CN104581870A - Energy Harvesting Based Wireless Sensor Networks and Its Low-Latency Routing Method - Google Patents

Abstract

The invention discloses a wireless sensor network based on energy acquisition and a low-delay routing method thereof, and solves the problem of high data transmission delay caused by low duty ratio during the operation of sensing nodes and the randomness of operation time caused by the influence on energy supply by external environment in a wireless sensor network system serving as novel energy supply. The wireless sensor predicates an operating schedule through an energy management system, establishes a node neighbor table, selects a neighbor node activity instance nearest to a sending time, establishes a minimum data selection delay mechanism, reduces the network data transmission delay, and provides the network operation efficiency.

Description

Energy Harvesting Based Wireless Sensor Networks and Its Low-Latency Routing Method

technical field

The invention relates to a wireless sensor network routing method, in particular to a low-delay routing method for a wireless sensor network based on energy collection.

Background technique

Wireless sensor network is a multi-hop wireless network formed by self-organization of a group of sensor nodes. It does not need fixed network support. It has the advantages of rapid deployment and strong invulnerability. resource constraints etc. It can work in harsh or special environments that people can't get close to. Due to the limited capacity and low cost of micro sensor nodes, a large number of micro sensor nodes and a base station node (or sink node) with unlimited energy and strong processing capability are usually deployed in wireless sensor networks. Sensor nodes cooperatively perceive, collect and process the data of sensing objects in the geographical area covered by the network, and transmit these data to the base station through multi-hop routes, and finally reach the management node through the Internet or satellites. Sensor networks are widely used in national defense, national security, environmental monitoring and medical and health fields. As an important supporting technology in wireless sensor network, routing technology is directly related to the operation quality of the network.

Sensor nodes usually adopt a large number of dense deployment methods, and the low price makes the nodes adopt relatively simple and cheap chip technology in terms of communication capabilities, information processing capabilities, and energy supply systems. Traditional wireless sensor networks usually use portable batteries as the energy supply system. The limited battery storage capacity makes the battery energy easily exhausted, and the sensor nodes will be abandoned after losing power. In recent decades, battery technology has not made breakthrough progress. The limited battery energy makes the network life a short board that affects the application and promotion of wireless sensor networks. cause some pollution. With the advancement of technology, people have turned their attention to natural clean energy, hoping to convert natural resources in the external environment into electrical energy that can be used by sensor nodes. Among them, solar energy is the most widely used. The time when human beings utilize solar energy is also earlier than the time of utilizing storage batteries.

With the advancement of technology, there are some energy conversion technologies that enable wireless sensor nodes to harvest or harvest energy from the environment. Energy harvesting technology is closely related to the application environment. Among them, solar cell technology is the most commonly used. In addition, there are various energy conversion technologies such as vibration power generation, temperature difference power generation, and mechanical motion triggering. The current environmental energy harvesting technology has been able to provide an appropriate amount of energy supply for wireless sensor network nodes. The change of energy supply system provides a new direction for the development of wireless sensor technology, especially the research of routing protocols. In the traditional wireless sensor network system, due to the use of batteries with limited energy, the routing protocol mainly aims at saving energy and improving energy utilization, and delaying the network lifetime to the maximum extent. In the wireless sensor network with energy harvesting or energy regeneration energy supply system, the network lifetime is no longer a major issue. If the effective harvesting energy can be used reasonably, the sensor system can work until the physical device of the node is damaged, and the time even Can exceed 10 years. Because the energy storage system is not easy to design too large, the energy storage capacity is limited, and the nodes can use up energy as soon as possible to continue to absorb more energy from the outside, saving energy but reducing the system's working efficiency. Therefore, the routing protocol designed for energy saving under the traditional wireless sensor network will no longer be suitable for the wireless sensor network system based on energy harvesting technology.

