Method for controlling access to a vde signal satellite

Abstract

The application relates to a VDE signal satellite access control method, which comprises the following steps: a satellite end dynamically clusters ships in a satellite signal coverage area and pre-allocates communication time slots; a ship end in a dynamic cluster group locally negotiates and allocates the communication time slots, and periodically reports to the satellite end; and the satellite end dynamically optimizes the pre-allocated communication time slots of the next period according to the report of each period. The application has the advantage of reducing transmission conflict rate in a heavy ship flow scene.

Description

Technical Field

[0001] This application relates to the field of satellite communications, and in particular to a method for controlling satellite access to VDE signals. Background Technology

[0002] The Data Exchange System (VDES) is an upgrade and extension of the AIS system, capable of real-time two-way data communication in any sea area globally. Compared to traditional AIS, VDES offers up to 32 times higher data transmission rates and supports satellite relay, achieving global coverage and two-way communication. This means that even when ocean-going vessels leave the coverage area of ​​coastal VHF base stations, they can maintain communication with shore via the VDES satellite link, thus extending the range of maritime communication.

[0003] The satellite control station acts as a centralized scheduler, managing the uplink channel through SBB announcements and assignment mechanisms. Multiple ship terminals can transmit in parallel using TDMA within the same frame. The system uses orthogonality technology to distinguish the access of different satellites; for example, when multiple VDES satellites cover overlapping areas, different frequencies / code patterns are used to ensure no interference. Furthermore, to protect traditional VHF services such as AIS and DSC from interference, the VDES system sets duty cycle limits and priority rules for time slot usage. For example, the number of time slots occupied by each ship station per minute on a single channel does not exceed a certain proportion (e.g., 2.2%) to ensure priority transmission of AIS messages and prevent the channel from being overwhelmed by excessive VDES data. Through these mechanisms, data exchange between ships and satellites can be carried out in an orderly and efficient manner, allowing ships to obtain reliable data communication services via satellite VDES even in open ocean areas without shore-based control.

[0004] One of the current recommended access schemes for VDES is the adoption of the AIS self-organizing TDMA protocol. However, studies have shown that under heavy ship traffic, the self-organizing TDMA protocol, due to each station's independent selection of time slots and the lack of global coordination, is prone to a significant increase in transmission collision rate. Especially over a large area covered by satellite, when a large number of mutually non-eavesdropping ships access the network simultaneously, using purely autonomous allocation will result in many collisions and reduce effective throughput. Even with the introduction of a centralized allocation mechanism, collisions may still occur in random access channels under high concurrency requests, with multiple ships potentially competing for access in the same RACH time slot, leading to access delays and reduced efficiency. Summary of the Invention

[0005] In order to reduce the transmission collision rate in scenarios with heavy ship traffic, this application provides a VDE signal satellite access control method.

[0006] This application provides a VDE signal satellite access control method, which adopts the following technical solution:

[0007] A VDE signal satellite access control method includes the following steps:

[0008] S1. The satellite terminal performs dynamic clustering and pre-allocation of communication time slots for ships within the satellite signal coverage area;

[0009] S2. Ships within the dynamic cluster negotiate and allocate communication time slots locally and periodically report to the satellite.

[0010] S3. The satellite dynamically optimizes the pre-allocated communication time slots for the next cycle based on reports from each region in each cycle.

[0011] By adopting the above technical solution, the time slot allocation results are broadcast to all ships via the satellite announcement channel, ensuring that ships within a cluster are aware of the available time slots corresponding to their cluster. This allows them to request and schedule slots based on this boundary during local negotiation, avoiding cross-cluster occupancy and conflicts. The system achieves dynamic rebalancing of resources among clusters, effectively alleviating access congestion in high-density ship areas and improving the overall system throughput and time slot utilization. The entire process requires no manual intervention; the automatic execution mechanism based on state feedback and threshold determination provides a strong guarantee for the stable operation of the VDE system in complex and dynamic maritime communication scenarios.

[0012] Optionally, S1 includes the following steps:

[0013] S11. The satellite terminal acquires the real-time location distribution and access density of ships that have established communication with it within the satellite signal coverage area;

[0014] S12. Based on the real-time location distribution and access density of ships within the satellite signal coverage area, the satellite end uses a density clustering algorithm to divide the ships into several dynamic clusters;

[0015] S13. Based on the regions defined in the previous step and the ship density and historical traffic within those regions, the satellite initially allocates a reserved TDMA time slot for each region to allow ships within the region to negotiate local access.

[0016] By adopting the above technical solutions, the satellite can perceive the spatial distribution of ships and access load within the coverage area in real time, providing a data foundation for the next step of rational allocation of clustering and time slot resources. This comprehensive perception method based on dynamic location and access behavior not only helps to achieve more reasonable network topology partitioning, but also improves the targeting and accuracy of access resource scheduling. Especially in the face of dense maritime traffic and high-concurrency communication demands, it can significantly improve the network's response capability and overall operational efficiency.

[0017] Optionally, S12 includes the following steps:

[0018] S121. Based on the density clustering algorithm, set the cluster partitioning parameters and calculate the clusters in real time;

[0019] S122. Based on the calculation results of the clusters, several logical clusters are formed;

[0020] S123. Record the cluster center location and boundary corresponding to each logical cluster so that subsequent satellites can perform targeted time slot pre-allocation.

[0021] By adopting the above technical solutions, the system can flexibly adapt to the dynamic changes in the number and distribution of ships, making each cluster relatively compact in space and relatively consistent in communication needs. This facilitates the subsequent allocation of communication resources on a partition-by-partition basis, reducing the complexity of global scheduling. Furthermore, due to the automatic removal of outliers and adaptive clustering characteristics of density clustering, it is more stable and reliable when facing highly dynamic ship networks, ensuring the system has good real-time performance and adaptability.

[0022] Optionally, S13 includes the following steps:

[0023] S131. Determine the VDE frame period to be 1 minute, with a total of 2250 basic time slots;

[0024] S132. The basic time slots are divided into unallocated time slots, global flexible time slots, and global emergency time slots; among which, global flexible time slots are used for subsequent dynamic adjustments and random access for individual ships, and global emergency time slots are used for emergency communication between satellites and ships without negotiation;

[0025] S133. Based on the regions divided in the previous step and the ship density and historical traffic within those regions, the time slots to be allocated are divided into various clusters to determine the initial state allocation of each cluster.

