A Multi-Hop TDMA Time Slot Allocation Method for UAV Ad hoc Networks

Abstract

This invention relates to the field of wireless ad hoc network technology, specifically disclosing a multi-hop TDMA time slot allocation method suitable for UAV ad hoc networks. The method includes: dividing each TDMA time frame into reservation subframes and data subframes according to time sequence; each reservation subframe contains K reservation periods, and each data subframe contains N data time slots; defining control short frames, service long frames, and a time slot occupancy table; fixing the allocation of a reservation period based on the node's ID and priority; each node that has completed network access sending a reservation request frame and a reservation notification frame to the data time slots within its allocated reservation period according to current service needs and time slot occupancy; each node that has completed network access maintaining its local time slot occupancy table based on the reservation notification frame; and after the reservation subframe of a TDMA time frame ends, each node communicates by sending service long frames to the reserved data time slots. This method achieves on-demand allocation of TDMA channels while prioritizing the channel needs of high-priority nodes and ensuring data timeliness.

Description

Technical Field

[0001] This invention relates to the field of wireless ad hoc network technology, and in particular to a multi-hop TDMA time slot allocation method suitable for UAV ad hoc networks. Background Technology

[0002] Unmanned Aerial Vehicle (UAV) Ad Hoc Networks (UANETs) possess advantages such as distributed nature, self-organization, multi-service capabilities, and long-range operation, making them widely used in military and civilian fields. Each UAV node simultaneously performs both data transmission and reception and relay forwarding functions. TDMA access is a commonly used access method for wireless ad hoc networks, and its efficient time slot allocation method can improve channel utilization and enhance network communication performance.

[0003] Traditional time slot allocation methods are mainly designed for static, short-range communication scenarios, where the topology between UAV nodes remains relatively static. However, in real-world environments, due to the rapid movement and vulnerability of nodes in UAV ad hoc networks, traditional methods often result in low data delivery rates and high latency.

[0004] Therefore, designing a reasonable time slot allocation strategy is of great significance for UAV self-organizing networks. Summary of the Invention

[0005] This invention provides a multi-hop TDMA time slot allocation method suitable for UAV ad hoc networks. The technical problem it solves is that the rapid movement of nodes and dynamic changes in network topology in UAV ad hoc networks increase the number of time slot conflicts between nodes, resulting in low communication efficiency.

[0006] To address the above technical problems, this invention provides a multi-hop TDMA time slot allocation method suitable for UAV ad hoc networks, comprising the following steps:

[0007] S1. Divide each TDMA time frame into two parts, a reservation subframe and a data subframe, according to the time sequence. The reservation subframe contains K reservation periods, where K is the maximum number of nodes on the network at the same time. The data subframe contains N data time slots, where N >> K.

[0008] S2. Define a control short frame for time slot reservation, a service long frame for data communication, and a time slot occupancy table for two-hop neighbor nodes; the control short frame includes a reservation request frame, a reservation notification frame, and a reservation reply frame; the time slot occupancy table contains the node's ID, priority, and occupied time slot number;

[0009] S3. After the node powers on and completes network synchronization, it occupies a fixed reservation period based on the node's ID and priority.

[0010] S4. Each node that has completed network access sends the reservation request frame and the reservation notification frame to the data time slot during its reserved period according to the current business needs and time slot occupancy.

[0011] S5. Each node that has completed network access receives the reservation request frame and the reservation notification frame sent by other nodes during the reservation period that is not occupied by it, and replies with the reservation reply frame, and maintains the local time slot occupancy table according to the reservation notification frame.

[0012] S6. After the reservation subframe of a TDMA time frame ends, each node sends the service long frame to communicate with the data time slot reserved in this TDMA time frame.

[0013] Furthermore, in step S1, each reservation period includes three stages: reservation application, reservation reply, and reservation broadcast, which correspond to the reservation application frame, the reservation reply frame, and the reservation notification frame, respectively.

[0014] Further, in step S2, the reservation request frame includes a frame control field, a source address, a relay address, a destination address, time slot request information, and verification information; the frame control field includes a frame type, a frame length, and a smart routing bit, the smart routing bit being used to indicate whether routing forwarding is required; the source address includes a source node ID and a node priority; the time slot request information is used to indicate which data time slots are requested and the priority of this information.

[0015] Further, in step S2, the reservation response frame includes a frame control field, a source address, a timeslot information, a confirmation information, and a frame verification information; the source address is the address of the node that sent the reservation request to this node, and the confirmation information is used to indicate whether the timeslot is available.

[0016] Furthermore, in step S2, the frame format of the reservation notification frame is the same as that of the reservation application frame, except that the frame type and smart routing bit in the frame control field of the reservation notification frame are sent in the form of broadcast.

[0017] Furthermore, in step S2, the service long frame includes frame type, source address, relay address, destination address, frame entity, and check sequence.

[0018] Further, step S4 specifically includes:

[0019] Each node that has completed network access will, according to the time slot occupancy table, initiate a reservation request for an idle time slot if the unoccupied data time slot meets the current service requirements; if there are no idle time slots or the remaining idle time slots cannot meet the current service requirements, the high-priority node will send the reservation request frame and the reservation notification frame to the data time slots already requested by the low-priority neighboring node; if there are no neighboring nodes with lower priority than this node or the time slots occupied by the neighboring nodes cannot meet the service requirements, the reservation of data time slots in this TDMA time frame period will fail.

[0020] Furthermore, step S5 specifically includes the following steps:

[0021] S51. Receiving reservation requests: Each node that has completed network access receives the reservation request frame from its neighboring nodes during a reservation period that is not its own.

[0022] S52. Data Slot Allocation: After receiving the reservation request frame from a neighboring node, the current node determines whether the requested slot is available based on the two-hop slot occupancy table. If the slot is not occupied, the node replies to the neighboring node with a reservation confirmation reply frame. If the slot is occupied, the node compares the sum of its priorities with the sum of the priorities of the nodes that have occupied the slot. If the current node's priorities are higher, the slot is allocated to the current node, and the node replies to its neighboring node with a reservation success reply frame. Otherwise, the data slot request fails, and the current node replies to its neighboring node with a reservation failure reply frame. The sum of a node's priorities is equal to the sum of the node's priorities and the priorities of its slot request information.

[0023] S53. Receiving reservation notifications: Each node receives the reservation notification frames sent by other nodes during reservation periods that are not occupied by it; if a lower-priority node receives a reservation notification frame in which a higher-priority node occupies the data time slot that the node has applied for, the lower-priority node will voluntarily give up occupying the data time slot.

[0024] S54. Maintain the local time slot occupancy table: Each node updates its local time slot occupancy table in real time based on the received reservation notification frames.

[0025] Furthermore, the priority of time slot application information increases with time; that is, if the application fails in the current time frame, the priority will automatically increase by one in the next time frame.

[0026] Furthermore, after each TDMA time frame begins, each node will clear its local time slot occupancy table.

[0027] The present invention provides a multi-hop TDMA time slot allocation method suitable for UAV ad hoc networks, the advantages of which are:

[0028] 1. This enables rapid feedback of node time slot reservation results to meet the high real-time requirements of UAV ad hoc networks;

[0029] 2. Nodes can dynamically request the number of data time slots based on their data volume and service priority, which can avoid wasting time slot resources and improve channel utilization.

[0030] 3. By adopting a node priority plus data priority approach, we can achieve on-demand allocation while prioritizing high-priority business needs, and at the same time, we can ensure the timeliness of real-time priority data.

[0031] 4. Maintaining the time slot occupancy table locally avoids the huge overhead of the reservation application stage, avoids time slot conflicts between nodes within two hops, and enables the reuse of data time slots of neighboring nodes outside two hops, thereby improving channel utilization. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of a TDMA time frame provided in an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of a long data frame provided in an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of the structure of the reservation application frame provided in an embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram of the structure of the reservation response frame provided in an embodiment of the present invention;

[0036] Figure 5 This is a schematic representation of time slot occupancy provided in an embodiment of the present invention;

[0037] Figure 6 This is a comparison chart of the throughput of the three protocols provided in this embodiment of the invention as a function of load rate;

[0038] Figure 7 This is a comparison chart of the average latency of the three protocols provided in this embodiment of the invention as a function of load rate;

[0039] Figure 8 This is a comparison chart of the effective delivery rate of the three protocols provided in this embodiment of the invention as a function of load rate. Detailed Implementation

[0040] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are given for illustrative purposes only and should not be construed as limiting the present invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0041] This invention provides a multi-hop TDMA time slot allocation method suitable for UAV ad hoc networks. In this embodiment, it includes steps S1 to S6:

[0042] S1, such as Figure 1 As shown, each TDMA time frame is divided into two parts: a reservation subframe (RF) and a data subframe (IF). The reservation subframe (RF) contains K reservation periods (RC1 to RC2). K K represents the maximum number of nodes simultaneously connected to the entire network. Each reservation period includes three stages: reservation request (RR), reservation response (RC), and reservation broadcast (RA). The data subframe contains N data time slots (IS1 to IS2). N ), N>>K.

[0043] S2. Define the control short frame used for time slot reservation, the service long frame used for data communication, and the time slot occupancy table of two-hop neighbor nodes; the control short frame includes reservation request frame, reservation reply frame and reservation notification frame (corresponding to the three stages of reservation request, reservation reply and reservation broadcast in the reservation period, respectively).

[0044] like Figure 2 As shown, a service long frame includes frame type, source address, relay address, destination address, frame entity, and check sequence.

[0045] like Figure 3 As shown, the reservation request frame includes a frame control field, source address, relay address, destination address, time slot request information, and verification information (frame verification sequence). The frame control field contains the frame type, frame length, and smart routing bits, which indicate whether routing is required; the source address contains the source node ID and node priority; the time slot information indicates which data time slots are being requested and the priority of that information.

[0046] like Figure 4 As shown, the reservation response frame includes a frame control field, source address, timeslot information, acknowledgment information (acknowledgment / rejection), and frame check information (frame check sequence); the source address is the address of the node that sent the reservation request to this node, and the acknowledgment information is used to indicate whether the timeslot is available.

[0047] The frame format of the appointment notification frame is the same as that of the appointment request frame. The difference is that the frame type and smart routing bits in the frame control field of the appointment notification frame are sent in broadcast form.

[0048] Controlling short frames allows nodes to receive rapid responses to their reservation requests; when the network topology changes, nodes can also quickly know the current time slot reservation status to avoid time slot conflicts.

[0049] In this embodiment, each node maintains a two-hop time slot occupancy table locally, and each node updates the time slot occupancy table in real time based on the received reservation notification frames. For example... Figure 5 As shown, the time slot occupancy table contains the node's ID, priority, and occupied time slot number. The time slot occupancy table is not broadcast; instead, it is maintained locally by the node, thus reducing channel overhead during the reservation phase.

[0050] S3. After a node completes network synchronization upon startup, it occupies a fixed reservation period based on its ID and priority, and this period remains unchanged during network operation.

[0051] S4. Each node that has completed network access sends a reservation request frame and a reservation notification frame to the data time slots within its reserved reservation period, based on current service needs and time slot occupancy (the required data time slots are calculated based on the current service volume: nodes initiate requests for data time slots in the current TDMA time frame based on the service volume of the upper layer). Specifically:

[0052] Each node that has completed network access will, according to the time slot occupancy table, initiate a reservation request for the idle time slot if the unoccupied data time slot meets the current service requirements; if there are no idle time slots or the remaining idle time slots cannot meet the current service requirements, the high-priority node will send a reservation request frame and a reservation notification frame to the data time slots already reserved by the low-priority neighboring node; if there are no neighboring nodes with lower priority than this node or the time slots occupied by the neighboring nodes cannot meet the service requirements, the reservation of data time slots in this TDMA time frame period will fail.

[0053] S5. Each node that has completed network access receives reservation request frames and reservation notification frames from other nodes during reservation periods not currently in their designated slots, and replies with a reservation reply frame. It also maintains its local time slot occupancy table based on the reservation notification frame. Step S5 specifically includes the following steps:

[0054] S51. Receiving reservation requests: Each node that has completed network access receives the reservation request frame from its neighboring nodes during a reservation period that is not its own.

[0055] S52. Data Slot Allocation: After receiving a reservation request frame from a neighboring node, the current node checks the availability of the requested slot based on the two-hop slot occupancy table. If the slot is not occupied, the node replies to the neighboring node with a reservation confirmation frame. If the slot is occupied, the node compares the sum of its priorities with the sum of the priorities of the nodes that have occupied the slot. If the current node's priorities are higher, the slot is allocated to the current node, and the node replies to its neighboring node with a reservation success frame. Otherwise, the data slot request fails, and the current node replies to its neighboring node with a reservation failure frame. The sum of a node's priorities is equal to the sum of the node's priorities and the priorities of its slot request information.

[0056] S53. Receiving reservation notifications: Each node receives the reservation notification frames sent by other nodes during reservation periods that are not occupied by it; if a lower-priority node receives a reservation notification frame in which a higher-priority node occupies the data time slot that the node has applied for, the lower-priority node will voluntarily give up occupying the data time slot.

[0057] S54. Maintain the local time slot occupancy table: Each node updates its local time slot occupancy table in real time based on the received reservation notification frames.

[0058] The priority of a node remains fixed. The priority of a time slot request increases over time; that is, if a request fails in the current time frame, the priority automatically increases by one in the next time frame.

[0059] This method sets both node priority and message priority, which can prioritize the channel needs of high-priority nodes while preventing low-priority nodes from losing channel access for extended periods, thus ensuring data timeliness.

[0060] S6. After the reservation subframe of a TDMA time frame ends, each node sends a service long frame to communicate in the data time slot reserved in this TDMA time frame.

[0061] The node sends business data in the data time slot it has applied for.

[0062] In this embodiment, the time slot occupancy table maintained locally by the node will be cleared after the start of each TDMA time frame period. That is, the data time slots of each TDMA time frame period need to be re-reserved and applied for, so as to avoid high-priority nodes occupying data time slots for a long time, which would prevent low-priority nodes from reserving data time slots.

[0063] The following is an experimental simulation.

[0064] The simulation sets up 50 mobile nodes distributed within a circular area with a diameter of 300 km. Each node generates data packets at different rates according to a Poisson distribution and sends data packets to any other node at a rate of 300 kbps. To highlight the performance of TDMA at the data link layer, the simulation assumes a zero physical layer bit error rate. In the simulation, a time frame period is set to 3 seconds, divided into 384 time slots (7.8125 ms each), with a maximum message length of 2048 bits per time slot. The total simulation duration is 1200 seconds.

[0065] This example studies the performance of a fixed TDMA protocol, a contention-based TDMA protocol, and the reservation-based TDMA protocol presented in this paper. Load rate, throughput, average latency, and effective delivery rate are defined as follows:

[0066] Load rate = Total number of data packets sent * Data packet length / (Data rate * Simulation duration);

[0067] Throughput = Total number of received data packets * Data packet length / (Data rate * Simulation duration);

[0068] Average latency = (data reception time - data transmission time) / total number of data packets received;

[0069] Effective delivery rate = Total number of valid data packets received / Total number of data packets received.

[0070] The changes in network throughput of the three TDMA protocols mentioned above with increasing network load are as follows: Figure 6 As shown in the figure, under low load, the network throughput of the three TDMA protocols increases with increasing load. When the load increases to a certain value, the throughput reaches its maximum and remains basically constant. The fixed-allocation TDMA protocol has the lowest throughput because it cannot send data in time slots not allocated to it; that is, data accumulates locally until the next time frame period. With increasing load, the probability of time slot contention in contention-based TDMA increases for each node, meaning data collisions require nodes to back off for a certain period before continuing to send. The reservation-based TDMA protocol has the highest throughput because nodes using this protocol dynamically request the number of data time slots based on their local data volume, thus avoiding data accumulation locally. Furthermore, the reservation method avoids data transmission collisions, thereby improving network throughput.

[0071] The changes in average latency of the three TDMA protocols mentioned above with increasing load are as follows: Figure 7 As shown in the figure, the average latency of all three protocols is relatively low under low load. When the load reaches a certain value, the average latency of fixed TDMA increases sharply, indicating that the nodes in the network cannot send out their local data packets in a timely manner. The average latency of contention-based TDMA is lower than that of fixed TDMA, which is due to the increase in network throughput, which reduces the waiting time for data packets. Among them, the average latency of reservation-based TDMA is the lowest.

[0072] The effective delivery rate of the three TDMA protocols changes with increasing load, for example... Figure 8As shown in the figure, under low load, the data packets delivered by the three protocols are basically effective, meaning that they can all be sent out in a timely manner. As the load increases, the effective delivery rate of the fixed TDMA and contention-based TDMA protocols decreases. This is because these two protocols do not have priority; even high-priority messages cannot be sent in time and must wait for the next transmission opportunity, leading to data loss. In contrast, this example uses reservation-based TDMA combined with the concept of priority. It sets a priority for each node and for each message. When requesting time slots, the node priority ensures that high-priority nodes request slots first, while the message priority ensures that the time slots requested by low-priority nodes are not occupied. Therefore, it can guarantee data integrity, i.e., improve the effective delivery rate of data.

[0073] In summary, the multi-hop TDMA time slot allocation method for UAV ad hoc networks provided by this invention has the following advantages:

[0074] 1. This enables rapid feedback of node time slot reservation results to meet the high real-time requirements of UAV ad hoc networks;

[0075] 2. Nodes can dynamically request the number of data time slots based on their data volume and service priority, which can avoid wasting time slot resources and improve channel utilization.

[0076] 3. By adopting a node priority plus data priority approach, we can achieve on-demand allocation while prioritizing high-priority business needs, and at the same time, we can ensure the timeliness of real-time priority data.

[0077] 4. Maintaining the time slot occupancy table locally avoids the huge overhead of the reservation application stage, avoids time slot conflicts between nodes within two hops, and enables the reuse of data time slots of neighboring nodes outside two hops, thereby improving channel utilization.

[0078] In short, this method enables TDMA channels to be allocated on demand while prioritizing the channel needs of high-priority nodes; it also enables spatial multiplexing of channels, thereby improving channel utilization.

[0079] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A multi-hop TDMA time slot allocation method suitable for unmanned aerial vehicle ad hoc networks, characterized in that, The method comprises the steps of: S1, dividing each TDMA time frame into a reservation sub-frame and a data sub-frame according to time sequence, wherein the reservation sub-frame contains K reservation periods, K being the maximum number of nodes in the network, and the data sub-frame contains N data slots, N>>K; S2, defining a control short frame for time slot reservation, a service long frame for data communication, and a time slot occupation table of two-hop neighbor nodes; the control short frame comprises a reservation application frame, a reservation notification frame and a reservation reply frame; the time slot occupation table contains the ID, priority and occupied time slot number of a node; S3, after a node is powered on and completes network synchronization, the node occupies a reservation period according to the ID and priority of the node; S4, each node that has completed network synchronization sends the reservation application frame and the reservation notification frame to the data slots according to current service demand and time slot occupation; S4 specifically comprises the steps of: each node that has completed network synchronization initiates a reservation application to an idle time slot if the unoccupied data slot meets current service demand according to the time slot occupation table; if there is no idle time slot or the remaining idle time slots cannot meet current service demand, a high-priority node sends the reservation application frame and the reservation notification frame to a data slot that has been applied for by a low-priority neighbor node; if there is no neighbor node with a lower priority than the node or the time slot occupied by the neighbor node also cannot meet service demand, the node fails to reserve the data slot in the TDMA time frame period; S5, each node that has completed network synchronization receives the reservation application frame and the reservation notification frame sent by other nodes in a reservation period that is not occupied by the node, replies to the reservation reply frame, and maintains the local time slot occupation table according to the reservation notification frame; S5 specifically comprises the steps of: S51, receiving a reservation application: each node that has completed network synchronization receives the reservation application frame of a neighbor node in a reservation period that is not occupied by the node; S52, allocation of a data slot: after the current node receives the reservation application frame of a neighbor node, it judges whether the applied time slot is available according to the two-hop time slot occupation table; if the time slot is unoccupied, the current node replies to the neighbor node with a reservation confirmation reservation reply frame; if the time slot is occupied, the current node compares the sum of the priorities of the current node and the node that has occupied the time slot; if the sum of the priorities of the current node is higher, the time slot is allocated to the current node and the current node replies to the neighbor node with a reservation application success reservation reply frame; otherwise, the current node replies to the neighbor node with a reservation application failure reservation reply frame; the sum of the priorities of a node is equal to the sum of the priority of the node and the priority of the time slot application information of the node; S53, receiving a reservation notification: each node receives the reservation notification frame sent by other nodes in a reservation period that is not occupied by the node; if a low-priority node receives the reservation notification frame in which a higher-priority node has occupied a data slot that has been applied for by the low-priority node, the low-priority node actively gives up occupying the data slot. S54, maintaining local time slot occupation table: each node updates local time slot occupation table in real time according to the received reservation notification frame; S6, after the end of a reservation subframe of one of the TDMA time frames, each node transmits the service long frame in the data time slot reserved in the TDMA time frame to communicate. 2.The multi-hop TDMA time slot allocation method for unmanned aerial vehicle ad hoc network of claim 1, wherein, In the step S1, each of the reservation periods includes three stages of reservation application, reservation reply and reservation broadcast, which correspond to the reservation application frame, the reservation reply frame and the reservation notification frame respectively. 3.The multi-hop TDMA time slot allocation method for unmanned aerial vehicle ad hoc network of claim 2, wherein: In the step S2, the reservation application frame includes a frame control field, a source address, a relay address, a destination address, time slot application information and check information; the frame control field includes frame type, frame length and intelligent routing bit, the intelligent routing bit is used to indicate whether routing forwarding is needed; the source address includes source node ID and node priority; the time slot application information is used to indicate which data time slots are applied and the priority of the information. 4.The multi-hop TDMA time slot allocation method for unmanned aerial vehicle ad hoc network of claim 3, wherein: In the step S2, the reservation reply frame includes a frame control field, a source address, time slot information, confirmation information and frame check information; the source address is the node address of the node sending the reservation application to the node; the confirmation information is used to indicate whether the time slot is available.

5. The multi-hop TDMA slot allocation method for unmanned aerial vehicle ad hoc network of claim 4, wherein: In the step S2, the frame format of the reservation notification frame is the same as that of the reservation application frame, and the difference lies in that the frame type and the intelligent routing bit in the frame control field of the reservation notification frame are sent in the form of broadcast.

6. The multi-hop TDMA slot allocation method for unmanned aerial vehicle ad hoc network of claim 5, wherein: In the step S2, the service long frame includes frame type, source address, relay address, destination address, frame entity and check sequence.

7. The multi-hop TDMA slot allocation method for unmanned aerial vehicle ad hoc network of claim 1, wherein: The priority of the time slot application information increases with time, that is, if the reservation application fails in the time frame, the priority is automatically increased by one in the next time frame. 8.The multi-hop TDMA time slot allocation method for unmanned aerial vehicle ad hoc network of claim 1, wherein: After the start of each of the TDMA time frames, each node will clear the local time slot occupation table.

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