A hexslot-based maritime VDES cognitive access method

Abstract

The application discloses a kind of Hexslot-based offshore VDES cognitive access method, comprising: S1: all users collect offshore information data;S2: establish the frame hierarchy of the transmission channel of user;S3: source node user obtains the state of the starting access slot in the Hexslot time slot group of destination node user;S4: if source node user can access starting access slot, and successfully upload offshore information data, then execute S5, otherwise execute S3;S5: if transmission is successful, then if source node user still needs to send, re-execute S3, otherwise transmission is finished;If transmission fails, re-execute S3.The application combines VDES and cognitive radio technology, without increasing additional frequency resource overhead, can improve the data throughput between offshore ships, ships and shore base station, guarantee the utilization efficiency of time slot, guarantee the reliable transmission of ship message, and further guarantee the safety of ship navigation.

Description

Technical Field

[0001] This invention relates to the field of maritime wireless communication network technology, and in particular to a maritime VDES cognitive access method based on Hexslot. Background Technology

[0002] As a crucial component of the next-generation international maritime communication system, the Very High Frequency Data Exchange System (VDES) adds Application Special Message (ASM) and VDE functions to the existing Automatic Identification System (AIS) functionality, enabling it to provide richer maritime communication services. In the future, it will also integrate with BeiDou, unmanned vessels, intelligent ships, and GMDSS to promote the sustainable development of e-navigation. However, the scarcity of available spectrum resources at sea, coupled with low spectrum utilization, means that the transmission capacity of VDES is far from meeting the growing user demand. The Media Access Control (MAC) layer of the network defines the user access method, and an efficient MAC access method plays a vital role in avoiding collisions between network users and improving network performance. Therefore, designing the VDES MAC access protocol and rationally allocating channels, reserving time slots, and allocating network resources are key to ensuring the effective transmission of messages from ships at sea.

[0003] The VDE channel of VDES is used for data transmission between ships and between ships and shore base stations, including hydrological and meteorological information, navigation aids, and ship position. The recommendations provided by the ITU and IALA have given relatively detailed MAC access schemes for how users can access the AIS and ASM channels of VDES. However, a mature solution for how users can access the VDE channel is still lacking. The Slot-Aloha access scheme given in the recommendations has a theoretical maximum time slot utilization of only 36.8%. Low VDES time slot utilization leads to inefficient message transmission for ships and a high transmission conflict rate between users, failing to meet the data transmission needs of ships at sea on the VDE channel. Summary of the Invention

[0004] This invention provides a Hexslot-based method for maritime VDES cognitive access to overcome the aforementioned technical problems.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A Hexslot-based method for cognitive access to a maritime VDES includes the following steps:

[0007] S1: All users in the maritime VDES cognitive communication network collect maritime information data; the users include primary users and cognitive users;

[0008] S2: Establish the frame hierarchy structure of the user's transmission channel:

[0009] The frame hierarchy of the user's transmission channel includes I sequentially connected Hexslot time slot groups, each of which includes a start access time slot, an intermediate transmission time slot, and an ACK transmission time slot; where I is an integer greater than 1.

[0010] The initial access time slot is the first time slot in the Hexslot time slot group;

[0011] The ACK transmission time slot is the last time slot in the Hexslot time slot group;

[0012] In the Hexslot time slot group, all time slots except for the initial access time slot and the ACK transmission time slot are intermediate transmission time slots;

[0013] S3: When the maritime information data needs to be sent, the source node user obtains the status of the starting access time slot in the Hexslot time slot group of the destination node user;

[0014] S4: Based on the status of the initial access time slot in the Hexslot time slot group, determine whether the source node user can access the initial access time slot in the Hexslot time slot group and successfully send the maritime information data to the destination node user.

[0015] If the source node user can access the initial access time slot in the Hexslot time slot group and successfully send the maritime information data to the destination node user, then execute S5; otherwise execute S3.

[0016] S5: The ACK transmission time slot sends confirmation information to the source node user, the confirmation information including successful maritime information data transmission and failed maritime information data transmission;

[0017] If the maritime information data transmission is successful, then if the source node user still has maritime information data to send, S3 is executed again; if the source node user no longer has maritime information data to send, the maritime information data transmission ends.

[0018] If maritime information data transmission fails, S3 will be re-executed.

