Monitoring information transmission topology of high voltage transmission line

High-voltage transmission lines are long and may cross areas without mobile networks. The transmission tower is equipped with monitoring equipment. The monitoring information of the transmission tower located in the non-mobile network area is difficult to return. What topology is used for transmission is an important engineering problem. When the number of transmission towers passing through the area without a mobile network is large, the traditional information transmission topology design method based on engineer experience cannot be applied. Aiming at the urgent demand of monitoring information transmission of high-voltage transmission lines in strip-shaped non-mobile network areas, an information transmission topology design method based on a unidirectional layered search algorithm is proposed. Firstly, the objective function and constraint function are designed. Then the unidirectional layered search algorithm is used to realize the planning of communication nodes and complete the design of the information transmission topology. The simulation results show that compared with the traditional information transmission topology design method, the design method proposed in this paper is suitable for complex networks, and the transmission delay of the designed information transmission topology is small.


Introduction
At present, China's low population density areas are still widely distributed.Considering the cost of operating manpower and material resources of mobile networks, the coverage of mobile networks in areas with low population density is not high, which cannot meet the needs of video surveillance information transmission [1][2].The high-voltage transmission line may pass through the area without a mobile network for a long time [3][4].The monitoring equipment is arranged on the transmission tower.The monitoring information of the transmission tower located in the area without a mobile network is difficult to return.What topology is used for transmission is an important engineering problem.
The hierarchical search algorithm can be used to design the monitoring information transmission topology of high-voltage transmission lines.Cagigas and Julio [5] applied the hierarchical search algorithm to path planning, the new hierarchical extended D* algorithm, optimality, and particularly low computational time.Jing et al. [6] applied the hierarchical search algorithm to millimeter-wave communication to solve the problem that the exhaustive search algorithm cannot accurately obtain narrow beams in the calculation.Sebastian et al. [7] applied the hierarchical search algorithm to video compression and used three different hierarchical search methods to resample the original image.The simulation results show that the algorithm has better PSNR performance under the premise of reducing complexity.
The existing hierarchical search algorithms are mostly used in scenarios such as path planning, millimeter-wave communication, and video compression and are not applied to strip-free mobile network scenarios [8][9][10][11][12].This paper creatively proposes an information transmission topology design method based on a unidirectional layered search algorithm.Compared with the traditional information transmission topology design method, the design method proposed in this paper is suitable for complex networks, and the designed information transmission topology has a low transmission delay.The rest of this letter is organized as follows.In Section II, we briefly introduce the information transmission topology design method based on the unidirectional layered search algorithm.Section III we introduce the principle of the unidirectional layered search algorithm.Simulation results and conclusion are presented in Section IV and Section V, respectively.

Design method of information transmission topology structure
The process of the high-voltage transmission line monitoring information transmission topology design method studied in this paper is shown in Figure 1.First, the objective and constraint functions need to be designed.Then, a unidirectional layered search algorithm is used to plan the communication nodes and complete the design of the information transmission topology structure.The purpose of the information transmission topology designed in this paper is to make the path of information transmission shortest.The objective function can be described as follows: where N is the number of monitoring nodes, i R is the distance from each node to the network area node.
According to the basic parameters of the strip without mobile network area and hardware communication equipment, the constraints are determined: the maximum data carrying capacity of a single line, the maximum number of connections of a single node, and the maximum distance of node transmission.

Maximum data carrying capacity of a single line
The maximum data-carrying capacity of a single line is the data-carrying capacity of a single wireless communication link when nodes transmit data with nodes under actual engineering conditions.
where _ max data N is the maximum data carrying capacity of a single line under actual engineering conditions, B is the bandwidth of bridge equipment, and p is the ratio of the actual engineering value and the calibration value.

The maximum number of connections per node
The maximum number of connections of a single node is the maximum number of bridge devices that can be connected to the monitoring node.This article defaults that all nodes use the same type of bridge equipment, and the performance is only a small gap between the factory batches.
where data N is the node data flow.

