Hybrid transmission method for time and event trigger streams in industrial wireless network

Abstract

The invention provides a hybrid transmission method for time and event trigger streams in an industrial wireless network. Comprising the following steps: step 1, establishing a first-order logic constraint model of time-triggered TT stream conflict-free transmission, realizing centralized scheduling of time slot resources based on a Gurobi solver, and realizing conflict-free transmission of TT streams in IWN; and step 2, on the basis of TT flow centralized scheduling, designing an ET flow competition transmission mechanism based on time slot Aloha, and on the basis that the ET flow does not occupy TT flow time slot resources, realizing mixed transmission of the TT flow and the ET flow. According to the method, the first-order logic constraint model of the time-triggered TT flow conflict-free transmission is established, so that the TT flow can exclusively share time slot resources; on the premise of not occupying TT stream transmission resources, an ET stream-oriented low-delay distributed competitive access mechanism is designed, and hybrid transmission of TT streams and ET streams is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial wireless networks; in particular, it relates to a hybrid transmission method for time and event-triggered streams in industrial wireless networks. Background Art

[0002] Industrial Wireless Network (IWN) uses wireless communication technology to achieve networking and data transmission of industrial field instruments, sensors and other equipment. Compared with industrial field bus technology, it has the characteristics of flexible deployment and low maintenance cost. IWN mainly includes two types of traffic: TT (Time-Triggered) flow and ET (Event-Triggered) flow.

[0003] TT streams have a fixed generation cycle and strict delay and delay jitter requirements, and are used to characterize periodic sampling data in industrial control systems; ET streams are used to characterize bursty traffic in industrial sound fields, and their sampling cycle is not constant, such as bursty data in sporadic emergency events, as well as audio and video data. Existing technologies still have the following deficiencies:

[0004] (1) Commercial wireless networks represented by WiFi, ZigBee and LoRa all use competitive transmission mechanisms such as Carrier Sense Multiple Access (CSMA) and Slotted Aloha at the Media Access Control (MAC) layer, which makes it difficult to guarantee the real-time transmission requirements of TT flows in industrial networks.

[0005] (2) The MAC layer of industrial wireless networks represented by WirelessHART, ISA100.11a and WIA-PA adopts the time division multiple access (TDMA) protocol to avoid transmission collisions. However, on the one hand, existing research has failed to establish a first-order logic model for conflict-free transmission of TT flows, making it difficult to achieve efficient allocation of time slot resources. On the other hand, considering the burstiness of ET flows, existing research has failed to design a transmission mechanism for ET flows based on conflict-free transmission of TT flows.

[0006] How to design hybrid transmission for TT and ET flows and complete end-to-end delay analysis of TT and ET flows is an important challenge facing IWN applications.

[0007] The present invention is based on the existing star-type IWN topology. Figure 1 As shown, it contains 1 gateway node (denoted as v GW), N TT nodes, M ET nodes, TT nodes generate TT flows (any i-th TT flow is represented as T i ), ET nodes generate ET flows (representing any i-th ET flow as E i ), both TT flow and ET flow are transmitted to the gateway node.

[0008] All nodes in IWN use half-duplex mode for communication, that is, any node can only be in any one of the states of sending, receiving or idle at the same time. Therefore, gateway conflict is the main factor affecting whether the data stream can be successfully transmitted. Gateway conflict is defined as follows: The situation where the gateway cannot successfully receive messages in the same time slot due to the sharing of communication nodes between wireless transmissions is called gateway conflict. Figure 2 As shown, at the same time v GW There will be a gateway conflict when receiving data from nodes v1 and v2 at the same time.

[0009] The essence of the mixed transmission of TT and ET flows in IWN is to meet the end-to-end delay requirements of each data flow while reducing gateway conflicts. i For , the following four-tuple is used:

[0010] T i ={T i .period,T i .birth,T i .length,T i .offset}

[0011] Where T i .period means T i The generation cycle, that is, T i With period T i .period generates messages with a period of T i .period is transmitted to the gateway node. T i The generation time of the first message is denoted as T i .birth,T i .length means T i The transmission delay, T i .offset means T i The sending time of the first message. Considering T i .period, T i .birth and T i.length are all constants, so the essence of conflict-free transmission of TT streams is to use centralized scheduling to determine the sending time of the first message of each TT stream. Considering that TT streams are generated and transmitted periodically, existing research lacks a first-order logic constraint model for conflict-free transmission of TT streams.