[0019] Furthermore, in S4, the method for determining whether the source node user can access the initial access time slot in the Hexslot time slot group and successfully send the maritime information data to the destination node user is as follows;

[0020] If the initial access slot in the i-th Hexslot group of the transport channel frame of the destination node user is idle, and the source node user selects the initial access slot in the i-th Hexslot group for access, and if the source node user includes M primary users and N cognitive users at this time, then

[0021] When M=1 and N=0, the m-th master user accesses the starting access time slot in the i-th Hexslot time slot group and transmits maritime information data through the starting access time slot and intermediate transmission time slot in the Hexslot time slot group. The m-th master user executes S5.

[0022] When M=1 and N≠0, the m-th primary user accesses the starting access time slot in the i-th Hexslot time slot group and transmits information through the starting access time slot and intermediate transmission time slots in the i-th Hexslot time slot group. The m-th primary user executes S5. At the same time, none of the N cognitive users access the starting access time slot in the i-th Hexslot time slot group, and the N cognitive users re-execute S3. m is the primary user's number.

[0023] When M>1 and N=0, all M master users access the starting access slot in the i-th Hexslot slot group, a data transmission conflict occurs between the M master users, and all M master users re-execute S3.

[0024] When M>1 and N≠0, all M primary users access the starting access slot in the i-th Hexslot time slot group, resulting in a data transmission conflict among the M primary users. All M primary users re-execute S3. At the same time, the cognitive user does not access the starting access slot in the i-th Hexslot time slot group, and the cognitive user re-executes S3.

[0025] When M=0 and N=1, the nth cognitive user accesses the starting access time slot in the i-th Hexslot time slot group and transmits maritime information data through the starting access time slot and intermediate transmission time slot in the i-th Hexslot time slot group. The nth cognitive user executes S5; n is the cognitive user number.

[0026] When M=0 and N>1, all N cognitive users access the starting access slot in the i-th Hexslot slot group, a data transmission conflict occurs among the N cognitive users, and all N cognitive users re-execute S3.

[0027] Furthermore, in step S4, the method for determining whether the source node user can access the initial access time slot in the Hexslot time slot group also includes:

[0028] When there are K users who need to send maritime information data to the destination node user, if at this time, in the frame of the transmission channel of the destination node user, there are P Hexslot time slot groups whose initial access time slots are idle; where k1∈{1,…,K},k2∈{1,…,K};

[0029] When the k1th user selects the state of the starting access time slot in the p1th Hexslot time slot group for access, and the k2th user selects the state of the starting access time slot in the p2th Hexslot time slot group for access, and p1≠p2, where p1∈{1,…,P}, p2∈{1,…,P}

[0030] Then the k1th user accesses the starting access time slot in the p1th Hexslot time slot group and transmits maritime information data through the starting access time slot and intermediate transmission time slot in the p1th Hexslot time slot group.

[0031] The k2nd user accesses the starting access time slot in the p2th Hexslot time slot group and transmits maritime information data through the starting access time slot and intermediate transmission time slots in the p2th Hexslot time slot group.

[0032] Furthermore, the main user's maritime information data is provided with a feedback bit, which is used to identify whether the main user's maritime information data has a periodic transmission requirement.

[0033] If the feedback bit determines that the master user's maritime information data has a periodic transmission requirement, then the status of the starting access time slot of the i-th Hexslot time slot group in the next frame of the destination node user is marked as non-idle, and the master user accesses the starting access time slot of the i-th Hexslot time slot group of the destination node user in the next frame.

[0034] Furthermore, the primary users in the maritime VDES cognitive communication network include VDES shore base stations, merchant ships, and cargo ships; the cognitive users include fishing vessels and operating vessels.

[0035] Furthermore, the aforementioned marine information data includes hydrological and meteorological data, navigation aid information data, coordinate and heading data, and marine environmental data.