The farthest transmission distance of the node
The farthest transmission distance of the node is the farthest transmission distance S of the bridge equipment at the node.The transmission distance here refers specifically to the transmission distance that satisfies the signal strength of the transmission information in the actual project.The general engineering experience is set to 60 % of the calibration transmission distance of the bridge equipment.

Unidirectional layered search algorithm
Firstly, the communication conditions between the two nodes are determined according to the constraints set in previous section so as to stratify the one-way communication link.Then, the number of bridges on the line is determined according to the hierarchical relationship of the one-way communication link.Finally, the bridge data flow of each node is searched to determine the placement position of bridge nodes and realize planning of communication nodes.
In the scenario of a bar-shaped non-mobile network area, the monitoring node of the high-voltage transmission line can determine the farthest wireless communication distance S of the bridge equipment by the constraint conditions.The distance between the two adjacent communication nodes is near S , the communication conditions between the two nodes can be defined as: where i and j are two node numbers, respectively.The single end of the path can be divided into k layers, and the node i belongs to the i k layer because the last node j in the i k layer can receive the signal of any node in the ( 1) i k  layer.We equivalently transmit the signal according to the node to the layer and place a bridge at node j that can receive the slave signal of any node in the ( 1) i k  layer.The hierarchical relationship of the unidirectional communication link can be described as: According to the hierarchical relationship of a one-way communication link, the corresponding relationship of each node bridge is determined as follows: it is known that the receiving bridge receives at most m signals of the transmitting bridge.If the i k layer receives the signal of the ( 1) where X is the number of nodes in the (  1)   i k  layer, and a total of main N bridges need to be added to the line: Since the data flow of each node is data N , and , each layer is moved from the right node to the left according to the position of the bridge, and the bridge data flow of each node is searched until it is evenly distributed.If , a bridge is added where the data flow exceeds the standard.
For the two-terminal communication link, there will be n communication nodes at both ends, and the two-terminal communication is equivalent to two single-ended communication. ) bridge needs to be added.

Simulation results and analysis
The experimental simulation uses a 300 MHz bandwidth bridge device, and the farthest distance of the bridge is 3 km.When p is 60%, the maximum data carrying capacity of a single line under actual engineering conditions is 180 MHz.The length of the non-mobile network area is set to 15 km, and the number of monitoring nodes is set to 38, where 1 node and 38 nodes have mobile network signals.The experiment uses H.264 video compression format, the camera pixel is 8 million, and the output bit rate is up to 15 Mbps. 5 Mbps is reserved as the margin bandwidth, so each camera has a bandwidth of 20 MHz.
In the above experimental environment, the monitoring information transmission topology of highvoltage transmission lines with 25, 38, and 50 nodes is simulated, as shown in Figure 2, Figure 3 and Figure 4 below.It can be seen from the above three graphs that the information transmission topology design method based on the unidirectional layered search algorithm proposed in this paper is suitable for scenarios with a large number of monitoring nodes and complex networks.Taking Figure 3 as an example, it can be seen that the node monitoring information in the strip-shaped non-mobile network area is transmitted to the node where the signal exists.There are 66 path edges that need to be passed.The total length of the transmission path is 165 km, and the transmission delay is 128 ms, which can efficiently return the monitoring information in complex network scenarios.

Conclusion
Aiming at the problem that the traditional information transmission topology design method based on engineer experience cannot be applied when the number of transmission towers passing through the area without a mobile network is large, this paper proposes an information transmission topology design method based on a one-way hierarchical search algorithm.The experimental simulation proves that the design method is suitable for a scene with a large number of monitoring nodes and complex networks and can efficiently return the monitoring information in the complex network scene.
In future work, the one-way hierarchical search algorithm will be further studied, and the shortest path algorithm and reinforcement learning will be integrated into the information transmission topology design method to improve the universality of the method further.

Figure 1 .
Figure 1.Topology design method of monitoring information transmission for high voltage transmission line

Figure 2 .Figure 3 .Figure 4 .
Figure 2. Topology of monitoring information transmission for high voltage transmission lines with 25 nodes