# An Extraction Method of Volleyball Spiking Trajectory and Teaching Based on Wireless Sensor Network

Authors: Meifang Wang; Zhange Liang
Journal: Security and Communication Networks
 (2021)

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## Abstract

It is helpful to analyze volleyball spiking technology and improve spiking quality to extract volleyball spiking trajectory. This article studies the extraction method and teaching method of volleyball spiking trajectory based on a wireless sensor network. The acceleration sensor and gyroscope sensor are used to collect the spiking action state information of volleyball players. The collected information is transmitted to the PC terminal through the wireless sensor network, including physical layer, data link layer, network layer, transmission layer, and application layer, using the LEACH clustering routing protocol algorithm. In the PC terminal, the feedback filtering method is used to preprocess the received information and calculate the integral of each sensor node’s acceleration, connecting the spatial coordinates of each time to obtain the upper limb trajectory in three-dimensional space and realize the trajectory extraction of volleyball spike action. The experimental results show that the position error is less than 0.01 m and the speed error is less than 0.15 m/s. The application of this method in volleyball teaching can effectively improve the quality of volleyball teaching.


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## Body

## 1. Introduction

With the rapid development of microelectromechanical system, computers, communication, automatic control, and artificial intelligence, a new intelligent information monitoring network, wireless sensor networks (WSN), has emerged. Wireless sensor network puts a large number of microsensor nodes with communication and computing capabilities into the monitoring area to sense, collect, and process the information of monitoring objects in real time. A wireless sensor network is a large-scale and resource-constrained fully distributed system [1]. Sensor nodes integrate sensor detection and analysis technology, low-power design, and wireless communication technology. Wireless sensor network nodes usually use self-organization, adaptive, and multihop cooperation communication mode to transmit relevant data information to the base station node or sink node. Due to the perfect integration of physical information and logical world information in nature [2], and compared with traditional wireless networks, WSN have many advantages, such as high-precision monitoring of distributed processing, large-scale deployment, and application in many fields, which have attracted wide attention of military departments, industrial fields, scientific research institutions, and academic circles in the world.With the vigorous development of sports, volleyball competition has gradually formed the characteristics of high-intensity competition with complete speed and height, the integration of technology and body, and the unity of will, intelligence, and technology. Volleyball competition is becoming more and more fierce in space and time so that volleyball players should not only master a variety of coordination techniques [3] but also have the ability to adapt to circumstances. For example, the strength of the upper limbs will suddenly increase with a strong smash. In the actual volleyball competition, if the players lack the ability of self-protection and adaptability, the wrist force is too large when making the volleyball spiking action, it is easy to cause the problem of upper limb joint movement. The trajectory extraction technology of volleyball spike action is introduced, and real-time analysis of spike action state information is carried out to reduce the loss rate of the game and improve the quality of the game [4]. Volleyball spiking trajectory extraction has become an important factor restricting the technical level of volleyball, which has attracted the attention of many experts and scholars.There are a lot of articles on the trajectory extraction of volleyball spiking, and some relative studies have been conducted. The study in [5] first gives the histogram model of the lower and upper limb action of the strong smash, adaptively updates the upper limb movement model, eliminates the cumulative variance in the continuous movement, and extracts the characteristics of the lower and upper limb movement of the strong smash in a volleyball match. This method has high efficiency of feature extraction, but when the current method is used to extract the upper limb movement features of the consecutive take-off, it is unable to describe the upper limb movement contour of the strong spike in volleyball competition, and there is a big error in the upper limb movement feature extraction of the strong spike in volleyball competition. In [6], the hard-driven spike action is firstly decomposed into action video clips with different lengths, and a classifier is designed to separate the lower and upper limb action boundary box from each frame image and give the upper limb action direction in each image. Based on this, the lower and upper limb action features of a hard-driven spike in a volleyball match are extracted. This method has high efficiency of feature extraction, but it has the problem of poor stability.At present, how to make a trade-off between the state tracking accuracy and the network energy cost is a hot topic in the discussion of volleyball spiking trajectory extraction based on wireless sensor network. It is required to improve the extraction accuracy as much as possible, save the node energy cost and extend the network life cycle. For example, the node wake-up mechanism is added to the extraction algorithm, and the sensor nodes in the monitoring area are in a periodic sleep state. Only when the node detects the event, will it wake up through the event trigger mode, reducing the node energy cost. Users can query and access the number, identity, and status of targets in any monitoring area. At the same time, there are little research on target region query and trajectory tracking. There are many studies on motion trajectory extraction at home and abroad. In [7], the Kalman filter, an approximate optimal method, is proposed, which can be used to deal with many kinds of tracking problems. The algorithm can obtain a more accurate estimation of the system state by recursively fusing the measured values of noisy data. The algorithm has strong tracking accuracy, but it is only used in single target tracking, and the computational overhead is large. In [8], a tree-based target tracking algorithm is proposed to track and monitor moving targets in the network. The algorithm is simple to implement, the routing structure is relatively stable, and the node computing and storage overhead is small. However, all nodes in the network have to work all the time, so the energy consumption is large and the tracking accuracy is not high. In [9], an algorithm based on cluster network structure is proposed. In order to detect the target information, all the network nodes form a boundary node to construct a dynamic tracking cluster. The nodes at the boundary may be divided into multiple clusters. The algorithm has high tracking accuracy and strong real-time performance, which can effectively reduce the calculation and communication overhead. However, when the trajectories of targets cross and meet frequently in the network, the dynamic tracking clusters will be synthesized and decomposed frequently, which will inevitably cause serious resource overhead and affect the system performance. In [10], an area tracking algorithm is proposed. The algorithm takes a continuous area as the monitoring target and has the characteristics of wide coverage, strong randomness, and being greatly affected by environmental factors. Compared with most traditional target tracking algorithms, it has strong real-time performance and stability and requires less energy cost. However, the algorithm takes fire monitoring, chemical gas leakage, radioactive material radiation, and other application scenarios and needs better physical protection for nodes. The number of nodes involved is large, which may increase the cost of the system.In this article, the method and teaching of trajectory extraction of volleyball spiking based on wireless sensor network is studied, and wireless sensor network is applied to extract volleyball spiking trajectory. The experimental results show that the method effectively extracts the trajectory of spiking action in volleyball, and the relevant strategies of applying the method to volleyball teaching are put forward.Our contribution is threefold:(1)
It is helpful to analyze volleyball spiking technology and improve spiking quality to extract volleyball spiking trajectory. This article studies the extraction method and teaching method of volleyball spiking trajectory based on wireless sensor network.(2)
In order to improve the operation efficiency, a feedback filtering method is proposed based on the signal characteristics of this link. This method uses the feedback idea of the heuristic filtering method, retains the core part of heuristic filtering, and makes great changes to the functions and operation methods of the two parts.(3)
The experimental results show that the position error is less than 0.01 m and the speed error is less than 0.15 m/s. The application of this method in volleyball teaching can effectively improve the quality of volleyball teaching.The remainder of this article is organized as follows. Section2 introduces the architecture of wireless sensor network and LEACH clustering routing protocol algorithm. Section 3 discusses the experiment analysis. Section 4 presents the conclusions of the study.


