KR101135432B1 - Method for duty cycle of sleep/active mode based on TDMA in a wireless sensor network system and sensor network system using the same - Google Patents

Abstract

The present invention is an active sleep / active duty cycle method in a wireless sensor network, in which a handshake is performed with a neighbor node of 1-hop distance in a free competition section of a time frame to search for a neighbor node of 1-hop distance, and the initial activation is performed. Selecting a schedule; And selecting one's own activation schedule by exchanging information about the activation schedule with a neighboring node one-hop distance in a non-competition period of a time frame. According to the present invention, it is possible to maximize the efficiency of channel reuse because the size of the virtual cluster is minimized to consist only of arbitrary nodes participating in direct communication and neighboring nodes of 1-hop distance.

Description

Active sleep / active duty cycle method in wireless sensor network and sensor network system using the same {Method for duty cycle of sleep / active mode based on TDMA in a wireless sensor network system and sensor network system using the same}

The present invention relates to an active sleep / active duty cycle method in a wireless sensor network. More particularly, the present invention relates to an active sleep / active duty cycle method for allowing each node constituting the wireless sensor network at the link layer to form a virtual cluster of a minimum size and to allow contention-free transmission in a TDMA manner.

This study was derived from the research conducted as part of the IT new growth engine core technology development project of the Ministry of Knowledge Economy and the Ministry of Information and Telecommunication Research and Development. [Task management number: 2006-S-085-03, Task name: Micro operating system for automotive sensor node Development].

Wireless sensor networks are a key technology infrastructure for enabling ubiquitous computing technology. Nodes of the wireless sensor network use a limited capacity battery to perform functions such as sensing or computing. However, unlike conventional wireless networks, a wireless sensor network uses a limited amount of battery power, and thus a technical configuration for transmitting sensed data using minimum energy is required.

Accordingly, there is a need for an efficient MAC protocol in a media access control (MAC) layer that controls error flow and flow of data and manages resources among the various layers constituting the wireless network. When applying the MAC protocol of the existing MANET (Mobile Ad-hoc Network) or IEEE 802.11 to the sensor network, packet collision, overhearing, control overhead, idle listening In order to solve this problem, a MAC protocol structure specially designed for a sensor network has been developed.

In wireless networks that share a single radio channel, the Medium Access Control (MAC) protocol is a basic feature that allows only one node among multiple adjacent nodes to access a wireless channel in order to successfully transmit a signal. To provide. Carrier Sense Multiple Access (CSMA) and Time Division Multiple Access (TDMA) are representative communication mechanisms that share a single channel in a wireless network.

Because of its simplicity and robustness, the CSMA technique is most commonly used in wireless network environments and does not require clock synchronization and overall network topology information. CSMA uses a carrier sensing technique to avoid packet collision problems between neighboring nodes of one hop distance. However, neighboring nodes that are more than two hops apart can not detect carriers from each other, so collision may occur. This problem is called the "hidden terminal" problem and can cause serious network performance degradation in CSMA based wireless networks.

The TDMA technique divides time into a plurality of time slots and controls frame transmission of adjacent nodes to be performed in different timeslots. Conventional TDMA schemes require arbitration nodes to efficiently schedule timeslots, and are not as adaptive as CSMA schemes when network topology changes frequently, and generally have low channel utilization and transmission delay compared to CSMA. However, since the TDMA technique is capable of contention-free transmission, the "hidden terminal" problem of CSMA can be naturally solved and efficient energy management is possible.

Unlike conventional wireless MAC protocols such as IEEE 802.11, where fairness, transmission delay, and bandwidth utilization are major performance evaluation factors, wireless sensor networks are composed of many battery-powered sensor nodes. This is an important factor in determining overall performance.

As described above, the main consumption factors of energy may be classified into packet collision, overhearing, control overhead, and idle listening.

In particular, in the case of the IEEE protocol of the ad hoc mode or the MAC protocol of the CSMA, each node has to wait most of the time in the idle listening mode to receive data, and 50 to 100 of the total energy consumed to receive the data. Consumes% on idle listening. In order to reduce energy due to collisions, overhearing and idle listening, the prior art has a duty cycle mode in which a node repeats an active mode and a sleep mode periodically according to a common schedule. Each node that operates and wakes up from the sleep mode to the active mode competes to gain access to the channel according to the CSMA / CA scheme.

