Portable emergency communication method based on Beidou short message

Abstract

The invention provides a portable emergency communication method based on a Beidou short message, and the method comprises the steps: an emergency communication device is used for receiving the data of a Beidou satellite, transmitting short message information and positioning information to a mobile terminal, and receiving an instruction from the mobile terminal; the emergency communication device comprises a forwarding unit which communicates with embedded software and is connected with a Bluetooth port of the mobile terminal equipment; two annular buffer areas, namely a Beidou data buffer area and a user data buffer area, are operated through embedded software, when the emergency communication device receives the Beidou data, the Beidou data are pressed into the Beidou data buffer area, whether the Beidou data are detected by a sending task or not is detected, and if the Beidou data exist, the Beidou data are transmitted to a user; and the emergency communication device presses the received user data into a user data buffer area, detects whether the user data exists in the user data buffer area or not through a receiving task, and then transmits the user data to a radio frequency module of the emergency communication device to be sent.

Description

Technical Field

[0001] The invention relates to the field of Beidou satellite communication positioning, and in particular to a portable emergency communication method based on Beidou short messages. Background Art

[0002] The BeiDou satellite system is a global active three-dimensional satellite positioning and communication system (CNSS) independently developed by China. It is the third mature satellite system after the US Global Positioning System (GPS) and Russia's GLONASS. The positioning accuracy of the BeiDou satellite system has reached the international advanced level. Its unique short message communication function has played an important role in emergency rescue, location tracking, information exchange and other applications. Its short message communication capacity has also increased from 120 Chinese characters per message to 1,000 Chinese characters compared to BeiDou-2, greatly improving the practicality of BeiDou communication. The BeiDou satellite system provides users with high-quality positioning, navigation and timing services. Its construction and development follow the principles of openness, autonomy, compatibility and gradualism.

[0003] The signal types of the Beidou system are mainly RDSS and RNSS. In the RNSS system, Beidou satellites will continuously transmit RNSS signals with time and location to the ground. After parsing the message, the real-time location of the navigation terminal can be solved. In the RDSS system, the satellite transmits an inquiry signal to the ground, and the terminal sends it to the ground station after receiving it. The ground station determines whether it is positioning or communication. For positioning requests, the ground station will calculate the user's current position based on the user parameters and return it to the user terminal. For communication requests, the ground station will directly send the data to the user terminal.

[0004] Terminals based on Beidou positioning and communication technology need to improve positioning accuracy, communication capabilities, practicality, convenience, reduce equipment power consumption, optimize performance and ensure reliability. Most of the existing communication and positioning terminals are based on the GPS navigation and positioning system, and must communicate with the outside world through the mobile communication network. This makes it impossible for the terminal to communicate with the outside world when the network signal is poor, and the received positioning information cannot be reported to the background server. The background server cannot know the location of the terminal, which makes it impossible to guarantee the safety of users using the terminal. Especially in unmanned areas and special areas, when there is no mobile communication network signal, the corresponding terminal cannot communicate with the outside world, which will cause huge safety hazards. At the same time, the existing Beidou communication and positioning terminals are limited to vehicle-mounted and handheld types, with large overall size and high power consumption. For outdoor users, it is inconvenient to carry and use, and has limited practicality.

[0005] Therefore, it is necessary to provide a portable emergency communication method based on Beidou short messages to solve the above problems. Summary of the invention

[0006] The present invention provides a portable emergency communication method based on Beidou short message, which solves the problems of single function and poor stability of existing Beidou communication positioning terminals, realizes the characteristics of high positioning accuracy, safety and reliability, and strong practicality, and truly has all-day, all-weather, and full coverage capabilities. Its technical solution is as follows: A portable emergency communication method based on Beidou short messages comprises an emergency communication device and embedded software of a mobile terminal, wherein the emergency communication device is used to receive data from Beidou satellites, send short message information and positioning information to the mobile terminal, and receive instructions from the mobile terminal; the emergency communication device comprises a forwarding unit for communicating with the embedded software to achieve connection with a Bluetooth port of a mobile terminal device; the embedded software needs to operate two circular buffers, namely a Beidou data buffer and a user data buffer; when the emergency communication device receives Beidou data, the Beidou data is pressed into the Beidou data buffer, a sending task is used to detect whether it is Beidou data, and if there is Beidou data, it is transmitted to the user; the emergency communication device presses the received user data into the user data buffer, detects whether there is user data in the user data buffer through a receiving task, and then transmits the user data to its own radio frequency module for transmission.

