An elastic dynamic access method for aerial search and rescue ad hoc network

Abstract

The application provides an elastic dynamic access method for an aerial search and rescue ad hoc network, and belongs to the technical field of aerial search and rescue communication. The method comprises the following steps: constructing a system model of the aerial search and rescue ad hoc network, wherein the system model comprises a master node and a plurality of discrete and independent to-be-networked nodes within the working range of the master node; the master node receives all the to-be-networked nodes into the network through a multi-round iteration mode; after each round of networking, the master node removes all the to-be-networked nodes that have entered the network, and uses all the to-be-networked nodes that have not entered the network in the next round of networking until all the to-be-networked nodes complete networking. The application can improve the access efficiency and stability of the aerial search and rescue ad hoc network in a multi-node random networking scene.

Description

Technical Field

[0001] This application relates to the field of aviation search and rescue communication technology, and in particular to a flexible dynamic access method for aviation search and rescue ad hoc networks. Background Technology

[0002] With the development of informatization and networking, modern air search and rescue missions are increasingly characterized by complex communication environments and high demands for multi-node coordination. Air search and rescue ad hoc networks typically consist of airborne nodes, handheld nodes, and a master node, requiring rapid establishment of a collaborative network in temporary mission areas. Due to the uncertainty of the number, deployment location, and power-on time of each node in the mission scenario, the master node usually cannot pre-determine the scale of unknown nodes in the early stages of network establishment and can only rely on broadcast access control information to guide unknown nodes to request access. In this scenario, without an effective random access control mechanism, multiple unknown nodes may send access request information to the same access request slot, causing network collisions or repeated waiting, thus prolonging network establishment time.

[0003] To address this type of random access problem, existing methods mostly employ a fixed window approach or a dynamic window approach based on collision feedback. However, both of these approaches have certain technical drawbacks, as follows:

[0004] First, while the fixed window approach is simple to implement, the window length remains constant and cannot be dynamically adjusted based on the number of nodes waiting to join the network. If the number of nodes waiting to join the network is large, the collision time slots will increase significantly; if the number of nodes waiting to join the network is small, the proportion of idle time slots will increase, resulting in wasted access request time slots.

[0005] Secondly, while the dynamic windowing method based on collision feedback can adjust the window length for the next round based on the results of the previous round of network entry, the feedback information is relatively simple, and window control can only rely on collision counts. In practical applications, there may be situations where the random selection of nodes fluctuates greatly or the number of nodes changes rapidly. Therefore, this type of method is prone to problems such as lag in window expansion and slow contraction, which leads to increased network construction delay and makes it difficult to achieve efficient and stable random access in aviation search and rescue ad hoc networks where the number of nodes to be added is unknown and dynamically changing.

[0006] Therefore, it is necessary to propose a solution to improve one or more problems existing in the above-mentioned related technical solutions.

[0007] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0008] This application provides a flexible dynamic access method for ad hoc aviation search and rescue networks, comprising the following steps:

[0009] A system model for constructing an autonomous network for air search and rescue is established. The system model includes a master node and multiple discrete and independent nodes within the working range of the master node that are waiting to join the network. The master node receives all nodes waiting to join the network through multiple rounds of iteration. After each round of joining the network, the master node removes all nodes that have joined the network and uses all the remaining nodes that have not yet joined the network for the next round of joining the network, until all nodes waiting to join the network have completed joining the network.

[0010] The first round of network access process includes:

[0011] Before joining the network, the system model divides all nodes waiting to join the network into a set of active nodes and a set of inactive nodes based on their waiting status during this round of network entry.

[0012] At the start of network access, the master node broadcasts a synchronization frame to all active nodes in this round of network access, and reserves multiple consecutive control time slots of equal length after the broadcast is completed;

[0013] During this round of network access, all active nodes receive and parse the synchronization frames, extract access control information from them, and each active node calculates the corresponding access enable state based on the access control information. They then use each access enable state to determine whether the corresponding active node meets the initial access conditions.

[0014] For each active node that meets the initial access conditions, it randomly selects a control time slot as its own access request window and sends an access request frame to the time slot center of the selected control time slot.

[0015] The master node calculates the average energy of all access request frames received in each control time slot, performs energy detection for each control time slot, and determines whether the corresponding access request frame falls within the effective reception range of the corresponding control time slot based on the energy detection result.

[0016] The master node demodulates and verifies each access request frame that falls within the effective reception interval of the control time slot, determines the status of the corresponding control time slot, and performs statistics.

[0017] Based on the statistical results, the master node calculates the total length of the control time slots for the next round of network access;

[0018] The above network entry process is repeated in multiple iterations until all nodes awaiting network entry have completed the process.

[0019] Furthermore, the first The set of active nodes before round-robin entry is represented as .

[0020] Furthermore, the synchronization frame includes access control information, which includes: the timestamp of the master node in the current round of network entry, the round of network entry, the total length of the control time slot, and the access permission flag;

[0021] The access control information expression is:

[0022] (1)

[0023] in, Indicates the first Access control information during network entry. Indicates the first The timestamp of the master node when it joins the network. Indicates the master node. Indicates the round of entry into the network. Indicates the first Total length of control time slots during wheel entry into the grid. Indicates the first Access permission flag during network entry. This indicates transpose.

[0024] Furthermore, during this round of network access, all active nodes receive and parse synchronization frames to extract access control information. Each active node calculates its corresponding access enable state based on the access control information, and uses each access enable state to determine whether the corresponding active node meets the initial access conditions. The steps include:

[0025] Each active node determines the validity of the synchronization frame; when the synchronization frame is valid and the access permission flag is valid, each active node calculates the corresponding access enable state.

[0026] The expression for the access enable state is:

[0027] (2)

[0028] in, Indicates the first When entering the net Access enable status of each active node Indicates the first When entering the net The results of the active nodes' determination of the synchronization frame. Indicates the first Access permission flag during network entry;

[0029] when When, it indicates the first When entering the net Each active node determines that the synchronization frame is valid;

[0030] when When, it indicates the first When entering the net One active node determines that the synchronization frame is invalid;

[0031] when When, it indicates the first The access permission flag is valid during round-trip network entry.

[0032] when When, it indicates the first The access permission flag during network entry is invalid.

[0033] Each access enable status is used to determine whether the corresponding active node meets the initial access conditions;

[0034] when When, it indicates the first When entering the net One active node meets the initial access conditions for this round of network entry and sends an access request frame.

[0035] when When, it indicates the first When entering the net One active node does not meet the initial access conditions for this round of network entry and therefore does not send an access request frame.

[0036] Furthermore, for each active node that meets the initial access conditions, the steps of randomly selecting a control time slot as its own access request window and sending an access request frame to the time slot center of the selected control time slot include:

[0037] For satisfying All active nodes select control time slots using a random slot selection method with equal probability;

[0038] The expression for the probability of an active node selecting a control slot is:

[0039] (3)

[0040] in, Indicates the first When entering the net The active node selects the first The probability of a control time slot, Indicates the first Total length of control time slots during wheel entry into the grid. Indicates the first When entering the net The number of the control slot selected by each active node.

