CN113490250B - Routing protocol of multi-hop wireless sensor network for raw data acquisition - Google Patents

Routing protocol of multi-hop wireless sensor network for raw data acquisition Download PDF

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CN113490250B
CN113490250B CN202110775059.8A CN202110775059A CN113490250B CN 113490250 B CN113490250 B CN 113490250B CN 202110775059 A CN202110775059 A CN 202110775059A CN 113490250 B CN113490250 B CN 113490250B
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energy
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CN113490250A (en
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刘丽华
张杨斌
李璇
王懋
吴继冰
黄宏斌
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National University of Defense Technology
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    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
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Abstract

The invention discloses a routing protocol of a multi-hop wireless sensor network for raw data acquisition, which comprises the following steps: the base station broadcasts to all nodes, so that all the nodes find a path to the base station to complete network initialization; a base station creates a transmission scheme, sets a next hop node for each node, and establishes an optimized tree structure and a cluster structure for a network; the base station distributes the transmission scheme to all nodes so that each node knows when and to which node it sends data; each node transmits data to the node's next hop node in its assigned time slot according to a transmission scheme; and the base station updates the transmission scheme according to the network operation condition. The WSN protocol provided by the invention can collect raw data from all nodes, obviously prolong the service life of the WSN and achieve satisfactory performance.

Description

Routing protocol of multi-hop wireless sensor network for raw data acquisition
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a routing protocol of a multi-hop wireless sensor network for raw data acquisition.
Technical Field
In order to play a greater role from practical applications, internet of things (IoT) technology has become a very popular research topic in recent years. The operation of the internet of things must be based on the perception of the environment, which is essentially the acquisition of data. With the development of technologies such as computer vision, data acquisition in terms of quantity and quality has become an indispensable requirement. Wireless Sensor Networks (WSNs) are an important data collection method that can effectively support networking applications.
A WSN is composed of a base station and a plurality of sensor nodes. The sensor node is a small object with sensing and wireless transmission functions. Each sensor node senses and collects near-end environment information, processes the information, and then forwards the data to the base station over a wireless channel. A wireless sensor network consisting of all sensor nodes can monitor a specified area and the data collected by the base station is provided to the user for further use.
The WSN has the outstanding advantage of convenient use. Because of the small size of the nodes, it is very easy to deploy, and WSNs can be deployed in target areas without the need for a communication infrastructure. Furthermore, the low cost of the sensor node makes it very suitable for commercial applications. Based on the advantages of wireless sensor networks, they have been widely used in various fields including industry, agriculture, marine monitoring, medicine and health care, environmental monitoring, and the like. A major limitation of wireless sensor networks is that their lifetime is limited by the energy of the sensor nodes. WSNs with small sized sensor nodes generally facilitate network deployment, but can limit the battery power of each node. Therefore, how to extend the lifetime of WSNs is a research focus.
From the point of view of routing protocols, there are mainly two approaches to extend the life cycle of a WSN under different conditions. In the case where all sensor nodes can directly communicate with a base station, clustering is a classic method that can extend the lifetime of a WSN, in which all nodes are first divided into several clusters according to different criteria, then one node is selected as a cluster head in each cluster to collect data in the entire cluster, then the data is aggregated, and the aggregated data is transmitted to the base station. For other nodes, the cluster head is typically closer than the base station, so communication within the cluster is more energy efficient. Data aggregation can greatly extend the lifetime of a network by reducing the amount of data transmitted over a wireless channel. However, information loss is inevitably caused due to data aggregation of the cluster heads. For example, the cluster head may use a maximum, minimum, or average value to represent the data collected by all nodes in the cluster during the aggregation phase. In the case where some sensor nodes cannot communicate directly with the base station, for example, mountains may prevent direct communication between the nodes and the base station, or the target area is so large that the distance between the nodes and the base station exceeds the communication radius of the nodes. The routing protocol based on the tree structure can realize data collection through a multi-hop method and prolong the service life of the network through a mechanism of avoiding hot spots. However, this approach is more used for dynamic networks and lacks an effective means for extending the lifetime of static networks.
The above conventional methods are all based on the assumption that there are redundant sensor nodes in the network and that data can be aggregated in the collection process. However, these assumptions do not necessarily hold in practical applications. In practical applications, users do not expect redundant nodes in the WSN, which can both control costs and facilitate the deployment of nodes. This means that each sensor node is a critical node. Without redundant sensor nodes, the entire network only counts as normal when its sensors are active. Thus, the lifetime of a network is defined as the lifetime of the node that first stops working. Furthermore, aggregating data may reduce the energy consumption of the network, but raw data containing more information may bring more benefits for practical applications. For example, computer vision techniques require image data as input, and if data aggregation is applied to the collection of image data using a WSN, the result of the data aggregation will be text or numeric data, rather than the original image data.
Disclosure of Invention
Based on the above considerations, the present invention proposes a new application scenario: 1) Raw data collected from the target area must be collected rather than aggregated data; 2) Each sensor node is a key node in the WSN. 3) There are situations where the sensor node cannot communicate directly with the base station. Aiming at the application scene, a new protocol is provided, namely a multi-hop wireless sensor network routing protocol (hereinafter referred to as HTC-RDC) facing to raw data acquisition and based on a tree and cluster mixed structure, so as to prolong the service life of the WSN. In the HTC-RDC protocol, a multi-hop network is constructed using a tree structure to establish communication between all sensor nodes and a base station. In addition, a cluster structure is added to the tree structure to save energy of the network. Mechanisms used in tree-based or cluster-based protocols (e.g., load balancing and hot spot avoidance) are also used in the proposed hybrid architecture to extend the lifetime of the network. The hybrid architecture is oriented to raw data collection and is built on the basis of analysis using combinatorial optimization theory.
