A hybrid transmission method for time-triggered and event-triggered streams

Abstract

This invention provides a hybrid transmission method for time-triggered and event-triggered streams in industrial wireless networks (IWNs). The method includes: Step 1, establishing a first-order logical constraint model for conflict-free transmission of time-triggered (TT) streams, and implementing centralized scheduling of time slot resources based on the Gurobi solver to achieve conflict-free transmission of TT streams in IWNs; Step 2, based on the centralized scheduling of TT streams, designing an ET stream contention transmission mechanism based on time slot Aloha, achieving hybrid transmission of TT and ET streams without consuming TT stream time slot resources. This invention ensures that TT streams can exclusively enjoy time slot resources by establishing a first-order logical constraint model for conflict-free transmission of time-triggered TT streams; and designs a low-latency distributed contention access mechanism for ET streams without consuming TT stream transmission resources, thus achieving hybrid transmission of TT and ET streams.

Description

Technical Field

[0001] This invention belongs to the field of industrial wireless network technology; in particular, it relates to a hybrid transmission method of time-triggered stream and event-triggered stream. Background Technology

[0002] Industrial Wireless Networks (IWNs) utilize wireless communication technology to network and transmit data between industrial field instruments and sensors. Compared to industrial fieldbus technology, they offer advantages such as flexible deployment and low maintenance costs. IWNs primarily include two traffic types: TT streams and ET streams. TT streams have a fixed generation period and strict requirements for latency and jitter, used to characterize periodic sampling data in industrial control systems. ET streams are used to characterize bursty traffic in industrial sound fields; their sampling period is not constant, such as bursty data from sporadic emergency events, as well as audio and video data. Existing technologies still have the following shortcomings:

[0003] (1) Commercial wireless networks such as WiFi, ZigBee and LoRa all use competitive transmission mechanisms such as Carrier Sense Multiple Access (CSMA) and Time Slot Aloha at the Media Access Control (MAC) layer, which makes it difficult to guarantee the real-time transmission requirements of TT streams in industrial networks.

[0004] (2) Industrial wireless networks such as WirelessHART, ISA100.11a and WIA-PA use 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 logical model for collision-free transmission of TT streams, making it difficult to achieve efficient allocation of time slot resources. On the other hand, considering the burstiness of ET streams, existing research has failed to design a transmission mechanism for ET streams based on collision-free transmission of TT streams.

[0005] Designing hybrid transmission for TT and ET streams and performing end-to-end delay analysis for both TT and ET streams are significant challenges for IWN applications.

[0006] This invention is based on the existing star IWN topology, see Figure 1 As shown, it contains one gateway node (represented as v). GW N TT nodes and M ET nodes, where TT nodes generate TT streams (represent any i-th TT stream as T). i ), ET nodes generate ET flows (representing any i-th ET flow as E). iBoth the TT stream and the ET stream are transmitted to the gateway node.

[0007] In IWN, all nodes communicate in half-duplex mode, meaning that any node can only be in one of three states—transmitting, receiving, or idle—at any given time. Therefore, gateway collisions are a major factor affecting the successful transmission of data streams. A gateway collision is defined as follows: a situation where a gateway cannot successfully receive messages in the same time slot due to shared communication nodes between wireless transmissions is called a gateway collision. See [link to relevant documentation] Figure 2 As shown, at the same time v GW Gateway conflicts can occur when receiving data from both nodes v1 and v2 simultaneously.

[0008] The essence of the mixed transmission problem of TT and ET streams in IWN is to reduce gateway conflicts while meeting the end-to-end latency requirements of each data stream. For any TT stream T i In this case, the following quadruple representation is used:

[0009] T i ={T i .period,T i .birth,T i .length,T i .offset}

[0010] Where T i .period represents T i The generation cycle, i.e., T i With period T i .period generates messages and uses a period T. i The .period data is transmitted to the gateway node. (T) i The time of generation of the first message is represented as T. i .birth, T i .length represents T i The transmission delay, T i .offset represents T i The sending time of the first message. Considering T in the TT stream. i .period、T i .birth and T i Since `.length` is a constant, the essence of collision-free TT stream transmission is to use centralized scheduling to determine the sending time of the first message in each TT stream. Considering that TT streams are generated and transmitted periodically, existing research lacks a first-order logical constraint model for collision-free TT stream transmission.