Nodes sharing a common schedule in sleep / active duty cycle mode in a conventional wireless sensor network form a virtual cluster. In this case, the size of the virtual cluster may be defined by the number of nodes sharing the schedule and the hop distance between the nodes. If all nodes in the network share a common schedule, the network will form only one virtual cluster, and all nodes will sleep and activate at the same time. The size of the virtual cluster has a problem that it is difficult to adaptively cope with changes in the situation of the dynamic network. In addition, each node competes with each other in CSMA / CA to access a channel in an active mode, causing problems such as energy consumption and transmission delay due to exchange of control packets.

The present invention is designed to solve the above problems,

Minimize the size of the virtual cluster so that it consists only of arbitrary nodes and neighboring nodes with 1-hop neighbor distances, and allow uncompetitive channel access based on TDMA when the nodes in the virtual cluster are activated, resulting in the exchange of control packets. It aims to maximize the efficiency of limited network resources such as energy and bandwidth by minimizing consumption and transmission delay.

In the wireless sensor network of the present invention, the active sleep / active duty cycle method performs a handshake with a 1-hop distance neighbor node in a free competition period of a time frame to search for a 1-hop distance neighbor node, and performs an initial activation schedule. Selecting; And selecting one's own activation schedule by exchanging information about an activation schedule with a neighboring node one-hop distance in a non-competition period of the time frame.

In particular, searching for a 1-hop distance neighbor node by performing a handshake with a neighbor node of 1-hop distance may perform a 3-step handshake of a Beacon / Approval / ACK frame with the neighbor node of the 1-hop distance. And dynamically search for the 1-hop distance neighbor node.

In addition, performing a three-stage handshake of the Beacon / Approval / ACK frame includes generating a Beacon frame and broadcasting it to a 1-hop distance neighbor node, wherein the Beacon frame is a non-competition period of the time frame. It is characterized in that it contains information indicating whether or not preemption of the timeslots located within a certain range.

In addition, searching for a 1-hop distance neighbor node by performing a handshake with the 1-hop distance neighbor node may include obtaining information about an activation schedule of the 1-hop distance neighbor node and maintaining it in an activation schedule table. Characterized in that it comprises a step.

The activation schedule table may further include information about an identifier of a neighboring node in a 1-hop distance, a logical number of hops between itself and a counterpart node, and timeslots at which a node in a sleep mode switches to an active mode in the non-competition period. It is characterized by being.

In addition, in the non-competition period of the time frame, the step of selecting an activation schedule by exchanging information about an activation schedule with a neighboring node at a distance of 1-hop, may be performed in an active mode as an owner in a time slot corresponding to the initial activation schedule. Switching; And generating a beacon frame including information indicating whether the time slots located within a predetermined range are in a non-competition period of the time frame and broadcasting to a neighbor node.

In addition, in the non-competition period of the time frame, the step of selecting an activation schedule by exchanging information about an activation schedule with a neighboring node 1-hop distance may include: And receiving an approval frame including information indicating whether a preemption is received from the 1-hop distance neighbor node.

The non-competition section of the time frame may include a plurality of timeslots, and each timeslot includes a control section and a data transmission section.

Meanwhile, the sensor network system of the present invention relates to a sensor network system including a plurality of nodes implemented using an active sleep / active duty cycle method in the wireless sensor network according to any one of claims 1 to 8. All.

According to the present invention has the following effects.

The efficiency of channel reuse can be maximized because the size of the virtual cluster is minimized to consist only of arbitrary nodes participating in direct communication and neighbor nodes 1-hop away.

In addition, efficient node management is possible because nodes in the virtual cluster support contention-free channel access based on TDMA.

The present invention will now be described in detail with reference to the accompanying drawings. Here, the repeated description, well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention, and detailed description of the configuration will be omitted. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art. Accordingly, the shape and size of elements in the drawings may be exaggerated for clarity.

