KR20210085298A - Wireless communiction method using routing metric for energy-efficient and low-delay path selection in duty-cycled wireless sensor network - Google Patents

Abstract

The present invention relates to a wireless communication method using a routing metric for energy-efficient and low-delay path selection in a duty-cycled wireless sensor network. The wireless communication method includes: a step in which a transfer node is woken up in a duty-cycled wireless sensor network, an address information-inserted preamble is generated, and the preamble is repeatedly transmitted with an interval for early-ACK reception; a step in which time information-inserted early-ACK for wake-up schedule prediction is transmitted to the transfer node in at least one preamble-received neighbor node; a step in which a receiving node to transfer data among the at least one neighbor node is selected based on the time information at the transfer node; and a step in which data transmission to the receiving node is performed at the selected transfer node. According to the present invention, path selection causing a long delay time and energy waste is prevented, and thus an energy-efficient and low-delay wireless sensor network can be configured.

Description

TECHNICAL FIELD [0002] Wireless communication method using routing metric for energy-efficient and low-delay path selection in duty-cycled wireless sensor network}

The present invention relates to a wireless communication method, and more particularly, to a wireless communication method using a routing metric supporting low-power and low-latency path setting in a duty cycle-based wireless sensor network.

The present invention is derived from the research results supported by MIST in Korea according to the National Program for Excellence in SW supervised by the IITP (task identification number: 2017-0-00096)

Wireless Sensor Network (WSN) is a technology that can be applied in various ways for sensor nodes to monitor the surrounding environment and collect data through sensors. It can be used for detecting animals in the environment, for monitoring environmental information such as humidity or temperature in a specific area, and the like.

Unlike other networks such as WLAN and Bluetooth, wireless sensor networks cannot change or recharge their own batteries, and usually use a limited-capacity energy source such as a battery. Accordingly, energy efficiency is a fundamental and important consideration when designing protocols for sensor nodes in wireless sensor networks. Energy constraints along with deploying a large number of nodes make it difficult to design routing protocols for sensor nodes, MACs and wireless sensor networks, and it is very important to manage and use energy efficiently.

As such, as the demand for low-power design for the wireless sensor network increases, a duty cycle that repeats a sleep state and an active state is frequently used. By using the duty cycle, it is possible to save energy by turning off both transmission and reception of radio waves during the sleep state, but at the same time, transmission delay occurs.

There are two types of duty cycle operations: a synchronous duty cycle and an asynchronous duty cycle. In the case of the synchronization method, the active period in the duty cycle of each node is synchronized by exchanging periodic control frames such as SYNC. These additional control frames result in wasted energy usage, and conflicts between frames occur when common periods for accessing the medium overlap. As described above, the synchronous duty cycle has a difficult problem of protocol overhead, so in reality, the asynchronous duty cycle is widely used.

However, the duty cycle of the asynchronous method can solve the problem of protocol overhead, but the delay time increases compared to the synchronous method because the operation period is different between sensor nodes. In particular, since the preamble is continuously transmitted while waiting for the duty cycle of the receiving node, the energy source of the node is wasted.

Therefore, if a route that minimizes the latency due to the duty cycle is selected in the routing protocol, not only the overall transmission time can be minimized, but also the energy used can be optimized.

Therefore, it is necessary to consider a wireless communication method capable of minimizing energy efficiency and time delay in a wireless sensor network through path setting capable of minimizing such waiting time.

Accordingly, it is an object of the present invention to provide a wireless communication method using a routing metric supporting low power and low latency path setting in a duty cycle-based wireless sensor network.

In a wireless communication method according to the present invention for achieving the above object, in a duty cycle-based wireless sensor network, a transmission node wakes up and generates a preamble into which address information is inserted, and early ACK (Early-ACK) Repeatedly transmitting the preamble with an interval capable of receiving the . At least one neighboring node that has received the preamble, an early acknowledgment in which time information for predicting its own wakeup schedule is inserted to the transmitting node. transmitting, the transmitting node selecting a receiving node to transmit data from among the at least one neighboring node based on the time information, and performing data transmission from the transmitting node to the selected receiving node. .

After the transmitting node completes data transmission to the selected receiving node, the method further includes switching to a sleep state, wherein the transmitting node refers to the time information and matches the wakeup time of the selected receiving node to the sleep state. Can be woken up from the state.