[0011] Compared to TT streams, ET streams do not have a fixed generation cycle; the generation time of each message typically follows a probability distribution such as a Poisson distribution. Considering the burstiness of messages in ET streams, it is difficult to use centralized scheduling to pre-plan the time slot resources occupied by each message. Therefore, the essence of ET stream transmission is that each message competes for time slot resources in a distributed manner to complete message transmission. However, on the one hand, existing research lacks hybrid transmission schemes for TT and ET streams, i.e., how to design transmission strategies for ET streams while avoiding the occupation of TT stream time slot resources; on the other hand, further analysis of the end-to-end average latency of ET streams based on the above transmission strategies will help IWN understand the degree to which network performance meets application requirements during the design phase, thereby guiding IWN deployment. Summary of the Invention

[0012] The purpose of this invention is to provide a hybrid transmission method for time-triggered streams and event-triggered streams.

[0013] This invention is achieved through the following technical solution:

[0014] This invention relates to a hybrid transmission method for time-triggered streams and event-triggered streams, comprising the following steps:

[0015] Step 1: Considering node conflicts and end-to-end delay factors, establish a first-order logical constraint model for time-triggered TT stream conflict-free transmission, and realize centralized scheduling of time slot resources based on the Gurobi solver to achieve conflict-free transmission of TT streams in IWN.

[0016] Step 2: Based on the centralized scheduling of TT streams, design an ET stream contention transmission mechanism based on time slot Aloha to achieve mixed transmission of TT streams and ET streams while ensuring that ET streams do not occupy TT stream time slot resources.

[0017] Preferably, in step 1, the specific process of establishing the first-order logical constraint model for time-triggered TT stream conflict-free transmission is as follows: see equation (1):

[0018]

[0019] In equation (1), T = {T1, T2, ..., T} N} represents the set of TT streams in IWN, GCD(T) k ,T j ) represents T k .period and T j The greatest common divisor of .period, where mod is the modulo operator;

[0020] The decision variables are N-dimensional vectors, as shown in equation (2):

[0021] Var={T1.offset,T2.offset,…,T N .offset} (2); For any TT stream T k In this regard, its end-to-end latency must meet the application requirements, and the end-to-end latency constraint is shown in equation (3):

[0022]

[0023] In equation (3), T k .maxdelay represents T k End-to-end latency requirements.

[0024] Preferably, in step 1, the centralized scheduling of time slot resources based on the Gurobi solver specifically involves: importing the constraint model and decision variables into the Gurobi solver for solving, as shown in the following pseudocode:

[0025] Input: A set of TT streams T = {T1, T2, ..., T} in IWN N}, constraint set ,decision making

[0026] The variable set Var = {T1.offset, T2.offset, ..., T} N .offset}

[0027] Output: Decision variable Var = {T1.offset, T2.offset, ..., T N The value of .offset}

[0028]

[0029] in,

[0030] Preferably, in step 2, the specific steps for designing the ET stream contention transmission mechanism based on time-slot Aloha are as follows:

[0031] (1) Set the ET node transmission probability P;

[0032] (2) Run after network initialization;

[0033] (3) The ET data packet has arrived;

[0034] (4) Determine if it is the first data packet; if so, send the data packet with probability P when the time slot is idle; if not, wait to become the first data packet for data transmission.

[0035] (5) No collision occurred, transmission successful.

[0036] In step 2, in a real-world network environment, the transmission probability p of an ET node can be adjusted according to network requirements. After selecting an appropriate transmission probability p and completing other initialization tasks, the network begins operation. When a data packet arrives at an event-triggered node in the network, it is stored in the node's buffer by default. If the buffer is empty when the data packet arrives, it becomes the first data packet. If the buffer is not empty when the data packet arrives, it needs to queue and wait for the first arriving data packet to finish sending until it becomes the first data packet. Once it becomes the first data packet, since the current time slot may be occupied by the TT stream, it is necessary to determine whether the current time slot is idle. If the current time slot is not occupied by the time-triggered stream, the time slot is idle, and the event-triggered node attempts to send with probability p. If it chooses to send, it may collide with other event-triggered nodes. If a collision occurs, it waits for the next idle time slot to try sending again; if no collision occurs, the transmission is successful. If it chooses not to send, it needs to wait for the next idle time slot to try sending again.

[0037] The present invention has the following advantages:

[0038] This invention establishes a first-order logical constraint model for time-triggered conflict-free transmission of TT streams, ensuring that TT streams can exclusively enjoy time slot resources. Without occupying TT stream transmission resources, a low-latency distributed contention access mechanism for ET streams is designed to achieve hybrid transmission of TT streams and ET streams. Attached Figure Description

[0039] Figure 1 This is a diagram of a network architecture for hybrid TT and ET stream transmission.