[0007] When the forwarding unit receives data, both the user data and the Beidou data formats start with a $ symbol, wherein the fifth and sixth digits are length information. During the receiving process, the received $ symbol is used as the starting symbol, and then the length of the received data message is calculated from the received fifth and sixth characters. Finally, the remaining characters are received according to the length, and after the remaining characters are received completely, the check values ​​of all characters are calculated, and the obtained check value is compared with the last digit. If the calculated check value is the same as the last check value, the complete packet is pressed into the data buffer; if they are inconsistent, the entire message is discarded.

[0008] When the forwarding unit encapsulates Beidou data, it is divided into the encapsulation of the following fields: S21: command type name, including time detection, power detection, version reading, system self-check, serial port output, positioning information and communication information; S22: Filling of user address value. The user address value is the address of the local user. The size of this field is only three bytes long. S23: content field. The information in the content field depends on different information categories, and the content length of different information categories is also different; S24: Checksum is generated by XORing each byte based on the previous category information, user address, and information content to ensure that the bit error rate is reduced during data reception.

[0009] When the forwarding unit sends data, the design of the user data and Beidou data sending processes is the same. In the data sending task, it is detected whether there is new data to be sent in the buffer. If there is new data to be sent, the Bluetooth sending serial port is opened and the data is sent out through the Bluetooth serial port. During the sending process, the message of each buffer is taken out, and according to the length information in the message, the message is sent out from the serial port in sequence according to the hexadecimal code.

[0010] The emergency communication device includes a main control unit circuit, a communication interface module, a Beidou RDSS communication module, and a Beidou RNSS positioning module. The Beidou RDSS communication module and the Beidou RNSS positioning module are both connected to the main control unit circuit. The Beidou RDSS communication module communicates with the Beidou satellite via the Beidou antenna, and the Beidou RNSS positioning module communicates with the Beidou satellite via the GNSS antenna. The main control unit circuit communicates with the mobile phone Bluetooth via the communication interface module.

[0011] The communication interface module includes a Bluetooth module and a USB interface. The Bluetooth module is used to connect to the mobile phone Bluetooth. The Bluetooth module and the USB interface are both connected to the ARM processor.

[0012] The emergency communication method includes three working modes: communication link, positioning link, and communication plus positioning link; the communication link receives the RDSS signal of the Beidou satellite, processes the signal and uses a mobile phone APP to check and display it, and issues instructions through the mobile phone APP, which are forwarded by the Bluetooth module to the main control unit circuit for information transmission; the positioning link receives the navigation telegram data of the Beidou satellite through the GNSS antenna, and the main control unit circuit sends the data to the mobile phone APP through the Bluetooth module, and extracts and displays the valid positioning data information through the mobile phone APP; the communication plus positioning link is that the main control unit circuit extracts valid positioning data from the navigation telegram data sent by the Beidou satellite, and uses the Beidou third-generation short message format to encapsulate it into a communication instruction, and the communication instruction is sent out through the Beidou antenna.

[0013] The Beidou RNSS positioning module is used to complete RF front-end processing, baseband signal processing, and positioning solution processing for the positioning signal sent by the Beidou satellite, and finally output the standard NMEA0183 protocol through the serial port. The positioning solution adopts the Kalman filter positioning algorithm.

[0014] The Kalman filter positioning solution process includes the following prediction steps: At each positioning epoch, the Kalman filter first uses the state equation to predict the current position, velocity, and clock error of the emergency communication device; Determine the Kalman filter state quantity and model it. Under low dynamic conditions, the uniform acceleration motion model is used. The state quantity is ; where xu ,y u 、z u is the position state quantity, v xu 、v yu 、v zu is the velocity state quantity, is the system clock error, is the clock drift state quantity; Create a state equation and make a one-step prediction. The state equation after discretization is: ,in, is the state transfer matrix, is the a posteriori state estimate of the k-1th epoch, that is, the state quantity after filtering of the k-1th epoch, and w is the system noise of the k-1th epoch; Calculate the prior estimate error variance covariance matrix ,in is the variance-covariance matrix of the system noise; is the filtered error covariance matrix for the k-1th epoch.