[0026] S134. Broadcast the time slot pre-allocation information via the satellite announcement channel.

[0027] By adopting the above technical solution, the system has achieved structured management of basic time slots.

[0028] Optionally, S2 includes the following steps:

[0029] S21. Within each cluster, the ship performs a local negotiation process, using a three-way handshake mechanism through pre-allocated local channels to complete the allocation of local time slots.

[0030] S22. After completing access negotiation within each VDE frame period, each ship terminal in each cluster periodically sends a regional access status message to the satellite terminal, which then performs regional load statistics based on the message.

[0031] Optionally, S21 includes the following steps:

[0032] S211. Each ship in the cluster listens to the pre-allocated time slot set and at the beginning of each frame, randomly selects an unoccupied time slot in the pre-allocated time slot set to send an initial time slot request message.

[0033] S212. Other ships in the cluster monitor and confirm the occupancy of the time slots in this area. If no conflict occurs, they will proactively send a permission message in the subsequent confirmation time slot. If a conflict is detected, they will send a rejection message.

[0034] S213. If the sender receives more than half of the permission messages, it sends an acknowledgment message to explicitly occupy the time slot; otherwise, it re-executes random backoff and re-requests.

[0035] S214. After the partial negotiation is completed, each ship sends data within the reserved time slot after the negotiation is completed, thus completing the partial access.

[0036] By adopting the above technical solutions, orderly and efficient data transmission is achieved with minimal control load, providing stable underlying support for communication scheduling in large-scale dynamic access scenarios.

[0037] Optionally, S22 includes the following steps:

[0038] S221. Select a central ship within the cluster;

[0039] S222. The central vessel terminal collects the status information of each vessel terminal within the cluster, wherein the status information includes negotiation success rate, number of conflicts, and number of idle time slots;

[0040] S223. At the end of each minute cycle, the central ship terminal, representing the cluster, sends a report message to the satellite terminal regarding the status information of the cluster during that cycle.

[0041] By adopting the above technical solutions, the system establishes an adaptive dynamic scheduling foundation, realizes closed-loop control of resource allocation based on network status, and significantly improves the network's flexibility and throughput efficiency in dealing with complex navigation environments.

[0042] Optionally, S3 includes the following steps:

[0043] S31. Determine the thresholds corresponding to each status information, including the negotiation success rate threshold, the conflict rate threshold, and the idle time slot ratio threshold;

[0044] S32. The satellite end compares the status information with the threshold based on the access status report of the area in each cycle;

[0045] S33. Based on the comparison results, allocate global elastic time slots to various regions or reclaim them to adjust the number of time slots pre-allocated in the next cycle.

[0046] In summary, this application includes at least one of the following beneficial technical effects:

[0047] 1. By using density clustering algorithm to dynamically cluster ships within the satellite coverage area in real time, communication resources can be allocated to local clusters as needed, ensuring sufficient access time slots in densely populated ship areas and effectively alleviating the access conflict problem of traditional SOTDMA scheme in large-scale, high-concurrency environments.

[0048] 2. By setting multi-dimensional state parameters such as negotiation success rate, conflict rate, and idle time slot ratio, and establishing a corresponding dynamic adjustment mechanism, the system can dynamically increase or decrease the time slot allocation of each cluster based on periodic state feedback, thereby achieving optimized resource distribution in the spatiotemporal dimension and improving the system's throughput and utilization efficiency.

[0049] 3. This invention adopts a three-step handshake mechanism within the cluster to achieve distributed time slot negotiation. Ships autonomously complete time slot allocation based on local listening, and the satellite only needs macro-configuration and periodic adjustment, thus avoiding the performance bottleneck of traditional centralized scheduling in large-scale access scenarios. Attached Figure Description

[0050] Figure 1 A flowchart illustrating a VDE signal satellite access control method according to an embodiment of the present invention is shown.

[0051] Figure 2 A flowchart illustrating the S1 sub-step in one embodiment of the present invention is shown.

[0052] Figure 3 A flowchart illustrating sub-step S12 in one embodiment of the present invention is shown.

[0053] Figure 4 A flowchart illustrating sub-step S13 in one embodiment of the present invention is shown.

[0054] Figure 5 A flowchart illustrating the S2 sub-step in one embodiment of the present invention is shown.

[0055] Figure 6 A flowchart illustrating sub-step S21 in one embodiment of the present invention is shown.

[0056] Figure 7 A flowchart illustrating sub-step S22 in one embodiment of the present invention is shown.

[0057] Figure 8 A flowchart illustrating sub-step S3 in one embodiment of the present invention is shown. Detailed Implementation

[0058] The present application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the application and are not intended to limit the scope of the application.

[0059] In the following description, numerous specific details are set forth for purposes of explanation in order to provide a thorough understanding of the inventive concept. As part of this specification, some of the accompanying drawings of this disclosure are block diagrams illustrating structures and devices to avoid complicating the disclosed principles. For clarity, not all features of the actual embodiment need to be described. Furthermore, the language used in this disclosure has been primarily chosen for readability and instructional purposes and may not have been chosen to define or limit the subject matter of the invention, thus requiring the necessary claims to determine such inventive subject matter. References to “an embodiment” or “an embodiment” in this disclosure mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment, and multiple references to “an embodiment” or “an embodiment” should not be construed as necessarily referring to the same embodiment.

[0060] Unless explicitly defined, the terms “a,” “an,” and “the” are not intended to refer to a singular entity, but rather to include a general category whose specific examples can be used for illustration. Therefore, the use of the terms “a” or “an” can mean any number of at least one, including “a,” “one or more,” “at least one,” and “one or more.” The term “or” means any of the options and any combination of the options, including all options unless explicitly indicated that the options are mutually exclusive. The phrase “at least one of” when combined with a list of items refers to a single item in the list or any combination of items in the list. The phrase does not require all items listed unless explicitly defined as such.

