A method for sending short messages using BeiDou.

Abstract

This invention discloses a method for sending BeiDou short messages, relating to the field of BeiDou RSMC short message communication. This invention detects the BeiDou RDSS satellite signal reception status, determines the signal power and navigation data error rate, and automatically selects a data frame number generation mode based on the signal reception status to ensure the continuity of satellite frame numbers. The generated frame number is then used to generate an IC card authentication code, and finally, the generated frame number is used for signal inbound operations, completing the BeiDou short message sending function.

Description

Technical Field

[0001] This invention relates to the field of BeiDou RSMC short message communication, and in particular to a BeiDou short message transmission method. Background Technology

[0002] The BeiDou RSMC short message transmission function is a key feature that distinguishes the BeiDou satellite navigation and positioning system from foreign navigation systems such as GPS and GLONASS. It is a communication method achieved through BeiDou satellites, and the success rate of short message communication is an important indicator. Under conditions of good BeiDou satellite signal reception and no external interference, the communication success rate can reach over 95%.

[0003] In some industry applications, communication systems integrate multiple wireless communication devices such as Wi-Fi (2.4G), Bluetooth, 4G, and RSMC, creating complex electromagnetic environments. Alternatively, in remote or mountainous areas, RSMC data acquisition terminals may only be powered by mobile operators' 4G base stations, resulting in strong 4G signal interference. Under these interference conditions, the success rate of RSMC short message transmission is significantly reduced, or even malfunctions, failing to meet communication requirements.

[0004] The success rate of short message transmission for commonly used BeiDou RSMC short message terminals is directly related to the quality of satellite signal reception. After acquiring and tracking satellite signals to achieve code synchronization, the BeiDou short message terminal can demodulate the modulated navigation message from the satellite signal. An RSMC navigation message data frame consists of 48 frames per superframe, with a duration of 6 seconds and a frame duration of 125ms. When the user terminal is locked onto the outgoing signal, the transmission time of its incoming signal must be precisely aligned with the reception time of the responding outgoing beam, with a time quantization unit of 32PPS. These frame numbers are used to generate the incoming authentication code and serve as the reference for a specific incoming time when sending short messages. If these frame numbers cannot be demodulated normally or the demodulated frame numbers are discontinuous, the authentication code cannot be generated, and the incoming operation cannot be performed at the set transmission time. This leads to a decrease in the short message communication success rate or even the inability to send short messages.

[0005] The RSMC receiving frequency band is 2491.75±4.08MHz, while the operating frequency bands for Wi-Fi and Bluetooth are 2.4GHz~2.48GHz, and the operating frequency band for 4G is 2510MHz~2590MHz. These frequency bands are close to the RSMC receiving frequency band and have a relatively high ground voltage, which will interfere with the RSMC signal reception, affect the continuity of navigation messages, and in more serious cases, make the Beidou terminal unable to receive signals at all, resulting in the inability to obtain the reception time of the outbound beam and the inability to carry out normal inbound communication transmission.

[0006] Currently, methods to improve the success rate of RSMC short message transmission include improving the quality of the received signal, adding anti-interference designs to the hardware circuitry, adding RF filters to filter out out-of-band interference, and maintaining good linearity of the RF receiving circuitry. However, this method cannot completely eliminate the influence of interference signals, and its success rate cannot be guaranteed when the interference signal strength is high, especially when located close to a 4G base station. Furthermore, this method requires the addition of filters and the use of specially designed anti-interference RF circuits or chips, significantly increasing hardware costs. Summary of the Invention

[0007] In view of this, the present invention proposes a BeiDou short message transmission method, which can ensure the BeiDou short message transmission function when the BeiDou RSMC receiving signal is interfered with, thereby improving the communication success rate.

[0008] The objective of this invention is achieved as follows:

[0009] A method for sending BeiDou short messages involves detecting the reception status of BeiDou RDSS satellite signals, determining the signal power and navigation data error rate, automatically selecting a data frame number generation mode based on the signal reception status to ensure the continuity of satellite frame numbers, using the generated frame numbers to generate IC card authentication codes, and using the generated frame numbers to perform signal entry operations, thus completing the BeiDou short message sending function.

[0010] A method for sending short messages using the BeiDou Navigation Satellite System includes the following steps:

[0011] Step 1: Construct a local clock that is independent of satellite signals. The overflow time of the local clock is a pulse flag of 32PPS. Generate a locally maintained satellite frame number.

