Resource Scheduling Method for Wireless Networked Control Systems Based on IEEE 802.11ax

Abstract

This invention relates to industrial wireless network technology, specifically a resource scheduling method for a wireless networked control system based on IEEE 802.11ax. This invention is applicable to wireless networked control systems composed of multiple independent discrete linear subsystems sharing an IEEE 802.11ax network. Specifically, considering the sensor data packet loss problem of the IEEE 802.11ax network, an optimal state estimator and LQG control law for the wireless networked control system are given; by analyzing the intrinsic relationship between LQG cost and IEEE 802.11ax transmission reliability, a resource scheduling problem model is established with the goal of minimizing the expected LQG cost; based on the state of each subsystem in each control cycle, a resource scheduling strategy prioritizing control performance is proposed to achieve high-speed wireless control of multiple independent subsystems.

Description

Technical Field

[0001] This invention relates to the field of resource scheduling technology for wireless networked control systems, specifically a resource scheduling method for wireless networked control systems based on IEEE 802.11ax. Background Technology

[0002] The development of wireless network technology is a significant driving force behind freeing industrial automation systems from the constraints of cables. Traditional industrial automation systems rely heavily on cabling, severely limiting their flexibility and scalability. Wireless network technology enables industrial automation systems to achieve more flexible online sensing and high-speed control, playing a disruptive role in the field of industrial control. Among numerous wireless technologies, IEEE 802.11ax is increasingly being adopted in industrial control applications due to its advantages such as low cost, ease of maintenance, and unlicensed bandwidth. However, in real-world factory environments, it faces adverse factors such as path loss, noise interference, and multipath effects. Coupled with limited communication resources, the real-time and reliable transmission of IEEE 802.11ax cannot be guaranteed, leading to difficulties in meeting the control performance requirements of the entire wireless network control system.

[0003] Scheduling methods determine the efficiency of network resource utilization and are crucial for improving the control performance of wireless network control systems. Existing resource scheduling methods mainly focus on network performance indicators such as throughput, transmission latency, and transmission reliability, resulting in poor system control performance. Summary of the Invention

[0004] To address the challenges of path loss, noise interference, and multipath effects in real-world factory environments, this invention proposes a resource scheduling method for wireless networked control systems based on the IEEE 802.11ax network. This method is applicable to wireless networked control systems comprised of multiple independent discrete linear subsystems sharing a common IEEE 802.11ax network.

[0005] This invention proposes a resource scheduling method for a wireless network-based control system based on IEEE 802.11ax. Specifically, considering the sensor data packet loss problem in IEEE 802.11ax networks, an optimal state estimator and LQG control law for the wireless network-based control system are given. By analyzing the intrinsic relationship between LQG cost and IEEE 802.11ax transmission reliability, a resource scheduling problem model with the objective of minimizing the expected LQG cost is established. Based on the state of each subsystem in each control cycle, a resource scheduling strategy prioritizing control performance is proposed.

[0006] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0007] The resource scheduling method for a wireless network-based control system based on IEEE 802.11ax includes the following steps:

[0008] 1) Calculate c for all subsystems k All subsystems are arranged according to c i,k Arrange the subsystems in ascending order, select the top few subsystems for scheduling, and denote the set of subsystems as follows:

[0009] 2) For Subsystem selection Σ k and α k And calculate the optimal value. Uplink transmission reliability vector for all subsystems Σ k For the allocation results of resource units RU in all subsystems, α k The allocation results for the largest protocol data unit (PPDU) of all subsystems, μ k These are the parameters for the modulation and coding scheme;

[0010] 3) For different μ k Repeat step 2) for ∈M, where M = {0, 1, 2, ..., 10, 11} is the range of parameter values ​​for the modulation and coding scheme, and the smallest Op is taken. k The corresponding scheduling result is Perform the initial transmission scheduling, setting the maximum Protocol Data Unit (PPDU) used in the initial transmission to be [value missing]. ss * The maximum PPDU sequence number used in the first transmission;

[0011] 4) After the initial transmission scheduling, if there is a subsystem that fails to transmit and there are still PPDUs remaining in the current control cycle, retransmission scheduling will be performed until all subsystems transmit successfully or the current control cycle ends.

[0012] 5) Update counter l i,k+1 ;

[0013] 6) Calculate control input Send to subsystem i;

[0014] 7) Subsystem i evolves in state i.

[0015] In step 1), the c of all subsystems is calculated. k Specifically:

[0016]

[0017] Where Tr represents the trace of the matrix; S i,k and T i,kA is the intermediate variable matrix in the calculation process; i P is the system matrix; i,k-1|k-1 Q is the error covariance matrix of the optimal estimate of subsystem i; i Let be the covariance matrix of the noise of subsystem i.