[0015] The Kalman filter positioning solution process includes a correction step: obtaining a correction amount of a system state estimate and its corrected optimal estimate by processing a measurement residual; according to Array, Array and The gain matrix is ​​calculated ,in, is the observation matrix, The matrix is ​​the variance-covariance matrix of the observed quantity error, which can be set according to the actual pseudorange and Doppler accuracy of the emergency communication device; Calculate the best estimate ,in is the prior residual, i.e., pseudorange and pseudorange rate Measure the one-step prediction residual; Calculate the posterior estimation error variance covariance matrix , is the identity matrix.

[0016] The portable emergency communication method based on Beidou short messages realizes RDSS two-way short message communication and positioning between the emergency communication device and the Beidou-3 satellite. The unique Beidou short message communication and positioning can provide users with more reliable security protection. The present invention is more powerful in functions such as positioning speed and accuracy, and is more practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A circuit diagram of a portable emergency communication device based on Beidou short messages provided by the present invention; Figure 2 is a flow chart of the Beidou RNSS positioning module; Figure 3 It is a data processing flow chart of the Kalman filter of the Beidou RNSS positioning module; Figure 4 The overall design framework diagram of the software system of the portable emergency communication method based on Beidou short message provided by the present invention; Figure 5 A data receiving flow chart of a portable emergency communication method based on Beidou short messages provided by the present invention; Figure 6 A flow chart of the Beidou data encapsulation process of the portable emergency communication method based on Beidou short message provided by the present invention; Figure 7 A data sending flow chart of a portable emergency communication method based on Beidou short messages provided by the present invention. DETAILED DESCRIPTION

[0018] The following will describe the technology in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative designs are within the scope of protection of the present invention.

[0019] like Figure 1 As shown, a portable emergency communication device based on Beidou short messages includes a main control unit circuit, a communication interface module, a Beidou RDSS communication module, and a Beidou RNSS positioning module. The Beidou RDSS communication module and the Beidou RNSS positioning module are both connected to the main control unit circuit. The Beidou RDSS communication module communicates with the Beidou satellite through the Beidou antenna, and the Beidou RNSS positioning module communicates with the Beidou satellite through the GPS antenna. The main control unit circuit communicates with the mobile phone Bluetooth through the communication interface module.

[0020] The main control unit circuit includes an ARM processor and a memory and auxiliary circuit connected thereto. The memory is provided with 128K FLASH and 20K SRAM. The auxiliary circuit is provided with 3 serial ports UART, an AD sampling pin, and many IO ports. The ARM processor has a power supply range of 2.0~3.6V, and the ripple can be tolerated within 50mV. LDO voltage regulator 3.3V power supply is selected to ensure that the chip works normally. The terminal also includes a JTAG debugging module connected to the ARM processor.

[0021] The communication interface module includes a Bluetooth module and a USB interface. The Bluetooth module is used to connect to the mobile phone Bluetooth. The Bluetooth module and the USB interface are both connected to the ARM processor. The Bluetooth module is highly integrated, has its own enabling pin, and does not require any additional peripheral devices. It is set to bridge mode and connected to the user CPU through a universal serial port to establish two-way communication between the user CPU and the mobile device.

[0022] The frequencies of the Beidou antenna and the GPS antenna are different. The frequencies used by the Beidou system are 1561.098MHz and 1589.742MHz, while the frequencies used by the GPS system are 1575.42MHz and 1227.60MHz. The signal processing methods of the Beidou antenna and the GPS antenna are also different. The Beidou system uses CDMA (code division multiple access) technology, while the GPS system uses TDMA (time division multiple access) technology. The Beidou antenna and the GPS antenna require different antenna designs and positioning methods to adapt to different coverage ranges. Furthermore, the Beidou antenna includes an RDSS receiving (S-band) antenna and an RDSS transmitting (L-band) antenna.

[0023] Through the above-mentioned device, the portable emergency communication method based on Beidou short message provided by the present invention includes three working modes: communication link, positioning link, and communication plus positioning link.

[0024] S1 Communication link: The RDSS signal received by the Beidou antenna is amplified, filtered, and down-converted by the RF module to form an intermediate frequency signal, which is sampled by the A / D analog-to-digital converter and sent to the baseband processor. The Beidou antenna adopts a multi-layer ceramic antenna design, supports Beidou B1I / B1C, B2a, and GPS L1C / A frequency points, has a higher dielectric constant than traditional antennas, and uses a low-noise amplifier to reduce the impact of antenna thermal noise and other circuits on the performance of emergency communication devices.

