Ad-hoc network system based on TDMA

Abstract

The invention discloses an ad hoc network system and method based on TDMA, and relates to the technical field of wireless communication. The system comprises a master node and a plurality of slave nodes which are respectively provided with a high-precision timing counter. A system defines a superframe structure containing time slots, a master node broadcasts access information, and slave nodes monitor access and allocate the time slots. A node broadcasts a beacon frame with a local timestamp in a sending time slot of the node, and calibrates a clock of the node when receiving a beacon of the node, so that distributed time synchronization is realized. When a node sends data, the sending time slot is ended in advance under the condition of distance so as to avoid crosstalk between the time slots. The system also defines a frequency sweeping time slot, and self-adaptive channel frequency hopping is realized through centralized decision of the main node so as to resist interference; and a dynamic time slot allocation mechanism is adopted, standby time slots are applied and released as required, and the resource utilization rate is improved. According to the invention, the problems of low synchronization precision, poor interference resistance, resource allocation rigidity, time delay influence and the like of the traditional TDMA ad hoc network are solved, and high-reliability and high-efficiency multi-hop ad hoc network communication is realized.

Description

Technical Field

[0001] This invention relates to the field of ad hoc network technology, specifically to an ad hoc network system based on TDMA. Background Technology

[0002] Currently, in the field of wireless communication, ad hoc networks are widely used in emergency communications, military communications, industrial control, and the Internet of Things (IoT) due to their ability to be deployed quickly without relying on fixed infrastructure. Time Division Multiple Access (TDMA), a classic multiple access method, divides the time axis into multiple discrete time slots and allocates them to different nodes, enabling ordered communication among multiple nodes on the same frequency channel. This has made it one of the commonly used resource scheduling schemes in ad hoc networks.

[0003] Ad hoc networks consist of a large number of mobile or fixed wireless nodes, each functioning as both a "terminal" and a "router," and must autonomously construct their communication topology using dynamic routing protocols. With the increasing complexity of application scenarios, the demand for "low interference, high bandwidth utilization, and low latency" in ad hoc networks is becoming increasingly urgent. Existing ad hoc networks mostly employ CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) multiple access methods, which, while simple to implement, suffer from high data collision rates and significantly reduced communication stability in multi-node scenarios. Furthermore, achieving network-wide synchronized frequency hopping is difficult when interference is present. Additionally, for long-distance communication, the ACK mechanism of CSMA greatly reduces communication efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a self-organizing network system based on TDMA to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A TDMA-based self-organizing network system includes:

[0007] A master node and several slave nodes;

[0008] Both the master node and each slave node are configured with a high-precision timer / counter to define a uniform time slot length;

[0009] The system defines a superframe structure containing several time slots, with each node being allocated at least one dedicated transmission time slot;

[0010] The master node is used to generate and broadcast access information containing slave node numbers, their assigned transmission time slot numbers, and initial network timing values, and acts as a network controller to manage channel switching.

[0011] The slave node is used to listen for access information to join the network and communicate within the allocated time slot; slave nodes that cannot communicate directly with the master node forward the access information through the slave nodes that have already joined.

[0012] Each node broadcasts a beacon frame carrying the current value of its local time counter during its own transmission time slot; each node receives beacon frames during non-transmission time slots and calibrates its local time counter value based on the received time counter value and the estimated signal propagation delay value to achieve network-wide time synchronization; the system determines the maximum signal propagation delay based on the maximum communication distance of the network, and each node ends transmission before the maximum signal propagation delay at the start time of its own transmission time slot to avoid the signal falling into adjacent transmission time slots.

[0013] Furthermore, the timer counter counts in microseconds; the system defines a timeout interrupt signal, which generates an interrupt when the timer counter counts to an integer multiple of the duration of a transmission time slot, and calculates the time slot number within the superframe corresponding to the current interrupt.

