A conflict-free dynamic time slot allocation method in directional aerial ad hoc networks

Abstract

A conflict-free dynamic time slot allocation method in directional aerial ad hoc network, time slot allocation of a link is divided into demand exchange stage and data transmission stage. In the demand exchange stage, each node runs the input consistent pairing exchange algorithm, after the stage is completed, each node can obtain the transmission demand of the neighbor node. In the data transmission stage, according to the transmission demand of the whole network, a conflict-free link set is constructed based on the time slot allocation algorithm of the maximum simultaneous transmission link, and as many parallel transmission links as possible in each scheduling are realized. Conflict-free is guaranteed, thereby meeting the special demand that key information cannot tolerate packet loss. According to the scheduling rule of the application, each node in the protocol globalizes 'thinking', and is distributedly run, unified control of the central node is avoided, the demand of conflict-free link scheduling is realized, and reliable transmission guarantee of the data packet is realized.

Description

Technical Field

[0001] This invention relates to a conflict-free dynamic time slot allocation method in a directional airborne ad hoc network. Background Technology

[0002] Aeronautical Ad Hoc Network (AANET), also known as Airborne Network (AN) or Fyling Ad Hoc Network (FANET), was originally developed by the US military to meet the needs of network-centric warfare. AANET is one manifestation of Mobile Ad Hoc Networks (MANET) in airspace networking and can be considered a special form of MANET. Its MANET architecture features no need for infrastructure, flexible dynamic networking, self-healing capabilities, and strong resilience, significantly enhancing the collaborative combat capabilities of various combat aircraft.

[0003] To overcome the challenges of long communication distances between UAVs and significant signal attenuation when using high-end frequency bands, directional antennas are generally used in the physical layer of aerospace ad hoc networks. In particular, with the development of integrated circuits and signal processing technologies, phased array antenna technology has rapidly advanced, making it the preferred choice for communication in aerospace ad hoc networks. Therefore, directional transmission is the primary communication method in aerospace ad hoc networks.

[0004] Currently, for directional transmission aviation ad hoc network media access protocols (MAC), based on different access mechanisms, they can be classified as follows: random access mechanism, scheduled access mechanism, and a hybrid mode of the two.

[0005] In media access protocols based on scheduling access mechanisms in aerospace ad hoc networks, Time Division Multiple Access (TDMA) is the most widely used. Its basic idea is to divide time into frames, and each frame is further divided into multiple time slots. According to the protocol's time slot allocation algorithm, a time slot is allocated to one or more links, allowing them to send packets from their transmission queues within the corresponding time slot. When a suitable algorithm is adopted, packet collisions can be completely avoided. Compared to MAC protocols based on contention mechanisms, TDMA reduces network flexibility to some extent, but it ensures reliable data transmission.

[0006] Depending on the frame structure design and time slot allocation algorithm, TDMA can be divided into fixed allocation TDMA and dynamic allocation TDMA. The former allocates a fixed number or a segment of time slots within each frame to the transmission link, while the latter dynamically adjusts the length of control frames and data transmission frames, as well as the time slot allocation strategy, according to the transmission needs of the nodes.

[0007] Current research on MAC protocols based on scheduling mechanisms in aeronautical ad hoc networks mainly focuses on the assumption of omnidirectional transmission. No publicly reported scheduling-based time slot allocation methods based on service requirements under directional transmission conditions have been found. To ensure network robustness, improve network throughput, and reduce the delivery latency of critical data, it is necessary to schedule radio resources simultaneously in both spatial and temporal dimensions, taking into account the characteristics of directional transmission networks. Summary of the Invention

[0008] The purpose of this invention is to provide a conflict-free dynamic time slot allocation method in directional airborne ad hoc networks, ensuring conflict-free operation and thus meeting the special requirement that critical information cannot tolerate packet loss.

[0009] A collision-free dynamic time slot allocation method for directional aerial ad hoc networks is proposed. The time slot allocation of a single scheduling link is divided into a demand exchange phase and a data transmission phase. In the demand exchange phase, each node runs a pairing exchange algorithm with consistent input. After this phase is completed, each node obtains the transmission requirements of its neighboring nodes. In the data transmission phase, based on the transmission requirements of the entire network, a collision-free link set is constructed based on a time slot allocation algorithm that maximizes simultaneous transmission links, thereby realizing parallel transmission links in each scheduling.

[0010] In this invention, each node runs the allocation method independently and in a distributed manner, recursively traversing the set of neighboring nodes, combining its own sending requirements with the sending requirements of other nodes that it has already learned, and exchanging message requirements with nodes that have not exchanged requirements with itself.

