CN109362122B

CN109362122B - Transmission scheduling method and system for communication data in low-power-consumption wide area network

Info

Publication number: CN109362122B
Application number: CN201811062056.4A
Authority: CN
Inventors: 江涛; 黄希; 崔莉
Original assignee: Institute of Computing Technology of CAS
Current assignee: Institute of Computing Technology of CAS
Priority date: 2018-09-12
Filing date: 2018-09-12
Publication date: 2020-09-04
Anticipated expiration: 2038-09-12
Also published as: CN109362122A

Abstract

The invention relates to a transmission scheduling method and a system of communication data in a low-power-consumption wide area network, which comprises the following steps: step S1, constructing a wide area network, wherein the wide area network comprises communication nodes and a gateway, the communication nodes are accessed to the gateway in a single-hop mode, and the gateway provides time for the communication nodes and allocates communication time slots during access; step S2, the communication node actively transmits the communication data and the generation time of the communication data to the gateway in the communication time slot; step S3, the gateway updates the communication time slot of the communication node according to the generation time and the communication time slot; step S4, loop through step S2 and step S3 to implement transmission scheduling for the wide area network. Therefore, for a low-power-consumption wide area network, the invention can realize high channel utilization rate, low delay and low-power-consumption transmission scheduling in an application layer.

Description

Transmission scheduling method and system for communication data in low-power-consumption wide area network

Technical Field

The present invention relates to the field of wireless communications, and in particular, to a method and a system for scheduling transmission of communication data in a low power consumption wide area network.

Background

The wireless sensor network is composed of a large number of autonomous nodes densely deployed in a monitoring area, and is a self-organizing network application system formed in a wireless communication mode, widely applied to multiple fields of military affairs, intelligent transportation, environment monitoring, medical health and the like, and is a high-technology industry recognized at home and abroad and having wide development prospects.

The power consumption, the cost and the deployment difficulty are three main problems faced by a wireless sensor network, and the existing wireless sensor network generally adopts Zigbee nodes with low cost and mature protocol stacks, wherein Zigbee is a standard low-power local area network protocol, and the Zigbee nodes connect the nodes together in a self-organizing manner to establish the network. However, the Zigbee network is limited by the node signal transmission distance, the nodes in the Zigbee network need to relay and forward data to the gateway in a multi-hop manner through other nodes, and the nodes need to listen and forward data packets of other nodes in the network, so that the energy overhead caused by listening is large, and the popularization of the application of the wireless sensor network is hindered.

In recent years, with the progress of communication technology, a low power consumption wide area network featuring low power consumption, low speed and long distance communication has become one of the development directions of sensor networks and internet of things. The advantage that low-power consumption wide area network signal transmission distance is far away allows the node single hop to transmit data to the gateway, and the node need not listen and forward data, allows the node to accomplish and close the radio frequency module with gateway data transmission back to reduced the node consumption, the advantage of low-power consumption lets low-power consumption wide area network become the important development direction of wireless sensor network gradually. However, for the low communication rate, the same data amount occupies a long channel time; the transmission distance is long, the deployment density of the same nodes is high, and the number of gateway load nodes is large. The characteristics of low communication speed and long transmission distance cause the shortage of network channel resources, and a novel transmission scheduling algorithm is needed to effectively improve the utilization rate of a wireless channel, so that the requirement of data transmission rate is met.

The transmission scheduling method in the wireless sensor network protocol stack is responsible for allocating wireless communication resources to the nodes, and is an important technology related to key performance indexes such as channel utilization rate, delay and the like of a wireless network. The method adopted by the prior art comprises the steps that a node immediately transmits data to be transmitted to compete for a channel, if the data transmission fails, the data is retransmitted after random delay, and the upper limit of the channel utilization rate is 18.6%. The improved method segments the channel in time, each node can only transmit data at the beginning of one segment, and the upper limit of the channel utilization rate is increased to 36.8%. The characteristics of low baud rate and long signal transmission distance of the low-power-consumption wide area network cause that data transmission needs to occupy a long time, the number of network load nodes is large, a transmission scheduling method requiring high channel utilization rate is required, and the Aloha of a random contention channel and an improvement method thereof have low channel utilization rate and are difficult to be applied to the low-power-consumption wide area network. Therefore, the probability of data collision can be reduced by adopting a mode of detecting the channel state, the channel utilization rate is improved, but the detection of the channel state requires the node to monitor the channel, and the method cannot be applied to a low-power-consumption wide area network in which the node does not continuously monitor. The transmission scheduling method based on scheduling allocates communication time slots for each node to avoid mutual interference among the nodes, and the method focuses on a multi-hop network, takes indexes such as network throughput, data delay and the like as optimization targets, for example, if the network is modeled as a graph model and is solved by using the Gaussian domain principle, the complexity of the transmission scheduling method is increased by using the multi-hop characteristic, and the network performance of the centralized low-power-consumption wide area network is reduced. In summary, the existing transmission scheduling method is difficult to be applied to the low-power-consumption wide area network, and a novel transmission scheduling method needs to be researched facing the low-power-consumption wide area network.

Disclosure of Invention

The invention aims to provide a transmission scheduling method facing a low-power-consumption network and having high channel utilization rate in a network application layer aiming at the defect of channel resource shortage in the low-power-consumption wide area network, and simultaneously effectively improves key performances of network data delay, power consumption and load capacity. It should be noted that the present invention may also be applied to a general wide area network, but in a low power consumption wide area network, the characteristic of channel resource shortage is more prominent, but the general wide area network is not in shortage in channel resource at present, and the method is not so much needed, and at the same time, the data types of the two are different, and the used channel allocation methods are also different.