[0018]

[0019]

[0020] c k =[c 1,k ,c 2,k ,...,c m,k ] T

[0021] Among them, W i,k and U i,k B is the intermediate variable matrix in the calculation process. i For the input matrix, For uplink transmission reliability, c i,k c for subsystem i k value.

[0022] In step 1), since the duration of the Protocol Data Unit (PPDU) required for each subsystem to transmit one data packet is τ(μ) k )=L / r(μ k ), where L is the data packet size of each subsystem, each control cycle is based on a time slot, and the length of each time slot is... From a length of T TF The trigger frame TF, a length of τ (μ k A PPDU of length T ACK The ACK slot, a slot of length T PIFS The point coordination function inter-frame interval and two lengths of T SIFS It consists of short inter-frame intervals (SIFS), i.e. The control cycle length is denoted as τ. max The number of time slots contained in each control cycle is in This represents the floor function, using a bandwidth of The bandwidth of one resource unit (RU) is Then a PPDU allows Parallel transmission of each subsystem, with a maximum allowed per control cycle. Each subsystem transmits data; therefore, the selection process must be completed beforehand. Each subsystem is scheduled.

[0023] In step 2), the Σ k and αk Specifically:

[0024] In the k-th control cycle, define f 1 ,f 2 ,…,f b This represents b different sub-bands with the same bandwidth, and a Boolean variable is defined for each subsystem. If subsystem i is in frequency band f j Upload, then on the contrary For subsystem i, the vector composed of the Boolean variables corresponding to all its frequency bands is denoted as . For all subsystems, their The matrix formed is denoted as

[0025] For PPDU allocation, a boolean variable is defined for each subsystem. If in the k-th control cycle, subsystem i transmits data on PDUs, s = 1, 2, ..., ss(μ k ),but on the contrary For subsystem i, the vector consisting of the Boolean variables corresponding to all its PPDUs is denoted as . For all subsystems, their α i,k The matrix formed is denoted as

[0026] The calculation of the optimal value Specifically:

[0027]

[0028] Among them, c k =[c 1,k ,c 2,k ,...,c m,k ] T Meanwhile, variable Σ k μ k α k The following constraints need to be met:

[0029]

[0030]

[0031]

[0032] Among them, set Let α be a Boolean vector i,k feasible set, set Boolean vector The feasible set, set M = {0, 1, 2, ..., 10, 11}, is the MCS value μ of the modulation and coding scheme parameter for each subsystem. k The feasible set.

[0033] The retransmission scheduling includes the following steps:

[0034] 4.1) Determine the set of subsystems that failed to transmit based on the transmission results. At this time, m1 = |I r |,

[0035] 4.2) If subsystem i successfully transmits, then c i,k =0;

[0036] 4.3) Set I r The subsystems in the c i,k Sort in ascending order, select the first The scheduling is performed on each subsystem, and the set of subsystems is denoted as .

[0037] 4.4) Based on the obtained feasible scheduling results and right The subsystem performs retransmission scheduling, that is, allocates ss1 PPDUs to Subsystems.

[0038] Step 5) specifically involves:

[0039] Transmission counter l i,k+1 The update in the k-th control cycle is as follows:

[0040]

[0041] Where, γ i,k Let be a Bernoulli random variable representing the flag indicating whether the uplink data packet transmission of subsystem i was successful or failed.

[0042] Step 6) specifically involves:

[0043]

[0044] Among them, A i For the system matrix, B i Given the input matrix S i,k+1 and U i,k This is a matrix of intermediate variables used in the calculation process. For state estimation in the k-th control cycle, L i,k The feedback matrix, i.e.

[0045] Step 7) specifically involves:

[0046] x i,k+1 =A i x i,k +Β i u i,k +w i,k

[0047] in, For the state vector, To control the input, For the system matrix, For the input matrix, w is a real number i,k With a mean of 0 and a covariance matrix of Q i Gaussian white noise;

[0048] In the k-th control cycle, the sensors of subsystem i will periodically sample the state information x. i,k The status information is transmitted wirelessly to the controller at the access point (AP); the controller then bases the received status information on the data received. Calculate state estimation and control input u i,k and through AP u i,k The control input u is sent to the actuator of subsystem i; the actuator will receive the control input u. i,k It acts on subsystem i.