Energy harvesting wireless sensor network is a new research direction of wireless sensor network technology, and the current research is in its infancy. In the wireless sensor network based on the energy harvesting system, although the problem of energy limitation of nodes can be solved, new problems will be faced in routing design. First of all, in order to facilitate large-scale random deployment of nodes, the nodes are usually small and easy to carry and throw away, so the energy conversion system of the node is usually small, such as the size of the solar panel on the sensor node is usually small. Furthermore, the storage system on the node occupies most of the space of the node, and is usually small, resulting in a small power storage capacity of the node. Coupled with the limitations of the current energy conversion technology, relying on the power provided by the energy harvesting technology of the node cannot guarantee the continuous operation of the node. The node is in the charging state most of the time, that is, the node must maintain a low duty cycle. . The energy harvesting system of a node has strong environmental dependence. When the external environment changes, the collected energy will change. Different nodes in different environments will also collect different energy, so the working time of the node has Strong randomness. Nodes work at a lower duty cycle and the randomness of the working time makes the data delay in the energy harvesting wireless sensor network system more serious and complex than the traditional wireless sensor network, and at some point the data transmission delay becomes unbearable.

In the energy harvesting wireless sensor network, to minimize the data transmission delay, two problems must be faced. The first is the uncertainty of the working time of the node due to the strong dependence on the environment, and the uncertainty of the working time. Determinism makes it impossible for nodes to know the working hours of neighboring nodes. Due to the limited energy collection, nodes cannot continuously detect the working status of other nodes like nodes in traditional networks, resulting in nodes not being able to transmit data to the next hop node in time. Another problem is that the work of the node must be maintained at a low duty cycle, that is, the node is in the charging state most of the time, and cannot forward the data in time. If these two problems cannot be effectively solved or the unfavorable factors cannot be minimized, the data delay will be uncontrollable, which will greatly affect the promotion and use of wireless sensor network systems based on new energy sources.

Contents of the invention

The technical problem to be solved by the present invention is aiming at the data transmission efficiency problem of the wireless sensor network system with energy harvesting technology. The large data transmission delay problem caused by the randomness of downtime and working hours can improve the efficiency of network operation and ensure that the data reaches the target node in time.

The present invention adopts the following technical solutions for solving the problems of the technologies described above:

A wireless sensor network, the wireless sensor network includes a base station node and a number of ordinary nodes randomly distributed in the monitoring area, characterized in that: each ordinary node includes a rechargeable system and an energy storage system, wherein the rechargeable system is used for Convert external natural energy into electrical energy and store it in the energy storage system. When the energy storage system is insufficient, start the rechargeable system of the node until the energy is full;

The entire working time of the common node is divided into several working cycles, and the states in one working cycle are composed of multiple working states and idle states, and the multiple working states are: charging state, data packet receiving state, data Packet sending state, listening state, among them, the charging state can work in parallel with other states, and other states cannot work in parallel.

Further, in the wireless sensor network of the present invention, the common nodes all have the same communication capability, information processing capability, and same transmission radius and unique identification.

Furthermore, in the wireless sensor network of the present invention, each common node contains one or more rechargeable systems and energy storage systems.

Furthermore, in a wireless sensor network of the present invention, before the common node joins the wireless sensor network, the energy storage system does not carry electricity, and after joining the wireless sensor network system, it first charges itself.

The present invention also proposes a low-latency routing method based on the above-mentioned wireless sensor network, comprising the following steps:

A. Each ordinary node generates its own work schedule according to its charging efficiency, specifically: Let the schedule of each work cycle t of an ordinary node be in is the kth working moment corresponding to a certain working state of node i in this cycle, k=1, 2,..., n, n is the number of time periods corresponding to each working state of node i in a working cycle;

B. Each ordinary node broadcasts its own work schedule to its neighbor nodes within its own communication radius, until all nodes have the work schedule of their neighbor nodes;

C. Each ordinary node is calculated according to its own work schedule and the work schedule of its neighbor nodes. The data transmission delay when sending data packets to all neighbor nodes at all times, the calculation formula of the data transmission delay is:

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In formula (1), For node i+1 and node i in its working cycle The working time corresponding to the time;

D. According to step C, each ordinary node obtains the data transmission delay of sending data packets to neighboring nodes in each working state; and obtains the next-hop node selected when sending data packets in each working state according to the following conditions : The selected next-hop node is closer to the base station node than itself, and the data transmission delay is the smallest;

E. Each ordinary node informs the selected next-hop node of the data transmission delay of the selected next-hop node when sending data packets in each working state, and calculates the data sent in each working state according to the following formula The minimum data delay for the packet to finally reach the base station s, that is, the end-to-end delay:

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

F. Establish a two-dimensional neighbor table for each node, which stores all the neighbor node information within the communication radius of the node, as well as the data delay and end point when the node sends data packets to the neighbor nodes in each working state. end-to-end delay;

G. When an ordinary node wants to select a data route at a certain moment, it selects the route that satisfies the minimum end-to-end delay of data transmission from the neighbor table according to the working status at that moment until the data is forwarded to the base station node.