[0025] The baseband processor processes the signal and sends the information corresponding to the signal to the main control unit circuit. The main control unit circuit sends the information to the Bluetooth module, which reaches the mobile phone through Bluetooth communication and is checked and displayed using the mobile phone APP. Conversely, when communication, positioning or inquiry is required, instructions are issued through the mobile phone APP, which is forwarded by the Bluetooth module to the main control unit circuit for information processing. The main control unit circuit composes a data packet according to the signal format of the RDSS signal and inputs the data packet into the baseband processor. The baseband processor performs convolution encoding and spread spectrum modulation on the data packet and then sends it to the RF module. Under the control of the baseband processor, it starts to send according to the specified timing.

[0026] S2 Positioning Link: The navigation message data of Beidou satellite is received through the GNSS antenna. The data is sent to the Beidou RNSS positioning module through a low noise amplifier (LAN) and a filter. The Beidou RNSS positioning module sends the received data to the baseband processor. The baseband processor obtains data information through demodulation and then sends it to the main control unit circuit for information processing. The main control unit circuit sends the data to the mobile phone APP through the Bluetooth module. The mobile phone APP extracts the effective positioning data information and displays it.

[0027] S3 communication plus positioning link: When the portable emergency communication device based on Beidou short message uses the SOS one-button alarm and continuous tracking and positioning functions, the main control unit circuit extracts effective positioning data from the navigation message data sent by the Beidou satellite, and encapsulates it into communication instructions using the Beidou third-generation short message format. The communication instructions are sent out through the Beidou antenna and can be operated by a single machine throughout the process.

[0028] The signal processing performed by the present invention is mainly that the Beidou satellite sends navigation information to ground users through radio signals. Ground users receive these signals through a portable emergency communication device based on Beidou short messages as a receiving device. The emergency communication device processes the received signals, including operations such as signal amplification, filtering, and demodulation to extract navigation information. The extracted navigation information needs to be decoded to obtain key information such as the satellite's position and time. At the same time, the satellite position and time information obtained by decoding are combined with the position and time information of the emergency communication device to obtain the position information of the emergency communication device. The emergency communication device outputs the calculated position information for user use.

[0029] In the first step of signal processing, the emergency communication device needs to search and capture signals from Beidou satellites. The key to the capture phase is to quickly and accurately identify and lock these weak satellite signals. Once the signal is captured, the emergency communication device needs to maintain synchronization with the satellite signal and continue to track changes in the signal. The most important thing is to accurately adjust the frequency, phase and amplitude of the signal to ensure that any changes in the signal transmission process can be accurately captured by the emergency communication device. After the signal is successfully tracked and synchronized, the emergency communication device begins to decode and process the navigation data received from the satellite. These data include the satellite's orbital parameters, clock errors, health status, etc. Using the decoded navigation data, the emergency communication device can calculate the position, speed and time.

[0030] Due to various factors, such as atmospheric delay, multipath effect, emergency communication device clock error, etc., the calculated position information may contain errors. Therefore, the emergency communication device needs to perform error correction to improve positioning accuracy. The positioning information corrected by filtering and solving is output and displayed in an appropriate format. At the same time, in order to improve positioning accuracy and reliability, the emergency communication device can integrate accelerometers, gyroscope sensors, and use GPS signals to further improve positioning accuracy and availability.

[0031] For the above three working modes, the main control unit circuit receives the intermediate frequency signal sent by the RF module on the one hand to complete the signal capture task, and on the other hand calculates the current position, speed, clock error and clock error change rate of the device to implement navigation services. In the communication link, the key lies in Beidou RDSS communication. The Beidou RDSS communication module is an important component for realizing the Beidou short message communication function. It integrates low-noise amplifiers, phase-locked loops, RF chips, baseband chips and power amplifiers. RX serves as the receiving channel input of the RDSS module, and the signal it receives is the satellite signal modulated by the inbound signal in the S band. TX is the transmitting channel of RDSS, and the transmitting signal is the signal modulated in the L band by the baseband protocol encapsulation of the message information.

