CN113709899B - Self-organizing time division multiple access method for ship automatic identification system - Google Patents
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access
- H04W74/08—Non-scheduled access, e.g. ALOHA
- H04W74/0833—Random access procedures, e.g. with 4-step access
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access
- H04W74/08—Non-scheduled access, e.g. ALOHA
- H04W74/0833—Random access procedures, e.g. with 4-step access
- H04W74/0841—Random access procedures, e.g. with 4-step access with collision treatment
- H04W74/085—Random access procedures, e.g. with 4-step access with collision treatment collision avoidance
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Abstract
The invention relates to a self-organizing time division multiple access method of a ship automatic identification system with a conflict feedback mechanism. When the number of users is large, the existing channel access method has high probability of time slot conflict, reduces the reliability of an AIS system, and is not beneficial to the safe navigation of ships. The invention is designed as follows: after the system is started, respectively monitoring the information of all time slots in one minute of two channels, and recording the information in a local frame time slot state table; then using proposal to select initial time slot and other sending time slot; then entering a continuous working stage, transmitting information on the transmission time slot by using an SOTDMA access mode, reserving the transmission time slot of the next frame, continuously monitoring the information of other time slots in one frame by the system, and recording reservation time slots of a local user and other users; and finally, the system processes the reserved time slot conflict between the local user and other users at the frame tail, and avoids the occurrence of the time slot conflict of the next frame.
Description
Technical Field
The invention belongs to the technical field of ship communication, and particularly relates to a self-organizing time division multiple access method of a ship automatic identification system with a conflict feedback mechanism.
Background
The on-board automatic identification system (Automatic Identification System, AIS) performs the functions of channel access and inter-device communication via an ad hoc time division multiple access (Self-organized Time Division Multiple Access, SOTDMA) protocol. SOTDMA channel access technology enables an AIS system to autonomously select transmission time slots to transmit information according to channel occupancy within a frame.
The SOTDMA time slot access protocol sets the duration of one frame of data to one minute (2250 time slots are numbered: 0-2249), and when each frame autonomously reserves a time slot, the time slot is generally selected by the channel condition detected by the previous frame (i.e. the previous minute). When the time slot reservation conflict occurs, the method does not adjust the reserved time slot to avoid the time slot conflict, which results in higher conflict probability under the condition of more users and endangers the safety performance of the system under the condition of crowded sea areas.
Aiming at the defects of the time slot selection method, the invention designs an SOTDMA access method with a conflict feedback mechanism in order to effectively reduce the conflict probability.
Disclosure of Invention
The invention aims to solve the defects and shortcomings of the method and provides a self-organizing time division multiple access method of a ship automatic identification system with a conflict feedback mechanism. According to the method, feedback information of time slot reservation conflict is added on the basis of an original SOTDMA protocol, so that a ship can adjust time slots with conflict according to the feedback information, and the time slot reservation conflict probability of a system is reduced.
