Marine positioning and search and rescue information coding method based on Beidou short message

Abstract

The invention provides an offshore positioning and search and rescue information coding method based on a Beidou short message, which comprises the following steps: a server acquires an SSR data stream in real time, and preprocesses and compressively codes the SSR data; the server encapsulates the compressed and encoded SSR data into a Beidou short message service data unit, and broadcasts or multicasts the Beidou short message service data unit to an offshore terminal in a target sea area through a Beidou GEO satellite; the offshore terminal receives the Beidou short message and recovers the SSR data; based on the received GNSS observed quantity and SSR data, the offshore terminal carries out three-dimensional position and speed estimation and obtains a horizontal precision factor at the same time; the maritime terminal encodes rescue information containing three-dimensional position and speed estimation and a horizontal precision factor, packages the rescue information into a rescue short message, and sends the rescue short message to the outside through a Beidou satellite according to a rescue judgment rule; and the received rescue short message is analyzed, and rescue decision and scheduling are carried out according to data obtained through analysis.

Description

Technical Field

[0001] This invention relates to a method for encoding maritime positioning and search and rescue information, and more particularly to a method for encoding maritime positioning and search and rescue information based on BeiDou short messages. Background Technology

[0002] This section provides only background information relevant to this disclosure and is not necessarily prior art.

[0003] With the continuous expansion of global shipping, deep-sea fishing, offshore wind power, and offshore oil and gas development, the waters in which ships navigate are gradually expanding from nearshore areas to the open sea and deep sea. This has led to a more complex maritime operating environment and a more diversified and frequent occurrence of emergencies. Typical maritime hazards include ship collisions, groundings, water ingress and loss of control, fires and explosions, and personnel falling overboard or going missing. In the event of such incidents, obtaining crucial information such as the precise location, time stamp, distress level, and identification of the distressed target as quickly as possible and transmitting it to the search and rescue command center via a reliable link is a key factor affecting the search and rescue scope, efficiency, and success rate.

[0004] Global Navigation Satellite Systems (GNSS) provide all-weather, globally covered navigation and positioning services for maritime targets. Among them, the BeiDou Navigation Satellite System, after completing its global network, in addition to conventional positioning, navigation, and timing services, also possesses short message communication capabilities, enabling small-capacity two-way information transmission without relying on terrestrial cellular networks. In recent years, high-precision positioning technologies such as Precise Point Positioning (PPP) have been widely used in land and near-shore areas. By broadcasting orbital clock corrections and SSR (Search Signal Range) and other precision products through ground-based augmentation station networks or satellite-based augmentation systems, it can provide users with high-precision location services at the decimeter or even centimeter level. However, the widespread application of high-precision positioning in open seas and communication-constrained waters still faces challenges such as unstable terrestrial communication links, uneven service coverage, and insufficient terminal availability in complex environments.

[0005] Specifically, the existing technology has the following drawbacks:

[0006] (1) Existing ground-based augmentation-based real-time PPP technology is difficult to obtain precise products in a timely and stable manner in the open sea and in communication-restricted sea areas, making it difficult to provide continuous high-precision positioning support for maritime emergency search and rescue. Although satellite-based augmentation systems can broadcast precise products independently of the Internet, they are limited by constellation resources and service range, making it difficult to cover multiple types of maritime targets and multi-regional application needs. The solution based on the combination of GNSS and maritime satellite communication is highly dependent on specific operators, has high link costs, and has potential security risks, which is not conducive to building an independent, controllable, cost-effective, and resistant high-precision positioning system for maritime emergency rescue.

