Underground space wireless ad hoc network time service network

Abstract

The invention provides an underground space wireless ad hoc network time service network, and belongs to the technical field of time synchronization. Aiming at the characteristics that underground space is narrow, long and shielded and wireless signal propagation distance is limited, a multi-layer, heterogeneous and multi-node network architecture is adopted, function layering is carried out on constituent units of a time synchronization network according to different node types, and the constituent units are divided into time reference nodes, dynamic center nodes and synchronization nodes; the network architecture also adopts a layered architecture of a dynamic center network and a time synchronization subnetwork; the underground space nodes adopt a Mesh wireless ad hoc network, so that the requirements of real-time movement and dynamic networking of the nodes can be met; according to the time service network, a clock coarse adjustment and fine adjustment mode is adopted, evaluation of a dynamic center network node state and self-adaptive updating of a time reference are achieved through node state monitoring, the problem of rapid maneuvering establishment and maintenance of the underground space network time reference can be solved, and the ductility and robustness of the time service network are improved.

Description

Technical Field

[0001] The invention relates to the technical field of time synchronization, and in particular to an underground space wireless self-organizing network timing network. Background Art

[0002] The underground space environment is generally composed of walls and corridors, which are narrow, deep, shielded by walls, and cannot be reached by satellite signals. In actual production and life applications, in order to ensure high-quality communication and navigation services, accurate time synchronization between devices is often required. Existing network time systems and methods often have a series of problems such as difficulty in laying out optical fiber and coaxial cables, low service coverage and poor scalability due to complex environments, and inability to guarantee normal timing services when links or nodes are damaged. Summary of the invention

[0003] In view of this, the present invention proposes an underground space wireless ad hoc timing network, which is used to realize the flexible and rapid establishment and maintenance of a time reference network in an underground space environment, thereby improving the scalability of the timing network.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] An underground space wireless self-organizing network timing network, comprising a time reference node, a dynamic center node and a synchronization node;

[0006] The time reference node is equipped with a high-performance atomic clock and satellite timing module and is deployed on the ground or at the entrance of a cave to provide a time reference for the entire network.

[0007] The dynamic central node is equipped with a high-performance crystal oscillator clock and has high-precision time distribution capabilities. It is deployed in underground space. The dynamic central nodes form a dynamic central network of the timing network through high-precision time comparison with each other, jointly establish and maintain the time base, and provide time base services to the entire network.

[0008] The synchronization nodes are deployed in each underground space in a clustered topology to form a time synchronization subnet. They do not have high-precision timekeeping capabilities and do not participate in the establishment of the time reference of the timing network. They only obtain time source information from the dynamic central node to perform time synchronization. The specific method is as follows:

[0009] (1) The time synchronization subnet establishes links with multiple dynamic central nodes to obtain information from multiple time sources;

[0010] (2) Calculate the average of the clock deviation values ​​of each dynamic central node that establishes a link with the time synchronization subnet to obtain the reference clock correction value, which provides a coarse clock adjustment value for the time synchronization subnet;

[0011] (3) The time synchronization subnet selects the nearest dynamic central node by default to provide the fine clock adjustment. When the difference between the coarse clock adjustment and the fine clock adjustment is greater than a threshold, the time base is updated.

[0012] Compared with the background technology, the present invention has the following advantages:

[0013] (1) The multi-layer network structure proposed in the present invention combines the advantages of each single-layer network, improves the coverage and scalability of the timing network, and is more suitable for the narrow and long underground space.

[0014] (2) The present invention proposes a coarse adjustment + fine adjustment of clock deviation and an adaptive update mechanism of network time reference to solve the problem of damage to the time reference network caused by abnormal node status and improve the robustness of the timing network. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural diagram of an underground space wireless self-organizing network timing network in an embodiment of the present invention.

[0016] Figure 2 yes Figure 1 Flowchart of adaptive update of time base in time synchronization subnet. DETAILED DESCRIPTION

[0017] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0018] like Figure 1 As shown, an underground wireless self-organizing network timing network is designed. In view of the narrow and long underground space and the limited propagation distance of wireless signals, the components of the time synchronization network are functionally layered according to the different node types, and divided into three categories: time reference nodes, dynamic central nodes and synchronization nodes. Wireless communication signals are used between nodes at all levels to achieve connection and transmission of time information. The network architecture also adopts a layered architecture of dynamic central network and time synchronization subnet; wherein:

[0019] The time reference node is equipped with a high-performance atomic clock and satellite timing module, and has high-precision time distribution capabilities. It can be deployed on the ground or at the entrance of a cave to provide a time reference for the entire network.

[0020] The dynamic central node is equipped with a high-performance crystal oscillator clock and has high-precision time distribution capabilities. It can be deployed in underground spaces. The dynamic central nodes form a dynamic central network of the timing network through high-precision time comparison with each other, jointly establish and maintain the time base, and provide time base services to the entire network.

