Cross-layer resource allocation method for reliable communication of unmanned aerial vehicle formation

Abstract

The invention relates to a wireless communication network domain, in particular to an unmanned aerial vehicle formation reliable communication-oriented cross-layer resource allocation method, which comprises the following steps that: a lead aircraft node acquires link state information and transmission demand information of each wing aircraft node; the lead aircraft node determines the optimal time slot length and time slot allocation for the wing aircraft node by taking maximization of the throughput of the unmanned aerial vehicle formation system as an optimization target according to the received link state information; the lead aircraft node calculates the transmission priority of each wing aircraft node according to the received transmission demand information and issues a time slot allocation result, and each wing aircraft node sequentially performs data transmission according to the transmission priority sequence. According to the method, the single conflict characteristic of the wireless channel can be effectively prevented, collision or conflict of multiple data packets during transmission at the same time is avoided, and the reliability of data transmission between the lead aircraft and the wing aircraft in the unmanned aerial vehicle formation is ensured.

Description

Technical Field

[0001] The present invention relates to a wireless communication network domain, and in particular to a cross-layer resource allocation method for reliable communication of an unmanned aerial vehicle formation. Background Art

[0002] With the rapid development of science and technology and economy, the scale and complexity of drone formations have shown explosive growth, which has brought great challenges to the reliable operation of the formation system. When performing tasks, drone formations exchange data such as mission planning, travel status and intelligence information through information interaction. Therefore, the smooth transmission of information and the efficient flow of information flow are the core support of unmanned formations and the key to the successful operation of unmanned formations. Among them, communication is the basis for information interaction and collaboration between various nodes in the drone formation. It is required to ensure the reliability of data interaction within the drone formation network. However, due to the single collision domain characteristics of the wireless channel, the drone formation network is usually sensitive to collisions. When multiple drones work simultaneously in the formation and share limited wireless time slot resources, the communication between drones is prone to collision or conflict, which may cause data loss, retransmission, damage, or even system crash, thereby reducing the reliability of the data.

[0003] The data reliability in UAV formations is mainly focused on the multi-access scheduling strategy. At present, CSMA / TDMA hybrid scheduling has attracted much attention. It combines CSMA and TDMA, fully utilizing the advantages of the two mechanisms while offsetting their weaknesses, thereby significantly enhancing network communication performance. However, the hybrid scheduling mechanism that adaptively switches the CSMA mechanism and the TDMA mechanism according to the network load level cannot accurately distinguish the network load level; and in the time slots fixedly allocated by TDMA, when the node has no data service demand or the time slots are idle, the hybrid scheduling mechanism of other nodes with more data services using this time slot through CSMA still cannot avoid the defects of the CSMA mechanism. Therefore, most hybrid scheduling mechanisms rely on strict and fixed time slot allocation, are insensitive to changes in network load and nodes, and cannot cope with UAV formation combat scenarios.

[0004] At present, the default size of transmitted data packets in the CSMA / TDMA hybrid scheduling mechanism is the same, and the set time slot length is fixed; however, in actual situations, the sizes of transmitted data packets are inconsistent. Therefore, the reliable transmission of data packets in a UAV formation when the lengths of transmitted data packets are inconsistent is an urgent problem to be solved in this field. Summary of the invention

[0005] In order to solve the problem of reliable transmission of data packets in a UAV formation when the packet lengths of the transmitted data packets are inconsistent, the present invention proposes a cross-layer resource allocation method for reliable communication of a UAV formation, which specifically includes the following steps:

[0006] The leader node obtains the link status information and transmission demand information of each wingman node;

[0007] The leader node determines the optimal time slot length and time slot allocation for the wingman node based on the received link status information with the optimization goal of maximizing the throughput of the UAV formation system;

[0008] The leader node calculates the transmission priority of each wingman node based on the received transmission demand information and sends the time slot allocation result. Each wingman node transmits data in turn according to the transmission priority.