Conventional time division multiple access (TDMA) scheme statically assigns timeslots to nodes either by an arbitration node or in a distributed manner. In contrast, in the present invention, each node may autonomously select its initial activation schedule (AS) in cooperation with 1-hop neighbor nodes according to its own needs. The activation schedule (AS) refers to a time slot in which a node switches from a sleep mode to an active mode. To this end, each node defines an activation schedule table (hereinafter, referred to as an 'AS table') as shown in FIG. 1 and manages one-hop distance neighbor node information.

1 is a view showing an example of an AS table applied to the present invention.

Referring to FIG. 1, the 'macNodeID' attribute represents an identifier of a 1-hop distance neighbor node, and the 'macHopCount' attribute represents a logical hop number between itself and a counterpart node. The 'nextAS' attribute indicates a time slot in which a node in a sleep mode transitions to an active mode in a contention free period (CFP).

2 is a view for explaining a time frame structure in an active sleep / active duty cycle method according to the present invention.

The active sleep / active duty cycle method according to the present invention divides the time into time frames according to the time frame structure shown in FIG. 2, and the time frame competes to access a channel based on CSMA. : Contention Access Period) and a non-competition interval (CFP) that grants a single node access to a channel based on TDMA.

Each node performs a three-step handshake of the Beacon / Approval / ACK frame in the free-competition interval (CAP) of the time frame to dynamically discover one-hop distance neighbor nodes and select an initial activation schedule (AS). Follow the steps.

The non-competition period (CFP) of the time frame is composed of a plurality of timeslots, and each timeslot includes a control period (CP) called a control period and a data period (DP), which is a data transmission period.

The node activated in the corresponding timeslot performs a two-stage handshake of the Beacon / Approval frame in the control interval (CP) to select the next activation schedule (AS), that is, the next timeslot to switch from the sleep mode to the active mode. In addition, a node activated as an owner in the corresponding timeslot has an exclusive channel access right during the corresponding timeslot and transmits data in the data transmission section DP.

The active sleep / active duty cycle method requires accurate neighbor node information to reduce network overload, and the neighbor node information can be dynamically obtained in a free competition period (CAP) of a time frame.

The length of the time frame may be set fluidly according to the degree of mobility of the node. That is, if the dynamic network in which node movement is frequent, the length of the time frame should be set short. In the static network without node movement, the length of the time frame may be set as long as the life cycle of the node.

In FIG. 2, each timeslot is divided into CP and DP, and CP is divided into a plurality of minislots. The number of minislots is calculated as follows.

-Number of minislots = number of 1-hop neighbors of nodes transmitting Beacon frames + 2

3 is a conceptual diagram illustrating a process of searching for a dynamic neighbor node and selecting an initial activation schedule in a free competition section of a time frame.

Each node selects its initial activation schedule (AS) according to the 3-step handshake process of the Beacon / Approval (or NApproval) / ACK frame in the free contention interval (CAP) of the time frame as shown in FIG. 1-hop distance neighbor node information is obtained and maintained in an activation schedule table (hereinafter referred to as an 'AS table').

In the CAP, the 'Beacon frame' informs neighboring nodes of one-hop distance of the selected activation schedule (AS), and the 'Approval frame' is an activation schedule included in the 'Beacon frame'. ) Is used to authorize the use. The 'ACK frame' is used to solve the problem of losing the 'Approval frame' due to a collision when a plurality of 'Approval frames' are transmitted at the same time, and serves to inform that the 'Approval frame' has been successfully received.

4 is a view for explaining the structure of a Beacon, Approval (or NApproval), and ACK frame, Figure 5 is a view showing an example of the configuration of AS_window [WinSize].

4, the Beacon, Approval (or NApproval), and MHR (MAC Header) and MFR (MAC Footer) in the ACK frame have the same structure as the conventional IEEE 802.15.4 MAC protocol.

The 'Next Active Schedule (NAS) field' of the "Beacon frame" indicates a time slot in which the node transmitting the Beacon frame switches from the sleep mode to the active mode. Each node dynamically creates an AS_window [WinSize] when it selects its activation schedule (AS) and schedules one of the empty timeslots within the AS_window [WinSize] range, taking into account its data buffers or changes in current network conditions. Select with (AS).