The time information is information about a time to wake up within the duty cycle period, and may further include the step of performing a random back-off process by the transmitting node in order to prevent a preamble collision with another node. .

In a wireless communication system according to the present invention for achieving the above object, in a duty cycle-based wireless sensor network, wake up and generate a preamble in which address information is inserted, an interval at which an Early-ACK can be received A transmitting node that repeatedly transmits the preamble while placing a , and at least one neighboring node that receives the preamble and transmits, to the transmitting node, an early acknowledgment into which time information for predicting its own wakeup schedule is inserted. , the transmitting node may select a receiving node to transmit data from among the at least one neighboring node based on the time information, and transmit data to the selected receiving node.

According to the present invention, by using an EDW routing metric that minimizes the total waiting time caused by the duty cycle, a node maintains an operating state while waiting, and causes interference between nodes by continuously transmitting unnecessary short preambles. problems can be reduced. This makes it possible to construct an energy-efficient and low-latency wireless sensor network by avoiding route setup that wastes a lot of energy with long latency.

In addition, the present invention can provide the TRIX-MAC protocol superior to the existing MAC protocol in terms of delay, throughput and energy consumption by avoiding collision and reducing overhead. In addition, by using the TRIX-MAC protocol, rapid communication can be performed in the wireless sensor network without sacrificing energy saving at both the transmitting and receiving nodes, and the lifespan of the sensor network can be increased by reducing collisions and unnecessary wake-ups. .

1 is a diagram showing an example of a wireless sensor network;
2 is a diagram referenced in the description of the duty cycle;
3 is a diagram referenced in the operation description for X-MAC;
4 is a diagram referenced in the operation description for the TRIX-MAC protocol used in the present invention;
5 is a diagram referenced in the description of random back-off in the TRIX-MAC protocol used in the present invention;
6 is a diagram referenced in the description of EDW, which is a routing metric used in the present invention, and
7 to 12 are diagrams showing simulation results of the method according to the present invention and the method using a different protocol under various conditions.

In this specification, when a component is referred to as being “connected” or “connected” to another component, the component may be directly connected or connected to another component, but another component in between. It should be understood that elements may exist. In addition, other expressions describing the relationship between elements, such as "between" or "neighboring to", etc., such as that one element "transmits" a signal to another element, should be interpreted similarly. do.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

1 shows an example of a wireless sensor network.

Referring to FIG. 1 , a wireless sensor network is basically composed of a large number of sensor nodes, and the sensor nodes collect information through sensors and transmit the collected information to a sink node, which is a final destination, every predetermined time. The sink node collects data from sensor nodes and transmits the collected data to the user.

In such a wireless sensor network, sensor nodes usually use an energy source with limited capacity, such as a battery, so it is very important to efficiently manage and use energy.

2 is a diagram referred to in the description of the duty cycle.

As shown in FIG. 2 , as a low-power design for a wireless sensor network is required, a duty cycle that repeats a sleep state and an active state is frequently used. By using such a duty cycle, it is possible to save energy by turning off all transmission and reception of radio waves during the sleep state, but at the same time, transmission delay occurs.

There are two types of duty cycle operation methods, such as a synchronous duty cycle and an asynchronous duty cycle. However, the synchronous duty cycle has a difficult problem of protocol overhead, so in reality, the asynchronous duty cycle is widely used.

3 is a diagram referenced in the description of the operation of the X-MAC.

X-MAC (Michael Buettner, Gray V. Yee, Eric Anderson and Richard Han, "X-MAC: a short preamble mac protocol for duty-cycled wireless sensor networks," Proc. of the 4th ACM Conference on Embedded Networked Sensor System, pp. 307-320, Nov 2006) is a B-MAC (Joseph Polastre, Jason Hill, and David Culler, "Versatile low power media access for wireless sensor networks," Proc. of the Second ACM Conference on Embedded Networked Sensor System, pp. 95-107, 2004) is an asynchronous duty cycle MAC protocol for a wireless sensor network that uses a series of short preambles to implement low-power communication without synchronization.

In X-MAC, since the short preamble carries the address of the receiving node, a node other than the receiving node can sleep while listening to the first short preamble. The receiving node may respond with an early-ACK to stop the preamble and start data transmission.