[0007] (2) Existing maritime emergency search and rescue information transmission mainly relies on VHF radio, satellite phone, AIS and other means. When the ground network coverage in remote sea areas is insufficient, the equipment is damaged or the sea conditions are bad, the communication link is prone to interruption or unstable performance, making it difficult to transmit key information for the rescue of distressed targets in a timely, continuous and reliable manner. This cannot meet the needs of maritime emergency search and rescue for high timeliness and high reliability information support. Existing distress information reporting based on Beidou short messages mostly treats short messages as a simple alarm channel. There is a lack of a unified and standardized integrated coding mechanism. The data formats between different terminals and platforms are not uniform and the interoperability is poor. Moreover, the key information such as high-precision location, dynamic navigation parameters, distress level and identity identification is not compactly expressed and completely verified within the limited message length. The anti-tampering design is not implemented, which leads to low efficiency of distress information parsing at the search and rescue command end and difficulty in integrated application. It is difficult to use in conjunction with high-precision positioning enhancement information such as PPP, which ultimately affects the overall positioning accuracy improvement and emergency response efficiency.

[0008] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0009] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for encoding maritime positioning and search and rescue information based on Beidou short message service, which addresses the shortcomings of the existing technology.

[0010] To address the aforementioned technical problems, this invention discloses a maritime positioning and search and rescue information encoding method based on BeiDou short message service, comprising the following steps:

[0011] Step 1: The server obtains the SSR data stream in real time and preprocesses and compresses the SSR data.

[0012] Step 2: The server encapsulates the compressed and encoded SSR data into BeiDou short message service data units and broadcasts or multicasts them to maritime terminals in the target sea area via BeiDou GEO satellites.

[0013] Step 3: The maritime terminal receives BeiDou short messages and restores SSR data;

[0014] Step 4: Based on the received GNSS observations and SSR data, the marine terminal performs three-dimensional position and velocity estimation and simultaneously obtains the horizontal accuracy factor.

[0015] Step 5: The maritime terminal encodes and encapsulates the rescue information, which includes three-dimensional position and velocity estimates and horizontal accuracy factors, into a short rescue message, and sends it outward via BeiDou satellite according to the rescue judgment rules.

[0016] Step 6: Parse the received rescue short message and make rescue decisions and dispatch based on the parsed data.

[0017] Furthermore, the SSR data stream described in step 1, in epoch units, includes orbital corrections, clock corrections, and quality indicators for multiple satellites.

[0018] The preprocessing includes time-stamp alignment, satellite number sorting, and outlier removal, forming enhanced data frames in epoch units.

[0019] Furthermore, the compression encoding described in step 1 involves quantizing and compressing the data in the enhanced data frame. The encoding format includes a data header, a data body, and an end portion; wherein,

[0020] The data header includes an 8-bit synchronization code, a 12-bit epoch time, and a 56-bit satellite number;

[0021] The data body includes 8 bits of orbital radial correction, 6 bits of orbital tangential correction, 6 bits of orbital normal correction, and 13 bits of clock error correction; among which, the orbital radial correction, orbital tangential correction, orbital normal correction, and clock error correction are represented by a fixed-point encoding method with bit depth and resolution.

[0022] The ending section includes a 24-bit checksum.

[0023] Furthermore, the recovery of SSR data described in step 3 includes:

[0024] Step 3-1: Parse the received BeiDou short message to obtain the SSR service payload;

[0025] Step 3-2 involves parsing and dequantizing according to the compression encoding rules in Step 1, specifically including:

[0026] Based on the resolution corresponding to the orbital radial correction, orbital tangential correction, orbital normal correction, and clock error correction, the encoded values ​​are restored to continuous values;

[0027] Based on the satellite number and epoch time tag, the orbital radial correction, orbital tangential correction, orbital normal correction and clock error correction of each satellite at the corresponding epoch are saved.

[0028] Furthermore, step 4, which involves estimating the three-dimensional position and velocity while simultaneously obtaining the horizontal accuracy factor, includes:

[0029] Step 4-1: The maritime terminal uses a GNSS receiver to collect GNSS observations, including pseudorange, carrier phase, Doppler raw observations, and navigation message information, and performs time stamping and satellite number association.