More specifically, AS_window [WinSize] consists of bits indicating whether to occupy time slots located within the WinSize range, and if the bit is set to '1' it indicates that the corresponding timeslot has already been preempted by another neighbor node. If the bit is set to '0', it means that the corresponding timeslot has not already been preempted by another neighbor node. 'WinSize' means the maximum range size of the timeslot that the node can select as an AS. WinSize 'size can be flexibly adjusted according to the density of nodes distributed in the network. In the embodiment of the present invention, the default value is 16 (see FIG. 5). For example, if the density of nodes distributed in the network is high, the size of 'WinSize' will increase, and if the density of nodes distributed in the network is low, the size of 'WinSize' will decrease.

The "REPLY Order field" of the "Beacon frame" generates a "Beacon frame" in the non-competition interval (CFP) to prevent a collision that occurs when multiple neighbor nodes transmit an "Approval frame" in response to the "Beacon frame". It is set only when doing so, and indicates the order in which the "Approval frames" are transmitted. The 'REPLY Order field' contains a 'NN (n) field' and a plurality of 'Addr of Nn fields', the former representing the current number of its 1-hop neighbors, the latter the address of the 1-hop neighboring node. Point to. In order to reduce the network load, the 'REPLY Order field' of the 'Beacon frame' generated in the free competition section (CAP) is preferably set to Null.

The "Approval (or NApproval) frame" includes an 'AS_check_window field'. The node receiving the "Beacon frame" checks its AS table to generate AS_check_window [WinSize], and inserts the generated AS_check_window [WinSize] into the 'AS Check Window field' to generate an "Approval or NApproval frame". The "Approval or NApproval Frame" is unicast to the node that sent the "Beacon Frame".

The "ACK frame" has the same structure as the conventional MAC protocol.

6 and 7 are flowcharts illustrating a process of generating and transmitting an ACK frame in response to receiving an Approval or NApproval frame after a node generates and transmits a Beacon frame in selecting an initial activation schedule (AS). .

When the free competition section (CAP) of the time frame starts, all nodes initialize the CAP_TIMER () (S122) and then start time counting (S124). The timer of CAP_TIMER () is set to the length of the free competition interval (CAP) of the time frame in FIG. 2, and the end of the timer of CAP_TIMER () starts the end of the free competition interval (CAP) or the start of the non-competition interval (CFP) in the time frame. It indicates the end of the initial activation schedule (AS) selection step.

Referring, for the node N ₃ of FIG. 3 as an example, the node N ₃ is the initialization CAP_TIMER (), and generates a Beacon frame (S110). After generating the Beacon frame, the node N ₃ checks the channel state after waiting for random backoff (S120 and S126). Random backoff in step S120 reduces the collision problem due to simultaneous transmission of Beacon frames.

If the channel is empty as a result of checking in step S126, a Beacon frame is broadcasted to neighbor nodes, that is, node N ₂ and node N ₄ (S128), and in response to the approval from node N ₂ and node N ₄ . (Or NApproval) wait for reception of a frame (S130). On the other hand, if the channel is not empty as a result of the check in step 126, after waiting for random backoff, the channel state is checked again.

When node N ₃ receives an approval frame from nodes N ₂ and N ₄ (S134), it updates the AS_window by OR-biting its AS_check_window and its AS_window inserted into the AS_check_window field of the approval frame (S138), and then owns AS. The table is updated (S140).

Since AS_window and AS_check_window indicate whether or not the time slots within the WinSize range are occupied by themselves and their 1-hop neighbors, the result of the OR bit operation of the two variables is the result of the self and their 2-hop neighbors within the WinSize range. This will indicate the timeslot that the nodes are preempting.

If the node N ₃ receives the NApproval frame in step S134, the AS_check_window inserted into the AS_check_window field of the NApproval frame and its AS_window are updated by OR bit operation (S136), and the Beacon generation and transmission process is repeated.

Next, the node N ₃ generates and unicasts an ACK frame in response to the approval frame (S142, S144), and subsequently waits for reception of an approval (or NApproval) frame from another neighbor node (S130).