## 2. Materials and Methods

### 2.1. Architecture of Wireless Sensor Network

WSN usually include distributed sensor nodes, sink nodes, Internet or satellite networks, management nodes of data control center. The traditional working mode of wireless sensor network is to deploy a large number of sensor nodes in or near the monitoring object according to a certain distribution through aircraft throwing, shell firing, and manual layout and quickly form a wireless network through a similar ad hoc self-organization mode. Usually, sensor nodes act as both information collectors and routing links. After the sensor node collects information, it transmits the data to the sink node in the form of single hop or multihop in the form of mutual cooperation and sends it to the management node through the Internet, satellite, or other mobile communication networks [11]. The sink node is the relay processing center of wireless sensor network, also known as the base station node. It is the hub connecting the management node and common sensor node. It is responsible for sending data acquisition or routing execution commands to common sensor nodes in the region, receiving and fusing data sent by other sensor nodes, and then sending the fused data to the management node. Users use remote management nodes to process the fusion information so as to realize the resource configuration and monitoring management of wireless network.A typical sensor node is usually composed of several miniaturized embedded systems, which are generally composed of sensor unit module, processing unit, wireless communication unit, power supply unit, and other auxiliary optional function unit modules, such as mobile system, positioning system, and self-powered system. The structure of its hardware model is shown in Figure1.Figure 1
Hardware structure diagram of wireless sensor node.The sensor unit is composed of sensors and digital to analog conversion modules. According to different application requirements, different sensors are configured to sense and acquire data information in the monitoring area, such as temperature, humidity, pressure, and acoustic energy, and convert these analog signals into digital signals for data processing. Simultaneous interpreting and processing unit is the center of the whole sensor node, including processor and memory. The wireless communication unit is composed of a wireless communication module [12], which is responsible for data exchange with other sensor nodes, control information exchange, and wireless transceiver data collection; the power supply unit is responsible for the energy supply of the whole sensor node. Ordinary sensor nodes usually use microbatteries, while some important sensor nodes need a renewable power supply, such as the photoelectric conversion unit of the solar system.The system of wireless sensor network is composed of a bottom-up hierarchical structure, which is composed of network communication protocol, application support technology platform, and application support technology platform running through all layers. The specific hierarchical structure is shown in Figure2.Figure 2
Hierarchical structure diagram of the wireless sensor network system.In Figure2, the network communication protocol layer of wireless sensor network is composed of physical layer, data link layer, network layer, transmission layer, and application layer. The main functions of each layer are as follows:(1)
Physical layer: it is responsible for channel carrier, data encryption, modulation and demodulation, and signal receiving and transmitting tasks. The main goal of the design is to exchange a small amount of energy consumption for a larger link capacity, for example, using advanced radiofrequency transmission technologies, such as orthogonal frequency division multiplexing (OFDM), multiple-input multiple-output (MIMO), and ultrawideband (UWB).(2)
Data link layer: it is responsible for data framing, frame detection, media access, and error control. The design is mainly to ensure that the data transmitted by the physical layer are as correct as possible and can provide the correct data link for the network layer.(3)
Network layer: it is mainly responsible for route generation, selection, and maintenance, searching for the optimal path, transmitting data along this path according to multihop communication forwarding mode, and solving network communication congestion control.(4)
Transport layer: it is responsible for data flow transmission control, providing reliable and reasonable data transmission service for the application layer on the basis of network layer [13], which is an important part of ensuring communication service quality.(5)
Application layer: a series of application detection software can complete various specific value-added functions, such as positioning function, data query and sending function, and network management function.Wireless sensor network realizes topology control through data link layer and network type and ensures service quality by using transmission layer, network layer, and data link layer.


### 2.2. LEACH Clustering Routing Protocol Algorithm

LEACH touting protocol algorithm is a typical low-power adaptive routing protocol algorithm based on a hierarchical clustering structure. Its basic idea is to randomly select cluster head nodes in a circular way and distribute the energy load of the whole network equally to each sensor node. After the cluster head node receives the information of the member nodes in the cluster, the same data are processed by compression and fusion technology, which greatly reduces the amount of secondary transmission data of the cluster head node so as to reduce the energy consumption of the network and improve the overall life cycle of the network.The selection of cluster head node is determined by the total number of cluster head nodes and the number of known nodes selected as cluster heads under the optimal energy consumption calculated in the network. In order to ensure that each node has an equal number of times to be selected as the cluster head node, it is required that each node can be selected as the cluster head node once in the runningN/k round on average, so as to ensure the balance of network energy consumption [14], where Nrepresents the total number of sensor nodes and krepresents the total number of cluster head nodes. 0-1 random number is not selected as cluster head node in the N/k round, which is less than a certain threshold Pi; then, the node is selected as the cluster head node. The threshold setting is calculated by the following equation:(1)Pi=kN−k×r×modN/k,ci=1,0,ci=0.In equation (1), r represents the number of transmission rounds of nodes in the network. When node i is selected as the cluster head node in each N/k round, function C assigns it to 0. Otherwise, 1 indicates that node i is waiting to be selected as the cluster head node. In this equation, the k×r×modN/k part is the total number of selected cluster head nodes after calculating r round. In this equation, the threshold Pi actually represents the average probability that the current remaining nodes may be selected as cluster head nodes in every N/k round.The algorithm of LEACH is as follows:Step 1: each sensor node is selected as the cluster head node according to a certain probability equation rule.Step 2: the cluster head node sends the broadcast packet containing its own ID number to other member nodes in the network. Any member node receiving the broadcast packet calculates the distance between itself and the cluster head. The distance calculation is based on the similar GPS positioning system chip set in the node hardware to determine its own position or the distance between nodes can be judged by the signal attenuation strength of other noncluster head nodes received by the cluster head node.Step 3: these member nodes will join the nearest or weakest cluster according to the distance or signal attenuation strength between nodes.Step 4: the cluster head node equationtes time-driven events for each member node in the cluster, and then each member node communicates with the cluster head node according to different time slots in the MAC protocol in TDMA mode, which can reduce the channel blocking or conflict caused by simultaneous sending packets.Step 5: the cluster head node compresses or fuses the received data packets of the member nodes and finally sends them to the master node of the base station. In the stable phase of data transmission of each node in the cluster [15], the member node sends the data to the cluster head node when its corresponding time slot arrives, and other time slots enter the sleep state to save energy. After one round of operation, the whole network enters a new round of work cycle, reselects cluster heads, and circulates the above process.At the same time, in order to avoid the extra overhead caused by the frequent selection of cluster head, the stable phase of data transmission is generally much longer than the cluster establishment phase. Each data transmission phase is generally divided into multiple frame operations. In each frame, all member nodes will complete a data transmission process to the cluster head node, which reduces the energy consumption and improves the working efficiency of nodes in WSN.