[0036] Beneficial Effects: This invention provides a Hexslot-based cognitive access method for maritime VDES, addressing the low channel utilization of maritime VDES. By defining the function of each time slot within a Hexslot time slot group, it mitigates the high collision rate caused by random user access. By combining VDES with cognitive radio technology, it improves the original frequency band channel allocation scheme and, without increasing additional frequency resource overhead, enhances data throughput between ships and between ships and shore base stations, ensuring efficient time slot utilization, reliable transmission of ship messages, and ultimately, safe navigation. This access method can also provide a reference for VDES-related standard development and technological advancements, supporting further development in the future of e-navigation. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a flowchart of the Hexslot-based maritime VDES cognitive access method of the present invention;

[0039] Figure 2 This is a schematic diagram of a maritime VDES cognitive communication network model in an embodiment of the present invention;

[0040] Figure 3 This is a schematic diagram of the feedback bit for the main user in an embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram of a frame structure scheme based on Hexslot improvement in an embodiment of the present invention;

[0042] Figure 5 This is a schematic diagram illustrating the access process of a cognitive user in a data transmission time slot in an embodiment of the present invention;

[0043] Figure 6 This is a schematic diagram of the time slot structure of a cognitive user in an embodiment of the present invention;

[0044] Figure 7 This is a schematic diagram illustrating the relationship between the number of ships and time slot utilization rate in an embodiment of the present invention when there is only a primary user.

[0045] Figure 8 This is a schematic diagram illustrating the relationship between the number of ships and time slot utilization when both primary users and recognized users exist in an embodiment of the present invention.

[0046] Figure 9 This is a schematic diagram illustrating the relationship between the number of ships and the time slot conflict rate in an embodiment of the present invention when there is only a primary user. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] This embodiment provides a Hexslot-based method for maritime VDES cognitive access, such as... Figure 1 As shown, this particularly relates to channel allocation strategies and access protocol methods for Very High Frequency Data Exchange Systems (VDES). It includes the following steps:

[0049] S1: All users in the maritime VDES cognitive communication network collect maritime information data, encapsulate the data into data packets in the VDES device, and wait to send them to other users; the users include main users and cognitive users;

[0050] The aforementioned maritime information data includes hydrological and meteorological data, navigation aids, coordinates, and heading.

[0051] Specifically, this embodiment refers to the actual situation of maritime communication. We select a certain near-shore sea area where many types of ships exist. These ships will send geographical location, hydrological and meteorological information to each other via VDES. For example... Figure 2 The diagram illustrates a maritime VDES cognitive network model. In different geographical locations within the nearshore waters, there is one VDES shore base station, m primary users, and n cognitive users. VDES, combined with cognitive radio technology, considers the base station and large vessels in this area as primary users, and small vessels as cognitive users. Point-to-point communication between vessels is considered, i.e., communication between one vessel and another. Signals are directly transmitted into the network, and the selected nearshore waters are all within the coverage area of ​​the VDES equipment. It is assumed that the shipborne VDES equipment can cover the entire network, and direct communication is possible between vessels and between vessels and shore base stations.

[0052] The newly added VDE channel in VDES supports various maritime services. Based on the content of the transmitted messages on the VDE channel and the navigation needs of ships at sea, all ships in the network can periodically transmit data such as hydrological and meteorological data, channel detection, navigation aids, and coordinate headings to other users in the network via the VDE channel of VDES. The maritime VDES network combines cognitive radio technology. Large ships at sea, such as merchant ships and cargo ships, act as primary users and have priority in occupying channel resources. Smaller vessels, such as fishing boats and work vessels, act as cognitive users, using cognitive radio technology to sense time slot status and access idle time slots. Before accessing a time slot, a cognitive user listens to the time slot status. If the time slot is idle, the cognitive user can access the channel; if a primary user is detected in the time slot, the cognitive user will back off the channel and hand over the access right to the primary user. The VDES equipment on primary and cognitive users can record and store the status information of 2250 time slots within a frame. The status of a time slot can be marked using a 1-bit binary number system, where 1 represents idle and 0 represents occupied. The time slot status information stored in the VDES device is defined as a "time slot status table". By listening to the broadcast content of the master user in the time slot, all users can continuously update their own time slot status table, and by periodically selecting the idle time slot in the time slot status table, they can realize channel access and point-to-point data transmission.

[0053] Channels 2024 and 2084 in the VDES are selected to form a 50kHz bandwidth VDE channel, which operates using the concept of frames. Each frame lasts for 1 minute and is divided into 2250 time slots. The duration of each time slot is approximately 26.67ms. Ships at sea have unique ID numbers. When a ship transmits data, it includes its own ID and the ID of the other ship in the data packet. VDES devices on other ships can parse the ID numbers from the data packet and analyze whether the message is intended for them.