[0012] Compared with TT flow, ET flow does not have a fixed generation cycle, and the generation time of each message usually obeys a certain probability distribution such as Poisson distribution. Considering the burstiness of messages in ET flow, it is difficult to use centralized scheduling to pre-plan the time slot resources occupied by each message. Therefore, the essence of ET flow transmission is that each message competes for time slot resources in a distributed manner and completes message transmission. However, on the one hand, existing research lacks a hybrid transmission scheme for TT flow and ET flow, that is, how to design a transmission strategy for ET flow while avoiding occupying TT flow time slot resources; on the other hand, further analyzing the end-to-end average delay of ET flow based on the above transmission strategy will help IWN to know the degree to which network performance meets application requirements during the design stage, thereby guiding the deployment of IWN. Summary of the invention

[0013] The purpose of the present invention is to provide a hybrid transmission method for time and event triggered streams in industrial wireless networks.

[0014] The present invention is achieved through the following technical solutions:

[0015] The present invention relates to a hybrid transmission method for time and event triggered streams in an industrial wireless network, comprising the following steps:

[0016] Step 1: Considering the factors of node conflict and end-to-end delay, a first-order logic constraint model for time-triggered conflict-free transmission of TT flows is established, and centralized scheduling of time slot resources is implemented based on the Gurobi solver to achieve conflict-free transmission of TT flows in IWN.

[0017] Step 2: Based on the centralized scheduling of TT flows, a time slot Aloha-based ET flow competition transmission mechanism is designed to achieve mixed transmission of TT flows and ET flows while ensuring that ET flows do not occupy TT flow time slot resources.

[0018] Preferably, in step 1, the specific process of establishing the first-order logic constraint model of time-triggered TT flow conflict-free transmission is as follows: as shown in formula (1):

[0019]

[0020] In formula (1), T = {T1, T2, ... T N} represents the TT flow set in IWN, GCD(T k ,T j ) indicates Tk .period and T j .The greatest common divisor of period, mod is the modulus operator;

[0021] Among them, the decision variable is an N-dimensional vector, as shown in formula (2):

[0022] Var={T1.offset,T2.offset,…,T N .offset} (2);

[0023] For any TT flow T k For , its end-to-end delay must meet the application requirements. The end-to-end delay constraint is shown in formula (3):

[0024]

[0025] In formula (3), T k .maxdelay means T k end-to-end latency requirement.

[0026] Preferably, in step 1, the centralized scheduling of time slot resources based on the Gurobi solver is specifically: the constraint model and decision variables are imported into the Gurobi solver for solving, and the overall pseudo code is as follows:

[0027] Input: TT flow set T in IWN = {T1, T2, ... T N}, constraint set Decision variable set Var = {T1.offset, T2.offset, …, T N .offset}

[0028] Output: Decision variable Var = {T1.offset, T2.offset, …, T N .offset}

[0029]

[0030] in,

[0031] Preferably, in step 2, the specific steps of designing the ET flow competition transmission mechanism based on time slot Aloha are as follows:

[0032] (1) Set the ET node sending probability P;

[0033] (2) Network operation after initialization;

[0034] (3) ET data packet arrives;

[0035] (4) Determine whether it is the first row of data packets; if so, send the data packet with probability P when the time slot is idle; if not, wait to become the first row of data packets for data transmission;

[0036] (5) No collision occurs and the transmission is successful.

[0037] In step 2, in a real network environment, the sending probability p of the ET node can be adjusted according to network requirements. After selecting the appropriate sending probability p and completing other initialization work, the network starts running; when a data packet arrives at the event-triggered node in the network, it will be stored in the node buffer by default. If the buffer is empty when the data packet arrives, the data packet is the first row data packet; if the buffer is not empty when the data packet arrives, it is necessary to queue and wait for the first data packet to be sent until it becomes the first row data packet. After becoming the first row data packet, since the current time slot may be occupied by the TT flow, it is necessary to determine whether the current time slot is idle. If the current time slot is not occupied by the time-triggered flow, the time slot is idle, and the event-triggered node attempts to send with probability p. If you choose to send, it may collide with other event-triggered nodes. If a collision occurs, wait for the next idle time slot to try to send again. If no collision occurs, the sending is successful. If you choose not to send, you need to wait until the next idle time slot to try to send again.