[0030] Step 4-2: Calculate the satellite position correction vector based on the orbital radial correction, orbital tangential correction, and orbital normal correction. The details are as follows:

[0031]

[0032] in, , and These are the track radial correction, track tangential correction, and track normal correction, respectively. , and These are the orbital tangential unit vector, orbital normal unit vector, and orbital radial unit vector, respectively; the calculation method is as follows:

[0033]

[0034]

[0035]

[0036] in, The satellite position vector in the Earth-fixed coordinate system. This represents the satellite velocity vector in the Earth-fixed coordinate system.

[0037] Step 4-3: Calculate the corrected satellite clock bias based on the clock bias correction. The details are as follows:

[0038]

[0039] in, Satellite clock bias calculated for broadcast ephemeris. This is the clock error correction number. The speed of light in a vacuum;

[0040] Step 4-4, based on GNSS observations and satellite position correction vectors and the corrected satellite clock bias An observation function is constructed using an ionosphere-free combined model. The three-dimensional position and velocity of the current offshore terminal are estimated by extended Kalman filtering. The horizontal accuracy factor obtained during the solution process is used as an accuracy evaluation index to characterize the reliability of the positioning results.

[0041] Furthermore, the encoding and encapsulation into a rescue short message as described in step 5 involves constructing a rescue short message using a fixed frame structure based on BeiDou short messages, including: a frame header and a security field, and a rescue information data body field.

[0042] Furthermore, the frame header and security fields include:

[0043] The system consists of an 8-bit synchronization code, a 4-bit protocol version number, a 4-bit message type, a 4-bit terminal type, a 4-bit reserved field, a 16-bit CRC checksum, and a 32-bit message authentication code (MAC).

[0044] Furthermore, the rescue information data body fields include:

[0045] The system includes a 20-digit timestamp, 32-digit latitude, 32-digit longitude, 16-digit altitude, 8-digit horizontal precision factor, 12-digit ground speed, 12-digit heading angle, 4-digit distress type, 2-digit distress level, 2-digit alarm source, 8-digit equipment status indicator, 30-digit crew identification, 16-digit terminal number, and 16-digit crew number.

[0046] Time stamps, latitude, longitude, altitude, horizontal precision factor, ground speed, and heading angle are represented using a fixed-point encoding method with bit depth and resolution.

[0047] Furthermore, step 5, which involves transmitting information externally via BeiDou satellite based on rescue judgment rules, includes:

[0048] The maritime terminal is pre-configured with a manual trigger button and environmental and status sensors. During operation, button signals and sensor data are collected in real time. When a manual button trigger is detected, or when sensor data indicators exceed a preset safety threshold and the duration meets preset criteria, a maritime distress event is determined, triggering the rescue process and sending a short rescue message to the outside world via the Beidou satellite.

[0049] Furthermore, step 6, which involves parsing the received rescue short message, includes:

[0050] According to the encoding and encapsulation rules of the rescue information in the rescue short message, the rescue short message is parsed and dequantized field by field to recover the time tag, latitude, longitude, altitude, horizontal precision factor, ground speed, heading angle, distress type, distress level, alarm source, equipment status flag, ship and personnel identification, terminal number and personnel number.

[0051] Beneficial effects:

[0052] 1. This invention designs a positioning enhancement information compression coding scheme adapted to the characteristics of BeiDou short message service. It compresses auxiliary positioning parameters and time tags and encapsulates them in BeiDou short messages, enabling key high-precision positioning information to be transmitted independently through satellite-based short message links. This reduces reliance on terrestrial cellular networks and specific commercial communication links, and enables high-precision location information to meet emergency search and rescue needs in areas such as the open sea and deep sea under communication-limited conditions.

[0053] 2. Under a unified coding framework, this invention structures and compacts key information such as the high-precision location, dynamic navigation parameters (speed, heading, etc.), distress level, identification, and time stamp of distressed targets. Verification and anti-tampering fields are introduced into the coding, enabling efficient, standardized, and verifiable expression of distress information within a limited message length. This coding mechanism allows the search and rescue command to quickly and accurately parse and integrate distress messages from different terminals and systems, significantly improving the reliability of distressed target information transmission and cross-system sharing and comprehensive analysis capabilities, thus meeting the comprehensive needs of maritime emergency search and rescue for low-latency and high-reliability information services. Attached Figure Description

[0054] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0055] Figure 1 This is a schematic diagram of the overall process of the method of the present invention.