[0041] Furthermore, the master node calculates the average energy of all access request frames received in each control time slot, performs energy detection for each control time slot, and determines whether the corresponding access request frame falls within the effective reception interval of the corresponding control time slot based on the energy detection result. The steps include:

[0042] The master node calculates the energy of each access request frame in each control time slot, and calculates the average energy of all access request frames in the corresponding control time slot.

[0043] The expression for calculating the average energy of all access request frames within a control time slot is:

[0044] (4)

[0045] in, Indicates the first When entering the net The average energy of all access request frames within a control time slot. Indicates the first When entering the net The number of all access request frames within a control time slot Indicates the number of the access request frame. Indicates the first When entering the net Within the first control time slot, the first The energy of access request frames sent by each active node. Represents absolute value;

[0046] Set an energy detection threshold, and the master node uses the energy detection threshold to perform energy detection for each control time slot;

[0047] The expression for the master node to perform energy detection on the control time slot is:

[0048] (5)

[0049] in, Indicates the first When entering the net Energy detection results for each control time slot Indicates the first Energy detection threshold when a wheel enters the network;

[0050] when When, it indicates the first When entering the net No access request frames were detected in the control time slot;

[0051] when When, it indicates the first When entering the net An access request frame was detected in one control time slot;

[0052] when At that time, the master node performs a valid arrival determination on the access request frame detected in each control time slot, and determines whether each access request frame falls within the valid reception range of the corresponding control time slot based on the results of all valid arrival determinations.

[0053] The expression for determining valid arrival is:

[0054] (6)

[0055] in, Indicates the first When entering the network, the master node has a relationship with the first... The first control time slot within the [number] time slot The result of valid arrival determination of access request frames sent by each active node. Indicates the first When entering the net The first control time slot received the first The time when an active node sends an access request frame. , Indicates the first When entering the net The active node sends to the first The ideal time to send an access request frame in a control time slot , Indicates the first The timestamp of the master node when it joins the network. Indicates the first The length of each control time slot when the wheel enters the network. Indicates the first When entering the net The number of the control slot selected by each active node. Indicates the first The pre-protection period for each control time slot when the wheel enters the network. Indicates the first When entering the net The active node sends to the first The duration for sending access request frames in each control time slot. , Indicates the first The post-protection time period for each control time slot during wheel entry into the network. Indicates the first When entering the net Local clock skew of each active node Indicates the first When entering the net The timing deviation of the transmission schedule of each active node Indicates the first When entering the network, the master node and the first The distance between active nodes This indicates the speed at which electromagnetic waves propagate through the air. Indicates the first When entering the net The length of the effective reception interval of each control time slot , Indicates the first The moment when the master node sends a synchronization frame during round-robin network entry;

[0056] when When, it indicates the first When entering the network, the master node determines the first... The access request frame sent by the active node did not fall into the first... Within the effective reception interval of each control time slot;

[0057] when When, it indicates the first When entering the network, the master node determines the first... The access request frame sent by the active node falls into the first... Within the effective reception interval of each control time slot.

[0058] Furthermore, the master node sequentially demodulates and verifies each access request frame falling within the valid reception interval of a control time slot, determines the status of the corresponding control time slot, and performs statistical analysis. The steps include:

[0059] when At that time, a synchronization header detection threshold is set, and the master node uses the synchronization header detection threshold to perform synchronization header detection on each access request frame that falls into the effective reception interval of the control time slot;

[0060] The expression for performing synchronization header detection is:

[0061] (7)

[0062] in, Indicates the first When entering the network in round 1, the master node falls into the first round. The result of synchronization header detection on access request frames within the effective reception interval of each control time slot. Indicates the first When entering the net The maximum normalized correlation detection value within the effective reception interval of each control time slot. , Indicates the first When entering the net Within the effective reception interval of the first control time slot The synchronization header sequence of access request frames sent by each active node. Indicates the first When entering the net Within the effective reception interval of the first control time slot Offset of access request frames sent by active nodes The conjugate value of the subsequent synchronization header sequence, Integer sample offset representing the synchronization header sequence. Indicates the first Synchronization head detection threshold during wheel entry into the network;

[0063] when When, it indicates the first The master node did not detect the first round of network entry. Synchronization header of access request frames within the effective reception interval of each control time slot;

[0064] when When, it indicates the first When entering the network, the master node detects the first Synchronization header of access request frames within the effective reception interval of each control time slot;

[0065] when At that time, the master node demodulates each access request frame that falls within the effective reception interval of the control time slot to obtain the format field of the corresponding access request frame;

[0066] The master node performs field consistency checks and cyclic redundancy checks on the format fields of each access request frame in sequence to obtain the corresponding valid parsed variables;

[0067] The expression that effectively resolves variables is:

[0068] (8)

[0069] in, Indicates the first The first time when entering the net Valid parsed variables corresponding to access request frames within the valid receive interval of each control time slot;

[0070] The master node uses the results of all valid arrival determinations, the results of all synchronization header detections, and all valid parsed variables to determine the status of each control time slot.

[0071] The expression for determining the state of the control time slot is:

[0072] (9)

[0073] in, Indicates the first When entering the net The status of each control time slot;

[0074] when When, it indicates the first When entering the net Each control time slot is an idle time slot;

[0075] when When, it indicates the first When entering the net Each control time slot is an access status time slot;

[0076] when When, it indicates the first When entering the net Each control time slot is a collision state time slot;

[0077] Based on the status of all control time slots during this round of network access, the master node counts the number of all idle time slots, the number of all access time slots, and the number of all collision time slots.

[0078] No. The expression for the number of all idle state time slots during round-trip networking is:

[0079] (10)

[0080] in, Indicates the first The number of all idle time slots during round-trip network entry. Indicates the first Total length of control time slots during wheel entry into the grid;

[0081] No. The expression for the number of all access state time slots during round-robin network entry is:

[0082] (11)

[0083] in, Indicates the first The number of all access state time slots during round-robin network entry;

[0084] No. The expression for the number of time slots in all collision states when a wheel enters the net is:

[0085] (12)

[0086] in, Indicates the first The number of time slots for all collision states when a wheel enters the net.

[0087] Furthermore, the steps for the master node to calculate the total length of the control time slots for the next round of network access based on the statistical results include:

[0088] Using the number of all idle state time slots, the number of all access state time slots, and the number of all collision state time slots, an observation error function is constructed, and the observation error function is used to obtain an estimate of the number of all active nodes among all remaining nodes waiting to join the network after this round of network entry.