The invention discloses a routing protocol of a multi-hop wireless sensor network for raw data acquisition, which comprises the following steps:
the base station broadcasts to all nodes, so that all the nodes find a path to the base station to complete network initialization;
a base station creates a transmission scheme, sets a next hop node for each node, and establishes an optimized tree structure and a cluster structure for a network;
the base station distributes the transmission scheme to all nodes so that each node knows when and to which node it sends data;
each node transmits data to the node's next hop node in its assigned time slot according to a transmission scheme;
and the base station updates the transmission scheme according to the network operation condition.
Further, each node has a hierarchy attribute.
Further, the broadcasting process of the base station is as follows:
step 1: the base station generates an integer as the current round number, and distributes the broadcast message with the maximum power of the radio module same as the node, wherein the content of the broadcast message comprises the round number, the ID of the broadcast node, the hierarchy and the residual energy information of the broadcaster;
and 2, step: a node receiving a broadcast message should record the broadcast message and calculate and record the distance between the node and a source node through RSSI, and then perform the following operations:
if the broadcast message is the first broadcast message received in the latest round, clearing the hierarchy information, and setting the hierarchy of the broadcast message as the hierarchy value contained in the broadcast message plus 1; meanwhile, storing the source node as a father node according to the information of the broadcast message; the node generates a new broadcast message with the same structure, but will modify it using its own information, after a certain time interval, the node issues the new broadcast message according to a carrier sense multiple access protocol that avoids collisions;
if the node has a latest round of broadcast messages in its memory, the node shall check and perform the following operations:
if the hierarchy in the broadcast message is less than the hierarchy, recording the source node as a parent node;
recording the source node as a peer node if the hierarchy in the broadcast message is equal to its hierarchy;
if the hierarchy in the broadcast message is greater than its hierarchy, the source node is recorded as a descendant node.
Further, after receiving the broadcast of the base station, the node may send feedback to the base station, where the feedback message includes all necessary information used by the node to create the transmission scheme, and the necessary information includes at least remaining energy and topology information of the node.
Further, the tree structure is built according to the following principle:
if a certain node has only one father node, the node sets the only father node as the next hop node of the node; if a plurality of father nodes exist, the next hop node is the father node with the largest residual energy or one of the equivalent nodes with the lowest in-degree, wherein the equivalent nodes are defined as the nodes meeting the energy equivalent criterion and the energy consumption equivalent criterion; the parent node with the largest remaining energy is denoted as the candidate node and the parent node, which may be an energy equivalent node, is denoted as the candidate node.
Further, the energy equivalence criterion is as follows:
Figure 502771DEST_PATH_IMAGE001
whereinE candidateRepresenting the remaining energy of the candidate node,E alternativerepresenting the residual energy, a, of the alternative node0Is a parameter defined in advance according to experimental results；
The energy consumption equivalence criterion is as follows:
Figure 591950DEST_PATH_IMAGE002
wherein the content of the first and second substances,c alternative-coorelatedrepresenting the energy consumption associated with the candidate node,c candidate-coorelatedrepresenting the energy consumption associated with the alternative node,
Figure 449047DEST_PATH_IMAGE003
is a parameter preset according to an experimental result.
Further, if the remaining energy of the candidate node is lower than that of the node performing the next-hop node selection, β is approximately calculated as:
Figure 205651DEST_PATH_IMAGE004
whereind node-alternativeIndicating the distance between the node and the standby node,d alternative-next-hopindicating the distance between the standby node and the next hop node of the standby node,d node-candidaterepresents the distance between the node and the candidate node, andd candidate-next-hoprepresenting the distance between the candidate node and the next hop node of the candidate node;
if the remaining energy of the candidate node is higher than that of the node for selecting the next hop node, the energy consumption of the candidate node tends to be unbalanced, the energy consumption of the node should be protected, and β is specifically expressed as:
Figure 388370DEST_PATH_IMAGE005
the candidate nodes that satisfy the above two equations are equivalent nodes.
Further, for nodes A, B, C of the same level, and for nodes of that levelA high-level node E, if the node A is a candidate node, the node B and the node C are alternative equivalent nodes, and the residual energy of the nodes A, B and C isE A, E B, E C，E E In aE A < E EIn the case of (2), it should be calculated according to the following formula:
Figure 200731DEST_PATH_IMAGE006
Figure 127098DEST_PATH_IMAGE007
wherein the content of the first and second substances,d EA representing the distance of node a from node E,d EB representing the distance of node B from node E,d BO representing the distance of the node B from the base station,d AO represents the distance of node A from the base station, assuming βBA>βCAIf so, the node C is the next hop node of the node E;
in thatE A>E EIn the case of (2), it should be calculated as follows:
Figure 472629DEST_PATH_IMAGE008
Figure 826250DEST_PATH_IMAGE009
whereind EC Represents the distance between node C and node E, assuming βBA<βCAThen node B is the next hop node for node E.
Further, when data are collected in the same hierarchy, the nodes select a peer node as a relay node, i.e. a cluster structure is formed.
The invention defines a new application scene, which is oriented to the original data acquisition, does not need redundant sensor nodes, obviously prolongs the service life of the WSN, and is more in line with the practical application, and the experiment also verifies the effectiveness of the invention.
Drawings
FIG. 1 is a schematic diagram of a network consumption model used by the present invention;
FIG. 2 is a flow chart of the various stages and sub-stages of operation of the HTC-RDC protocol of the present invention;
FIG. 3 is a schematic diagram of a broadcast process;
FIG. 4 is a node process broadcast message flow diagram;
FIG. 5 is a network topology after the broadcast process is finished;
FIG. 6 is an example optimized tree structure building process;
FIG. 7 is a schematic diagram of an indirect path search;
FIG. 8 is a schematic diagram of a tree and cluster hybrid structure;
FIG. 9 application scenario for experiments;
FIG. 10 illustrates the transmission scheme created in round 0 by the present invention;
fig. 11 the transmission scheme created by the MHT protocol in round 0;
fig. 12 MTE protocol creates a transmission scheme in round 0;
FIG. 13 illustrates the transmission scheme of the present invention created in round 100;
fig. 14 MHT protocol creates a transmission scheme in round 100;
fig. 15 MTE protocol creates a transmission scheme in round 100;
FIG. 16 different α0And beta0The impact of the combination on the network lifecycle;
FIG. 17 lifetime of a WSN employing the HTC-RDC protocol under the same experimental conditions;
FIG. 18 shows the lifetime of a WSN using MHT protocol under the same experimental conditions;
FIG. 19 lifetime of a WSN employing the MTE protocol under the same experimental conditions;
FIG. 20 shows the results of Monte Carlo experiments performed with the present invention at different node distributions;
FIG. 21 shows the results of Monte Carlo experiments with MHT protocols at different node distributions;
fig. 22 shows monte carlo experimental results of MTE protocol under different node distributions.
Detailed Description
The invention is further described with reference to the accompanying drawings, but the invention is not limited in any way, and any alterations or substitutions based on the teaching of the invention are within the scope of the invention.
The mechanism for prolonging the life cycle of the network is analyzed as follows:
since it is difficult to obtain candidate transmission schemes by solving the optimization problem in a large scale, the candidate scheduling will be constructed by the routing protocol without solving the optimization problem. Constructing the candidate transmission scheme needs to be based on the properties of the candidate transmission scheme.
Properties of candidate transmission schemes
Designing an example of a network consumption model as shown in FIG. 1, assuming that the residual energy of node A is fixedE A=1000E 2Node B residual energy of 0 to 10000 E 2And other conditions remain unchanged. The optimal solution of these 10000 models was solved using the CPLEX solver, the results of which showed, althoughS 2Overall, the energy efficiency is lowest, but whenE B Smaller, transmission schemes should still be usedS 2Because node B is inS 2With the least energy consumption. And, as the node B energy increases, it consumes more node B energy than node AS 3The ratio of (a) to (b) increases.
It can be concluded that the remaining energy is one of the most important factors affecting the schedule combination, not the factor affecting energy efficiency. Another conclusion that can be drawn is that it is a global optimum when the remaining energy of the nodes reaches equilibrium.
Load balancing
When the network starts up, the nodes typically have the same remaining energy. Thus, maintaining load balancing will maintain the remaining energy of the nodes equal or similar.
In cluster-based protocols, fuzzy logic is used to maintain load balancing. The present invention does not directly use fuzzy logic. But based on the idea of fuzzy logic, some definitions such as equivalent nodes are introduced to achieve load balancing.
In tree-based protocols, it is certain nodes that inevitably die first due to heavy loading because of their location in the topology, and load balancing can be maintained by adjusting the choice of relay nodes. The present invention uses the concept of "degrees" in graph theory to help achieve load balancing.
Transmission scheme update
For a particular transmission scheme, the cumulative effect of unbalanced energy consumption will degrade the balance of the remaining energy over several cycles of operation. Therefore, after a certain number of rounds, a new transmission scheme should be generated and executed according to the current state of the network, without executing the previous transmission scheme. This process is called transmission scheme update. The essence of transmission scheme updating is to implement a combination with transmission schemes that can complement each other in terms of energy consumption.
In addition, in practical applications, transmission scheme updates have two important effects. The first is to cope with topology changes caused by node death and environmental changes. At this time, the node in the network needs to get in touch with the base station again by updating the transmission scheme. And secondly to cope with the uncertainty of energy consumption. The energy consumption of the sensor modules and processor modules of the sensor nodes is uncertain, so the energy consumption of the entire sensor node can be considered as a markov process, while the current state of the network is the only factor to consider for generating the transmission scheme. This is one way to handle the uncertain energy consumption.
Inserting relay nodes to reduce energy consumption
When the network size is large, various alternative transmission schemes may still be available under the premise of load balancing. At this time, selecting a power-saving transmission scheme may provide more options for subsequent operations.
A model was built to analyze the energy saving principle. Suppose node 0 at coordinate (0, 0) will pass through (0)n-1) relay nodes, each relay node having coordinates (0,d) Node pointnSendinglBit data. Wherein the nodeiHas the coordinates of (x i , y i )。
Total energy consumption for data transmission
Figure 624442DEST_PATH_IMAGE010
（1）
Whereind i i(+1)Representing nodes iAnd a node (i+1) of the distance between the two. Then the
Figure 354500DEST_PATH_IMAGE011
（2）
The solution of this function is
Figure 554537DEST_PATH_IMAGE012
（3）
This means that the relay nodes are evenly distributed between node 0 and nodenWhen the connection between the two is on, the total energy consumption is the lowest.
The lowest total energy consumption is
Figure 79060DEST_PATH_IMAGE013
（4）
Equation (4) shows that even under the optimal condition that the relay nodes are uniformly distributed, the effectiveness of energy saving by increasing the number of relay nodes is still limited. However, in practical applications, the deployment of the nodes is determined by the positions of the targets to be detected, and therefore, the uniform distribution of the nodes is difficult to achieve.
Furthermore, even under optimal conditions, if one more relay node is added, the energy consumption can be reduced, but with the number of nodesnThe marginal utility decreases rapidly. Furthermore, if the number of optional nodes is large, the computational complexity of the transmission scheme design will multiply as the number of relay nodes increases.
From the above analysis, if it is possible to select some nodes as relay nodes and to efficiently save energy in terms of saving data transmission, selecting only one node is a satisfactory method of balancing efficiency and computational complexity. In addition to the above mechanism, when the difference between the residual energies of the nodes is not large, the direct transmission mode should be selected by the node.
Based on the above research, the operation of the HTC-RDC protocol proposed by the present invention comprises five phases. The relationship between the phases and the sub-phases is shown in fig. 2.
S10: network initialization
Since some nodes cannot communicate directly with the base station, they should first find a path to the base station. Although some dynamic routing protocols (e.g., OLSR and AODV protocols) can implement path discovery from a node to a base station, the overhead of energy consumption is large, and thus these methods are only applicable to nodes with continuous performance source provisioning. The protocol proposed by the present invention uses a method of broadcasting from the base station to all nodes to perform network initialization so that all nodes can find a path to the base station. The phase is divided into two sub-phases.
S101: broadcasting
The broadcast process is shown in figure 3. Each node should have an attribute named level (Hierarchy). And defining the level value of the base station as 0, and starting from the base station, increasing the level value of the nodes of each level from near to far.
Step 1: the base station starts an initialization procedure. The base station generates an integer as the current round number and then issues the broadcast message with the maximum power of the same radio module as the node. The contents of the broadcast message include the number of rounds, the ID of the broadcasting node, the hierarchy, and remaining energy information of the broadcaster (the remaining energy of the base station may be set to infinity).
Step 2: the node maintains the initialization process as shown in fig. 4. A node receiving a broadcast message should record the message, calculate the distance between the node and a source node through RSSI, record the distance information, and then perform the following operations:
case 1: if it is the first broadcast message received in the last round, the level information is cleared and its level is set to the level value contained in the broadcast message plus 1. Meanwhile, the source node is stored as its parent node according to the information of the broadcast message.
The node should then generate a new broadcast message with the same structure, but will modify it using its own information. After a certain time interval, the node issues a new broadcast message according to the CSMA/CA (carrier sense multiple access with collision avoidance) protocol.
Case 2: if there is already a last round of broadcast messages in memory, the node should check and perform the following:
if the hierarchy in the broadcast message is less than its hierarchy, the source node is recorded as a parent node.
If the hierarchy in the broadcast message is equal to its hierarchy, the source node is recorded as a peer node.
If the hierarchy in the broadcast message is greater than its hierarchy, the source node is recorded as a descendant node.
Each node will receive at least one broadcast message as long as it has at least one path to the base station. Therefore, the problem that the node cannot directly communicate with the base station can be effectively solved, whether the distance exceeds the transmission radius of the node or an obstacle exists.
During the broadcast, each node will broadcast once and only once. As a result of the broadcast phase, each node has local topology information associated with it. Each node belongs to a particular hierarchy and has at least one parent node, and may or may not have siblings and children. The topology of the entire network is shown in fig. 5.
The hierarchy of a node means the minimum number of hops the node reaches the base station, while the lower hierarchy refers to the direction towards the base station, i.e. as long as the node transmits its data to the node with the lower hierarchy, it can finally transmit its data to the base station.
S102: feedback
If each node only retains one edge of one parent node in the topology graph, the graph will become a tree structure. Each node forwards data received from its descendant nodes and sends its own data to its parent node in a hierarchy from high to low, which is the simplest tree-structure based routing protocol. However, this simplest routing protocol is hardly the most efficient protocol that can extend the lifetime of a network, because no mechanism is employed that can extend the lifetime of a network.
A better approach is that all nodes provide their own information to the base station via feedback messages and the optimized centralized routing protocol to be executed is generated by the base station and distributed to all nodes for execution by the nodes. Another advantage of the centralized approach is that the computational overhead is borne by the base stations with unlimited energy supply. However, each node has only local topology information at this time. To ensure that the base station can collect topology information, each node retains the edges to which its parent node with the highest remaining energy is connected when sending feedback messages to the base station. The feedback message for each node should contain all the necessary information for the node to create the transmission scheme, including its remaining energy and topology information, e.g. hierarchy, parent, sibling and child nodes.
The network initialization process ends when the base station collects all feedback messages. The energy consumption of the process is the additional functional energy consumption of the network, since there is no target data to collect to transmit to the base station.
S20: generation of transmission schemes
After network initialization, data for each node may be collected in the same manner as the feedback process. Since it does not effectively extend the network lifetime, an optimized transmission scheme should be created by the base station that has all the information throughout the network. One of the most important tasks in creating a transmission scheme is to set a next hop node for each node.
Building optimized tree structures
For the network transmission mode, the direct transmission mode should be considered first. For one node, the direct transmission path means that the next hop is set as a parent node because a lower hierarchy node is inevitably passed in the path to the base station. If a node has only one parent node, e.g., a node with a level 1, the node will set the only parent node as its next hop node. If there are multiple parents, the next hop node should be the parent with the largest remaining energy, or one of its lowest-in equivalent nodes. An equivalent node is defined as a node that meets the criteria of energy equivalence and energy consumption equivalence.
The parent node with the largest remaining energy is denoted as the candidate node and the parent node, which may be an energy equivalent node, is denoted as the candidate node.
The energy equivalence criterion is as follows:
Figure 866012DEST_PATH_IMAGE001
（5）
whereinE candidateRepresenting the remaining energy of the candidate node,E alternativerepresenting the residual energy, a, of the alternative node0Are parameters defined in advance based on experimental results.
The energy consumption equivalence criterion is as follows:
Figure 665341DEST_PATH_IMAGE002
（6）
wherein the content of the first and second substances,c alternative-coorelatedrepresenting the energy consumption associated with the candidate node,c candidate-coorelatedrepresents the energy consumption associated with the alternative node, and beta0Are parameters predefined according to experimental results.
In the case of two different situations, it is,c alternative-coorelatedandc candidate-coorelatedthere are different specific expressions:
1) if the remaining energy of the candidate node is lower than that of the node for next hop node selection, which is generally more reasonable, because the node close to the root in the tree structure tends to bear more load, the energy consumption as a whole should be considered, and the specific expression of equation (6) is:
Figure 719885DEST_PATH_IMAGE014
（7）
whereinc node-alternativeRepresenting the energy consumption of the node in transmitting data to the standby node,c alternative-next-hoprepresenting the energy consumption of the node in transmitting data to the next hop node of the standby node,c node-candidaterepresenting the energy consumption of the node in transmitting data to the candidate node,c candidate-next-hoprepresenting the energy consumption of the node in transmitting data to the next hop node of the candidate node.
In the application scenario proposed by the present invention, equation (7) can be approximately calculated as:
Figure 149729DEST_PATH_IMAGE004
（8）
whereind node-alternativeIndicating the distance between the node and the standby node,d alternative-next-hopindicating the distance between the standby node and the next hop node of the standby node,d node-candidaterepresents the distance between the node and the candidate node, andd candidate-next-hoprepresenting the distance between the candidate node and the next hop node of the candidate node.
2) If the remaining energy of the candidate node is higher than that of the node for next-hop node selection, the energy consumption of the candidate node tends to be unbalanced, so that the energy consumption of the node is protected, and the formula (6) is specifically expressed as:
Figure 922513DEST_PATH_IMAGE015
（9）
the candidate nodes satisfying the above two conditions are equivalent nodes. If a node has an equivalent node of the candidate node, the node with the lowest number of the candidate node and the equivalent node should be set as the next hop node of the node. Furthermore, if there are multiple nodes with the same lowest in-degree, the node that minimizes β should be selected.
The setup process must be performed by every node from a lower hierarchy level to a higher hierarchy level, since a direct transmission path of the lower hierarchy level may be referenced in the process. Compared with the tree structure used by the feedback message, the tree structure is optimized in terms of load balancing.
As shown in fig. 6, a simple specific example is used to illustrate the establishment process of the optimized tree structure. Nodes a, B, C have a level 1, so they all have only one parent node, i.e. the base station (denoted node O). Thus, their direct transmission paths are AO, BO and CO. Nodes D and E have level 2 and node D has a unique parent node a, so the direct transmission path for node D is DA. Node E has 3 parents: nodes a, B and C. Assuming that the residual energy of nodes A, B, C isE A, E B, E CAnd is andE A>E B>E Cand is and
Figure 994374DEST_PATH_IMAGE016
（10）
that is, node a is a candidate node, node B and node C are candidate nodes, and the energy equivalence criterion is satisfied.
In thatE A<E EIn the case of (1), the following calculation is carried out according to the formula (8)
Figure 903424DEST_PATH_IMAGE017
Figure 35329DEST_PATH_IMAGE018
（11）
Suppose that
Figure 531294DEST_PATH_IMAGE019
,
Figure 406846DEST_PATH_IMAGE020
I.e., node B and node C are equivalent nodes. For node a with an in-degree of 1, the in-degrees of node B and node C are both 0, so the next hop node of node E should select between node B and node C. Then will be
Figure 170403DEST_PATH_IMAGE021
And
Figure 473208DEST_PATH_IMAGE022
make a comparison, assume
Figure 955005DEST_PATH_IMAGE023
Node C is the next hop node for node E.
In thatE A>E EIn the case of (b), β should be calculated as follows
Figure 368669DEST_PATH_IMAGE024
（12）
Figure 252311DEST_PATH_IMAGE025
（13）
Suppose that
Figure 510640DEST_PATH_IMAGE026
,
Figure 479733DEST_PATH_IMAGE027
I.e., node B and node C are equivalent nodes. For node a with an in-degree of 1, the in-degrees of node B and node C are both 0, so the next hop node of node E should select between node B and node C. Then will be
Figure 431509DEST_PATH_IMAGE028
And
Figure 169658DEST_PATH_IMAGE029
make a comparison, assume
Figure 814266DEST_PATH_IMAGE030
Then node B is the next hop node for node E.
Adding cluster structure for further optimization
From the foregoing analysis, if the cluster structure can be added to an already established tree structure, more mechanisms can be used to further extend the lifetime of the network. A cluster structure with the following functions is one that we wish to add to the tree structure: tending to balance the remaining energy of the nodes, or to make the network more energy efficient, or both.
It can be inferred that such a cluster structure is formed because some nodes become cluster head nodes and other nodes select indirect paths through the cluster head nodes, and the indirect paths have the following characteristics:
it will tend to equalize the node residual energy or make the path more energy efficient than a direct transmission path.
The relay node in the indirect path, i.e. the cluster head node, should be the peer node; otherwise, it will be a direct transmission path, or a misdirected path to a successor node.
If a node is selected as a relay node by another node, it can no longer select an indirect transmission path; otherwise, for the node that selects the node as the relay node, there will be more than two relay nodes, and the purpose of energy saving will not be achieved.
The way to find a better path is to check if an indirect path with any peer node as a relay node is better than a direct transmission path.
The criteria for a better path are detailed as shown in fig. 7.
Node A and node B have a hierarchyiNode C and node D have a hierarchyi+1, having passed C =>A and D =>B determines the direct transmission path of node C and node D. It is necessary to find a better indirect transmission path for node C and node D doesBeing a peer node of node C, C => D =>A is an alternative indirect path.
A better indirect path can be determined by the following criteria:
d = > B is a direct transmission path.
Figure 270655DEST_PATH_IMAGE031
Otherwise, it is not beneficial to the remaining energy balance.
d CD<d CAOtherwise more energy must be consumed.
E D>E CFrom the experimental results, it is best to ensureE DTo a certain extent greater thanE C. In the present invention, it is proposed
Figure 26121DEST_PATH_IMAGE032
。
If there is no alternative path that satisfies the above condition, the direct transmission path should be reserved.
If there are multiple nodes D that make the alternative path satisfy the above condition, the node D with the smallest degree should be selected to avoid the hot spot.
If there is still more than one node D having an alternative path that satisfies the above conditions, then it should be chosen such that
Figure 884356DEST_PATH_IMAGE033
Node D with the smallest value to save energy.
This method is still effective in the case where node B and node a coincide (they are the same node as the parent nodes of node C and node D).
When data are collected in the same hierarchy, a node selects a peer node as a relay node, which is a cluster structure. If a cluster structure exists in the topology of the entire network, the network topology becomes a mixed structure of trees and clusters, as shown in fig. 8.
S30: forming a transmission scheme
Based on a mixed structure of a tree and clusters consisting of all nodes and edges of the next hop, a transmission scheme is formed after allocating one slot to each node. The function of the slot allocation is to cause a node, after receiving data from all descendant nodes and peer nodes that choose them as relay nodes, to send all the received data to its next hop node, along with their own generated data, causing the data to flow from the highest level to the lowest level (base station). The purpose of the time slot allocation is to reduce the standby time and to reduce the energy consumption caused by data retransmission after channel collision.
S40: distributed transmission scheme
The transmission scheme should be distributed from the base station to all nodes so that each node knows when and to which node it sends data.
The distribution process is performed by means of multicast. The base station broadcasts the transmission scheme and any node that receives the transmission scheme then multicasts the transmission scheme to its descendant nodes (if it has descendant nodes).
The multicast power only needs to cover the farthest child node. This power generally need not be the maximum transmit power of the node and nodes without descendant nodes also need not multicast, so the energy overhead of the transmission scheme distribution process will be much less than the initialization of the network.
Data collection
Each node transmits its data to its next hop node in the time slot allocated to it according to the transmission scheme. This is a steady state operation of the network, which will last for a certain time until the transmission scheme is updated.
S50: updating a transmission scheme
In both cases, the transmission scheme should be updated in different ways.
The first case is that the network has run a fixed round of data collection determined a priori. In this case, a new transmission scheme is created by the known topology and the remaining energy information of the nodes extracted from the reception data of all the nodes. The advantage of this approach is energy saving, since all the energy consumption created by the transmission scheme is taken by the powered base station, the node only consumes energy when distributing the transmission scheme, which is much lower than the energy consumption for network initialization.
Another situation is that the topology of the network has changed. In this case, data of not all nodes may be received. Therefore, the topology information of the network is incomplete and insufficient to support the re-creation of the transmission scheme. Therefore, only the network can be reinitialized. The process of broadcasting and feedback is repeated, a new transmission scheme is created using the new network information, and then the transmission scheme is distributed to all nodes. The advantages of this approach are simplicity and robustness. This method will work whatever factors cause the topology to change. And has the disadvantage that it consumes more energy.
In order to verify and analyze the validity of the proposed HTC-RDC protocol, the present invention envisages an application scenario as shown in fig. 9. There are two obstacles in the target area, which are abstracted as two line segments. The role of the obstacle in the experiment is to hinder the transmission of radio waves between nodes (or base stations) when a line segment between the nodes (or base stations) intersects the obstacle.
Table 1 parameters used in the experiment
Figure 434286DEST_PATH_IMAGE034
The data size is set to the capacity of the medium resolution color picture.
After the network topology is obtained, two visual methods can be adopted to realize the function of the WSN. Another approach is the Minimum Hop Transmission (MHT) protocol. With the MHT protocol, the path selected by each node contains only one node in each hierarchy and the path meeting the lowest energy consumption (ignoring circuit energy consumption) of the above conditions is selected. The method uses the square of the distance between nodes as the weight of the edge in the topological graph and can be realized by programming through a Dijkstra algorithm. Another approach is the Minimum Transmission Energy (MTE) routing protocol. With the MTE protocol, each node selects the path with the lowest energy consumption (neglecting the energy consumption of the circuit) in the entire single path. This method can also be implemented by Dijkstra algorithm programming. The protocol proposed by the present invention will be compared to both methods.
Results of the experiment
Transmission scheme comparison created by different protocols
For the same experimental environment, the schedules created by the HTC-RDC, MHT, MTE protocols in round 0 and round 100 are shown in fig. 10-15. The result shows that the network can be initialized through a protocol in the advertisement feedback process, and after the topology information is collected, the problems of the distance exceeding the transmission radius of the node, the existence of obstacles, topology change and the like caused by the death of the node are solved by adopting the multi-hop path. Furthermore, HTC-RDC balances the load of the relay nodes better than the other two protocols. In round 100, the network using the three protocols died 0, 1, and 3 nodes, respectively.
Parameter optimization
There are two system parameters alpha in the protocol0And beta0A priori determination is required. The optimal setting of these two parameters is related to the topology of the network, but its value should be greater than 1, since α0And beta0The significance of this is to avoid selecting the next hop node uniquely to achieve hot spot avoidance, while, to ensure balance of the remaining energy, they should not be too large than 1, so that the selection of the next hop node can be limited to nodes with relatively more remaining energy. Experiments were performed to optimize the settings of these two parameters and the results are shown in fig. 16.
The results show that the lifetime of the network is not strictly linear with the settings of these two parameters, and the effect is better when the sum is around 1.5. In the experiments of the present invention, α0And beta0Are all set to 1.5.
Lifecycle of network
For application scenarios with the same node deployment, FIGS. 17-19 show the lifetime of WSNs using the HTC-RDC, MHT, MTE protocol. The blue line represents the number of surviving nodes and the red line represents the number of nodes that the base station can receive data. Some points in the red line are below the envelope of the line because in these rounds some nodes are alive but cannot be received by the base station because their parent node dies. In the next round, the point returns to the envelope of the line due to the transmission scheme update.
It can be seen that the FNL of HTC-RDC is significantly greater than the FNL of the other two methods. Furthermore, the red line drops rapidly between FNL and HNL, which demonstrates that the remaining energy of those nodes that have to die first is balanced.
Monte Carlo experiments
To verify the performance of the proposed protocol in different node distributions, 500 monte carlo experiments were performed. The experiment used the same target area with the same obstacles and simulated 500 different node distributions. The results are shown in fig. 20 to 22, and the statistical information is shown in table 2. The results show a significant improvement in FNL for networks using HTC-RDC. At the same time, the HNL of networks with HTC-RDC is not significantly smaller than that of the other two protocols that have energy efficiency as an important target. This indicates that HTC-RDC has better energy efficiency despite the FNL pursuit at the expense of reduced energy efficiency.
Table 2 statistical data of the monte carlo experimental results.
Figure 879436DEST_PATH_IMAGE035
The larger each of FNL and HNL the better. Experimental results show that the FNL of the network using HTC-RDC protocol is obviously higher as the key performance index of the network. Meanwhile, as a reference index, the HNL of the network reflects the energy efficiency of the protocol, but the HNL using HTC-RDC is not obviously reduced. This indicates that the HTC-RDC protocol effectively enhances FNL while taking energy efficiency into account.
The invention provides a new wireless sensor network application scene according to the requirements of practical application. In this application scenario, 1) each sensor node is crucial; 2) The data to be collected from the sensor nodes is raw data, not aggregated data; 3) Some sensor nodes cannot communicate directly with a base station. Aiming at the application scene, a mathematical model based on an optimization theory is established. Because the model cannot be solved accurately when the network scale is large, a new centrally generated protocol is proposed, which is oriented to collect raw data and has a mixed structure of a tree structure and a cluster structure, and is called HTC-RDC. Experimental results show that WSNs with the proposed protocol can collect raw data from all nodes and can significantly extend WSN lifetime and achieve satisfactory performance compared to MHT and MTE methods.
The invention has the following beneficial effects:
1) a new application scene is defined, the application scene is oriented to original data acquisition, redundant sensor nodes are not needed, the service life of the WSN is obviously prolonged, and the WSN is more suitable for practical application.
2) The effectiveness of the invention is verified by experiments.
The above embodiment is an embodiment of the present invention, but the embodiment of the present invention is not limited by the above embodiment, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be regarded as equivalent replacements within the protection scope of the present invention.