[0009] The present invention aims at the CSMA / TDMA hybrid scheduling mechanism in the UAV formation, considers the reliable transmission of data packets in the UAV formation when the packet lengths of the transmitted data packets are inconsistent, improves the backoff mechanism based on the physical layer MCS mechanism in the CSMA stage, and reduces the collision probability to a certain extent; and in the time slot allocation stage, by maximizing the throughput of the formation system, reasonably designs and allocates the time slot resources of the CSMA / TDMA hybrid scheduling mechanism, avoids data collision, improves the overall data throughput of the system, and at the same time improves the transmission efficiency of the formation system, and ensures the reliable transmission of data in the formation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is an application scenario diagram of an accurate, closed-loop cross-layer resource allocation method for reliable communication of UAV formations according to the present invention;

[0011] Figure 2 It is a time slot request frame structure diagram constructed by a wingman node having a transmission demand in the CSMA phase of the present invention;

[0012] Figure 3 It is a time slot allocation frame structure diagram constructed by the long machine node in the time slot allocation stage of the present invention;

[0013] Figure 4 is a flow chart of a cross-layer resource allocation method for reliable communication of a UAV formation in an embodiment of the present invention;

[0014] Figure 5 It is a schematic diagram of data transmission between the leader node and the wingman node in a superframe in the present invention. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] The present invention proposes a cross-layer resource allocation method for reliable communication of UAV formation, which specifically includes the following steps:

[0017] The leader node obtains the link status information and transmission demand information of each wingman node;

[0018] The leader node determines the optimal time slot length and time slot allocation for the wingman node based on the received link status information with the optimization goal of maximizing the throughput of the UAV formation system;

[0019] The leader node calculates the transmission priority of each wingman node based on the received transmission demand information and sends the time slot allocation result. Each wingman node transmits data in turn according to the transmission priority.

[0020] Figure 1 The specific application scenario of the present invention is given. Figure 1 In the scenario, a UAV formation is composed of a leader node and multiple wingman nodes. The leader node forwards the command issued by the control center to each wingman node. The wingman node performs attitude change according to the command, and the wingman node transmits the data obtained from reconnaissance and surveillance back to the command center through the leader node. In this scenario, it is necessary to ensure the security and reliability of transmission between the wingman node and the leader node, and at the same time, it is necessary to ensure the transmission efficiency between the leader node and the wingman node.

[0021] like Figure 5 In the present invention, the wireless channel superframe is divided into a CSMA phase, a time slot allocation phase and a TDMA phase, wherein:

[0022] In the CSMA phase, each wingman node that successfully enters the network counts the link status and transmission requirements between itself and the leader node, and constructs a time slot request frame. In the CSMA channel access phase, in order to avoid unfair competition caused by the randomness of the backoff time of the traditional binary backoff mechanism, the wingman nodes with transmission requirements use the backoff mechanism improved based on the physical layer MCS mechanism to take turns accessing the channel and initiate time slot requests to the leader node.

[0023] In the time slot allocation phase, the leader node extracts the link status and transmission requirements of each wingman node from the received time slot request frame, and determines the time slot and transmission priority allocated to each wingman node in the TDMA phase accordingly. The leader node constructs a time slot allocation frame and broadcasts the time slot allocation result to each wingman node.

[0024] In the TDMA phase, each wingman node accesses the channel in sequence according to the time slot allocation result in the time slot allocation frame to transmit data.

[0025] In this embodiment, a specific implementation process of a cross-layer resource allocation method for reliable communication of a UAV formation is proposed, such as Figure 4 , including the following steps:

[0026] 101. In the CSMA phase, each wingman node that successfully enters the network counts the link status and transmission requirements between itself and the leader node, and constructs a time slot request frame.