[0054] S2: Establish the frame structure for the user's transmission channel; such as Figure 4 As shown.

[0055] The user's transmission channel frame includes I sequentially connected Hexslot time slot groups, each Hexslot time slot group including a start access time slot, an intermediate transmission time slot, and an ACK transmission time slot; where I is an integer greater than 1;

[0056] The initial access time slot is the first time slot in the Hexslot time slot group, which is used to ensure that the source node user is in an idle access state in the initial access time slot of the Hexslot time slot group.

[0057] The ACK transmission time slot is the last time slot in the Hexslot time slot group, and is used to transmit maritime information data transmission status information to the source node user, including whether the maritime information data transmission was successful or failed.

[0058] In the Hexslot time slot group, all time slots except for the initial access time slot and the ACK transmission time slot are intermediate transmission time slots used for the transmission of maritime information data.

[0059] This embodiment establishes the frame structure of the user's transmission channel based on the Hexslot partitioning scheme. In this embodiment, starting from the first time slot of each frame, every six time slots are called a Hexslot time slot group, and one frame is divided into 375 Hexslot time slot groups. The six time slots in each group are further divided according to their function: the first time slot in each group serves as the initial access time slot, the middle four as data transmission time slots, and the last as the ACK transmission time slot. The initial access time slot is used for ship reservation. Ships can only reserve 375 initial access time slots and access the time slot when the reserved time slot arrives. They remain in a listening state in the remaining time slots. Both the initial access time slot and the data transmission time slot are used for ship data packet transmission, and it is required that the data packets transmitted by the user occupy no more than five consecutive time slots. After ship A transmits data packets in the initial access time slot and the data transmission time slot, ship B, which receives the message, will transmit an ACK message to ship A in the ACK transmission time slot to indicate whether the message transmission was successful.

[0060] S3: When the maritime information data needs to be sent, the source node user that needs to send the information obtains the status of the starting access time slot in the Hexslot time slot group in the frame of the transmission channel of the destination node user; and waits to send the maritime information data to the destination node user.

[0061] S4: Based on the status of the initial access time slot in the Hexslot time slot group, determine whether the source node user can access the initial access time slot in the Hexslot time slot group and successfully send the maritime information data to the destination node user.

[0062] If the source node user can access the initial access time slot in the Hexslot time slot group and successfully send the maritime information data to the destination node user, then execute S5; otherwise execute S3.

[0063] Preferably, the method for determining whether the source node user can access the initial access time slot in the Hexslot time slot group and successfully send maritime information data to the destination node user is as follows:

[0064] When the starting access slot in the i-th Hexslot group of the transport channel frame of the destination node user is idle, and the source node user selects the starting access slot in the i-th Hexslot group for access, if the source node user includes M primary users and N cognitive users at this time,

[0065] If M=1 and N=0, there is only one main user sending maritime information data to the destination node user. Then the m-th (m can only be equal to 1 at this time) main user directly accesses the starting access time slot in the i-th Hexslot time slot group and transmits maritime information data through the starting access time slot and intermediate transmission time slot in the Hexslot time slot group. Execute S5.

[0066] When M = 1 and N ≠ 0, there is one primary user and one cognitive user sending maritime information data to the destination node user. The m-th primary user (m can only be equal to 1 at this time) accesses the starting access time slot in the i-th Hexslot time slot group and transmits information through the starting access time slot and intermediate transmission time slot in the i-th Hexslot time slot group. The m-th primary user executes S5. At the same time, none of the N cognitive users access the starting access time slot in the i-th Hexslot time slot group. The N cognitive users re-execute S3. m is the primary user's number.

[0067] When M>1 and N=0, there are multiple master users sending maritime information data to the destination node user. Then, all M master users access the starting access time slot in the i-th Hexslot time slot group. Data transmission conflict occurs among the M master users, and all M master users re-execute S3.

[0068] When M>1 and N≠0, there are multiple primary users and cognitive users sending maritime information data to the destination node user. All M primary users access the initial access slot in the i-th Hexslot time slot group, resulting in a data transmission conflict. Consequently, the maritime information data is not transmitted to the destination node user, and all M primary users re-execute S3. Simultaneously, the cognitive user does not access the initial access slot in the i-th Hexslot time slot group and also fails to transmit maritime information data to the destination node user. Information transmission by both primary users and cognitive users fails, and S3 is re-executed.

