Beidou split type dual-mode communication terminal suitable for ocean buoy and communication link switching method

Abstract

The application discloses a Beidou split type dual-mode communication terminal suitable for a marine buoy and a communication link switching method, an antenna unit comprises a passive antenna, a filter circuit, a low-noise amplifier, a power amplifier, a multiplexer and a voltage switching circuit; a host unit comprises a processor, a public network communication module and a Beidou short message communication module, the processor is connected with the public network communication module and the Beidou short message communication module; a radio frequency cable connecting the antenna unit and the host unit is used for simultaneously transmitting radio frequency signals and direct current power supply; the processor is used for acquiring signal quality parameters of a public network communication link, and determining a target communication link from the public network communication link and a Beidou short message communication link according to a matching result of the signal quality parameters and preset conditions. The application realizes seamless connection of offshore large-capacity data high-speed transmission and reliable guarantee of key data in the open sea, and improves the reliability and maintainability of the marine buoy communication system.

Description

Technical Field

[0001] This invention relates to the field of marine monitoring and satellite communication technology, and in particular to a Beidou split-type dual-mode communication terminal and communication link switching method suitable for marine buoys. Background Technology

[0002] Ocean buoys are crucial infrastructure for marine environmental monitoring, weather forecasting, and disaster early warning. With the advancement of "smart ocean" initiatives, higher demands are being placed on the real-time performance, reliability, and transmission capacity of data collected by buoys.

[0003] Currently, there are three main types of communication solutions for ocean buoys: First, data transmission is carried out using terrestrial public networks such as 5G / 4G, relying on coastal base stations. This solution has the advantages of high transmission speed and low latency in near-shore areas, but in offshore areas far from the coast, communication links are often interrupted or unavailable due to the limited coverage of base stations.

[0004] Second, relying on foreign commercial satellite communication systems (such as Iridium and Inmarsat) for long-distance data transmission. While this solution can achieve global coverage, on the one hand, communication costs are high, resulting in huge long-term operating costs; on the other hand, data relay via foreign satellites poses a risk of leakage of sensitive monitoring data, making it difficult to meet the security requirements of critical infrastructure for independent and controllable information.

[0005] Third, the short message service of the BeiDou Navigation Satellite System is used for data backhaul. This solution achieves autonomous control of the communication link, but the transmission frequency and single message capacity are extremely limited, which cannot meet the real-time transmission requirements of buoys for high-frequency, high-capacity observation data.

[0006] Existing technologies have attempted to integrate the aforementioned communication methods in a simple manner, but these still suffer from the following significant drawbacks: First, there is a significant conflict between equipment integration and marine environmental protection. For example, while traditional BeiDou integrated terminals have high functional integration, they are extremely difficult to repair or replace on-site if the antenna or main unit malfunctions during long-term service in high-salt-spray and highly corrosive marine environments due to the highly coupled internal structure. Furthermore, to balance internal heat dissipation and antenna signal transmission, the overall waterproof and dustproof rating (IP rating) of the equipment is difficult to achieve, further shortening its reliable service life under harsh sea conditions.

[0007] Secondly, the data link switching lacks an intelligent decision-making mechanism. Existing buoy communication systems mostly rely on manual remote intervention or simple signal triggering for switching between near-shore and offshore communication modes. This passive and delayed switching method lacks comprehensive assessment and prediction of the real-time communication quality of each link (such as signal strength, bit error rate, packet loss rate, etc.), resulting in untimely or poor-quality switching, severely affecting the continuity and reliability of data transmission, and failing to meet the requirements of 24 / 7 unattended automated operation.

[0008] In summary, designing a marine buoy communication system that can integrate multiple types of communication link resources to achieve autonomous control and wide-area coverage, intelligently switch links based on communication quality, and possess high environmental adaptability and ease of maintenance is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0009] In order to overcome the above-mentioned problems in the prior art, the present invention proposes a Beidou split-type dual-mode communication terminal and communication link switching method suitable for marine buoys.

[0010] The technical solution adopted by the present invention to solve its technical problem is: a Beidou split-type dual-mode communication terminal suitable for marine buoys, including an antenna unit, wherein the antenna unit includes a passive antenna, a filter circuit, a low-noise amplifier, a power amplifier, a multiplexer, and a voltage switching circuit; The host unit includes a processor, a public network communication module, and a BeiDou short message communication module, wherein the processor is connected to the public network communication module and the BeiDou short message communication module respectively; An RF cable connects the antenna unit and the host unit, and is used to simultaneously transmit RF signals and DC power. The processor is used to acquire signal quality parameters of the public network communication link, determine the target communication link from the public network communication link and the Beidou short message communication link based on the matching result of the signal quality parameters and preset conditions, and transmit the monitoring data of the marine buoy through the target communication link.

[0011] The aforementioned Beidou split-type dual-mode communication terminal suitable for marine buoys includes a voltage switching circuit comprising a voltage comparator and a switching transistor. The voltage comparator is used to monitor the feed voltage on the radio frequency cable and output a control signal according to the feed voltage. The switching transistor is used to connect or disconnect the power supply path of the power amplifier according to the control signal.

[0012] The above-mentioned Beidou split-type dual-mode communication terminal suitable for marine buoys includes a multiplexer comprising a power divider and a bandpass filter. The power divider is used to distribute the multi-band signals received by the passive antenna to signal processing branches at different frequency points. The bandpass filter is disposed on the signal processing branch and is used to filter the signal at the corresponding frequency point.

[0013] The aforementioned Beidou split-type dual-mode communication terminal for marine buoys includes an upper board and a lower board electrically connected via an inter-board connector. The upper board is equipped with the Beidou short message communication module, public network communication module, RNSS positioning module, and power management module; The lower board carries the processor and peripheral interface circuitry; The power management module is used to convert the voltage provided by the lower board into different voltages to power the Beidou short message communication module, public network communication module, and RNSS positioning module.

[0014] The aforementioned Beidou split-type dual-mode communication terminal for marine buoys includes, in its peripheral interface circuitry, at least one of the following: gigabit Ethernet port, USB interface, RS-232 serial interface, SIM card slot, SPI interface, and I2C interface.