Specifically, the invention discloses a transmission scheduling method of communication data in a low-power-consumption wide area network, which comprises the following steps:

step S1, constructing a wide area network, wherein the wide area network comprises a communication node and a gateway, the communication node accesses the gateway in a single-hop mode, and the gateway provides time for the communication node and allocates communication time slots when accessing;

step S2, the communication node actively transmits the communication data and the generation time of the communication data to the gateway in the communication time slot;

step S3, the gateway updates the communication time slot of the communication node according to the generation time and the communication time slot;

step S4, looping through step S2 and step S3 to implement transmission scheduling for the wide area network.

The method for scheduling transmission of communication data in a low power consumption wide area network, wherein the step S1 includes: and constructing a time frame comprising N time slots, wherein the first time slot of the time frame is a public time slot, and when the communication node fails to successfully perform data transmission with the gateway in the allocated communication time slot, the communication node performs data transmission again with the gateway in the public time slot in the next time frame.

In the method for scheduling transmission of communication data in a low power consumption wide area network, the specific process of accessing the gateway by the communication node in step S1 includes:

step S11, resetting variables of Retry _ times and Reconnect _ times, wherein Retry _ times is used for recording the times of the communication nodes joining the network through a random back-off method, and Reconnect _ times is used for the times of the nodes transmitting data with the gateway through the public time slot;

step S12, checking whether Retry _ times exceeds a threshold value, if yes, executing step S13, otherwise, executing step S14;

step S13, the communication node exits the processing flow;

step S14, after the communication node carries out random backoff delay, the communication node starts radio frequency to send broadcast data and increases Retry _ times count;

step S15, if the communication node receives the gateway reply packet within the longest waiting gateway reply time threshold, the communication node joins the network successfully, step S17 is executed, otherwise, step S16 is executed;

step S16, turning off the radio frequency, and executing step S12;

step S17, closing the radio frequency, and clearing the Retry _ times parameter;

step S18: and analyzing the gateway loopback packet, updating the local time of the communication node, and acquiring the communication time slot.

The method for scheduling transmission of communication data in a low power consumption wide area network, wherein the step S2 specifically includes:

step S21, the communication node checks whether the time corresponding to the communication time slot is coming, if so, step S22 is executed, otherwise, the communication node continues to wait for the time slot to start;

step S22, checking whether there is communication data to be transmitted in the data queue of the communication node, if yes, executing step S23, otherwise, continuing to wait for data generation and executing step S21;

step S23, the communication node sends communication data to the gateway;

step S24, if the communication node receives the gateway return packet within the preset time threshold, the communication data transmission is successful, step S25 is executed, otherwise, step S27 is executed;

step S25, deleting the successfully transmitted communication data from the data queue;

step S26, updating the local time of the node and the communication time slot of the node by analyzing the gateway repackage;

step S27, checking whether the current communication time slot is finished, if yes, closing the radio frequency, otherwise, executing step S28;

step S28: checking whether the communication data to be transmitted still exist in the data queue, if so, executing step S23, otherwise, turning off the radio frequency.

The method for scheduling transmission of communication data in a low power consumption wide area network, wherein the step S3 includes:

step S31, the gateway always keeps the wireless radio frequency open and listens the channel;

step S32, when the gateway receives the communication data and the communication data is broadcast data or the number field of the gateway in the communication data is the same as the number of the gateway itself, executing step S33, otherwise, continuing to wait for the next communication data, executing step S32;

step S33, analyzing the communication data according to the format definition of the communication data, extracting the number of the communication node transmitting the communication data and the generation time of the communication data;

step S34, checking whether the gateway has access record corresponding to the communication node according to the number, if yes, executing step S38, otherwise executing step S35;

step S35, allocating a storage space for the communication node corresponding to the number, storing the communication node information by using a dictionary structure, and inserting the key value of the communication node into a dictionary, wherein the key is the number and the value is the storage position of the storage space corresponding to the communication node;

step S36, zeroing variables in the storage space of the communication nodes;

step S37, the gateway receives the node data packet for the first time, and the communication time slot allocated to the node is the public time slot;

step S38, judging whether a node flow model is established, if so, executing step S310, otherwise, executing step S39;

step S39, after the gateway obtains the communication node twice, the gateway initializes the traffic model of the communication node, and sets the current state S of the communication node as (Data _ time-last _ flow _ time)/T_slotInto a state space of which T_slotFor the length of the communication time slot, last _ flow _ time is the last communication Data generation time of the communication node, and Data _ time is the current communication Data generation time of the communication node;

step S310, updating a time slot occupation probability table according to a communication time slot occupied by the current communication data of the communication node;

step S311, updating the traffic model of the node according to the current node state and carrying out state transition;

step S312: predicting the next time communication data generation time and the corresponding probability of the communication node through a Markov chain, obtaining the delay expectation and the communication data collision probability of the communication node corresponding to each communication time slot in an allocation time frame according to the predicted communication data generation time and the corresponding probability, selecting the communication time slot with the minimum weighted sum of the delay expectation and the collision expectation as the optimal time slot, and enabling the communication node to occupy the optimal time slot for transmitting communication data next time.