Further, in the low-delay routing method of the present invention, during the data transmission process, if the working state of a common node changes temporarily, the node selects the node with the latest working state from the neighbor nodes as the next step according to steps C-D. The hop node performs data transmission until the data is forwarded to the base station node.

In order to solve the uncertainty of node working time, the present invention adopts the node energy system test method to ensure that the nodes can wake up at certain fixed time points. Although the duty cycle of the system will be further reduced, it can ensure that the nodes can effectively grasp the neighbor's work schedule. During the working process of the sensor node, according to the change of the external environment, the energy harvesting efficiency of the node is predicted. With the delay of time, the accuracy of the prediction will be improved, and the working schedule of the node will be more stable. When the external environment changes slightly, the energy harvesting efficiency of the node may increase or decrease. If the energy harvesting efficiency increases, it is theoretically possible to increase the activity instance in the work schedule, but in order to maintain a relatively stable The working schedule does not need to change the activity instances in the working schedule; when the energy harvesting efficiency decreases, the node has to reduce the active instances in the working schedule, and the neighbor nodes must be notified when the active instances are reduced. In order to solve the problem of data transmission delay caused by the low duty cycle of node working time, the data transmission method of the nearest active instance is adopted. Although the working duty cycle of the node is relatively low, it is possible to select the nearest node for the current data transmission time point among a large number of neighbor nodes around the node. The active instance ensures that the data is forwarded in the fastest time, thereby reducing the data transmission delay.

As a low-latency routing method for wireless sensor networks based on energy harvesting, the present invention adopts the above technical solutions and compared with the prior art, has the following technical effects:

(1) The present invention is an earlier analysis of the characteristics of the wireless sensor network for energy harvesting, and its difference with the traditional wireless sensor network that uses portable batteries as energy supply, and analyzes the main problems faced by the wireless sensor network for energy harvesting in terms of routing. question.

(2) In the wireless sensor network for energy collection, the randomness of the working time caused by the influence of the external environment on the work of nodes, the present invention manages the collected energy through the energy management system, and through the energy collection process for a certain period of time Monitoring, nodes can predict the daily energy harvesting efficiency to some extent. At the nodes, respective work schedules are generated according to approximate charging efficiencies, and in the subsequent time, the work schedules can be corrected until the work schedules are relatively stable. The relatively stable working schedule of nodes is conducive to the control of other nodes on the data forwarding time.

(3) In solving the delay problem caused by the low duty cycle of the node, the present invention selects the best neighbor node and the best neighbor node activity instance for the activity instance at the node forwarding time to ensure that the collected data is Forward it in time.

(4) The wireless sensor network low-latency routing protocol for energy harvesting of the present invention includes several parts such as initialization of node working schedule, next-hop node selection method, routing establishment process, and routing maintenance. The method establishes neighbor work schedules through nodes, selects the nearest active instance for data transmission, and establishes a minimum delay selection mechanism. Based on the present invention, the network data transmission delay is effectively reduced, the network operation efficiency is improved, and the data can be ensured to arrive at the target node in time.

Description of drawings

Figure 1 shows that the data generated by the source node at three different times is forwarded to the base station node through multi-hop routing with low transmission delay.

Figure 2 is a schematic diagram of the wireless sensor network architecture for energy harvesting.

Fig. 3 is a flowchart of a low-latency routing protocol in a wireless sensor network for energy harvesting.

Detailed ways

In order to make the above objects, features and advantages of the present invention more obvious and comprehensible, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Those skilled in the art can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should also be understood that terms such as those defined in commonly used dictionaries should be understood to have a meaning consistent with the meaning in the context of the prior art, and will not be interpreted in an idealized or overly formal sense unless defined as herein explain.