[0061] This application discloses a VDE signal satellite access control method. (Refer to...) Figure 1 The method includes the following steps S1-S3.

[0062] S1. The satellite terminal performs dynamic clustering and pre-allocation of communication time slots for ships within the satellite signal coverage area.

[0063] In this step, the satellite-based system dynamically clusters ships within its signal coverage area and pre-allocates communication time slots. Specifically, the satellite-based system refers to a satellite payload deployed in low Earth orbit or geostationary orbit. Its main functions include signal transmission and reception, receiving ship information and forwarding data, as well as unified communication resource scheduling for ships within its coverage area based on its own coverage range.

[0064] Dynamic clustering refers to the process by which satellites, based on real-time acquired ship location distribution and communication needs, dynamically and logically divide ships within a region into several clusters using specific algorithms. Unlike traditional static region division, dynamic clustering adjusts in real time according to changes in ship positions, effectively adapting to the unevenness and mobility of ship distribution. For example, assuming 300 ships are sailing in a certain sea area, the satellite collects the current geographical locations of these ships at regular intervals and uses density clustering algorithms, such as the DBSCAN algorithm, to divide ships with high spatial density and close proximity into independent clusters. Each cluster typically includes a dozen to several dozen ships. For instance, in the Bohai Bay area, dense shipping routes may form several distinct clusters, and the satellite performs communication resource scheduling for each cluster separately.

[0065] A communication time slot is a unit of time resource defined in the TDMA communication mechanism. The satellite communication cycle is typically set to one minute, which can be divided into 2250 basic time slots. Based on the number of ships in each cluster, historical data communication traffic, and real-time access density, the satellite pre-allocates a certain number of time slots for subsequent communication negotiations between the ships and the cluster. These pre-allocated time slots are broadcast to all ships within the cluster via the satellite announcement channel, allowing ships to select available resources for communication within the pre-allocated time slots according to their own communication needs, without having to directly request them from the satellite.

[0066] Specifically, in one embodiment, S1 includes the following steps S11-S13.

[0067] S11. The satellite terminal acquires the real-time location distribution and access density of ships that have established communication with it within the satellite signal coverage area.

[0068] The satellite first needs to comprehensively perceive all ships within its signal coverage area, primarily by acquiring the real-time geographical location and current access density information of each ship. The satellite signal coverage area refers to the service area formed in real-time by the satellite in its orbit, generally a large radius area centered on the satellite's nadir point. In VDE systems, the coverage radius is typically around 1000 kilometers, covering an area of ​​up to one million square kilometers. Ships within this area that have established a handshake connection with the satellite are considered to have established communication with the satellite, and their status and information can be effectively received and processed by the satellite.

[0069] The satellite periodically receives position information from ships via uplink channels. This information typically includes the ship's latitude and longitude coordinates, altitude, speed, and equipment identification code. Each ship usually reports its own position automatically at certain time intervals (such as every 30 seconds or every minute), thus the satellite can build a real-time position database of all active ships within the coverage area. In a certain area of ​​the South China Sea, assuming a VDES satellite simultaneously receives reports from 300 ships, the system will mark these 300 position data points on a geographic coordinate system to obtain a map of the ship position distribution within the coverage area.

[0070] Besides location, the satellite also needs to acquire access density information, i.e., how many ships are simultaneously attempting to access the network within a unit area. This can be estimated by statistically analyzing the uplink communication frequency, data packet count, and random access collision rate of ships within a certain range. For example, the entire coverage area can be divided into multiple 50km × 50km grid areas, and the number of ships actively sending access requests per unit time in each grid can be counted to create a heat map reflecting the access pressure in each area. For instance, in a strait passage area with dense shipping lanes, there might be 5 ships simultaneously requesting access per square kilometer, while in waters far from the main shipping lanes, there might only be sporadic requests.

[0071] S12. Based on the real-time location distribution and access density of ships within the satellite signal coverage area, the satellite end uses a density clustering algorithm to divide the ships into several dynamic clusters.

[0072] Based on the acquired real-time ship location distribution and access density information, the satellite employs a density clustering algorithm to logically divide the ships into multiple dynamic clusters. The core of this process lies in automatically dividing the large number of unevenly distributed ships within the coverage area into several locally consistent partitioned units based on their spatial proximity and communication load characteristics. This provides logical boundaries and a basis for independent scheduling of subsequent communication time slot resource allocation. The chosen clustering method is a density clustering algorithm, namely Density-Based Spatial Clustering of Applications with Noise (DBSCAN) or its improved version. It does not rely on a preset number of clusters but dynamically generates cluster structures based on the density relationships between data points, making it particularly suitable for target groups such as maritime ships, whose numbers fluctuate and spatial distribution is highly uneven.

[0073] In the implementation process, the satellite first sets clustering parameters, including the neighborhood radius ε and the minimum density threshold MinPts. The neighborhood radius ε defines the distance range within which a ship is considered adjacent, and MinPts defines how many ships must exist within that distance range to constitute a valid cluster core. For example, if ε is set to 30 kilometers and MinPts to 5, then a ship can be considered a cluster core when it detects at least 5 other ships within its 30-kilometer radius. Based on this rule, the algorithm starts from the core point and gradually expands outwards into the neighborhood, incorporating ships with achievable density into the same cluster, until it can no longer expand.

[0074] For example, in the densely shipping area of ​​the Yellow Sea, satellites received position data for 600 ships. After analysis using a density clustering algorithm, this data was divided into eight clusters. One cluster included 80 ships sailing between the Shandong Peninsula and the Korean Peninsula, while another cluster covered the waters near Lianyungang, Jiangsu Province, with 60 ships. The distance between these two clusters exceeded the neighborhood threshold of the clustering algorithm, so they were classified as separate clusters. Individual ships sailing in remote areas with insufficient surrounding ship density were treated as noise points and not assigned to any clusters. These were then processed separately by the satellite or their allocation was delayed.

[0075] Specifically, in one embodiment, S12 includes the following steps S121-S123.

[0076] S121. Based on the density clustering algorithm, set the cluster partitioning parameters and calculate the clusters in real time.