The invention also discloses a transmission scheduling system of communication data in the low-power-consumption wide area network, which comprises the following steps:

the wide area network construction module is used for constructing a wide area network, the wide area network comprises a communication node and a gateway, the communication node is accessed to the gateway in a single-hop mode, and the gateway gives time to the communication node and allocates communication time slots when the communication node is accessed;

the data sending module is used for enabling the communication node to actively transmit communication data and the generation time of the communication data to the gateway in the communication time slot;

a communication time slot updating module, wherein the gateway updates the communication time slot of the communication node according to the generation time and the communication time slot;

and the circulating module is used for circularly calling and executing the data sending module and the communication time slot updating module so as to realize the transmission scheduling of the communication data in the wide area network.

The transmission scheduling system of the communication data in the low-power-consumption wide area network comprises a wide area network construction module and a scheduling module, wherein the wide area network construction module comprises: and constructing a time frame comprising N time slots, wherein the first time slot of the time frame is a public time slot, and when the communication node fails to successfully perform data transmission with the gateway in the allocated communication time slot, the communication node performs data transmission again with the gateway in the public time slot in the next time frame.

The transmission scheduling system of the communication data in the low-power-consumption wide area network, wherein the specific process of accessing the communication node into the gateway in the wide area network building module comprises the following steps:

the first judging module is used for zeroing variables of Retry _ times and Reconnect _ times, the Retry _ times is used for recording the times of the communication nodes joining the network through a random backoff method, the Reconnect _ times is used for recording the times of data transmission between the nodes and the gateway through a public time slot, whether the Retry _ times exceeds a threshold value is judged, if yes, the executing quitting module is called, and if not, the data broadcasting module is executed;

the exit module and the communication node exit the processing flow;

the data broadcasting module starts radio frequency to send broadcast data and increases Retry _ times count after the communication node carries out random backoff delay, if the communication node receives a gateway loopback packet within the longest waiting gateway reply time threshold, the communication node successfully joins the network and calls the execution gateway loopback packet analysis module, otherwise, the execution radio frequency closing module is called;

the radio frequency closing module is used for closing the radio frequency and judging whether the Retry _ times exceeds a threshold value, if so, the execution quitting module is called, and otherwise, the execution data broadcasting module is executed;

and the gateway loopback analyzing module is used for closing the radio frequency, clearing the Retry _ times parameter, and updating the local time of the communication node by analyzing the gateway loopback to obtain the communication time slot.

The transmission scheduling system of the communication data in the low-power-consumption wide area network specifically comprises the following modules:

the communication node judges whether the time corresponding to the communication time slot is coming, if so, the communication node calls and executes a third judgment module, otherwise, the communication node continues to wait for the time slot to start;

the third judging module is used for judging whether the communication data to be transmitted is in the data queue of the communication node or not, if so, the execution data sending module is called, otherwise, the data generation is continuously waited and the second judging module is called and executed;

the data sending module is used for sending communication data to the gateway by the communication node;

the fourth judgment module is used for judging whether the communication node receives the gateway return packet within a preset time threshold, if so, the execution deletion module is called, and otherwise, the fifth judgment module is called and executed;

the deleting module deletes the successfully transmitted communication data from the data queue, updates the local time of the node through analyzing the gateway return packet, and updates the communication time slot of the node;

and the fifth judging module is used for judging whether the current communication time slot is finished, if so, closing the radio frequency, otherwise, checking whether the communication data to be transmitted still exist in the data queue, if so, invoking and executing the data sending module, and otherwise, closing the radio frequency.

The transmission scheduling system of the communication data in the low-power-consumption wide area network, wherein the communication time slot updating module comprises:

the radio frequency opening module is used for always keeping the wireless radio frequency opening and monitoring a channel, and when the gateway receives the communication data and the communication data is broadcast data or the number field of the gateway in the communication data is the same as the number of the gateway, the gateway calls the execution data analysis module, otherwise, the gateway continues to wait for the next communication data;

the data analysis module is used for analyzing the communication data according to the format definition of the communication data and extracting the number of a communication node for transmitting the communication data and the generation time of the communication data;

a sixth judging module, which judges whether the gateway has access records corresponding to the communication nodes according to the number, if so, the seventh judging module is called to execute, otherwise, the time slot allocation module is called to execute;

the time slot distribution module is used for distributing a storage space for the communication node corresponding to the number, storing communication node information by using a dictionary structure, inserting a key value of the communication node into a dictionary, wherein the key is the number, the value is the storage position of the storage space corresponding to the communication node, setting variables in the storage space of the communication node to zero, the gateway receives a node data packet for the first time, and the communication time slot distributed for the node is the public time slot;

the seventh judging module is used for judging whether a node flow model is established or not, if so, the execution time slot occupation probability table updating module is called, and if not, the execution flow model building module is called;

the gateway initializes the traffic model of the communication node after acquiring the communication Data of the communication node twice, and sets the current state of the communication node as (Data _ time-last _ flow _ time)/T_slotInto a state space of which T_slotFor the length of the communication time slot, last _ flow _ time is the last communication Data generation time of the communication node, and Data _ time is the current communication Data generation time of the communication node;

the time slot occupation probability table updating module is used for updating the time slot occupation probability table according to the communication time slot occupied by the current communication data of the communication node;

and the state transition module is used for updating the flow model of the node according to the current node state, carrying out state transition, predicting the next communication data generation time and the corresponding probability of the communication node through a Markov chain, obtaining the delay expectation and the communication data collision probability of the communication node corresponding to each communication time slot in an allocation time frame according to the predicted communication data generation time and the corresponding probability, selecting the communication time slot with the minimum weighted sum of the delay expectation and the collision expectation as the optimal time slot, and enabling the communication node to occupy the optimal time slot for transmitting the communication data next time.