In order to explain the technical solution of the present invention conveniently, the distribution of energy harvesting wireless sensor network nodes shown in FIG. 1 is taken as an example below. It should be noted that the energy harvesting wireless sensor network shown in FIG. 1 is not a limitation to the energy harvesting wireless sensor network used in the present invention.

The present invention establishes a wireless sensor network low-latency routing method for energy collection, and its basic system composition includes:

Ordinary node: a wireless sensor network node that can perceive environmental information such as temperature, humidity and illuminance in its surrounding space. The node is equipped with one or more energy conversion devices and an energy storage device, excluding portable batteries. Ordinary nodes have data collection, data processing and data forwarding capabilities. They can perceive specific information within a fixed radius around the node and send the data generated by perception or data received from other nodes to any node with reachable communication capabilities after simple processing. .

Source node: an ordinary node that undertakes monitoring tasks and has sensing capabilities and perceives the generated data; relay node: an ordinary node that undertakes data forwarding tasks. The relay node has a data receiving buffer for temporarily storing the received data. The relay node can perform simple processing such as fusion and de-redundancy on the received data as needed, and waits for forwarding to the next hop node after the processing is completed. , after the forwarding is completed, part of the buffer occupied by the data is released. It is defined in the present invention that any ordinary node in the network can become a source node and a relay node.

Base station node (Sink node): Compared with ordinary nodes, base station nodes have stronger data processing and data communication capabilities. The energy of base station nodes is usually not limited, and can use alternating current or large-capacity batteries, which is the center of the entire network system. All the data collected by the source node is forwarded by the relay node and finally reaches the base station node. The base station node is responsible for all the data fusion processing, and sends it to the remote terminal, and finally reaches the management node through the Internet or satellite. In a wireless sensor network system, at least one base station node is deployed.

It is assumed that the energy harvesting wireless sensor network contains multiple nodes with energy harvesting technology and a base station node. As an implementation method of the present invention, in the energy harvesting wireless sensor network shown in FIG. 1 , source nodes and base station nodes are located at the edge of the monitoring area covered by the sensor nodes. In the wireless sensor network system for energy collection involved in the present invention, the source node and the base station node can be in any position within the monitoring area covered by the sensor node, and the base station node can even be located outside the monitoring area covered by the sensor node, as long as the The base station node communicates normally with at least one sensor node in the monitoring area, that is, the base station node is located within the communication radius of at least one sensor node. The node density in the monitoring area must guarantee the connectivity between the nodes, guarantee that there is at least one path between the source node and the base station node, and in the case of one or more hop links, adopting the routing protocol method provided by the present invention can guarantee the Implementing a lower network latency route in energy harvesting wireless sensor networks.

In the entire network system, except for the base station nodes, other nodes are common nodes, and their energy supply systems are all renewable, and the energy can be supplemented by an external conversion system, which is limited and discontinuous. The base station node uses alternating current, and the energy is not limited. Each common node is equipped with at least one rechargeable system and an energy storage system. The rechargeable system converts external natural energy into electrical energy and stores it in the reserve system. Due to the limitations of the conversion system technology, the converted energy cannot maintain the continuous work of ordinary nodes, and ordinary nodes can only work at a lower duty cycle, that is, the nodes are idle most of the time.

Each node has five states, namely: charging state, data packet receiving state, data packet sending state, listening state and idle state. Among them, the charging state can work in parallel with the other four states, and the other four states cannot work in parallel, that is, the data packet receiving and sending can be completed in the charging state, but the data packet receiving and sending cannot occur at the same time. When the energy storage system of an ordinary node is not full of power, the node starts the charging system and keeps charging until the power is full.

Each ordinary node is equal in physical devices and has the same function. Due to the influence of the physical environment on the spot, the charging efficiency of the node is different. After the node is added to the network system, it will charge itself first, and the duty cycle and schedule. The entire working time of a common node is divided into multiple working periods t, and each working period includes five states, among which the data packet receiving state, data packet sending state, and listening state are working states. A working cycle t is composed of multiple working states τ and idle states, and the format is in It is a working state or an activity instance in a certain working cycle of node i.