[0014] Furthermore, a specific frequency sweeping time slot is defined in each superframe; within the frequency sweeping time slot, all nodes in the network switch to the receiving state, scan and record the interference strength information of the preset working channel; the slave nodes report the scanned interference strength information to the master node; the master node determines whether to switch the working channel based on the interference strength information reported by itself and the slave nodes; when it is determined that frequency hopping is required, the master node generates and broadcasts a frequency hopping command, which includes the target channel number and the switching execution time; the system reserves at least several superframes of delay time for multi-hop transmission in the network to ensure that all nodes in the network switch to the target channel synchronously.

[0015] Furthermore, when the network is established, at least one transmission time slot is allocated to each node, and a spare time slot is reserved. When a node needs communication resources exceeding the number of currently allocated time slots, it actively requests additional time slots from the master node. The master node dynamically allocates the spare time slots according to the request, and reclaims the allocated additional time slots after the node finishes communication or times out.

[0016] Furthermore, when the master node performs dynamic time slot allocation, it uses the system throughput as the allocation standard.

[0017] Furthermore, the system employs a shortest path algorithm based on wireless link throughput as a metric for route construction.

[0018] On the other hand, the present invention provides a self-organizing network method applied to the above-mentioned system, comprising the following steps:

[0019] S1: Network initialization. The master node generates access information according to the configuration and broadcasts it. The access information includes the slave node number, the corresponding transmission time slot number, and the initial value of the timer for network startup.

[0020] S2: Access from a slave node. After powering on, the slave node enters the receiving state, listens for and receives the access information or other access information relayed by other slave nodes, calculates its own transmission time slot number based on the frame content, and completes network access and time synchronization.

[0021] S3: Runtime synchronization. Each node broadcasts a beacon frame carrying a local timing value in its own transmission time slot and receives beacon frames in the transmission time slots of other nodes to update its local time counter, thus maintaining network-wide synchronization.

[0022] S4: Data communication, where nodes send service data within their allocated transmission time slots;

[0023] S5: Dynamic channel management. During the dedicated frequency sweeping time slot of the superframe, all nodes perform channel quality measurement and evaluation. The results are reported from the nodes to the master node. The master node makes decisions and broadcasts frequency hopping instructions when necessary, leading the entire network to switch to a better channel.

[0024] Furthermore, in the above method, when each node transmits data within its own transmission time slot, the transmission time is advanced by a protection time calculated based on the maximum communication distance to compensate for transmission delay.

[0025] Furthermore, in step S5, the channel quality assessment includes: each node recording the RSSI value of each channel, performing long-term statistics and sorting to identify the channels with the least and greatest interference; the master node comprehensively evaluates the network-wide assessment results and selects the channel with the least interference as the handover target.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] This invention utilizes the periodic broadcasting of beacon frames carrying local timestamps by each node and mutual calibration using the received beacon frames. Even in multi-hop environments, it effectively suppresses the accumulation of synchronization errors and ensures the stability of the TDMA time slot structure. Through dedicated frequency sweeping time slots and a centralized decision-making mechanism by the master node, it achieves proactive perception of the working environment and adaptive frequency hopping. The entire network can collaboratively avoid strong interference channels, significantly improving the system's robustness and communication quality. It adopts a "transmit time slot + spare time slot" allocation strategy and supports dynamic application and release on demand. It introduces a transmission advance mechanism based on the maximum communication distance to compensate for signal propagation time at the transmitting end, fundamentally avoiding inter-slot interference caused by time delay in multi-hop, large-scale networks and ensuring the strictness of TDMA time slot boundaries. Attached Figure Description

[0028] Figure 1 This is a flowchart of the self-organizing network method of the present invention;

[0029] Figure 2 This is a schematic diagram of the self-organizing network system topology of the present invention;

[0030] Figure 3 This is a schematic diagram of the superframe structure and frequency sweep time slot of the present invention.