The invention provides a transmission scheduling method with high channel utilization rate, low delay and low power consumption, which is realized in an application layer and faces to a low-power-consumption wide area network.

Drawings

FIG. 1 is a frame format diagram;

FIG. 2 is a diagram of a packet format;

FIG. 3 is a diagram of an ACK packet format;

FIG. 4 is a flow chart of the node operation of the present invention;

fig. 5 is a flow chart of the gateway operation of the present invention.

Detailed Description

Aiming at the defect of channel resource shortage in a low-power-consumption wide area network, the transmission scheduling method with high channel utilization rate is provided, and key performances of network data delay, power consumption and load capacity are effectively improved. The following two technical problems are solved: 1. the low-overhead node flow modeling method realizes accurate prediction of stationarity period and event-driven node flow. 2. The transmission scheduling method with high channel utilization rate, the gateway allocates time slots for the nodes according to the prediction of the corresponding time slots of the node data flow by taking the avoidance of data collision and packet loss and the reduction of data delay as optimization targets,

the transmission scheduling method based on time slot allocation provided by the invention comprises frame format definition, node and gateway data communication flow definition and an optimal time slot allocation algorithm. The technical effects are as follows: the node starts radio frequency transmission data in the assigned designated time slot, the node does not need to compete for the communication time slot in a channel interception mode, and the node only intercepts a short-duration channel after transmitting data to the gateway to receive a gateway ACK packet, so that the method has the advantages that the node interception time is short, and the radio frequency is closed during the period that the node does not intercept, thereby obviously reducing the power consumption; meanwhile, through the communication time slots of the designated nodes and the gateway, the nodes are awakened in the network without a method of applying lead codes, so that the extra channel overhead caused by the lead codes is avoided, and the channel utilization rate is improved.

The node flow modeling method of the Markov chain comprises the step of generating a time difference T, namely a time difference between two data packets of a node_n+1-T_nDefined as the Markov chain state and a counting method for counting the number of times the node is transferred in different states to establish the transition probability of the Markov chain state, as shown in formula (1), p(s)_i|s_i-1) Is the slave state is s_i-1Transition to state s_iProbability of (C, s)_i-1) Is the slave state is s_i-1The number of transitions to state s, the exponential growth counting method is defined to increase the response speed to the state transitions, K is the number of times the state is kept the same, MAX _ K is the prevention of C (s, s)_i-1) The threshold set for easy overflow is preferably 5.

The technical effects are as follows: after receiving a data packet of a node, a gateway needs to allocate a communication time slot for next data transmission to the node, the gateway can predict the generation time of data to be transmitted by the node by establishing a node flow model, the influence of allocating different time slots on data delay can be calculated, and the gateway allocates the time slot close to the data generation time to the node, so that the network data delay is reduced. Meanwhile, the probability that the nodes occupy for data communication in different periods is obtained by predicting the generation time of the node data and integrating the communication time slot information distributed to the nodes by the gateway, on one hand, the utilization rate of a channel is improved by distributing the time slots corresponding to the unoccupied periods to other nodes in the network, on the other hand, the data transmission is carried out by avoiding that a plurality of nodes occupy the same period when the time slots are distributed, the collision and packet loss of data are avoided, the effective bandwidth of the network is improved, and the data delay and the energy consumption expense caused by data retransmission are avoided. Meanwhile, the flow modeling method based on the Markov chain can predict the flow under the stable periodicity and event-driven node flow mode, has wide applicability, and has the advantages of low calculation and storage cost and capability of operating on an embedded platform.

step S13, the communication node exits the processing flow;

step S16, turning off the radio frequency, and executing step S12;

step S23, the communication node sends communication data to the gateway;

step S36, zeroing variables in the storage space of the communication nodes;

In order to make the aforementioned features and effects of the present invention more comprehensible, embodiments accompanied with figures are described in detail below.

The invention comprises two parts, namely transmission scheduling based on time slot allocation and low-overhead node flow modeling.

In the traditional data transmission process, a lead code is used for waking up a data receiver to enable data to be synchronously transmitted, the lead code is added into transmitted data, an infinite sensor in a network is used as a communication node (hereinafter referred to as a node) to periodically start a radio frequency and monitor a channel, and the wireless sensor is switched into a receiving state or a dormant state according to whether the lead code is received, but the low-power-consumption wide area network channel resources are insufficient, the lead code is applied to cause extra channel overhead, meanwhile, the monitoring channel causes energy consumption overhead, and the lead code is difficult to apply in the low-power-consumption wide area network. The method has the characteristics that the low-power-consumption wide area network node single-hop access gateway and the data communication between the nodes are not carried out, a star network topological structure taking the gateway as the center is formed, communication time slots are distributed for the loaded nodes through the gateway, the nodes start a radio frequency data transmission mode in the distributed designated time slots, the nodes in the network do not need to compete for the communication time slots in a channel interception mode, the nodes in the network are controlled to access channels in order, and meanwhile, the nodes only intercept a short-time channel after transmitting data to the gateway to receive a gateway message to achieve Acknowledgement (ACK) packet return; meanwhile, through the communication time slots of the appointed nodes and the gateway, the nodes start radio frequency at the appointed time slots and carry out data transmission with the gateway, a lead code method is not needed to be applied to awaken the nodes and carry out synchronous transmission, extra channel overhead caused by the lead codes is avoided, and the channel utilization rate is improved.