[0069] When M=0 and N=1, there is only one cognitive user sending maritime information data to the destination node user. Then, the nth and n=1th cognitive users access the starting access time slot in the i-th Hexslot time slot group and transmit maritime information data through the starting access time slot and intermediate transmission time slot in the i-th Hexslot time slot group. Execute S5; n is the cognitive user number.

[0070] When M=0 and N>1, there are multiple cognitive users sending maritime information data to the destination node user, but no master user. In this case, all N cognitive users access the initial access slot in the i-th Hexslot slot group. Data transmission conflicts occur among the N cognitive users, and the maritime information data is not transmitted to the destination node user. The conflict between the N cognitive users returns to the execution of S3. Specifically, before accessing, multiple cognitive users will first enter the 1ms perception slot state stage, and all of them will perceive that there is no master user in the slot. After the 1ms perception stage ends, all of them will access the slot. Two cognitive users will conflict, and the message transmission will fail.

[0071] S5: The ACK transmission time slot sends confirmation information to the source node user, the confirmation information including successful maritime information data transmission and failed maritime information data transmission;

[0072] If the maritime information data transmission is successful, then if the source node user still has maritime information data to send, S3 is executed again. If the source node user no longer has maritime information data to send, the maritime information data transmission ends; the source node user (including the primary user and the cognitive user) leaves the maritime VDES cognitive communication network.

[0073] If maritime information data transmission fails, S3 will be re-executed.

[0074] Specifically, in the embodiments of the present invention, the primary user has a high access priority. Before the start of each frame, it selects the starting access time slot in the Hexslot time slot group marked as idle and directly accesses when the time slot arrives. It transmits maritime information data through the starting access time slot and intermediate transmission time slot in the Hexslot time slot group. Then, the primary user receives the message from the ACK transmission time slot of the destination node user in the ACK transmission time slot to confirm whether the maritime information data has been successfully transmitted.

[0075] Cognitive users have low access priority. Before the start of each frame, they select the initial access slot from a Hexslot time slot group marked as idle. When a time slot arrives, the cognitive user first senses the time slot status. If no primary user is simultaneously accessing within the time slot, the cognitive user accesses. If a primary user is simultaneously accessing within the time slot, the cognitive user backs off the channel. After information transmission is completed in the initial access slot and intermediate transmission slots within the Hexslot time slot group, the ACK transmission slot in the Hexslot time slot group informs the source node user whether the maritime information data transmission was successful.

[0076] Preferably, in step S4, the method for determining whether the source node user can access the initial access time slot in the Hexslot time slot group and successfully send the maritime information data to the destination node user further includes:

[0077] When there are K users who need to send maritime information data to the destination node user, if at this time, in the frame of the transmission channel of the destination node user, there are P Hexslot time slot groups whose initial access time slots are idle; where k1∈{1,…,K},k2∈{1,…,K};

[0078] When the k1th user selects the state of the starting access time slot in the p1th Hexslot time slot group for access, and the k2th user selects the state of the starting access time slot in the p2th Hexslot time slot group for access, and p1≠p2, where p1∈{1,…,P}, p2∈{1,…,P}

[0079] Then the k1th user accesses the starting access time slot in the p1th Hexslot time slot group and transmits maritime information data through the starting access time slot and intermediate transmission time slot in the p1th Hexslot time slot group.

[0080] The k2nd user accesses the starting access time slot in the p2th Hexslot time slot group and transmits maritime information data through the starting access time slot and intermediate transmission time slot in the p2th Hexslot time slot group.

[0081] Preferably, the main user's maritime information data includes a feedback bit, which is used to identify whether the main user's maritime information data has a periodic transmission requirement;

[0082] If the feedback bit determines that the primary user's maritime information data has a periodic transmission requirement, then the primary user accesses the starting access slot of the i-th Hexslot time slot group in the next frame of the destination node user. Simultaneously, other users in the network listen to and parse the feedback bit information transmitted by the primary user, and mark the starting access slot state of the i-th Hexslot time slot group in the next frame as non-idle. At this time, the starting access slot state of the destination node user in the i-th Hexslot time slot group in the next frame, as monitored by other users, is not idle.