[0089] The expression for the observation error function is:

[0090] (13)

[0091] in, Indicates the first The observation error of all active nodes among all remaining nodes waiting to join the network after round-robin joining. Indicates the first The weighting coefficient of the expected number of all idle state time slots when the system enters the network. Indicates the first The weighting coefficient of the expected number of all access state time slots during round-robin network entry. Indicates the first The weighting coefficient for the expected number of time slots in all collision states when a wheel enters the network. Indicates the first The expected number of all idle state time slots during round-trip networking. Indicates the first The expected number of all access state time slots during round-robin network entry. Indicates the first The expected number of all collision state time slots when a wheel enters the net. This represents a candidate value for the number of all active nodes participating in the network entry process during the r-th round.

[0092] The expression for estimating the number of all active nodes among all remaining nodes awaiting network entry after this round of network entry is:

[0093] (14)

[0094] in, Indicates the first An estimated number of all active nodes among all remaining nodes waiting to join the network after round-robin joining. This indicates taking the maximum value. Indicates the first The estimated number of all active nodes obtained from statistical results during round-robin network entry. , Indicates the first Within the range of the number of active nodes after the round-robin network, the value of the number of active nodes that minimizes the observation error function;

[0095] Set a maximum collision ratio threshold, and the master node uses the maximum collision ratio threshold to calculate the target access load for the next round of network access.

[0096] The expression for the target access load is:

[0097] (15)

[0098] in, Indicates the first The target access load when the system is connected to the network. Indicates collision-limited target load. Indicates the collision status. Indicates a typical target load. Indicates the first The observed collision ratio when the wheel enters the net. , Indicates the first The maximum allowed collision ratio threshold when a wheel enters the net;

[0099] Set the threshold for the total length of control time slots during this round of network access, and calculate the total length of control time slots during the next round of network access based on the estimated number of all active nodes among all remaining nodes waiting to be connected to the network after this round of network access, the target access load during the next round of network access, and the threshold for the total length of control time slots during this round of network access.

[0100] The expression for the total length of the control time slots in the next round of network access is:

[0101] (16)

[0102] in, Indicates the first Total length of control time slots during wheel entry into the grid. This indicates taking the minimum value. Indicates the first The maximum allowed total length of control time slots when the wheel enters the network. Indicates the first The minimum total length of control time slots allowed when the wheel enters the network. Indicates the first Control time slot protection coefficient when wheel enters the grid. This indicates rounding up to the nearest integer.

[0103] Beneficial effects:

[0104] This application provides a flexible dynamic access method for ad hoc networks in aviation search and rescue, which has at least the following beneficial effects:

[0105] This application introduces the concept of random access control based on synchronous broadcast into the aviation search and rescue ad hoc network. The master node sends a synchronization frame, and active nodes randomly select control time slots based on the synchronization frame and send access request frames. The master node then dynamically estimates the number of nodes to be added in the next round of network entry based on the feedback of the control time slot status. This enables adaptive adjustment of the total length of control time slots in the next round of network entry when the master node does not know the number of nodes to be added. This reduces the problems of continuous node collisions and waste of control time slot resources caused by the fixed length of control time slots, shortens the network establishment time, improves the utilization rate of control time slots, and enhances the access efficiency and stability of the aviation search and rescue ad hoc network in multi-node random network entry scenarios. Attached Figure Description

[0106] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0107] Figure 1 This illustration shows a flowchart of a flexible dynamic access method for an ad hoc aviation search and rescue network according to an exemplary embodiment of this application.

[0108] Figure 2 This diagram illustrates a comparison of the total length of control time slots during each round of network entry in a small-scale air search and rescue ad hoc network random entry scenario using different algorithms in the simulation experiment of this application.

[0109] Figure 3 This diagram illustrates a comparison of the cumulative network entry success rates when using different algorithms to perform multiple rounds of iterative network entry in a small-scale air search and rescue ad hoc network random entry scenario during simulation experiments of this application.

[0110] Figure 4 This diagram illustrates a comparison of the number of cumulative collision state time slots when using different algorithms to perform multiple rounds of iterative network entry in a small-scale air search and rescue ad hoc network random entry scenario during the simulation experiment of this application.

[0111] Figure 5 This diagram illustrates a comparison of the expected number of various control time slots and the number of control time slots when using different algorithms for the next round of network access based on the current network access situation in the simulation experiment of this application.

[0112] Figure 6 This diagram illustrates a comparison of the cumulative network entry success rates when using different algorithms in a large-scale air search and rescue ad hoc network random entry scenario during multiple rounds of iterative network entry in the simulation experiment of this application.

[0113] Figure 7 This diagram illustrates a comparison of statistical results obtained from 100 random repetitions of simulations using different algorithms in a large-scale air search and rescue ad hoc network random entry scenario. Detailed Implementation

[0114] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0115] Furthermore, the accompanying drawings are merely illustrative of this application and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0116] The following section will provide a more detailed description of the elastic dynamic access method for ad hoc aviation search and rescue networks proposed in this example embodiment.

[0117] This example implementation provides a flexible dynamic access method for ad hoc aviation search and rescue networks, such as... Figure 1 As shown, the method may include the following steps:

[0118] Step S101: Construct a system model for an aviation search and rescue self-organizing network. This system model includes a master node and multiple discrete and independent nodes to be added to the network within the working range of the master node.

[0119] Furthermore, the master node receives all nodes waiting to join the network through multiple rounds of iteration. After each round of joining, the master node removes all nodes that have joined the network and uses all remaining nodes that have not yet joined the network for the next round of joining, until all nodes waiting to join the network have completed joining.

[0120] Furthermore, the types of nodes to be added to the network include airborne nodes and handheld nodes.

[0121] Step S101 of this embodiment clarifies the networking relationship between the master node and all nodes awaiting network entry. After each round of network entry, the master node removes all already joined nodes awaiting network entry, thus preventing them from competing for the next round. This multi-round iterative network entry method adapts to situations where the number of nodes is unknown and node states change dynamically in aviation search and rescue self-organizing network scenarios.

[0122] Step S102: The system model executes the first round of network access procedures. The first round of network access procedures includes:

[0123] Sub-step S1021: Before network access, the system model divides all nodes awaiting network access into an active node set and an inactive node set based on their current network access status. This allows the master node to process access requests only for nodes that meet the access requirements, reducing the processing of invalid access requests and improving the utilization rate of control time slot resources.

[0124] Furthermore, the first The set of active nodes before round-robin entry into the network can be represented as .

[0125] Sub-step S1022: Network entry begins. The master node broadcasts a synchronization frame to all active nodes in this round of network entry and reserves multiple consecutive control time slots of equal length after the broadcast is completed.

[0126] Furthermore, the synchronization frame includes access control information, which includes: the timestamp of the master node during the current round of network entry, the round number of network entry, the total length of the control time slot, and the access permission flag. The expression for the access control information is:

[0127] (1)

[0128] in, Indicates the first Access control information during network entry. Indicates the first The timestamp of the master node when it joins the network. Indicates the master node. Indicates the round of entry into the network. Indicates the first Total length of control time slots during wheel entry into the grid. Indicates the first Access permission flag during network entry. This indicates transpose.