In the transmission scheduling method based on time slot allocation, the time relationship between a node communication time slot and the generation time of data to be transmitted influences the utilization rate of a network channel and the data delay performance, the node communication time slot is earlier than the data generation time to cause channel waste, and the node communication time slot is later than the data generation time to cause larger data delay. Therefore, a traffic model of the node needs to be established to realize that after the gateway and the node complete data transmission, the gateway allocates a communication time slot for next data transmission to the node according to the prediction of the node traffic, and the communication time slot is the node data generation time, so as to avoid channel waste and reduce data delay. In the low-power-consumption wide area network, node flow mainly refers to stable periodic data flow, but event-driven data flow exists at the same time, for example, in an environment monitoring application, when monitoring data are in a normal range, the sampling period of a node is long, and when the monitoring data exceed the normal range, the sampling period of the node is reduced, so that the real-time performance of monitoring amount is improved. Meanwhile, nodes and gateways in a low-power-consumption wide area network are generally embedded devices with limited computing and storage capacities, so that a flow model method is required to accurately predict the flow of stationary periodicity and event-driven nodes with low cost.

The characteristic of low power consumption wide area network channel resource shortage requires that the improvement of the channel utilization rate is taken as a core target, and meanwhile, data delay, energy consumption and load capacity are also key performances of the network. Data collision packet loss caused by that a plurality of nodes use the same time slot to carry out data communication and channel waste caused by that no data to be transmitted exists in the allocated time slot of the nodes are main factors for reducing the utilization rate of the channel; the power consumption generated by starting the radio frequency module for data transmission of the node is an important component of the overall power consumption of the node, the power consumption of the node can be obviously reduced by reducing the radio frequency starting time, and the main method for reducing the radio frequency power consumption of the node is to reduce the time for monitoring a channel by the node and avoid data retransmission caused by data collision and packet loss; the data delay refers to the time delay from the time when the node generates data through modes of sensor sampling and the like to the time when the data is transmitted to the gateway in a communication time slot and is successfully received by the gateway, and the main method for reducing the data delay is to allocate the time slot close to the data generation moment and avoid data retransmission caused by data collision and packet loss; channel resources in a low-power wide area network are in shortage, and improving the channel utilization rate so as to allow more nodes in the network to use channels for data transmission is a main method for improving the network load capacity.

In order to make the technical scheme of the invention clearer, the invention is further described in detail with reference to the accompanying drawings.

Fig. 1 illustrates a frame format of the present invention, where a frame is composed of N equal-length time slots, where N is a positive integer, and a first time slot is a common time slot, and is used to solve the problem that a node fails to successfully perform data transmission with a gateway in an allocated time slot due to factors such as signal interference, and the node performs data transmission again with the gateway in the common time slot in the next frame to rejoin a network and acquire a communication time slot. N is preferably 8, T_slotThe length of the time slot is taken as the value of the time slot, the value is related to the time synchronization precision among the nodes and the gateways and the time required for the nodes to complete one-time data transmission, wherein the one-time data transmission of the nodes comprises two processes of sending data packets to the gateways and receiving ACK packets of the gateways, T_slotA preferred value is 5 s.

Fig. 2 and 3 depict data packet and ACK packet formats related to the present invention. The Data packet is used for transmitting Data to the gateway by the node, the Data field in the Data packet is the Data transmitted by the node, and the ACK packet is a packet which is replied to the node after the gateway successfully receives the Data packet of the node and is used for confirming the success of Data transmission, synchronizing the time of the node and allocating a communication time slot for the node. The different fields in the data packet and the ACK packet are described as follows:

and the Sink _ ID is a gateway number, the Sink _ ID in the data packet is used for specifying a target gateway of the data packet, and the Sink _ ID is 0, which means that the data packet is broadcast data and no target gateway is specified.

Node _ ID, Node number, the Node _ ID in the ACK packet is used for designating the target Node of the ACK packet.

Data _ time, Data generation time, and the gateway establishes a node flow model through the Data _ time.

Data, Data transmitted by the nodes to the gateway, such as sensing Data collected by the nodes.

Network time, the node maintains time synchronization with the gateway through the Sys _ time.

And the Slot _ index is the time Slot position in the frame allocated by the gateway for the node, and is an integer of the interval of [0, N).

Fig. 4 depicts the work flow of the node, and the flow chart depicts the processing flow of the node joining the network for the first time, performing data transmission through the designated time slot allocated by the gateway, and performing data transmission through the common time slot.

The workflow of the first joining of the node into the network is described as follows:

step 11: the node initializes a radio frequency module, sets zero variable of Retry _ times and Reconnect _ times, the Retry _ times is used for recording the times of the node joining the network by a random back-off method, and the Reconnect _ times is used for the times of the node transmitting data with the gateway through a public time slot.

Step 12: check if Retry _ times exceeds a threshold Max _ Retry _ times, Max _ Retry _ times being the maximum number of times a node is allowed to continuously attempt to join the network by random backoff, with a preferred value of 5. If Retry _ times > Max _ Retry _ times, go to step 13, otherwise go to step 14.

Step 13: and judging that the node fails to join the network for multiple times, the radio frequency module has hardware faults, and the node exits the processing flow.