[0011] The control of the switching action in this invention is determined by the principal expression of the transmission demand matrix (TRM) combined with the concurrency decision matrix (CDM).

[0012] In this invention, each node maintains N-1 Packet Arrival Time Vectors (PATVs) to record the queue of packets to be transmitted from neighboring nodes. Based on the PATVs, a conflict-free subset of available links is gradually constructed in the Transmission Link Set (TLG).

[0013] The time slot allocation for a single scheduling link is divided into a demand exchange phase and a data transmission phase. In the demand exchange phase, each node runs a consistent pairing exchange algorithm, ensuring that each node receives the transmission requests from its neighbors. In the data transmission phase, based on the overall network transmission demand, a conflict-free link set is constructed using a time slot allocation algorithm that maximizes simultaneous transmission links, achieving as many parallel transmission links as possible in each scheduling process. Attached Figure Description

[0014] The invention will be further described below with reference to the accompanying drawings.

[0015] Figure 1 This is a schematic diagram of the k-th scheduling frame structure. Detailed Implementation

[0016] A collision-free dynamic time slot allocation method for directional aerial ad hoc networks is proposed. The time slot allocation of a single scheduling link is divided into a demand exchange phase and a data transmission phase. In the demand exchange phase, each node runs a pairing exchange algorithm with consistent input. After this phase is completed, each node obtains the transmission requirements of its neighboring nodes. In the data transmission phase, based on the transmission requirements of the entire network, a collision-free link set is constructed based on a time slot allocation algorithm that maximizes simultaneous transmission links, thereby realizing parallel transmission links in each scheduling.

[0017] The aerial ad hoc network used in this invention has the following network abstract model description:

[0018] (1) Each flight node has a unique and unchanging ID number across the entire network;

[0019] (2) All flight nodes can obtain their own precise location information and achieve strict time synchronization;

[0020] (3) Time is divided into time slots of equal length;

[0021] (4) Each flight node is equipped with a single-beam phased array antenna with a beamwidth θ. The beam can be directed to any direction in three-dimensional space, and the antenna can switch between omnidirectional and directional transmission modes.

[0022] (5) The obstruction of the signal by the wings of the aircraft during the signal transmission process is not considered;

[0023] (6) All flight nodes are equipped with half-duplex wireless transceivers with identical parameters.

[0024] 1. Scheduling time slot allocation

[0025] The conflict-free link scheduling algorithm based on demand notification divides the protocol into a demand notification phase and a data transmission phase.

[0026] The time of a single scheduling operation is divided into a demand notification phase and a data transmission phase. For example... Figure 1 The diagram shows the frame structure of the k-th scheduling operation, where the Requirement Inform phase of the k-th scheduling operation is divided into RI. k Each time slot is divided into two sub-time slots. In the first sub-time slot, the sending and receiving nodes switch their sending and receiving states in the second sub-time slot while maintaining the sending and receiving relationship between the two nodes, thus ensuring that a pair of nodes can exchange their transmission needs.

[0027] Accordingly, the data transmission phase of the k-th scheduling is divided into DT. kEach data transmission time slot is divided into two sub-time slots. The sending node transmits data packets to the receiving node in the first sub-time slot, and the receiving node uses the second sub-time slot to reply with an ACK packet to the sending node. Under special application requirements, data packets arriving at one time are of equal length, and the duration of one sub-time slot can meet the processing, transmission, and propagation delays of data packets or ACK packets.

[0028] 2. Information matrix maintained by nodes

[0029] The following section provides a detailed description of the type and corresponding function of the information matrix maintained by each node.

[0030] (1) Packet arrival and scheduling rules

[0031] Assume that each node's packet arrival occurs only at the beginning of a time slot, and the packet arrival interval follows an exponential distribution with parameter λ. This means that at the beginning of a time slot, each node has a 1 / λ probability of receiving a packet, and its neighbors have an equal probability of receiving this packet. Therefore, in each time slot, each transmission link has a 1 / [λ(N-1)] probability of having a packet transmission request. During a scheduling process, newly arrived packets are stored in the node's pending transmission queue. After this scheduling ends, they are transmitted in the data transmission phase following the request exchange phase in the next scheduling. That is, the (k+1)th scheduling only handles packets already stored in the node's queue during the kth scheduling process. Specifically, the first scheduled packet is the packet awaiting transmission on each transmission link at the initial moment of network establishment, when neighbor discovery is completed across the entire network.