[0129] Here, by sending synchronization frames carrying access control information uniformly by the master node, all active nodes can obtain consistent access timing and access rules, thereby reducing the probability of erroneous access caused by timing disorder between nodes.

[0130] Sub-step S1023: All active nodes during this round of network access receive and parse synchronization frames, extracting access control information from them. Each active node calculates its corresponding access enable state based on the access control information and uses each access enable state to determine whether the corresponding active node meets the initial access conditions. The specific process is as follows:

[0131] The first step is for each active node to determine the validity of the synchronization frame. When the synchronization frame is valid and the access permission flag is valid, each active node calculates the corresponding access enable state.

[0132] Furthermore, the expression for the access enable state is:

[0133] (2)

[0134] in, Indicates the first When entering the net Access enable status of each active node Indicates the first When entering the net The results of the active nodes' determination of the synchronization frame. Indicates the first Access permission flag during round-trip network entry.

[0135] The value is determined by the first The result of the active node's judgment on the synchronization frame is used to determine its validity. When an active node receives a synchronization frame that simultaneously satisfies the following conditions: the frame start flag is correct, the frame type is a synchronization frame, the master node identifier field is valid, the access round field matches the current network access round, the total control time slot length field is within the allowable range, the access permission flag field is identifiable, and the cyclic redundancy check passes, the synchronization frame is deemed valid. At this point, let... If any of the above conditions are not met, the synchronization frame is deemed invalid. In this case, let... .

[0136] when When, it indicates the first When entering the net Each active node determines that the synchronization frame is valid;

[0137] when When, it indicates the first When entering the net An active node determined that the synchronization frame was invalid.

[0138] when When, it indicates the first The access permission flag is valid during round-trip network entry.

[0139] when When, it indicates the first The access permission flag during the round-trip network entry is invalid.

[0140] The second step is to use the access enable status of each node to determine whether the corresponding active node meets the initial access conditions.

[0141] when When, it indicates the first When entering the net If an active node meets the initial access conditions for this round of network entry, then the active node sends an access request frame.

[0142] when When, it indicates the first When entering the net If an active node does not meet the initial access conditions for this round of network entry, the active node will be in a state of listening to synchronization frames and will not send access request frames.

[0143] In this embodiment, sub-step S1023 uses the validity of the synchronization frame and the access permission flag to jointly determine whether an active node meets the initial access conditions. This effectively filters out synchronization frame errors, inconsistent rounds, and invalid transmissions under access-prohibited conditions. This reduces the amount of control time slot resources occupied by abnormally active nodes and improves the reliability of the network access process.

[0144] Sub-step S1024: For each active node that meets the initial access conditions, randomly select a control time slot as its access request window and send an access request frame to the time slot center of the selected control time slot. The specific process is as follows:

[0145] The first step is to satisfy All active nodes select control time slots using a randomized, equal-probability method.

[0146] The expression for the probability of an active node selecting a control slot is:

[0147] (3)

[0148] in, Indicates the first When entering the net The active node selects the first The probability of a control time slot, Indicates the first The length of the control time slot when the wheel enters the grid. Indicates the first When entering the net The number of the control slot selected by each active node.

[0149] Sub-step S1024 in this embodiment enables active nodes to send access request frames even when the master node has not pre-allocated dedicated control time slots. This is suitable for network construction scenarios where the master node does not know the number of nodes to join the network. Using an equal-probability random slot selection method can reduce centralized scheduling overhead and also provides a basis for adjusting the total length of control time slots in the next round of network entry based on control time slot status feedback.

[0150] Sub-step S1025: The master node calculates the average energy of all access request frames received in each control time slot, performs energy detection for each control time slot, and determines whether the corresponding access request frame falls within the effective reception range of the corresponding control time slot based on the energy detection result. The specific process is as follows:

[0151] The first step is for the master node to calculate the energy of each access request frame in each control time slot, and to calculate the average energy of all access request frames in the corresponding control time slot.

[0152] Furthermore, the expression for calculating the average energy of all access request frames within the control time slot is:

[0153] (4)

[0154] in, Indicates the first When entering the net The average energy of all access request frames within a control time slot. Indicates the first When entering the net The number of all access request frames within a control time slot Indicates the number of the access request frame. Indicates the first When entering the net Within the first control time slot, the first The energy value of the access request frames sent by each active node. Represents absolute value;

[0155] The second step is to set an energy detection threshold, and the master node uses the energy detection threshold to perform energy detection on each control time slot.

[0156] Furthermore, the expression for the master node to perform energy detection on the control slot is:

[0157] (5)

[0158] in, Indicates the first When entering the net Energy detection results for each control time slot Indicates the first Energy detection threshold when a wheel enters the network.

[0159] when When, it indicates the first When entering the net No access request frames were detected in the control time slot;

[0160] when When, it indicates the first When entering the net An access request frame was detected in one control time slot;

[0161] The third step, when At that time, the master node performs a valid arrival determination on the access request frame detected in each control time slot, and determines whether each access request frame falls within the valid reception range of the corresponding control time slot based on the results of all valid arrival determinations.

[0162] Furthermore, the expression for valid arrival determination is:

[0163] (6)

[0164] in, Indicates the first When entering the network, the master node has a relationship with the first... The first control time slot within the [number] time slot The result of valid arrival determination of access request frames sent by each active node. Indicates the first When entering the net The first control time slot received the first The time when an active node sends an access request frame. , Indicates the first When entering the net The active node sends to the first The ideal time to send an access request frame in a control time slot , Indicates the first The timestamp of the master node when it joins the network. Indicates the first The length of each control time slot when the wheel enters the network. Indicates the first When entering the net The number of the control slot selected by each active node. Indicates the first The pre-protection period for each control time slot when the wheel enters the network. Indicates the first When entering the net The active node sends to the first The duration for sending access request frames in each control time slot. , Indicates the first The post-protection time period for each control time slot during wheel entry into the network. Indicates the first When entering the net Local clock skew of each active node Indicates the first When entering the net The timing deviation of the transmission schedule of each active node Indicates the first When entering the network, the master node and the first The distance between active nodes This indicates the speed at which electromagnetic waves propagate through the air. Indicates the first When entering the net The effective reception interval of each control time slot , Indicates the first The moment when the master node sends a synchronization frame during round-trip networking.

[0165] Each control time slot includes a pre-protection period, an effective reception interval, and a post-protection period.

[0166] when When, it indicates the first When entering the network, the master node determines the first... The access request frame sent by the active node did not fall into the first... Within the effective reception interval of each control time slot;

[0167] when When, it indicates the first When entering the network, the master node determines the first... The access request frame sent by the active node falls into the first... Within the effective reception interval of each control time slot.

[0168] In this embodiment, sub-step S1025 first uses the average energy of all access request frames to determine whether there is an access request frame in the corresponding control time slot, and then combines the effective reception interval to determine whether the access request frame falls into the correct time. This can reduce misjudgments caused by noise, clock deviation and propagation delay, and improve the accuracy of the master node's reception judgment.