[0056] Figure 2 This is a data comparison diagram from one embodiment. Detailed Implementation

[0057] The core content of this invention is a maritime positioning and communication coding method based on BeiDou short message service, such as... Figure 1 As shown, the process includes the following four stages: (1) Real-time acquisition and compression broadcast of satellite orbit and clock correction data at the server end; (2) Receiving satellite orbit and clock correction data at the maritime terminal and performing PPP positioning calculation; (3) Encoding and sending rescue information based on BeiDou short messages; (4) Decoding and timely rescue at the search and rescue command end. The specific technical solution is as follows:

[0058] (1) Real-time acquisition and compressed broadcast of satellite orbit and clock correction data on the server side

[0059] 1) Real-time acquisition of SSR data

[0060] The server acquires SSR (State-Space Representation) data streams, including satellite orbit corrections and clock corrections, generated in real time by the Wuhan University IGS Data Center via the network. This data stream contains orbit corrections, clock corrections, and necessary mass indicators for multiple satellites, organized in epoch units.

[0061] 2) SSR Data Preprocessing

[0062] The server performs time-stamp alignment, satellite number sorting, and outlier removal on the received SSR data. It constructs a frame of enhanced data from multiple satellite corrections within the same epoch, providing a foundation for subsequent compression encoding.

[0063] 3) SSR data compression encoding

[0064] In the "Compression Encoding" module, each frame of SSR enhanced data is quantized and compressed. The designed encoding format includes three parts: data header, data body, and end. The specific encoding scheme is shown in the table below:

[0065] Table 1. Header and End of Data

[0066]

[0067] Table 2 Data Body Coding

[0068]

[0069] To facilitate the transmission of high-precision enhanced information within a limited number of bits, the parameters such as the orbital radial correction, orbital tangential correction, orbital normal correction, and clock error correction are all represented using a fixed-point encoding method combining "bit count + resolution." Specifically, the actual physical quantity is divided by a preset resolution and rounded to obtain the encoded value, which is then stored in the short message with a predetermined number of bits. During terminal decoding, this encoded value is multiplied by the corresponding resolution to recover the continuous physical quantity with actual physical meaning.

[0070] With the above bit and resolution design, the orbital three-axis correction can be expressed in the range of approximately ±4 m, and the clock error correction can be expressed in the range of approximately ±123 m, which meets the current operational requirements for ephemeris and clock error correction, while ensuring accuracy and dynamic range with a limited number of bits.

[0071] 4) Positioning Enhancement Information Dissemination Based on BeiDou Short Message Service

[0072] The server encapsulates the compressed SSR data frame into a BeiDou short message service data unit, which is then reported to the BeiDou GEO satellite via the "BeiDou short message terminal". The satellite then broadcasts or multicasts the information to the maritime terminals in the target sea area through the BeiDou short message service, enabling real-time transmission of satellite orbit and clock correction data.

[0073] (2) The marine terminal receives satellite orbit and clock correction data and performs PPP positioning calculation.

[0074] 1) SSR Short Message Reception and Demodulation

[0075] The BeiDou short message communication module built into the maritime terminal continuously monitors the downlink service signals of the BeiDou GEO satellite. When a short message frame carrying SSR enhancement information is detected, the physical layer signal demodulation and channel decoding are first completed. Then, at the link layer, the frame header, length and check field are checked according to the short message protocol to obtain the SSR service payload carried in it, providing input data for subsequent decoding processing.