[0015] A communication link switching method, based on the above-mentioned Beidou split-type dual-mode communication terminal suitable for marine buoys, includes: Step 1: Obtain the signal quality parameters of the public network communication link; Step 2: Based on the matching result of the signal quality parameters and preset conditions, determine the target communication link from the public network communication link and the Beidou short message communication link; Step 3: Transmit the monitoring data of the ocean buoy through the target communication link.

[0016] In the above-described communication link switching method, the signal quality parameters in step 1 include signal strength and signal-to-noise ratio.

[0017] In the above-mentioned communication link switching method, step 2 specifically involves: if the signal quality parameters meet the preset conditions, then the target communication link is determined to be a public network communication link; If the signal quality parameters do not meet the preset conditions, the target communication link is determined to be a BeiDou short message communication link; The preset conditions are that the signal strength is greater than a first preset threshold and the signal-to-noise ratio is greater than a second preset threshold.

[0018] The aforementioned communication link switching method further includes obtaining the attitude status parameters of the ocean buoy; if the attitude status parameters indicate that the ocean buoy is in an abnormal state, then the target communication link is forcibly determined as a BeiDou short message communication link.

[0019] In the above-mentioned communication link switching method, step 3 specifically involves: if the target communication link is a BeiDou short message communication link, then the transmission function of the public network communication module is turned off; if the target communication link is the BeiDou short message communication link, then the key data in the monitoring data is compressed, encapsulated according to the BeiDou short message format, and sent.

[0020] The beneficial effects of this invention are that, through the separate architecture design of the antenna unit and the main unit, the antenna unit is installed on the top of the buoy mast to obtain a wide field of view for receiving satellite signals, while the main unit is installed inside the buoy cabin to utilize the cabin structure to provide environmental protection. The two are connected by a single radio frequency cable to transmit radio frequency signals and DC power simultaneously, solving the problem that traditional all-in-one terminal protection performance and maintainability are difficult to balance. This invention is especially suitable for long-term unattended operation scenarios of marine buoys.

[0021] This invention uses BeiDou-3 RDSS / RNSS dual-mode communication as the core satellite communication method. The core components are independently controllable, effectively avoiding the data security risks and high costs associated with relying on foreign satellite communication systems. It provides a reliable guarantee for the secure transmission of marine monitoring data and meets the strategic requirements of national marine information security.

[0022] This invention utilizes a multi-link autonomous switching mechanism to collect quality parameters such as signal strength and signal-to-noise ratio of public network links in real time. Combined with preset conditions, it automatically determines the optimal communication link, achieving seamless connection between high-speed transmission of large-capacity data in nearshore areas and reliable protection of critical data in offshore areas. This effectively solves the communication continuity problem in complex marine environments and avoids the lag and uncertainty of manual intervention.

[0023] This invention also enables on-demand power supply to the antenna-end power amplifier through a voltage switching circuit, significantly reducing standby power consumption and heat loss; achieves dynamic optimization of link resources through a periodic re-evaluation mechanism; and ensures reliable transmission of distress information under extreme conditions through an emergency forced switching mechanism. These multiple mechanisms work together to construct a highly reliable, low-power, and easy-to-maintain marine buoy communication solution. Attached Figure Description

[0024] Figure 1 This is a block diagram of the overall system architecture of the present invention; Figure 2 This is a block diagram of the internal components of the one-line antenna unit of the present invention; Figure 3 This is a block diagram of the main unit board of the present invention; Figure 4 This is a block diagram of the lower board of the host unit of the present invention; Figure 5 This is a schematic diagram of the voltage switching circuit of the present invention; Figure 6 This is a flowchart of the communication link switching method of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] In this invention, the terms "antenna unit" and "antenna" are used interchangeably, both referring to the physical component that realizes the signal transmission and reception function; the terms "host unit" and "host" are used interchangeably, both referring to the physical component that processes and controls the signal. The term "BeiDou short message communication link" refers to a communication link established through the BeiDou RDSS satellite radio ranging service; the term "public network communication link" refers to a communication link established through the 5G / 4G mobile communication network.

[0027] like Figure 1 As shown, this invention provides a BeiDou split-type dual-mode communication terminal suitable for marine buoys. The terminal consists of an antenna unit and a main unit, electrically connected by a single radio frequency (RF) cable. The antenna unit is mounted on the top of the buoy mast for receiving and transmitting satellite signals; the main unit is installed inside the buoy hull and handles communication protocol processing, data acquisition management, and link switching decisions. The RF cable between the antenna unit and the main unit simultaneously carries both RF signal transmission and DC power supply transmission functions. On one hand, BeiDou L1, B1, and S-frequency satellite signals received by the antenna unit are amplified and combined before being transmitted to the main unit via the RF cable. On the other hand, the L-frequency transmission signal generated by the main unit is transmitted to the antenna unit via the RF cable, amplified by the power amplifier within the antenna unit, and then transmitted via a passive antenna. Simultaneously, the main unit provides DC power to the antenna unit via the RF cable, supplying power to active components such as the low-noise amplifier, power amplifier, and voltage switching circuit within the antenna unit. This single-cable multiplexing transmission structure achieves physical separation between the antenna and the main unit, avoiding the complexity and reliability risks associated with laying additional power supply cables.

[0028] like Figure 2As shown, the antenna unit includes a passive antenna, a filtering circuit, a low-noise amplifier, a power amplifier, a multiplexer, a voltage switching circuit, and a power management circuit. The passive antenna receives satellite signals at frequencies L1, B1, and S, and transmits uplink signals at frequency L. The filtering circuit includes bandpass filters corresponding to frequencies L1, B1, S, and L, used for frequency-selective filtering of signals at each frequency to suppress out-of-band interference. The low-noise amplifier is located in the receiving link to amplify the weak satellite signals received by the passive antenna with low noise, thereby improving receiving sensitivity. The power amplifier is located in the transmitting link to amplify the L-frequency signal to be transmitted to the rated transmit power before radiating it through the passive antenna. The multiplexer is used to combine and split multi-band signals—in the receiving direction, the multiplexer combines the L1, B1, and S-frequency signals received by the passive antenna and transmits them to the main unit via RF cables; in the transmitting direction, the multiplexer splits the L-frequency signal from the main unit to the corresponding transmitting branch. The voltage switching circuit controls the power amplifier's power supply based on the transmit status of the RDSS module in the main unit, ensuring the power amplifier operates only during transmission. The power management circuit regulates, filters, and distributes the DC power input from the RF cable, providing the necessary operating voltage for the various circuits within the antenna unit.