Each common node has the same transmission radius, and the nodes generate their own timetables according to the charging efficiency, and broadcast the timetables to neighboring nodes until all nodes have the working timetables of neighboring nodes. The working schedule of each node is relatively fixed, and status adjustment is usually not performed, which is conducive to time scheduling and work synchronization.

Each node calculates the data transmission delay according to its own work schedule and the work schedule of neighboring nodes. The formula for calculating the data delay is shown in formula (1):

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In formula (1), is an active instance of node i+1, is an active instance of node i, k∈(1,2,…,n). Node i is at When it is necessary to send a data packet to the next node, node i calculates the data delay to the neighbor node, and one neighbor node i+1 has multiple active instances, and node i calculates the minimum time delay to the neighbor node i+1 At the same time, node i calculates the minimum data delay to every other neighbor node Among these minimum data delays, choose a node with the minimum data delay As the next hop neighbor node.

Each node can calculate the minimum data delay to neighbor nodes for each active instance, from node i in The minimum data delay calculation formula for forwarding data packets to neighbor nodes and finally arriving at base station s is shown in formula (2):

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Each node has a neighbor table. The neighbor table is a two-dimensional table. The neighbor table stores the information of all neighbor nodes within the communication radius of the node and the data delay from each active instance in the node to any active instance of the neighbor node.

In the energy harvesting wireless sensor network of the present invention, data packets can always be received and forwarded correctly.

Specifically, as shown in Figure 2, the specific implementation method of the wireless sensor network low-latency routing method for energy harvesting in the present invention is as follows:

(1) In the monitoring environment shown in Figure 1, multiple common sensor nodes with the same communication capability, information processing capability and equipped with one or more energy conversion devices and energy storage devices are randomly scattered. The sensor nodes know their geographical location through the positioning system. Each common node has the same transmission radius and a unique identifier in the monitoring system. The nodes can keep track of their own energy conditions through the equipped energy management system. Before the node enters the monitoring environment, the energy storage device does not carry electricity, and enters the charging state after entering the monitoring environment. The sensor nodes are randomly scattered in the monitoring environment, and the energy conversion device of each node is affected by the environment, and its energy harvesting efficiency is different. The base station node is the aggregation node in the monitoring area, which is responsible for the aggregation of data. The data collected by all sensor nodes is finally forwarded to the base station node. The base station node can be randomly scattered or laid on the ground. The base station node has strong communication capabilities and data Processing capacity, base station nodes can carry high-power energy storage devices or directly use alternating current, and the energy is not limited. After the base station is added to the website, it broadcasts its own coordinate position to the nodes in the monitoring area, because the energy of the base station nodes is not limited. , can directly broadcast signals to all sensor nodes in the monitoring area with a relatively high communication radius, communicate directly with all sensor nodes, and do not need to be forwarded by other sensor nodes. According to the instructions of the external terminal, the base station node can issue an instruction task to any sensor node in the monitoring area, requiring the sensor node in a specific coordinate to perform data collection or environment perception. After receiving the signal from the base station, all sensor nodes within the communication radius of the base station check whether their coordinates are within the coordinate range specified by the base station. If they are within the coordinate range specified by the base station, the node acts as a source node and undertakes the data collection task. If its own coordinates are not within the coordinate range specified by the base station, the node acts as a relay node and undertakes data forwarding tasks or is in an idle state.

(2) The node manages the collected energy through the energy management system. By monitoring the energy collection process for a certain period of time, the node can predict the daily energy collection efficiency to a certain extent. The nodes generate their own work schedules based on the approximate energy harvesting efficiency, and in the subsequent time, the work schedules are continuously corrected until the work schedules are relatively stable.

(3) The system sets a time length t for the work schedule, and t can be one minute, one hour, or one day. Each node sets the working time within the length of time t. If t is one hour, the node can set when it is in the working state within the hour according to the charging efficiency. The format is t _i represents the working schedule of the i-th node, Indicates that node i is in the working state at this moment and can collect, receive or send data. In Fig. 3, the working schedules generated by 10 sensor nodes are: t _a = (1,3,6), t _b = (2,3,6), t _c = (3,4,6) , t _d =(1,5,6), t _e =(1,4,6), t _f =(1,2,3), t _g =(1,2,5), t _h =(2 ,3,6), t _i =(1,2,4), t _j =(3,4,6).