[0076] 2) Correction number decoding and recovery

[0077] The obtained SSR service payload is sent to the terminal's "correction quantity decoding" module. This module, following the same encoding rules as the server, sequentially parses and dequantizes the bit-encoded data fields in the payload: based on the resolution corresponding to each field, it restores the encoded values ​​to continuous quantities with actual physical meaning, such as orbital radial, tangential, and normal corrections, as well as clock corrections; and based on the satellite number and epoch time stamp, it stores the orbital corrections, clock corrections, and other parameters for each satellite at the corresponding epoch into the local SSR cache, providing complete enhanced correction information for subsequent PPP calculations.

[0078] 3) GNSS observation data acquisition

[0079] Under normal operating conditions, the GNSS receiver built into the maritime terminal synchronously outputs raw observation data, including pseudorange, carrier phase, and Doppler readings, as well as navigation message information, at preset sampling intervals. This observation data is then time-stamped and associated with satellite numbers by the terminal's internal data acquisition module, forming a raw observation dataset that meets the requirements of PPP (Public-Private Partnership) calculations, providing reliable input for subsequent PPP calculations.

[0080] 4) PPP solution

[0081] In the "Precise Point Positioning" module, the terminal applies the obtained orbit and clock error corrections to the broadcast ephemeris to calculate the precise orbit and precise clock error:

[0082] Calculate satellite position correction vector :

[0083]

[0084] in, , , These are the radial, normal, and tangential correction numbers in the SSR orbit correction information broadcast based on BeiDou short messages. , , ; This is the satellite position vector in the Earth-fixed coordinate system; This represents the satellite velocity vector in the Earth-fixed coordinate system.

[0085] Calculate satellite clock correction:

[0086]

[0087] in, Satellite clock bias calculated for broadcast ephemeris, in seconds; For the corrected satellite clock bias, This refers to the clock bias correction value obtained from the SSR clock bias correction broadcast by BeiDou short messages, expressed in meters. It is the speed of light in a vacuum.

[0088] The observation function model of the real-time PPP algorithm is constructed using an ionospheric-free combination model (reference: Liu Xitian, Gao Jingxiang, Yu Zhihao, et al. Three-frequency GNSS precise single-point positioning model and evaluation without ionospheric combination [J]. Surveying and Mapping Science, 2023, 48(10):10-19.DOI:10.16251 / j.cnki.1009-2307.2023.10.002.). High-precision estimation of the three-dimensional position and velocity of the distressed target (current terminal) is achieved through extended Kalman filtering. The horizontal accuracy factor obtained in the solution process is used as the accuracy evaluation index to quantitatively characterize the reliability of the PPP positioning results.

[0089] (3) Encoding and transmission of rescue information based on Beidou short message

[0090] 1) Determining whether rescue is needed

[0091] The offshore terminal is pre-configured with a manual trigger button and environmental and status sensors for water ingress, capsizing, fire, and impact acceleration, and corresponding judgment thresholds and logic rules are set in the main control unit. During operation, the terminal collects the above-mentioned button signals and sensor data in real time. When a manual button trigger is detected, or when any indicator such as water ingress, tilt angle, temperature / smoke concentration, or acceleration exceeds a preset safety threshold and the duration meets the preset criteria, the current state is judged to constitute a maritime distress event, and the rescue process is triggered; if all indicators are within the normal range, the monitoring state is maintained and the rescue information encoding and transmission are not initiated.

[0092] 2) Rescue Information Coding

[0093] When rescue is deemed necessary, the terminal triggers the "Rescue Information Encoding" module, which encapsulates key information related to the current distress event into a rescue short message according to a predefined unified encoding mechanism. The rescue information includes at least the following:

[0094] High-precision latitude, longitude, altitude, and horizontal accuracy factor of the distressed target obtained from real-time PPP calculation;

[0095] Dynamic navigation parameters such as ground speed and heading angle output by the navigation calculation module are used to reflect the motion state of the distressed target;

[0096] Status fields used to describe the current event attributes, including distress type, distress level, alarm source (manual or automatic triggering), etc.