Referring to FIG. 7, the step S110 will be described in more detail. First, it is determined whether the AS_window exists (S112). If the AS_window already exists, the AS_window is updated (S115) after the AS_window already exists. One of the timeslots is selected as the activation schedule (AS) (S116). On the other hand, if AS_window does not exist, after generating AS_window (S114), one of the empty timeslots in AS_window [WinSize] is selected as the activation schedule (AS). In order to reduce the network load, the REPLY Order field generated in the free competition section (CAP) is set to Null (S117), and a Beacon frame is generated by setting MHR and MFR (S118).

FIG. 8 is a flowchart for describing a processing procedure when nodes N ₂ and N ₄ of FIG. 3 receive a Beacon frame from a neighbor node in a free competition period (CAP) of a time frame.

Referring to FIGS. 3 and 8, when nodes N ₂ and N ₄ receive a Beacon frame from node N ₃ , the nodes N ₂ and N ₄ check whether they have received the same Beacon frame from node N ₃ . (S210). For example, it is determined whether prior to using the node N ₃ is the location identifier (e.g., a source IP) has been received in the Beacon frame from the node N _3.

If the Beacon frame has been received from the node N ₃ before, it is determined whether the newly received Beacon frame is more recent than the previously received Beacon frame (S212). If the newly received Beacon frame is more recent than the previously received Beacon frame, the processing performed according to the process of FIG. 8 after the previous Beacon frame is invalidated, and the process moves to step S218 to perform the process of FIG. 8 again. If the newly received Beacon frame is not newer than the previously received Beacon frame in step S212, the Beacon frame received from the node N ₃ is discarded (S216).

If no Beacon frame has been received from node N ₃ before, node N ₂ and node N ₄ extract the NAS field value included in the Beacon frame received from node N ₃ (S218) and maintain it in its AS table. It is determined whether the same NAS field value exists in the AS table by comparing with the nextAS field value of each entity (S220).

As a result of the determination in step S220, if the same value as the NAS field included in the Beacon frame exists in the nextAS field of the AS table, the NApproval frame is generated (S228), otherwise, the own AS table is updated and an Approval frame is generated ( S222, S224).

In step S220, the same value as the NAS field in the nextAS field of the AS table means that the timeslot selected by the node N ₃ as the activation schedule has already been preempted by another neighboring node. That is, if node N ₃ and the neighbor node simultaneously activate data transmission in the same timeslot, it means that a collision occurs and smooth communication cannot be achieved. Therefore, to avoid this, node N ₃ needs to reselect another timeslot as its activation schedule (AS), which is used by the NApproval frame instead of the Approval frame. That is, the NApproval frame means that the node N ₃ does not allow the use of the activation schedule selected by the node, and the Approval frame means that the node N ₃ permits the use of the selected activation schedule.

Next, in order to reduce the collision, the node N ₂ and the node N ₄ check the channel state after waiting for a random backoff (S226) (S240). If at S240 step the channel is empty, the node N ₂ and the node N ₄ is waiting to receive the ACK frame to the node N ₃ transmitted to the node N ₃ for Approval (or NApproval) frame broadcast, and (S242), In response, (S244). If the corresponding ACK frame is received (S246), if the received ACK frame is not the corresponding ACK frame, it is discarded (S248). If the corresponding ACK frame is received, the process is terminated.

So far, the process of selecting each initial activation schedule by each node in the free competition interval (CAP) of the time frame has been described.

Hereinafter, an active sleep / active duty cycle process performed in the non-competition period CFP after the free competition period CAP will be described.

FIG. 9 is a diagram for explaining an example of an active sleep / active duty cycle process performed in a non-competition period (CFP) after the free competition period (CAP) ends in a time frame.

Each node in FIG. 9 switches from the active mode to the sleep mode when the CAP ends. In the non-competition period (CFP), each node continuously maintains the sleep mode, checks the AS table, and switches from the sleep mode to the active mode only in its own activation schedule and the activation schedule of neighboring nodes 1-hop distance.

9, node N ₁ , node N ₂ , node N ₃ , node N ₄ , and node N ₅ are t ₈ , t ₂ , t ₅ , t in the initial activation schedule selection step of the previous free competition interval (CAP). It is assumed that ₈ and t ₁₀ timeslots are selected as their activation schedules, and an AS table is configured based on these.