(4) Each sensor node broadcasts its own working schedule within its own communication radius until all nodes have mastered the working schedule of its neighbor nodes. Each node has a neighbor table, which records the relevant information of neighbor nodes, including the coordinate position and working schedule of neighbor nodes. The neighbor table is a two-dimensional table, and the format of the neighbor table is: (neighbor node ID, neighbor node coordinates, neighbor node work schedule).

(5) The working schedule of the nodes should be kept as stable as possible, but the sensor nodes are dependent on the external environment. When the external environment changes or the node’s working schedule changes due to its own failure, the node must update the new working time The table informs the neighbor nodes to go to step (4), otherwise go to step (5).

(6) The source node at time The node preparing to send the data packet selects the next hop node to accept its data packet, and the selected next hop node satisfies the following conditions A and B,

The condition A is: the selected next-hop node is closer to the base station node than the node ready to send the data packet. The node has its own coordinate information, and by checking its neighbor table, the coordinate position of the neighbor node is extracted from the neighbor table. That is to say: d _j,s <d _i,s , Wherein, (i _x ,i _y ) is the coordinate of node i, (j _x ,j _y ) is the coordinate of node j, and (s _x ,s _y ) is the coordinate of base station s. This can ensure that the data is constantly approaching the base station when being forwarded.

The condition B is: the selected next-hop node can receive the data of the node ready to send the data packet as soon as possible, and the node extracts the working schedule of the neighbor node from the neighbor table by checking its neighbor table, and the working schedule Contains the active instance of the neighbor node. That is, the next hop node contains an activity instance in the work schedule The activity instance satisfies the $d_{i,j}(t_j^k,t_i^1)=|t_j^k-t_i^1|,d_{i,j}(t_j^k,t_i^1)\&le;d_{i,m}(t_j^l,t_i^1),$ $m\&Element;(\mathrm{1,2},...,\mathrm{no}),l\&Element;(\mathrm{1,2},...,k).$

The selected node first satisfies condition A, and then finds the next-hop node that satisfies condition B in the neighbor nodes that satisfy condition A. Each node selects next-hop routes for all active instances of itself according to the next-hop selection method until all active instances of all nodes establish data transmission links. After the data link is established, each node calculates the data transmission delay from its active instance to the next hop node, and informs the next hop node of the delay at the same time, and finally all active instances of each node master each active instance of the node The sum of the data delays to the base station, that is, the end-to-end delay, is saved in the neighbor table. In Figure 3, node a is at time A data packet needs to be sent to the next hop node. After calculation, there are 3 neighbor nodes that meet the condition A, namely b, c, and d, and their distances from the base station node are all smaller than the distance between the source node a and the base station node. Continue to calculate which of their nodes meets condition B, and get the activity instance of sensor node b If condition B is met, sensor node b is selected as sensor node a at time The next-hop node of , where the active instance of sensor node b Will accept data from the previous hop node.

When a node wants to perform data routing selection at a certain moment, it selects a route that meets the end-to-end delay requirements of data transmission from the neighbor table according to the active instance at that moment. If there are multiple links in the link that meet the requirements, choose the smallest A link for data transmission. When the link is determined, the data is forwarded along the selected link until it is forwarded to the base station node. In FIG. 3 , after performing step (6) on the nodes in the link, all nodes on the link responsible for data forwarding have completed the selection of the next hop node. Sensor node a at time There is a data packet that needs to be sent to the next hop node, and finally a link with a lower delay is selected for data forwarding. The link is: PATH _{(a, 1)} = {a, b, f, i, s}.

During the data transmission process, if the active instance of a certain node changes temporarily, the node restarts the next-hop node selection method, and selects the node with the nearest active instance from the neighbor nodes as the next-hop node for data transmission until the data is transferred. forwarded to the base station node.

The source node generates data, and the data is finally forwarded to the base station node through the relay node. If the source node continues to generate data, the data link will be maintained until all the data generated by the source node is forwarded to the base station node.

After the data generated by the source node is forwarded, the link established from the source node to the base station node is released, and the active instance of the node re-enters the link selection state, allowing neighboring nodes to perform link selection.