[0169] Sub-step S1026: The master node demodulates and verifies each access request frame falling within the valid reception interval of a control time slot, determines the status of the corresponding control time slot, and performs statistical analysis. The specific process is as follows:

[0170] First step, when At that time, a synchronization header detection threshold is set, and the master node uses the synchronization header detection threshold to perform synchronization header detection on each access request frame that falls into the effective reception interval of the control time slot.

[0171] The expression for performing synchronization header detection is:

[0172] (7)

[0173] in, Indicates the first When entering the network in round 1, the master node falls into the first round. The result of synchronization header detection on access request frames within the effective reception interval of each control time slot. Indicates the first When entering the net The maximum normalized correlation detection value within the effective reception interval of each control time slot. , Indicates the first When entering the net Within the effective reception interval of the first control time slot The synchronization header sequence of access request frames sent by each active node. Indicates the first When entering the net Within the effective reception interval of the first control time slot Offset of access request frames sent by active nodes The conjugate value of the subsequent synchronization header sequence, Integer sample offset representing the synchronization header sequence. Indicates the first Synchronization head detection threshold when a wheel enters the network.

[0174] Here, the range of integer sample offset values ​​for the synchronization header sequence is determined based on the maximum allowable time deviation within the effective reception interval. Let the length of the synchronization header sequence be... If there are 1 sampling point, then The range of values ​​is Within the range of values, the master node calculates the normalized correlation detection value corresponding to the offset of each integer sample point, and determines the maximum normalized correlation detection value. Then Synchronization head detection threshold A comparison is made to determine whether the synchronization header of the access request frame has been detected.

[0175] when When, it indicates the first The master node did not detect the first round of network entry. The synchronization header of the access request frame within the effective reception interval of a control time slot indicates a node collision.

[0176] when When, it indicates the first When entering the network, the master node detects the first Synchronization header of access request frames within the effective reception interval of a control time slot.

[0177] The second step, when At that time, the master node demodulates each access request frame that falls within the effective reception interval of the control time slot to obtain the format field of the corresponding access request frame.

[0178] The third step involves the master node performing field consistency checks and cyclic redundancy checks on the format fields of each access request frame in sequence to obtain the corresponding valid parsed variables.

[0179] Furthermore, the expression for effectively resolving variables is:

[0180] (8)

[0181] in, Indicates the first The first time when entering the net Valid parsed variables corresponding to access request frames within the valid receive interval of each control time slot.

[0182] Fourth, the master node uses the results of all valid arrival determinations, all synchronization header detections, and all valid parsed variables to determine the status of each control time slot.

[0183] Furthermore, the expression for determining the state of the control time slot is:

[0184] (9)

[0185] in, Indicates the first When entering the net The state of each control time slot.

[0186] when When, it indicates the first When entering the net Each control time slot is an idle time slot;

[0187] when When, it indicates the first When entering the net Each control time slot is an access status time slot;

[0188] when When, it indicates the first When entering the net Each control time slot is a collision state time slot.

[0189] The fifth step involves the master node counting the number of idle time slots, access time slots, and collision time slots based on the status of all control time slots during this round of network access.

[0190] Furthermore, the first The expression for the number of all idle state time slots during round-trip networking is:

[0191] (10)

[0192] in, Indicates the first The number of all idle time slots during round-trip network entry. Indicates the first Total length of control time slots when the wheel enters the network.

[0193] Furthermore, the first The expression for the number of all access state time slots during round-robin network entry is:

[0194] (11)

[0195] in, Indicates the first The number of all access state time slots during round-trip networking.

[0196] Furthermore, the first The expression for the number of time slots in all collision states when a wheel enters the net is:

[0197] (12)

[0198] in, Indicates the first The number of time slots for all collision states when a wheel enters the net.

[0199] In this embodiment, sub-step S1026 distinguishes between idle state time slots, access state time slots, and collision state time slots through synchronization header detection, field consistency detection, and cyclic redundancy check. Then, statistics are performed on these three types of control time slots to more accurately reflect the access results of this round of network access and provide reliable feedback for estimating the number of active nodes and adjusting the total length of control time slots in the next round of network access.

[0200] Sub-step S1027: The master node calculates the total length of the control time slots for the next round of network access based on the statistical results. The specific process is as follows:

[0201] Using the number of all idle state time slots, the number of all access state time slots, and the number of all collision state time slots, an observation error function is constructed, and the observation error function is used to obtain an estimate of the number of all active nodes among all remaining nodes waiting to join the network after this round of network entry.

[0202] Furthermore, the expression for the observation error function is:

[0203] (13)

[0204] in, Indicates the first The observation error of all active nodes among all remaining nodes waiting to join the network after round-robin joining. Indicates the first The weighting coefficient of the expected number of all idle state time slots when the system enters the network. Indicates the first The weighting coefficient of the expected number of all access state time slots during round-robin network entry. Indicates the first The weighting coefficient for the expected number of time slots in all collision states when a wheel enters the network. Indicates the first The expected number of all idle state time slots during round-trip networking. Indicates the first The expected number of all access state time slots during round-robin network entry. Indicates the first The expected number of all collision state time slots when a wheel enters the net. This represents a candidate value for the number of all active nodes participating in the network entry process during the r-th round.

[0205] Furthermore, the expression for obtaining the estimated number of all active nodes among all remaining nodes awaiting network entry after this round of network entry is:

[0206] (14)

[0207] in, Indicates the first An estimated number of all active nodes among all remaining nodes waiting to join the network after round-robin joining. This indicates taking the maximum value. Indicates the first The number of all active nodes obtained from statistical results during round-robin network entry. , Indicates the first Within the range of the number of active nodes after the round-robin is added to the network, the value of the number of active nodes that minimizes the observation error function is taken.

[0208] Set a maximum collision ratio threshold, and the master node uses the maximum collision ratio threshold to calculate the target access load for the next round of network access.

[0209] Furthermore, the expression for the target access load is:

[0210] (15)

[0211] in, Indicates the first The target access load when the system is connected to the network. Indicates collision-limited target load. Indicates the collision status. Indicates a typical target load. Indicates the first The observed collision ratio when the wheel enters the net. , Indicates the first The maximum allowed collision ratio threshold when a wheel enters the net.

[0212] here, and These are all target access load parameters pre-set by the master node. Collision-limited target load. This is used to reduce the expected number of competing nodes in a single control slot in the next round when the collision ratio exceeds the maximum collision ratio threshold. (Regular target load) This is used to maintain normal access efficiency when the observed collision ratio does not exceed the maximum collision ratio threshold. Both can be preset according to the maximum collision ratio threshold allowed by the system model, the expected access success rate, and the requirements for control slot utilization.

[0213] Set the threshold for the total length of control time slots during this round of network access, and calculate the total length of control time slots for the next round of network access based on the estimated number of all active nodes among all remaining nodes waiting to be connected to the network after this round of network access, the target access load for the next round of network access, and the threshold for the total length of control time slots during this round of network access.