[0032] (2) Packet arrival time vector

[0033] Suppose the total number of network nodes is N, and each node maintains N-1 packet arrival time vectors (PATVs) to record the queue of packets to be transmitted to its neighbors. i (j) k+1 , k≥0. This means the packet arrival time vector from node i to node j in the (k+1)th scheduling iteration. Based on the above scheduling criterion, the dimension of the packet arrival vector in the (k+1)th scheduling iteration is equal to the time slot length consumed in the kth scheduling iteration, i.e., PATV. i (j) k+1 for (RI k +DT k A column vector of dimension RI, where the variable RI k DT represents the number of time slots in the demand notification phase of the k-th scheduling. k This represents the number of time slots in the data transmission phase of the k-th scheduling.

[0034] (2) Transmission demand matrix

[0035] Define an N×N Transmission Requirement Matrix (TRM). k+1 (m,n)=(tr ij ) k+1 , k≥0, indicates that before the nth time slot (inclusive) of the (k+1)th scheduling request notification phase, the node numbered m has already learned about the cumulative transmission requests of other nodes in the network during the kth scheduling period.

[0036] Based on the definition of the packet arrival time vector above, at the beginning of the demand notification phase of the (k+1)th scheduling, since each node only knows its own transmission demand, the transmission demand matrix of any numbered node can be represented as:

[0037]

[0038] Let the demand notification phase of the (k+1)th scheduling session cost RI. k+1 If a time slot is available, then after the requirement notification phase is completed, the TRM of any node... k+1 The following formula should be satisfied:

[0039]

[0040] Assuming that in the third scheduling, the demand notification phase takes 3 time slots and the data transmission takes 9 time slots, then PATV3(2)4=(001000100000) T This indicates that in the third scheduling, node 3 received packet requests from the upper layer for node 2 as the destination node in the third and seventh time slots. The packet requests from this scheduling will be transmitted in the fourth scheduling.

[0041] Assuming that nodes 1 and 2 exchange requests in the first time slot of the (k+1)th scheduling request notification phase, then for nodes 1 and 2, we have:

[0042]

[0043] 3. Protocol Design for the Demand Exchange Phase

[0044] During the demand notification phase, each node exchanges its own transmission needs and the transmission needs of other nodes that it has already learned about with nodes that have not exchanged needs with it; this is essentially a gossip-like exchange of information. After the demand notification phase is completed, each node is aware of the transmission needs of other nodes in the network.

[0045] Define the Concurrency Definition Matrix (CDM).

[0046] CDM N(N-1)×N(N-1)=(cdm i,j If link i and link j can transmit concurrently, then cdm i,j The maximum principal child of a CDM is 1, and the maximum concurrent links are 0.

[0047] In order to make full use of the spatial multiplexing capability of directional transmission, multiple pairs of nodes should be allowed to transmit requests while avoiding conflicts between concurrent transmission links as much as possible within a time slot, so as to complete the request exchange phase more quickly.

[0048] Algorithm 1: Demand Exchange Algorithm

[0049]

[0050]

[0051]

[0052] 4. Data Transmission Phase Protocol Design

[0053] The Total Link Group (TLG) is defined as the set of all N(N-1) transmission links in a network:

[0054] TLG = {link(1,2,PATV1(2)} k ),link(1,3,PATV1(3) k ),…,link(1,N,PATV1(N) k ),…,

[0055] link(N,N-1,PATV N (N-1) k )}={L1,L2,...,L N(N-1)}

[0056] Define a Transmission Link Group (TXLG), where TXLG = {TXLG1, TXLG2, ..., TXLG}. m}, each subset of TXLG i It is a set of links that can transmit simultaneously.

[0057] In each time slot, to maximize the number of links transmitting simultaneously, the output of each time slot is the subset of TXLG that has the most links transmitting simultaneously. max A time slot allocation algorithm based on maximizing the number of concurrent transmission links (MCTL) is proposed:

[0058] In the c-th time slot of the data transmission phase, the first link with a non-zero PATV in the TLG is added to the subset TXLG1, and then the second link with a non-zero PATV (let it be L) is determined. i Whether it can transmit simultaneously with the link within TXLG1.

[0059] If possible, then add a new subset TXLG2 = TXLG1 + {L} i} and TXLG3={L i If simultaneous transmission is not possible, then TXLG will only add a new subset TXLG2 = {L}. i}

[0060] Continue to determine the third link L with a non-zero PATV. m With TXLG = {TXLG1, TXLG2, ..., TXLG} m Can the various collections in} be transmitted simultaneously?