For example, node N ₂ switches to active mode as an owner in a t ₂ timeslot, where node N ₁ and node N ₃ switch to active mode as a non-owner. The node N ₃ switches to the active mode as the owner at the t ₅ timeslot, and at this time, the nodes N ₂ and N ₄ switch to the active mode as the non-owner. Here, the owner of the timeslot is a node having exclusive access rights of the channel during the timeslot, and the non-owner means a node which can only receive data. The non-owner is the owner's one-hop street neighbor. The node activated as the owner creates and broadcasts a Beacon frame.

10 and 11 are flowcharts illustrating a process of determining whether each node in the wireless sensor network switches from a sleep mode to an active mode at a boundary of a timeslot.

Hereinafter, the process of determining the mode switching is equally applied to all nodes constituting the wireless sensor network. Therefore, in order to facilitate understanding of the present invention, a process of determining whether the node N ₄ of FIG. 9 switches from the sleep mode to the active mode at the boundary of the timeslot will be described as an example.

When the timeslot starts, that is, when the non-competition section (CFP) starts, the node N ₄ checks its AS table (S310). The node N ₄ checks its AS table to determine whether it should switch to the active mode at the boundary of the corresponding timeslot (S320). For node N ₄ , referring to the AS table shown in FIG. 9, it is necessary to switch to the active mode in the t ₅ , t ₈ , and t ₁₀ timeslots. As a result of the determination in S310, if it is necessary to switch to the active mode at the boundary of the corresponding timeslot, it is determined whether the user should switch to the active mode as the owner or the non-owner to the active mode with reference to the AS table (S330). Steps S312 to S318 of FIG. 11 specifically illustrate a determination process for switching the active mode of FIG. 10 and a process of determining whether to switch to the active mode as the owner or to the active mode as the non-owner. For node N ₄ , we need to switch to active mode as the owner at t ₈ timeslot and to active mode as the non-owner at t ₅ timeslot and t ₁₀ timeslot.

As a result of the determination in step S330, if the owner needs to be switched to the active mode, that is, if t ₈ timeslot, node N ₄ generates a Beacon frame and broadcasts it to the neighbor node (S340).

As a result of the determination in step S330, if it is necessary to switch to the active mode as the non-owner, that is, if t ₅ timeslot and t ₁₀ timeslot, the node N ₄ receives the Beacon frame from the neighbor node, and then receives the corresponding Approval (or NApproval). ) Unicast the frame to the neighbor node (S350).

On the other hand, after checking the AS table in step S320, if the corresponding time slot is not a time slot for node N ₄ to switch to active mode, it initializes TIMESLOT_TIMER () (S326), counts the time by the length of the time slot, and then proceeds. It ends (S326).

FIG. 12 is a conceptual view illustrating a Beacon / Approval two-step handshake process for an active sleep / active duty cycle in a non-competition period (CFP) after the free competition period of the time frame is finished, and FIGS. 13 to 16 are FIGS. A flowchart for describing a process of generating and transmitting a beacon frame in any 12 nodes.

Hereinafter, the node N ₂ illustrated in FIG. 12 will be described as an example. In this case, it is assumed that the node N ₂ configures the AS table defined in FIG. 9.

According to the AS table defined in FIG. 9, the node N ₂ waking from the t ₂ timeslot determines its AS_window [st, et] range in consideration of the current timeslot t ₂ and WinSize (16), and the AS table. Check and generate an AS_window (S410). At this time, WinSize and size is 16, so the node N ₃ and the node N by ₁ time slot and t ₅ t ₈ time slots are reserved, respectively, such as a AS_window AS_window [0010010000000000] is generated. The process of generating the AS_window in step S410 may be achieved through steps S412 to S417 of FIG. 14. Where st = current_ts + 1, et = current_ts + WinSize, current_ts represents the current timeslot.

Next, node N ₂ selects one of timeslots not currently preempted in its AS_window [0010010000000000] generated in step S410 as its next activation schedule (AS) (S420). It is assumed here that node N ₂ has selected timeslot t ₁₀ as its next activation schedule. Node N ₂ indicates that time slot t ₁₀ has been selected as an activation schedule and is inserted into the 'NAS field' of the Beacon frame (S425), and the address of the 1-hop neighbor node in its AS table, that is, node N ₁ and node Extract N ₃ . In addition, the beacon frame is generated by inserting the addresses of the node N ₁ and the node N ₃ into the 'REPLY Order field' according to the order of extracting each node (S430). The process of setting the 'REPLY Order field' by extracting the address of the 1-hop neighbor node from its AS table in step S430 may be accomplished through steps S432 to S436 of FIG. 15.