[0027] The wireless channel superframe is divided into the CSMA phase, the time slot allocation phase and the TDMA phase. In the CSMA phase, each wingman node that successfully enters the network counts the link status and transmission requirements between it and the leader node, and uses this information to construct a time slot request frame, which specifically includes the following steps:

[0028] 1) Wingman node link status statistics

[0029] The link status of wingman node i includes transmission rate, received signal strength, and transmission distance, where:

[0030] The transmission rate R of wingman node i i :The physical layer MCS mechanism selects the appropriate rate index value MCS based on the wireless link quality of wingman node i i , and index to get the transmission rate R i ;

[0031] Received signal strength RSSI of wingman node i i :When the wingman node i receives the beacon frame sent by the leader node, the wireless network card of the wingman node converts the received radio wave signal into an electrical signal and calculates the received signal strength RSSI through the signal processing circuit i value;

[0032] The transmission distance d of wingman node i i : The wireless path between the wingman node i and the leader node is regarded as a free space path, and the free space path loss model is used to estimate the transmission distance. The estimation process includes:

[0033] The free space path loss model is:

[0034]

[0035] Where PL is the path loss, P tx is the transmission power, d is the transmission distance, f is the signal frequency, and c is the speed of light;

[0036] The distance between wingman i and the leader is calculated by path loss:

[0037]

[0038] 2) Statistics of wingman node transmission requirements

[0039] The transmission demand of wingman node i includes the queue length Q i, data priority weight, and packet length distribution of cache queue data packets, where:

[0040] Data priority weight ω i It is expressed as:

[0041]

[0042] Among them, k represents the priority value of the data. The smaller the value, the higher the priority, and vice versa. is the proportion of data packets with priority k in the cache queue of wingman node i.

[0043] In a drone formation, the lengths of various data packets are different. Control signal packets are usually shorter, while sensor data packets are usually longer. Therefore, the length of data packets does not follow a simple exponential distribution, but can be estimated as a superposition of multiple exponentials. The distribution of data packet lengths is considered as an Irish distribution, and its probability distribution function is:

[0044]

[0045] Where M is the shape parameter, which indicates the number of exponential stages involved in the distribution; λ is the rate parameter, which is equivalent to the rate parameter in the exponential distribution, λ i represents the rate parameter of the i-th wingman node; p represents the arrival probability of the data packet, which conforms to the Bernoulli process; x represents the packet length of the data packet.

[0046] 3) Construct a time slot request frame

[0047] The wingman node reports the time slot request to the leader node by constructing a time slot request frame at the MAC layer. This frame only acts on the MAC layer. After receiving this frame, the leader node extracts the key information of each wingman node and discards the frame. When constructing this frame, the wingman node with transmission requirements fills the link status information and service transmission requirement information into the payload part of the frame. The structure of the constructed time slot request frame is as follows: Figure 2The frame structure adopted in this embodiment is the 802.11 frame structure, including frame control (FrameControl), duration ID (Duration ID), address field (including up to 4 address fields, namely Addressr 1, Addressr2, Addressr 3, Addressr 4), (Address1, Address2, Address3, Address4), sequence control (SequenceControl), frame body (Frame Body), frame check sequence (FCS). In this embodiment, the frame body (Frame Body) carries the link status information and transmission requirement information of the wingman node, including MCS index value (MCS), received signal strength (RSSI), transmission distance (d), queue length (Q), data priority weight (w), and parameters of probability distribution function (M / λ / p).

[0048] 102. The wingman nodes with transmission requirements use the backoff mechanism improved based on the physical layer MCS mechanism to access the channel in turn and send time slot request frames to the leader node.

[0049] In 802.11 wireless networks, the MCS index value can reflect the link quality between network devices. A higher MCS index value indicates that the link quality between nodes is better and can support high data transmission rates. When the link quality is poor, in order to ensure the transmission success rate, the data transmission rate needs to be reduced and a smaller MCS index value is selected.

[0050] In the CSMA channel access phase, wingman nodes with transmission needs take turns to access the channel and initiate time slot requests to the leader node. In order to avoid unfair competition caused by the randomness of the traditional binary backoff time, an improved backoff mechanism based on the physical layer MCS mechanism is used.

[0051] The MCS index value reflects the link quality between network devices. The physical layer MCS mechanism is used to set different backoff window intervals for different MCS index values, that is, different backoff intervals are set for links with different link qualities. Each wingman node randomly selects a backoff count in the corresponding backoff interval based on the MCS index value selected by its own link quality to back off, which reduces the collision probability to a certain extent. As an optional implementation scheme, the backoff interval is divided into:

[0052] Table 1 Division of backoff interval

[0053]

[0054]

[0055] 103. In the time slot allocation phase, the leader node allocates time slots and establishes transmission priorities according to the transmission demand information and link status information of each wingman node in the time slot request frame.