Step 14: because a plurality of nodes possibly exist in the network to compete to join the network, after the nodes need to perform random backoff delay, the radio frequency is started, the Sink _ ID field in the zero setting data packet represents broadcast data, the data packet is sent, the Retry _ time count is increased, and meanwhile, the zero setting and the timer RF _ wait are started.

And 15, if the node receives the gateway ACK packet within the longest time waiting for the gateway ACK reply time threshold value Max _ rf _ wait, the node is successfully added into the network, and the step 17 is executed, otherwise, the node does not receive the ACK after overtime, and the step 16 is executed. The Max _ rf _ wait preferred value is 3 s.

Step 16: the radio frequency is turned off and step 12 is performed.

And step 17: and closing the radio frequency and clearing the Retry _ times parameter.

Step 18: and analyzing the ACK data packet, specifying a target gateway for node data transmission through a Sink _ ID field, updating the local time of the node through Sys _ time, and specifying a time Slot for node data communication through a Slot _ index.

Step 19: checking whether the equation Slot _ index is true, wherein the equation is true, the node uses the public time Slot to communicate with the gateway, executing step 31, otherwise, the node uses the appointed time Slot to communicate with the gateway, executing step 21.

The data transmission flow between the nodes and the gateways by using the designated time slots is described as follows:

step 21: checking whether the time corresponding to the time slot allocated to the node is coming, starting the time slot 22, otherwise continuing to wait for the time slot to start, executing step 21, and formula (2) describes the condition of starting the communication time slot.

Step 22: checking whether the data queue of the node has data to be transmitted, if so, executing 23, otherwise, continuing to wait for data generation and executing step 21.

Step 23: and starting radio frequency, sending a data packet, zeroing a Next communication time slot Next _ slot _ index of the node to wait for the gateway to reallocate the communication time slot for the node, and simultaneously zeroing and starting a timer Retry _ time.

Step 24: if the node receives the gateway ACK packet within the time threshold Max _ rf _ wait, the data transmission of the node is successful, step 25 is executed, otherwise, the node fails to perform the data transmission with the node due to factors such as interference, and step 27 is executed.

Step 25: and the node successfully transmits the data packet to the gateway and deletes the data packet from the data queue to be transmitted by the node.

Step 26: and analyzing the ACK data packet, updating the local time of the node through Sys _ time, and assigning and updating a Next Slot _ index of the Next data communication of the node through a Slot _ index field.

Step 27: checking whether the communication time slot of the node is finished, closing the radio frequency when the communication time slot is finished, otherwise, the node is still in the communication time slot, continuously transmitting data, and executing step 29. Equation (3) describes the condition that the communication slot is not ended.

Sys_time％(N×T_slot)/T_slot≥(Slot_index+1)％N (3)

Step 28: and checking whether the data queue has data to be transmitted or not, executing the step 23 if the data queue has the data to be transmitted, and otherwise, closing the radio frequency.

The flow of the node using the common time slot to perform data transmission with the gateway is described as follows:

step 31: checking whether the number of times, Reconnect _ times, that the node transmits data with the gateway through the common slot exceeds a threshold value Max _ Reconnect _ times. When the gateway does not establish a node flow model, the communication time slot acquired by the node is a public time slot, or the node does not acquire the specified time slot of communication due to signal interference and the like, the node needs to communicate with the gateway again through the public time slot, and the Max _ connect _ times is the maximum number of times that the node is allowed to continuously use the public time slot for communication, and the optimal value is 5. When the Reconnect _ time exceeds the threshold value Max _ Reconnect _ time, the node is considered to be unable to join the network through the common time slot, and needs to join the network through a random back-off mode, and step 3-2 is executed. Otherwise, the nodes continue to use the common time slot for communication, and step 3-3 is executed.

Step 32: resetting the connection _ times and the Retry _ times, wherein the reset Sink _ ID indicates that the current gateway is unavailable and needs to be searched, and executing step 12.

Step 33: checking whether the time corresponding to the common time slot of the node is coming, executing step 34 when the time slot starts, otherwise, continuing to wait for the time slot to start, executing step 33, and formula (2) describes the condition of starting the communication time slot.

Step 34: because a plurality of nodes may use a common time slot to transmit data, the nodes need to transmit the data after random back-off, and the back-off time is less than T_slotThe random number of (2).

Step 35: because the node may perform multiple random backoffs in the common time slot, it is necessary to check whether the current time exceeds the time corresponding to the common time slot, so as to prevent the common time slot from ending after multiple random backoffs. If yes, go to step 41, otherwise go to step 36. Equation (3) describes the conditions for the end of the common time slot.

Step 36: starting radio frequency, sending a data packet, increasing a Reconnect variable by 1, zeroing a Next communication time slot Next _ slot _ index of a node to wait for a gateway to reallocate the communication time slot for the node, and simultaneously zeroing and starting a timer Retry _ time.

Step 37: and (3) if the node receives the gateway ACK packet within the time threshold value Max _ rf _ wait, the data transmission of the node is successful, step 38 is executed, otherwise, the node fails to successfully perform the data transmission with the node due to factors such as interference, and step 3-1 is executed.

Step 38: and the node successfully transmits the data packet to the gateway and deletes the data packet from the data queue to be transmitted by the node.

Step 39: and analyzing the ACK data packet, updating the local time of the node through Sys _ time, and assigning and updating a Next Slot _ index of the Next data communication of the node through a Slot _ index field.