[0012] Step 2: Calculate the signal-to-noise ratio and perform CRC check on the navigation message;

[0013] Step 3: Based on the verification results of Step 2, determine the current interference situation of the received signal;

[0014] Step 4: Confirm the transmission beam;

[0015] Repeat steps 2 to 4 every 10 milliseconds; when it is necessary to send a BeiDou short message, execute the following steps:

[0016] Step 5: Based on the judgment result of Step 3, generate consecutive satellite frame numbers using different frame number generation methods;

[0017] Step 6: Use the satellite frame number to generate the identity authentication code, thereby encoding the entry information and determining the entry time.

[0018] Step 7: Use the confirmed transmission beam to send BeiDou short messages.

[0019] Furthermore, step 4 is specifically implemented as follows: periodically select an available satellite beam as the transmission beam and save the beam number; when the user terminal receives strong and continuous interference and is unable to complete beam selection, use the saved beam number as the transmission beam.

[0020] Furthermore, there are two possibilities for the judgment result in step 3:

[0021] The first scenario is that the satellite signal is subject to periodic interference, resulting in more than a quarter of the frame numbers being incorrect or discontinuous.

[0022] The second type: The satellite signal is subjected to strong and continuous interference, making it impossible to extract the frame number information from the satellite navigation message or the frame number is completely discontinuous;

[0023] In step 5, if the first judgment result occurs, consecutive satellite frame numbers are generated in the following manner:

[0024] 511) Sample the local clock using 8PPS of the received satellite downlink signal;

[0025] 512) Calculate the time deviation between the locally constructed 8PPS and the 8PPS of the satellite downlink signal sampling;

[0026] 513) Synchronize the local 8PPS to the satellite downlink signal 8PPS and quantize the time to 32PPS;

[0027] 514) Generate a 31.25ms interrupt signal using the synchronized 32PPS;

[0028] 515) Using the local 32PPS that has been synchronized with the satellite downlink signal as the time reference, and taking the last consecutive frame number parsed from the navigation message as the starting point, maintain a local consecutive satellite frame number;

[0029] In step 5, if the second judgment result occurs, consecutive satellite frame numbers are generated in the following manner:

[0030] 521) Generate a 31.25ms interrupt signal using a locally built 32PPS;

[0031] 522) Using the locally generated 32PPS as the time base, 1 as the start frame number, and 1920 frames as the end frame number, a local continuous satellite frame number is generated by repeating this process.

[0032] The beneficial effects of this invention compared to the prior art are as follows:

[0033] 1. This invention does not require redesigning the hardware circuit or adding other anti-interference devices such as RF filters; it only involves changes to the software algorithm, which greatly reduces costs.

[0034] 2. This invention improves the method for detecting the quality of received signals by adding the detection of message quality, thus avoiding situations where the signal power meets the standard but a large number of bit errors occur.

[0035] 3. This invention can greatly improve the success rate of short message transmission when RSMC satellite signals are interfered with, ensuring that the short message transmission function can be implemented normally. Attached Figure Description

[0036] Figure 1 This is a flowchart of satellite signal detection;

[0037] Figure 2 This is a flowchart of the satellite frame number generation process;

[0038] Figure 3 This is a flowchart of the BeiDou short message sending method. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings.

[0040] A method for sending BeiDou short messages involves detecting the BeiDou RSMC satellite signal reception status, determining the signal power and navigation data error rate, and using a baseband signal processing algorithm to automatically select a data frame number generation mode based on the signal reception status to ensure the continuity of satellite frame numbers. The generated frame number is then used to generate an IC card authentication code, and finally, the generated frame number is used for signal inbound operations, thus completing the BeiDou short message transmission function. Figure 3 As shown, the method includes the following steps:

[0041] Step 1: Construct a local clock that is independent of satellite signals. The overflow time of the local clock is a pulse flag of 32PPS. Generate a locally maintained satellite frame number.

[0042] Step 2: Calculate the signal-to-noise ratio and perform CRC check on the navigation message;

[0043] Step 3: Based on the verification results of Step 2, determine the current interference situation of the received signal;

[0044] Step 4: Confirm the transmission beam;

[0045] Repeat steps 2 to 4 every 10 milliseconds; when it is necessary to send a BeiDou short message, execute the following steps:

[0046] Step 5: Based on the judgment result of Step 3, generate consecutive satellite frame numbers using different frame number generation methods;

[0047] Step 6: Use the satellite frame number to generate the identity authentication code, thereby encoding the entry information and determining the entry time.

[0048] Step 7: Use the confirmed transmission beam to send BeiDou short messages.

[0049] There are two possible outcomes for the judgment in step 3:

[0050] The first scenario is that the satellite signal is subject to periodic interference, resulting in more than a quarter of the frame numbers being incorrect or discontinuous.