The invention relates to a self-organizing time division multiple access method of an automatic ship identification system, which comprises the following specific steps:
step one, initializing a system: starting the system, opening two AIS receivers to monitor two channels A and B for one minute respectively, recording the information of each time slot of the two channels in the minute, and establishing a frame time slot state table of the channels A and B; confirming that the number of times of transmitting messages per minute of the ship is the report frequency, and recording the report frequency as Rr;
step two, network access: according to the frame time slot state table obtained in the step one, taking the current time as the starting time, adopting a random access time division multiple access channel access mode, and selecting an idle time slot as a first sending time slot; the time slot is used for sending AIS message type 3 to report the position of the user, so that the user can be perceived by other users in the network; once the system selects an idle time slot, entering a step three; otherwise, continuing to select by adopting a random access time division multiple access channel access mode until an idle time slot is found;
step three, a first frame is sent: continuously dividing Rr sending time slots by using an incremental time division multiple access channel access scheme and the frame time slot state table obtained in the first step according to the idle time slot selected in the second step as a first sending time slot, and sending AIS message type 3 by using the time slots; setting a holding flag in a communication state of the incremental time division multiple access channel access scheme to 1, and generating a corresponding time slot timeout value for each transmission time slot, wherein the time slot timeout value is a random integer between 3 and 7; in this stage, the system continues to monitor the information of the rest time slots in the frame, and updates the time slot state table according to the detected information after the frame is finished, and then proceeds to step four;
step four, entering a continuous working mode: the system uses an self-organizing time division multiple access method to send messages when a sending time slot arrives; waiting for arrival of a time slot and judging whether the current time slot is a transmitting time slot or not; if the current time slot is the transmitting time slot, entering a step five, otherwise, entering a step eight;
step five, judging whether the time slot timeout value of the current sending time slot is 0; if the time slot timeout value is 0, entering a step six, otherwise entering a step seven;
step six, selecting reserved time slots: the system uses the time slot selection method specified in ITU-R M.1371-5 proposal and the last updated frame time slot state table of the previous frame to reserve a new transmission time slot for the next frame; if the reservation is successful, a new time slot timeout value is given to the new transmission time slot, and the reserved new transmission time slot and the current transmission time slot form a pair of mapping relations to be recorded in a local user time slot reservation information table; if the reservation of the new time slot is not achieved, the current time slot is taken as the reserved time slot, and a new time slot timeout value is given to the time slot; transmitting a message with reservation information in a self-organizing time division multiple access mode, and entering a step nine;
step seven, the next frame still uses the current time slot to send information, the time slot timeout value count of the current time slot is reduced by 1, the updated information of the time slot timeout value is sent in an ad hoc time division multiple access mode, and then step nine is entered;
step eight, receiving the information of the current time slot and analyzing the content of the information: if the current time slot receives the message with the reservation information sent by other users, the time slot reservation information is recorded in a time slot reservation information table of the other users, and the step nine is entered;
step nine, judging whether the current frame is finished, namely judging whether the time slot number of the current time slot is 2249; if the time slot number of the time slot is smaller than 2249, indicating that one frame is not finished, returning to the step four, otherwise, entering the step ten;
step ten, comparing the reserved time slot of the user recorded in the local user time slot reserved information table in the frame with reserved time slots of other users in the other user time slot reserved information table, and judging whether time slot reserved conflict occurs or not;
if the time slot reservation conflict occurs, the system gives up the time slot reserved for the conflict as the next frame transmission time slot, and uses the current transmission time slot corresponding to the conflict reserved time slot as the transmission time slot of the next frame according to the mapping relation formed by the reserved transmission time slot and the current transmission time slot in the local user time slot reservation information table, and sets the time slot timeout value as 1; if no slot reservation conflict occurs, reserving the slot is regarded as successful reservation;
updating a frame time slot state table according to the processed information of all the reservation time slots, and clearing a local user time slot reservation information table and other user time slot reservation information tables; then, step four is entered to start processing the slot information of the next frame.
The invention has the beneficial effects that: compared with the existing access method, the self-organizing time division multiple access method of the ship automatic identification system can adjust own reservation time slot according to conflict feedback information, so that the time slot reservation conflict rate is reduced, the AIS system can still keep good safety performance under the condition of a large number of users, and the time slot utilization rate and throughput of a channel can be effectively improved.
Detailed Description
The self-organizing time division multiple access method of the ship automatic identification system comprises the following specific steps:
step one, initializing a system. The system is started, two AIS receivers are opened to monitor A, B two channels for one minute respectively, information of each time slot of the two channels in the minute is recorded, and a A, B frame time slot state table of the two channels is established respectively. Confirming relevant parameters of the system: the number of messages sent per minute by the vessel, i.e. the reporting frequency, is denoted Rr.