The main features of X-MAC are short preamble sampling and early acknowledgment mechanism. The X-MAC sends multiple short preambles to notify the receiving node instead of the long preamble used in the B-MAC. When the receiving node detects a short preamble during the awake period, it sends an early acknowledgment to the transmitting node before receiving the actual data frame, and the transmitting node knows that the receiving node stays in the awake period, Immediately transmit the data frame.

As a result, X-MAC can save more energy than B-MAC due to its short preamble sampling and early acknowledgment mechanism.

As shown in FIG. 3 , all nodes in the network have their own wake-up schedule to transmit and receive frames with a period of T. The TX node continues to send a short preamble until the RX node wakes up. No other node interferes with the communication between the TX node and the RX node. When the TX node receives the acknowledgment, it starts sending data frames to the RX node.

Since X-MAC is asynchronous, the average communication time of a TX node is T/2 + data frame length. When two or more TX nodes wake up and start sending preambles at the same time, all other nodes including the RX node cannot check the address information of the preamble, so the TX node does not stop transmitting the preamble until the next wakeup schedule. Thus, for each conflicting data frame, the average communication time to the sender is T.

4 is a diagram referenced in the description of the operation of the TRIX-MAC protocol used in the present invention.

The TRIX-MAC protocol used in the present invention is based on X-MAC. Every node in the network has a cycle equal to C cycle, which is divided into two states: wakeup and sleep state. The wake-up state is an active state in which a node turns on wireless communication and receives or transmits data, and the sleep state is a state in which the node saves power by turning off the wireless communication.

The wake-up state consists of two periods: a scheduled wakeup period and a synch-wakeup period, in which the synchronization-wakeup cycle is optional when the node is about to transmit a data frame. Synchronized wakeup is optional if you want to transmit data frames.

4 shows the basic operation of the TRIX-MAC protocol, and the TX node transmits a short preamble and wakes up twice. Each node wakes up periodically according to its own schedule and checks whether there is an incoming short preamble. If a short preamble is not received after the schedule is generated, the TX node goes into a power saving state. When there is a data frame to transmit, the TX node wakes up again from a Synchronized Wakeup synchronized to the RX node. When the channel is idle, the TX-node starts transmitting the short preamble before transmitting the data frame.

In the TRIX-MAC protocol, every node independently has its own wake-up schedule and has a temporary wake-up schedule synchronized with the wake-up of the RX node, and the wake-up schedule of the RX node is obtained as a wake-up time within the field of the early awake frame. can Therefore, the TX node using the TRIX-MAC wakes up twice periodically when there is data to be transmitted from the TX node to the RX node. In the TX node, the first wakeup receives a data frame according to its own schedule (Sched-wakeup), and the second wakeup transmits data to the RX node (Synch-wakeup) as shown in FIG. 4 .

The TRIX-MAC behaves like an X-MAC during the first cycle of transmission because the TX node initially has no information about the wakeup schedule of the RX node. When the TX node has data to transmit to the RX node, the TX node searches for a wakeup schedule of the specified RX node in the table. If it does not find an appropriate wakeup schedule for the RX node, the TX node continues to transmit a short preamplifier in its own schedule as in the X-MAC. Upon receiving the early acknowledgment from the RX node, the TX node immediately starts transmitting the data frame, extracts the wakeup information of the RX node from the wakeup time field of the early ag frame, and adds the wakeup information to up-wakeup and Synch-wakeup Store the wake-up time table as the time difference between

5 is a diagram referenced in the description of random back-off in the TRIX-MAC protocol used in the present invention.

In Fig. 5, it is shown that TX1 and TX2 precede TX2 in occupying the medium by transmitter R and TX1 trying to transmit data to the receiver. TX1 acquires the medium to transmit a short preamble and RX response as an early acknowledgment preamble. TX2 receives an early acknowledgment from RX and sets the NAV to the end of data transmission. The duration of the early acknowledgment frame specifies the number of time slots that TX2 must wait during data transmission. When data transmission is complete, TX2 counts the remaining slot count again and transmits the preamble in the next time slot.