### 2.3. Extraction of Volleyball Spiking Trajectory

#### 2.3.1. Feedback Filtering Method

Feedback filtering method is simplified from the heuristic filter. Heuristic filtering is called heuristic drift reduction (HDR). The core part of heuristic filtering is the attenuation function controller and integral controller, which complete the processing of feedback value and current value. The attenuation function controller mainly analyzes the previous value to determine the current state of the carrier, such as moving or stationary, and then reports the result to the integral controller. The main work of the integral controller is to compensate the current signal according to the analysis results of the attenuation controller. In the structure diagram, we can also see that before the gyroscope signal is compensated by the integral controller, a double low-pass filter is needed [16], which is to remove the high-frequency noise interference. The main work of the heuristic filter is to calculate the compensation factor I and feed it back to the signal. The calculation of attenuation controller and the integral controller is very large. In order to improve the operation efficiency, a feedback filtering method is proposed based on the signal characteristics of this link. This method uses the feedback idea of the heuristic filtering method, retains the core part of heuristic filtering, and makes great changes to the functions and operation methods of the two parts. The purpose is to reduce the calculation amount of the algorithm and ensure the filtering effect.The principle of the feedback filtering method is shown in Figure3.Figure 3
Schematic diagram of feedback filtering method.There are two important links in the feedback filtering method. One is how to calculate the current gain valueI in the feedback link, which is equivalent to the attenuation controller in heuristic filtering, but this link has been greatly simplified.The equation for gainIis as follows:(2)Ii=ai−1′Path,ai−1′≤ath,1,ai−1′>ath.In equation (2), Ii is the current gain obtained by calculation, ai−1 is the previous output value of the filter, ath is the set reference value, P is the adopted gain factor, P>0. From the equation, it can be seen that the value of I is between 0 and 1, and the larger the value of I is, the smaller the current gain is.The second is how to use this gain to update the current acceleration value so as to effectively filter the motion noise and the errors introduced by the coordinate conversion link and gravity compensation link [17]. The equation for updating the current acceleration value by direct multiplication is as follows:(3)ai′=Iiai,where ai′ is the current filtered value, Ii is the current gain, and ai is the signal value before filtering.


#### 2.3.2. Integral Acceleration Calculation

Because the collected data of the MEMS acceleration sensor are discrete, the sampling time interval of the sensor is set toΔt, and after iteration, the following results can be obtained:(4)vn=vn−1+an+an−12⋅Δtn>1,sn=sn−1+vn−1⋅Δt+14an+n−1⋅Δtn>1.In the above equation,vn is the instantaneous velocity at time tn, an is the acceleration at time tn, and sn is the accumulated displacement at time 0−tn.The output data of the MEMS acceleration sensor is acceleration inx, y, and z directions. According to the above equation, the instantaneous velocity of athletes' upper limbs in the direction of x, y, and z of acceleration sensor at time tn can be calculated, respectively. The equation is as follows:(5)vxn=vxn−1+axn+axn−12⋅Δtn>1,vyn=vyn−1+ayn+ayn−12⋅Δtn>1,vzn=vzn−1+azn+azn−12⋅Δtn>1.In the same way, the displacement equation of athletes' upper limbs along thex, y, and z directions of acceleration sensor at time tn can be obtained as follows:(6)sxn=sxn−1+vxn−1⋅Δt+14axn+axn−1⋅Δt,syn=syn−1+vyn−1⋅Δt+14ayn+ayn−1⋅Δt,szn=szn−1+vzn−1⋅Δt+14azn+azn−1⋅Δt.Then, the space position coordinate of the upper limb attn time is sxn,syn,szn, and the movement track of the upper limb in three-dimensional space can be obtained by connecting the space position coordinate points at each time.


#### 2.3.3. Filtering of Gravity Acceleration Component

The operator may turn over in the air when operating the gesture. At this time, the gravity acceleration will produce components [18, 19] on the x, y, and z axes of the acceleration sensor, and the acceleration on the z axis is no longer the gravity acceleration g. At this time, the acceleration integral calculation results will have serious errors. Before integral calculation, the component of gravity acceleration on the three axes of acceleration sensors x, y and z should be filtered.The components of gravity acceleration in each axis of the acceleration sensor can be calculated by the attitude matrix, and the quaternion parameter method is selected to calculate the attitude matrix. The transformation relationship between the absolute coordinate system and relative coordinate system can be expressed by quaternionQ, namely,(7)Q=q0+q1ib+q2jb+q3kb.The quaternion differential equation is as follows:(8)Q˙=12QW.The equation of matrix form is as follows:(9)q˙0q˙1q˙2q˙3=120−wx−wy−wzwx0wz−wywy−wz0wxwzwy−wx0q0q1q2q3.The above equation is the quaternion differential equation, wherewx, wy, and wz are the output components of the gyroscope.Through the differential equation, parametersq0, q1, q2, and q3 can be obtained. According to the attitude matrix, the components of g on each axis in the relative coordinate system can be obtained. The components gx, gy, and gz are as follows:(10)gxgygz=q02+q12−q22−q322q1q2−q0q32q1q3+q0q22q1q2+q0q3q02−q12+q22−q322q2q3−q0q12q1q3−q0q22q2q3+q0q1q02−q12−q22+q3200g.The actual acceleration of the upper limb in each direction can be obtained by subtracting the component of gravity acceleration on the axis from the measured acceleration before acceleration integral operation.The displacement of the upper limb in relative space in timeΔt is obtained by integral operation, and the displacement of the upper limb in absolute space is obtained by posture matrix [20]. The movement track of the upper limb in absolute space is obtained by iteration.


## 2.1. Architecture of Wireless Sensor Network

WSN usually include distributed sensor nodes, sink nodes, Internet or satellite networks, management nodes of data control center. The traditional working mode of wireless sensor network is to deploy a large number of sensor nodes in or near the monitoring object according to a certain distribution through aircraft throwing, shell firing, and manual layout and quickly form a wireless network through a similar ad hoc self-organization mode. Usually, sensor nodes act as both information collectors and routing links. After the sensor node collects information, it transmits the data to the sink node in the form of single hop or multihop in the form of mutual cooperation and sends it to the management node through the Internet, satellite, or other mobile communication networks [11]. The sink node is the relay processing center of wireless sensor network, also known as the base station node. It is the hub connecting the management node and common sensor node. It is responsible for sending data acquisition or routing execution commands to common sensor nodes in the region, receiving and fusing data sent by other sensor nodes, and then sending the fused data to the management node. Users use remote management nodes to process the fusion information so as to realize the resource configuration and monitoring management of wireless network.A typical sensor node is usually composed of several miniaturized embedded systems, which are generally composed of sensor unit module, processing unit, wireless communication unit, power supply unit, and other auxiliary optional function unit modules, such as mobile system, positioning system, and self-powered system. The structure of its hardware model is shown in Figure1.Figure 1
Hardware structure diagram of wireless sensor node.The sensor unit is composed of sensors and digital to analog conversion modules. According to different application requirements, different sensors are configured to sense and acquire data information in the monitoring area, such as temperature, humidity, pressure, and acoustic energy, and convert these analog signals into digital signals for data processing. Simultaneous interpreting and processing unit is the center of the whole sensor node, including processor and memory. The wireless communication unit is composed of a wireless communication module [12], which is responsible for data exchange with other sensor nodes, control information exchange, and wireless transceiver data collection; the power supply unit is responsible for the energy supply of the whole sensor node. Ordinary sensor nodes usually use microbatteries, while some important sensor nodes need a renewable power supply, such as the photoelectric conversion unit of the solar system.The system of wireless sensor network is composed of a bottom-up hierarchical structure, which is composed of network communication protocol, application support technology platform, and application support technology platform running through all layers. The specific hierarchical structure is shown in Figure2.Figure 2
Hierarchical structure diagram of the wireless sensor network system.In Figure2, the network communication protocol layer of wireless sensor network is composed of physical layer, data link layer, network layer, transmission layer, and application layer. The main functions of each layer are as follows:(1)
Physical layer: it is responsible for channel carrier, data encryption, modulation and demodulation, and signal receiving and transmitting tasks. The main goal of the design is to exchange a small amount of energy consumption for a larger link capacity, for example, using advanced radiofrequency transmission technologies, such as orthogonal frequency division multiplexing (OFDM), multiple-input multiple-output (MIMO), and ultrawideband (UWB).(2)
Data link layer: it is responsible for data framing, frame detection, media access, and error control. The design is mainly to ensure that the data transmitted by the physical layer are as correct as possible and can provide the correct data link for the network layer.(3)
Network layer: it is mainly responsible for route generation, selection, and maintenance, searching for the optimal path, transmitting data along this path according to multihop communication forwarding mode, and solving network communication congestion control.(4)
Transport layer: it is responsible for data flow transmission control, providing reliable and reasonable data transmission service for the application layer on the basis of network layer [13], which is an important part of ensuring communication service quality.(5)
Application layer: a series of application detection software can complete various specific value-added functions, such as positioning function, data query and sending function, and network management function.Wireless sensor network realizes topology control through data link layer and network type and ensures service quality by using transmission layer, network layer, and data link layer.


## 2.2. LEACH Clustering Routing Protocol Algorithm

LEACH touting protocol algorithm is a typical low-power adaptive routing protocol algorithm based on a hierarchical clustering structure. Its basic idea is to randomly select cluster head nodes in a circular way and distribute the energy load of the whole network equally to each sensor node. After the cluster head node receives the information of the member nodes in the cluster, the same data are processed by compression and fusion technology, which greatly reduces the amount of secondary transmission data of the cluster head node so as to reduce the energy consumption of the network and improve the overall life cycle of the network.The selection of cluster head node is determined by the total number of cluster head nodes and the number of known nodes selected as cluster heads under the optimal energy consumption calculated in the network. In order to ensure that each node has an equal number of times to be selected as the cluster head node, it is required that each node can be selected as the cluster head node once in the runningN/k round on average, so as to ensure the balance of network energy consumption [14], where Nrepresents the total number of sensor nodes and krepresents the total number of cluster head nodes. 0-1 random number is not selected as cluster head node in the N/k round, which is less than a certain threshold Pi; then, the node is selected as the cluster head node. The threshold setting is calculated by the following equation:(1)Pi=kN−k×r×modN/k,ci=1,0,ci=0.In equation (1), r represents the number of transmission rounds of nodes in the network. When node i is selected as the cluster head node in each N/k round, function C assigns it to 0. Otherwise, 1 indicates that node i is waiting to be selected as the cluster head node. In this equation, the k×r×modN/k part is the total number of selected cluster head nodes after calculating r round. In this equation, the threshold Pi actually represents the average probability that the current remaining nodes may be selected as cluster head nodes in every N/k round.The algorithm of LEACH is as follows:Step 1: each sensor node is selected as the cluster head node according to a certain probability equation rule.Step 2: the cluster head node sends the broadcast packet containing its own ID number to other member nodes in the network. Any member node receiving the broadcast packet calculates the distance between itself and the cluster head. The distance calculation is based on the similar GPS positioning system chip set in the node hardware to determine its own position or the distance between nodes can be judged by the signal attenuation strength of other noncluster head nodes received by the cluster head node.Step 3: these member nodes will join the nearest or weakest cluster according to the distance or signal attenuation strength between nodes.Step 4: the cluster head node equationtes time-driven events for each member node in the cluster, and then each member node communicates with the cluster head node according to different time slots in the MAC protocol in TDMA mode, which can reduce the channel blocking or conflict caused by simultaneous sending packets.Step 5: the cluster head node compresses or fuses the received data packets of the member nodes and finally sends them to the master node of the base station. In the stable phase of data transmission of each node in the cluster [15], the member node sends the data to the cluster head node when its corresponding time slot arrives, and other time slots enter the sleep state to save energy. After one round of operation, the whole network enters a new round of work cycle, reselects cluster heads, and circulates the above process.At the same time, in order to avoid the extra overhead caused by the frequent selection of cluster head, the stable phase of data transmission is generally much longer than the cluster establishment phase. Each data transmission phase is generally divided into multiple frame operations. In each frame, all member nodes will complete a data transmission process to the cluster head node, which reduces the energy consumption and improves the working efficiency of nodes in WSN.


## 2.3. Extraction of Volleyball Spiking Trajectory

### 2.3.1. Feedback Filtering Method

Feedback filtering method is simplified from the heuristic filter. Heuristic filtering is called heuristic drift reduction (HDR). The core part of heuristic filtering is the attenuation function controller and integral controller, which complete the processing of feedback value and current value. The attenuation function controller mainly analyzes the previous value to determine the current state of the carrier, such as moving or stationary, and then reports the result to the integral controller. The main work of the integral controller is to compensate the current signal according to the analysis results of the attenuation controller. In the structure diagram, we can also see that before the gyroscope signal is compensated by the integral controller, a double low-pass filter is needed [16], which is to remove the high-frequency noise interference. The main work of the heuristic filter is to calculate the compensation factor I and feed it back to the signal. The calculation of attenuation controller and the integral controller is very large. In order to improve the operation efficiency, a feedback filtering method is proposed based on the signal characteristics of this link. This method uses the feedback idea of the heuristic filtering method, retains the core part of heuristic filtering, and makes great changes to the functions and operation methods of the two parts. The purpose is to reduce the calculation amount of the algorithm and ensure the filtering effect.The principle of the feedback filtering method is shown in Figure3.Figure 3
Schematic diagram of feedback filtering method.There are two important links in the feedback filtering method. One is how to calculate the current gain valueI in the feedback link, which is equivalent to the attenuation controller in heuristic filtering, but this link has been greatly simplified.The equation for gainIis as follows:(2)Ii=ai−1′Path,ai−1′≤ath,1,ai−1′>ath.In equation (2), Ii is the current gain obtained by calculation, ai−1 is the previous output value of the filter, ath is the set reference value, P is the adopted gain factor, P>0. From the equation, it can be seen that the value of I is between 0 and 1, and the larger the value of I is, the smaller the current gain is.The second is how to use this gain to update the current acceleration value so as to effectively filter the motion noise and the errors introduced by the coordinate conversion link and gravity compensation link [17]. The equation for updating the current acceleration value by direct multiplication is as follows:(3)ai′=Iiai,where ai′ is the current filtered value, Ii is the current gain, and ai is the signal value before filtering.


### 2.3.2. Integral Acceleration Calculation

Because the collected data of the MEMS acceleration sensor are discrete, the sampling time interval of the sensor is set toΔt, and after iteration, the following results can be obtained:(4)vn=vn−1+an+an−12⋅Δtn>1,sn=sn−1+vn−1⋅Δt+14an+n−1⋅Δtn>1.In the above equation,vn is the instantaneous velocity at time tn, an is the acceleration at time tn, and sn is the accumulated displacement at time 0−tn.The output data of the MEMS acceleration sensor is acceleration inx, y, and z directions. According to the above equation, the instantaneous velocity of athletes' upper limbs in the direction of x, y, and z of acceleration sensor at time tn can be calculated, respectively. The equation is as follows:(5)vxn=vxn−1+axn+axn−12⋅Δtn>1,vyn=vyn−1+ayn+ayn−12⋅Δtn>1,vzn=vzn−1+azn+azn−12⋅Δtn>1.In the same way, the displacement equation of athletes' upper limbs along thex, y, and z directions of acceleration sensor at time tn can be obtained as follows:(6)sxn=sxn−1+vxn−1⋅Δt+14axn+axn−1⋅Δt,syn=syn−1+vyn−1⋅Δt+14ayn+ayn−1⋅Δt,szn=szn−1+vzn−1⋅Δt+14azn+azn−1⋅Δt.Then, the space position coordinate of the upper limb attn time is sxn,syn,szn, and the movement track of the upper limb in three-dimensional space can be obtained by connecting the space position coordinate points at each time.


### 2.3.3. Filtering of Gravity Acceleration Component

The operator may turn over in the air when operating the gesture. At this time, the gravity acceleration will produce components [18, 19] on the x, y, and z axes of the acceleration sensor, and the acceleration on the z axis is no longer the gravity acceleration g. At this time, the acceleration integral calculation results will have serious errors. Before integral calculation, the component of gravity acceleration on the three axes of acceleration sensors x, y and z should be filtered.The components of gravity acceleration in each axis of the acceleration sensor can be calculated by the attitude matrix, and the quaternion parameter method is selected to calculate the attitude matrix. The transformation relationship between the absolute coordinate system and relative coordinate system can be expressed by quaternionQ, namely,(7)Q=q0+q1ib+q2jb+q3kb.The quaternion differential equation is as follows:(8)Q˙=12QW.The equation of matrix form is as follows:(9)q˙0q˙1q˙2q˙3=120−wx−wy−wzwx0wz−wywy−wz0wxwzwy−wx0q0q1q2q3.The above equation is the quaternion differential equation, wherewx, wy, and wz are the output components of the gyroscope.Through the differential equation, parametersq0, q1, q2, and q3 can be obtained. According to the attitude matrix, the components of g on each axis in the relative coordinate system can be obtained. The components gx, gy, and gz are as follows:(10)gxgygz=q02+q12−q22−q322q1q2−q0q32q1q3+q0q22q1q2+q0q3q02−q12+q22−q322q2q3−q0q12q1q3−q0q22q2q3+q0q1q02−q12−q22+q3200g.The actual acceleration of the upper limb in each direction can be obtained by subtracting the component of gravity acceleration on the axis from the measured acceleration before acceleration integral operation.The displacement of the upper limb in relative space in timeΔt is obtained by integral operation, and the displacement of the upper limb in absolute space is obtained by posture matrix [20]. The movement track of the upper limb in absolute space is obtained by iteration.


## 2.3.1. Feedback Filtering Method

Feedback filtering method is simplified from the heuristic filter. Heuristic filtering is called heuristic drift reduction (HDR). The core part of heuristic filtering is the attenuation function controller and integral controller, which complete the processing of feedback value and current value. The attenuation function controller mainly analyzes the previous value to determine the current state of the carrier, such as moving or stationary, and then reports the result to the integral controller. The main work of the integral controller is to compensate the current signal according to the analysis results of the attenuation controller. In the structure diagram, we can also see that before the gyroscope signal is compensated by the integral controller, a double low-pass filter is needed [16], which is to remove the high-frequency noise interference. The main work of the heuristic filter is to calculate the compensation factor I and feed it back to the signal. The calculation of attenuation controller and the integral controller is very large. In order to improve the operation efficiency, a feedback filtering method is proposed based on the signal characteristics of this link. This method uses the feedback idea of the heuristic filtering method, retains the core part of heuristic filtering, and makes great changes to the functions and operation methods of the two parts. The purpose is to reduce the calculation amount of the algorithm and ensure the filtering effect.The principle of the feedback filtering method is shown in Figure3.Figure 3
Schematic diagram of feedback filtering method.There are two important links in the feedback filtering method. One is how to calculate the current gain valueI in the feedback link, which is equivalent to the attenuation controller in heuristic filtering, but this link has been greatly simplified.The equation for gainIis as follows:(2)Ii=ai−1′Path,ai−1′≤ath,1,ai−1′>ath.In equation (2), Ii is the current gain obtained by calculation, ai−1 is the previous output value of the filter, ath is the set reference value, P is the adopted gain factor, P>0. From the equation, it can be seen that the value of I is between 0 and 1, and the larger the value of I is, the smaller the current gain is.The second is how to use this gain to update the current acceleration value so as to effectively filter the motion noise and the errors introduced by the coordinate conversion link and gravity compensation link [17]. The equation for updating the current acceleration value by direct multiplication is as follows:(3)ai′=Iiai,where ai′ is the current filtered value, Ii is the current gain, and ai is the signal value before filtering.


## 2.3.2. Integral Acceleration Calculation

Because the collected data of the MEMS acceleration sensor are discrete, the sampling time interval of the sensor is set toΔt, and after iteration, the following results can be obtained:(4)vn=vn−1+an+an−12⋅Δtn>1,sn=sn−1+vn−1⋅Δt+14an+n−1⋅Δtn>1.In the above equation,vn is the instantaneous velocity at time tn, an is the acceleration at time tn, and sn is the accumulated displacement at time 0−tn.The output data of the MEMS acceleration sensor is acceleration inx, y, and z directions. According to the above equation, the instantaneous velocity of athletes' upper limbs in the direction of x, y, and z of acceleration sensor at time tn can be calculated, respectively. The equation is as follows:(5)vxn=vxn−1+axn+axn−12⋅Δtn>1,vyn=vyn−1+ayn+ayn−12⋅Δtn>1,vzn=vzn−1+azn+azn−12⋅Δtn>1.In the same way, the displacement equation of athletes' upper limbs along thex, y, and z directions of acceleration sensor at time tn can be obtained as follows:(6)sxn=sxn−1+vxn−1⋅Δt+14axn+axn−1⋅Δt,syn=syn−1+vyn−1⋅Δt+14ayn+ayn−1⋅Δt,szn=szn−1+vzn−1⋅Δt+14azn+azn−1⋅Δt.Then, the space position coordinate of the upper limb attn time is sxn,syn,szn, and the movement track of the upper limb in three-dimensional space can be obtained by connecting the space position coordinate points at each time.


## 2.3.3. Filtering of Gravity Acceleration Component

The operator may turn over in the air when operating the gesture. At this time, the gravity acceleration will produce components [18, 19] on the x, y, and z axes of the acceleration sensor, and the acceleration on the z axis is no longer the gravity acceleration g. At this time, the acceleration integral calculation results will have serious errors. Before integral calculation, the component of gravity acceleration on the three axes of acceleration sensors x, y and z should be filtered.The components of gravity acceleration in each axis of the acceleration sensor can be calculated by the attitude matrix, and the quaternion parameter method is selected to calculate the attitude matrix. The transformation relationship between the absolute coordinate system and relative coordinate system can be expressed by quaternionQ, namely,(7)Q=q0+q1ib+q2jb+q3kb.The quaternion differential equation is as follows:(8)Q˙=12QW.The equation of matrix form is as follows:(9)q˙0q˙1q˙2q˙3=120−wx−wy−wzwx0wz−wywy−wz0wxwzwy−wx0q0q1q2q3.The above equation is the quaternion differential equation, wherewx, wy, and wz are the output components of the gyroscope.Through the differential equation, parametersq0, q1, q2, and q3 can be obtained. According to the attitude matrix, the components of g on each axis in the relative coordinate system can be obtained. The components gx, gy, and gz are as follows:(10)gxgygz=q02+q12−q22−q322q1q2−q0q32q1q3+q0q22q1q2+q0q3q02−q12+q22−q322q2q3−q0q12q1q3−q0q22q2q3+q0q1q02−q12−q22+q3200g.The actual acceleration of the upper limb in each direction can be obtained by subtracting the component of gravity acceleration on the axis from the measured acceleration before acceleration integral operation.The displacement of the upper limb in relative space in timeΔt is obtained by integral operation, and the displacement of the upper limb in absolute space is obtained by posture matrix [20]. The movement track of the upper limb in absolute space is obtained by iteration.


## 3. Results

### 3.1. Method Validation

In order to verify the effectiveness of the method, a professional volleyball athlete in a university is selected as the experimental object. The acceleration sensor and gyroscope sensor are installed on the athlete’s arm, and the collected volleyball spike action signal is transmitted to the data processing module in the PC terminal by using wireless sensor network. In order to show the effectiveness of the proposed method, the support vector machine method, Kinect method [20], and references [16] and [21] are selected as comparison methods.The proposed method is used to extract the average transmission time and average energy consumption of volleyball spiking trajectory when the network node is upgraded from 100 to 800. The scale of the wireless sensor network is improved, and the average energy consumption and average query time are improved. Query time and energy consumption can effectively measure the effectiveness of transmission information in wireless sensor network. The average transmission time of the volleyball spike trajectory extracted by different methods is shown in Figure4.Figure 4
Average transmission time.As can be seen from the experimental results in Figure4, the average transmission time of the volleyball spiking trajectory extracted by the proposed method is lower than that of the other two methods when the wireless sensor network contains different nodes, which indicates that this method can realize the data transmission of the nodes in a short time. The average data transmission time of the proposed method is significantly lower than the other two methods, which verifies that this method has high data transmission performance and can improve the real-time performance of volleyball spike trajectory extraction.The average energy consumption of the volleyball spike trajectory extracted by different methods is shown in Figure5.Figure 5
Average energy consumption.As can be seen from the experimental results in Figure5, the average energy consumption of the proposed method is the lowest when the wireless sensor network contains different nodes, and the average energy consumption of volleyball spiking trajectory extracted by the proposed method is significantly lower than that of the other two methods. The average energy consumption of the proposed method is lower than 20 JJ in different nodes; the average energy consumption of volleyball spiking trajectory extracted by [16] and [21] methods in different nodes is between 35 J and 45 J; the average energy consumption of volleyball spiking trajectory extracted by SVM method and Kinect method is higher than 50 J in different nodes. The experimental results show that the method of this article can save the energy of wireless sensor network nodes and prolong the life cycle of wireless sensor network by extracting the ball smashing trajectory.When using this method to extract volleyball spiking trajectory, the increasing scale of wireless sensor network does not affect the average energy cost and average processing delay of wireless sensor network in the process of operation, almost not affected by the size of the network. Compared with the above method, the proposed method can reduce the average update cost and update delay to a great extent in the same network size.In this article, the acceleration sensor and gyroscope sensor are used to collect volleyball players' spiking trajectory, and some original data results of the acceleration sensor are collected. The acceleration values ofx-axis, y-axis, and z-axis acceleration sensors are represented by ax, ay, and az, and the unit is m/s2. From top to bottom, the acceleration sensor data changes with time, and the time interval is 20 ms. The statistical results are shown in Table 1.Table 1
Acceleration sensor output data.
Time (ms)axayaz200.1938540.5846529.536421400.1939850.5964219.541261600.1942540.5975419.551324800.1965840.5985419.5631811000.1984520.5996219.5716421200.1995540.6015489.5846211400.2001420.6024859.5941211600.2012540.6035419.6424151800.2123540.6048529.6585412000.2158460.6058419.681122Table2 shows part of the original data of the gyroscope sensor received by the PC terminal. Each row contains a group of data. wx, wy, and wz are the angular velocity values of the gyroscope sensor on the x, y, and z axes, respectively, in rad/s. From top to bottom, the data of the gyroscope sensor changes with time, and the time interval is 20 ms. The statistical results are shown in Table 2.Table 2
Gyro sensor output data.
Time (ms)wxwywz20−0.009510.052410.01235140−0.005540.068540.01628560−0.002510.078410.166874800.012540.084610.1678411000.013520.095210.1866541200.023640.102510.1954231400.035420.113250.2034851600.048520.123450.2156461800.056950.135240.2235452000.062570.148520.238451The experimental results in Tables1 and 2 show that the wireless sensor network can effectively transmit the data collected by the acceleration sensor and gyroscope sensor to the PC, which is convenient for the PC to extract the volleyball spiking trajectory of volleyball players.Different sampling periods have a great influence on position error and speed error. The position error results of extracting volleyball spiking trajectory in different sampling periods are shown in Figure6.Figure 6
The influence of sampling period on position error.As can be seen from the experimental results in Figure6, with the increase of sampling time, the position error of the volleyball spiking trajectory extracted by the proposed method in different sampling periods is less than 0.01 m. The experimental results show that using the proposed method to extract volleyball spiking trajectory has high extraction accuracy. This method can effectively extract volleyball spiking trajectory and has high extraction effectiveness.Statistics of the speed error results of different sampling periods to extract volleyball spike trajectory are shown in Figure7.Figure 7
The influence of sampling period on speed error.As can be seen from the experimental results in Figure7, with the increase of sampling time, the speed error of the volleyball spiking trajectory extracted by the proposed method in different sampling periods is less than 0.15 m/s. The experimental results show that the speed error of this method is low, and it is verified that this method can effectively extract the volleyball spike trajectory, and the volleyball spike trajectory extraction accuracy is high.When counting the number of different sampling points, three methods are used to extract the mean square error of volleyball spike trajectory. The statistical results are shown in Figure8.Figure 8
Comparison of mean square error.The experimental results in Figure8 show that with the increase of the number of sampling points, the mean square error of different methods to extract volleyball spike trajectory decreases, which indicates that increasing the number of sampling points can effectively improve the accuracy of volleyball spike trajectory extraction. When the number of sampling points is different, the mean square error of the proposed method is lower than that of the other two methods, which shows that the proposed method has higher extraction accuracy when the number of sampling points is different.


### 3.2. The Application of Volleyball Spiking Trajectory Extraction in Teaching

The basic requirement of physical education teaching is intuitive and vivid. The quality of students’ imitation directly affects the final teaching effect. The more timely the feedback teachers give students is, the more conducive it is to the formation of students’ action memory is and effectively improve students’ tactical level. There are two problems in traditional volleyball teaching and competition: traditional sports teaching process mainly teaches students sports technology through teachers’ explanation and demonstration, students’ practice, teachers’ error correction, and so on and students’ autonomous learning is less; teaching and competition analysis mostly adopts special person observation and manual recording, which is time-consuming and laborious, and the judgment results are affected by the subjective and inaccurate factors of the recorder. As a result, the results of data analysis and statistics are not authoritative. Taking the volleyball teaching in colleges and universities as the research object, this article discusses the application of volleyball spike trajectory extraction in volleyball teaching. The results of volleyball spiking trajectory extraction have higher real-time and accuracy than manual recording results. Volleyball spiking trajectory extraction has the ability to quickly “capture” the moving target, record the target data, and analyze and provide the motion trajectory. These motion data can provide a more intuitive way of expression for students’ motion quality.Volleyball spiking trajectory extraction is applied in teaching mainly through the following ways:(1)
Presentation of the complete volleyball spiking movement for the student:In volleyball, the technical movements of different links, especially the movement deformation in the tense competition, are easy to make students develop bad sports habits. The whole action track of volleyball spiking of excellent volleyball players and the panorama of attack and defense tactics of the whole team can be statically frozen and replayed frame by frame through the extracted track so that students can master the technical essentials of volleyball spiking and understand their own position at both ends of attack and defense.(2)
Cycle demonstration of key technology links:In the process of volleyball teaching, teachers can use the extracted volleyball action track to extract the technical parameters of students’ volleyball spiking action through analysis software. Teachers can provide guidance and suggestions for students’ training in time by analyzing the extracted volleyball action track so as to effectively improve students’ volleyball training level.(3)
Improvement of the classroom feedback and error correction ability:By superimposing and comparing the movement track of volleyball spiking action with students’ spiking action, a seamless video can be synthesized, which can intuitively reflect the volleyball players’ foot moving position and arm raising spiking time through the continuity of the video so as to grasp the technical essentials faster and improve the ability of volleyball spiking. Teachers can listen to students’ feelings at the first time and provide direct technical guidance for students.(4)
Stimulation of students’ perception and attention effectively:The analysis of the trajectory of volleyball spiking greatly improves the effect of classroom training. Through intuitive stimulation, students can feed it back to the brain and transform it into stronger motivation for volleyball learning.The research method in this article can accurately extract the trajectory of volleyball spiking action. Using the extracted trajectory of volleyball spiking action, the athletes’ spiking action trajectory and volleyball movement trajectory can be drawn in three-dimensional coordinates, which provides the basis for physical education teaching and referee judgment. At the same time, it has important theoretical guidance and application value to improve the research level of intelligent analysis of ball games and provides important clues for the application of strategic and tactical analysis, team action analysis, and other professional applications. The key to the optimization and innovation of college volleyball teaching mode is to further diversify the teaching methods of college volleyball. Accurate volleyball training course analysis and diversified development of teaching methods can effectively stimulate students’ learning enthusiasm so as to improve students’ participation in the teaching process. In the process of volleyball teaching in colleges and universities, teachers should play their main role and make use of modern multimedia teaching equipment and technology to make volleyball teaching more vivid, flexible, and obvious so as to give full play to students’ learning enthusiasm and initiative. The use of visual and information-based teaching methods is a trend in the future of physical education, which is loved by students and easy to accept, so that the teaching effect of volleyball has been significantly improved.


## 3.1. Method Validation

In order to verify the effectiveness of the method, a professional volleyball athlete in a university is selected as the experimental object. The acceleration sensor and gyroscope sensor are installed on the athlete’s arm, and the collected volleyball spike action signal is transmitted to the data processing module in the PC terminal by using wireless sensor network. In order to show the effectiveness of the proposed method, the support vector machine method, Kinect method [20], and references [16] and [21] are selected as comparison methods.The proposed method is used to extract the average transmission time and average energy consumption of volleyball spiking trajectory when the network node is upgraded from 100 to 800. The scale of the wireless sensor network is improved, and the average energy consumption and average query time are improved. Query time and energy consumption can effectively measure the effectiveness of transmission information in wireless sensor network. The average transmission time of the volleyball spike trajectory extracted by different methods is shown in Figure4.Figure 4
Average transmission time.As can be seen from the experimental results in Figure4, the average transmission time of the volleyball spiking trajectory extracted by the proposed method is lower than that of the other two methods when the wireless sensor network contains different nodes, which indicates that this method can realize the data transmission of the nodes in a short time. The average data transmission time of the proposed method is significantly lower than the other two methods, which verifies that this method has high data transmission performance and can improve the real-time performance of volleyball spike trajectory extraction.The average energy consumption of the volleyball spike trajectory extracted by different methods is shown in Figure5.Figure 5
Average energy consumption.As can be seen from the experimental results in Figure5, the average energy consumption of the proposed method is the lowest when the wireless sensor network contains different nodes, and the average energy consumption of volleyball spiking trajectory extracted by the proposed method is significantly lower than that of the other two methods. The average energy consumption of the proposed method is lower than 20 JJ in different nodes; the average energy consumption of volleyball spiking trajectory extracted by [16] and [21] methods in different nodes is between 35 J and 45 J; the average energy consumption of volleyball spiking trajectory extracted by SVM method and Kinect method is higher than 50 J in different nodes. The experimental results show that the method of this article can save the energy of wireless sensor network nodes and prolong the life cycle of wireless sensor network by extracting the ball smashing trajectory.When using this method to extract volleyball spiking trajectory, the increasing scale of wireless sensor network does not affect the average energy cost and average processing delay of wireless sensor network in the process of operation, almost not affected by the size of the network. Compared with the above method, the proposed method can reduce the average update cost and update delay to a great extent in the same network size.In this article, the acceleration sensor and gyroscope sensor are used to collect volleyball players' spiking trajectory, and some original data results of the acceleration sensor are collected. The acceleration values ofx-axis, y-axis, and z-axis acceleration sensors are represented by ax, ay, and az, and the unit is m/s2. From top to bottom, the acceleration sensor data changes with time, and the time interval is 20 ms. The statistical results are shown in Table 1.Table 1
Acceleration sensor output data.
Time (ms)axayaz200.1938540.5846529.536421400.1939850.5964219.541261600.1942540.5975419.551324800.1965840.5985419.5631811000.1984520.5996219.5716421200.1995540.6015489.5846211400.2001420.6024859.5941211600.2012540.6035419.6424151800.2123540.6048529.6585412000.2158460.6058419.681122Table2 shows part of the original data of the gyroscope sensor received by the PC terminal. Each row contains a group of data. wx, wy, and wz are the angular velocity values of the gyroscope sensor on the x, y, and z axes, respectively, in rad/s. From top to bottom, the data of the gyroscope sensor changes with time, and the time interval is 20 ms. The statistical results are shown in Table 2.Table 2
Gyro sensor output data.
Time (ms)wxwywz20−0.009510.052410.01235140−0.005540.068540.01628560−0.002510.078410.166874800.012540.084610.1678411000.013520.095210.1866541200.023640.102510.1954231400.035420.113250.2034851600.048520.123450.2156461800.056950.135240.2235452000.062570.148520.238451The experimental results in Tables1 and 2 show that the wireless sensor network can effectively transmit the data collected by the acceleration sensor and gyroscope sensor to the PC, which is convenient for the PC to extract the volleyball spiking trajectory of volleyball players.Different sampling periods have a great influence on position error and speed error. The position error results of extracting volleyball spiking trajectory in different sampling periods are shown in Figure6.Figure 6
The influence of sampling period on position error.As can be seen from the experimental results in Figure6, with the increase of sampling time, the position error of the volleyball spiking trajectory extracted by the proposed method in different sampling periods is less than 0.01 m. The experimental results show that using the proposed method to extract volleyball spiking trajectory has high extraction accuracy. This method can effectively extract volleyball spiking trajectory and has high extraction effectiveness.Statistics of the speed error results of different sampling periods to extract volleyball spike trajectory are shown in Figure7.Figure 7
The influence of sampling period on speed error.As can be seen from the experimental results in Figure7, with the increase of sampling time, the speed error of the volleyball spiking trajectory extracted by the proposed method in different sampling periods is less than 0.15 m/s. The experimental results show that the speed error of this method is low, and it is verified that this method can effectively extract the volleyball spike trajectory, and the volleyball spike trajectory extraction accuracy is high.When counting the number of different sampling points, three methods are used to extract the mean square error of volleyball spike trajectory. The statistical results are shown in Figure8.Figure 8
Comparison of mean square error.The experimental results in Figure8 show that with the increase of the number of sampling points, the mean square error of different methods to extract volleyball spike trajectory decreases, which indicates that increasing the number of sampling points can effectively improve the accuracy of volleyball spike trajectory extraction. When the number of sampling points is different, the mean square error of the proposed method is lower than that of the other two methods, which shows that the proposed method has higher extraction accuracy when the number of sampling points is different.


## 3.2. The Application of Volleyball Spiking Trajectory Extraction in Teaching

The basic requirement of physical education teaching is intuitive and vivid. The quality of students’ imitation directly affects the final teaching effect. The more timely the feedback teachers give students is, the more conducive it is to the formation of students’ action memory is and effectively improve students’ tactical level. There are two problems in traditional volleyball teaching and competition: traditional sports teaching process mainly teaches students sports technology through teachers’ explanation and demonstration, students’ practice, teachers’ error correction, and so on and students’ autonomous learning is less; teaching and competition analysis mostly adopts special person observation and manual recording, which is time-consuming and laborious, and the judgment results are affected by the subjective and inaccurate factors of the recorder. As a result, the results of data analysis and statistics are not authoritative. Taking the volleyball teaching in colleges and universities as the research object, this article discusses the application of volleyball spike trajectory extraction in volleyball teaching. The results of volleyball spiking trajectory extraction have higher real-time and accuracy than manual recording results. Volleyball spiking trajectory extraction has the ability to quickly “capture” the moving target, record the target data, and analyze and provide the motion trajectory. These motion data can provide a more intuitive way of expression for students’ motion quality.Volleyball spiking trajectory extraction is applied in teaching mainly through the following ways:(1)
Presentation of the complete volleyball spiking movement for the student:In volleyball, the technical movements of different links, especially the movement deformation in the tense competition, are easy to make students develop bad sports habits. The whole action track of volleyball spiking of excellent volleyball players and the panorama of attack and defense tactics of the whole team can be statically frozen and replayed frame by frame through the extracted track so that students can master the technical essentials of volleyball spiking and understand their own position at both ends of attack and defense.(2)
Cycle demonstration of key technology links:In the process of volleyball teaching, teachers can use the extracted volleyball action track to extract the technical parameters of students’ volleyball spiking action through analysis software. Teachers can provide guidance and suggestions for students’ training in time by analyzing the extracted volleyball action track so as to effectively improve students’ volleyball training level.(3)
Improvement of the classroom feedback and error correction ability:By superimposing and comparing the movement track of volleyball spiking action with students’ spiking action, a seamless video can be synthesized, which can intuitively reflect the volleyball players’ foot moving position and arm raising spiking time through the continuity of the video so as to grasp the technical essentials faster and improve the ability of volleyball spiking. Teachers can listen to students’ feelings at the first time and provide direct technical guidance for students.(4)
Stimulation of students’ perception and attention effectively:The analysis of the trajectory of volleyball spiking greatly improves the effect of classroom training. Through intuitive stimulation, students can feed it back to the brain and transform it into stronger motivation for volleyball learning.The research method in this article can accurately extract the trajectory of volleyball spiking action. Using the extracted trajectory of volleyball spiking action, the athletes’ spiking action trajectory and volleyball movement trajectory can be drawn in three-dimensional coordinates, which provides the basis for physical education teaching and referee judgment. At the same time, it has important theoretical guidance and application value to improve the research level of intelligent analysis of ball games and provides important clues for the application of strategic and tactical analysis, team action analysis, and other professional applications. The key to the optimization and innovation of college volleyball teaching mode is to further diversify the teaching methods of college volleyball. Accurate volleyball training course analysis and diversified development of teaching methods can effectively stimulate students’ learning enthusiasm so as to improve students’ participation in the teaching process. In the process of volleyball teaching in colleges and universities, teachers should play their main role and make use of modern multimedia teaching equipment and technology to make volleyball teaching more vivid, flexible, and obvious so as to give full play to students’ learning enthusiasm and initiative. The use of visual and information-based teaching methods is a trend in the future of physical education, which is loved by students and easy to accept, so that the teaching effect of volleyball has been significantly improved.


## 4. Conclusion

In view of the poor accuracy of the existing methods to extract volleyball spiking trajectory, the wireless sensor network is applied to extract volleyball spiking trajectory. The experimental results show that this method has high accuracy in extracting volleyball spiking trajectory, which provides a strong scientific basis for improving volleyball players’ spiking technology. The experimental results show that the average energy consumption and average delay of applying wireless sensor network to volleyball spiking trajectory extraction are greatly reduced, which can effectively extend the network cycle and enhance the practicability. The accuracy of using this method to extract volleyball spiking trajectory is high, which can be applied to volleyball teaching. The proposed routing protocol algorithm can be improved accordingly. Moreover, the proposed method can also integrate the advantages of different methods to build a method that coexists with both speed and performance. In future work, we should combine theory with practice and put forward corresponding methods for specific tasks.



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*Source: 9966994-2021-06-04.xml*