[0083] Specifically, in embodiments of the present invention, primary users and cognitive users continuously collect feedback bit information broadcast by all primary users in the maritime VDES cognitive communication network and update the time slot status table in their own VDES devices. When not sending messages to others, all users continuously collect messages broadcast by primary users and parse the feedback bit information of maritime information data packets through VDES to determine the usage status of a particular hexslot in the next frame. All users can collect feedback bit information broadcast by all primary users in the network to determine whether a primary user has a periodic data transmission requirement. Figure 3As shown, the last bit of the data packet sent by the primary user is set as a feedback bit. This feedback bit is 1 bit long, where 1 indicates that the primary user with periodic transmission needs needs to occupy the same position in the next frame to send data, and 0 indicates that the primary user does not need to occupy the same position in the next frame to send data. All users in the network can parse the last bit of the primary user's data packet using their own VDES devices.

[0084] In maritime scenarios, ships have a periodic need to transmit data during their operations. For example, when a ship is monitoring the weather in a certain sea area, it needs to send an image of the marine environment to another user every minute. Typically, maritime information data transmission is set to a transmission cycle of one minute (one frame), meaning a message is sent every minute (one frame). Therefore, the feedback bit confirms that the source node user is transmitting information in the current frame, and the message is sent again in the same Hexslot time slot group in the next frame. Other users listen to the feedback bit information from the primary user and mark the Hexslot time slot group as non-idle in the next frame.

[0085] In one embodiment of the invention, each time slot on the VDE channel can transmit up to 1024 bits of data, with a transmission time of approximately 26.67 ms. The improved frame hierarchy groups six time slots together, with the first five slots capable of transmitting data, thus each group has 5120 bits for data transmission. The sixth time slot is used for transmitting ACK messages. When the primary user and the cognitive user transmit data, one data packet is transmitted at a time. The data packet contains a easing mechanism, training sequence, signal information, valid data bits, CRC, and buffer bits, such as... Figure 5 and Figure 6 As shown, excluding the specified bit length and the gradually increasing data length perceived by the cognitive user in the first 1ms of access, the effective data bits in the cognitive user's data packet cannot exceed 4928 bits. The time slot structure for the master user's message transmission is similar to that of the cognitive user. The difference is that the master user does not need to perceive the state in the first 1ms. Therefore, the effective data bits in the master user's data packet cannot exceed 4960 bits, and the last bit of the effective data bits is used as a feedback bit to broadcast to other users whether to occupy the Hexslot time slot group at the same position in the next frame to transmit data when the next frame arrives. The feedback bit is 1, which indicates that the same position in the next frame needs to be occupied, and 0 indicates that it is not occupied.

[0086] In this embodiment, when the primary user reaches the initial access slot, it will directly enter the easing phase, which lasts for 1 ms, followed by data transmission. The final 1 ms is the user's buffer phase, and the total duration does not exceed 5 slots. The cognitive user's access principle involves judging the state of the initial access slot in the first 1 ms. The cognitive user uses cognitive radio technology to listen for the slot status within the first 1 ms of the access slot; this phase is the cognitive user's perception phase. When no primary user is detected, the cognitive user accesses the slot and transmits data. When a primary user is detected, the cognitive user backs off the slot, relinquishes access to the primary user, and randomly selects another slot in the next frame to access the slot until an idle slot is detected, at which point it accesses the slot again to complete data transmission. If a primary user that has successfully transmitted data has periodic transmission needs, it can continue to occupy the same slot in the next frame as in the previous frame to send data.

[0087] The ACK transmission slot is used to inform the source node user whether the transmission was successful. The ACK transmission slot occupies one slot length and can transmit up to 1024 bits of data. The transmitted data packet must include the source vessel ID, destination vessel ID, and a 2-bit ACK bit. A message bit of 00 in the ACK transmission slot indicates successful transmission of the primary user message, 01 indicates failure, 10 indicates successful transmission of the cognitive user message, and 11 indicates failure. When conflicts occur between vessels, multiple source node users may simultaneously access the initial access slot of the same Hexslot slot group. Data packets overlap, the destination node user cannot receive messages, and no ACK message is sent. Simultaneously, multiple source node users will not receive ACK messages, resulting in transmission failure. Alternatively, if other reasons cause data packet parsing errors, a message with an ACK bit of 01 or 11 will be sent in the ACK transmission slot (acknowledge) to indicate that the primary user or cognitive user's data transmission has failed.