[0031] In the diagram: 1. Master node; 2. Slave node; 3. Superframe; 4. Transmit time slot; 5. Sweep time slot; 6. Spare time slot. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Please see Figure 1-3 This invention provides a TDMA-based self-organizing network system, comprising:

[0034] The network consists of a master node 1 and several slave nodes 2. The master node 1 is responsible for network initialization, time slot allocation, and channel management. The slave nodes 2 can be fixed nodes or mobile nodes.

[0035] Both master node 1 and each slave node 2 are equipped with a high-precision timer / counter (such as a TCXO temperature-compensated crystal oscillator) to define a uniform time slot length.

[0036] The system defines a superframe 3 structure containing several time slots, with each node being allocated at least one dedicated transmission time slot; assuming a time slot duration of 1024us, a superframe 3 defines 64 time slots, and the length of a superframe 3 is 1024us * 64, or 65536us.

[0037] The master node 1 is used to generate and broadcast access information containing the slave node 2 number and its assigned transmission time slot number and network timing initial value, and to manage channel switching as a network controller;

[0038] Master node 1 initializes the network and generates an access information broadcast frame, which includes a list of slave nodes 2, the corresponding time slot number allocation table, and the initial value of the timer for network startup.

[0039] The slave node 2 is used to listen for access information to join the network and communicate within the allocated transmission time slot; slave nodes 2 that cannot communicate directly with master node 1 forward the access information frame through the already connected slave node 2.

[0040] Each node broadcasts a beacon frame carrying the current value of its local time counter within its own transmission time slot 4; each node receives the beacon frame during non-transmission time slot 4 and calibrates its local time counter value based on the received time counter value and the estimated signal propagation delay value to achieve network-wide time synchronization.

[0041] After powering on, node 2 enters the receiving state. If it directly receives a broadcast frame from master node 1, it parses its own time slot number and sets a local timer. If it does not receive a signal from master node 2, it listens for relay frames forwarded by neighboring nodes and obtains network configuration through multi-hop methods to achieve "branching" or "cascaded access". The system determines the maximum signal propagation delay based on the maximum communication distance of the network. Each node ends its transmission at the start time of its own transmission time slot 4 before the maximum signal propagation delay to avoid the signal falling into adjacent transmission time slots 4 (e.g., node A sends a beacon frame (carrying a timestamp T1) at the start time T1 of its own time slot. Node B receives the beacon frame at time T2. Node B calculates the propagation delay according to the formula T2 = T1 + propagation delay + jitter, and modulates the end time of A's transmission accordingly. To prevent node B's signal from interfering with the node in the next time slot due to the propagation delay, node B must start transmitting before the theoretical end of the time slot by a "maximum protection time" (calculated based on the maximum diameter of the network).

[0042] Furthermore, the timer counter counts in microseconds; the system defines a timeout interrupt signal, which generates an interrupt when the timer counter counts to an integer multiple of the duration of a transmission time slot 4, and calculates and determines the time slot number in the superframe 3 corresponding to the current interrupt. This mechanism ensures that even without an external GPS signal, the node can maintain accurate TDMA communication for a long time by relying on the internal counter and initial synchronization information.

[0043] Furthermore, each superframe 3 defines a specific frequency sweeping time slot 5; within the frequency sweeping time slot 5, all nodes in the network switch to the receiving state, scan and record the interference strength information of the preset working channel; the slave node 2 reports the scanned interference strength information to the master node 1; the master node 1 determines whether to switch the working channel based on the interference strength information reported by itself and the slave node 2; when it is determined that frequency hopping is required, the master node 1 generates and broadcasts a frequency hopping command, which includes the target channel number and the switching execution time; the system reserves at least several superframe 3 delay times for multi-hop transmission in the network to ensure that all network nodes switch to the target channel synchronously.

[0044] In a specific frequency sweeping time slot 5 of superframe 3, all nodes stop transmitting data, switch to receive mode, scan multiple preset working channels, record RSSI values, and perform long-term statistical sorting.