[0056] The leader node receives the time slot request frame and extracts the link status information and transmission requirement information of each wingman node from it. The packet length distribution of each wingman node is:

[0057]

[0058] Therefore, the average data packet length of each wingman node is is the arrival rate, T S is the duration of a time slot.

[0059] The long-distance node uses the extracted link status information and transmission demand information to determine the time slot length T in the TDMA phase. S , the number of time slots and transmission priority allocated to each wingman node. Specifically, the following steps are included:

[0060] 1) Time slot allocation: Determine the time slot length T S and the number of time slots allocated to the wingman node β i .

[0061] The length of a single time slot in the TDMA phase is T S , then the total number of time slots A in the TDMA phase is:

[0062]

[0063] Where T represents the duration of a superframe, T CSMA represents the duration of the CSMA phase in the superframe, T TSAP represents the duration of the time slot allocation phase, Indicates rounding up.

[0064] The leader node allocates the number of time slots in the TDMA phase according to the amount of data that each wingman node needs to transmit. The number of time slots that each wingman node needs to allocate for successful transmission is β i for:

[0065]

[0066] Among them, Sum i Indicates the total amount of data to be transmitted in the cache queue of wingman node i that has transmission requirements:

[0067]

[0068] Among them, δ irepresents the packet loss rate of the link between wingman node i and leader node. If the bit error rate of the link is τ, the transmission of each data bit between wingman node i and leader node follows the binomial distribution Therefore, the packet loss rate δ of the link between the wingman node i and the leader node is i It is expressed as:

[0069]

[0070] In the combat scenario of drone formations, in order to ensure the reliability of wireless communication, the reliability of wireless communication can be ensured by maximizing the utilization of the data link layer time slot, that is, seeking the optimal time slot length to ensure the maximum data transmission efficiency. At this time, the entire formation system can achieve the maximum throughput. Therefore, the optimization function is constructed with maximizing the throughput of the entire formation system as the optimization goal:

[0071]

[0072] stC1:T=T CSMA +T TSAP +T TDMA

[0073]

[0074] C3:β aid ≥1 aid∈[1,N]

[0075] C4:μ i ≤R i i∈[1,N]

[0076] Among them, C1 represents the superframe length constraint, T represents the length of a superframe; C2 represents the number of time slots in the TDMA phase; C3 represents the transmission fairness constraint, that is, each wingman node with transmission requirements is assigned at least one time slot; C4 represents the congestion avoidance constraint, that is, the average arrival rate of each wingman node cache queue is not greater than its transmission rate to ensure the normal transmission of data in the node cache queue:

[0077]

[0078] Right now: In this way, the minimum time slot value based on the link status information and transmission demand information of the wingman node i is obtained.

[0079] The Lagrange relaxation method can transform the original complex optimization problem into a sub-problem that is easier to solve. By introducing Lagrange multipliers, the constraints can be relaxed and the original problem can be decomposed into a single variable problem that is easy to handle. Usually, an iterative method is used to adjust the Lagrange multipliers to flexibly control the tightness of the constraints of the optimization problem, so as to find an approximation of the optimal solution. Therefore, in the UAV formation, the Lagrange relaxation method can be used to select the optimal time slot length T S , maximizing the throughput of the entire formation while satisfying the data queue transmission requirements of each wingman node and the constraints of time slot resources. The Lagrangian multiplier ζ is introduced to transform the constraints into penalty terms. Construct the Lagrangian function:

[0080]

[0081] in: σ∈[1,N].

[0082] By iteratively adjusting the Lagrangian multiplier ζ, the constraint condition gradually approaches the actual total time slot limit to maximize the Lagrangian function; the iterative process of the Lagrangian multiplier is:

[0083]

[0084] Among them, (k) represents the Lagrange multiplier at the kth iteration; ε represents the iteration step size.