Step 310: the reset _ times parameter is set to zero.

Step 41: and closing the radio frequency, and updating the communication time Slot of the node by assigning the operation Slot _ index to Next _ Slot _ index.

The working flow of the gateway is described in the fifth figure, and the specific steps are explained as follows.

Step 51: the gateway initializes the wireless radio frequency module, and always keeps the wireless radio frequency module on and listens to the channel. And allocating a storage space of a probability table conflict _ list [ L ] occupied by the time slots, wherein the conflict _ list [ L ] is used for recording the probability of using continuous L time slots as communication time slots by the nodes, and the optimal value of L is 5-8 times of the number of the time slots corresponding to the longest data period of the nodes in the network. And setting a zero variable conflict _ list _ tail, wherein the conflict _ list _ tail is used for recording the position of the time slot corresponding to the distributed farthest moment in the time slot occupation probability table.

Step 52: the gateway continuously listens to the channel, and when the data packet is received and is broadcast data or the Sink _ ID field in the data packet is the same as the number of the gateway itself, step 53 is executed, otherwise, the gateway continuously waits for the data packet, and step 52 is executed.

Step 53: and defining and analyzing the Data packet according to the Data packet format of the second graph, and extracting the Node _ ID, the Data _ time and the Data fields.

Step 54: checking whether the gateway has the access record of the Node _ ID field corresponding Node in the data packet, if not, executing step 55, otherwise, executing step 58.

Step 55: and allocating storage space for the nodes, and in order to improve the retrieval efficiency, storing Node information by using a dictionary structure, and inserting key values of the nodes into a dictionary, wherein the keys are Node _ IDs of the nodes, and the values are storage positions of the storage space corresponding to the nodes.

Step 56: variables in the storage space of the zero node, and the names and the purposes of the variables in the storage space are explained as follows, and the assignment of the formula (4) is executed.

Variable last _ flow _ time: recording the last data generation time of the node;

variable last _ sys _ time: recording the network time when the gateway allocates time slots for the nodes last time;

variable first _ visit _ flag: the gateway receives the flag bit of the node data packet for the first time, and the flag bit is 1 to indicate that the node data packet is received for the first time;

variable flow _ model _ flag: a gateway establishes a node flow model zone bit, and the establishment is represented as 1;

variable State _ list [ S _ N ]: and the state space of the node Markov chain with the length of S _ N, wherein the S _ N value is related to the size of the storage space of the gateway and the maximum possible state number of the node.

Variable state _ index: recording the index position of State _ list [ S _ N ] of the current State of the node in a State space;

variable assign _ slot _ index: recording the time slot position distributed by the node in the frame period;

a variable k: recording the continuous same times of the node states, wherein the upper limit of the value of the node state is MAX _ K;

variable State _ transfer _ count [ S _ N ] [ S _ N ]: recording the number of transitions between state space states

Variable State _ transfer _ sum [ S _ N ]: recording the sum of times of transferring a certain state to other states

And 57, because the gateway needs at least two node data packets to establish the traffic model of the node, the gateway receives the node data packet for the first time and does not establish the traffic model of the node, and at this time, a public time Slot is allocated to the node, namely, the Slot _ index is 0.

Step 58: and checking whether an equation flow _ model _ flag is satisfied, and judging whether the node traffic model is established or not, wherein the satisfied equation represents that the node traffic model is established, executing the step 510, and otherwise executing the step 59.

Step 59: after acquiring the Data packets of the node twice, the gateway initializes the flow model of the node, and sets the current state s as (Data _ time-last _ flow _ time)/T_slotAnd inserting the state space, and assigning the state _ index as the position of the current state s in the state space.

Step 510: since the time slot situation occupied by the current data packet of the node is accurately known, the time slot occupancy probability table is updated to eliminate the influence on the time slot occupancy probability table after the time slot is allocated to the node in step 513, as shown by the pseudo code.

Step 511: according to the currently observed node State, a traffic model of the node is updated, and a State index of the node is updated, wherein the pseudo code is as shown in the specification, the 8-13 rows are used for preventing the overflow of the State _ transfer _ SUM [ S _ N ] value caused by long-time accumulation from attenuating the corresponding value to half, and the MAX _ SUM preferred value is 255.

Step 512: and the optimal time slot allocation algorithm is used for sequentially completing node flow prediction, delay expectation calculation, conflict expectation calculation and optimal time slot selection.

Predicting the node flow;

and predicting the generation time of the next data of the node and the corresponding probability by a Markov chain-based method.

p(T_n+1＝last_flow_time+State_list[i]×T_slot)＝p(State_list[i]|State_list[state_index]),i＜S_N

Delay expectation calculation:

and calculating the delay expectation of each time slot and node in the distribution frame according to the prediction of the node flow.

delay(x,i)＝(i+N-s_t(x)mod N)mod N

t＝last_flow_time

Calculating the conflict expectation:

and calculating the data collision probability of each time slot and node in the distribution frame according to the prediction of the node flow. The data collision refers to an event that two or more devices in the same communication range simultaneously transmit wireless data, so that the wireless data cannot be correctly received due to mutual interference. The data collision probability is the probability that other devices possibly transmit packets at the same time in each time slot of a finger frame predicted by a Markov chain. If the communication time of the node is allocated to the time slot, there is a possibility that data collision occurs with the above probability.

s＝State_list[state_index]

f(t,i)＝(t+(i+N-t％N))％L

And (3) selecting an optimal time slot:

the time slot with the smallest sum of delay expectation and collision expectation weights is selected, and λ is a weighting coefficient, and the preferred value is 5.

