KR101441433B1 - Method for varying wakwup period based on channel environment in duty-based mac protocol - Google Patents

Abstract

A method for dynamically varying a wakeup period (interval or period) according to a channel environment in a DutyCycle-based MAC protocol, the method comprising: counting traffic of a neighboring node based on a channel state checked in a Wakeup interval of a duty cycle; The reception success rate and the energy efficiency can be improved by dynamically varying the wakeup interval in the same duty cycle according to the traffic of the counted neighbor node.

Description

[0001] METHOD FOR VARYING WAKWUP PERIOD BASED ON CHANNEL ENVIRONMENT IN DUTY-BASED MAC PROTOCOL [0002] TECHNICAL FIELD [0001] The present invention relates to a method for dynamically varying a wake-

The present invention relates to a method of dynamically allocating a wakeup interval according to a channel environment in a duty cycle based MAC protocol to improve energy performance and reception success rate.

Recently, researches on WSN (Wireless Sensor Networks) that collect environmental data wirelessly through remote sensors have been actively conducted. In the above WSN, energy efficiency is most important, unlike existing network technologies that aim at high performance, broadband, and long distance communication.

In the WSN field, the MAC (Medium Access Control) protocol uses a duty cycle method in order to reduce energy consumption. The duty cycle method divides an RF transceiver into a sleep state (sleep state) and a wakeup state (active state), and repeatedly operates two states to transmit and receive data.

The goal of the duty cycle method is to reduce the wakeup period (interval or period) and to increase the sleep period to minimize energy consumption. However, the minimized wakeup interval can reduce the reception success rate and increase the delay time. If there are many neighboring nodes in 1-hop, there is a disadvantage that the channel occupancy competition increases within the limited wakeup interval and the retransmission rate increases.

Most WSN MAC protocols use a fixed duty cycle method.

In the fixed duty cycle, when the wakeup interval is set long, the channel competition is low, the number of re-transmissions and the delay time are lowered and the reception success rate is increased, but the energy efficiency is low. Conversely, when the wakeup interval is set to be short, the energy efficiency becomes high, but the network performance mentioned above becomes low. That is, when the number of neighboring nodes in 1-hop is high and traffic is high, the wakeup period should be set long, and in the opposite case, the wakeup period should be set short for energy efficiency.

Thus, in the conventional fixed-duty-cycle-based MAC protocol, there is a disadvantage that it is difficult to maintain the MAC protocol performance due to the trade-off between the reception success rate and the energy efficiency due to the length of the wakeup interval in the duty cycle.

An object of the present invention is to provide a method of simultaneously guaranteeing a reception success rate and energy efficiency by dynamically allocating a length of a wakeup interval according to a channel environment.

According to another aspect of the present invention, there is provided a method of dynamically changing a wakeup interval, comprising: checking a channel state in a wakeup interval of a duty cycle; Counting traffic of a neighboring node based on the checked channel state; And dynamically varying a wakeup interval within the same duty cycle according to the traffic of the counted neighbor node.

The channel state is checked through CSMA / CA performance for the asynchronous MAC protocol and periodic CCA check for the synchronous MAC protocol.

The traffic of the neighbor node is incremented by 1 when the channel state is busy and decremented by 1 when it is idle.

The step of dynamically varying the wakeup interval may include comparing the traffic of the counted neighbor node with a limit range; And if the traffic of the neighboring node is out of the limited range, the wakeup interval is doubled, and if the traffic of the neighboring node is within the limited range, the wakeup interval is reduced to 1/2.

When the environment of the channel is intrusion detection or disaster detection, the wakeup interval is doubled at the time of the first detection event, and then the wakeup interval is dynamically changed according to the traffic of the neighboring node.

The present invention finds an appropriate wakeup interval in consideration of the channel environment in the WSN MAC protocol using the duty cycle method. This increases the wakeup period (activity period) in order to increase the reception success rate in the environment where the traffic of the neighbor node is high, and increases the energy efficiency by decreasing the length of the wakeup interval unnecessary in the low traffic environment.

The present invention is designed to be applicable to any protocol regardless of synchronous and asynchronous types with the WSN MAC protocol employing the duty cycle method. Thus, it is possible to improve energy efficiency while maintaining the operation modes of many MAC protocols There is an effect.

FIG. 1 is a flowchart illustrating a method of changing a wakeup interval using a channel environment in a Duty Cycle-based MAC protocol according to an embodiment of the present invention.
2 is a diagram illustrating a change in each wakeup interval when traffic of a neighboring node is out of a limit range.
FIG. 3 is a graph illustrating a method of varying a wakeup interval in a situation where an event is frequently generated.

In order to solve the problem occurring in the conventional asynchronous WSN MAC protocol, the present invention proposes a technique of dynamically allocating a wakeup period (interval or period) by detecting a channel state in a 1-hop.