[0040] Figure 2 It is v GW A diagram illustrating node conflict generated by simultaneously receiving data from v1 and v2;

[0041] Figure 3 This is a diagram showing the macro-cycle scheduling results when the TT flow length is less than the basic cycle.

[0042] Figure 4 This is a graph showing the end-to-end delay results of macro-periodic scheduling when the TT stream length is less than the fundamental period.

[0043] Figure 5 This is a diagram showing the macro-cycle scheduling results when the TT stream length is greater than the basic cycle.

[0044] Figure 6 This is a graph showing the end-to-end delay results of macro-cycle scheduling when the TT stream length is greater than the basic period;

[0045] Figure 7 It is N E Comparison of average delay for different ET flow average arrival rates when P=5 and P=0.5;

[0046] Figure 8 It is N E Comparison of average latency for different ET stream transmission probabilities when λ = 20 and λ = 0.001;

[0047] Figure 9 This is a comparison chart of the average time delay for different numbers of ET nodes when p = 0.2 and λ = 0.01;

[0048] Figure 10 This is a flowchart of the specific scheme for the ET stream transmission mechanism;

[0049] Figure 11 This is a schematic diagram of the method of the present invention. Detailed Implementation

[0050] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are merely further illustrations of the present invention, but the scope of protection of the present invention is not limited to the following embodiments.

[0051] Example

[0052] This embodiment relates to a hybrid transmission method for time-triggered streams and event-triggered streams, see [link to documentation]. Figure 11 As shown, it includes the following steps:

[0053] Step 1: Considering node conflicts and end-to-end delay factors, establish a first-order logical constraint model for time-triggered TT stream conflict-free transmission, and realize centralized scheduling of time slot resources based on the Gurobi solver to achieve conflict-free transmission of TT streams in IWN.

[0054] Step 2: Based on the centralized scheduling of TT streams, design an ET stream contention transmission mechanism based on slotted Aloha. This mechanism ensures that ET streams do not occupy TT stream slot resources, thus enabling mixed transmission of TT and ET streams. (See...) Figure 10 As shown;

[0055] In step 1, the specific method for establishing the first-order logical constraint model for time-triggered TT stream conflict-free transmission is as follows: see equation (1):

[0056]

[0057] In equation (1), T = {T1, T2, ..., T} N} represents the set of TT streams in IWN, GCD(T) k ,T j ) represents T k .period and T j The greatest common divisor of .period, where mod is the modulo operator;

[0058] The decision variables are N-dimensional vectors, as shown in equation (2):

[0059] Var={T1.offset,T2.offset,…,T N .offset} (2);

[0060] For any TT stream T k In this regard, its end-to-end latency must meet the application requirements, and the end-to-end latency constraint is shown in equation (3):

[0061]

[0062] In equation (3), T k .maxdelay represents T k End-to-end latency requirements.

[0063] In step 1, the centralized scheduling of time slot resources based on the Gurobi solver specifically involves: importing the constraint model and decision variables into the Gurobi solver for solving. The overall pseudocode is as follows:

[0064] Input: A set of TT streams T = {T1, T2, ..., T} in IWN N}, constraint set ,decision making

[0065] The variable set Var = {T1.offset, T2.offset, ..., T} N .offset}

[0066] Output: Decision variable Var = {T1.offset, T2.offset, ..., T} N The value of .offset}

[0067]

[0068] in,

[0069] D ee Delay represents the sum of the end-to-end delays of all TT streams. i N represents the time required for a TT stream to be generated and successfully sent, in total. T The sum of the TT streams is the total end-to-end delay of all TT streams; D lcm This represents the sum of end-to-end delays of all individual TT streams within the macrocycle, compared to D. ee The difference is that the TT stream may be sent multiple times within a macro period, while the D stream... ee Calculated only once, D lcmThe calculation is performed multiple times (the number of times the data is actually transmitted within the macro period is accumulated). LCM stands for Greatest Common Multiple, which in this invention represents the greatest common multiple of all TT flow periods, i.e., the macro period. For example, if there are only TT flows in the network... A With TT B These two types of TT flow, and TT A The period is 2, TT B If the period is 3, then the LCM is 6.