And step two, accessing the network. The system uses the Random Access Time Division Multiple Access (RATDMA) scheme provided in ITU-R M.1371-5 recommendation and a time slot selection method to select an idle time slot as a first transmission time slot within 4 seconds according to the frame time slot state table obtained in the step one by taking the current time as a starting time. This slot will be used to send AIS message type 3 (location information) reports where itself is located so that itself can be perceived by other users within the network. Once the system has selected an idle slot, step three is entered. Otherwise, continuing to select by adopting the RATDMA mode until the idle time slot is found.
And step three, transmitting the first frame. The system uses the Incremental Time Division Multiple Access (ITDMA) scheme set forth in the ITU-R m.1371-5 recommendation and the frame slot state table obtained in step one to divide Rr transmit slots continuously according to the free slot selected in step two as the first transmit slot and uses these slots to transmit AIS message type 3. The hold flag in the ITDMA communication state is set to 1 and a corresponding slot timeout value (slot timeout value is a random integer between 3 and 7, the following) is generated for each transmit slot. In this stage, the system continues to listen to the information of the rest of the slots in this frame except for the message type 3 sent in Rr slots, updates the slot state table according to the information detected after this frame is over, and then proceeds to step four.
And step four, entering a continuous working mode. The system starts sending messages when the sending time slot arrives using the SOTDMA access method. Waiting for the arrival of a time slot and determining whether the current time slot is a transmit time slot. If the current time slot is the transmitting time slot, entering a step five; otherwise, step eight is entered.
And step five, judging whether the time slot timeout value of the current transmission time slot is 0. If the time slot timeout value is 0, entering a step six, otherwise entering a step seven;
and step six, selecting reserved time slots. The system reserves a new transmission slot for the next frame using the slot selection method specified in the ITU-R m.1371-5 recommendation and the last updated frame slot state table of the previous frame. If the reservation is successful, a new time slot timeout value is assigned to the new transmission time slot, and the reserved new transmission time slot and the current transmission time slot form a pair of mapping relations to be recorded in a local user time slot reservation information table. If the reservation is not completed, the current time slot is regarded as the reserved time slot, and a new time slot timeout value is assigned to the time slot. And (3) transmitting a message with reservation information in an SOTDMA access mode, and proceeding to step nine.
And step seven, the next frame still uses the current time slot to send information, the time slot timeout value count of the current time slot is reduced by 1, the updated time slot timeout value message is sent in an SOTDMA access mode, and then step nine is entered.
And step eight, receiving the information of the current time slot and analyzing the content of the information. And if the current time slot receives the message with the reservation information sent by other users, recording the time slot reservation information into a time slot reservation information table of the other users, and entering a step nine.
And step nine, judging whether the current frame is ended, namely judging whether the time slot number of the current time slot is 2249. If the time slot number of the time slot is less than 2249, it indicates that one frame has not ended, and the step four is returned at this time, otherwise, the step ten is entered.
And step ten, comparing the reserved time slot of the user recorded in the local user time slot reserved information table in the frame with reserved time slots of other users in the other user time slot reserved information table, and judging whether time slot reserved conflict occurs.
If the time slot reservation conflict occurs, the system gives up the time slot reserved for the conflict as the next frame transmission time slot, and uses the current transmission time slot corresponding to the conflict reserved time slot as the transmission time slot of the next frame according to the mapping relation formed by the reserved transmission time slot and the current transmission time slot in the local user time slot reservation information table, and sets the time slot timeout value as 1. If no slot reservation conflict occurs, the reserved slot is considered to be reserved successfully.
And updating a frame time slot state table according to the processed information of all the reserved time slots, and clearing a local user time slot reserved information table and other user time slot reserved information tables. Then, step four is entered to start processing the slot information of the next frame.