As described above with reference to FIG. 2, each time slot is divided into a CP and a DP, and the CP is divided into a plurality of mini slots in a non-competition period (CFP) of the time frame. The node N ₂ broadcasts a Beacon frame in the first minislot of the CP (S435).

And node N ₂ is node N ₁ or node Wait for the reception of the approval frame or the NApproval frame from N ₃ (S440, S445). When the node N ₂ receives the approval frame in step S445, it updates its AS_window (S445) and waits for reception of the next approval frame until the CP section ends in the timeslot. If the node N ₂ receives the NApproval frame in step S445, it is recognized that the previously selected activation schedule (AS) has been preempted by another neighbor node, and as described above, the AS_check_window field included in the NApproval frame is used. After updating its AS_window (S460), the process of generating and transmitting the beacon is repeated (S470). The process of updating the AS_window in step S445 or step S460 may be accomplished through steps S462 to S465 of FIG. 16. In other words, the AS_check_window field and its own AS_window field included in the Approval frame or NApproval frame are updated by OR bit operation.

When the CP section ends (S446, S447), in the DP section, the node N ₂ exclusively accesses the channel and transmits a data packet. After the DP section ends, node N ₂ , node N ₁ , and node N ₃ switches from the active mode to the sleep mode and waits.

FIG. 17 is a flowchart illustrating a process in which nodes N ₁ and N ₃ of FIG. 12 generate a Approval (or NApproval) frame after receiving a Beacon frame from node N ₂ , and then transmit it.

When the Beacon frame is received from the node N ₂ , the nodes N ₁ and N ₃ extract NAS field values from the received Beacon frame (S510 and S520). The nodes N ₁ and N ₃ respectively check whether the NAS field values extracted from the Beacon frame are duplicated using their AS tables (S530 and S540). As a result of the determination in step S540, if the NAS field value of the Beacon frame exists in its AS table, a NApproval frame is generated (S545), and if the NAS field value of the Beacon frame does not exist in its AS table, an Approval frame is generated. (S547). At this time, the node N ₁ and the node N ₃ determine the range of AS_check_window [st, et] as described above, check their own AS table, and set AS_check_window [st, et].

Thereafter, the nodes N ₁ and N ₃ unicast the approval frame during the corresponding minislot of the CP according to the transmission order described in the REPLY Order field of the Beacon frame (S560 to S575). FIG. 18 is a diagram illustrating a configuration of an AS_check_window field included in an Approval frame when the node N ₃ transmits an Approval frame in response to a Beacon frame of the node N ₂ in FIG. 9. Node N ₃ extracts the ASs (ie timeslot t ₅ and timeslot t ₈ ) of its own and one-hop distance neighbor nodes from its AS table and sets the bits of AS_check_window [3] and AS_check_window [6] to 1 Set it.

On the other hand, when the node N ₁ and the node N ₃ receive the Beacon frame from the node N ₂ , it initializes the TIMESLOT_TIMER () (S512), counts the time by the length of the time slot, and ends the process (S514).

The present invention can be embodied as computer-readable codes on a computer-readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of computer-readable recording media may include ROM, RAM, CD-ROM, magnetic tape, floppy disk, and optical data storage. Also included are those implemented in the form of carrier waves (eg, transmission over the Internet). The computer readable recording medium can also be distributed over network coupled systems so that the computer readable code is stored and executed in a distributed fashion.

As described above, the best embodiment has been disclosed in the drawings and the specification. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a diagram illustrating an example of an active schedule table applied to the present invention.

2 is a view for explaining a time frame structure in an active sleep / active duty cycle method according to the present invention.

3 is a conceptual diagram illustrating a process of searching for a dynamic neighbor node and selecting an initial activation schedule in a free competition section of a time frame.

4 is a view for explaining the structure of the Beacon, Approval (or NApproval), and ACK frame.