[0097] The identity and timing information used to uniquely identify objects and messages includes the ship or personnel identification, terminal number, and time stamp corresponding to the PPP epoch;

[0098] The integrity verification field and message authentication code security field are used to ensure data security, and are used to implement integrity verification and anti-tampering verification of messages during transmission.

[0099] Maritime rescue information based on BeiDou short messages adopts a fixed frame structure. The overall frame format includes: frame header; position and accuracy information; dynamic navigation parameters; distress status information; identity and time information; and security and verification fields. Each field is represented using a fixed-point encoding method of "bits + resolution". The specific encoding scheme is shown in the table below:

[0100] Table 3 Encoding Scheme for Frame Header and Security Fields

[0101] Field Name Number of bits Value range / description Synchronization code 8 0-255, used as frame synchronization identifiers. Protocol version number 4 0-15 are used to distinguish different versions of the encoding rules. Message type 4 0-15, where 0001 represents a distress rescue message, and other values ​​are reserved. Terminal type 4 0-15 is used to distinguish between shipborne terminals, personal terminals, platform terminals, etc. Reserved fields 4 0-15, reserved for future expansion. CRC checksum 16 The payload is calculated for the entire frame or within a frame and is used for integrity verification. Message Authentication Code (MAC) 32 Calculations based on pre-shared keys or certificate systems are used for tamper prevention and identity authentication.

[0102] Table 4 Encoding Scheme for Rescue Information Data Body Fields

[0103]

[0104] In summary, the total length of the distress rescue short message designed in this invention is approximately 282 bits (about 36 bytes) when carrying a message authentication code, and approximately 250 bits (about 32 bytes) when not carrying a message authentication code. Both are far less than the single payload limit of the BeiDou short message service, thus enabling the complete transmission of all critical rescue information in a single short message transmission, meeting the requirements for low-latency and high-reliability information transmission in maritime emergency scenarios.

[0105] 3) Rescue information transmission based on BeiDou short message service

[0106] After encoding the rescue information, the terminal initiates an uplink service through its built-in BeiDou short message communication module, requesting that the rescue short message be sent to the BeiDou GEO satellite. Upon receiving the short message, the BeiDou GEO satellite relays it according to a pre-defined process, sending the rescue short message downlink to the ground-based BeiDou short message receiving station. The receiving station then forwards it to the maritime search and rescue command center, thus achieving reliable reporting and distribution of rescue information based on the BeiDou short message link.

[0107] (4) Search and rescue command terminal (e.g.) Figure 1 The server in the middle decodes and provides timely rescue.

[0108] 1) Rescue Short Message Reception and Verification

[0109] The search and rescue command center platform receives rescue short messages relayed by BeiDou GEO satellites via the BeiDou short message ground gateway. The receiving module first checks the message header and length field according to the BeiDou short message service protocol, and verifies the message integrity based on the CRC checksum carried in the message. Simultaneously, it verifies the MAC address using a pre-shared key or corresponding authentication mechanism to determine the legitimacy of the message source and the tamper-proof nature of the content. Messages that fail the CRC check or MAC authentication are discarded or marked as invalid to prevent abnormal data from entering subsequent decoding and rescue decision-making processes.

[0110] 2) Decoding rescue information and recovery of high-precision location information

[0111] In the "Data Information Decoding" module of the search and rescue command center platform, the rescue short messages that have passed the verification are parsed and dequantized field by field according to the rescue information encoding format predefined in this invention, so as to recover the high-precision latitude and longitude, altitude, horizontal accuracy factor, ground speed, heading angle, distress type, distress level, alarm source, equipment status flag, as well as ship / personnel identification, terminal number, time tag and other information of the distressed target.