In FIG. 5, the number of slots is set to 1 in the case of TX1 and is set to 3 in the case of TX2. TX1 grabs the medium and transmits a short preamble in the first time slot and RX responds with an early acknowledgment preamble. TX2 receives an early acknowledgment from RX and sets the Network Allocation Vector (NAV) to end data transmission. The duration of the early acknowledgment frame specifies the number of time slots that TX2 must wait during data transmission. When data transmission is completed, TX2 may count down the remaining slot count again and transmit a preamble in the next time slot.

Meanwhile, in a general wireless network, the most widely used routing metric as a reference value for optimal path selection is the expected number of transmission (ETX), which means the total number of transmissions occurring in the entire path. In a situation where all nodes are always ready for transmission, the path with the minimum ETX means the fastest and least energy-consuming path, and eventually shows the best performance. However, in a wireless sensor network having an asynchronous duty cycle, the minimum delay time or optimal energy efficiency is not guaranteed despite the selection of a path having the minimum number of transmissions, that is, the smallest ETX value. This is because the latency due to the asynchronous duty cycle can occur randomly.

In the present invention, Estimated Duty-cycled Wait (EDW) is used as a new routing metric for optimal path selection during routing. EDW is an estimate of the total waiting time that nodes in charge of relaying on the entire path must wait until the next node to receive reception wakes up. The path that minimizes the EDW not only reduces the overall transmission delay but also reduces energy consumption, which in turn can have the effect of prolonging the survival life of the wireless sensor network.

In a duty cycle-based wireless sensor network, all sensor nodes can determine their sleep/activation timing independently of other sensor nodes, and share this information with neighboring nodes. However, the characteristics of all sensor nodes in the wireless sensor network are the same and have the same duty cycle cycle. When a sensor node wants to transmit a message, the node waits for the receiving node to wake up in operation mode and then completes the transmission.

라고 정의할 수 있고, 전체 경로에 걸친 총 대기 시간

는 다음과 같이 정의할 수 있다. At any time t , when the transmitting node i and the receiving node j

can be defined as, the total latency over the entire path

can be defined as

In general, duty cycle-based wireless sensor networks have relatively high latency, so this EDW can be an important routing metric.

6 is a diagram referenced in the description of the routing metric EDW (Estimated Duty-cycled Wait) used in the present invention.

Referring to FIG. 6 , when an S node transmits a message to a node D, there are two paths, which are transmitted through node A or transmitted through node B and node C. Here, the value marked on each node indicates the time at which each node wakes up from the operating state within the cycle of the duty cycle.

In this case, in order to deliver a message from node S to node A in the path transmitted through node A, since the time for waking up from node S to an operating state is greater than that of node A, the transmission goes beyond one cycle to the next cycle. is done

On the other hand, in the path through Node B and Node C, the transmission is finally completed within one cycle to Node D. EDX, a new metric, selects a path through node B and node C, and has a smaller delay time than the path delivered through node A to be selected through ETX, which is the existing routing metric.

Therefore, it is possible to search for an optimal path by using such an EDW as a routing metric.

7 to 12 show simulation results of the method according to the present invention and the method using a different protocol under various conditions.

First, the parameter values for the sensor node and network environment for simulation are shown in [Table 1] below.

Parameters

Value
Duty cycle rate
0.65%
Default sleep sustain time
2.79 second
Default wakeup time
0.0182 second
Agent (Traffic model)
CBR/Poisson
Message interval in sources
20s
message size
60 bytes
Number of simulation flows
8 flows
Link bandwidth
250 Kbps
Rx power in mode
15.2 mA
Tx power in mode
28.9 mA
Sleep power in state
0.0004 mA
Idle (wake-up) power in state
12.8 mA
RX(TX) / CS range
250 / 300 meters

Also, three types of traffic were used for simulation. That is, static traffic that always generates a constant amount of transmission, random amount of traffic having a Poisson distribution (poisson), and traffic (RCE) in a form resembling the interrelated traffic in time and space of an actual sensor network was used for simulation. And ns-2 (version 2.32) was used as a network simulator.

7 to 9 show simulation results of average end-to-end delay.

Here, EDW+RIX-MAC When EDW is used as the TRIX protocol and routing metric according to the present invention, EDW+X-MAC is X-MAC and EDW is used as the routing metric, ETX+RIX-MAC is TRIX-MAC and In the case of using ETX as the routing metric, ETX+X-MAC indicates the case of using X-MAC and ETX as the routing metric.