[0077] S122. Based on the calculation results of the clusters, several logical clusters are formed;

[0078] S123. Record the cluster center location and boundary corresponding to each logical cluster so that subsequent satellites can perform targeted time slot pre-allocation.

[0079] The parameters need to be set based on the actual distribution characteristics of ships in the sea area and communication features. For example, setting ε to 25 kilometers and MinPts to 5 means that at least 5 other ships must be present within a 25-kilometer radius of a given ship to trigger clustering. In actual deployment, the satellite applies these parameters to the set of ship position information it receives. Whenever a new VDE frame period of ship-reported data is received, the system initiates clustering calculations, performing a complete cluster division calculation for all ships within the current satellite coverage area.

[0080] Taking the East China Sea route as an example, the satellite receives position reports from approximately 450 vessels per minute. After parameter settings, a clustering algorithm is initiated. The system checks the number of neighboring vessels within a 25-kilometer radius of each vessel. For vessels meeting the condition MinPts=5, they are used as the core cluster point, and the system expands to group vessels with attainable density into the same cluster. In this cycle, the system identified 10 valid clusters, each containing an average of 30 to 60 vessels.

[0081] S13. Based on the regions defined in the previous step and the ship density and historical traffic within those regions, the satellite initially allocates a reserved TDMA time slot for each region to allow ships within the region to negotiate local access.

[0082] The satellite first calculates the current number of ships and the ship density per unit area for each cluster, and then retrieves historical communication traffic data collected over several communication cycles, including average packet length, transmission frequency, and access failure rate, to comprehensively assess the communication resource demand intensity of the cluster. In terms of scheduling strategy, the satellite prioritizes allocating more time slots to high-density, high-traffic clusters.

[0083] Specifically, in one embodiment, S13 includes the following steps S131-S134.

[0084] S131. Determine the VDE frame period to be 1 minute, with a total of 2250 basic time slots.

[0085] Based on the established dynamic cluster structure and the ship density and historical communication traffic data within each cluster, the satellite allocates a corresponding number of TDMA (Time Division Multiple Access) time slots to each cluster for subsequent ship-to-ship local negotiation and access within the cluster. In the TDMA communication mechanism, the entire communication frame is divided into several basic time slots, each of which can be independently occupied by a ship for data transmission. In the VDES system, a one-minute frame period contains 2250 basic time slots, which are the key resource scheduling units in this invention.

[0086] S132. The basic time slots are divided into unallocated time slots, global flexible time slots, and global emergency time slots; among which, global flexible time slots are used for subsequent dynamic adjustments and random access of individual ships, and global emergency time slots are used for emergency communication between satellites and ships without negotiation.

[0087] The satellite-side structurally divides the basic communication time slot resources within the entire VDE frame period, subdividing the 2250 basic time slots into three categories based on their functional uses: unallocated time slots, globally flexible time slots, and globally emergency time slots. Unallocated time slots constitute the majority of the regular communication resource allocation between clusters, and the satellite-side allocates them to different clusters in segments based on indicators such as access density and historical communication load. Globally flexible time slots are reserved for periodic dynamic adjustments and random access requests from individual vessels not in the pre-allocated set, serving as a buffer for the system to cope with sudden changes in traffic and load. Globally emergency time slots are reserved channels specifically for transmitting high-priority information that does not require handshake negotiation, such as distress alerts and reports of maritime emergencies, ensuring reliable transmission paths for critical communications even in high-congestion scenarios.

[0088] This allocation is completed uniformly by the satellite before the start of each cycle and broadcast to all terminals via an announcement channel, ensuring that each ship is aware of the numbering range and usage restrictions of various time slots during the access cycle. In implementation, the satellite first determines the network load for the current cycle and slices time slot resources according to a static ratio set by the system or dynamic parameters based on feedback. For example, 75% of the time slots (i.e., 1687) are designated as unallocated time slots for each cluster to negotiate and use as needed; 15% (approximately 338) are designated as global elastic time slots, flexibly scheduled by the satellite based on real-time status; and 10% (225) are designated as global emergency time slots, distributed in fixed positions within the frame cycle, prioritizing emergency communications. Each type of time slot comes with usage rules; for example, elastic time slots are prohibited from continuous long-term occupation, and emergency time slots require a high-priority identifier to be allowed transmission.

[0089] S133. Based on the regions divided in the previous step and the ship density and historical traffic within those regions, the time slots to be allocated are divided into various clusters to determine the initial state allocation of each cluster.

[0090] After completing the three-category division of basic time slots, the specific time slot resources in the set of time slots to be allocated are segmented and allocated according to the communication needs of each cluster as previously defined, forming the time slot usage segment for each cluster in this period. This allocation process constructs a weighted model based on multi-dimensional parameters such as ship density, historical traffic intensity, access success rate, and collision rate within each cluster, and adjusts the resource allocation ratio among clusters accordingly.

[0091] The satellite access system retrieves operational metrics for each cluster from the historical access status database over recent periods to generate a cluster demand weight table for the current period. For example, cluster A has a high ship density, with 680 access requests and a conflict rate of 9% in the previous period; cluster B is relatively sparse, with 320 requests and a conflict rate of 2%. The system calculates the demand weights for clusters A and B to be 0.68 and 0.32, respectively, using a weighting function. If the total number of time slots to be allocated is 1687, the allocation result is 1147 time slots for cluster A and 540 time slots for cluster B. The specific time slot numbers are arranged sequentially by the system, for example, cluster A's basic time slot numbers range from 100 to 1246, and cluster B's from 1247 to 1786. Segment boundaries are set to be non-intersecting to ensure physical isolation between clusters and avoid conflicts and interference caused by channel overlap.

[0092] S134. Broadcast the time slot pre-allocation information via the satellite announcement channel.