[0214] Furthermore, the expression for the total length of the control time slots in the next round of network access is:

[0215] (16)

[0216] in, Indicates the first Total length of control time slots during wheel entry into the grid. This indicates taking the minimum value. Indicates the first The maximum allowed total length of control time slots when the wheel enters the network. Indicates the first The minimum total length of control time slots allowed when the wheel enters the network. Indicates the first Control time slot protection coefficient when wheel enters the grid. This indicates rounding up to the nearest integer.

[0217] Step S103: Iterate through the above process until all nodes to be added to the network have completed the process.

[0218] To verify the superiority of the elastic dynamic access method for ad hoc aviation search and rescue networks proposed in this application, the following simulation experiment was conducted.

[0219] This simulation experiment constructs a circular coverage area centered on the master node, with a working range radius of 120 km. Nodes to be added to the network include airborne and handheld nodes. The position of each node to be added is randomly generated using polar coordinates; the azimuth angle is randomly selected from 0° to 360°, representing the direction of the node relative to the master node; the distance between the node and the master node is randomly selected from 0 km to 120 km, representing different distance positions of the node within the master node's coverage area. This setup simulates the random distribution of nodes to be added within the mission area in an ad hoc aerial search and rescue network.

[0220] This application constructs a small-scale air search and rescue ad hoc network random entry scenario, including 4 airborne nodes and 16 handheld nodes, for a total of 20 nodes waiting to join the network. Simultaneously, it constructs a large-scale air search and rescue ad hoc network random entry scenario, including 16 airborne nodes and 256 handheld nodes, for a total of 272 nodes waiting to join the network. Each control time slot is 200ms long, with a 10ms pre-protection period and a 10ms post-protection period. The effective reception interval length for each control time slot is 180ms. The initial total control time slot length is 10 control time slots, the maximum total control time slot length is 256 control time slots, and the maximum number of entry rounds is 30 rounds.

[0221] This simulation experiment compares three algorithms: Algorithm 1: Fixed Frame Length and Frame Slotted ALOHA (FFLFSA); Algorithm 2: Schoute Dynamic Frame Slotted ALOHA (Schoute DFSA); and Algorithm 3: the method proposed in this application.

[0222] like Figure 2The diagram illustrates the changes in the total control time slot length during each round of network entry for three algorithms in a small-scale air search and rescue ad hoc network random entry scenario. It can be seen that: Algorithm 1 maintains a constant total control time slot length and cannot be adjusted based on the number of remaining nodes waiting to join the network. Algorithm 2 can adjust the total control time slot length based on the number of collision state time slots, with the curve showing a step-like change. Algorithm 3 can adjust the total control time slot length based on the status feedback results of idle state time slots, access state time slots, and collision state time slots; its curve rises when the number of collision state time slots is high and falls when the number of remaining nodes waiting to join the network decreases. This demonstrates that the proposed method can maintain a match between the number of control time slots and the node competition intensity.

[0223] like Figure 3 As shown, the cumulative network access success rate of the three algorithms in a small-scale aerial search and rescue ad hoc network random access scenario is illustrated. Figure 3 The horizontal axis represents simulation time, and the vertical axis represents the cumulative network entry success rate. Using Algorithm 1, the cumulative network entry success rate increases slowly due to the fixed total length of the control time slots. Using Algorithm 2, the total length of the control time slots can be expanded based on collision results, thus improving the network entry speed. Using Algorithm 3, the cumulative network entry success rate increases even faster, achieving full network entry in a shorter time. This demonstrates that the method proposed in this application can shorten the network establishment time of the aerial search and rescue ad hoc network.

[0224] like Figure 4 As shown, the number of cumulative collision state time slots varies for the three algorithms in a small-scale aerial search and rescue ad hoc network random entry scenario. Figure 4 The horizontal axis represents the number of network entry rounds, and the vertical axis represents the cumulative number of collision state time slots. When using Algorithm 1, collisions occur continuously during multiple network entry rounds, leading to a rapid increase in the cumulative number of collision state time slots. When using Algorithm 2, the total length of control time slots for the next network entry round is adjusted based on the state feedback results of the collision state time slots, resulting in a lower cumulative number of collision state time slots compared to Algorithm 1. When using Algorithm 3, the proposed method estimates the remaining number of nodes to be networked based on the state feedback results of idle state time slots, access state time slots, and collision state time slots, and updates the total length of control time slots for the next network entry round accordingly, thus minimizing the cumulative number of collision state time slots. This demonstrates that the proposed method can reduce the consumption of access request resources.

[0225] like Figure 5 As shown, Figure 5The value 'a' in the diagram represents the number of observations and the expected number of control time slots for three types: idle state time slots, access state time slots, and collision state time slots. The curves showing the number of observations for the three types of time slots exhibit the same trend as the curves showing the expected number of observations. This indicates that when Algorithm 3 is used, the master node can estimate the size of nodes waiting to join the network in the next round by utilizing the state feedback results of the control time slots. Figure 5 Figure b shows the relationship between the total length of the control time slots, the Schoute reference window, the estimated number of remaining nodes to be joined in the current round, and the total length of the control time slots for the next round when Algorithm 3 is used. This indicates that the method proposed in this application can increase the total length of the control time slots when there are many collision state time slots and decrease the total length of the control time slots when there are few remaining nodes to be joined in the current round, thereby achieving adaptive updating of the total length of the control time slots.

[0226] like Figure 6 The diagram illustrates the changes in the cumulative network access success rate of three algorithms under a large-scale air search and rescue ad hoc network random access scenario. When using Algorithm 1, it cannot support a large number of nodes joining the network, and collisions continuously occur in the control time slots, resulting in a consistently low success rate. With Algorithm 2, the total length of the control time slots can be expanded based on the collision results, but the overall network access time remains relatively long. Using Algorithm 3, under high-density random access conditions, the cumulative network access success rate maintains rapid growth and reaches the overall network access state earlier. This demonstrates that the method proposed in this application has better scalability.

[0227] like Figure 7 As shown, the statistical results of 100 randomized repeated simulations of the three algorithms in a large-scale air search and rescue ad hoc network random entry scenario are presented. Figure 7 The value 'a' in the figure shows a comparison of the percentage of access state time slots. Figure 7 The value 'b' in the figure shows a comparison of network access times across the entire network.

[0228] It can be seen that when using Algorithm 1, the proportion of access state time slots remains at a low level for a long period, and the overall network access time curve shows a consistently low value. This phenomenon indicates that under the condition of large-scale, high-density random network access by 272 nodes waiting to join the network, the fixed control time slot length cannot expand with the increase in node competition intensity, resulting in a large number of nodes being in a collision waiting state for a long time. Algorithm 1 is no longer able to support all nodes waiting to join the network to complete their access. Therefore, Figure 7 The curves for Algorithm 1 in a and b are mainly used to illustrate that the fixed window method has obvious limitations in the applicability of random entry scenarios in large-scale air search and rescue self-organizing networks.

[0229] When using Algorithm 2, the proportion of access state time slots is significantly higher than that of Algorithm 1, indicating that Algorithm 2 can expand control time slots through collision state feedback and has a certain adaptability to high-density random network access. However, in terms of the overall network access time, Algorithm 2 takes a longer time in 100 random repeated simulations and exhibits significant fluctuations, indicating that its adjustment of control time slots mainly depends on the number of collision state time slots and cannot fully utilize the information from idle state time slots and access state time slots.

[0230] When using Algorithm 3, the proportion of access state time slots remains high in most randomized repeated simulations, and the overall network access time is lower than that of Algorithm 2. This result demonstrates that the proposed method can comprehensively utilize three types of control time slot state feedback—idle state time slots, access state time slots, and collision state time slots—to dynamically estimate the number of all active nodes among the remaining nodes waiting to join the network, and adjust the total length of control time slots for the next round of network access accordingly. This maintains good network access efficiency and stability even with large-scale random node distribution and random slot selection.

[0231] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0232] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0233] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in this application, and such modifications or substitutions should all be covered within the scope of protection of this application.

[0234] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

Claims

1. A flexible dynamic access method for ad hoc networks in aviation search and rescue, characterized in that, Includes the following steps: A system model for constructing an autonomous aerial search and rescue network is provided. The system model includes a master node and multiple discrete and independent nodes to be added to the network within the working range of the master node. The master node receives all the nodes to be joined to the network through multiple rounds of iteration. After each round of joining, the master node removes all the nodes that have been joined to the network and uses all the remaining nodes that have not yet joined to the network for the next round of joining, until all the nodes to be joined to the network have completed joining. The first round of network access process includes: Before joining the network, the system model divides all the nodes to be joined into a set of active nodes and a set of inactive nodes based on their status during this round of network joining. At the start of network access, the master node broadcasts a synchronization frame to all active nodes in this round of network access, and reserves multiple consecutive control time slots of equal length after the broadcast is completed; During this round of network access, all active nodes receive and parse the synchronization frame, extract access control information from it, and each active node calculates the corresponding access enable state based on the access control information, and uses each access enable state to determine whether the corresponding active node meets the initial access conditions. For each active node that meets the initial access conditions, it randomly selects a control time slot as its own access request window and sends an access request frame to the time slot center of the selected control time slot. The master node calculates the average energy of all access request frames received in each control time slot, performs energy detection on each control time slot, and determines whether the corresponding access request frame falls within the effective reception range of the corresponding control time slot based on the energy detection result. The master node demodulates and verifies each access request frame that falls within the effective reception interval of the control time slot, determines the status of the corresponding control time slot, and performs statistics. The master node calculates the total length of the control time slots for the next round of network access based on the statistical results; The above network entry process is repeated in multiple iterations until all the nodes to be entered into the network have completed the process.

2. The elastic dynamic access method for ad hoc networks for air search and rescue according to claim 1, characterized in that, No. The set of active nodes before the round-robin entry into the network is represented as follows: .

3. The elastic dynamic access method for ad hoc networks for air search and rescue according to claim 1, characterized in that, The synchronization frame includes the access control information, which includes: the timestamp of the master node during the current round of network entry, the round of network entry, the total length of the control time slot, and the access permission flag. The access control information expression is: (1) in, Indicates the first Access control information during network entry. Indicates the first The timestamp of the master node when it joins the network. Indicates the master node. Indicates the round of entry into the network. Indicates the first Total length of control time slots during wheel entry into the grid. Indicates the first Access permission flag during network entry. This indicates transpose.

4. The elastic dynamic access method for ad hoc networks for air search and rescue according to claim 3, characterized in that, The steps of all active nodes receiving and parsing the synchronization frame during this round of network access, extracting access control information from it, calculating the corresponding access enable state based on the access control information, and determining whether the corresponding active node meets the initial access conditions using each access enable state include: Each active node determines the validity of the synchronization frame; when the synchronization frame is valid and the access permission flag is valid, each active node calculates the corresponding access enable state. The expression for the access enable state is: (2) in, Indicates the first When entering the net Access enable status of each active node Indicates the first When entering the net The results of the active nodes' determination of the synchronization frame. Indicates the first Access permission flag during network entry; when When, it indicates the first When entering the net Each active node determines that the synchronization frame is valid; when When, it indicates the first When entering the net Each of the active nodes determines that the synchronization frame is invalid; when When, it indicates the first The access permission flag is valid during round-trip network entry; when When, it indicates the first The access permission flag mentioned during the round-trip network entry is invalid; Each access enable state is used to determine whether the corresponding active node meets the initial access conditions; when When, it indicates the first When entering the net Each active node that meets the initial access conditions during this round of network entry sends the access request frame. when When, it indicates the first When entering the net If an active node does not meet the initial access conditions for this round of network entry, it will not send the access request frame.

5. The elastic dynamic access method for ad hoc networks for air search and rescue according to claim 4, characterized in that, The step of randomly selecting a control time slot as its own access request window for each active node that meets the initial access conditions, and sending an access request frame to the time slot center of the selected control time slot includes: For satisfying All active nodes select the control time slot using an equal-probability random slot selection method; The expression for the probability that the active node selects the control slot is: (3) in, Indicates the first When entering the net The active node selects the first The probability of a control time slot, Indicates the first Total length of control time slots during wheel entry into the grid. Indicates the first When entering the net The number of the control slot selected by each active node.

6. The elastic dynamic access method for ad hoc networks for air search and rescue according to claim 1, characterized in that, The steps of the master node calculating the average energy of all access request frames received in each control time slot, performing energy detection for each control time slot, and determining whether the corresponding access request frame falls within the effective reception interval of the corresponding control time slot based on the energy detection result include: The master node calculates the energy of each access request frame in each control time slot, and calculates the average energy of all access request frames in the corresponding control time slot. The expression for calculating the average energy of all access request frames within the control time slot is: (4) in, Indicates the first When entering the net The average energy of all access request frames within a control time slot. Indicates the first When entering the net The number of all access request frames within a control time slot. Indicates the number of the access request frame. Indicates the first When entering the net Within the first control time slot, the first The energy of access request frames sent by each active node. Represents absolute value; An energy detection threshold is set, and the master node uses the energy detection threshold to perform energy detection on each of the control time slots; The expression for the master node to perform energy detection on the control time slot is: (5) in, Indicates the first When entering the net Energy detection results for each control time slot Indicates the first Energy detection threshold when a wheel enters the network; when When, it indicates the first When entering the net No access request frames were detected in the aforementioned control time slot; when When, it indicates the first When entering the net The access request frame was detected in the control time slot; when At that time, the master node performs a valid arrival determination on the access request frame detected in each control time slot, and determines whether each access request frame falls within the valid reception range of the corresponding control time slot based on the results of all valid arrival determinations. The expression for determining the valid arrival is: (6) in, Indicates the first When entering the network, the master node has a relationship with the first... The first control time slot within the [number] time slot The result of valid arrival determination of access request frames sent by each active node. Indicates the first When entering the net The first control time slot received the first The time when an active node sends an access request frame. , Indicates the first When entering the net The active node sends to the first The ideal time to send an access request frame in a control time slot , Indicates the first The timestamp of the master node when it joins the network. Indicates the first The length of each control time slot when the wheel enters the network. Indicates the first When entering the net The number of the control slot selected by each active node. Indicates the first The pre-protection period for each control time slot when the wheel enters the network. Indicates the first When entering the net The active node sends to the first The duration for sending access request frames in each control time slot. , Indicates the first The post-protection time period for each control time slot during wheel entry into the network. Indicates the first When entering the net Local clock skew of each active node Indicates the first When entering the net The timing deviation of the transmission schedule of each active node Indicates the first When entering the network, the master node and the first The distance between active nodes This indicates the speed at which electromagnetic waves propagate through the air. Indicates the first When entering the net The effective reception interval of each control time slot , Indicates the first The moment when the master node sends a synchronization frame during round-robin network entry; when When, it indicates the first When entering the network, the master node determines the first... The access request frame sent by the active node did not fall into the first... Within the effective reception interval of the control time slot; when When, it indicates the first When entering the network, the master node determines the first... The access request frame sent by the active node falls into the first Within the effective reception interval of the control time slot.