7 shows CBR static traffic, FIG. 8 shows Poisson random traffic, and FIG. 9 shows RCE traffic.

7 to 9 , it can be seen that the performance is improved by about 30% regardless of traffic when EDW is used as the TRIX protocol and routing metric according to the present invention.

9 to 12 show the total energy consumption results.

Since a high level of energy is consumed to transmit the short preamble until the receiver wakes up, the X-MAC consumes a large amount of energy to transmit the preamble. In particular, when the wakeup latency of the receiver is large in X-MAC, a large amount of energy is wasted due to many short preambles.

As shown in Figures 9 to 12, energy savings of about 25% can be achieved by using EDW instead of ETX as the routing metric. As a result, it can be seen that the method according to the present invention is effective in terms of energy consumption in various traffics. Since the energy consumption of a node is closely related to the lifespan of the network, when the method according to the present invention is used, the lifespan of the node can be expected to be significantly longer than when other methods are used.

As such, the wireless communication method according to the present invention uses an EDW routing metric that minimizes the total waiting time caused by the duty cycle, thereby preventing the path setting that wastes a lot of energy with a long delay time, thereby providing energy-efficient and low-latency Design a wireless sensor network.

In addition, the TRIX-MAC protocol used in the present invention is superior to the existing protocol in terms of latency, throughput and energy consumption by avoiding collisions and reducing overhead. As a result, TRIX-MAC can perform fast communication in a wireless sensor network without sacrificing energy saving at both the transmitting and receiving nodes, and can increase the lifespan of the sensor network by reducing collisions and unnecessary wake-ups.

On the other hand, in the wireless communication method according to the present invention, the configuration and method of the embodiments described above are not limitedly applicable, but all or part of each embodiment is selective so that various modifications can be made to the embodiments. It may be configured in combination with .

In addition, although preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above, and the technical field to which the present invention belongs without departing from the gist of the present invention as claimed in the claims In addition, various modifications may be made by those of ordinary skill in the art, and these modifications should not be individually understood from the technical spirit or perspective of the present invention.

Claims (10)

In a duty cycle-based wireless sensor network, a transmission node wakes up and generates a preamble into which address information is inserted, and repeatedly transmits the preamble with an interval at which an Early-ACK can be received. step;
transmitting, from at least one neighboring node receiving the preamble, an early acknowledgment in which time information for predicting its own wakeup schedule is inserted to the transmitting node;
selecting a receiving node to transmit data from among the at least one neighboring node based on the time information at the transmitting node; and
and transmitting data from the transmitting node to the selected receiving node. According to claim 1,
After the transmitting node completes data transmission to the selected receiving node, the method further comprising the step of switching to a sleep state. 3. The method of claim 2,
The transmitting node refers to the time information, the wireless communication method, characterized in that the wake up from the sleep state according to the wake up time of the selected receiving node. According to claim 1,
The time information is a wireless communication method, characterized in that it is information about a time to enter the wake-up state within the duty cycle period. According to claim 1,
The method further comprising the step of the transmitting node performing a random back-off process in order to prevent a preamble collision with another node. According to claim 1,
and switching to a sleep state when the transmitting node does not receive the early acknowledgment into which the time information is inserted within a predetermined time from the neighboring node. In a duty cycle-based wireless sensor network, a transmission node that wakes up and generates a preamble into which address information is inserted, and repeatedly transmits the preamble with an interval at which an Early-ACK can be received; and
at least one neighbor node that receives the preamble and transmits, to the transmitting node, an early ACK in which time information for predicting its own wakeup schedule is inserted;
The transmitting node selects a receiving node to transmit data from among the at least one neighboring node based on the time information, and transmits the data to the selected receiving node. 8. The method of claim 7,
The transmitting node, when there is data to be transmitted to the receiving node, refers to the time information, and operates a next wakeup according to a wakeup schedule of the selected receiving node. 8. The method of claim 7,
After the transmitting node completes data transmission to the selected receiving node, it switches to a sleep state. 8. The method of claim 7,
The time information is a wireless communication system, characterized in that stored in a wake-up time table of the transmission node.

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