5 is a diagram illustrating an example of a configuration of AS_window [WinSize].

6 to 7 are flowcharts illustrating a process of generating and transmitting an ACK frame according to reception of an Approval or NApproval frame after a node generates and transmits a Beacon frame in selecting an initial activation schedule (AS). .

FIG. 8 is a flowchart illustrating a processing process when an arbitrary node receives a Beacon frame from a neighbor node in a free contention period (CAP) of a time frame.

FIG. 9 is a diagram for explaining an example of an active sleep / active duty cycle process performed in a non-competition period (CFP) after the free competition period (CAP) ends in a time frame.

10 and 11 are flowcharts illustrating a process of determining whether each node in the wireless sensor network switches from a sleep mode to an active mode at a boundary of a timeslot.

FIG. 12 is a conceptual diagram illustrating a Beacon / Approval two-step handshake processing process for an active sleep / active duty cycle in a non-competition period (CFP) after the free competition period of the time frame is finished.

13 to 16 are flowcharts for describing a process of generating and transmitting a beacon frame in any node of FIG. 12.

FIG. 17 is a flowchart illustrating a process in which nodes N ₁ and N ₃ of FIG. 12 generate a Approval (or NApproval) frame after receiving a Beacon frame from node N ₂ , and then transmit it.

FIG. 18 is a diagram illustrating a configuration of an AS_check_window field included in an Approval frame when the node N ₃ transmits an Approval frame in response to a Beacon frame of the node N2 in the example of FIG. 9.

Claims (9)

An active sleep / active duty cycle method in a wireless sensor network, Performing a handshake with a one-hop distance neighbor node in a free contention period of a time frame, searching for a one-hop distance neighbor node, and selecting an initial activation schedule; And In the non-competition period of the time frame, exchanging information about an activation schedule with a neighboring node one-hop distance, and selecting an activation schedule thereof; Searching for the 1-hop distance neighbor node and selecting an initial activation schedule Selecting a first activation schedule using an activation schedule table; Broadcasting a beacon frame including information about the first activation schedule to the 1-hop distance neighbor node; And And updating an activation schedule table using an AS Check Window field included in the approval frame when an approval frame is received from the 1-hop distance neighbor node. The method according to claim 1, Searching for the 1-hop distance neighbor node and selecting an initial activation schedule Updating the activation schedule table using an AS Check Window field included in the NApproval frame when a NApproval frame is received from the 1-hop distance neighbor node; Selecting a second activation schedule using the updated activation schedule table; And And broadcasting a Beacon frame including information about the second activation schedule to the 1-hop distance neighbor node. The method according to claim 1, The Beacon frame Active sleep / active duty cycle method in a wireless sensor network, characterized in that it comprises information indicating whether the time slots located within a predetermined range in the non-competition period of the time frame. The method according to claim 1, Updating the activation schedule table And obtaining information on an activation schedule of the 1-hop distance neighbor node included in the approval frame and maintaining the information on the activation schedule in the activation schedule table. The method according to claim 4, The activation schedule table, Wireless sensor network comprising an identifier of a 1-hop distance neighbor node, a logical number of hops between itself and a counterpart node, and timeslots at which a node in sleep mode transitions to an active mode in the non-competition interval Active sleep / active duty cycle method in The method according to claim 1, In the non-competition period of the time frame, the step of selecting an activation schedule by exchanging information about an activation schedule with a neighboring node 1-hop distance, Switching to an active mode as an owner in a timeslot corresponding to the initial activation schedule; And Active sleep in the wireless sensor network, comprising the step of generating a Beacon frame containing information indicating whether the time slots located within a certain range in the non-competition period of the time frame to a neighboring node / Active duty cycle method. The method according to claim 1, In the non-competition period of the time frame, the step of selecting an activation schedule by exchanging information about an activation schedule with a neighboring node 1-hop distance, Receiving an approval frame from the 1-hop distance neighbor node including information indicating whether the time slots within a predetermined range are preempted in the non-competition period of the time frame. Sleep / Active Duty Cycle Method. The method according to claim 1, The non-competition section of the time frame, An active sleep / active duty cycle method in a wireless sensor network comprising a plurality of timeslots, each timeslot comprising a control interval and a data transmission interval. delete

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