[0093] After generation, the allocation scheme is cached in the satellite's broadcast information structure and then distributed to each cluster via the announcement channel in the next step. Each vessel, upon receiving the time slot number corresponding to its cluster, can conduct local negotiation operations. In practical applications in the Beibu Gulf region of the South China Sea, six clusters are formed within a single frame period, each with varying proportions of active vessels and historical data traffic. Based on feedback, the satellite determines that cluster E has extremely high access density and a history of collisions, and allocates 900 basic time slots to it, accounting for 53% of the entire set to be allocated, with the corresponding numbering range being time slots #300 to #1199. Simultaneously, only 120 time slots are allocated to the sparsely populated cluster F for maintaining basic periodic reporting and non-emergency data communication, with the numbering range being #1640 to #1759.

[0094] S2. Ships within the dynamic cluster negotiate and allocate communication time slots locally and periodically report to the satellite.

[0095] Within the cluster, ships perform local negotiation procedures and complete data access based on time slot resources pre-allocated by the satellite. Simultaneously, at the end of each communication cycle, they feed back their access status to the satellite. This distributed resource coordination avoids the centralized processing burden of assigning resources to each ship individually by the satellite, achieving an efficient and low-collision channel access control mechanism.

[0096] Specifically, in one embodiment, S2 includes the following steps S21-S22.

[0097] S21. Within each cluster, the ship performs a local negotiation process, using a three-way handshake mechanism through pre-allocated local channels to complete the allocation of local time slots.

[0098] Specifically, in one embodiment, S21 includes the following steps S211-S214.

[0099] S211. Each ship in the cluster listens to the pre-allocated time slot set and at the beginning of each frame, randomly selects an unoccupied time slot in the pre-allocated time slot set to send an initial time slot request message.

[0100] After monitoring the pre-allocated time slot set, the ship initiates the first step of the local negotiation process. At the beginning of each frame period, it randomly selects one of the TDMA time slots reserved by the satellite within its cluster that is not yet occupied by other ships and sends a time slot request message. The pre-allocated time slot set is a continuous segment of time slot resources independently allocated by the satellite for each cluster in S13 based on factors such as the number of ships, access density, and historical traffic. After being broadcast via the satellite announcement channel, all ships within the cluster can learn about the time slot range corresponding to their respective cluster. For example, the time slot set corresponding to cluster A is the basic time slots from 500 to 799.

[0101] In practice, the ship selects a target time slot from this set using a pseudo-random number generator. The generation process constructs a random factor based on information such as the system timestamp and ship ID, ensuring that each ship's selection is unique and reducing the probability of overlapping selections. To determine whether the target time slot has been occupied by other ships, each ship maintains a short-term cluster access state cache locally, recording the request, permission, and confirmation broadcast content listened to in the previous frame period. For example, if time slot 520 has been confirmed as occupied by ship X in the previous frame, other ships will consider time slot 520 as temporarily unavailable at the beginning of the current frame and skip it to avoid applying for it. In addition, the ship also listens to the cluster broadcast channel at the beginning of the current period to monitor in real time whether other ships have already requested the same time slot, ensuring that the selected time slot is in an unoccupied state.

[0102] After the random selection is completed, the vessel immediately constructs and broadcasts a time slot request message. This message includes at least the following fields: vessel identifier (e.g., MMSI number), target time slot number, request priority flag, data service type identifier, and request duration. The priority flag indicates whether the communication is urgent or time-sensitive data, such as a course change or collision avoidance command. The service type field specifies the structure and expected length of the data transmission, helping negotiating nodes determine whether permission is granted. The broadcast of this request message serves to trigger the response mechanism of other vessels in the same cluster, initiating the listening and permission process in S212, and laying the signaling foundation for subsequent confirmation of time slot ownership.

[0103] Taking a cluster in the East China Sea as an example, ship A selects time slot 602 from time slots 500 to 799 within its cluster using a random number algorithm. After checking the cache and confirming that the time slot is not occupied, it broadcasts a time slot request message with the request number 602, declaring that it will soon send updated ship position information data. Other ships receiving this request enter a permission judgment process. If no conflict is found, permission messages are returned in subsequent time slots. This process ensures that ships can autonomously complete their access requests based on sufficient information awareness, reducing the scheduling burden on the satellite end and significantly improving the flexibility and efficiency of resource allocation within the cluster.

[0104] S212. Other ships in the cluster monitor and confirm the occupancy of the time slots in this area. If no conflict occurs, they proactively send a permission message in the subsequent confirmation time slot. If a conflict is detected, they send a rejection message.

[0105] Upon receiving a time slot request message from a member, other vessels within the cluster immediately initiate a listening and judgment process to determine whether to grant permission for the request. This listening is accomplished through continuous local monitoring of the cluster communication channel. Each vessel continuously monitors the reserved time slots allocated within its cluster during each VDE frame period, paying particular attention to whether any time slots are already occupied or whether overlapping requests are occurring. Occupancy records are divided into two parts: one part comes from the confirmation message records of the previous period; vessels maintain a local time slot usage status table, marking which time slots were occupied in the previous period, which is automatically cleared after a period of time. The other part comes from real-time monitoring; time slot request messages, permission messages, and confirmation messages sent by other vessels in the current frame period are all recorded in this table to determine conflict status.

[0106] Subsequent confirmation slots refer to the dedicated time slots during which the receiving vessel broadcasts its response message to the cluster within the next few basic time slot windows after the time slot request message is sent. The entire handshake mechanism is time-based, with each round of negotiation setting several standard response windows within a frame, including permission response slots and confirmation response slots, ensuring strict timing and synchronization during the negotiation process. During monitoring, if a vessel detects that two or more vessels have broadcast requests for the same basic time slot in the same frame, or detects that a confirmation message for that time slot has already been sent, it considers that a time slot conflict to exist. Typical conflict scenarios include: multiple request messages from different vessels being received in the same basic time slot, or another request preempting the same time slot before one request message has been confirmed.

[0107] After the assessment is completed, the monitoring party must respond with either a permission message or a rejection message within the designated confirmation time slot. A permission message broadcasts a response message explicitly agreeing to the requester's use of the target time slot. This message includes the licensor's vessel identifier, the target time slot number, and a permission flag field, supporting the requester in completing the negotiation. A rejection message indicates that the monitoring party has detected a conflict risk or that the time slot is already occupied, and therefore disagrees with the vessel's request. Its structure is similar to the permission message, but the permission flag field is set to "no." All vessels respond according to a unified conflict assessment rule to ensure consistent assessment standards and synchronized feedback actions.