[0051] The second type: The satellite signal is subjected to strong and continuous interference, making it impossible to extract the frame number information from the satellite navigation message or the frame number is completely discontinuous;

[0052] In step 5, if the first judgment result occurs, consecutive satellite frame numbers are generated in the following manner:

[0053] 511) Sample the local clock using 8PPS of the received satellite downlink signal;

[0054] 512) Calculate the time deviation between the locally constructed 8PPS and the 8PPS of the satellite downlink signal sampling;

[0055] 513) Synchronize the local 8PPS to the satellite downlink signal 8PPS and quantize the time to 32PPS;

[0056] 514) Generate a 31.25ms interrupt signal using the synchronized 32PPS;

[0057] 515) Using the local 32PPS that has been synchronized with the satellite downlink signal as the time reference, and taking the last consecutive frame number parsed from the navigation message as the starting point, maintain a local consecutive satellite frame number;

[0058] In step 5, if the second judgment result occurs, consecutive satellite frame numbers are generated in the following manner:

[0059] 521) Generate a 31.25ms interrupt signal using a locally built 32PPS;

[0060] 522) Using the locally generated 32PPS as the time base, 1 as the start frame number, and 1920 frames as the end frame number, a local continuous satellite frame number is generated by repeating this process.

[0061] Step 4 requires periodically selecting an available satellite beam as the transmission beam and saving the beam number; when the user terminal receives strong and continuous interference and is unable to complete the beam selection, the saved beam number is used as the transmission beam.

[0062] Here is a more specific example:

[0063] A method for sending short messages using the BeiDou Navigation Satellite System includes the following steps:

[0064] 1) Construct a local clock that is independent of satellite signals, with the overflow time of the local clock marked by a 32PPS pulse flag;

[0065] The local external clock uses a 48.96MHz crystal oscillator, and all the time of the user machine is obtained by dividing this crystal oscillator frequency.

[0066] 2) Calculate the signal-to-noise ratio and perform CRC check on the navigation message;

[0067] First, calculate the signal-to-noise ratio (SNR) of the received signals from the 10 channels, SNR = 10log 10 (P s / P n ), where P S P represents the effective power of the signal. n This represents the effective power of the noise. Satellite navigation message parsing involves performing a CRC check on each frame of information. A correct check result flag is incremented by 1, and the flag count is recorded. After accumulating one second of time, the count is tallied. The process is as follows... Figure 1 As shown.

[0068] 3) Based on the satellite signal detection results in step 1), determine the current interference situation of the received signal;

[0069] If the calculated SNR value is less than a certain threshold, it is considered that the user equipment cannot receive the signal normally and is suffering from strong signal suppression interference.

[0070] If the calculated SNR value is within the normal range, the cumulative number of correct check flags is counted. If it is less than the number of correct flags that should be received, it is considered that the user equipment is experiencing periodic interference and the satellite frame number is discontinuous.

[0071] 4) Confirm the transmitted beam number;

[0072] Select the beam with a high SNR and a large cumulative count of CRC checksums as the transmit beam, and store this beam number. If none of the channels can receive satellite signals normally, then select the stored beam number as the transmit beam.

[0073] 5) Repeat steps 1) to 3) every second to check the signal reception quality.

[0074] The signal is detected every second.

[0075] 6) Based on the judgment result of step 2), use different frame number generation algorithms to generate consecutive satellite frame numbers.

[0076] The process is as follows Figure 2As shown. When the user terminal experiences strong signal suppression interference, the baseband processing module cannot receive satellite signals normally and configures the frame number generation mode to local 32PPS, unaffected by satellite signals. The user terminal's external clock is 48.96MHz, which is divided to obtain a 32Hz signal with a period of 31.25ms. This clock signal is used to maintain the locally generated frame number.

[0077] When the user terminal is subjected to periodic interference, resulting in discontinuous satellite frame numbers, the local clock is synchronized with the symbol of the satellite signal during the satellite signal synchronization process. After determining the position of the frame flag, the accumulated value of the local clock NCO is latched on the pulse edge corresponding to the frame flag.

[0078] Compare whether the frame numbers are consecutive to determine whether the current frame number can be used as the starting point for maintaining local frame numbers.

[0079] Using the time deviation τ between the 8PPS obtained from satellite signal sampling and the locally generated 8PPS, the local 8PPS is synchronized to the satellite-sampled 8PPS, and the time is quantized to 32PPS.

[0080] Using the determined frame number starting point and the synchronized 32PPS, generate local continuous satellite frame numbers.

[0081] 7) Use the generated frame number to generate the identity authentication code, complete the encoding of the entry information, and determine the entry time.

[0082] For BeiDou short message transmission, the transmission frame number needs to be sent as a parameter to the IC card. The IC card then generates the inbound authentication information. The user terminal obtains the current satellite frame number (Frame) and transmits after a delay of 10 frame numbers. This 10-frame delay (312.5ms) is used by the IC card to generate the authentication and inbound information encoding. When the frame number reaches Frame+10, the power amplifier module is activated, and transmission begins through the antenna.