[0032] like Figure 2 The internal signal flow of the Beidou RNSS positioning module shown in the figure, the Beidou RNSS positioning module can complete a series of tasks including RF front-end processing, baseband signal processing, and positioning solution, and finally output the standard NMEA0183 protocol through the serial port. In the positioning of emergency communication devices, the measured values ​​at each moment contain a certain error. Since the least squares method used to achieve positioning does not link the positioning values ​​at different moments, the traditional positioning results that simply use the least squares method are usually rough and messy. When a user moves in a uniform straight line on a horizontal plane, the least squares positioning solution may show that the user's position is shaking left and right, up and down, or even back and forth in space. The positioning solution adopts the Kalman filter positioning algorithm. The Kalman filter can link the user's position status at adjacent moments, thereby overcoming the disadvantage that the least squares method positioning values ​​at different moments are not correlated with each other, making the filtered positioning results smoother and more accurate.

[0033] The Kalman filter positioning solution process is divided into two processes: prediction and correction, which specifically include the following steps: S11: At each positioning epoch, the Kalman filter first uses the state equation to predict the current position, speed, clock error and other states of the emergency communication device; Determine the Kalman filter state quantity and model it. Under low dynamic conditions, the uniform acceleration motion model is used. The state quantity is ; where x u ,y u 、zu is the position state quantity, v xu 、v yu 、v zu is the velocity state quantity, is the system clock error, It is the clock drift state quantity.

[0034] Create a state equation and make a one-step prediction. The state equation after discretization is: ,in, is the state transfer matrix, is the a posteriori state estimate of the k-1th epoch, that is, the state quantity after filtering of the k-1th epoch, and w is the system noise of the k-1th epoch; Calculate the one-step forecast error variance-covariance matrix ,in is the variance-covariance matrix of the system noise; is the filtered error covariance matrix for the k-1th epoch.

[0035] Based on this state prediction estimate and the satellite position and velocity provided by the satellite ephemeris, the Kalman filter can predict the pseudorange and Doppler frequency shift values ​​of the emergency communication device for each satellite, and the difference between these measurement predictions and the actual measurement values ​​of the emergency communication device forms the measurement residual.

[0036] S12: The correction process of the Kalman filter obtains the correction amount of the system state estimate and its corrected optimal estimate by processing the measurement residual.

[0037] according to Array, Array and The gain matrix is ​​calculated ,in, is the observation matrix, The matrix is ​​the variance-covariance matrix of the observation error, which can be set according to the actual pseudorange and Doppler accuracy of the emergency communication device.

[0038] Calculate the best estimate ,in To measure the one-step prediction error, namely the pseudorange and pseudorange rate Measures the one-step forecast residual.

[0039] Calculate the variance-covariance matrix of the state error after filtering , is the identity matrix.

[0040] It can be seen that the Kalman filter not only outputs smoother positioning and velocity measurement results, but also outputs the variance and covariance estimates of the state quantity errors, which can roughly characterize the quality of the current filter state. If the absolute values ​​of multiple satellite measurement residuals are too large at multiple times, it is very likely that the state estimate of the Kalman filter has serious deviations, and the system state and filter need to be reset.

[0041] like Figure 4 As shown, the portable emergency communication device based on Beidou short message interacts with a mobile phone, and the mobile phone needs to install an APP of embedded software. The portable emergency communication method based on Beidou short message provided by the present invention is mainly divided into two parts for the design and implementation of embedded software.

[0042] The first part is the design of the embedded forwarding unit. Traditional mobile terminal devices do not have Beidou communication function. To realize Beidou emergency communication on mobile phones, a forwarding unit needs to be introduced to connect to the Bluetooth port of the mobile terminal device. The forwarding unit receives and parses the data of the Beidou module through the serial port and transmits it to the mobile phone through Bluetooth. At the same time, the data of the mobile phone can also be sent to the forwarding unit through Bluetooth, and the forwarding unit sends the data to the Beidou RF module, so that ordinary mobile terminals have the function of data communication through the Beidou communication channel.

[0043] The second part is the implementation of the embedded forwarding software. The control process of the embedded forwarding software is to operate two circular buffers, one is the Beidou data buffer and the other is the user data buffer. When the emergency communication device receives Beidou data through the first serial port, it pushes the Beidou data into the buffer, and the sending task detects whether it is Beidou data. If there is Beidou data, it will be transmitted to the user through the third serial port using Bluetooth. For the user data of the third serial port, it is pushed into the user data buffer, and the receiving task detects whether there is user data in the buffer, and then the user data is transmitted to the RF module through the serial port.