[0088] This embodiment compares the proposed protocol with the suggested S-Aloha protocol, comparing the relationship between the number of ships and time slot utilization in a network with only primary users. Figure 7 As shown, in the simulation parameter settings, the number of ships ranges from 50 to 800, and ships can randomly select to occupy 3 to 5 consecutive time slots. With the increase in the number of ships, both protocols show an initial increase followed by a decrease. This is attributed to the greater number of available idle time slots when fewer ships are present. As more ships need to access time slots, the number of collisions between ships increases, leading to a decrease in time slot utilization. Furthermore, the proposed protocol achieves a maximum time slot utilization of approximately 70%, while S-Aloha only achieves approximately 20% of its maximum time slot utilization when processing longer data packets, falling short of the theoretical value of 36.8%.

[0089] When both primary users and cognitive users exist, such as Figure 8 As shown, the number of primary users ranges from 1 to 800, while the number of cognitive users is set to 0, 30, 60, and 90. Ships can randomly occupy 3 to 5 consecutive time slots. When the number of primary users is small, there are many idle time slots that cognitive users can access. When the number of primary users is fixed, the time slot utilization rate increases with the increase in the number of cognitive users. However, when the number of primary users increases, the available idle time slots decrease, and the time slots that cognitive users can access decrease. At this point, the time slot utilization rate is mainly determined by the number of primary users.

[0090] The proposed protocol is compared with the suggested S-Aloha protocol. In a network with only primary users, the relationship between the number of vessels and the time slot conflict rate is compared. Figure 9 As shown in the simulation parameters, the number of ships ranges from 50 to 800, and ships randomly select 3 to 5 consecutive time slots for transmission. With the increase in the number of ships, the collision rate of the two protocols gradually increases. When the number of ships is large, the probability of ships selecting the same time slot increases, leading to a higher collision rate. However, because the proposed protocol adds a feedback bit, all ships can avoid ships with periodic transmission needs, thus effectively reducing the collision rate. The proposed protocol performs better under different ship numbers.

[0091] Beneficial Effects: This invention provides a Hexslot-based cognitive access method for maritime VDES, addressing the low channel utilization of maritime VDES. By defining the function of each time slot within a Hexslot time slot group, it mitigates the high collision rate caused by random user access. By combining VDES with cognitive radio technology, it improves the original frequency band channel allocation scheme and, without increasing additional frequency resource overhead, enhances data throughput between ships and between ships and shore base stations, ensuring efficient time slot utilization, reliable transmission of ship messages, and ultimately, safe navigation. This access method can also provide a reference for VDES-related standard development and technological advancements, supporting further development in the future e-navigation field. Furthermore, by setting a feedback mechanism with a feedback bit in the primary user, it reduces the access collision rate between ships and improves the ship access success rate.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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 or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A maritime VDES cognitive access method based on Hexslot, characterized in that, Includes the following steps: S1: All users in the maritime VDES cognitive communication network collect maritime information data; the users include primary users and cognitive users; S2: Establish the frame hierarchy structure of the user's transmission channel: The frame hierarchy of the user's transmission channel includes I sequentially connected Hexslot time slot groups, each of which includes a start access time slot, an intermediate transmission time slot, and an ACK transmission time slot; where I is an integer greater than 1. The initial access time slot is the first time slot in the Hexslot time slot group; The ACK transmission time slot is the last time slot in the Hexslot time slot group; In the Hexslot time slot group, all time slots except for the initial access time slot and the ACK transmission time slot are intermediate transmission time slots; S3: When the maritime information data needs to be sent, the source node user obtains the status of the starting access time slot in the Hexslot time slot group of the destination node user; S4: Based on the status of the initial access time slot in the Hexslot time slot group, determine whether the source node user can access the initial access time slot in the Hexslot time slot group and successfully send the maritime information data to the destination node user. If the source node user can access the initial access time slot in the Hexslot time slot group and successfully send the maritime information data to the destination node user, then execute S5; otherwise execute S3. S5: The ACK transmission time slot sends confirmation information to the source node user, the confirmation information including successful maritime information data transmission and failed maritime information data transmission; If the maritime information data transmission is successful, then if the source node user still has maritime information data to send, S3 is executed again; if the source node user no longer has maritime information data to send, the maritime information data transmission ends. If maritime information data transmission fails, S3 will be re-executed.