Claims (1)
1. A self-organizing time division multiple access method of a ship automatic identification system is characterized by comprising the following specific steps:
step one, initializing a system: starting the system, opening two AIS receivers to monitor two channels A and B for one minute respectively, recording the information of each time slot of the two channels in the minute, and establishing a frame time slot state table of the channels A and B; confirming that the number of times of transmitting messages per minute of the ship is the report frequency, and recording the report frequency as Rr;
step two, network access: according to the frame time slot state table obtained in the step one, taking the current time as the starting time, adopting a random access time division multiple access channel access mode, and selecting an idle time slot as a first sending time slot; the time slot is used for sending AIS message type 3 to report the position of the user, so that the user can be perceived by other users in the network; once the system selects an idle time slot, entering a step three; otherwise, continuing to select by adopting a random access time division multiple access channel access mode until an idle time slot is found;
step three, a first frame is sent: continuously dividing Rr sending time slots by using an incremental time division multiple access channel access scheme and the frame time slot state table obtained in the first step according to the idle time slot selected in the second step as a first sending time slot, and sending AIS message type 3 by using the time slots; setting a holding flag in a communication state of the incremental time division multiple access channel access scheme to 1, and generating a corresponding time slot timeout value for each transmission time slot, wherein the time slot timeout value is a random integer between 3 and 7; the system continues to monitor the information of the rest time slots in the frame, updates the time slot state table according to the monitored information after the frame is finished, and then enters the step four;
step four, entering a continuous working mode: the system uses an self-organizing time division multiple access method to send messages when a sending time slot arrives; waiting for arrival of a time slot and judging whether the current time slot is a transmitting time slot or not; if the current time slot is the transmitting time slot, entering a step five, otherwise, entering a step eight;
step five, judging whether the time slot timeout value of the current sending time slot is 0; if the time slot timeout value is 0, entering a step six, otherwise entering a step seven;
step six, selecting reserved time slots: the system uses the time slot selection method specified in ITU-R M.1371-5 proposal and the last updated frame time slot state table of the previous frame to reserve a new transmission time slot for the next frame; if the reservation is successful, a new time slot timeout value is given to the new transmission time slot, and the reserved new transmission time slot and the current transmission time slot form a pair of mapping relations to be recorded in a local user time slot reservation information table; if the reservation of the new time slot is not achieved, the current time slot is taken as the reserved time slot, and a new time slot timeout value is given to the time slot; transmitting a message with reservation information in a self-organizing time division multiple access mode, and entering a step nine;
step seven, the next frame still uses the current time slot to send information, the time slot timeout value count of the current time slot is reduced by 1, the updated information of the time slot timeout value is sent in an ad hoc time division multiple access mode, and then step nine is entered;
step eight, receiving the information of the current time slot and analyzing the content of the information: if the current time slot receives the message with the reservation information sent by other users, the time slot reservation information is recorded in a time slot reservation information table of the other users, and the step nine is entered;
step nine, judging whether the current frame is finished, namely judging whether the time slot number of the current time slot is 2249; if the time slot number of the time slot is smaller than 2249, indicating that one frame is not finished, returning to the step four, otherwise, entering the step ten;
step ten, comparing the reserved time slot of the user recorded in the local user time slot reserved information table in the frame with reserved time slots of other users in the other user time slot reserved information table, and judging whether time slot reserved conflict occurs or not;
if the time slot reservation conflict occurs, the system gives up the time slot reserved for the conflict as the next frame transmission time slot, and uses the current transmission time slot corresponding to the conflict reserved time slot as the transmission time slot of the next frame according to the mapping relation formed by the reserved transmission time slot and the current transmission time slot in the local user time slot reservation information table, and sets the time slot timeout value as 1; if no slot reservation conflict occurs, reserving the slot is regarded as successful reservation;
updating a frame time slot state table according to the processed information of all the reservation time slots, and clearing a local user time slot reservation information table and other user time slot reservation information tables; then, step four is entered to start processing the slot information of the next frame.
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| CN115696448B (en) * | 2023-01-03 | 2023-03-21 | 成都实时技术股份有限公司 | AIS self-organizing time division multiple access network implementation method and device |
| CN118316829B (en) * | 2024-06-05 | 2024-08-09 | 交通运输部北海航海保障中心天津航标处 | Time slot reservation compliance detection method for self-organizing time division multiple access |
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