[0021] The synchronization nodes are deployed in each underground space in a clustered topology to form a time synchronization subnet. They do not have high-precision timekeeping capabilities and do not participate in the establishment of the time reference of the timing network. They only obtain time synchronization information from the dynamic central node through time comparison and other methods.

[0022] The timing network is established using Mesh wireless self-organizing networks. Each node can not only move freely but also has the functions of a router and a host. It can quickly deploy adaptive networking without relying on pre-existing network infrastructure and connect to each other through multi-hop transmission. Each node has multiple connection channels and dynamically creates new links to connect to other nodes, forming a network with distributed self-organizing networking capabilities.

[0023] To ensure the accuracy of timing services and the robustness of the timing network, the time synchronization subnet achieves time synchronization by combining coarse synchronization with fine synchronization. The specific methods are as follows:

[0024] (1) The time synchronization subnet can generally establish links with multiple dynamic central nodes and obtain multiple synchronization source information.

[0025] (2) Calculate the average of the clock deviation values ​​of each dynamic central node that establishes a link with the time synchronization subnet to obtain the reference clock adjustment value, and provide a coarse clock adjustment value for the time synchronization subnet.

[0026] (3) The time synchronization subnet selects the nearest dynamic central node by default to provide the subnet with the fine clock adjustment. When the difference between the coarse clock adjustment and the fine clock adjustment is greater than a threshold, the time reference update mechanism is started.

[0027] Taking the time synchronization device with a hardware sampling rate of 250MHz as an example, its time resolution is 4ns. Assume that there are 5 dynamic central nodes connected to the time synchronization subnet A, and the reference clock adjustment amount obtained by average calculation is i. Through two-way time comparison, the dynamic central node B closest to subnet A obtains the clock adjustment amount j for A. When the difference between i and j is less than 100ns, it is considered that the timing network is working normally, and the fine clock adjustment amount is selected as the clock adjustment value of the time synchronization subnet A; when the difference between i and j is greater than 100ns, it is considered that the dynamic central node may be abnormal, and the coarse clock adjustment amount is selected as the clock adjustment value of the time synchronization subnet A and the time reference update mechanism is started.

[0028] Figure 2 This is the time base adaptive update flow chart. The network base node realizes real-time status monitoring through data transmission with the dynamic central node, and evaluates the timekeeping performance of the dynamic central node by means of two-way time comparison and time-frequency signal tracing, and determines whether to trigger the update of the dynamic central node to which the synchronization node cluster belongs. Figure 1Taking the central location time synchronization subnet as an example, when the state of the dynamic central node to which the time synchronization subnet belongs is monitored to be abnormal, the time base adaptive update mechanism is started to adaptively update the time base of the time synchronization subnet.

[0029] Aiming at the problem of timely updating of abnormal status of dynamic central nodes, the present invention proposes a mechanism for fast response and automatic update of dynamic central nodes to abnormal status. In order to ensure the stability and accuracy of the time base, the dynamic central node that maintains the base must be monitored in real time, and the timekeeping performance of the dynamic central node is evaluated by means of time-frequency tracing and timing. Once an abnormal situation directly affecting the timekeeping performance occurs, such as the clock frequency exceeding the threshold or the working state being abnormal, the time base update of the synchronization node cluster to which the node belongs is immediately triggered.

[0030] In summary, the present invention can provide absolute time reference service and relative time reference service according to the underground space node situation and task requirements. After the network time reference is established, the evaluation of the dynamic center network node status and the adaptive update of the time reference are realized through node status monitoring. In addition, the time reference adaptive update method based on node status detection solves the technical problem of damaged timing service caused by abnormal node status, and improves the robustness of the timing network.

Claims

1. An underground space wireless ad hoc timing network, characterized in that: Including time reference node, dynamic center node and synchronization node; The time reference node is equipped with a high-performance atomic clock and satellite timing module and is deployed on the ground or at the entrance of a cave to provide a time reference for the entire network. The dynamic central node is equipped with a high-performance crystal oscillator clock and has high-precision time distribution capabilities. It is deployed in underground space. The dynamic central nodes form a dynamic central network of the timing network through high-precision time comparison with each other, jointly establish and maintain the time base, and provide time base services to the entire network. The synchronization nodes are deployed in each underground space in a clustered topology to form a time synchronization subnet. They do not have high-precision timekeeping capabilities and do not participate in the establishment of the time reference of the timing network. They only obtain time source information from the dynamic central node to perform time synchronization. The specific method is as follows: (1) The time synchronization subnet establishes links with multiple dynamic central nodes to obtain information from multiple time sources; (2) Calculate the average of the clock deviation values ​​of each dynamic central node that establishes a link with the time synchronization subnet to obtain the reference clock correction value, which provides a coarse clock adjustment value for the time synchronization subnet; (3) The time synchronization subnet selects the nearest dynamic central node by default to provide the fine clock adjustment. When the difference between the coarse clock adjustment and the fine clock adjustment is greater than a threshold, the time base is updated.

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