[0045] The interference intensity information is reported from node 2 to master node 1;

[0046] Master Node 1 integrates data from the entire network. If it finds that the current channel interference exceeds the threshold, it selects the channel with the least interference as the target channel. Master Node 1 broadcasts a frequency hopping command (including the target channel number and the switching time) and reserves sufficient multi-hop transmission time (e.g., 3-5 superframes) to ensure that all nodes in the network (including nodes at the end of the multi-hop) receive the command and switch synchronously, thus avoiding network fragmentation.

[0047] Furthermore, when the network is established, at least one transmission time slot 4 is allocated to each node, and a spare time slot 6 is reserved. When a node needs communication resources exceeding the currently allocated number of time slots, it actively requests additional time slots from the master node 1. The master node 1 dynamically allocates the spare time slots 6 according to the request, and reclaims the allocated additional time slots after the node's communication ends or times out.

[0048] Furthermore, when the master node 1 performs dynamic time slot allocation, it uses the system throughput as the allocation standard.

[0049] During system initialization, a fixed transmission time slot of 4 is allocated to each node for information transmission.

[0050] When a node (such as a video surveillance node) needs to transmit a large amount of data, it sends a time slot request to the master node 1.

[0051] Master Node 1 assesses the current network load and system throughput. If resources allow, it allocates an additional time slot from "Reserved Spare Time Slot 6" to the node. After the service ends, Master Node 1 reclaims the time slot for use by other nodes.

[0052] Furthermore, the system employs a shortest path algorithm based on wireless link throughput as a metric for route construction; from node 2, links with high throughput and low error rate are preferentially selected as the main path, thereby improving overall network efficiency.

[0053] On the other hand, the present invention provides a self-organizing network method applied to the above-mentioned system, comprising the following steps:

[0054] S1: Network initialization. Master node 1 generates and broadcasts an access information broadcast frame according to the configuration. The broadcast frame includes the slave node 2 number, the corresponding transmission time slot 4, and the initial value of the timer for network startup.

[0055] S2: Access from node 2. After node 2 is powered on, it enters the receiving state, listens for and receives the access information broadcast frame or its relay frame, calculates its own transmission time slot number based on the frame content, and completes network access and time synchronization.

[0056] S3: Runtime synchronization. Each node broadcasts a beacon frame carrying a local timing value in its own transmission time slot and receives beacon frames in transmission time slot 4 of other nodes to update its local time counter and maintain network synchronization.

[0057] S4: Data communication, the node sends service data within the allocated transmission time slot 4;

[0058] S5: Dynamic channel management. Within the dedicated frequency sweep time slot 5 of superframe 3, all nodes perform channel quality measurement and evaluation, and report the results from node 2 to master node 1. Master node 1 makes decisions and broadcasts frequency hopping instructions when necessary, leading the entire network to switch to a better channel.

[0059] Furthermore, in the above method, when each node transmits data within its own transmission time slot 4, the transmission time is advanced by a protection time calculated based on the maximum communication distance to compensate for transmission delay.

[0060] Furthermore, in step S5, the channel quality assessment includes: each node recording the RSSI value of each channel, performing long-term statistics and sorting to identify the channels with the least and greatest interference; the master node 1 comprehensively evaluates the network-wide assessment results and selects the channel with the least interference as the handover target.

[0061] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A self-organizing network system based on TDMA, characterized in that, include: The master node (1) and several slave nodes (2); The master node (1) and each slave node (2) are equipped with a high-precision timer counter to define a uniform time slot length; The system defines a superframe (3) structure containing several time slots, and each node is assigned at least one dedicated transmission time slot (4). The master node (1) is used to generate and broadcast access information containing the slave node (2) number and its assigned transmission time slot number and network timing initial value, and to manage channel switching as a network controller; The slave node (2) is used to listen for access information to join the network and communicate within the allocated transmission time slot (4); the slave node (2) that cannot communicate directly with the master node (1) forwards the access information through the slave node (2) that has already joined; Each node broadcasts a beacon frame carrying the current value of its local time counter within its own transmission time slot (4); each node receives the beacon frame in the non-transmission time slot (4) and calibrates the local time counter value based on the received time counter value and the estimated signal propagation delay value to achieve network-wide time synchronization; the system determines the maximum signal propagation delay based on the maximum communication distance of the network, and each node ends transmission ahead of the maximum signal propagation delay at the start time of its own transmission time slot (4) to avoid the signal falling into the adjacent transmission time slot (4).