[0085] The entire iterative process is:

[0086] S1: Initial selection of iteration step size ε and time slot allocation β for each wingman node i ×T S ;

[0087] S2: Calculate the Lagrangian function L(T S ,ζ);

[0088] S3: Adjust the time slot allocation β of each wingman node i ×T S , maximize the current Lagrangian function;

[0089] S4: Use the subgradient method to update the Lagrange multiplier and adjust the constraints;

[0090] S5: Repeat S2-S4 until the convergence condition is met.

[0091] After several iterations, the long-distance node will find an optimal time slot length T s and time slot allocation β i , while satisfying the total time slot constraint, the total throughput of the system is maximized.

[0092] 2) Transmission priority

[0093] The technical personnel in this field can set the transmission priority according to the task requirements, for example, giving priority to the transmission of business types with higher real-time requirements; the technical personnel in this field can also set it according to the transmission quality of the link, for example, giving priority to the transmission of nodes with better link quality.

[0094] As an optimal implementation method, this embodiment takes into account the different priority values ​​and link states of cached data of each wingman node with transmission requirements, and assigns different data transmission orders to them, so as to ensure that high-priority data transmission is guaranteed while ensuring that the data of wingman nodes with good link states is transmitted first, so as to achieve the goal of maximizing the total throughput of the system. Therefore, the transmission priority of each wingman node consists of two parts: service priority and link priority.

[0095] The service priority is the data priority weight ω in the wingman node cache queue i The normalization of is expressed as:

[0096]

[0097] in, is the service priority of wingman node i, ω i is the data priority weight of wingman node i, minω is the minimum value of the data priority weight of the wingman node, and maxω is the maximum value of the data priority weight of the wingman node.

[0098] The link priority is composed of the normalized MCS index value and the transmission distance weight, expressed as:

[0099]

[0100] in, is the link priority of wingman node i, MCS i is the MCS index value of wingman node i, maxMCS is the maximum value of the MCS index, and minMCS is the minimum value of the MCS index; d i is the distance between the wingman node i and the leader node, and D is the maximum communication distance between the wingman node and the leader node.

[0101] Therefore, the transmission priority of wingman node i is:

[0102]

[0103] The leader determines the order of transmission of each wingman node by comparing the transmission priorities of each wingman node.

[0104] 104. The leader node constructs a time slot allocation frame and broadcasts the time slot allocation result to each wingman node.

[0105] The leader node constructs a time slot allocation frame and broadcasts the time slot allocation result to each wingman node; the constructed time slot allocation frame is as follows: Figure 3 As shown, the information carried by the frame body includes the start time of the TDMA phase (TDMA begintime), the time slot length (Time slot length), the time slot number (Time slot number), the length of a single time slot in the TDMA phase of each wingman node T S allocation table (Ts allocation table), the end time of the TDMA phase (TDMA endtime), where the length of a single time slot in the TDMA phase of each wingman node is T S The allocation table searches for the corresponding allocation information according to the unique identifier (AID) of the wingman node. The unique identifier of the wingman node is followed by the time slot number (numberslot), the start time slot (begin slot), and the end time slot (end slot) of the wingman node.

[0106] In the TDMA phase, each wingman node accesses the channel in sequence according to the time slot allocation result in the time slot allocation frame to transmit data.

[0107] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A cross-layer resource allocation method for reliable communication of UAV formation, characterized in that: It includes the following parts: The leader node obtains the link status information and transmission demand information of each wingman node; The leader node determines the optimal time slot length and time slot allocation for the wingman node based on the received link status information with the optimization goal of maximizing the throughput of the UAV formation system; The leader node calculates the transmission priority of each wingman node based on the received transmission demand information and sends the time slot allocation result. Each wingman node transmits data in turn according to the transmission priority.

2. A cross-layer resource allocation method for reliable communication of UAV formation according to claim 1, characterized in that: The link status information of the wingman node with transmission demand includes transmission rate, received signal strength and transmission distance; the transmission demand information includes queue length, data priority weight and packet length distribution of cache queue data packets.

3. A cross-layer resource allocation method for reliable communication of UAV formation according to claim 1, characterized in that: When the wingman node competes for the channel in the access phase, the backoff mechanism based on the physical layer MCS mechanism takes turns to access the channel, and sets different backoff window intervals for different MCS index values. The smaller the MCS index value, the larger the minimum value of the backoff interval and the longer the length of the backoff interval.