[0029] The multiplexer comprises a power divider and bandpass filters. The power divider uses a basic model combination to achieve a 1-to-4 split, operating from 1 GHz to 3 GHz and covering the L1, B1, S, and L frequencies. The bandpass filters consist of four independent bandpass filter branches, corresponding to the L1, B1, S, and L frequencies respectively. The common terminal of the power divider connects to the feed point of the passive antenna, and the four distribution terminals connect to the bandpass filters corresponding to their respective frequencies. In the receiving direction, after the passive antenna receives satellite signals at L1, B1, and S frequencies, the power divider distributes the signal power and transmits it to the respective bandpass filter branches. The bandpass filters in each branch perform frequency-selective filtering on the signals at their corresponding frequencies before outputting to the next-stage low-noise amplifier circuit or combining the signals to the RF cable. In the transmitting direction, the L-frequency transmitted signal from the RF cable is filtered by the bandpass filter and then transmitted to the passive antenna and radiated through the power divider. The isolation specification of the power divider ensures that there is no crosstalk between signals at different frequencies. This multiplexer design enables multiple frequency signals to share a single RF cable and antenna port, providing crucial RF front-end support for the implementation of a split architecture. In practical implementation, the multiplexer uses simulation optimization to determine the circuit parameters of the power divider and bandpass filter.

[0030] The host unit includes an upper board and a lower board, and the block diagrams of the upper and lower boards are shown below. Figure 3-4As shown, the upper and lower boards are electrically connected and communicate with each other via an inter-board connector. The upper board carries an RDSS module, an RNSS module, a first-stage power conversion circuit, a second-stage power conversion circuit, and a power switching circuit. The lower board carries the processor core board and peripheral interface circuits, including Ethernet, USB, serial, SPI, I2C, a SIM card slot, and an M.2 module interface. Furthermore, the host unit includes a public network communication module, which connects to the processor core board via the M.2 module interface to establish a 5G / 4G public network communication link.

[0031] In the upper board of the main unit, the first-stage power conversion circuit uses the MP2319GJ DC-DC power chip to convert the 12V voltage provided by the lower board into a stable 5V voltage. The second-stage power conversion circuit uses two SGM61032B DC-DC power chips. One chip converts the 5V voltage to 3.3V to power the RNSS module, and the other chip converts the 5V voltage to 3.7V to power the RDSS module. Simultaneously, the stable 12V voltage and the 5V voltage generated by the first-stage power conversion circuit are fed to the antenna unit via a power switching circuit. This feed voltage is then supplied to the antenna unit via RF cables to power the active components inside the antenna unit. The power switching circuit consistently outputs the rated feed voltage after the system is powered on, ensuring that the antenna unit is operational from the moment the terminal starts working. In one possible implementation, the power switching circuit can also adjust the amplitude of the feed voltage based on the transmit enable signal of the RDSS module—when the RDSS module is transmitting, the feed voltage rises to a first voltage value; when the RDSS module is in standby mode, the feed voltage drops to a second voltage value, where the first voltage value is higher than the second voltage value. Accordingly, the voltage switching circuit in the antenna element determines whether the RDSS module is in a transmitting state by detecting changes in the feed voltage.

[0032] The lower board of the host unit employs a four-stage power supply architecture. The first-stage power conversion circuit uses the LM5157 DC-DC power chip to convert a wide-range external DC voltage (e.g., 9V to 36V) into a stable 12V, providing power input for the lower board's communication interface circuits and the upper board. The second-stage power conversion circuit uses the MP4315 DC-DC power chip to convert the 12V voltage to 5V, powering the lower board's USB interface circuits and serial interface circuits. The third-stage power conversion circuit uses the MP2147 DC-DC power chip to convert the 5V voltage to 3.3V, powering the processor core board's I / O interfaces and other 3.3V devices. The fourth-stage power conversion circuit uses the RT9193-18GB DC-DC power chip to convert the 3.3V voltage to 1.8V, powering the processor core board's internal logic circuits.

[0033] The public network communication module can use a 4G communication module instead of a 5G communication module. This implementation is suitable for application scenarios where 5G network coverage is not yet complete in near-shore areas. The 4G communication module has lower power consumption and more mature network compatibility. The terminal accesses the LTE network through the 4G communication module. The processor core board reads parameters such as signal strength and signal-to-noise ratio of the 4G network through AT commands and executes the same link adaptive switching process as in the above embodiments. In this embodiment, the first and second preset thresholds in the preset conditions can be adjusted according to the signal characteristics of the 4G network. Those skilled in the art will understand that regardless of whether the public network communication module adopts the 5G or 4G standard, its monitoring method for public network link quality and the transmission method for monitoring data are the same or equivalent to the methods in the above embodiments, and all fall within the protection scope of this invention.

[0034] The RDSS module uses the BeiDou-3 one-line communication module, which has a built-in 5W power amplifier and low-noise amplifier. It supports BeiDou-3 regional short message communication and is compatible with BeiDou-2 RDSS communication. The RDSS module also has GNSS positioning signal input / output switching capability, enabling one-line positioning communication. The RNSS module uses a full-system, full-frequency high-precision positioning module, supporting five major satellite navigation systems: BDS, GPS, GLONASS, Galileo, and QZSS. It can output high-precision position, velocity, and time information. Both the RDSS and RNSS modules communicate with the processor core board in the lower board via serial interfaces.

[0035] The processor core board in the lower board uses the FET3568 core board, whose processor is an RK3568 quad-core ARM architecture chip, supporting the Linux operating system (Ubuntu), with a memory capacity of no less than 1GB and an eMMC storage capacity of no less than 32GB. The processor core board runs a link switching decision program, reads the signal quality parameters of the public network communication module and the working status parameters of the RDSS module in real time through the serial interface, executes an adaptive link switching algorithm, and interfaces with various data acquisition sensors on the buoy through Ethernet interface circuits, USB interface circuits, and serial interface circuits to acquire hydrological and meteorological monitoring data. There are two SIM card slots, one for the RDSS module and the other for the public network communication module. The M.2 module interface is used to plug in the public network communication module, which is a 5G communication module and is also compatible with 4G network standards.

[0036] like Figure 5As shown, the voltage switching circuit includes a voltage comparator, a switching transistor, a gate driver chip, and a Schottky diode. The two inputs of the voltage comparator are connected to the feed line of the RF cable and a reference voltage source, respectively, to detect the magnitude of the feed voltage and output a comparison result signal. A high-power MOSFET is selected as the switching transistor, with a source-drain withstand voltage of not less than -30V and a drain current rating of not less than 3A. The gate driver chip has a supply voltage range of 4.5V to 24V. Its input is connected to the output of the voltage comparator or the control terminal of the processor core board, and its output is connected to the gate of the switching transistor. When the control signal output by the processor core board or the voltage comparator is low, the gate driver chip outputs a low level, the gate-source capacitance of the switching transistor discharges, the switching transistor turns off, the power amplifier's power supply path is disconnected, there is no output voltage, and transmission is off. When the control signal is high, the gate driver chip outputs a high level, the gate-source capacitance of the switching transistor charges, the switching transistor conducts, the power amplifier's power supply path is connected, there is output voltage, and transmission is on. A Schottky diode is placed between the output terminal of a switching transistor and the low-voltage power supply line. Its anode is connected to the output terminal of the switching transistor, and its cathode is connected to the power supply terminal of the power amplifier. It is used to prevent current from flowing back to the low-voltage output terminal of the power management circuit when operating at high voltage, so as to avoid damage to the low-voltage circuit caused by high voltage.

[0037] The voltage switching circuit in this embodiment can automatically switch the power amplifier's power supply between the RDSS module's transmit and standby states, achieving low standby power consumption and high reliability for the antenna unit. In practice, the power amplifier is only powered on when the RDSS module is transmitting. Compared to the traditional approach where the power amplifier is constantly powered on, this embodiment effectively reduces the accumulation of heat loss in the power amplifier, extending its lifespan in high-temperature, high-salt-fog marine environments. Simultaneously, because the power amplifier and RDSS module are connected via an RF cable, the insertion loss of the transmit link is effectively controlled, ensuring stable transmit power output.

[0038] Before implementing the link switching method, it is necessary to clarify the technical meaning of each term in this application. "Signal quality parameters" refer to quantifiable indicators that reflect the transmission quality of the communication link, including but not limited to signal strength, signal-to-noise ratio, bit error rate, reference signal received power, and reference signal received quality. "Preset conditions" refer to the judgment conditions pre-stored in the processor to determine whether the link quality meets the data transmission requirements. These judgment conditions can be a single threshold or a combination of multiple thresholds. "Monitoring data" refers to data collected by various sensors carried by the ocean buoy, including but not limited to wind speed, wind direction, air temperature, air pressure, water temperature, salinity, depth, wave height, wave period, ocean current speed, ocean current direction, buoy position, buoy attitude, and equipment operating status.

[0039] After the terminal is powered on, the system initializes the antenna unit and the host unit. This initialization process includes: the processor core board starts the RDSS module via the control interface, and the RDSS module begins searching for BeiDou satellites and registering with the network; simultaneously, the processor core board starts the public network communication module, which registers with and attaches to the mobile network; the RNSS module starts synchronously and begins outputting positioning data. After initialization, the system enters normal data acquisition and link monitoring operation. During this process, the antenna unit continuously receives RNSS satellite signals at L1 and B1 frequencies and RDSS downlink signals at S frequency through a passive antenna. These signals are filtered to suppress out-of-band spurious signals, then amplified by a low-noise amplifier, combined by a multiplexer, and finally transmitted to the upper board of the host unit via an RF cable. The RDSS module on the upper board demodulates the S frequency downlink signal, and the RNSS module processes the L1 and B1 frequency signals to complete real-time buoy position calculation and short message reception. When a short message needs to be sent, the RDSS module modulates the information to be sent to the L frequency point, generates the L frequency point transmission signal, and transmits the transmission signal to the antenna unit via the radio frequency cable. The signal is then split by the multiplexer to the L frequency point transmission branch, filtered by the filter circuit, amplified by the power amplifier, and radiated into space by the passive antenna.

[0040] Meanwhile, the voltage switching circuit monitors the power supply voltage status on the RF cable in real time. When the RDSS module transmits, the power supply voltage rises, and the voltage switching circuit automatically turns on the power amplifier's power supply path, putting the power amplifier into operation. When the RDSS module is in standby mode, the power supply voltage drops, and the voltage switching circuit automatically disconnects the power amplifier's power supply path, putting the power amplifier into a power-off state. This avoids the problem of heat loss accumulation and device reliability degradation caused by the power amplifier being powered on for a long time.

[0041] The adaptive switching method for communication links provided in this application refers to... Figure 6 The process includes the following steps: Step 1, obtaining the signal quality parameters of the public network communication link. Step 2, determining the target communication link from the public network communication link and the BeiDou short message communication link based on the matching results of the signal quality parameters and preset conditions. Step 3, transmitting the monitoring data of the marine buoy through the target communication link.

[0042] In this embodiment, the method described above first acquires real-time signal quality parameters of the public network communication link, enabling the processor to quantitatively perceive the current channel status of the public network link and provide objective data input for link selection. Signal quality parameters are used as the basis for link decision because the availability of a communication link depends on the real-time transmission capability of the channel, and signal strength and signal-to-noise ratio directly reflect channel quality, providing advantages in real-time performance and accuracy. Based on this, the processor compares the acquired signal quality parameters with preset conditions and determines the target communication link according to the matching results. This process is entirely automated by the processor without manual intervention. When the public network link quality meets the preset conditions, the public network communication link is selected to transmit data, fully leveraging the advantages of large bandwidth and low latency of the public network to achieve rapid transmission of large-capacity monitoring data. When the public network link quality does not meet the preset conditions, the BeiDou short message communication link is selected, utilizing the wide coverage and immunity to marine environmental influences of BeiDou satellite communication to ensure reliable transmission of critical data.

[0043] The aforementioned dual-link collaborative mechanism organically combines high-speed near-shore transmission with reliable offshore support. Furthermore, the separate architecture of the antenna and main unit allows the antenna to be mounted on top of the buoy mast for unobstructed satellite signal reception, while the main unit can be installed inside the buoy hull for excellent environmental protection, thus ensuring link transmission quality from a physical perspective.

[0044] Reference Figure 6 In one specific implementation, the above method achieves link switching through the following process. After the system powers on, the processor core board simultaneously starts the public network communication module and the RDSS module to complete public network registration and BeiDou satellite search, i.e., link initialization. Subsequently, the processor core board reads the signal strength (RSSI) and signal-to-noise ratio (SNR) parameters reported by the public network communication module. The processor core board compares the read RSSI and SNR values ​​with preset conditions—the preset conditions are RSSI higher than -85dBm and SNR higher than 20dB. If RSSI is higher than -85dBm and SNR is higher than 20dB, the public network link is determined to be available, and the system enters the near-shore high-speed mode; otherwise, the public network link is determined to be unavailable, and the system enters the far-shore energy-saving mode. In the near-shore high-speed mode, the terminal transmits all sensor data through the public network communication module, the BeiDou short message link remains in hot backup state, and heartbeat packets are periodically sent to maintain the link online. In the offshore energy-saving mode, the terminal disables the transmission function of the public network communication module to reduce power consumption and sends compressed key data through the RDSS module. The key data includes buoy position, equipment status and alarm information. The data packets are encapsulated in the Beidou-3 regional short message format.

[0045] In the offshore energy-saving mode, the processor core board re-detects the quality parameters of the public network communication link according to a preset cycle (e.g., every 5 minutes, this application does not limit this). When the public network signal quality recovers to meet the preset conditions, it automatically switches the target communication link back to the public network communication link. Furthermore, when the buoy attitude sensor detects an abnormal state such as capsizing or submersion of the buoy, regardless of the public network signal quality, the processor core board forcibly switches the target communication link to the BeiDou short message communication link and sends distress information at the highest frequency. Once the abnormal state is resolved, the terminal returns to the link operation mode before the abnormality.

[0046] In practice, the steps described above for obtaining signal quality parameters require a stable parameter reading channel between the processor and the public network communication module. In one optional implementation, the processor core board connects to the public network communication module via a serial interface or USB interface, using the AT command set or the API interface provided by the module manufacturer to obtain real-time signal quality parameters. The RSSI value of the public network communication module reflects the signal coverage strength of the public terrestrial mobile network at the terminal's current location, while the SNR value reflects the degree of noise interference during signal transmission. These two parameters together constitute a comprehensive evaluation index for the quality of the public network link. Compared to schemes relying solely on a single index, using a combined RSSI and SNR approach can effectively distinguish between complex scenarios such as "high signal strength but high noise" and "low signal strength but low noise," avoiding misjudgments caused by distortion from a single index. For example, in near-shore waters where there is co-channel interference or neighboring-cell interference, the RSSI may show a strong signal strength, but the SNR may be significantly low. In this case, if only the RSSI is relied upon for decision-making, the terminal may mistakenly determine that the public network link is available and select it, but the actual transmission quality cannot meet the data backhaul requirements. However, by using a dual-indicator joint judgment, the low SNR will cause the matching result of the preset conditions to be unmet, and the terminal will correctly switch to the BeiDou short message link. Therefore, the dual-indicator joint judgment significantly improves the accuracy of link switching decisions.

[0047] In practical implementation, the steps for determining the target communication link described above need to handle different input scenarios during the actual decision-making process. In one optional implementation, the processor core board compares the acquired signal quality parameters with preset conditions item by item, obtains the comparison result of each parameter with the corresponding threshold, and then performs a logical AND operation on each comparison result. When all comparison results meet the conditions, the matching result is satisfied; when any comparison result does not meet the conditions, the matching result is not satisfied. The processor core board outputs a link selection instruction based on the matching result—outputting a public network link selection signal when the matching result is satisfied, and outputting a BeiDou link selection signal when the matching result is not satisfied. The above conditional branch judgment logic is simple and efficient, suitable for real-time processor operation scenarios, and can ensure that a deterministic link selection result can be output under any input state, without any ambiguity or hanging state in the judgment.

[0048] In practice, the steps described above for transmitting monitoring data via the target communication link require differentiated data processing and transmission strategies for different link types. When the target communication link is a public network communication link, the processor core board receives the raw monitoring data collected by various sensors on the buoy, encapsulates the data according to TCP / IP or UDP protocols, and sends it to the shore station data center through the public network communication module. The public network link has ample bandwidth and can transmit complete sensor datasets, including wind speed and direction, temperature, salinity, depth, and wave spectrum.

[0049] When the target communication link is a BeiDou short message communication link, due to the limited message length of a single BeiDou short message communication, the processor core board first performs priority classification and compression processing on the monitoring data—alarm information and equipment status are classified as the highest priority data, location information as high priority data, and routine hydrological and meteorological parameters as ordinary priority data; then, the data is encapsulated according to the BeiDou-3 regional short message format, and the encapsulated message is transmitted to the BeiDou satellite via the antenna unit through the RDSS module. Through the above-mentioned data hierarchical compression strategy, the reliable transmission of critical information is prioritized within the limited short message channel capacity.

[0050] To precisely control the quality of the criteria during link switching, in one optional implementation, the first and second preset thresholds in the aforementioned preset conditions can be dynamically adjusted based on the communication environment of the sea area where the buoy is located. Specifically, when the buoy is in nearshore waters, the density of shore-based base stations is high and public network signal coverage is good. The first and second preset thresholds can be set to relatively strict values ​​(e.g., RSSI higher than -85dBm and SNR higher than 20dB) to ensure that the public network link is only activated when the public network quality is indeed excellent. When the buoy drifts to offshore waters, the public network signal itself is weak. If the preset thresholds are set too high, the terminal will be in BeiDou communication mode for a long time. In this case, the first and second preset thresholds can be appropriately relaxed (e.g., RSSI higher than -100dBm and SNR higher than 15dB) so that the terminal can still use the public network link to transmit some data when the public network signal is barely available. To adapt to the above dynamic adjustment requirements, the processor core board can query a preset sea area communication environment database based on the buoy position information output by the RNSS module and automatically match and adjust the preset thresholds. In another alternative implementation, the threshold configuration command can be remotely issued by the shore station, and the new threshold parameters can be written into the processor core board via a public network link or a Beidou short message link.