In the WSN field, the MAC protocol using the duty cycle method is generally divided into a synchronous method and an asynchronous method. In synchronous mode, all nodes synchronize the duty cycle to increase energy efficiency by reducing the idle listening time (the amount of time that they must continuously consume their communication power in spite of not participating in data communication). On the other hand, in the asynchronous scheme, all nodes increase the energy efficiency by eliminating periodic synchronous signal exchange. In order to maintain the merits of each method, the present invention is designed to be applied as an add-on type in the conventional method, and the compatibility is maintained.

Generally, in the MAC protocol based on the duty cycle, the length of the wakeup period in the duty cycle greatly affects the energy efficiency. If the wakeup interval is relatively long in the same duty cycle, the energy efficiency becomes lower while the reception success rate of each node is increased. If the wakeup interval is short, the energy efficiency becomes higher but the reception success rate becomes lower. That is, the length of the wakeup interval is a trade-off factor that greatly affects the reception success rate and energy efficiency when determining the MAC protocol performance based on the duty cycle.

In order to improve the performance of the MAC protocol of the duty cycle method in consideration of the environmental characteristic, the present invention proposes a method of variably changing the wakeup interval according to the channel environment. That is, the present invention proposes a method of varying the wakeup interval by periodically monitoring the CCA (Clear Channel Assessment) that can be observed in the physical layer, and is designed to be applicable to both the synchronous type and the asynchronous type.

Generally, each node in the asynchronous MAC protocol does not know the wakeup state of the neighboring nodes, and since there is no negotiation process on its own transmission interval and reception interval, it uses CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) And transmits the data.

That is, the transmitting node waits for a predetermined time (random back-off delay) to perform carrier sensing before transmitting data in the wakeup interval in the duty cycle, and then checks the CCA to determine the channel state . At this time, if the channel state is idle, the transmitting node transmits data, and if the channel state is busy, the transmitting node performs the transmitting wave detecting step again. Since the asynchronous MAC protocol always performs transmission wave detection in all situations where data transmission is required, there is no need for a separate procedure for CCA identification.

On the other hand, in the synchronous MAC protocol, all nodes do not use the CSMA / CA method because they share the interval with the synchronized wakeup time. Therefore, in the synchronous MAC protocol, all nodes can not grasp the traffic environment of the neighboring node in real time. Also, even in the asynchronous MAC protocol, a node that does not generate a transmission request relatively does not detect the transmission wave for a long time, and therefore can not grasp the traffic environment of the neighboring node.

Accordingly, the present invention proposes a method of periodically monitoring the CCA in order to grasp the channel state and the traffic volume of the neighboring node in the above situation, and this is called CCA sampling.

1 is a flowchart illustrating a method of changing a wakeup interval using a channel environment in a Duty Cycle-based MAC protocol according to an embodiment of the present invention.

As shown in FIG. 1, each node grasps a channel state and models a traffic amount of a neighboring node. The present invention defines a BHC (Busy-state Hit Count) variable as shown in Equation (1) to model the traffic volume of a neighboring node.

.......식(1)

... (1)

The BHC variable indicates a traffic amount of a neighboring node in a channel environment of each node, and has a positive integer value and a negative integer value, and the initial value is set to zero.

The CCA value determined after the CSMA / CA execution of the asynchronous MAC protocol or the CCA sampling of the synchronous MAC protocol is shown as busy or idle. Accordingly, each node checks the CCA value and increases the BHC value when the CCA value is busy (S10_S12). On the contrary, if the CCA value is " idle ", the BHC is decreased (S13). All nodes manage these BHCs. The range of the BHC is limited to K _max representing the maximum threshold value and K _min representing the minimum threshold value.

The variable wakeup period scheme proposed in the present invention is a method of dynamically varying the wakeup interval within the same duty cycle according to the BHC value indicating the traffic amount of the neighboring node.

When each node operates the BHC, the BHC value increases or decreases according to the CCA value, that is, the channel state. Each node compares the BHC value with the range of two thresholds (K _max , K _min ) to adjust the wakeup interval when the duty cycle starts (S14 to S21). That is, if the BHC value is greater than the maximum threshold value (K _max ) as a result of the comparison, the node increases the wakeup interval twice, initializes the BHC to 0 (S16 to S18) If it is smaller than the threshold value ( _Kmin ), the wakeup interval is reduced to 1/2 and initialized (S19 to S21).

FIG. 2 shows a change in each wakeup interval when the traffic of the neighboring node is out of the limit range.

The K _max and K _min values used in the BHC operation in the variable wakeup period scheme proposed in the present invention should be determined carefully since they are constants that greatly affect the network performance. Characteristics should be considered.