[0038] The present invention has the following advantages:

[0039] The present invention establishes a first-order logic constraint model for time-triggered conflict-free transmission of TT streams to ensure that TT streams can exclusively use time slot resources; without occupying TT stream transmission resources, a low-latency distributed competition access mechanism for ET streams is designed to achieve mixed transmission of TT streams and ET streams. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the network architecture diagram for mixed transmission of TT and ET streams;

[0041] Figure 2 Yes GW Receive data from v1 and v2 at the same time to generate a node conflict demonstration diagram;

[0042] Figure 3 This is the macrocycle scheduling result diagram when the TT flow length is less than the basic cycle;

[0043] Figure 4 This is the end-to-end delay result of macrocycle scheduling when the TT flow length is less than the basic cycle.

[0044] Figure 5 This is the macrocycle scheduling result diagram when the TT flow length is greater than the basic cycle;

[0045] Figure 6This is the end-to-end delay result diagram of macrocycle scheduling when the TT flow length is greater than the basic cycle;

[0046] Figure 7 YesN E =5,P=0.5, the average delay comparison chart of different ET flow average arrival rates;

[0047] Figure 8 YesN E =20,λ=0.001, the average delay comparison diagram of different ET flow sending probabilities;

[0048] Fig. 9 This is the average delay comparison chart for different numbers of ET nodes when p = 0.2 and λ = 0.01;

[0049] Fig.10 It is a flow chart of the specific scheme of ET stream transmission mechanism;

[0050] Fig.11 It is a schematic diagram of the method of the present invention. DETAILED DESCRIPTION

[0051] The present invention is described in detail below in conjunction with specific embodiments. It should be noted that the following embodiments are only further descriptions of the present invention, but the protection scope of the present invention is not limited to the following embodiments.

[0052] Example

[0053] This embodiment relates to a hybrid transmission method for time and event triggered streams in an industrial wireless network. Fig.11 As shown, the following steps are included:

[0054] Step 1: Considering the factors of node conflict and end-to-end delay, a first-order logic constraint model for time-triggered conflict-free transmission of TT flows is established, and centralized scheduling of time slot resources is implemented based on the Gurobi solver to achieve conflict-free transmission of TT flows in IWN.

[0055] Step 2: Based on the centralized scheduling of TT flows, a time slot Aloha-based ET flow competition transmission mechanism is designed to achieve mixed transmission of TT flows and ET flows while ensuring that ET flows do not occupy TT flow time slot resources. Fig.10 As shown;

[0056] In step 1, the specific method of establishing the first-order logic constraint model of time-triggered TT flow conflict-free transmission is as follows: as shown in formula (1):

[0057]

[0058] In formula (1), T = {T1, T2, ... T N} represents the TT flow set in IWN, GCD(T k ,T j ) indicates T k .period and T j .The greatest common divisor of period, mod is the modulus operator;

[0059] Among them, the decision variable is an N-dimensional vector, as shown in formula (2):

[0060] Var={T1.offset,T2.offset,…,T N .offset} (2);

[0061] For any TT flow T k For , its end-to-end delay must meet the application requirements. The end-to-end delay constraint is shown in formula (3):

[0062]

[0063] In formula (3), T k .maxdelay means T k end-to-end latency requirement.

[0064] In step 1, the centralized scheduling of time slot resources based on the Gurobi solver is specifically as follows: the constraint model and decision variables are imported into the Gurobi solver for solving. The overall pseudo code is as follows: Input: TT flow set T in IWN = {T1, T2, ... T N}, constraint set Decision variable set Var = {T1.offset, T2.offset, …, T N .offset}

[0065] Output: Decision variable Var = {T1.offset, T2.offset, …, T N .offset}

[0066]

[0067] in,

[0068] Results Figure 3-Figure 6 As shown in FIG. 1 , this embodiment realizes centralized scheduling of time slot resources and optimizes end-to-end delay on the basis of achieving conflict-free transmission. ee The scheduling method with the scheduling target (referred to as TS1) and D lcm Compared with the scheduling method for scheduling target (referred to as TS2), TS1 can guarantee D ee Minimize, that is, NT The average delay of each TT flow is the smallest. TS2 can ensure the minimum total delay of the scheduling table that cycles with a macro cycle, but the delay of a single TT flow may be large. Therefore, in actual industrial applications, it is necessary to select a scheduling method based on specific application requirements and scenarios.