2. The maritime VDES cognitive access method based on Hexslot according to claim 1, characterized in that, In S4, the method for determining whether the source node user can access the initial access time slot in the Hexslot time slot group and successfully send the maritime information data to the destination node user is as follows; If the initial access slot in the i-th Hexslot group of the transport channel frame of the destination node user is idle, and the source node user selects the initial access slot in the i-th Hexslot group for access, and if the source node user includes M primary users and N cognitive users at this time, then When M=1 and N=0, the m-th master user accesses the starting access time slot in the i-th Hexslot time slot group and transmits maritime information data through the starting access time slot and intermediate transmission time slot in the Hexslot time slot group. The m-th master user executes S5. When M=1 and N≠0, the m-th primary user accesses the starting access time slot in the i-th Hexslot time slot group and transmits information through the starting access time slot and intermediate transmission time slots in the i-th Hexslot time slot group. The m-th primary user executes S5. At the same time, none of the N cognitive users access the starting access time slot in the i-th Hexslot time slot group, and the N cognitive users re-execute S3. m is the primary user's number. When M>1 and N=0, all M master users access the starting access slot in the i-th Hexslot slot group, a data transmission conflict occurs between the M master users, and all M master users re-execute S3. When M>1 and N≠0, all M primary users access the starting access slot in the i-th Hexslot time slot group, resulting in a data transmission conflict among the M primary users. All M primary users re-execute S3. At the same time, the cognitive user does not access the starting access slot in the i-th Hexslot time slot group, and the cognitive user re-executes S3. When M=0 and N=1, the nth cognitive user accesses the starting access time slot in the i-th Hexslot time slot group and transmits maritime information data through the starting access time slot and intermediate transmission time slot in the i-th Hexslot time slot group. The nth cognitive user executes S5; n is the cognitive user number. When M=0 and N>1, all N cognitive users access the starting access slot in the i-th Hexslot slot group, a data transmission conflict occurs among the N cognitive users, and all N cognitive users re-execute S3.

3. The maritime VDES cognitive access method based on Hexslot according to claim 1, characterized in that, In step S4, the method for determining whether the source node user can access the initial access time slot in the Hexslot time slot group further includes: When there are K users who need to send maritime information data to the destination node user, if at this time, in the frame of the transmission channel of the destination node user, there are P Hexslot time slot groups whose initial access time slots are idle; where k1∈{1,…,K},k2∈{1,…,K}; When the k1th user selects the state of the starting access time slot in the p1th Hexslot time slot group for access, and the k2th user selects the state of the starting access time slot in the p2th Hexslot time slot group for access, and p1≠p2, where p1∈{1,…,P}, p2∈{1,…,P} Then the k1th user accesses the starting access time slot in the p1th Hexslot time slot group and transmits maritime information data through the starting access time slot and intermediate transmission time slot in the p1th Hexslot time slot group. The k2nd user accesses the starting access time slot in the p2th Hexslot time slot group and transmits maritime information data through the starting access time slot and intermediate transmission time slots in the p2th Hexslot time slot group.

4. The maritime VDES cognitive access method based on Hexslot according to claim 1, characterized in that, The main user's maritime information data is equipped with a feedback bit, which is used to identify whether the main user's maritime information data has a periodic transmission requirement. If the feedback bit determines that the master user's maritime information data has a periodic transmission requirement, then the status of the starting access time slot of the i-th Hexslot time slot group in the next frame of the destination node user is marked as non-idle, and the master user accesses the starting access time slot of the i-th Hexslot time slot group of the destination node user in the next frame.

5. The maritime VDES cognitive access method based on Hexslot according to claim 1, characterized in that, The primary users in the maritime VDES cognitive communication network include VDES shore base stations, merchant ships, and cargo ships; cognitive users include fishing vessels and operating vessels.

6. The maritime VDES cognitive access method based on Hexslot according to claim 1, characterized in that, The marine information data includes hydrological and meteorological data, navigation aid information data, coordinate and heading data, and marine environmental data.

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