[0044] like Figure 5 As shown, the data receiving flow chart implemented by the forwarding unit, the user data and Beidou data formats both start with the $ symbol, wherein the fifth and sixth bits are length information, so the design of the receiving process of the two is completely consistent. In the receiving process, the received $ symbol is used as the starting symbol, and then the length of the received data message is calculated from the fifth and sixth characters received, and finally the remaining characters are received according to the length, and the check values ​​of all characters are calculated after the remaining characters are received completely, and the obtained check value is compared with the last bit, if the calculated check value is the same as the last check value, then this complete packet is pressed into the data buffer, if it is inconsistent, the entire message is discarded.

[0045] like Figure 6As shown, when the forwarding unit encapsulates Beidou data, Beidou command encapsulation is mainly divided into several fields: S21. Command type name. The type name refers to the type of command being sent. The type names in the Beidou-1 commands are: time detection, power detection, version reading, system self-test, serial port output, positioning information, and communication information.

[0046] S22, filling of user address, the user address value is the address of the local user, the size of this field is only three bytes long. It can be all 0 when querying the local address information.

[0047] S23, content field, the content field is relatively complex. Because the content fields of different Beidou information are different, the content field of time detection only contains output frequency information. The power detection only contains the frame number, but the communication information includes information category, user address, message length and other information. The specific content of the content information depends on the different information categories, and the content length of different information categories is also different.

[0048] S24, checksum, checksum is generated by XORing each byte based on the previous category information, user address, and information content. Its purpose is to ensure that the bit error rate is reduced during the data reception process.

[0049] like Figure 7 As shown, when the forwarding unit sends data, the design of the user data and Beidou data sending process is the same. In the data sending task, it is detected whether there is new data to be sent in the buffer. If there is new data to be sent, the Bluetooth sending serial port is opened and the data is sent out through the Bluetooth serial port. In the sending process, the message in each buffer is taken out, and according to the length information in the message, the message is sent out from the serial port in sequence according to the hexadecimal code.

[0050] The portable emergency communication method based on Beidou short messages realizes RDSS two-way short message communication and positioning between the emergency communication device and the Beidou-3 satellite. The unique Beidou short message communication and positioning can provide users with more reliable security protection. The present invention is more powerful in functions such as positioning speed and accuracy, and is more practical.

[0051] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A portable emergency communication method based on Beidou short message, characterized in that: The invention comprises an emergency communication device and embedded software for a mobile terminal, wherein the emergency communication device is used to receive data from Beidou satellites, send short message information and positioning information to the mobile terminal, and receive instructions from the mobile terminal; the emergency communication device comprises a forwarding unit for communicating with the embedded software to realize connection with the Bluetooth port of the mobile terminal device; the embedded software needs to operate two circular buffers, namely, a Beidou data buffer and a user data buffer; when the emergency communication device receives Beidou data, the Beidou data is pressed into the Beidou data buffer, a sending task is used to detect whether it is Beidou data, and if there is Beidou data, it is transmitted to the user; the emergency communication device presses the received user data into the user data buffer, detects whether there is user data in the user data buffer through a receiving task, and then transmits the user data to its own radio frequency module for transmission.

2. The portable emergency communication method based on Beidou short message according to claim 1, characterized in that: When the forwarding unit receives data, both the user data and the Beidou data formats start with a $ symbol, wherein the fifth and sixth digits are length information. During the receiving process, the received $ symbol is used as the starting symbol, and then the length of the received data message is calculated from the received fifth and sixth characters. Finally, the remaining characters are received according to the length, and after the remaining characters are received completely, the check values ​​of all characters are calculated, and the obtained check value is compared with the last digit. If the calculated check value is the same as the last check value, the complete packet is pressed into the data buffer; if they are inconsistent, the entire message is discarded.

3. The portable emergency communication method based on Beidou short message according to claim 1 is characterized in that: When the forwarding unit encapsulates Beidou data, it is divided into the encapsulation of the following fields: S21: command type name, including time detection, power detection, version reading, system self-check, serial port output, positioning information and communication information; S22: Filling of user address value. The user address value is the address of the local user. The size of this field is only three bytes long. S23: content field. The information in the content field depends on different information categories, and the content length of different information categories is also different; S24: Checksum is generated by XORing each byte based on the previous category information, user address, and information content to ensure that the bit error rate is reduced during data reception.