[0070] See results Figures 3-6 As shown, this embodiment implements centralized scheduling of time slot resources and optimizes end-to-end latency while achieving conflict-free transmission. Furthermore, results demonstrate that... ee The scheduling method for the scheduling target (TS1) and the scheduling method based on D lcm Compared to scheduling methods for scheduling target (TS2), TS1 can guarantee D ee Minimize, i.e., N T While TS2 can guarantee the minimum average latency for all TT streams and minimize the total latency of the scheduling table that cycles around the macro period, it may result in significant latency for individual TT streams. Therefore, in practical industrial applications, the scheduling method needs to be selected based on specific application requirements and scenarios.

[0071] In step 2, the specific steps of designing the ET stream contention transmission mechanism based on time-slot Aloha are as follows:

[0072] (1) Set the ET node transmission probability P;

[0073] (2) Run after network initialization;

[0074] (3) The ET data packet has arrived;

[0075] (4) Determine if it is the first data packet; if so, send the data packet with probability P when the time slot is idle; if not, wait to become the first data packet for data transmission.

[0076] (5) No collision occurred, transmission successful.

[0077] In step 2, in a real-world 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 tasks, the network begins operation. The ET stream transmission mechanism designed in this invention is as described above. Figure 10As shown. When a data packet arrives at an event-triggered node in the network, it is stored in the node's buffer by default. If the buffer is empty when the data packet arrives, it becomes the first data packet. If the buffer is not empty, the data packet needs to queue and wait for the first arriving data packet to finish sending until it becomes the first data packet. Once it becomes the first data packet, since the current time slot may be occupied by a TT stream, it is necessary to determine whether the current time slot is idle. If the current time slot is not occupied by a time-triggered stream, the time slot is idle, and the event-triggered node attempts to send with probability p. If it chooses to send, it may collide with other event-triggered nodes. If a collision occurs, it waits for the next idle time slot to try sending again; if no collision occurs, the transmission is successful. If it chooses not to send, it needs to wait for the next idle time slot to try sending again.

[0078] like Figures 7-9 As shown, experimental verification under different network parameters is presented. The experiments demonstrate that network utilization can be maximized by adjusting appropriate parameters under different network environments.

[0079] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A hybrid transmission method for time-triggered streams and event-triggered streams, characterized in that, Includes the following steps: Step 1: Considering node conflicts and end-to-end delay factors, establish a first-order logical constraint model for time-triggered TT stream conflict-free transmission, and realize centralized scheduling of time slot resources based on the Gurobi solver to achieve conflict-free transmission of TT streams in IWN. Step 2: Based on the centralized scheduling of TT streams, design an ET stream contention transmission mechanism based on time slot Aloha to achieve mixed transmission of TT streams and ET streams without ET streams occupying TT stream time slot resources. In step 1, the specific process of establishing the first-order logical constraint model for time-triggered TT stream conflict-free transmission is as follows: see equation (1): In equation (1), T = {T1, T2, ..., T} N } represents the set of TT streams in IWN, GCD(T) k ,T j ) represents T k .period and T j The greatest common divisor of .period, where mod is the modulo operator; T i .offset, T j .offset represents the sending time offset of any TT stream, where T i and T j For different TT streams; T i .length、T j .length represents the length of any TT stream; where T i and T j For different TT streams; The decision variables are N-dimensional vectors, as shown in equation (2): Where={T1.offset,T2.offset,…,T N .offset} (2); For any TT stream T k In this regard, its end-to-end latency must meet the application requirements, and the end-to-end latency constraint is shown in equation (3): In equation (3), T k .maxdelay represents T k End-to-end latency requirements; T k .offset represents the sending time of any TT stream, relative to the TT stream generation time T. k .birth offset; T k .birth represents the generation time of any TT stream; T k .length represents the length of any TT stream; In step 1, the centralized scheduling of time slot resources based on the Gurobi solver specifically involves: importing the constraint model and decision variables into the Gurobi solver for solving. in, With D ee For scheduling objectives or with D lcm Select the scheduling method for the scheduling target; D ee This represents the total end-to-end latency of a single transmission of all TT streams; D lcm This represents the sum of the end-to-end delays of all individual TT streams within the macro cycle; In step 2, the specific steps of designing the ET stream contention transmission mechanism based on time-slot Aloha are as follows: (1) Set the ET node transmission probability P; (2) Run after network initialization; (3) The ET data packet has arrived; (4) Determine if it is the first data packet; if so, send the data packet with probability P when the time slot is idle; if not, wait to become the first data packet for data transmission. (5) No collision occurred, transmission successful.

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