[0112] 3) Rescue decision-making and dispatch execution

[0113] Based on the high-precision location, accuracy assessment indicators, and dynamic navigation status of the distressed target, the search and rescue command center platform, combined with the real-time distribution and accessibility information of surrounding maritime rescue forces (including search and rescue vessels, helicopters, unmanned surface vessels / drones, etc.), automatically or manually generates corresponding rescue plans, determines the priority rescue units to be dispatched and their navigation routes, and sends action instructions to the selected rescue units to ensure they reach the target sea area as soon as possible to carry out search and rescue. Simultaneously, the command terminal dynamically tracks and updates the location and movement status of the distressed target based on continuously received multiple frames of short rescue messages, and corrects target markers and estimated drift ranges on electronic nautical charts in real time, thereby ensuring the timeliness and accuracy of rescue operations and improving the overall success rate of maritime emergency search and rescue.

[0114] Example:

[0115] like Figure 2As shown in the figure, in a specific embodiment, by comparing the positioning accuracy of SMC-PPP (based on Beidou short message compression coding) and SSR-PPP (based on IGS real-time products), it can be seen that although SMC-PPP has a slower convergence speed and slightly lower accuracy than SSR-PPP, it can still achieve decimeter-level positioning accuracy, meeting the requirements for maritime rescue.

[0116] In its specific implementation, this application provides a computer storage medium and a corresponding data processing unit. The computer storage medium is capable of storing a computer program, which, when executed by the data processing unit, can run the invention's content regarding a maritime positioning and search and rescue information encoding method based on BeiDou short messages, as well as some or all of the steps in various embodiments. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc.

[0117] Those skilled in the art will clearly understand that the technical solutions in the embodiments of the present invention can be implemented using computer programs and their corresponding general-purpose hardware platforms. Based on this understanding, the technical solutions in the embodiments of the present invention, or the parts that contribute to the prior art, can be embodied in the form of computer programs, i.e., software products. These computer program software products can be stored in a storage medium and include several instructions to cause a device containing a data processing unit (which may be a personal computer, server, microcontroller, MCU, or network device, etc.) to execute the methods described in various embodiments or certain parts of the embodiments of the present invention.

[0118] This invention provides a concept and method for encoding maritime positioning and search and rescue information based on BeiDou short messages. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for encoding maritime positioning and search and rescue information based on BeiDou short message service, characterized in that, Includes the following steps: Step 1: The server obtains the SSR data stream in real time and preprocesses and compresses the SSR data. Step 2: The server encapsulates the compressed and encoded SSR data into BeiDou short message service data units and broadcasts or multicasts them to maritime terminals in the target sea area via BeiDou GEO satellites. Step 3: The maritime terminal receives BeiDou short messages and restores SSR data; Step 4: Based on the received GNSS observations and SSR data, the marine terminal performs three-dimensional position and velocity estimation and simultaneously obtains the horizontal accuracy factor. Step 5: The maritime terminal encodes and encapsulates the rescue information, which includes three-dimensional position and velocity estimates and horizontal accuracy factors, into a short rescue message, and sends it outward via BeiDou satellite according to the rescue judgment rules. Step 6: Parse the received rescue short message and make rescue decisions and dispatch based on the parsed data.

2. The maritime positioning and search and rescue information encoding method based on BeiDou short message service according to claim 1, characterized in that, The SSR data stream described in step 1, in epoch units, includes orbital corrections, clock corrections, and quality indicators for multiple satellites. The preprocessing includes time-stamp alignment, satellite number sorting, and outlier removal, forming enhanced data frames in epoch units.

3. The maritime positioning and search and rescue information encoding method based on BeiDou short message service according to claim 2, characterized in that, The compression encoding described in step 1 involves quantizing and compressing the data in the enhanced data frame. The encoding format includes a data header, a data body, and an end portion; wherein, The data header includes an 8-bit synchronization code, a 12-bit epoch time, and a 56-bit satellite number; The data body includes 8 bits of orbital radial correction, 6 bits of orbital tangential correction, 6 bits of orbital normal correction, and 13 bits of clock error correction; among which, the orbital radial correction, orbital tangential correction, orbital normal correction, and clock error correction are represented by a fixed-point encoding method with bit depth and resolution. The ending section includes a 24-bit checksum.

4. The maritime positioning and search and rescue information encoding method based on BeiDou short message service according to claim 3, characterized in that, The recovery of SSR data described in step 3 includes: Step 3-1: Parse the received BeiDou short message to obtain the SSR service payload; Step 3-2 involves parsing and dequantizing according to the compression encoding rules in Step 1, specifically including: Based on the resolution corresponding to the orbital radial correction, orbital tangential correction, orbital normal correction, and clock error correction, the encoded values ​​are restored to continuous values; Based on the satellite number and epoch time tag, the orbital radial correction, orbital tangential correction, orbital normal correction and clock error correction of each satellite at the corresponding epoch are saved.

5. The maritime positioning and search and rescue information encoding method based on BeiDou short message service according to claim 4, characterized in that, Step 4, which involves estimating the three-dimensional position and velocity while simultaneously obtaining the horizontal accuracy factor, includes: Step 4-1: The maritime terminal uses a GNSS receiver to collect GNSS observations, including pseudorange, carrier phase, Doppler raw observations, and navigation message information, and performs time stamping and satellite number association. Step 4-2: Calculate the satellite position correction vector based on the orbital radial correction, orbital tangential correction, and orbital normal correction. ; Step 4-3: Calculate the corrected satellite clock bias based on the clock bias correction. ; Step 4-4, based on GNSS observations and satellite position correction vectors and the corrected satellite clock bias An observation function is constructed using an ionosphere-free combined model. The three-dimensional position and velocity of the current offshore terminal are estimated by extended Kalman filtering. The horizontal accuracy factor obtained during the solution process is used as an accuracy evaluation index to characterize the reliability of the positioning results.

6. The maritime positioning and search and rescue information encoding method based on BeiDou short message service according to claim 5, characterized in that, The encoding and encapsulation into a rescue short message in step 5 refers to constructing a rescue short message using a fixed frame structure based on BeiDou short messages, which includes: a frame header and security field and a rescue information data body field.

7. A maritime positioning and search and rescue information encoding method based on BeiDou short message service according to claim 6, characterized in that, The frame header and security fields include: The system consists of an 8-bit synchronization code, a 4-bit protocol version number, a 4-bit message type, a 4-bit terminal type, a 4-bit reserved field, a 16-bit CRC checksum, and a 32-bit message authentication code (MAC).

8. A maritime positioning and search and rescue information encoding method based on BeiDou short messages according to claim 7, characterized in that, The rescue information data body fields include: The system includes a 20-digit timestamp, 32-digit latitude, 32-digit longitude, 16-digit altitude, 8-digit horizontal precision factor, 12-digit ground speed, 12-digit heading angle, 4-digit distress type, 2-digit distress level, 2-digit alarm source, 8-digit equipment status indicator, 30-digit crew identification, 16-digit terminal number, and 16-digit crew number. Time stamps, latitude, longitude, altitude, horizontal precision factor, ground speed, and heading angle are represented using a fixed-point encoding method with bit depth and resolution.

9. A maritime positioning and search and rescue information encoding method based on BeiDou short message service according to claim 8, characterized in that, Step 5, which involves transmitting information via BeiDou satellite based on rescue assessment rules, includes: The maritime terminal is pre-configured with a manual trigger button and environmental and status sensors. During operation, button signals and sensor data are collected in real time. When a manual button trigger is detected, or when sensor data indicators exceed a preset safety threshold and the duration meets preset criteria, a maritime distress event is determined, triggering the rescue process and sending a short rescue message to the outside world via the Beidou satellite.

10. A maritime positioning and search and rescue information encoding method based on BeiDou short message service according to claim 9, characterized in that, Step 6, which involves parsing the received rescue short message, includes: According to the encoding and encapsulation rules of the rescue information in the rescue short message, the rescue short message is parsed and dequantized field by field to recover the time tag, latitude, longitude, altitude, horizontal precision factor, ground speed, heading angle, distress type, distress level, alarm source, equipment status flag, ship and personnel identification, terminal number and personnel number.

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