Loss[i]＝delay_loss[i]+λ×conflict_loss[i]

Step 513: since the assigned time slot is allocated to the node, the node will occupy the time slot in the future for data transmission, and the time slot occupancy probability table needs to be updated according to the node flow prediction, as shown by pseudo codes, 9-15 is used for zeroing the time slot covered by the current time in the data occupancy probability table.

Step 514: and judging whether the data packet of the node is broadcast data or not according to the judgment of whether the equation Sink _ ID is 0 or not, if so, executing step 515, otherwise, executing step 516.

Step 515: because a plurality of gateways exist in the network, after the nodes send the broadcast data, a plurality of gateways can reply ACK (acknowledgement character), in order to avoid data collision packet loss caused by the fact that the gateways reply the ACK at the same time, the gateways need to carry out random delay backoff, and the backoff time is less than T_slotIs calculated.

Step 516: the gateway assigns a field in the ACK packet, assigns a Sink _ ID to the gateway number, assigns a Node _ ID to the Node _ ID in the Data packet, assigns a Data _ time to the gateway current time, assigns a Slot _ index to the optimal Slot _ index, and executes step 52 after replying the ACK.

According to the invention, through the transmission scheduling method of time slot allocation, the node only monitors a short time in the communication time slot to wait for the ACK packet return of the gateway, so that the power consumption of the node is reduced. By establishing a flow model of the node, the gateway can predict the generation time of the node data, calculate the data delay of each time slot, and allocate the time slot with short data delay to reduce the data delay of the node. Meanwhile, the situation that the data transmission is carried out on channels occupied by the nodes in different periods is obtained by comprehensively predicting the data generation time of the nodes and the communication time slot information distributed to the nodes by the gateway, on one hand, the utilization rate of the channels is improved by distributing the time slots corresponding to the unoccupied periods to other nodes in the network, on the other hand, the data transmission is carried out by avoiding that a plurality of nodes occupy the same period when the time slots are distributed, so that the data collision and packet loss are avoided, the data delay and the energy consumption expense caused by data retransmission are avoided, and the load capacity of the network is improved.

The following are system examples corresponding to the above method examples, and this embodiment can be implemented in cooperation with the above embodiments. The related technical details mentioned in the above embodiments are still valid in this embodiment, and are not described herein again in order to reduce repetition. Accordingly, the related-art details mentioned in the present embodiment can also be applied to the above-described embodiments.

the exit module and the communication node exit the processing flow;

Although the present invention has been described in terms of the above embodiments, the embodiments are merely illustrative, and not restrictive, and various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention, and the scope of the invention is defined by the appended claims.

Claims

1. A transmission scheduling method of communication data in a low-power-consumption wide area network is characterized by comprising the following steps:

step S4, looping the step S2 and the step S3 to implement transmission scheduling of the wide area network;

wherein, the step S1 includes: constructing a time frame comprising N time slots, wherein the first time slot of the time frame is a public time slot and is used for carrying out data transmission again with the gateway in the public time slot in the next time frame when the communication node fails to successfully carry out data transmission with the gateway in the allocated communication time slot;

the specific process of accessing the gateway by the communication node in step S1 includes:

step S13, the communication node exits the processing flow;

step S16, turning off the radio frequency, and executing step S12;

step S18: updating the local time of the communication node by analyzing the gateway loopback packet to obtain the communication time slot;

the step S2 specifically includes:

step S23, the communication node sends communication data to the gateway;

step S28: checking whether the communication data to be transmitted still exist in the data queue, if so, executing a step S23, otherwise, closing the radio frequency;

the step S3 includes:

step S36, zeroing variables in the storage space of the communication nodes;

step S312: predicting the next time communication data generation time and the corresponding probability of the communication node through a Markov chain, obtaining the delay expectation and the communication data collision probability of the communication node corresponding to each communication time slot in an allocation time frame according to the predicted communication data generation time and the corresponding probability, selecting the communication time slot with the minimum weighted sum of the delay expectation and the collision expectation as the optimal time slot, and enabling the communication node to occupy the optimal time slot for transmitting the communication data next time.

2. A system for scheduling the transmission of communication data in a low power wide area network, comprising:

the circulating module is used for circularly calling and executing the data sending module and the communication time slot updating module so as to realize the transmission scheduling of the communication data in the wide area network;

wherein, this wide area network construction module includes: constructing a time frame comprising N time slots, wherein the first time slot of the time frame is a public time slot and is used for carrying out data transmission again with the gateway in the public time slot in the next time frame when the communication node fails to successfully carry out data transmission with the gateway in the allocated communication time slot;

the specific process of accessing the communication node to the gateway in the wide area network building module comprises the following steps:

the exit module and the communication node exit the processing flow;

the gateway loopback analysis module is used for closing the radio frequency, clearing the Retry _ times parameter, and updating the local time of the communication node by analyzing the gateway loopback to obtain the communication time slot;

the data sending module specifically comprises:

a fifth judging module, which judges whether the current communication time slot is finished, if so, the radio frequency is closed, otherwise, whether the communication data to be transmitted still exist in the data queue is checked, if so, the data sending module is called to execute, and if not, the radio frequency is closed;

the communication time slot updating module comprises: