CN110868727A - Data transmission delay optimization method in wireless sensor network - Google Patents
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Abstract
The invention relates to a data transmission delay optimization method in a wireless sensor network, which solves the problems of serious data packet loss and higher end-to-end delay in the wireless sensor network. Firstly, classifying channel detection conditions according to a data packet transmission result, and introducing effective detection occupation ratio and transmission efficiency as evaluation indexes of nodes; then, estimating the queuing delay of the data packet according to the difference value of the actual delay and the theoretical delay; and finally, setting maximum and minimum queuing delay thresholds, and judging whether to change the transmission path according to the interval to which the queuing delay belongs. Compared with other methods, the method of the invention respectively reduces the average end-to-end delay of the node by 78.87 percent and 51.81 percent, reduces the packet loss rate of the node by 40.71 percent and 68.43 percent, and reduces the death rate of the node by 25.42 percent and 44.62 percent. The result shows that the DTDO can effectively reduce the end-to-end delay, reduce the packet loss rate and prolong the life cycle of the network.
Description
Technical Field
The invention relates to a data transmission delay optimization method (DTDO) in a wireless sensor network, belonging to the technical field of wireless sensor networks.
Background
Wireless Sensor Networks (WSNs) are widely used in various fields because of their low cost. It consists of a limited set of mobile or static nodes that sense various phenomena and forward the sensed information to the destination. The sensor network has strong application relevance, and routing protocols in different applications can be very different, so that a common routing protocol is not provided. For some low-delay events, the problem of high end-to-end delay of a data packet caused by large network flow needs to be solved, and meanwhile, the quality of data transmission between nodes is ensured.
A link quality and delay based composite Load Balancing routing protocol (ComLoB) measures the path quality from a node to a base station using packet queuing delay and expected transmission count, and distributes traffic Load fairly by randomly selecting a next hop node to avoid congestion; but the updating of the routing table and the monitoring of the queue will generate more data packets to be sent in the network and occupy the data packet queue, so that the end-to-end delay of the protocol is higher.
The Congestion Avoidance multi-path routing protocol (CA-RPL) effectively combines delay, link reliability and load balancing factors, and reduces average delay and packet loss rate; however, CA-RPL is evaluated at a lower data traffic, and as the data traffic decreases, the packet loss rate tends to increase compared to RPL (Routing Protocol for Low-power and traffic network).
A Multipath OLSR routing protocol (A Multipath OLSR routing protocol based on Expected Transmission Time, SETT _ MPOLSR), the routing between nodes is based on Expected Transmission times and bandwidth value; but when the packet sending rate of the node is increased, the packet delivery rate of the network is reduced more quickly. A Routing protocol (RDR) with high robustness and low Delay searches a path with optimal Delay expression and a potential assisting node through path detection, and dynamically selects the path by using multicast in a data sending stage; however, the use of multicast may increase the number of packets in the network causing packet collisions and congestion.
Disclosure of Invention
In order to solve the problems of high Data Transmission Delay and serious packet loss, the invention provides a Data Transmission Delay Optimization method (DTDO). The DTDO gives a new routing function, and factors such as effective detection occupation ratio and transmission efficiency of the node are comprehensively considered for routing, so that the routing accuracy is improved; meanwhile, a delay optimization method is provided, and queuing delay of the data packets is effectively reduced by changing the transmission path of the data packets.
In order to achieve the purpose, the invention adopts the technical scheme that: the method for optimizing data transmission delay in the wireless sensor network is characterized by comprising the following steps:
step 1: network initialization: the Sink node broadcasts an initialization message, sends data detection packets among the nodes, calculates the value of a routing function and updates a routing table;
step 2: data transmission: the data sending node sends data to the selected next hop node;
and step 3: calculating queuing delay: the data receiving node calculates queuing delay;
and 4, step 4: and (3) path change judgment: the node judges whether the data can be continuously received or not according to the link quality information and the queuing delay information of the node, and if the condition of continuously receiving the data is met, the flag is 0; otherwise, the flag is 1, and the flag is returned to the data sending node;
and 5: path change: the data sending node judges whether to change the path according to the value of the flag, if so, the step 6 is executed; otherwise, executing step 2;
step 6: and (3) node selection: when the path is changed, the node selects a proper node in the routing table as a next hop node, and step 2 is executed.
The routing function calculation method in the step 1 is as follows:
1.1) dividing the detection condition of the node into effective detection and invalid detection according to whether the data packet is successfully received, and giving related definitions as follows:
and (3) effective detection: after the node performs c times of detection, if the node successfully sends a data packet and receives an acknowledgement packet, the node is called to perform c times of effective detection;
invalid detection: after the node performs c times of detection, the node gives up transmission or does not receive a confirmation packet, and the node is called to perform c times of invalid detection;
when the node detects for c times and the channel is idle, the node A sends a data packet, and the node A receives ACK to indicate that the data is successfully received;
when the node sends a data packet after c times of detection and does not receive ACK, the data packet is lost in the transmission process;
when the node detects for 4 times, the channel is still busy, therefore, the transmission is abandoned;
1.2) node effective probing ratio measurement:
for any node NxWith RxkRepresenting a node NkForwarding node NxEffective probing ratio, R, of data packets ofxkThe larger the data transmission quality, the better, given by equation (3):
wherein: s represents the number of successfully transmitted data packets; u represents the number of failed data packet transmissions; c. CiRepresenting the number of times of channel detection in the ith data transmission;
1.3) node transmission efficiency metric:
with ExkRepresenting a node NkForwarding node NxA transmission efficiency measure of the data packets of, ExkThe higher the communication capacity between the nodes is; is given by equation (4):
wherein, ti eThe time of the node successfully sending the data packet is represented, namely the time difference between the node starting to detect the channel and receiving the ACK message; t is ti uIndicating the time of invalid probing performed by the node before the failure of sending or confirming;
1.4) routing function of the node:
the value of the routing function is a composite calculation of the effective probe occupancy metric and the transmission efficiency metric of the node, given by equations (5) and (6):
wherein: MaxRxAnd minRxRespectively represent nodes NxThe maximum value and the minimum value of the effective detection ratio metric of the candidate routing node; r isxkRepresenting a node NkA normalized value of the effective probe occupancy metric of (a);
wherein: MaxExAnd minExRespectively represent nodes NxThe maximum value and the minimum value of the transmission efficiency metric of the candidate routing node of (1); e.g. of the typexkRepresenting a node NkA normalized value of the transmission efficiency metric of (a);
for node NxThe routing function is given by equation (7):
selectx(Nk)＝αrxk+βexk(7)
wherein: selectx(Nk) Is node NkAt node Nxα is the weight coefficient of each metric index, and α + β is 1;
the node selects the candidate routing node with the largest select value as the next hop, and sets α -0.6 and β -0.4.
And 3, calculating queuing delay:
estimating queuing delay T of data packet according to difference value of actual delay and theoretical delay of data packetqueGiven by equation (8):
t＝tsend+2ttrans(10)
wherein: t isjIndicating the actual delay of the jth data packet;
the time for the node to receive the acknowledgement message of the jth data packet is represented;
indicating the time when the jth data packet starts to be transmitted; t represents the theoretical delay of the data packet; t is tsendRepresenting the transmission delay of a theoretical node; t is ttransRepresenting the propagation delay of the nodes theoretically, and m represents the number of the data packets in the buffer area; z represents the number of packets sent over a period of time.
The judging process of the path change in the step 4 is as follows:
the node judges whether to continue receiving data according to the interval to which the queuing delay belongs, and the following three conditions exist specifically:
4.1) when TqueWhen Min is less than or equal to Min, the node can continue to receive data, and the data sending node does not need to switch paths;
4.2) when TqueWhen the data transmission node is not less than Max, the node can not continuously receive the data, and the data transmission node needs to switch the path;
4.3) when Min<Tque<In Max, the node needs to make further judgment;
wherein Min is a minimum queuing delay threshold value, and Max is a maximum queuing delay threshold value;
for case 4.3), the present invention adopts the following two kinds of information as the node NxThe basis for judging whether to continue receiving data is as follows:
4.3.1) link quality information: if node NxAnd routing node NkLink quality between is lower thanNxThe average level of the candidate routing nodes represents the node NxThe current transmission quality is poor, the data is not suitable for data forwarding, and routing nodes need to be replaced;
representing a node NkForwarding node NxLink quality of data and NxThe relation of the candidate route node link quality mean value is given by equation (11):
wherein: n represents a node NxThe number of candidate routing nodes; selectxiRepresenting a node NxThe value of the routing function for the ith candidate routing node;
4.3.2) queuing delay information: the closer the queuing delay of the data packet of the node is to the Max value, the larger the queuing delay of the current node is, the larger the influence on the time of the data packet arriving at the base station is;
representing a node NxThe relationship between packet queuing delay and queuing delay threshold is given by equation (12):
wherein, Tx queRepresenting a node NxThe queuing delay of (1);
when routing node NxWhen the link quality is poor and the queuing delay is high, the node is not suitable for continuously receiving data; dec is a reference to dxk selectAnd dx thIs given by equation (13):
when the Dec value is 1, the node N is indicatedxIs not suitable forContinuing to receive data, wherein when the Dec value is 0, the node is indicated to be suitable for continuing to receive data; and setting a flag bit, setting the flag to be 1 if the node can not continuously receive data, and setting the flag to be 0 if the node cannot continuously receive data.
The beneficial effects created by the invention are as follows:
by adopting the scheme, the invention provides the delay optimization method aiming at the problems of serious data packet loss and higher end-to-end delay in the wireless sensor network. Firstly, classifying channel detection conditions according to a data packet transmission result, and introducing effective detection ratio and transmission efficiency as evaluation indexes of nodes; then, estimating the queuing delay of the data packet according to the difference value of the actual delay and the theoretical delay; and finally, setting maximum and minimum queuing delay thresholds, and judging whether to change the transmission path according to the interval to which the queuing delay belongs. Simulation results show that the method can effectively reduce end-to-end delay, reduce packet loss rate and prolong the life cycle of the network.
Drawings
Fig. 1 is a schematic transmission diagram.
Fig. 2 is a schematic diagram of packet transmission.
Fig. 3 shows the weight coefficient values and the average end-to-end delay.
Fig. 4 shows the threshold value and the average end-to-end delay.
Fig. 5 is a graph comparing average end-to-end delay of packets.
FIG. 6 is a graph comparing node mortality.
Fig. 7 is a flowchart of an implementation of the delay optimization method.
FIG. 8 is a flow chart of the method of the present invention.
Detailed Description
The invention provides a DTDO (delay tolerant data optimized) method for data transmission delay in a wireless sensor network, which comprises the following steps:
step 1: network initialization: the Sink node broadcasts initialization information, sends data detection packets among the nodes, calculates the value of a routing function and updates a routing table.
Step 2: data transmission: and the data sending node sends the data to the selected next hop node.
And step 3: calculating queuing delay: the data receiving node calculates the queuing delay.
And 4, step 4: and (3) path change judgment: the node judges whether the data can be continuously received or not according to the link quality information and the queuing delay information of the node, and if the condition of continuously receiving the data is met, the flag is 0; otherwise, the flag is 1, and the flag is returned to the data sending node.
And 5: path change: and the data sending node judges whether to change the path according to the value of the flag, and if the path is changed, the step 6 is executed. Otherwise, step 2 is executed.
Step 6: and (3) node selection: when the path is changed, the node selects a proper node in the routing table as a next hop node, and step 2 is executed.
Example 1:
the system model, routing function, related method, specific application flow and verification process based on the method are detailed as follows:
network model
The invention is suitable for network application with higher requirements on data real-time performance and reliability. Sensor nodes in the network model are randomly distributed in a monitoring area, and Sink nodes are fixed in position and sufficient in energy. The sensor node properties are as follows:
the nodes have unique ID numbers and are evenly distributed in the monitoring area.
All nodes are fixed in position and limited in energy.
All nodes have the same transmission capabilities.
The nodes may calculate the distance between each other based on the strength of the received signal.
Energy consumption model
The invention adopts the same wireless communication energy consumption model as DEBUC. In the model, the energy consumption of the wireless communication module for transmitting data is mainly in the transmitting circuit and the power amplifying circuit, and the energy consumption of the received data is mainly in the receiving circuit. Under the condition of ensuring a reasonable signal-to-noise ratio, the energy consumption of the nodes for sending data is as follows:
wherein: k represents the number of transmitted binary bits; d represents a transmission distance; eelec(nJ/bit) represents the radio frequency coefficient of energy consumption; efs(pJ/bit/m2) And Emp(pJ/bit/m4) And the energy consumption coefficient of the power amplification circuit under different channel propagation models is represented.
The energy consumption of the nodes for receiving the data is as follows:
ERx(k)＝kEelec(2)
routing function
In the data transmission process, the quality of the communication link between the nodes directly influences whether the data packet can be successfully transmitted. When data is transmitted between nodes, a plurality of transmission attempts are required before the nodes successfully send data packets or lose packets, so as to detect whether a channel is idle. According to the Carrier Sense multiple access/Collision Avoidance (CSMA/CA) algorithm of IEEE 802.15.4, when a node has data transmission, the node is allowed to perform channel sounding up to 4 times. According to whether the data packet is successfully received, the detection condition of the node is divided into effective detection and invalid detection, and the following relevant definitions are given:
define 1 valid probing. After the node performs c (c ═ 4) times of probing, it is said that the node performs c times of effective probing if it successfully transmits a data packet and receives an acknowledgement packet.
Invalid probes are defined 2. After c (c ═ 4) times of probing, the node gives up transmission or does not receive an acknowledgement packet, and the node is said to have performed c times of invalid probing.
Fig. 1 shows a transmission diagram of a node. Fig. (a) is a schematic diagram of a node successfully sending a data packet. And when the node A detects for c times and the channel is idle, the node A sends a data packet, and the node A receives the ACK to indicate that the data is successfully received. Fig. b is a diagram illustrating a node failure. After c times of detection, the node A sends a data packet, but does not receive ACK, which indicates that the data packet is lost in the transmission process. Fig. c is a diagram illustrating a packet transmission failure. Node a performs 4 probes and the channel is still busy, therefore, abandoning this transmission.
(1) Node-efficient probe occupancy metrics
Whether the node can successfully send the data packet after the channel detection directly reflects the quality of the link between the nodes. In a certain time, the larger the proportion of the effective detection times of the nodes to the total detection times is, the better the quality of data transmission between the nodes is. For any node NxWith RxkRepresenting a node NkForwarding node NxThe effective probing ratio of the data packet of (a) is given by equation (3):
wherein: s represents the number of successfully transmitted data packets; u represents the number of failed data packet transmissions; c. CiIndicating the number of times the channel was probed at the ith data transmission.
(2) Node transmission efficiency metric
The invention uses the transmission efficiency of the nodes as another index for evaluating the communication capacity between the nodes. The higher the transmission efficiency of the nodes, the better the communication capability between the nodes. With ExkRepresenting a node NkForwarding node NxThe transmission efficiency metric of the data packet of (4) is given by equation (4):
wherein, ti eThe time of the node successfully sending the data packet is represented, namely the time difference between the node starting to detect the channel and receiving the ACK message; t is ti uIndicating the time of invalid probing by the node before a transmission failure or an acknowledgement failure.
(3) Routing function of a node
The routing function is the basis for routing by the data sending node, and comprises the effective detection ratio metric and the transmission efficiency metric of the node, which are the composite calculation of the two. In order to eliminate the influence of the dimension, it is normalized, and the result after processing is given by equation (5) and equation (6):
wherein: MaxRxAnd minRxRespectively represent nodes NxThe maximum value and the minimum value of the effective detection ratio metric of the candidate routing node; r isxkRepresenting a node NkIs measured by the effective probe occupancy metric.
Wherein: MaxExAnd minExRespectively represent nodes NxThe maximum value and the minimum value of the transmission efficiency metric of the candidate routing node of (1); e.g. of the typexkRepresenting a node NkIs measured by the transmission efficiency metric.
For node NxThe routing function is given by equation (7):
selectx(Nk)＝αrxk+βexk(7)
wherein: selectx(Nk) Is node NkAt node Nxα is the weight coefficient of each metric index, α + β is 1, the larger the data value of all the indexes is, the better the node selects the candidate route node with the maximum select value as the next hop, α is set to 0.6, β is set to 0.4, and the experimental analysis of the weight coefficient value will be given in the following text.
Path establishment and data transmission
And in the network initialization stage, the Sink node broadcasts an initialization message. And sending a data detection packet between the nodes, calculating the value of a routing function, selecting the adjacent node close to the base station direction as a candidate routing node by the node, and storing the candidate routing node in a routing table. The node stores a plurality of candidate routing nodes, so that data transmission is not easily affected by node failure.
The candidate routing nodes are divided into small parts according to the select valuePriorities are assigned (1,2,3, …, n). If node N is in use for a period of timexIf the candidate routing node participates in the data packet transmission, calculating the value of the routing function according to the transmitted data packet, otherwise, periodically sending a data detection packet between adjacent nodes to update the routing table.
And the nodes within the range of one hop of the Sink node directly send data to the Sink, and the nodes outside the range of one hop of the Sink node send data to the Sink in a multi-hop mode. And when transmitting data each time, the data transmitting node selects the node with the highest priority from the candidate routing nodes as a next hop node. When the remaining energy of the node is not enough for data transmission, the node is deleted from the routing table.
Time delay optimization method
When the monitoring area generates an emergency and the traffic is large, the data needs to be transmitted to the base station with as low delay as possible. Due to the fact that data flow in the network is large, congestion and collision phenomena of the network can cause data packet loss or delay forwarding, and therefore the data packet generates large queuing delay at a node. In this section, a delay optimization method is proposed, which can effectively reduce the queuing delay of the data packet, so that the data packet is transmitted to the base station with a lower delay as much as possible. The method solves the problem of increased queuing delay by changing the transmission path of the data packet. And giving a maximum queuing delay threshold and a minimum queuing delay threshold for dividing queuing delay intervals, and determining whether to inform a data sending node to change a transmission path or not by the data receiving node according to the interval to which the queuing delay of the data packet belongs. The delay optimization method is described in five parts as follows: the method comprises the steps of threshold value analysis, queuing delay calculation, path change judgment, path selection and realization thereof.
Analysis of threshold values
The optimal settings of the minimum queuing delay threshold Min and the maximum queuing delay threshold Max trade off between efficient utilization of sensor nodes and lower average end-to-end delay. While the optimal setting of the threshold value also depends on the size of the node buffer. When the threshold value is small, and the network flow is large, the data sending node can frequently change the path, and the utilization rate of the sensor node is reduced. Meanwhile, the node has lower tolerance to burst conditions existing in the data packet transmission process, such as data packet delay forwarding caused by data packet collision, packet loss and the like. When the value of the threshold is large, the duration of an invalid link can be prolonged and the end-to-end delay of a data packet can be increased for the condition that the link between nodes is poor.
Queuing delay calculation
The queuing delay in the DTDO method represents the waiting time required for the data packet about to enter the queue from entering the queue to being successfully transmitted, i.e. the time required for the data packet in the current buffer to be completely transmitted. The invention estimates the queuing delay of the data packet by the difference value of the actual delay and the theoretical delay of the data packet, and the queuing delay TqueGiven by equation (8):
t＝tsend+2ttrans(10)
wherein: t isjIndicating the actual delay of the jth data packet;
the time for the node to receive the acknowledgement message of the jth data packet is represented;
indicating the time when the jth data packet starts to be transmitted; t represents the theoretical delay of the data packet; t is tsendRepresenting the transmission delay of a theoretical node; t is ttransRepresenting the propagation delay of the nodes theoretically, and m represents the number of the data packets in the buffer area; z represents the number of packets sent over a period of time.
Fig. 2 is a schematic diagram of data packet transmission between nodes. The queuing time required for the packet p to enter the queue to start transmission is calculated by node a.
Determination of a path change
And the node judges whether the data can be continuously received or not according to the interval to which the queuing delay belongs. The following three situations exist according to the judgment of the interval to which the queuing delay belongs:
1) when T isqueWhen Min is less than or equal to Min, the node can continue to receive data, and the data sending node does not need to switch paths.
2) When T isqueAnd when the data transmission node is not less than Max, the node can not continuously receive the data, and the data transmission node needs to switch the path.
3) When Min<Tque<And in Max, the node needs to make further judgment.
For case 3), the present invention adopts the following two kinds of information as the node NxThe basis for judging whether to continue receiving data is as follows:
1) link quality information. The link quality of a node is evaluated with the value of the routing function of the node. If node NxAnd routing node NkLink quality between is lower than NxThe average level of the candidate routing nodes represents the node NxThe current transmission quality is poor, the data forwarding is not suitable, and the routing node may need to be replaced.
Representing a node NkForwarding node NxLink quality of data and NxThe relation of the candidate route node link quality mean value is given by equation (11):
wherein: n represents a node NxThe number of candidate routing nodes; selectxiRepresenting a node NxThe value of the routing function for the ith candidate routing node.
2) And queuing delay information. Node pointThe closer the queuing delay of the data packet is to the Max value, the larger the queuing delay at the current node is, and the time of the data packet arriving at the base station is seriously influenced.
Representing a node NxThe relationship between the packet queuing delay and the queuing delay threshold is given by equation (12):
wherein, Tx queRepresenting a node NxThe queuing delay.
In order to avoid frequent replacement of the routing node in a short time, the routing node selected by the data sending node should meet the requirement of better link quality or lower queuing delay. When routing node NxWhen the link quality is poor and the queuing delay is high, the link of the node is unstable, and the data transmission between the nodes is easily influenced, so that the node is not suitable for continuously receiving data. Dec is a term ofxk selectAnd dx thIs given by equation (13):
when the Dec value is 1, the node N is indicatedxAnd is not suitable for continuously receiving data, and when the Dec value is 0, it indicates that the node is suitable for continuously receiving data. And setting a flag bit, and setting the flag to be 1 if the node can not continuously receive data. Otherwise, flag is set to 0.
Path selection
After the node continuously receives data for a period of time, the condition of receiving the data is not met any more, and then a message that flag is 1 is returned to the data sending node through an ACK message to inform the data sending node of changing the path. When the node changes the path each time, the node with higher priority in the routing table is selected in sequence to send data, and whether the data can be transmitted or not is judged. When the node receives the data packet and the flag is 0, only returning an ACK message; otherwise, the information of flag 1 is carried by the ACK message. When the data sending node receives the message with the flag being 1 or does not receive the ACK message after the maximum retransmission waiting time, the node is reselected; otherwise, the current node is selected as the next hop node to continue transmitting data. When the flag values of the nodes in the routing table are all 1, in order to prevent more data packets from being transmitted in the network, the network load is increased, meanwhile, the sent data packets can be received, the data sending node reduces the sending rate of the data, the node with higher priority is selected to send the data, and the routing node is reselected only when the ACK packet is not received after the maximum retransmission waiting time.
The framework and the application process of the model of the method are verified through simulation experiments, and the specific flow is as follows:
in order to evaluate the performance of the delay optimization method provided by the invention, the performance of DTDO is verified by using an OMNeT + + simulation environment, and the whole simulation experiment comprises three parts, namely 1) the influence of α values in a verification formula (7) on the average end-to-end delay of a data packet, 2) the values of a queuing delay threshold Min and a Max are analyzed, and 3) the DTDO is compared with ComLoB and CA-RPL in the aspects of network timeliness, network reliability, network energy efficiency and the like.
1. Experimental parameter settings
Randomly distributing 100 nodes at 100 × 100m2The node initial energy is 0.5J, the packet size is 500Byte, and the node initial communication radius R0 is 20 m.
2. Weight coefficient selection
In order to verify the influence of the weight coefficients of the two indexes, namely the effective probing duty ratio metric and the transmission efficiency metric in the equation (7), on the end-to-end delay, the weight coefficient values under 9 cases (Q1, Q2, … and Q9) are taken to perform simulation under the same network environment, as shown in table 1. And judging the optimal weight coefficient value by comparing the average end-to-end delay conditions under different values.
TABLE 1 weight coefficient value-taking Table
Fig. 3 is a comparison between the weight coefficient value and the average end-to-end delay relationship, and it can be seen from fig. 3 that when α is 0.6 and β is 0.4, the DTDO can obtain better performance.
3. Value of threshold
In order to verify the influence of Min and Max values on end-to-end delay of a data packet, different threshold values are adopted for simulation under the same network environment. In the experiment, firstly, a data packet is sent between one-hop adjacent nodes, the single-hop transmission delay is calculated, and the average value of the single-hop transmission delay is 0.03s and the minimum value is 0.02s after multiple experiments. The value range of the threshold is estimated according to the size of the buffer, the interval is (T, T. buf), wherein T is the transmission delay of a data packet, and the value is 0.03; buf is the buffer size and takes the value of 15. Therefore, in the experiment in this section, Min values are selected in ascending order of 0.02 from 0.03, Max values are selected in descending order of 0.02 from 0.45, and only 9 threshold values (Q1, Q2, …, Q9) are shown in this section, as shown in table 2. Figure 4 is a comparison of threshold values with average end-to-end delay. As can be seen from fig. 4, when the threshold value is too small or too large, the end-to-end delay of the data packet is increased. When Min is 0.15 and Max is 0.33, the network performance is better, so the threshold value of the relevant experiment in the invention is: min is 0.15, Max is 0.33.
TABLE 2 threshold value taking Table
4. Performance analysis of DTDO
(1) Network timeliness
The transmission delay of the data packets between the single-hop nodes is analyzed, and the network flow is distributed on different links by replacing the routing nodes, so that the queuing delay of the data packet queue at each node is effectively reduced. The transmission delay of the data packet is mainly determined by queuing delay at the node, and although a certain processing time is needed for changing the routing node, the transmission delay is negligible compared with the queuing delay.
The invention adopts the average end-to-end delay of the data packet to evaluate the timeliness of the network. The end-to-end delay of a data packet is one of the important evaluation parameters of real-time data, and is expressed as the time required for the data packet to be sent from a data generation node to a base station. Fig. 5 shows the variation of the average end-to-end delay of packets at different packet transmission rates. As can be seen from FIG. 5, as the rate of sending packets by the node increases, the end-to-end delay of the packets of the ComLoB and CA-RPL protocols tends to increase rapidly, while the increase of the DTDO tends to be slower. The average end-to-end delay of DTDO is reduced by 78.87% and 51.81% compared to ComLoB and CA-RPL protocols, respectively.
(2) Network reliability
The collision between the data packets can cause the loss of the data packets, and when the network traffic increases, the packet loss rate of the nodes increases. The quality of the communication between the nodes can be effectively ensured by measuring the quality of the link between the nodes; meanwhile, the reliability of the link can be improved by using the multipath, the service time of an invalid link is shortened, and the probability of losing data packets due to invalid links is reduced.
The invention adopts the packet loss rate of the node to evaluate the reliability of the network. The packet loss rate of a node is expressed as the ratio of the number of lost data packets to the total number of transmitted data packets in the data transmission process. Fig. 6 shows the variation of the packet loss rate of a node at different packet transmission rates. As can be seen from fig. 6, compared with the ComLoB and CA-RPL protocols, the packet loss rate of the DTDO is reduced by 40.71% and 68.43%, respectively, so that the DTDO can effectively reduce the packet loss rate of the node.
(3) Network energy efficiency
Compared with the ComLoB protocol which continuously monitors the queue flow of the nodes and sends warning messages when the queue flow reaches the critical value, the DTDO sends the flag message only when data is transmitted between the nodes, thereby effectively reducing the transmission quantity of control packets in the network and reducing the energy expenditure.
The invention adopts the death rate of the nodes to evaluate the energy efficiency of the network. Fig. 7 is a graph of the mortality rate of a node as the network runtime increases. As is apparent from FIG. 7, the ComLoB and CA-RPL protocols have higher node mortality than DTDO. The mortality rate of the DTDO node is reduced by 25.42% and 44.62% compared to the ComLoB and CA-RPL protocols, respectively.
Claims (4)
1. The data transmission delay optimization method in the wireless sensor network is characterized by comprising the following steps:
step 1: network initialization: the Sink node broadcasts an initialization message, sends a data detection packet between nodes, calculates the value of a routing function and updates a routing table;
step 2: data transmission: the data sending node sends data to the selected next hop node;
and step 3: calculating queuing delay: the data receiving node calculates queuing delay;
and 4, step 4: and (3) path change judgment: the node judges whether the data can be continuously received or not according to the link quality information and the queuing delay information of the node, and if the condition of continuously receiving the data is met, the flag is 0; otherwise, the flag is 1, and the flag is returned to the data sending node;
and 5: path change: the data sending node judges whether to change the path according to the value of the flag, if so, the step 6 is executed; otherwise, executing step 2;
step 6: and (3) node selection: and when the path is changed, the node selects a proper node in the routing table as a next hop node, and the step 2 is executed.