4. A cross-layer resource allocation method for reliable communication of UAV formation according to claim 1, characterized in that: In the current superframe, an optimization function is constructed with the goal of maximizing the throughput of the UAV formation system to select the best time slot length and time slot allocation for the current UAV formation system. The optimization function is expressed as: Optimization function: Constraint C1: T = T CSMA +T TSAP +T TDMA C2: C3:β aid ≥1aid∈[1,N] C4:m i ≤R i i∈[1,N] Among them, H represents the system throughput of the UAV formation, N is the number of wingman nodes in the UAV formation; β i The number of time slots required for wingman node i to successfully transmit; T S is the optimal time slot length in the TDMA phase; R i is the transmission rate of wingman node i; T represents the duration of a superframe, T CSMA is the duration of the CSMA phase in the superframe, T TSAP To represent the duration of the time slot allocation phase, T TDMA is the duration of the TDMA phase in the superframe; A is the total number of time slots in the TDMA phase; β aid The number of time slots allocated to wingman nodes with transmission requirements; μ i is the average arrival rate of data packets at wingman node i.

5. A cross-layer resource allocation method for reliable communication of UAV formation according to claim 4, characterized in that: The number of allocated time slots required for wingman node i to successfully transmit β i It is expressed as: Among them, Sum i represents the total amount of data to be transmitted in the cache queue of wingman node i, δ i It represents the packet loss rate of the link between wingman node i and leader node.

6. A cross-layer resource allocation method for reliable communication of UAV formation according to claim 4, characterized in that: The Lagrangian multiplier ζ is introduced to transform the constraints of the optimization function into penalty terms to construct the Lagrangian function, and the optimal time slot length T is selected by the Lagrangian relaxation method. s and time slot allocation β i , specifically including the following steps: S1, initialize the iteration step of the Lagrange multiplier and the time slot allocation of each wingman node; S2, calculating the Lagrangian function under the current time slot allocation of each wingman node; S3, adjusting the time slot allocation of each wingman node with the goal of maximizing the current Lagrangian function; S4, use the subgradient method to update the Lagrange multiplier and adjust the constraints; S5. Determine whether the current Lagrangian function meets the convergence condition. If so, output the current optimal time slot length T. s , otherwise return to step 102.

7. A cross-layer resource allocation method for reliable communication of UAV formation according to claim 6, characterized in that: The Lagrangian function is expressed as: Among them, L(T S ,ζ) represents the Lagrangian function; T Sσ is the length of a single time slot in the TDMA phase set according to the transmission requirements of the σth wingman node, expressed as is the average data packet length of the σth wingman node, R σ is the transmission rate of the σth wingman node, p represents the arrival probability of the data packet; ζ is the Lagrange multiplier.

8. A cross-layer resource allocation method for reliable communication of UAV formation according to claim 6, characterized in that: The process of updating the Lagrange multiplier using the subgradient method is expressed as: Among them, (k) represents the Lagrange multiplier of the kth iteration, and ε represents the iteration step size of the Lagrange multiplier.

9. A cross-layer resource allocation method for reliable communication of UAV formation according to claim 1, characterized in that: The transmission priority calculation process of the wingman node includes: Among them, G i is the transmission priority of wingman node i, G i The smaller the value, the higher the priority; is the service priority of wingman node i, ω i is the data priority weight of wingman node i, minω is the minimum value of the data priority weight of the wingman node, and maxω is the maximum value of the data priority weight of the wingman node; is the link priority of wingman node i, MCS i is the MCS index value of wingman node i, maxMCS is the maximum value of the MCS index, and minMCS is the minimum value of the MCS index; d i is the distance between the wingman node i and the leader node, and D is the maximum communication distance between the wingman node and the leader node.

10. A cross-layer resource allocation method for reliable communication of UAV formation according to claim 9, characterized in that: The data priority weight of wingman node i is expressed as: Among them, k represents the priority value of the data, and the smaller the value, the higher the priority; It represents the proportion of data packets with priority k in the cache queue of wingman node i.

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