoch : ; Where, Indicates from the 1st to the The cumulative epoch-by-epoch differential integral coseismic deformation value of epochs, Indicates the The integer epoch-wise difference value of the co-seismic displacement for each epoch.

[0009] When the client and server are transmitting data, after receiving the information sent by the client, the server verifies whether it has received all the information with sequence numbers before the maximum value. If no information is lost, the server will not send any response. If information is lost, the server will send an error message to the client, indicating the smallest sequence number that is lost. When the user receives the error message Error, it resends the corresponding Beidou short message and continues to send subsequent messages in sequence. After all Beidou short messages are sent, the user sends an End message to the server, indicating that the data transmission task has been completed. After receiving the end message, the server checks whether it has received all the data information with sequence numbers before the end message sequence number. If all the short messages have been received, the server replies with an end message End. If any short messages are lost, the server sends another error message Error, indicating the missing minimum sequence number. After receiving the error message Error, the user end retransmits the lost message.

[0010] A GNSS method for calculating coseismic deformation of real estate uses the Beidou short message method for transmitting coseismic deformation of real estate, including collecting SSR corrections broadcast by IGS RTS via the Internet on a server side, determining the position of a user side through daily post-processing RP or PPP and storing the corrections on the server, generating an equivalent range correction for satellites visible at each BDS SMC broadcast epoch based on the user side position and the SSR corrections, encoding the range corrections, and transmitting the corrections to Beidou GEO satellites via a BDS SMC terminal; The user end collects GNSS raw observations and broadcast ephemeris, downloads equivalent distance corrections from BeiDou GEO satellites through the BDS SMC terminal, and uses the GNSS raw observations, broadcast ephemeris, and equivalent distance corrections to construct a TPP positioning model for co-seismic deformation resolution.

[0011] The precise satellite clock error recovered from the SSR correction is: ; ; Where, is the satellite clock error calculated from the broadcast ephemeris, is the precise satellite clock error recovered from the SSR corrections, is the SSR clock correction number, 、 and are three polynomial constant terms, is the current time of the satellite clock error, is the reference time of the satellite clock error, is the time domain point value of the satellite clock error, is the speed of light in a vacuum.

[0012] The precise orbital position of the satellite restored by the SSR correction number is: ; ; ; ; Where, represents the precise satellite orbit ECEF coordinate vector restored using SSR corrections, represents the satellite orbit ECEF coordinate vector calculated by broadcast ephemeris, is the SSR orbit correction number, 、 、 are the radial, tangential and normal corrections to the SSR epoch time, 、 、 are the radial, tangential and normal corrections to the SSR epoch velocity, 、 、 yes In the radial, tangential and normal components, is the time domain point value of the satellite orbit error, and They represent the satellite orbit position vector and velocity vector calculated using the GNSS broadcast ephemeris.

[0013] The TPP positioning model is: ; ; Where, is the time domain point differential carrier phase OMC value after linearization, represents the unit vector of the direction from the receiver to the satellite at the current epoch, Relative to the reference epoch The coseismic deformation increment is equivalent to the three-dimensional coseismic deformation, represents the time domain point difference value of the directional unit vector, is the position of the reference epoch obtained by daily post-processing RP or PPP, is the geometric distance from the user receiver to the GNSS satellite. is the receiver clock bias, is the time-domain point difference of the measurement noise of the IF composite carrier phase observation value, is the time domain point difference score of the satellite orbit error, Indicates the time domain point difference score of the satellite clock error.

[0014] Generating the equivalent range corrections for visible satellites at each BDS SMC broadcast epoch includes calculating the satellite orbit corrections and clock corrections for each SSR epoch within the BDS SMC broadcast interval, and subtracting the precise orbit and clock corrections calculated based on the same broadcast ephemeris from the orbit and clock corrections provided by the broadcast ephemeris to obtain the orbit and clock corrections for each SSR epoch; Calculate the equivalent distance correction for each SSR epoch, the equivalent distance correction for each epoch of satellite orbit correction and clock correction The calculation formula is: ; A first-order polynomial fit is performed on the equivalent distance correction value and the time interval between the SSR broadcast time and the reference time. The constant term represents the equivalent distance correction number, and the first-order term is the correction number for the equivalent distance change rate relative to the reference time.

[0015] Compared with the existing technology, the present invention has the following beneficial effects: the present invention maintains as many epochs as possible, takes into account the high resolution and time correlation of the co-seismic displacement sequence, and solves the problem that the bandwidth and frequency of Beidou short message communication limit the co-seismic deformation data of high-frequency GNSS / strong motion detectors; it realizes the reliable transmission of compressed real estate co-seismic displacements, and can avoid the risk of data packet loss in the transmission process of Beidou short messages. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the flow chart of the GNSS co-seismic displacement solution model based on BDS SMC; Figure 2 This is the flow chart of the coseismic deformation data compression algorithm; Figure 3 This is a diagram showing the normal broadcasting of the Beidou short message transmission mechanism; Figure 4 This is a diagram showing abnormal broadcasting of Beidou short message transmission mechanism; Figure 5 This is the Beidou short message co-seismic displacement transmission flow chart. DETAILED DESCRIPTION

[0017] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0018] The BeiDou short message real estate co-seismic deformation transmission method includes: a user end performs co-seismic deformation compression, executes information encoding and information packetization to obtain a short message, broadcasts information sub-packets, and uploads the short message to the BeiDou GEO satellite through the BDS SMC terminal of the user end; a server end downloads the short message from the BeiDou GEO satellite to the BDS SMC terminal of the server end, performs information sub-packet verification, information decoding, co-seismic deformation recovery, and co-seismic deformation splicing and integration.

[0019] The coseismic deformation compression involves dimensionless processing of the coseismic deformation and then rounding it off to the nearest integer: ; Where, Represents the rounding operator, is the GNSS co-seismic displacement time series, is the selected data resolution, is the rounded result; Calculate the integer co-seismic displacement epoch difference between two adjacent epochs Further compress the integral co-seismic displacement: ; Where, and Represents the current epoch and the previous epoch The integer co-seismic displacement value of ; The following conversion formula is used to convert the integer co-seismic displacement time series into an unsigned integer displacement time series: ; Where, is an integer unsigned integer coseismic deformation time series, is the minimum value of the integer co-seismic displacement epoch difference time series; The number of bits required to encode the co-seismic deformation time series of integer and unsigned integer is determined according to the following inequality: ; Where, is the maximum value of the coseismic deformation time series of integer unsigned integer, The number of bits required to binary encode the coseismic deformation time series of unsigned integer.

[0020] The information encoding includes, the encoding format includes a header file and a body file; The header file includes an 8-bit binary start tag, a message type, a message number, a first epoch time, a sampling interval, an epoch number, an initial co-seismic deformation value, an integer epoch differential co-seismic deformation value, and a bit number. The message type is used to distinguish data types. The message number is a unique identifier used to distinguish and sort messages. The first epoch time is determined by the time the information is received and is the number of milliseconds within the hour of transmission. The sampling interval is the time interval between consecutive observation epochs. The epoch number indicates the total number of epochs contained in the information. The initial co-seismic deformation value indicates the initial co-seismic deformation value of the first epoch in the north, east, and sky directions. The integer epoch differential co-seismic deformation value indicates the integer epoch differential co-seismic deformation value in the north, east, and sky directions. The bit number indicates the unsigned integer co-seismic deformation time series in the north, east, and sky directions. The volume file includes all epochs to be transmitted, arranged in the order of north, east and sky. value.

[0021] Information decoding includes, each epoch The value is used to calculate the corresponding The epoch difference value corresponding to the value: ; Where, for Corresponding ; From the first epoch in each direction value Start by accumulating Calculate the subsequent epochs value, will Multiply the value by , get the first BDS SMC decoded value of each epoch The coseismic deformation value of epoch : ; Where, Indicates from the 1st to the The cumulative epoch-by-epoch differential integral coseismic deformation value of epochs, Indicates the The integer epoch-wise difference value of the co-seismic displacement for each epoch.

[0022] When the client and server are transmitting data, after receiving the information sent by the client, the server verifies whether it has received all the information with sequence numbers before the maximum value. If no information is lost, the server will not send any response. If information is lost, the server will send an error message to the client, indicating the smallest sequence number that is lost. When the user receives the error message Error, it resends the corresponding Beidou short message and continues to send subsequent messages in sequence. After all Beidou short messages are sent, the user sends an End message to the server, indicating that the data transmission task has been completed. After receiving the end message, the server checks whether it has received all the data information with sequence numbers before the end message sequence number. If all the short messages have been received, the server replies with an end message End. If any short messages are lost, the server sends another error message Error, indicating the missing minimum sequence number. After receiving the error message Error, the user end retransmits the lost message.

[0023] A GNSS method for calculating coseismic deformation of real estate uses the Beidou short message method for transmitting coseismic deformation of real estate, including collecting SSR corrections broadcast by IGS RTS via the Internet on a server side, determining the position of a user side through daily post-processing RP or PPP and storing the corrections on the server, generating an equivalent range correction for satellites visible at each BDS SMC broadcast epoch based on the user side position and the SSR corrections, encoding the range corrections, and transmitting the corrections to Beidou GEO satellites via a BDS SMC terminal; The user end collects GNSS raw observations and broadcast ephemeris, downloads equivalent distance corrections from BeiDou GEO satellites through the BDS SMC terminal, and uses the GNSS raw observations, broadcast ephemeris, and equivalent distance corrections to construct a TPP positioning model for co-seismic deformation resolution.

[0024] The precise satellite clock error recovered from the SSR correction is: ; ; Where, is the satellite clock error calculated from the broadcast ephemeris, is the precise satellite clock error recovered from the SSR corrections, is the SSR clock correction number, 、 and are three polynomial constant terms, is the current time of the satellite clock error, is the reference time of the satellite clock error, is the time domain point value of the satellite clock error, is the speed of light in a vacuum.

[0025] The precise orbital position of the satellite restored by the SSR correction number is: ; ; ; ; Where, represents the precise satellite orbit ECEF coordinate vector restored using SSR corrections, represents the satellite orbit ECEF coordinate vector calculated by broadcast ephemeris, is the SSR orbit correction number, 、 、 are the radial, tangential and normal corrections to the SSR epoch time, 、 、 are the radial, tangential and normal corrections to the SSR epoch velocity, 、 、 yes In the radial, tangential and normal components, is the time domain point value of the satellite orbit error, and They represent the satellite orbit position vector and velocity vector calculated using the GNSS broadcast ephemeris.

[0026] The TPP positioning model is: ; ; Where, is the time domain point differential carrier phase OMC value after linearization, represents the unit vector of the direction from the receiver to the satellite at the current epoch, Relative to the reference epoch The coseismic deformation increment is equivalent to the three-dimensional coseismic deformation, represents the time domain point difference value of the directional unit vector, is the position of the reference epoch obtained by daily post-processing RP or PPP, is the geometric distance from the user receiver to the GNSS satellite. is the receiver clock bias, is the time-domain point difference of the measurement noise of the IF composite carrier phase observation value, is the time domain point difference score of the satellite orbit error, Indicates the time domain point difference score of the satellite clock error.

[0027] Generating the equivalent range corrections for visible satellites at each BDS SMC broadcast epoch includes calculating the satellite orbit corrections and clock corrections for each SSR epoch within the BDS SMC broadcast interval, and subtracting the precise orbit and clock corrections calculated based on the same broadcast ephemeris from the orbit and clock corrections provided by the broadcast ephemeris to obtain the orbit and clock corrections for each SSR epoch; Calculate the equivalent distance correction for each SSR epoch, the equivalent distance correction for each epoch of satellite orbit correction and clock correction The calculation formula is: ; A first-order polynomial fit is performed on the equivalent distance correction value and the time interval between the SSR broadcast time and the reference time. The constant term represents the equivalent distance correction number, and the first-order term is the correction number for the equivalent distance change rate relative to the reference time.

[0028] In the present invention, "real estate" refers to an object that forms a fixed connection with the land and cannot be moved at will, including but not limited to land, houses, bridges, dams, underground pipelines, cadastral control points, etc. The "co-seismic deformation of real estate" refers to the three-dimensional displacement (north, east, and sky directions) of the above-mentioned real estate body or the sensor reference point rigidly connected thereto caused by an earthquake event. In the application scenario of co-seismic displacement information, after an earthquake occurs, the present invention can quickly obtain high-precision three-dimensional deformation results by combining the co-seismic displacement data transmitted by Beidou short messages with the GNSS precision solution method. These results are directly applied to the following real estate management scenarios: by analyzing the co-seismic displacement of the structural points of the house, it is determined whether it exceeds the safety threshold, and a preliminary screening of dangerous houses is achieved, providing real-time and reliable deformation data support for post-disaster personnel resettlement, property rights protection and reconstruction planning. In the connection between the co-seismic deformation results and the real estate registration business system, data connection specifications between the displacement monitoring results and the real estate registration system were formulated to ensure that the deformation data format is compatible with the registration system; secondly, the solved three-dimensional deformation results are transmitted back to the server, and then automatically pushed to the earthquake setting assistant, which can be used for post-disaster dangerous house identification.

[0029] The TPP positioning model (standard time-domain point positioning model) used in this paper directly calculates the station displacement by differencing the carrier observations between the current epoch and the reference epoch. This model avoids the cumulative displacement calculation process used in the VADASE model, thereby reducing the impact of epoch noise. The standard TPP model must meet the following conditions: the raw GNSS observations remain continuous for several minutes, and their ionospheric ambiguity can be eliminated through differencing; at the same time, atmospheric conditions do not change suddenly within a few minutes of the earthquake, and the residual of the tropospheric error, after correction by the a priori model, can be maintained within a few centimeters. However, in actual calculations, the displacement calculated by the TPP method can experience large step changes due to discontinuities in the observation data. This error accumulates over time, resulting in false coseismic displacement peaks in the displacement series. These false peaks can have two impacts on the subsequent determination of earthquake elements: first, they can interfere with the convergence of the estimated PGD magnitude time series, and second, they can cause misjudgment of the arrival time of seismic waves. Therefore, once a cycle slip occurs in the TPP observation, cycle slip detection is required, and the repaired cycle slip integer solution is accumulated from the reference epoch to the current epoch, and then corrected to the deionized combined time domain point difference observation value.

[0030] IGS RTS is a real-time positioning service. Its real-time SSR orbit and clock products can be used to extract GNSS co-seismic displacements. However, IGS real-time precise ephemeris is broadcast over the Internet, and during near-field earthquakes, it can be interrupted due to server or network failures. BDS SMC (clock correction prediction technology based on the BeiDou Navigation Satellite System) can be used as a low-cost communication method to transmit IGS RTS corrections, providing technical support for GNSS co-seismic displacement calculations.

[0031] According to the RTCM standard protocol, satellite orbit and clock corrections are expressed in SSR format. However, these SSR corrections require a large bandwidth. Taking the GPS system's 1060 message as an example, broadcasting the orbit and clock corrections for 32 GPS satellites in SSR format requires at least 6628 bits. The required bandwidth exceeds the bandwidth capabilities of the BDS-2 RSMC (628 bits per minute) and the BDS-3 GSMC (560 bits per minute). Although the bandwidth of the BDS-3 RSMC has been expanded to 14,000 bits and the transmission frequency is better than 60 seconds, directly broadcasting RTS corrections for multi-mode GNSS systems still faces challenges. To reduce the amount of information to meet bandwidth requirements, the SSR orbit and clock corrections within the BDS SMC transmission interval are uniformly converted into equivalent range corrections, and an encoding strategy consistent with the SSR correction format is designed.

[0032] Similar to the SSR message of the IGS RTS service, the structure of the BDS SMC correction message consists of a header, body, and cyclic redundancy check (CRC). Table 1 lists the header portion of the BDS SMC correction message, including the start tag, minute count, satellite number, and IOD SSR fields. The start tag, containing a 7-bit binary number, marks the beginning of the data packet. The minute count indicates the reference time for the ranging corrections. The satellite number indicates the number of visible satellites whose equivalent range corrections will be broadcast in this message. The IOD SSR represents the SSR version number and is used to match SSR corrections used in different message types. It is generally updated only when the system configuration changes.

[0033] Table 1 BDS SMC correction information header file ; The BDS SMC correction information file contains equivalent range and range rate corrections for all visible satellites. These parameters are provided in satellite order. The format of the satellite-specific portion is detailed in Table 2 and includes fields such as the satellite ID, IODN, range correction, and range rate correction. Each satellite ID can be mapped to a pseudo-random number (PRN). The IODN serves as a reference for users to retrieve broadcast ephemeris. The calculation method for the IODN varies among GNSS systems. For BDS-2 signals, the IODN is calculated based on the ephemeris reference time (TOE) broadcast in the D1 or D2 navigation message. This calculation is performed by dividing TOE by 720 and taking the remainder modulo 240, resulting in a number between 0 and 235. BDS-3 and GPS systems use an 8-bit binary number (IODE) to represent the IODN. The BDS-3 IODE is derived directly from the B-CNAV1 broadcast ephemeris message, while the GPS IODE is derived from the LNAV broadcast ephemeris message. In the GALILEO system, the IODN is represented by the eight least significant bits (LSBs) of the IODnav field broadcast in the I / NAV broadcast ephemeris message. For the GLONASS system, the IODN is determined by the 7-bit binary time parameter (tb) derived from the navigation information transmitted by the GLONASS-M satellites. Bits 0-6 correspond to the 7 bits of the tb field in the GLONASS-M navigation message. Bit 7 is the most significant bit (MSB).

[0034] Table 2 BDS SMC correction information file ; In the entire encoding format of BDS SMC correction information, the blue blocks represent the message header, which has a total size of 24 bits. The green blocks represent the message body, which contains equivalent range corrections to maximize capacity. Each green block corresponds to the specific encoding information for a satellite. The total bandwidth of each satellite correction message is 42 bits. At the end of the message, the 24-bit CRC (CRC-24Q) represented by the gray blocks ensures message integrity verification. Based on the proposed encoding strategy and format, a single BDS-2 RSMC short message can broadcast correction information for 14 satellites, while a single BDS-3 GSMC short message can broadcast correction information for 12 satellites. In addition, a single BDS-3 RSMC short message can accommodate correction information for up to 332 satellites. This data capacity ensures sufficient support for the rapid calculation of GNSS co-seismic displacements.

[0035] The process of GNSS co-seismic displacement solution based on BDS SMC is as follows: Figure 1 As shown in the figure, the system consists of two main parts: the server and the user. The whole process can be described as follows: First, the server collects the SSR correction products broadcast by the IGS RTS through the Internet. At the same time, the position of the user is determined through daily post-processing RP or PPP and stored on the server. Secondly, based on the user position and satellite position, the elevation angle of each satellite is calculated, and the equivalent range correction of the visible satellites at each BDS SMC broadcast epoch is generated. The range correction is encoded according to the proposed method and transmitted through the BDS SMC. Finally, the GNSS carrier phase observation data and broadcast ephemeris are collected at the user end and incorporated into the TPP positioning model together with the received BDS SMC equivalent range correction to solve the co-seismic displacement.

[0036] BeiDou-3's unique two-way short message communication service can serve as a backup link for data transmission, but it has frequency and bandwidth limitations and cannot directly transmit high-sampling-rate GNSS / strong-motion seismometer-fused coseismic deformation data. Therefore, it is necessary to develop a BeiDou short message compression algorithm for coseismic deformation to achieve effective compression of high-sampling-rate coseismic deformation data. The specific process of deformation data compression is as follows: Figure 2 As shown in Figure 2, coseismic deformation compression mainly involves two steps: dimensionless processing and epoch differencing. The goal of dimensionless processing is to ensure that the data volume meets the bandwidth limit of the BDS SMC while maintaining high data resolution. The epoch differencing method, on the other hand, exploits the temporal correlation of the coseismic deformation time series to further reduce the data volume.

[0037] In the complete encoding format of the BDS SMC coseismic deformation time series information, the blue block represents the message header, with a total size of 152 bits. The green block is the main segment, which is used to accommodate the continuous coseismic displacement time series to achieve maximum bandwidth. Each green block corresponds to the encoded information of a single epoch. At the end of the message, the 24-bit CRC checksum in the gray block is used to verify the integrity of the information. Taking 20 observation epochs as an example, the header file has the message type 1, the message number 200, the first epoch time is set to 2106000ms (i.e., 35 minutes and 6 seconds), the sampling interval is 20 ms (i.e., 50 Hz), and the total number of epochs accommodated is 2302.

[0038] Testing of short-message communication equipment in the Beidou region shows that short message transmission has a high success rate (reaching over 95%), but occasional failures occur. This requires the design of a suitable Beidou short message transmission mechanism to detect packet loss and resend the data. The design principle is to perform more checks through the program and send fewer Beidou short messages, thereby reducing the overall transmission volume and transmission time.

[0039] BDS SMC relies on satellite communication links for data transmission. However, due to channel transmission quality, the transmission success rate cannot reach 100%. Research results from channel performance testing and statistical analysis of Beidou short message communications show that the theoretical transmission success rate of a single BDS SMC data packet is approximately 96%, with an average transmission delay of 3.8 seconds. This demonstrates that BDS SMC equipment is very stable and reliable in sending and receiving messages, but packet loss due to transmission failures may occur occasionally.

[0040] High-frequency co-seismic deformation is an important information for earthquake emergency response and earthquake early warning. It usually requires a transmission success rate of more than 99% to ensure the timely and accurate release of information. Therefore, the theoretical transmission success rate of 96% cannot meet the reliability requirements of earthquake emergency response. It is necessary to develop a robust transmission mechanism for co-seismic displacement time series through BDS SMC to detect data packet loss and ensure data retransmission. To address this problem, a co-seismic displacement BDS SMC transmission mechanism based on the principle of minimizing data transmission is proposed. Figure 3 and Figure 4As shown in Figure 2, the process is as follows: This transmission mechanism involves two key entities: the server and the user. Initially, the user encodes the coseismic displacement time series into a series of short messages in chronological order and transmits them to the server. Upon receiving the message sent by the user, the server verifies that it has received all messages with sequence numbers before the maximum. If no messages are lost, the server does not send any response. If any messages are lost, the server sends an error message to the user, indicating the smallest missing sequence number. If the user receives an error message, it resends the corresponding Beidou short message and continues to send subsequent messages in sequence. After all Beidou short messages have been sent, the user sends an End message to the server. This message indicates that the data transmission task has been completed. Upon receiving this message, the server checks whether it has received all data messages with sequence numbers before the sequence number in the End message. If all short messages have been received, the server responds with an End message. If any short messages are still lost, the server sends another Error message, indicating the smallest missing sequence number. Upon receiving the Error message, the user retransmits the lost message.

[0041] Table 3 shows the formats of Error and End messages. Each short message consists of three fields: a start tag, a message number, and a message type. The start tag, consisting of an 8-bit binary number, marks the beginning of the check packet. Message Type 2 and Message Type 3 represent Error and End messages, respectively. In Error messages, the message number indicates the message number of the co-seismic displacement of the lost packet. The message number of the End message is equal to the maximum time series message sequence number plus 1.

[0042] Table 3 Error message and End message content ; In the encoding format and HEX examples of the Error and End messages, the total bandwidth of the Error and End messages is 16 bits, and a CRC-24Q checksum is performed at the end to ensure information integrity. The server periodically verifies that all co-seismic displacement information has been received and only responds with an End message after confirmation, signaling the end of the transmission process. In the HEX encoding examples of the End and Error messages, the End message type is 2, indicating that the lost message number 173 needs to be retransmitted; the Error message type is 3, indicating that the message number 208 has been transmitted.

[0043] The co-seismic displacement BDS SMC transmission flow chart is as follows Figure 5As shown in the figure, the user first compresses the co-seismic displacement time series using a specially designed compression algorithm. Based on the data resolution and size of the compressed co-seismic displacement time series, the user determines the required amount of information. This information is then formatted according to the BDS SMC encoding strategy. The encoded co-seismic displacements are packetized into short messages and transmitted to the server via BDS SMC. After receiving the data packets, the server checks each packet according to the predetermined transmission mechanism. If any data packet is lost due to a transmission error, the server generates an error message for each lost data packet. After receiving the error message, the user retransmits the specified lost data packet. Once all data packets have been successfully transmitted, including any retransmissions, the user sends an end message to the server. After confirming that all data packets have been received (including previously lost data packets), the server sends back an end message. Finally, the server processes and recovers the entire set of co-seismic displacement time series from the received BDS SMC information.

[0044] To evaluate the performance of the TPP-SMC method, six IGS stations were selected, and observational data were collected and processed from 03:45:00 to 03:59:59 (GPS time) on November 30, 2023. This 15-minute processing period, which is longer than the typical duration of a mainshock (typically several minutes), provides sufficient support for evaluating displacement accuracy. Static experiments were conducted to evaluate the accuracy of displacements derived using the TPP method using the BDSSMC equivalent distance correction. Furthermore, static displacements obtained using the TPP-RTS (Standard Time-Domain Point Positioning Model with Real-Time Service) and PPP-GBM (Precise Point Positioning Broadcast Model) methods were calculated for comparative analysis. Since the selected IGS stations are stationary, the static displacements should ideally be zero at each epoch, which serves as a reference for evaluation. The RMS displacements derived from the different schemes were calculated to ensure a reliable evaluation of the TPP method's performance. According to the TPP-SMC method (the method of this invention), the average displacements in the north, east, and zenithal directions are 0.33 cm, 0.42 cm, and 1.19 cm, respectively. In comparison, the average displacements obtained by TPP-RTS are slightly lower, at 0.28 cm in the north, 0.44 cm in the east, and 1.09 cm in the zenith. The displacements obtained by PPP-GBM are closest to the reference values. The average displacements of PPP-GBM in the north, east, and zenithal directions are 0.31 cm, 0.27 cm, and 0.79 cm, respectively, slightly superior to the TPP-SMC and TPP-RTS methods. Experimental results show that there are slight differences in the performance of different schemes in resolving coseismic displacements. Compared with the PPP-GBM and TPP-RTS methods, the TPP-SMC scheme achieves comparable static displacement accuracy, with all displacements in the north, east, and zenithal directions deviating from the reference values ​​at the same order of magnitude.

[0045] For the PPP-GBM scheme, the RMS in the north, east, and sky directions were 0.36 cm, 0.31 cm, and 0.75 cm, respectively. In contrast, the TPP-SMC scheme achieved RMS in these three directions of 0.42 cm, 0.51 cm, and 1.09 cm, respectively. These values ​​are very close to those of the TPP-RTS method, which achieved RMS in the north, east, and sky directions of 0.34 cm, 0.43 cm, and 0.97 cm, respectively.

[0046] Table 4 summarizes the average RMS displacement values ​​obtained by the three different schemes at six IGS stations. The average RMS values ​​for the TPP-SMC scheme in the horizontal and vertical directions are 0.66 cm and 1.09 cm, respectively, showing no significant difference in displacement accuracy compared to the TPP-RTS scheme. Therefore, the static displacement extraction performance of the TPP method using BDS SMC equivalent range corrections and IGS RTS real-time products is nearly equivalent, but slightly inferior to the post-processed static displacements estimated using the PPP-GBM scheme.

[0047] ; The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. Beidou short message real estate co-seismic deformation transmission method, characterized by: It includes co-seismic deformation compression on the user side, information encoding and information packetization to obtain short messages, information sub-packet broadcasting, and uploading the short messages to the Beidou GEO satellite through the BDS SMC terminal on the user side; the server side downloads the short messages from the Beidou GEO satellite to the BDS SMC terminal on the server side, performs information sub-packet verification, information decoding, co-seismic deformation recovery, and co-seismic deformation splicing and integration.

2. The BeiDou short message real estate co-seismic deformation transmission method according to claim 1, characterized in that: The coseismic deformation compression involves dimensionless processing of the coseismic deformation and then rounding it off to the nearest integer: ； Where, Represents the rounding operator, is the GNSS co-seismic displacement time series, is the selected data resolution, is the rounded result; Calculate the integer co-seismic displacement epoch difference between two adjacent epochs Further compress the integral co-seismic displacement: ； Where, and Represents the current epoch and the previous epoch The integer co-seismic displacement value of ; The following conversion formula is used to convert the integer co-seismic displacement time series into an unsigned integer displacement time series: ； Where, is an integer unsigned integer coseismic deformation time series, is the minimum value of the integer co-seismic displacement epoch difference time series; The number of bits required to encode the co-seismic deformation time series of integer and unsigned integer is determined according to the following inequality: ； Where, is the maximum value of the coseismic deformation time series of integer unsigned integer, The number of bits required to binary encode the coseismic deformation time series of unsigned integer.

3. The BeiDou short message real estate co-seismic deformation transmission method according to claim 2, characterized in that: The information encoding includes, the encoding format includes a header file and a body file; The header file includes an 8-bit binary start tag, a message type, a message number, a first epoch time, a sampling interval, an epoch number, an initial co-seismic deformation value, an integer epoch differential co-seismic deformation value, and a bit number. The message type is used to distinguish data types. The message number is a unique identifier used to distinguish and sort messages. The first epoch time is determined by the time the information is received and is the number of milliseconds within the hour of transmission. The sampling interval is the time interval between consecutive observation epochs. The epoch number indicates the total number of epochs contained in the information. The initial co-seismic deformation value indicates the initial co-seismic deformation value of the first epoch in the north, east, and sky directions. The integer epoch differential co-seismic deformation value indicates the integer epoch differential co-seismic deformation value in the north, east, and sky directions. The bit number indicates the unsigned integer co-seismic deformation time series in the north, east, and sky directions. The volume file includes all epochs to be transmitted, arranged in the order of north, east and sky. value.

4. The BeiDou short message real estate co-seismic deformation transmission method according to claim 3, characterized in that: Information decoding includes, each epoch The value is used to calculate the corresponding The epoch difference value corresponding to the value: ； Where, for Corresponding ; From the first epoch in each direction value Start by accumulating Calculate the subsequent epochs value, will Multiply the value by , get the first BDS SMC decoded value of each epoch The coseismic deformation value of epoch : ； Where, Indicates from the 1st to the The cumulative epoch-by-epoch differential integral coseismic deformation value of epochs, Indicates the The integer epoch-wise difference value of the co-seismic displacement for each epoch.

5. The BeiDou short message real estate co-seismic deformation transmission method according to claim 4, characterized in that: When the client and server are transmitting data, after receiving the information sent by the client, the server verifies whether it has received all the information with sequence numbers before the maximum value. If no information is lost, the server will not send any response. If information is lost, the server will send an error message to the client, indicating the smallest sequence number that is lost. When the user receives the error message Error, it resends the corresponding Beidou short message and continues to send subsequent messages in sequence. After all Beidou short messages are sent, the user sends an End message to the server, indicating that the data transmission task has been completed. After receiving the end message, the server checks whether it has received all the data information with sequence numbers before the end message sequence number. If all the short messages have been received, the server replies with an end message End; If a short message is lost, the server sends another error message Error, indicating the lost minimum sequence number. After receiving the error message Error, the user end retransmits the lost message.

6. A GNSS method for calculating co-seismic deformation of real estate, characterized by: The BeiDou short message real estate co-seismic deformation transmission method according to claim 5 includes the following steps: a server collects SSR corrections broadcast by IGS RTS via the Internet, determines the user terminal position through routine post-processing RP or PPP and stores the corrections on the server; generates an equivalent range correction for visible satellites at each BDS SMC broadcast epoch based on the user terminal position and the SSR corrections; encodes the range corrections, and transmits them to BeiDou GEO satellites via a BDSSMC terminal; The user end collects GNSS raw observations and broadcast ephemeris, downloads equivalent distance corrections from BeiDou GEO satellites through the BDS SMC terminal, and uses the GNSS raw observations, broadcast ephemeris, and equivalent distance corrections to construct a TPP positioning model for co-seismic deformation resolution.

7. The GNSS method for calculating coseismic deformation of real estate according to claim 6, characterized in that: The precise satellite clock error recovered from the SSR correction is: ； ； Where, is the satellite clock error calculated from the broadcast ephemeris, is the precise satellite clock error recovered from the SSR corrections, is the SSR clock correction number, 、 and are three polynomial constant terms, is the current time of the satellite clock error, is the reference time of the satellite clock error, is the time domain point value of the satellite clock error, is the speed of light in a vacuum.

8. The GNSS method for calculating coseismic deformation of real estate according to claim 7, characterized in that: The precise orbital position of the satellite restored by the SSR correction number is: ； ； ； ； Where, represents the precise satellite orbit ECEF coordinate vector restored using SSR corrections, represents the satellite orbit ECEF coordinate vector calculated by broadcast ephemeris, is the SSR orbit correction number, 、 、 are the radial, tangential and normal corrections to the SSR epoch time, 、 、 are the radial, tangential and normal corrections to the SSR epoch velocity, 、 、 yes In the radial, tangential and normal components, is the time domain point value of the satellite orbit error, and They represent the satellite orbit position vector and velocity vector calculated using the GNSS broadcast ephemeris.

9. The GNSS method for calculating co-seismic deformation of real estate according to claim 8, characterized in that: The TPP positioning model is: ； ； Where, is the time domain point differential carrier phase OMC value after linearization, represents the unit vector of the direction from the receiver to the satellite at the current epoch, Relative to the reference epoch The coseismic deformation increment is equivalent to the three-dimensional coseismic deformation, represents the time domain point difference value of the directional unit vector, is the position of the reference epoch obtained by daily post-processing RP or PPP, is the geometric distance from the user receiver to the GNSS satellite. is the receiver clock bias, is the time-domain point difference of the measurement noise of the IF composite carrier phase observation value, is the time domain point difference score of the satellite orbit error, Indicates the time domain point difference score of the satellite clock error.

10. The GNSS method for calculating co-seismic deformation of real estate according to claim 9, characterized in that: Generating the equivalent range corrections for visible satellites at each BDSSMC broadcast epoch involves calculating the satellite orbit corrections and clock corrections for each SSR epoch within the BDS SMC broadcast interval, and subtracting the precise orbit and clock corrections calculated based on the same broadcast ephemeris from the orbit and clock corrections provided by the broadcast ephemeris to obtain the orbit and clock corrections for each SSR epoch. Calculate the equivalent distance correction for each SSR epoch, the equivalent distance correction for each epoch of satellite orbit correction and clock correction The calculation formula is: ； A first-order polynomial fit is performed on the equivalent distance correction value and the time interval between the SSR broadcast time and the reference time. The constant term represents the equivalent distance correction number, and the first-order term is the correction number for the equivalent distance change rate relative to the reference time.

Images