[0051] Furthermore, to improve the accuracy of link switching, in one optional implementation, the signal quality parameters may further include Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ). When the public network communication module accesses the 5G network, the system message carries the RSRP and RSRQ measurement results of the serving cell and neighboring cells, and the processor core board reads the above measurement results through AT commands. RSRP reflects the reference signal power level received by the terminal, and RSRQ reflects the ratio of reference signal received quality to received signal strength. When RSRP is greater than a third preset threshold and RSRQ is greater than a fourth preset threshold, the public network link is determined to be available. Further, in another optional implementation, the four parameters of signal strength, signal-to-noise ratio, reference signal received power, and reference signal received quality can be comprehensively evaluated, and a weighted scoring algorithm can be used to obtain a comprehensive link quality score. The comprehensive score is then compared with a preset scoring threshold to determine the target communication link. In this embodiment, the processor core board configures different weighting coefficients for signal strength, signal-to-noise ratio, RSRP, and RSRQ based on the correlation between each parameter and the link transmission success rate. For example, the weighting coefficient for signal strength is 0.3, the weighting coefficient for signal-to-noise ratio is 0.3, the weighting coefficient for RSRP is 0.2, and the weighting coefficient for RSRQ is 0.2. Then, after normalizing each parameter, multiplying it by its corresponding weight, and summing them, a comprehensive link quality score is obtained. When the comprehensive score is greater than a preset score threshold, the public network link is determined to be usable. This embodiment does not limit the weighting coefficients for each parameter; those skilled in the art can adjust them according to actual application scenarios.

[0052] To further optimize the handover timing after public network link recovery, in one optional implementation, the aforementioned detection of public network communication link signal quality parameters according to a preset cycle includes: performing trend analysis on the signal quality parameters acquired over multiple consecutive detection cycles, and determining the changing trend of the public network signal based on the trend analysis results. Specifically, the processor core board records a sampled value of the signal quality parameter once in each detection cycle and saves the most recent N sampled values. When the most recent N sampled values ​​show a continuous upward trend and the current sampled value meets a preset condition, it is determined that the public network signal has been fully recovered, and link switching is performed; when the most recent N sampled values ​​show a fluctuating state but the current sampled value meets the preset condition, the BeiDou short message communication link is maintained to ensure communication stability, and switching is performed only after the signal has stabilized continuously. Through this trend analysis mechanism, frequent link switching can be avoided when the public network signal has just crossed the threshold boundary but is still unstable, improving the stability of link switching and user experience.

[0053] In one optional implementation, the aforementioned attitude parameters are acquired using attitude sensors configured on the buoy. These attitude sensors include a roll sensor and a water immersion sensor. The roll sensor detects the roll and pitch angles of the buoy body in real time, while the water immersion sensor detects whether water has entered the buoy's hull. When the roll angle exceeds a first angle threshold (e.g., 15°, not limited in this application) or the pitch angle exceeds a second angle threshold (e.g., 15°, not limited in this application), the processor core board determines that the buoy is at risk of capsizing. When the water immersion sensor outputs a valid signal, the processor core board determines that the buoy has experienced a water immersion anomaly. When any of the above anomaly conditions are triggered, the processor core board immediately executes an emergency forced switching procedure, forcibly identifying the target communication link as a BeiDou short message communication link, and sending the distress information via the BeiDou short message link at the highest transmission frequency. In one possible implementation, the distress information includes the buoy's unique identifier, latest position coordinates, anomaly type code, anomaly occurrence time, and current heading and attitude data. The above-mentioned emergency mechanisms ensure that the buoy can still send a last reliable message to the shore station in extreme conditions such as capsizing or submersion, providing a basis for decision-making in search and rescue and emergency response.

[0054] In one optional implementation, the aforementioned disabling of the public network communication module's transmission function is achieved by the processor core board sending a flight mode switching command to the public network communication module. Upon receiving the command, the public network communication module disables the radio frequency transmission path but maintains the reception path in a low-power monitoring state to periodically detect the public network signal strength. Since the power consumption of the public network communication module is mainly concentrated in the transmission path during actual operation, disabling the transmission path can reduce the overall power consumption of the public network communication module by more than 60%, thereby significantly extending the buoy's battery life under unattended conditions. When the processor core board detects that the public network signal quality has recovered to meet preset conditions, it sends an exit flight mode command to the public network communication module, re-enabling the transmission path and restoring normal operation.

[0055] In one optional implementation, the process of compressing key data from the monitoring data and encapsulating it according to the BeiDou short message format before transmission includes: after the processor core board acquires sensor data, it filters out key data from all monitoring data. The filtering rules for key data include: all alarm information (e.g., anchor light malfunction, hatch water ingress, low battery voltage, etc.) is included as key data; equipment status information (e.g., communication module operating status, processor load, power supply voltage, etc.) is encoded based on changes exceeding a preset range; and positioning information is selected from the most recent valid positioning data. After the processor core board performs lossy or lossless compression on the filtered key data, it adds a message header, checksum, and timestamp according to the BeiDou-3 regional short message format, generates a short message frame conforming to the protocol requirements, and sends it to the RDSS module via a serial interface. The RDSS module then performs channel coding and modulation before transmitting it via the antenna unit. This implementation maximizes the transmission of effective information within the limited short message capacity constraints.

[0056] Furthermore, to further improve the information utilization efficiency of BeiDou short message transmission, in one optional implementation, the processor core board employs differential encoding for numerical parameters in key data. Specifically, the processor core board retains the complete value from the initial transmission as a reference value, and in subsequent transmissions only transmits the difference between the current value and the previously transmitted value. Since marine environmental parameters (such as temperature, salinity, depth, and waves) typically change gradually within continuous sampling periods, differential encoding can significantly reduce the number of bits required for each parameter. Combined with a predefined data dictionary, the receiver can reconstruct the original value based on the differential code and the reference value. This encoding method further enhances the effective information throughput of the short message channel.

[0057] In one optional implementation, the terminal further includes an antenna status monitoring mechanism. The processor core board monitors the feed voltage and reflected power on the RF cable in real time via a voltage comparator in the voltage switching circuit. When an abnormal feed voltage is detected (e.g., a voltage drop exceeding a preset ratio) or excessive reflected power, it determines that the antenna element has an open circuit, short circuit, or poor contact fault. The processor core board generates an antenna alarm message and sends it to the shore station via an available communication link (public network link or BeiDou short message link). This mechanism can promptly detect abnormal states of the antenna element, facilitating remote diagnosis and timely repair by maintenance personnel, thus improving the maintainability of the system.