Claims (5)

1. A routing protocol of a multi-hop wireless sensor network for raw data acquisition is characterized by comprising the following steps:
the base station broadcasts to all nodes so that all nodes find paths to the base station to complete network initialization, wherein after receiving the broadcast of the base station, the nodes can send feedback to the base station, the feedback comprises all necessary information used for establishing a transmission scheme by the nodes, and the necessary information at least comprises residual energy and topology information of the nodes;
the base station establishes a transmission scheme, sets a next hop node for each node, and establishes an optimized tree structure and a cluster structure for the network, wherein the tree structure is established according to the following principle: if a certain node has only one father node, the node sets the only father node as the next hop node of the node; if a plurality of father nodes exist, the next hop node is one of equivalent nodes with the lowest degree of income, wherein the equivalent nodes are defined as nodes meeting an energy equivalent criterion and an energy consumption equivalent criterion; representing a parent node with the maximum residual energy as a candidate node, and representing a parent node which is possible to be an energy equivalent node as an alternative node; when data are collected in the same hierarchy, the nodes select one peer node as a relay node, namely a cluster structure is formed; the energy equivalence criterion is as follows:
Figure FDA0003557652660000011
wherein EcandidateRepresenting the residual energy of the candidate node, EalternativeRepresenting the residual energy, a, of the alternative node0Is a parameter defined in advance according to an experimental result;
the energy consumption equivalence criterion is as follows:
Figure FDA0003557652660000012
wherein, calternative-coorelatedRepresenting energy consumption associated with the candidate node, ccandidate-coorelatedRepresenting the energy consumption, beta, associated with the alternative node0Is a parameter preset according to the experimental result
The base station distributes the transmission scheme to all nodes so that each node knows when and to which node it sends data; the distribution is executed in a multicast mode, the base station broadcasts the transmission scheme, and then any node receiving the transmission scheme multicasts the transmission scheme to the descendant nodes of the node;
each node transmits data to the node's next hop node in its assigned time slot according to a transmission scheme;
and the base station updates the transmission scheme according to the network operation condition.
2. The raw data acquisition-oriented multi-hop wireless sensor network routing protocol of claim 1, wherein each node has hierarchical attributes.
3. The routing protocol for the raw data acquisition-oriented multi-hop wireless sensor network of claim 1, wherein the broadcasting process of the base station is as follows:
step 1: the base station generates an integer as the current round number, and distributes the broadcast message with the maximum power of the radio module same as the node, wherein the content of the broadcast message comprises the round number, the ID of the broadcast node, the hierarchy and the residual energy information of the broadcaster;
step 2: a node receiving a broadcast message should record the broadcast message and calculate and record the distance between the node and a source node through RSSI, and then perform the following operations:
if the broadcast message is the first broadcast message received in the latest round, clearing the hierarchy information, and setting the hierarchy of the broadcast message as the hierarchy value contained in the broadcast message plus 1; meanwhile, storing the source node as a father node according to the information of the broadcast message; the node generates a new broadcast message with the same structure, but will modify it using its own information, after a certain time interval, the node issues the new broadcast message according to a carrier sense multiple access protocol that avoids collisions;
if the node has a latest round of broadcast messages in its memory, the node shall check and perform the following operations:
recording the source node as a parent node if the hierarchy in the broadcast message is less than its hierarchy;
recording the source node as a peer node if the hierarchy in the broadcast message is equal to its hierarchy;
if the hierarchy in the broadcast message is greater than its hierarchy, the source node is recorded as a descendant node.
4. The original data acquisition-oriented multi-hop wireless sensor network routing protocol according to claim 1, wherein if the remaining energy of the candidate node is lower than that of the node that should perform next-hop node selection, β is approximately calculated as:
Figure FDA0003557652660000031
wherein d isnode-alternativeIndicating the distance between the node and the stand-by node, dalternative-next-hopIndicating the distance between the standby node and the next-hop node of the standby node, dnode-candidateRepresents the distance between the node and the candidate node, and dcandidate-next-hopRepresenting the distance between the candidate node and the next hop node of the candidate node;
if the remaining energy of the candidate node is higher than that of the node which should perform next-hop node selection, the energy consumption of the candidate node tends to be unbalanced, the energy consumption of the candidate node should be protected, and β is specifically expressed as:
Figure FDA0003557652660000032
the candidate nodes that satisfy the above two equations are equivalent nodes.
5. The raw data acquisition-oriented multi-hop wireless sensor network routing protocol according to claim 1, wherein for nodes a, B, C of the same level and node E of a higher level of the level, if node a is a candidate node, node B and node C are candidate equivalent nodes, and the remaining energy of nodes a, B, C, E is EA,EB,EC，EEAt EA<EEIn the case of (2), it should be calculated according to the following formula:
Figure FDA0003557652660000041
Figure FDA0003557652660000042
wherein d isEARepresents the distance between node A and node E, dEBRepresenting the distance of node B from node E, dBORepresenting the distance of the node B from the base station, dAORepresents the distance of node A from the base station, assuming βBA>βCAIf so, the node C is the next hop node of the node E;
at EA>EEIn the case of (2), it should be calculated as follows:
Figure FDA0003557652660000043
Figure FDA0003557652660000044
wherein d isECRepresents the distance between node C and node E, assuming βBA<βCAThen node B is the next hop node for node E.
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