7. The elastic dynamic access method for ad hoc networks for air search and rescue according to claim 6, characterized in that, The steps of the master node demodulating and verifying each access request frame falling within the effective reception interval of the control time slot, determining the status of the corresponding control time slot, and performing statistics include: when At that time, a synchronization header detection threshold is set, and the master node uses the synchronization header detection threshold to perform synchronization header detection on each access request frame that falls within the effective reception interval of the control time slot; The expression for performing the synchronization head detection is: (7) in, Indicates the first When entering the network in round 1, the master node falls into the first round. The result of synchronization header detection on access request frames within the effective reception interval of each control time slot. Indicates the first When entering the net The maximum normalized correlation detection value within the effective reception interval of each control time slot. , Indicates the first When entering the net Within the effective reception interval of the first control time slot The synchronization header sequence of access request frames sent by each active node. Indicates the first When entering the net Within the effective reception interval of the first control time slot Offset of access request frames sent by active nodes The conjugate value of the subsequent synchronization header sequence, Integer sample offset representing the synchronization header sequence. Indicates the first Synchronization head detection threshold during wheel entry into the network; when When, it indicates the first The master node did not detect the first round of network entry. Synchronization header of the access request frame within the effective reception interval of the control time slot; when When, it indicates the first When the master node detects the first round of network entry... Synchronization header of the access request frame within the effective reception interval of the control time slot; when At that time, the master node demodulates each access request frame that falls within the effective reception interval of the control time slot to obtain the format field of the corresponding access request frame; The master node performs field consistency checks and cyclic redundancy checks on the format fields of each access request frame in sequence to obtain the corresponding valid parsed variables; The expression for the valid parsed variable is: (8) in, Indicates the first The first time when entering the net Valid parsed variables corresponding to access request frames within the valid receive interval of each control time slot; The master node uses the results of all valid arrival determinations, the results of all synchronization header detections, and all valid parsed variables to determine the state of each control time slot. The expression for determining the state of the control time slot is: (9) in, Indicates the first When entering the net The status of each control time slot; when When, it indicates the first When entering the net The control time slot is an idle time slot; when When, it indicates the first When entering the net The control time slot mentioned above is an access status time slot; when When, it indicates the first When entering the net The control time slot is a collision state time slot; Based on the status of all control time slots during this round of network access, the master node counts the number of all idle time slots, the number of all access time slots, and the number of all collision time slots. No. The expression for the number of all idle state time slots during round-trip networking is: (10) in, Indicates the first The number of all idle time slots during round-trip network entry. Indicates the first Total length of control time slots during wheel entry into the grid; No. The expression for the number of all access state time slots during round-robin network entry is: (11) in, Indicates the first The number of all access state time slots during round-robin network entry; No. The expression for the number of time slots for all the aforementioned collision states when a wheel enters the net is: (12) in, Indicates the first The number of time slots for all collision states when a wheel enters the net.

8. The elastic dynamic access method for ad hoc networks for air search and rescue according to claim 7, characterized in that, The steps for the master node to calculate the total length of the control time slot for the next round of network access based on the statistical results include: Using the number of all idle state time slots, the number of all access state time slots, and the number of all collision state time slots, an observation error function is constructed, and the observation error function is used to obtain an estimated value of the number of all active nodes among all the remaining nodes waiting to join the network after this round of network entry; The expression for the observation error function is: (13) in, Indicates the first The observation error of all active nodes among all remaining nodes waiting to join the network after round-robin joining. Indicates the first The weighting coefficient of the expected number of all idle state time slots when the system enters the network. Indicates the first The weighting coefficient of the expected number of all access state time slots during round-robin network entry. Indicates the first The weighting coefficient for the expected number of time slots in all collision states when a wheel enters the network. Indicates the first The expected number of all idle state time slots during round-trip networking. Indicates the first The expected number of all access state time slots during round-robin network entry. Indicates the first The expected number of all collision state time slots when a wheel enters the net. This represents a candidate value for the number of all active nodes participating in the network entry process during the r-th round. The expression for obtaining the estimated number of all active nodes among all remaining nodes awaiting network access after this round of network access is: (14) in, Indicates the first An estimated number of all active nodes among all remaining nodes waiting to join the network after round-robin joining. This indicates taking the maximum value. Indicates the first The number of all active nodes obtained from statistical results during round-robin network entry. , Indicates the first Within the range of the number of active nodes after the round-robin network, the value of the number of active nodes that minimizes the observation error function; The master node sets a maximum collision ratio threshold and uses the maximum collision ratio threshold to calculate the target access load for the next round of network access. The expression for the target access load is: (15) in, Indicates the first The target access load when the system is connected to the network. Indicates a collision-limited target load. Indicates the collision status. Indicates a typical target load. Indicates the first The observed collision ratio when the wheel enters the net. , Indicates the first The maximum allowed collision ratio threshold when a wheel enters the net; Set the threshold for the total length of control time slots during this round of network access, and calculate the total length of control time slots during the next round of network access based on the estimated number of all active nodes among all remaining nodes to be networked after this round of network access, the target access load during the next round of network access, and the threshold for the total length of control time slots during this round of network access. The expression for the total length of the control time slots in the next round of network access is: (16) in, Indicates the first Total length of control time slots during wheel entry into the grid. This indicates taking the minimum value. Indicates the first The maximum allowed total length of control time slots when the wheel enters the network. Indicates the first The minimum total length of control time slots allowed when the wheel enters the network. Indicates the first Control time slot protection coefficient when wheel enters the grid. This indicates rounding up to the nearest integer.

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