[0061] If the link can connect to a subset TXLG k Simultaneous transmission will result in the addition of a subset TXLG. m+1 =TXLG k +{L m}, and add the subset TXLG m+2 ={L m}; If L m If all subsets of the subset TXLG cannot be transmitted simultaneously, then only the new subset itself and TXLG are added. m+1 ={L m}

[0062] Repeat the above process until L. N(N-1) The judgment has been completed.

[0063] The subset containing the most elements in TXLG max Then this set represents the link scheduling result for this time slot. Under the principle of prioritizing first-arriving packets, TXLG... max The non-zero element with the smallest row number in the PATV of all links (indicating that the packet to be transmitted arrived earliest) is added to the c-th column of the LSM, and the corresponding elements of these links in the PATV are set to 0, representing the TXLG in the c-th time slot. max All links in the network send the earliest arriving packet in the transmission queue.

[0064] If all PATVs corresponding to all transmission links in the TLG are zero vectors, then the current scheduling is terminated, the number of time slots consumed (DT) is recorded, and the demand exchange phase of the next scheduling begins. Otherwise, the current time slot value is incremented by 1, and the above process is repeated.

[0065] During the data transmission phase, each node adopts the same criteria for allocating time slots for this phase.

[0066] Algorithm 2: Maximize Simultaneous Transmission Link Time Slot Allocation (MCTL) Algorithm

[0067]

[0068] According to the above scheduling rules, each node in the protocol "thinks" globally and operates in a distributed manner, which avoids the unified control of the central node and meets the requirement of conflict-free link scheduling, thus ensuring reliable transmission of data packets.

Claims

1. A method for conflict-free dynamic time slot allocation in a directional aerial ad hoc network, characterized in that: The time slot allocation of a scheduling link is divided into a demand exchange stage and a data transmission stage; In the demand exchange stage, each node runs an input consistent pairing exchange algorithm, and after the stage is completed, each node obtains the transmission demand of the neighbor nodes; in the data transmission stage, according to the transmission demand of the whole network, a time slot allocation algorithm based on the maximum simultaneous transmission link is used to construct a conflict-free link set, and parallel transmission links in each scheduling are realized; The rule of the packet arrival time vector in the information matrix maintained by each node is: Let the scheduling criterion be: Let the total number of network nodes be N, and each node maintains N-1 packet arrival time vectors PATV to record the queue of the packets to be transmitted from the network node to the neighbor nodes, denoted as PATV i (j) k+1 , k≥0, represents the packet arrival time vector of node i to node j in the k+1th scheduling; based on the above scheduling criterion, the dimension of the packet arrival vector in the k+1th scheduling is equal to the time slot length consumed in the kth scheduling, i.e. PATV i (j) k+1 is an (RI k +DT k )-dimensional column vector, where the variable RI k represents the number of time slots in the demand exchange phase of the kth scheduling, and the variable DT k represents the number of time slots in the data transmission phase of the kth scheduling; In the data transmission stage, a set TLG composed of all N(N-1) transmission links in the network is defined as: TLG={link(1,2,PATV1(2) k ),link(1,3,PATV1(3) k ),…,link(1,N,PATV1(N) k ),…,link(N,N-1,PATV N (N-1) k )}={L1,L2,...,L N(N-1) , Define a transmission link set TXLG, TXLG = {TXLG1, TXLG2, ..., TXLG} m }, each subset of TXLG i It is the set of links that can transmit simultaneously; m is the total number of TXLG transmission links; In each time slot, in order to maximize the number of simultaneous transmission links, i.e. the output of each time slot is a subset TXLG of TXLG with the most simultaneous transmission links max , a MCTL time slot allocation algorithm based on the maximization of the number of simultaneous transmission links is proposed: In the cth time slot of the data transmission stage, the first link with non-zero PATV in the TLG is added to the subset TXLG1, and it is determined whether the second link with non-zero PATV can be simultaneously transmitted with the links in TXLG1, and the non-zero PATV link is denoted as L i ; If so, add the subset TXLG2 = TXLG1 + {L i} and TXLG3 = {L i}; if not, TXLG only adds the subset TXLG2 = {L i}; Continue to determine the third link L with non-zero PATV m whether each set in {TXLG1, TXLG2, …, TXLG m} can transmit simultaneously; If the link can be simultaneously transmitted with some subset TXLG k , then add the subset TXLG m+1 = TXLG k + {L m} to the subset TXLG m+2 = {L m}; if L m cannot be simultaneously transmitted with all the subsets in the subset TXLG, then only add itself to the subset TXLG m+1 = {L m}; The above process is repeated until L N(N-1) is determined.

2. The conflict-free dynamic time slot allocation method in the directional aerial ad hoc network according to claim 1, characterized in that: The rule of the packet arrival and scheduling in the information matrix maintained by each node is: Suppose that the arrival of a packet at each node only occurs at the beginning of a time slot, and the interval between the arrivals of packets obeys an exponential distribution with a parameter λ, that is, at the beginning of a time slot, each node has a probability of 1 / λ of arriving at a packet, and the probability of the neighbor of the node receiving the packet is equal, that is, in each time slot, each transmission link has a probability of 1 / [λ(N-1)] of existing a transmission demand of a packet, where N is the total number of network nodes; in a scheduling process, a newly arrived packet is stored in the transmission queue of the node, and after the end of the current scheduling, the data transmission stage after the demand exchange stage is completed in the next scheduling, that is, the k+1th scheduling is only responsible for the packets stored in the queue of the node in the kth scheduling process; in particular, the packets of the first scheduling are the packets to be transmitted of each transmission link when the neighbor discovery of the whole network is completed, that is, at the initial moment of network building.

3. The conflict-free dynamic time slot allocation method in the directional aerial ad hoc network according to claim 2, characterized in that: The rule of the transmission demand matrix maintained by each node is: Let TRMbe the N x N transmission requirement matrix defined as TRM k+1 (m,n) = (tr ij ) k+1 , k > 0, where tr ij denotes the element in the i-th row and j-th column of the matrix. The transmission demand matrix represents that, before the nth time slot of the k+1th scheduling demand exchange stage, including the nth time slot, the node numbered m has learned the sending demand accumulated by other nodes in the network during the kth scheduling; According to the definition of the packet arrival time vector, at the beginning of the demand exchange stage of the k+1th scheduling, since each node only knows its own transmission demand, the transmission demand matrix of any numbered node can be expressed as: where TRM k+1 (random,0) denotes the transmission requirement matrix of an arbitrarily numbered node, where random denotes an arbitrarily labeled matrix; PATV random (N) k denotes the arrival time of the Nth packet to be transmitted of an arbitrarily numbered node; TRM k+1 (random,RI k+1 ) denotes the value of the transmission requirement matrix of an arbitrarily numbered node at the Rth k+1 time slot; PATV N (2) k denotes the arrival time of the 2nd packet to be transmitted of the Nth node; PATV N (N) k denotes the arrival time of the Nth packet to be transmitted of the Nth node; Let the demand exchange phase of the (k+1)th scheduling cost RI. k+1 If there is a time slot, then after the demand exchange phase is completed, the TRM of any node... k+1 It should satisfy equation (2).

4. The conflict-free dynamic time slot allocation method in the directional aerial ad hoc network according to claim 3, characterized in that: In the demand exchange stage, each node exchanges its own sending demand and the sending demand of other nodes that has been learned with the nodes that have not exchanged demands with itself, that is, the information is exchanged in a gossip manner; After the completion of the demand exchange stage, each node learns the transmission demand of other nodes in the network; define a concurrency determination matrix, CDM N(N-1)×N(N-1) = (cdm i,j ), cdm i,j represents the ith row and jth column element of the concurrency determination matrix CDM N(N-1)×N(N-1) = (cdm i,j ), i.e. whether the ith link and jth link can be concurrently transmitted; if the ith link and jth link can be concurrently transmitted, cdm i,j is 1, otherwise, is 0; thus, the largest principal minor of CDM is the set of the largest number of concurrently transmitted links.

5. The conflict-free dynamic time slot allocation method in the directional aerial ad hoc network according to claim 4, characterized in that: the subset of TXLG containing the most elements max If the set is empty, then the set is the link scheduling result of this time slot; under the rule of serving the first arrived packet first, the non-zero element with the minimum row number in PATV of all links in TXLG max is added to the cth column of the link scheduling matrix LSM, and the corresponding elements of these links in PATV are set to 0, representing that the earliest arrived packets in the transmission queue are transmitted by all links in TXLG max in the cth time slot; If the PATV corresponding to all transmission links in TLG is a zero vector, the current scheduling is terminated, the number of time slots DT consumed is recorded, and the demand exchange stage of the next scheduling is entered; otherwise, the current time slot value is increased by 1, and the above process is repeated. In the data transmission phase, each node takes the same criteria for time slot allocation for this phase.

Images