[0058] When the buoy is nearshore and the public network signal is good, the terminal operates in nearshore high-speed mode. In nearshore high-speed mode, the public network communication module interacts with the processor core board at high speed through the M.2 module interface. The processor core board is connected to the data acquisition and control board on the buoy through an Ethernet interface circuit, actively acquiring sensor data as a TCP client. The sensor data includes wind speed and direction data collected by the wind speed and direction sensor, temperature, salinity, and depth data collected by the temperature, salinity, and depth sensor, and wave height and period data collected by the wave sensor. The above data is sent to the shore-based data center through the 5G / 4G network of the public network communication module, completely preserving all the raw data required for marine monitoring. At the same time, the RDSS module maintains a hot backup state, sending a heartbeat packet containing the buoy's position and equipment status every preset time interval (e.g., 5 minutes, this application does not limit this), ensuring that the Beidou link can quickly take over the data transmission task when the public network is interrupted.

[0059] When the buoy drifts to the open sea and the public network signal strength drops below a preset threshold, the terminal automatically switches to the open-sea energy-saving mode. In this mode, the processor core board sends a low-power command to the public network communication module, shutting down its transmission path and retaining only the periodic monitoring function of the reception path. Simultaneously, the processor core board collects and caches sensor data according to a preset strategy, prioritizing the latest alarm and device status information, compressing the data to generate short message frames, and sending them to the BeiDou satellite via the RDSS module. The data transmission cycle in the open-sea energy-saving mode can be dynamically adjusted based on remaining battery power and data importance—when the battery is fully charged, the transmission cycle can be set to 10 minutes; when the battery power is below a preset threshold, the transmission cycle automatically extends to 30 minutes, and only alarm and device status information is transmitted, suspending the transmission of regular location information. Through this dynamic adjustment mechanism, the terminal's battery life is maximized while ensuring the availability of critical information.

[0060] When the buoy is located in the area where nearshore and offshore waters meet, the public network signal strength fluctuates frequently, and the terminal may face frequent link switching issues. To address this scenario, in one optional implementation, a link switching hysteresis mechanism is introduced—when the terminal is currently operating in nearshore high-speed mode, switching to the BeiDou short message communication link is only performed after the public network signal quality parameter has been continuously lower than a first preset condition for a first duration (e.g., 30 seconds, this application does not limit this); when the terminal is currently operating in offshore energy-saving mode, switching to the public network communication link is only performed after the public network signal quality parameter has been continuously higher than a second preset condition for a second duration (e.g., 60 seconds, this application does not limit this). The first and second preset conditions can be the same threshold condition or different threshold conditions. Through this hysteresis mechanism, the probability of frequent link switching when the public network signal fluctuates at threshold boundaries is effectively reduced, improving the stability of the communication link.

[0061] When the buoy capsizes or takes on water, the terminal immediately enters an emergency forced switchover mode. The processor core board reads the output data from the attitude sensor via a serial interface. When it detects that the tilt angle exceeds a preset angle or that a water immersion signal is valid, regardless of whether the current public network signal quality meets preset conditions, the processor core board immediately interrupts the current data transmission process, generates a distress message containing the buoy's unique identifier, latest position coordinates, anomaly type, and occurrence time, and sends the distress message to the BeiDou satellite via the RDSS module with the highest priority. In emergency forced switchover mode, the terminal continuously sends distress messages at the preset maximum transmission frequency until it receives confirmation from the shore station via the BeiDou short message link, or the processor core board detects that the buoy's attitude has returned to normal. This mechanism ensures that distress information can be transmitted to the shore station with the highest reliability when the buoy encounters extremely severe sea conditions.

[0062] To ensure the safe operation of the communication system, this application embodiment also includes several pre-start conditions and boundary protection mechanisms. Regarding pre-start conditions, after the system is powered on, the processor core board first executes a self-test program, sequentially checking the connection status of the RF cable between the antenna unit and the host unit, the registration status of the public network communication module, the satellite search status of the RDSS module, and the positioning status of the RNSS module. If any of the above self-tests fails, the processor core board generates a corresponding fault code and sends it to the shore station through an available communication link. Specifically, if the RDSS module has not completed the BeiDou satellite search, even if the public network signal quality parameters do not meet preset conditions, the terminal should not enter the BeiDou short message communication mode, but should continue to attempt public network communication and wait for the BeiDou satellite search to complete. Regarding boundary protection mechanisms, the processor core board monitors the operating temperature and RF transmission power of the public network communication module. When the temperature of the public network communication module exceeds a preset temperature threshold, the transmission power level is automatically reduced. The short message transmission frequency of the RDSS module is limited to avoid overheating protection caused by continuous high-frequency transmission. The aforementioned protection mechanism not only ensures communication functionality but also effectively extends the lifespan of key components.

[0063] refer to Figure 6 The complete link switching process of the embodiments of the present invention will be described.

[0064] In step S101, the system powers on, and the processor core board starts the public network communication module and the RDSS module, simultaneously performing mobile network registration and BeiDou satellite search to complete link initialization. At the same time, the RNSS module starts and outputs positioning data, and the processor core board acquires initial buoy position information.

[0065] Step S102: The processor core board reads the signal strength RSSI value and signal-to-noise ratio SNR value reported by the public network communication module.

[0066] In step S103, the processor core board compares the RSSI value with a first preset threshold and the SNR value with a second preset threshold. For example, the first preset threshold is -85dBm and the second preset threshold is 20dB. If the RSSI value is higher than the first preset threshold and the SNR value is higher than the second preset threshold, it is determined that the public network signal quality meets the preset conditions, and step S104 is executed; otherwise, step S105 is executed.

[0067] Step S104: Enter near-shore high-speed mode. The processor core board transmits all sensor data through the public network communication module, and the BeiDou short message communication link remains in hot backup mode, periodically sending heartbeat packets. Return to step S102 to continue monitoring the public network signal quality.

[0068] Step S105: Enter the offshore energy-saving mode. The processor core board disables the transmission function of the public network communication module, while retaining periodic monitoring of the receiving channel. Sensor data is compressed and filtered, and key data is encapsulated in the BeiDou-3 regional short message format and sent through the RDSS module.

[0069] Step S106: Re-detect the signal quality parameters of the public network communication link according to a preset period (e.g., every 5 minutes). Read the RSSI and SNR values ​​of the public network communication module.

[0070] Step S107: Determine whether the public network communication link signal quality has recovered to meet the preset conditions. If it does, proceed to step S108; otherwise, continue to step S106.