As described above, the variable wakeup period method can be defined as a method of setting the wakeup interval of the current state to two or half when the BHC value is out of the limit range as follows. First, I {A} is defined as in Equation (2).

.............식(2)

... (2)

In addition, the range of K _max and K _min can be limited as shown in Equation (3), and finally the change policy of the variable wakeup period can be generalized as Equation (4).

...............식(3)

... (3)

........식(4)

(4)

Here, τ _{w, n} represents a wakeup period in the n-th duty cycle. According to the state of BHC _n representing the n-th BHC, the ( _{n + 1} ) -th wakeup interval (τ _{w, n + 1} ) can be finally defined as Equation (4) by I defined in Equation (2).

In Equation (4), n represents the number of duty cycles, and the above-mentioned CCA sampling is performed at a very short interval in comparison with the duty cycle interval. Therefore, the change of BHC can occur from several times to dozens of times within the same duty cycle, and since the duty cycle number and the CCA sampling number are different, n variable is used in equation (4) unlike k in equation (1).

As described above, the present invention efficiently and selectively operates the energy efficiency and the reception success rate, which are trade-off parameters in the existing duty cycle based WSN MAC protocol, considering the traffic volume of neighbor nodes according to the channel environment. In addition, it calculates the optimal wakeup interval dynamically and satisfies the requirements of energy efficiency and reception success rate suitable for the network situation.

Meanwhile, the attributes of traffic may be different according to various application fields, and thus energy efficiency can be improved by changing the duty cycle allocation method. In an environment such as intrusion detection or disaster detection, there is a high probability that an intruder will move for a certain time or a natural disaster will occur continuously. These events are generally very unlikely to occur, but there is a characteristic that events are generated multiple times after occurrence.

Therefore, the present invention additionally proposes an application method of a variable wakeup period method in consideration of the case where the MAC protocol to be used is operated in a situation (or an environment) where a plurality of events occur.

The present invention proposes a method of temporarily suspending a wakeup state in order to improve the reception success rate of each node in a situation where an event is frequently generated (intrusion detection or disaster detection).

FIG. 3 is a graph illustrating a method of changing a wakeup interval in a situation where an event is frequently generated.

In FIG. 3, the X-axis represents the duty cycle, and the Y-axis represents the wakeup period ratio within a given duty cycle in units of percent.

In FIG. 1, when the channel is busy, each node gradually increases the wakeup interval. However, in an environment where multiple events occur, the wakeup interval is temporarily increased to twice (100%) at the time of the first event to increase the reception success rate for the event occurrence. After each node confirms that all events are successfully received, the wakeup interval is reduced using the BHC as described above to find an appropriate wakeup interval.

As described above, the present invention allocates an appropriate wakeup interval in consideration of the channel environment in the WSN MAC protocol using the duty cycle method. That is, the present invention increases the reception success rate by increasing the wakeup interval in the environment where the traffic of the neighbor node is high, and increases the energy efficiency by reducing the unnecessary wakeup interval in the low traffic environment.

Accordingly, the present invention can be applied to any protocol regardless of the synchronous and asynchronous types with the WSN MAC protocol employing the duty cycle method. In particular, the present invention can improve the reception success rate and energy efficiency while maintaining the operation form of many MAC protocols There is an effect that can be made.

The above-described dynamic change method of the wakeup period is not limited to the configuration and method of the above-described embodiments, but the embodiments may be modified so that all or some of the embodiments are selectively As shown in FIG.

Claims (5)

Checking a channel state and a surrounding environment in a wakeup period of the duty cycle;
Counting traffic of a neighboring node in the checked channel state; And
And dynamically varying a wakeup interval in the same duty cycle by selectively using the traffic of the counted neighbor node and the checked environment, wherein dynamically varying the wakeup interval comprises:
Temporarily increasing the wake-up interval at the occurrence of the first event when the checked environment has a plurality of events; And
And incrementally decreasing the temporarily increased wakeup interval according to the traffic of the counted neighbor node when all events are received,
Wherein the checked channel state comprises an asynchronous MAC protocol or a synchronous MAC protocol. 2. The method of claim 1,
Wherein the asynchronous MAC protocol is checked for CSMA / CA performance and the synchronous MAC protocol is checked for periodic CCA check. 2. The method of claim 1, wherein the traffic of the neighboring node
Is incremented by 1 when the channel state is busy and decremented by 1 when the channel state is idle. ≪ RTI ID = 0.0 > 31. < / RTI > The method of claim 1, wherein dynamically varying the wakeup interval comprises:
Comparing the traffic of the counted neighbor node with a limit range; And
And if the traffic of the neighboring node is out of the limit range, increasing the wakeup period by a factor of two and decreasing the wakeup period by half when the traffic of the neighboring node is within the limit range, Dynamic Variation Method of Wakeup Period. delete

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