2. The method for optimizing data transmission delay in a wireless sensor network according to claim 1, wherein the routing function calculating method in step 1 is as follows:
1.1) dividing the detection condition of the node into effective detection and invalid detection according to whether the data packet is successfully received, and giving related definitions as follows:
and (3) effective detection: after the node performs c times of detection, if the node successfully sends a data packet and receives an acknowledgement packet, the node is called to perform c times of effective detection;
invalid detection: after the node performs c times of detection, the node gives up transmission or does not receive a confirmation packet, and the node is called to perform c times of invalid detection;
when the node detects for c times and the channel is idle, the node A sends a data packet, and the node A receives ACK to indicate that the data is successfully received;
when the node sends a data packet after c times of detection and does not receive ACK, the data packet is lost in the transmission process;
when the node detects for 4 times, the channel is still busy, therefore, the transmission is abandoned;
1.2) node effective probing ratio measurement:
for any node NxWith RxkRepresenting a node NkForwarding node NxEffective probing ratio, R, of data packets ofxkThe larger the data transmission quality, the better, given by equation (3):
wherein: s represents the number of successfully transmitted data packets; u represents the number of failed data packet transmissions; c. CiRepresenting the number of times of channel detection in the ith data transmission;
1.3) node transmission efficiency metric:
with ExkRepresenting a node NkForwarding node NxA transmission efficiency measure of the data packets of, ExkThe higher the communication capacity between the nodes is, the better the communication capacity between the nodes is; is given by equation (4):
wherein, ti eThe time of the node successfully sending the data packet is represented, namely the time difference between the node starting to detect the channel and receiving the ACK message; t is ti uIndicating the time of invalid probing performed by the node before the failure of sending or confirming;
1.4) routing function of the node:
the value of the routing function is a composite calculation of the effective probe occupancy metric and the transmission efficiency metric of the node, given by equations (5) and (6):
wherein: MaxRxAnd minRxRespectively represent nodes NxThe maximum value and the minimum value of the effective detection ratio metric of the candidate routing node; r isxkRepresenting a node NkA normalized value of the effective probe occupancy metric of (a);
wherein: MaxExAnd minExRespectively represent nodes NxThe maximum value and the minimum value of the transmission efficiency metric of the candidate routing node; e.g. of the typexkRepresenting a node NkA normalized value of the transmission efficiency metric of (a);
for node NxThe routing function is given by equation (7):
selectx(Nk)＝αrxk+βexk(7)
wherein: selectx(Nk) Is node NkAt node Nxα is the weight coefficient of each metric index, and α + β is 1;
the node selects the candidate routing node with the largest select value as the next hop, and sets α -0.6 and β -0.4.
3. The method for optimizing data transmission delay in a wireless sensor network according to claim 1, wherein the calculation of queuing delay in step 3:
estimating queuing delay T of data packet according to difference value of actual delay and theoretical delay of data packetqueGiven by equation (8):
t＝tsend+2ttrans(10)
wherein: t isjIndicating the actual delay of the jth data packet;
indicating the time when the node receives the acknowledgement message of the jth data packet;
indicating the time when the jth data packet starts to be transmitted; t represents the theoretical delay of the data packet; t is tsendRepresenting the transmission delay of the theoretical node; t is ttransRepresenting the propagation delay of the nodes theoretically, and m represents the number of the data packets in the buffer area; z represents the number of packets sent over a period of time.
4. The method according to claim 1, wherein the determining process of the path change in the step 4 is as follows:
the node judges whether to continue receiving data according to the interval to which the queuing delay belongs, and the following three conditions exist specifically:
4.1) when TqueWhen Min is less than or equal to Min, the node can continue to receive data, and the data sending node does not need to switch paths;
4.2) when TqueWhen the data transmission node is not less than Max, the node can not continuously receive the data, and the data transmission node needs to switch the path;
4.3) when Min<Tque<In Max, the node needs to make further judgment;
wherein Min is a minimum queuing delay threshold value, and Max is a maximum queuing delay threshold value;
for case 4.3), the present invention adopts the following two kinds of information as the node NxThe basis for judging whether to continue receiving data is as follows:
4.3.1) Link PropertiesAmount information: if node NxAnd routing node NkLink quality between is lower than NxThe average level of the candidate routing nodes represents the node NxThe current transmission quality is poor, the data is not suitable for data forwarding, and routing nodes need to be replaced;
representing a node NkForwarding node NxLink quality of data and NxThe relation of the candidate route node link quality mean value is given by equation (11):
wherein: n represents a node NxThe number of candidate routing nodes; selectxiRepresenting a node NxThe value of the routing function for the ith candidate routing node;
4.3.2) queuing delay information: the closer the queuing delay of the data packet of the node is to the Max value, the larger the queuing delay of the current node is, the larger the influence on the time of the data packet arriving at the base station is;
representing a node NxThe relationship between the packet queuing delay and the queuing delay threshold is given by equation (12):
wherein, Tx queRepresenting a node NxThe queuing delay of (1);
when routing node NxWhen the link quality is poor and the queuing delay is high, the node is not suitable for continuously receiving data; dec is a term ofxk selectAnd dx thIs given by equation (13):
when the Dec value is 1, the node N is indicatedxThe node is not suitable for continuously receiving data, and when the Dec value is 0, the node is indicated to be suitable for continuously receiving data; and setting a flag bit, setting the flag to be 1 if the node can not continuously receive data, and setting the flag to be 0 if the node cannot continuously receive data.
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