[0049] The present invention has the following beneficial effects and advantages:

[0050] 1. Considering the sensor data packet loss problem in IEEE 802.11ax networks, an optimal state estimator and LQG control law for wireless network-based control systems are given; by analyzing the intrinsic relationship between LQG cost and IEEE 802.11ax transmission reliability, a resource scheduling problem model with the goal of minimizing the expected LQG cost is established.

[0051] 2. Based on the state of each subsystem in each control cycle, a resource scheduling strategy prioritizing control performance is proposed to achieve high-speed wireless control of multiple independent subsystems. Attached Figure Description

[0052] Figure 1 It is a wireless network control system;

[0053] Figure 2 This is a timing diagram of the system model. Detailed Implementation

[0054] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings.

[0056] This invention mainly comprises three parts: modeling of wireless networked control systems, a resource scheduling problem model with the goal of minimizing the expected LQG cost, and a resource scheduling strategy that prioritizes control performance.

[0057] 1. Modeling of Wireless Networked Control Systems

[0058] like Figure 1 As shown, the wireless network control system is specifically as follows:

[0059] The wireless network control system consists of one access point (AP) (including a controller) and m subsystems. The discrete-time state-space equation of subsystem i (i = 1, 2, ..., m) is as follows:

[0060] x i,k+1 =A i x i,k +Β i u i,k +w i,k

[0061] in For the state vector, To control the input, For the system matrix, Given the input matrix, w i,k With a mean of 0 and a covariance matrix of Q i Gaussian white noise. In the k-th control cycle, the sensors of subsystem i will periodically sample the obtained state information x. i,k The status information is transmitted wirelessly to the controller at the access point (AP); the controller then bases the received status information on the data received. Calculate state estimation and control input u i,k and through AP u i,k The control input u is sent to the actuator of subsystem i; finally, the actuator receives the control input u. i,k It acts on subsystem i.

[0062] Uplink transmission is conducted wirelessly via IEEE 802.11ax, introducing a Bernoulli random variable γ. i,k Modeling this process, i.e. in This indicates the status information obtained by the AP. If the sensor data arrives at the controller correctly, then... otherwise And for γ i,k have This refers to uplink transmission reliability. Downlink transmission occurs on an ideal channel.

[0063] 2. Resource scheduling problem model with the objective of minimizing expected LQG cost

[0064] The resource scheduling problem model with the objective of minimizing the expected LQG cost is as follows:

[0065] First, the scheduling parameters of the resource scheduling problem model are introduced:

[0066] In the k-th control cycle, define f 1 ,f 2 ,…,f b Let b be the number of different sub-bands with the same bandwidth, and define a Boolean variable for each subsystem. If subsystem i is in frequency band f j Upload, then on the contrary For subsystem i, the vector composed of the Boolean variables corresponding to all its frequency bands is denoted as . Furthermore, for all subsystems, their The matrix formed is denoted as Only one RU is allocated to each subsystem, that is... 2,…,m). The set Defined as a Boolean vector The feasible set, which defines all feasible RU assignments.

[0067] Assign the same MCS value μ to each subsystem k Its value range is M = {0, 1, 2, ..., 10, 11}.

[0068] For PPDU allocation, a boolean variable is defined for each subsystem. If in the k-th control cycle, subsystem i is in PPDUs(s=1,2,...,ss(μ) k Then, transmission on the uplink on the contrary For subsystem i, the vector consisting of the Boolean variables corresponding to all its PPDUs is denoted as . Furthermore, for all subsystems, their α i,k The matrix formed is denoted as set Defined as a Boolean vector α i,k The feasible set, which defines all feasible PPDU allocations.

[0069] like Figure 2 As shown, the scheduling parameters mentioned above determine the network transmission timing: MCS determines the transmission data rate r (μ kIf the data packet size of each subsystem is the same and fixed (denoted as L), then the PPDU time required for a subsystem to transmit one data packet is τ (μ). k )=L / r(μ k Each control cycle is based on a time slot, and the length of each time slot is... A TF(TriggerFrame, length T) TF ), a PPDU (length τ(μ) k An ACK (Acknowledgement), of length T ACK A point coordination function inter-frame interval (PIFS, length T) PIFS Two short inter-frame intervals (SIFS, length T) SIFS Composed of, i.e. The control cycle length is denoted as τ. max The number of time slots contained in each control cycle is in This represents the floor function.

[0070] Using bandwidth The bandwidth of one RU is Then a PPDU can allow Parallel transmission of each subsystem, with a maximum allowed per control cycle. Each subsystem transmits data.

[0071] Define the channel gain vector of subsystem i as follows: in This indicates that subsystem i is in the wireless fading frequency band f j Channel gain on h. Assume h i,k It remains constant within a control cycle. Given h ik The transmission success rate of subsystem i By MCSμ k and RU allocation The decision is made jointly. Therefore, transmission reliability... The following expression can be used:

[0072]

[0073] Define the channel gain matrix of all subsystems as follows: Then in H k Given the conditions, the reliability vector of all subsystems is:

[0074] Secondly, the LQG performance metrics are given:

[0075] The available information set of the controller in the k-th control cycle is: in

[0076] For cases where data packet loss occurs during transmission, the optimal estimator is as follows:

[0077]

[0078]

[0079]

[0080] in and P i,k+1|k+1 Let represent the prior estimate, the optimal estimate, and the error covariance matrix of the optimal estimate for subsystem i in the (k+1)th control cycle, respectively.

[0081] Based on the finite-time LQG control method, the value function V is defined. i,k (x i,k )as follows:

[0082]

[0083]

[0084] Where N is the length of the time domain being considered. It is a non-negative definite matrix. It is a positive definite matrix.

[0085] The optimal state feedback is:

[0086] Substituting the optimal state feedback into the value function, we get:

[0087]

[0088] in All are non-negative definite matrices, with the following specific values:

[0089]

[0090]

[0091]

[0092] And satisfy S i,N =W i,N T i,N =W i,N D i,N =0.

[0093] Data transmission counter l i,k+1 The value is updated in the k-th control cycle.

[0094]

[0095] The controller can obtain the state prediction value of subsystem i in the k-th control cycle:

[0096]

[0097] Real state x i,k With predicted state The error is:

[0098]

[0099] The expected LQG cost of subsystem i in the k-th control cycle is:

[0100]

[0101] Define the state prediction matrix as Then the sum of the expected LQG costs of the m subsystems in the kth control cycle is:

[0102]

[0103] Finally, an optimization model for the scheduling problem is presented:

[0104] The optimization objective of network resource scheduling is to minimize the LQG cost of the entire system, i.e.:

[0105]

[0106] make The above problem is equivalent to:

[0107]

[0108] Where c k =[c 1,k ,c 2,k ,...,c m,k ] T At the same time, the variable Σ k μ k α k The following constraints need to be met:

[0109]

[0110]

[0111]

[0112] 3. Performance-prioritized resource scheduling strategy

[0113] The resource scheduling strategy prioritizing control performance is as follows:

[0114] Given m and c k , where c k , which are process variables with no substantial meaning, are all subsystems according to c i,k Sort in ascending order, select the first The scheduling is performed on each subsystem, and the set of subsystems is denoted as . The RUs allocated to the subsystem should be closely arranged and the PPDUs with smaller sequence numbers should be allocated first, according to (1)-(4). Subsystem selection Σ k and α k And calculate the optimal value. For different μ k Repeat the above process for ∈M, and take the smallest Op. k The corresponding scheduling result (denoted as) Perform the initial transmission scheduling, setting the maximum PPDU used by the initial transmission to ss. * .

[0115] After the initial transmission scheduling, if any subsystems experience transmission failures and there are still remaining PPDUs in the current control cycle, retransmission scheduling can be performed. The set of subsystems that failed to transmit is determined based on the transmission results. At this time, m1 = |I r |, If subsystem i successfully transmits, then c i,k =0. Similar to the initial transmission scheduling, set I... r The subsystems in the c i,k Sort in ascending order, select the first The scheduling is performed on each subsystem, and the set of subsystems is denoted as . The retransmission process still uses The essence of the problem at this point is to allocate ss1 PPDUs to Each subsystem, and then based on the obtained feasible scheduling results and right The subsystems within the system perform retransmission scheduling. The retransmission process continues until all subsystems have successfully transmitted or the current control cycle ends.

Claims

1. A resource scheduling method for a wireless network-based control system based on IEEE 802.11ax, characterized in that, Includes the following steps: 1) Calculate all subsystems All subsystems are arranged according to Arrange the subsystems in ascending order, select the top few subsystems for scheduling, and denote the set of subsystems as follows: , ,in, For resource scheduling process variables, For subsystem i of value; 2) For Subsystem selection in and And calculate the optimal value. , Uplink transmission reliability vector for all subsystems ; Assignment results to all subsystem resource units (RUs). Assignment results for the largest protocol data unit (PPDU) to all subsystems. These are the parameters for the modulation and coding scheme; 3) For different Repeat step 2), where, For the range of parameter values ​​for the modulation and coding scheme, take the minimum value. The corresponding scheduling result is Perform the initial transmission scheduling, setting the maximum Protocol Data Unit (PPDU) used in the initial transmission to be [value missing]. , The maximum PPDU sequence number used in the first transmission; 4) After the initial transmission scheduling, if there is a subsystem that fails to transmit and there are still PPDUs remaining in the current control cycle, retransmission scheduling will be performed until all subsystems transmit successfully or the current control cycle ends. 5) Update the counter ; 6) Calculate control input Send to subsystem i ; 7) Subsystem i The state evolves; In step 1), since the Protocol Data Unit (PPDU) duration required for each subsystem to transmit one data packet is... ,in L Data packet size for each subsystem, For data rate, each control cycle is based on a time slot as the basic unit, and the length of each time slot is... From a length of The trigger frame TF, a length of PPDU, a length of The ACK slot, a length of The point coordination function inter-frame interval and two lengths are It consists of short inter-frame intervals (SIFS), i.e. The control cycle length is denoted as The number of time slots contained in each control cycle is ,in This represents the floor function, using a bandwidth of The bandwidth of one resource unit (RU) is Then a PPDU allows Parallel transmission of each subsystem, with a maximum allowed per control cycle. Each subsystem transmits data; therefore, the selection process must be completed beforehand. Each subsystem is scheduled; The step 2) described above and Specifically: In the k One control cycle, defined Indicates having the same bandwidth b Each sub-band has a different sub-frequency band, and a Boolean variable is defined for each subsystem. If the subsystem i In frequency band Upload, then ,on the contrary For subsystems i The vector consisting of the Boolean variables corresponding to all its frequency bands is denoted as For all subsystems, their The matrix formed is denoted as ; For PPDU allocation, a boolean variable is defined for each subsystem. If in the first k One control cycle, subsystem i In PPDU s Upload, ,but ,on the contrary For subsystems i The vector consisting of the Boolean variables corresponding to all PPDUs is denoted as For all subsystems, their The matrix formed is denoted as .

2. The resource scheduling method for a wireless network-based control system according to claim 1, characterized in that, In step 1), all subsystems are calculated. Specifically: Where Tr represents the trace of the matrix; and This is a matrix of intermediate variables used in the calculation process; For the system matrix; For subsystem i The error covariance matrix of the optimal estimate; For subsystem i The covariance matrix of system noise; in, and This is a matrix of intermediate variables used in the calculation process. For the input matrix, For uplink transmission reliability, For subsystem i of value.

3. The resource scheduling method for a wireless network-based control system according to claim 1, characterized in that, The calculation of the optimal value Specifically: in, Meanwhile, variables , , The following constraints need to be met: Among them, set Boolean vector feasible set, set Boolean vector feasible set, set MCS values ​​for modulation and coding scheme parameters of each subsystem The feasible set.

4. The resource scheduling method for a wireless network control system based on IEEE 802.11ax according to claim 1, characterized in that, The retransmission scheduling includes the following steps: 4.1) Determine the set of subsystems that failed to transmit based on the transmission results. ,at this time , ; 4.2) If the subsystem i Successful transmission, ; 4.3) Set Subsystems in Sort in ascending order, select the first The scheduling is performed on each subsystem, and the set of subsystems is denoted as . ; 4.4) Based on the obtained feasible scheduling results and ,right The subsystem in the middle performs retransmission scheduling, which is about to PPDUs are allocated to Subsystems.

5. The resource scheduling method for a wireless network control system based on IEEE 802.11ax according to claim 1, characterized in that, Step 5) specifically involves: Transmission counter In the Each control cycle is updated to: in, Subsystem for representing Bernoulli random variables i A flag indicating whether the uplink data packet transmission was successful or failed.

6. The resource scheduling method for a wireless network control system based on IEEE 802.11ax according to claim 1, characterized in that, Step 6) specifically involves: in, For the system matrix, For the input matrix, and This is a matrix of intermediate variables used in the calculation process. In the first k State estimation for each control cycle The feedback matrix, i.e. .

7. The resource scheduling method for a wireless network control system based on IEEE 802.11ax according to claim 1, characterized in that, Step 7) specifically involves: in, For the state vector, To control the input, For the system matrix, For the input matrix, For real numbers, The mean is 0 and the covariance matrix is Q i Gaussian white noise; In the k In each control cycle, the subsystem i The sensor will periodically sample the obtained state information The status information is transmitted wirelessly to the controller at the access point (AP); the controller then bases the received status information on the data received. Calculate state estimation and control input and through AP Send to subsystem i The actuator; the actuator receives control input Acting on subsystems i .

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