Those skilled in the art can understand that the various operations, methods, and steps, measures, and solutions in the processes discussed in the present invention can be replaced, changed, combined, or deleted. Further, other steps, measures, and schemes in the various operations, methods, and processes that have been discussed in the present invention may also be replaced, changed, rearranged, decomposed, combined, or deleted. Further, steps, measures, and schemes in the prior art that have operations, methods, and processes disclosed in the present invention can also be alternated, changed, rearranged, decomposed, combined, or deleted.

The above descriptions are only part of the embodiments of the present invention. It should be pointed out that those skilled in the art can make some improvements and modifications without departing from the principles of the present invention. It should be regarded as the protection scope of the present invention.

Claims (6)

1. a wireless sensor network, described wireless sensor network comprises base-station node and is randomly dispersed in the some ordinary nodes in monitored area, it is characterized in that: each ordinary node includes chargeable system and energy reserve system, wherein chargeable system is used for outside natural energy resources to be converted into electrical energy for storage in energy reserve system, when the electric energy of energy reserve system is not enough, start the chargeable system of this node also till electric energy is full of;

The whole operating time of described ordinary node is divided into several work periods, state residing in the work period is made up of multiple operating state and idle condition, described multiple operating state is: charged state, receives data packets state, Packet Generation state, intercept state, wherein charged state can work with other states in parallel, can not concurrent working between other state.

2. a kind of wireless sensor network according to claim 1, is characterized in that: described ordinary node all has identical communication capacity, information processing capability, and identical transmission radius and unique identification.

3. a kind of wireless sensor network according to claim 1, is characterized in that: the quantity of the chargeable system that each ordinary node comprises and energy reserve system is one or more.

4. a kind of wireless sensor network according to claim 1, is characterized in that: described ordinary node is before adding wireless sensor network, and energy reserve system does not carry electricity, is joining after in wireless sensor network system, first charges voluntarily.

5., based on a low delay method for routing for the arbitrary described wireless sensor network of claim 1-4, it is characterized in that, comprise the following steps:

A, each ordinary node produce respective operating schedule according to its charge efficiency, are specially: set the timetable of each work period t of ordinary node as wherein for the kth operation time that node i is corresponding with a certain operating state within this cycle, k=1,2 ..., n, n are in the work period and the corresponding time hop count divided of each operating state of node i;

The operating schedule of oneself is broadcast to its neighbor node by B, each ordinary node in self communication radius, until all nodes all have the operating schedule of its neighbor node;

C, each ordinary node calculate according to the operating schedule of the operating schedule of oneself and its neighbor node data transfer delay when moment sends from packet to all neighbor nodes, the computing formula of described data transfer delay is:

$d_{i,i+1}(t_i^k,t_{i+1}^k)=|t_{i+1}^k-t_i^k|---\left(1\right)$

In formula (1), for node i+1 exists with node i within its work period operation time corresponding to moment;

D, each ordinary node obtain it according to step C under each operating state, send the data transfer delay of packet to neighbor node; And next-hop node selected when obtaining sending packet under each operating state according to following condition: selected next-hop node is relative to self closer to base-station node, and data transfer delay is minimum;

The data transfer delay of next-hop node selected when sending packet under each operating state is informed the next-hop node of this selection by E, each ordinary node, and the minimum data that the packet sent under going out each operating state according to following formulae discovery finally arrives base station s postpones, i.e. end-to-end delay:

$d_{i,s}(t_i^k,s)=\underset{i=1}{\overset{m}{\mathrm{\&Sigma;}}}{d}_{i,i+1}(t_i^k,t_{i+1}^k)---\left(2\right)$

F, set up two-dimentional neighbor table for each node, this neighbor table preserves all information of neighbor nodes in this node communication radius, and data delay this node sends packet arrival neighbor node during when being in each operating state and end-to-end delay;

When G, ordinary node at a time will carry out data Route Selection, select to meet the minimum route of transfer of data end-to-end delay, until data are forwarded to base-station node from neighbor table according to the operating state in this moment.

6. low delay method for routing according to claim 5, is characterized in that:

In data transmission procedure, if the interim change of the operating state of a certain ordinary node, then this node is according to step C-D, selects the node with nearest operating state to carry out transfer of data as next-hop node, until data are forwarded to base-station node from neighbor node.