[0108] Taking a cluster in the Bohai Bay as an example, ship A requests time slot 550. Ships B and C, after listening, find that this time slot was unoccupied in the previous frame and no other requests were seen in the current frame. Therefore, they broadcast permission messages in the permissioned time slot. At the same time, ship D hears that ship E sends a request to time slot 550 almost simultaneously, determines that there is a conflict, and sends a rejection message to ship E within the permission window. This mechanism ensures that all ships respond quickly to access behavior based on consistent perception logic, enabling the system to maintain high resource utilization and scheduling fairness while avoiding conflicts.

[0109] S213. If the sender receives more than half of the permission messages, it sends an acknowledgment message to explicitly occupy the time slot; otherwise, it re-executes random backoff and re-requests.

[0110] After broadcasting, the vessel initiating the time slot request enters a listening phase, awaiting permission or rejection messages from other vessels in the cluster. The number of permission messages received determines whether the time slot usage right has been successfully negotiated. This step is a crucial decision-making stage in the three-way handshake mechanism, its core being the formation of a decentralized consensus decision through collective response, ensuring fairness and conflict-free time slot allocation. The initiating vessel continuously listens to the cluster channel within the permission response window, counting all responses to its request. Whether to proceed to the confirmation phase depends on whether the number of permission messages exceeds a set threshold. The permission threshold is typically set to require permission from more than half of the vessels in the cluster; that is, confirmation broadcasting is only permitted when a majority of vessels agree, thus avoiding conflicts caused by insufficient permission messages or ambiguous judgments.

[0111] The confirmation message is a broadcast signaling message containing the vessel's unique identifier, the requested time slot number, permission statistics, and a formal occupancy declaration. After broadcasting, all other vessels in the cluster immediately update their local time slot usage status tables, marking the time slot as occupied by the designated vessel to avoid subsequent duplicate requests or responses. The issuance of the confirmation message signifies that the vessel's exclusive right to the time slot is established for the current period. In subsequent transmission windows, the vessel will use this time slot as planned to complete data communication. If the number of permission messages does not reach a set threshold, the negotiation is considered a failure, and the initiating vessel will activate a backoff mechanism, temporarily relinquishing the current target time slot, delaying for a certain number of base time slots, randomly selecting a new target time slot, and restarting the request process.

[0112] For example, in a cluster in the Zhoushan Port channel, vessel X requests basic time slot 720 during this period. Within the permission window, it receives permission messages from 18 out of 30 vessels in the cluster, exceeding the half-permission threshold. Therefore, it immediately broadcasts a confirmation message in the subsequent confirmation window. After confirmation, other vessels in the cluster mark time slot 720 as occupied to ensure it is not reused. Simultaneously, vessel Y also requests time slot 720 but receives only 8 permission messages, failing to meet the permission standard, triggering a backoff and entering the next available time slot application process.

[0113] S214. After the partial negotiation is completed, each ship sends data within the reserved time slot after the negotiation is completed, thus completing the partial access.

[0114] After successfully completing the three-way handshake and broadcasting an acknowledgment message, the ship officially enters the data transmission phase. At this point, the ship has obtained exclusive access to the target base time slot within the current cycle, and therefore can transmit service data within the corresponding time slot window without additional conflict detection. Data transmission is strictly limited to the allocated base time slots following the acknowledgment time slot, ensuring the communication order and physical isolation of the entire cluster under the time-division multiple access architecture.

[0115] Before sending data, the ship retrieves ready-to-use service data from its local cache and performs necessary encapsulation, encoding, and error checking. The content of the transmitted data packets may include navigation status reports, ship-to-shore data synchronization, meteorological measurement data, distress alarm information, etc., depending on the service scenario, and the format conforms to the structure protocol specified by the VDE communication standard. In actual operation, the ship transmits the encapsulated data frames after precise time synchronization in the target base time slot, which is then received by the satellite and forwarded or stored. Because the communication time slots are pre-negotiated and approved by the cluster, the problem of multiple ships contending for the channel in the same time slot is avoided, fundamentally solving the packet loss and retransmission overhead caused by concurrent conflicts in traditional ALOHA-type access methods.

[0116] S22. After completing access negotiation within each VDE frame period, each ship terminal in each cluster periodically sends a regional access status message to the satellite terminal, which then performs regional load statistics based on the message.

[0117] Sending messages from the ship to the satellite is equivalent to communication from the MAC layer to the network layer.

[0118] Specifically, in one embodiment, S22 includes the following steps S221-S223.

[0119] S221. Select a central ship within the cluster.

[0120] To improve the efficiency of cluster access status aggregation and reduce the information processing load on the satellite end, the system designates one vessel from each cluster as the "central vessel," specifically responsible for collecting, organizing, and reporting the communication status information of its cluster. The selection of the central vessel is typically based on indicators such as stability, central location, and communication capabilities, and is configured dynamically or semi-statically. For example, nodes within the current cluster that are close to the geographical center of gravity, have relatively stable speeds, and have good communication records with other vessels can be preferentially selected for the central role. The selection mechanism for the central vessel can be announced by the satellite end through a public announcement channel after each round of clustering, and the identity information of the central node can be broadcast before the start of each cycle, enabling other vessels within the cluster to identify its role and report local status data to it.

[0121] S222. The central vessel terminal collects the status information of each vessel terminal within the cluster, wherein the status information includes the negotiation success rate, the number of conflicts, and the number of idle time slots.

[0122] The central vessel is responsible for collecting access status information for all member vessels within the cluster during the access cycle, constructing an overview of the communication behavior for this cycle. The status information includes three key indicators: negotiation success rate, number of collisions, and number of idle time slots. These indicators collectively reflect the cluster's resource utilization efficiency, access congestion level, and remaining channel capacity during the current communication cycle.

[0123] The negotiation success rate is calculated based on the ratio of the number of valid acknowledgment messages received by the central vessel to the total number of vessels in the cluster. Whenever a vessel completes the three-way handshake and broadcasts a successful acknowledgment message within the acknowledgment window, the central vessel records a successful access event and associates it with the vessel's identifier and the corresponding timeslot number. During the statistical process, the central vessel can extract key fields from the acknowledgment message, such as the MMSI number, timeslot number, and acknowledgment flag, by parsing the access frame structure, ensuring accurate and unique statistical results.

[0124] The number of conflicts is determined by monitoring conflict feedback information. When any vessel within the cluster broadcasts a rejection message within the permission window, this action is recorded as a conflict event by the central vessel. To avoid counting duplicate rejections, the system employs conflict filtering logic, where multiple rejections on the same target time slot are counted as only one valid conflict. The central vessel compiles these conflict events into a conflict details table, including the conflict time slot number and the number of vessels involved, providing support for further analysis of access efficiency.

[0125] The number of idle time slots is obtained by statistically analyzing the base time slots in the pre-allocated time slot set that have not been requested or confirmed by any ship. Before the end of each frame period, the central ship performs a reverse comparison of all the occupancy confirmations and time slot request information it has monitored, identifying which base time slots have not been accessed throughout the period, thereby determining the actual number of idle time slots. This indicator directly reflects the resource redundancy within the cluster and is the basis for determining whether to reduce the time slot allocation of the cluster.

[0126] S223. At the end of each minute cycle, the central ship terminal, representing the cluster, sends a report message to the satellite terminal regarding the status information of the cluster during that cycle.

[0127] After completing the statistical analysis of the cluster's access status, the central vessel sends a status report message to the satellite at the end of each minute frame cycle, achieving a closed-loop status feedback from the cluster to the satellite. This process ensures that the satellite can promptly grasp the real-time access performance of each cluster for resource optimization and scheduling decisions in the next cycle. The report message is encoded using a structured message format and typically includes fields such as cluster identifier, statistical period number, total number of vessels in the cluster, number of successful accesses, number of conflict events, and number of idle time slots. A brief summary of conflict time slot numbers or data utilization information may also be added if necessary.

[0128] The messages are broadcast using a dedicated reporting channel or reserved global control time slots to ensure they do not conflict with ordinary service data. The central vessel needs to reserve a certain number of basic time slots within the frame period for system-level control signaling reporting. These time slots are pre-allocated by the satellite during the time slot pre-allocation phase and broadcast through an announcement channel, allowing the central vessel to plan data transmission timing in advance. When constructing a message, the central vessel packages the statistical data organized in its local cache in the previous stage, adds its own identifier, timestamp, and cluster number fields, and then sends it periodically within the allocated reporting window. To ensure reliable information delivery, the satellite, upon receiving the report, can return an acknowledgment according to the ACK mechanism defined in the frame structure. The central vessel uses this to determine whether the reporting task has been completed. If no acknowledgment is received, it can retransmit according to the set backoff strategy.

[0129] For example, in a cluster in the Yangtze River Estuary, the central vessel Z identified 50 vessels in the cluster during the current period, successfully connecting to 45 of them, recording 5 collisions, and having 48 unused basic time slots. Time slots 2245 to 2249 at the end of the frame were reserved by the satellite announcement channel as dedicated channels for the central vessel to report. Vessel Z sent a status report message in time slot 2246, which included the period number #37981, cluster ID #A5F, success rate of 90%, and a list of collision time slot numbers [680, 681, 687, 690].

[0130] S3. The satellite dynamically optimizes the pre-allocated communication time slots for the next cycle based on reports from each region in each cycle.

[0131] Specifically, in one embodiment, S3 includes the following steps S31-S33.

[0132] S31. Determine the thresholds corresponding to each status information, including the negotiation success rate threshold, the conflict rate threshold, and the idle time slot ratio threshold.

[0133] Based on the system control strategy and network operation model, the satellite determines the evaluation thresholds corresponding to various access status information, including negotiation success rate threshold, conflict rate threshold, and idle time slot ratio threshold. These thresholds constitute the standard lines for judging the operating status of each cluster, and are used to determine whether a cluster is overloaded, inefficient, or wasting resources during subsequent resource reallocation.

[0134] The negotiation success rate threshold measures the normal access level of ships within a cluster. The success rate is the ratio of the number of ships that successfully complete the handshake mechanism and send data within a communication cycle to the total number of participating ships. If the negotiation success rate of a cluster is lower than a set threshold, such as 85%, it is considered that the cluster has problems with congestion, insufficient time slots, or a failed negotiation mechanism. The conflict rate threshold is used to determine the degree of time slot contention within a cluster. It is defined as the ratio of the number of conflict events to the total number of time slot requests within a cycle. If it is higher than a set value such as 10%, it indicates that the current allocation method cannot effectively meet the coordination needs in dense ship scenarios. The idle time slot ratio threshold is used to identify areas of resource over-allocation. If more than 30% of the time slots in a cluster are not used within a cycle, it is considered resource redundancy, and its allocation share in the next cycle should be appropriately reduced.

[0135] The setting of these thresholds is accomplished by the software control unit on the satellite. They can be static fixed values ​​or dynamically fine-tuned based on historical operational data. For example, during peak periods in the Nansha Islands, the system analyzed data from the past 100 cycles using a machine learning model and found that the negotiation success rate often fluctuated around 88%. To ensure throughput, it was decided to adjust the negotiation success rate threshold for this cluster to 90%, and the conflict rate threshold to 8%. In contrast, the success rate threshold for the sparse cluster in the Zhoushan Islands was maintained at 75%. Each type of threshold is stored in the system configuration table after being set and participates in the automatic judgment process of subsequent status comparisons and resource adjustment logic, forming a complete closed-loop feedback mechanism oriented towards changes in network situation.

[0136] S32. The satellite compares the status information with the threshold based on the access status report of the area in each cycle.