2. The self-organizing network system based on TDMA according to claim 1, characterized in that, The timer counter counts in microseconds; the system defines a timeout interrupt signal, which generates an interrupt when the timer counter counts to an integer multiple of the duration of a time slot, and determines the time slot number in the superframe (3) corresponding to the current interrupt by calculation.

3. The self-organizing network system based on TDMA according to claim 1, characterized in that, Each superframe (3) defines a specific frequency sweeping time slot (5); within the frequency sweeping time slot (5), all nodes in the network switch to the receiving state, scan and record the interference intensity information of the preset working channel; the slave node (2) reports the scanned interference intensity information to the master node (1); the master node (1) determines whether to switch the working channel based on the interference intensity information reported by itself and the slave node (2); when it is determined that frequency hopping is required, the master node (1) generates and broadcasts a frequency hopping instruction, which includes the target channel number and the switching execution time; the system reserves at least several superframes (3) of delay time for multi-hop transmission in the network to ensure that all network nodes switch to the target channel synchronously.

4. The self-organizing network system based on TDMA according to claim 1, characterized in that, When the network is established, at least one transmission time slot (4) is allocated to each node and a spare time slot (6) is reserved. When a node needs communication resources beyond the number of currently allocated time slots, it actively requests additional time slots from the master node (1). The master node (1) dynamically allocates the spare time slots (6) according to the request and reclaims the allocated additional time slots after the node's communication ends or times out.

5. A self-organizing network system based on TDMA according to claim 4, characterized in that, When the master node (1) performs dynamic time slot allocation, the system throughput is used as the allocation standard.

6. A self-organizing network system based on TDMA according to claim 1, characterized in that, The system uses a shortest path algorithm based on wireless link throughput as a metric for route construction.

7. A self-organizing network method based on the system described in any one of claims 1-6, characterized in that, Includes the following steps: S1: Network initialization, the master node (1) generates access information according to the configuration and broadcasts it. The access information includes the slave node (2) number, the corresponding transmission time slot number and the initial value of the timer for network startup; S2: Access from node (2), after node (2) is powered on, it enters the receiving state, listens for and receives the access information or other access information relayed by node (2), calculates its own transmission time slot number according to the frame content, and completes network access and time synchronization; S3: Runtime synchronization: Each node broadcasts a beacon frame carrying a local timing value in its own transmission time slot (4), and receives beacon frames in the transmission time slot (4) of other nodes to update the local time counter and maintain network synchronization. S4: Data communication, the node sends service data within the allocated transmission time slot (4); S5: Dynamic channel management. In the dedicated frequency sweeping time slot (5) of the superframe (3), all nodes perform channel quality measurement and evaluation, and report the results from node (2) to the master node (1). The master node (1) makes a decision and broadcasts frequency hopping instructions when necessary, leading the entire network to switch to a better channel.

8. The self-organizing network method according to claim 7, characterized in that, When each node sends data within its own transmission time slot, it advances the transmission time by a protection time calculated based on the maximum communication distance to compensate for transmission delay.

9. The self-organizing network method according to claim 7, characterized in that, In step S5, the channel quality assessment includes: each node records the RSSI value of each channel, performs long-term statistics and sorts them to identify the channels with the least and greatest interference; the master node (1) integrates the network-wide assessment results and selects the channel with the least interference as the handover target.

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