[0069] In step 2, the specific steps of designing the ET flow competition transmission mechanism based on time slot Aloha are as follows:

[0070] (1) Set the ET node sending probability P;

[0071] (2) Network initialization and operation;

[0072] (3) ET data packet arrives;

[0073] (4) Determine whether it is the first row of data packets; if so, send the data packet with probability P when the time slot is idle; if not, wait to become the first row of data packets for data transmission;

[0074] (5) No collision occurs and the transmission is successful.

[0075] In step 2, in a real network environment, the transmission probability p of the ET node can be adjusted according to network requirements. After selecting a suitable transmission probability p and completing other initialization work, the network starts to run. The ET stream transmission mechanism designed by the present invention is as follows: Fig.10 As shown. When a data packet arrives at an event-triggered node in the network, it will be stored in the node buffer by default. If the buffer is empty when the data packet arrives, the data packet is the first row of data packets; if the buffer is not empty when the data packet arrives, it is necessary to queue and wait for the first data packet to be sent until it becomes the first row of data packets. After becoming the first row of data packets, since the current time slot may be occupied by the TT flow, it is necessary to determine whether the current time slot is idle. If the current time slot is not occupied by the time-triggered flow, the time slot is idle, and the event-triggered node attempts to send with a probability of p. If you choose to send, it may collide with other event-triggered nodes. If a collision occurs, wait for the next idle time slot to try to send again. If no collision occurs, the sending is successful. If you choose not to send, you need to wait until the next idle time slot to try to send again.

[0076] like Figure 7-Figure 9 As shown in the figure, experimental verification under different network parameters is demonstrated. The experiment shows that in different network environments, the network utilization can be maximized by adjusting appropriate parameters.

[0077] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which will not affect the essence of the present invention.

Claims

1. A hybrid transmission method for time and event triggered streams in industrial wireless networks, characterized in that: The following steps are involved: Step 1: Considering the factors of node conflict and end-to-end delay, a first-order logic constraint model for time-triggered conflict-free transmission of TT flows is established, and centralized scheduling of time slot resources is implemented based on the Gurobi solver to achieve conflict-free transmission of TT flows in IWN. Step 2: Based on the centralized scheduling of TT flows, a time slot Aloha-based ET flow competition transmission mechanism is designed to achieve mixed transmission of TT flows and ET flows without occupying TT flow time slot resources.

2. The hybrid transmission method for time and event triggered streams in industrial wireless networks according to claim 1, characterized in that: In step 1, the specific process of establishing the first-order logic constraint model of time-triggered TT flow conflict-free transmission is as follows: In formula (1), T = {T1, T2, ... T N } represents the set of TT flows in IWN, GCD(T k ,T j ) indicates T k .period and T j .The greatest common divisor of period, mod is the modulus operator; Among them, the decision variable is an N-dimensional vector, as shown in formula (2): Where={T1.offset,T2.offset,…,T N .offset} (2); For any TT flow T k For , its end-to-end delay must meet the application requirements. The end-to-end delay constraint is shown in formula (3): In formula (3), T k .maxdelay means T k end-to-end latency requirement.

3. The hybrid transmission method for time and event triggered streams in industrial wireless networks according to claim 1, characterized in that: In step 1, the centralized scheduling of time slot resources based on the Gurobi solver is specifically as follows: the constraint model and decision variables are imported into the Gurobi solver for solving. The overall pseudo code is as follows: Input: TT flow set T in IWN = {T1, T2, ... T N }, constraint set Decision variable set Var = {T1.offset, T2.offset, …, T N .offset} Output: Decision variable Var = {T1.offset, T2.offset, …, T N .offset} in, 4. The hybrid transmission method for time and event triggered streams in industrial wireless networks according to claim 1, characterized in that: In step 2, the specific steps of designing the ET flow competition transmission mechanism based on time slot Aloha are as follows: (1) Set the ET node sending probability P; (2) Network operation after initialization; (3) ET data packet arrives; (4) Determine whether it is the first row of data packets; if so, send the data packet with probability P when the time slot is idle; if not, wait to become the first row of data packets for data transmission; (5) No collision occurs and the transmission is successful.

Images