[0137] In S32, the satellite retrieves the access status reports of each cluster from the previous frame period, mainly including negotiation success rate, conflict rate, and idle time slot ratio. These data are then compared item by item with the evaluation thresholds set in S31. The comparison results for each indicator are used to determine whether the cluster has insufficient or wasted resources. If the negotiation success rate of a cluster is lower than the threshold, it indicates that some ships have failed to access successfully, and the system determines that there is a shortage of time slots in that area. If the conflict rate is higher than the threshold, it indicates severe time slot contention in that area, and even with pre-allocation, overlapping access cannot be effectively avoided. When the idle time slot ratio is too high, it reflects that the currently allocated resources exceed the actual needs of the cluster, indicating over-allocation of resources. The satellite generates cluster status labels based on these comparison results, such as "congestion," "high conflict," and "resource surplus."

[0138] S33. Based on the comparison results, allocate global elastic time slots to various regions or reclaim them to adjust the number of time slots pre-allocated in the next cycle.

[0139] The satellite executes a global elastic time slot allocation strategy based on the aforementioned status labels. Allocation methods include "increase allocation," "decrease allocation," and "maintain," with adjustments made based on the current status of each cluster. For example, for clusters in a "congested" state, the satellite allocates additional resources from the global elastic time slot pool to that cluster to increase its access capacity; for clusters labeled "resource surplus," the system reclaims their excess pre-allocated time slots and returns them to the elastic pool, releasing resources for other clusters. All adjustments form a new table of unallocated time slots, which is broadcast synchronously via the announcement channel before the start of the next cycle, allowing the ship to perform access scheduling based on the updated time slot set.

[0140] For example, during a frame period in the Beibu Gulf, cluster C's negotiation success rate was only 82%, and its conflict rate reached 12%. The satellite determined that cluster C was under resource strain and immediately allocated an additional 150 basic time slots from the elastic pool, expanding its available time slot segment numbering range for the next period. Simultaneously, cluster F had 45% idle time slots during this period, and the satellite reclaimed 80 of its time slots, releasing them back into the elastic pool. Through this addition and subtraction mechanism, the system achieved dynamic resource rebalancing among clusters, effectively alleviating access congestion in high-density ship areas and improving the overall system throughput and time slot utilization. The entire process required no manual intervention; the automatic execution mechanism based on state feedback and threshold determination provided a strong guarantee for the stable operation of the VDE system in complex and dynamic maritime communication scenarios.

[0141] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0142] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0143] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for VDE signal satellite access control, characterized by, The method comprises the following steps: S1. The satellite end dynamically clusters and pre-allocates communication time slots for ships in the satellite signal coverage area; S2. The ship end in the dynamic cluster group locally negotiates and allocates the communication time slots, and periodically reports to the satellite end; S3. The satellite end dynamically optimizes the pre-allocated communication time slots of the next period according to the report of each region in each period; The S1 comprises the following steps: S11. The satellite end obtains the real-time position distribution and access density of the ships in the satellite signal coverage area that establish communication with the satellite end; S12. The satellite end divides the ships into several dynamic cluster groups by using a density clustering algorithm based on the real-time position distribution and access density of the ships in the satellite signal coverage area; S13. The satellite end initially allocates a reserved TDMA time slot segment for each region according to the divided cluster groups and the ship density and historical traffic in the cluster groups, so as to be used for local negotiation access of the ships in the region; The S3 comprises the following steps: S31. Determine the threshold values corresponding to the state information, including the negotiation success rate threshold value, the conflict rate threshold value, and the idle time slot proportion threshold value; S32. The satellite end compares the state information and the threshold values according to the access state report of each region in each period; S33. According to the comparison result, the global flexible time slots are allocated to each region or withdrawn, so as to adjust the number of time slots pre-allocated in the next period.

2. The VDE signal satellite access control method according to claim 1, wherein, The S12 comprises the following steps: S121. According to the density clustering algorithm, set the cluster division parameters, and calculate the clusters in real time; S122. Form several logical cluster groups according to the calculation result of the clusters; S123. Record the cluster group center position and boundary corresponding to each logical cluster group, so as to be used for subsequent satellite targeted time slot pre-allocation.

3. The VDE signal satellite access control method according to claim 2, wherein, The S13 comprises the following steps: S131. Determine that the VDE frame period is 1 minute, and there are 2250 basic time slots; S132. Divide the basic time slots into to-be-allocated time slots, global flexible time slots, and global emergency time slots; wherein, the global flexible time slots are used for subsequent dynamic adjustment and random access of individual ships, and the global emergency time slots are used for emergency communication between the satellite and the ships without negotiation; S133. According to the region divided in the last step and the ship density and historical traffic in the region, divide the to-be-allocated time slots to each cluster group, so as to determine the initial state allocation of each cluster group; S134. Broadcast the time slot pre-allocation information through the satellite announcement channel.

4. The VDE signal satellite access control method according to claim 3, wherein, The S2 comprises the following steps: S21. In each cluster group, the ship end performs a local negotiation process through the pre-allocated local channel, and completes the local time slot allocation by using a three-step handshake mechanism; S22. After each ship end in each cluster group completes the access negotiation in each VDE frame period, the ship end periodically sends a regional access state message to the satellite end, and the satellite end completes the regional load statistics according to the message.

5. The VDE signal satellite access control method according to claim 4, wherein, The S21 comprises the following steps: S211. Each ship end in the cluster group listens to the pre-allocated time slot set, and at the beginning of each frame, randomly selects a time slot in the pre-allocated time slot set that has not been occupied to send an initial time slot request message; S212. Other ships in the cluster group listen to and confirm the occupation of the time slots in the region, and actively send a permission message in the subsequent confirmation time slot when no conflict occurs, or feed back a veto message if a conflict is detected; S213. If the sender receives more than half of the permission messages, the sender sends a confirmation message to explicitly occupy the time slot; otherwise, the random backoff is re-executed and the request is re-sent; S214. After the local negotiation is completed, each ship terminal sends data in the reserved time slot to complete the local access.

6. The VDE signal satellite access control method according to claim 5, wherein, The S22 includes the following steps: S221. Select a center ship in the cluster; S222. The center ship terminal counts the state information of each ship terminal in the cluster, wherein the state information includes the negotiation success rate, the number of conflict occurrences, and the number of idle time slots; S223. After each minute cycle ends, the center ship terminal sends a report message of the state information of the cluster to the satellite terminal.

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