4. The portable emergency communication method based on Beidou short message according to claim 1, characterized in that: When the forwarding unit sends data, the design of the user data and Beidou data sending processes is the same. In the data sending task, it is detected whether there is new data to be sent in the buffer. If there is new data to be sent, the Bluetooth sending serial port is opened and the data is sent out through the Bluetooth serial port. During the sending process, the message of each buffer is taken out, and according to the length information in the message, the message is sent out from the serial port in sequence according to the hexadecimal code.

5. The portable emergency communication method based on Beidou short message according to claim 1 is characterized in that: The emergency communication device includes a main control unit circuit, a communication interface module, a Beidou RDSS communication module, and a Beidou RNSS positioning module. The Beidou RDSS communication module and the Beidou RNSS positioning module are both connected to the main control unit circuit. The Beidou RDSS communication module communicates with the Beidou satellite via the Beidou antenna, and the Beidou RNSS positioning module communicates with the Beidou satellite via the GPS antenna. The main control unit circuit communicates with the mobile phone Bluetooth via the communication interface module.

6. The portable emergency communication method based on Beidou short message according to claim 5 is characterized in that: The communication interface module includes a Bluetooth module and a USB interface. The Bluetooth module is used to connect to the mobile phone Bluetooth. The Bluetooth module and the USB interface are both connected to the ARM processor.

7. The portable emergency communication method based on Beidou short message according to claim 5 is characterized in that: The emergency communication method includes three working modes: communication link, positioning link, and communication plus positioning link; the communication link receives the RDSS signal of the Beidou satellite, processes the signal and uses a mobile phone APP to check and display it, and issues instructions through the mobile phone APP, which are forwarded by the Bluetooth module to the main control unit circuit for information transmission; the positioning link receives the navigation telegram data of the Beidou satellite through the GNSS antenna, and the main control unit circuit sends the data to the mobile phone APP through the Bluetooth module, and extracts and displays the valid positioning data information through the mobile phone APP; the communication plus positioning link is that the main control unit circuit extracts valid positioning data from the navigation telegram data sent by the Beidou satellite, and uses the Beidou third-generation short message format to encapsulate it into a communication instruction, and the communication instruction is sent out through the Beidou antenna.

8. The portable emergency communication method based on Beidou short message according to claim 7 is characterized in that: The Beidou RNSS positioning module is used to complete RF front-end processing, baseband signal processing, and positioning solution processing for the positioning signal sent by the Beidou satellite, and finally output the standard NMEA0183 protocol through the serial port. The positioning solution adopts the Kalman filter positioning algorithm.

9. The portable emergency communication method based on Beidou short message according to claim 8, characterized in that: The Kalman filter positioning solution process includes the following prediction steps: At each positioning epoch, the Kalman filter first uses the state equation to predict the current position, velocity, and clock error of the emergency communication device; Determine the Kalman filter state quantity and model it. Under low dynamic conditions, the uniform acceleration motion model is used. The state quantity is ; where x u ,y u 、z u is the position state quantity, v xu 、v yu 、v zu is the velocity state quantity, is the system clock error, is the clock drift state quantity; Create a state equation and make a one-step prediction. The state equation after discretization is: ,in, is the state transfer matrix, is the a posteriori state estimate of the k-1th epoch, that is, the state quantity after filtering of the k-1th epoch, and w is the system noise of the k-1th epoch; Calculate the prior estimate error variance covariance matrix ,in is the variance-covariance matrix of system noise; is the filtered error covariance matrix for the k-1th epoch.

10. The portable emergency communication method based on Beidou short message according to claim 9, characterized in that: The Kalman filter positioning solution process includes a correction step: obtaining a correction amount of a system state estimate and its corrected optimal estimate by processing a measurement residual; according to Array, Array and The gain matrix is ​​calculated ,in, is the observation matrix, The matrix is ​​the variance-covariance matrix of the observed quantity error, which can be set according to the actual pseudorange and Doppler accuracy of the emergency communication device; Calculate the best estimate ,in is the prior residual, i.e., pseudorange and pseudorange rate Measure the one-step prediction residual; Calculate the posterior estimation error variance covariance matrix , is the identity matrix.

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