[0083] This method first optimizes the response beam selection algorithm to avoid situations where the SNR meets the standard but the received satellite frame numbers are widely discontinuous when the received signal is interfered with, thus improving the transmission success rate. Secondly, a local satellite frame number maintenance system is built to prevent the terminal from failing to enter the station normally when it cannot receive signals. This method requires the data processing module and baseband signal processing module of the BeiDou short message terminal to coordinate and cooperate to achieve successful short message transmission. The data processing module detects the received satellite signals in the S-band and monitors the quality of the received satellite signal in real time. When the satellite signal reception power is too low or there is no received signal, or when the satellite reception power is normal but the satellite navigation data CRC check has continuous errors, it sends a frame number information switching signal to the baseband signal processing module. After receiving this signal, the baseband signal processing module opens the local frame number generation module and obtains a 32PPS signal with a period of 31.25ms by frequency division from the local clock. This signal maintains a local virtual satellite frame number. The initial value of this frame number is set to a value ranging from 1 to 1920, incrementing by 1 every 31.25ms, and resetting to 1 after reaching 1920, repeating this cycle. The baseband signal processing module transmits the generated local frame number to the data processing module via the data bus. The data processing module chooses to abandon the frame number obtained from satellite navigation information and instead uses the locally generated frame number to generate short message authentication information and control the transmission time, thereby enabling short message transmission. This method significantly reduces the short message terminal's dependence on the received signal and can guarantee the success rate of short message communication even under continuous and strong interference, making it suitable for applications with extremely high requirements for communication success rates.

[0084] This invention completely solves the problem of discontinuous satellite navigation information frame numbers caused by the weak satellite signal power and high bit error rate when the downlink signal S-band is subjected to periodic interference and long-term continuous suppression interference from wireless signals such as Wi-Fi, Bluetooth, 4G or adjacent frequency bands. It also solves the problem of the discontinuous satellite frame numbers leading to a significant reduction in the success rate of BeiDou short message communication or even its inability to be used.

[0085] This invention is completely independent of satellite signal reception quality, and even in situations where satellite signals are completely unavailable, it can guarantee the continuity of satellite frame numbers, thereby improving the success rate of BeiDou short message communication. This method requires no changes to the hardware circuitry; only modifications to the software code of the baseband processing algorithm and data processing algorithm are needed for implementation.

Claims

1. A method for sending short messages using the BeiDou Navigation Satellite System, characterized in that, Includes the following steps: Step 1: Construct a local clock that is independent of satellite signals. The overflow time of the local clock is a pulse flag of 32PPS. Generate a locally maintained satellite frame number. Step 2: Calculate the signal-to-noise ratio and perform CRC check on the navigation message; Step 3: Based on the verification results of Step 2, determine the current interference situation of the received signal; there are two possible results: The first scenario is that the satellite signal is subject to periodic interference, resulting in more than a quarter of the frame numbers being incorrect or discontinuous. The second type: The satellite signal is subjected to strong and continuous interference, making it impossible to extract the frame number information from the satellite navigation message or the frame number is completely discontinuous; Step 4, confirm the transmit beam; specifically, periodically select an available satellite beam as the transmit beam and save the beam number; when the user terminal receives strong and continuous interference and is unable to complete beam selection, use the saved beam number as the transmit beam. Repeat steps 2 to 4 every 10 milliseconds; when it is necessary to send a BeiDou short message, execute the following steps: Step 5: Based on the judgment result of Step 3, generate consecutive satellite frame numbers using different frame number generation methods; if the first judgment result occurs, then generate consecutive satellite frame numbers in the following manner: 511) Sample the local clock using 8 PPS of the received satellite downlink signal; 512) Calculate the time deviation between the locally constructed 8PPS and the 8PPS of the satellite downlink signal sampling; 513) Synchronize the local 8PPS to the satellite downlink signal 8PPS and quantize the time to 32PPS; 514) Generate a 31.25ms interrupt signal using the synchronized 32PPS; 515) Using the local 32PPS that has been synchronized with the satellite downlink signal as the time reference, a local continuous satellite frame number is maintained, starting from the last continuous frame number parsed from the navigation message. If the second judgment result occurs, consecutive satellite frame numbers will be generated in the following manner: 521) Generate a 31.25ms interrupt signal using a locally built 32PPS; 522) Using the locally generated 32PPS as the time base, 1 as the start frame number, and 1920 frames as the end frame number, repeating this process, a local continuous satellite frame number is generated. Step 6: Use the satellite frame number to generate the identity authentication code, thereby encoding the entry information and determining the entry time. Step 7: Use the confirmed transmission beam to send BeiDou short messages.

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