[0071] Step S108: Exit the offshore energy-saving mode, restore the transmission function of the public network communication module, switch the target communication link to the public network communication link, and return to step S104.

[0072] In step S109, when the processor core board detects an abnormal buoy attitude (tilt angle exceeding a threshold or a valid immersion signal), it triggers an emergency forced switching procedure, forcibly identifying the target communication link as a BeiDou short message communication link and sending distress information at the highest frequency. Once the abnormal state is resolved, the procedure returns to step S103.

[0073] In the above process, steps S101 to S108 constitute the link adaptive switching closed loop under normal circumstances, and step S109 constitutes the emergency backup branch under abnormal circumstances. All steps are automatically executed by the link switching decision program in the processor core board without manual intervention.

[0074] The technical solution provided in this application achieves the following overall technical effects. First, through a split-architecture design, the antenna unit and the main unit are physically separated. The antenna unit is installed on the top of the buoy mast to obtain a good satellite signal reception field of view, while the main unit is installed inside the buoy cabin to obtain protection and heat dissipation conditions. Both transmit radio frequency signals and DC power simultaneously through a single radio frequency cable, fundamentally solving the contradiction between protection level and maintainability in traditional integrated terminals. Second, through the dual-mode configuration of the Beidou RDSS module and the public network communication module, a dual-link communication system of "high-speed public network transmission + reliable Beidou guarantee" is constructed. The core communication method is based on my country's independently controllable Beidou satellite navigation system, effectively ensuring the security and independent controllability of marine monitoring data. Third, through the link switching decision program, the signal quality parameters of the public network communication link are collected in real time, and the target communication link is automatically selected according to preset conditions, realizing intelligent and autonomous switching of communication links, avoiding the lag of manual intervention, and ensuring the communication continuity of the buoy throughout its entire voyage from nearshore to offshore. Fourth, by automatically controlling the power amplifier's power supply through a voltage switching circuit and disabling the public network communication module's transmission function through a deep-sea energy-saving mode, the overall power consumption of the terminal is effectively reduced, extending the buoy's operational lifespan under unattended conditions. Fifth, by providing standardized Ethernet, USB, and serial interfaces, various data acquisition sensors on the buoy can be flexibly connected to the terminal without the need for customized dedicated interface circuits, improving the system's versatility and scalability. These technological effects work synergistically to construct a highly reliable, low-power, and easy-to-maintain marine buoy communication terminal and system, capable of meeting the practical needs of marine intelligent three-dimensional networked buoy data acquisition systems for deep-sea communication support.

[0075] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its scope and protection, and such modifications or equivalent substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A Beidou split-type dual-mode communication terminal suitable for marine buoys, characterized in that, It includes an antenna unit, which includes a passive antenna, a filter circuit, a low-noise amplifier, a power amplifier, a multiplexer, and a voltage switching circuit. The host unit includes a processor, a public network communication module, and a BeiDou short message communication module, wherein the processor is connected to the public network communication module and the BeiDou short message communication module respectively; An RF cable connects the antenna unit and the host unit, and is used to simultaneously transmit RF signals and DC power. The processor is used to acquire signal quality parameters of the public network communication link, determine the target communication link from the public network communication link and the Beidou short message communication link based on the matching result of the signal quality parameters and preset conditions, and transmit the monitoring data of the marine buoy through the target communication link.

2. A Beidou split-type dual-mode communication terminal suitable for marine buoys according to claim 1, characterized in that, The voltage switching circuit includes a voltage comparator and a switching transistor. The voltage comparator is used to monitor the feed voltage on the radio frequency cable and output a control signal according to the feed voltage. The switching transistor is used to turn the power supply path of the power amplifier on or off according to the control signal.

3. A Beidou split-type dual-mode communication terminal suitable for marine buoys according to claim 1, characterized in that, The multiplexer includes a power divider and a bandpass filter. The power divider is used to distribute the multi-band signals received by the passive antenna to signal processing branches at different frequency points. The bandpass filter is disposed on the signal processing branch and is used to filter the signal at the corresponding frequency point.

4. A Beidou split-type dual-mode communication terminal suitable for marine buoys according to claim 1, characterized in that, The host unit includes an upper board and a lower board that are electrically connected via an inter-board connector; The upper board is equipped with the Beidou short message communication module, public network communication module, RNSS positioning module, and power management module; The lower board carries the processor and peripheral interface circuitry; The power management module is used to convert the voltage provided by the lower board into different voltages to power the Beidou short message communication module, public network communication module, and RNSS positioning module.

5. A Beidou split-type dual-mode communication terminal suitable for marine buoys according to claim 4, characterized in that, The peripheral interface circuit includes at least one of the following: Gigabit Ethernet port, USB interface, RS-232 serial interface, SIM card slot, SPI interface, and I2C interface.

6. A communication link switching method, characterized in that, A Beidou split-type dual-mode communication terminal for marine buoys according to any one of claims 1-5 includes: Step 1: Obtain the signal quality parameters of the public network communication link; Step 2: Based on the matching result of the signal quality parameters and preset conditions, determine the target communication link from the public network communication link and the Beidou short message communication link; Step 3: Transmit the monitoring data of the ocean buoy through the target communication link.

7. A communication link switching method according to claim 6, characterized in that, The signal quality parameters in step 1 include signal strength and signal-to-noise ratio.

8. A communication link switching method according to claim 7, characterized in that, Specifically, step 2 involves: if the signal quality parameters meet the preset conditions, then the target communication link is determined to be a public network communication link; If the signal quality parameters do not meet the preset conditions, the target communication link is determined to be a BeiDou short message communication link; The preset conditions are that the signal strength is greater than a first preset threshold and the signal-to-noise ratio is greater than a second preset threshold.

9. A communication link switching method according to claim 6, characterized in that, It also includes acquiring the attitude status parameters of the ocean buoy; if the attitude status parameters indicate that the ocean buoy is in an abnormal state, then the target communication link is forcibly identified as a Beidou short message communication link.

10. A communication link switching method according to claim 6, characterized in that, Step 3 specifically involves: if the target communication link is a BeiDou short message communication link, then the transmission function of the public network communication module is turned off; if the target communication link is the BeiDou short message communication link, then the key data in the monitoring data is compressed and encapsulated in the BeiDou short message format before being sent.

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