KR20100006314A - Method for transmitting and receiving data using multi-channel in wireless sensor networks - Google Patents

Abstract

PURPOSE: A data transmission method through a multi channel including a basic channel and an addition channel in wireless sensor network is provided to receive an additional data message to an addition channel and receive the data message through the basic channel. CONSTITUTION: Sensor nodes performs time synchronization by receiving a control message from a sensor node(S10). The sensor nodes grasp the time slot occupied by the sensor nodes by using the information included in the control message. The sensor nodes select the time slot, transmit the sensor nodes and enters into a standby mode(S20). The sensor nodes attempt the reception of a broadcast message through the default channel(S40).

Description

Method for transmitting and receiving data using multi channel in wireless sensor networks

The present invention relates to a method for transmitting and receiving data through multiple channels in a wireless sensor network. In particular, the transmitting and receiving nodes use multiple channels to increase the limited bandwidth of the wireless sensor network. Receiving a data message through the additional channel, the additional data message to the additional channel, by transmitting and receiving data over a multi-channel in a wireless sensor network that does not interfere with the communication of other nodes proceeding data transmission and reception through the base channel will be.

In the proposed wireless sensor network, the multi-channel media access control protocols can be divided into protocols for allocating fixed network resources to each sensor node and protocols for newly allocating resources as necessary.

MMSN [Gang Zhou, Chengdu Huang, Ting Yan, Tian He, John A. Stankovic and Tarek F. Abdelzaher. MMSN: Multi-Frequency Media Access Control for Wireless Sensor Networks. INFOCOM, 2006] increased the bandwidth of the entire network by assigning one channel to each node, but allocating fixed channels to nodes limits the optimal use of each channel.

Chen Xun, Han Peng, He Qiu-sheng, Tu Shi-liang, Chen Zhang-long. A Multi-Channel MAC Protocol for Wireless Sensor Networks. In the media access control protocol proposed by In Proceedings of The Sixth IEEE International Conference on Computer and Information Technology (CIT), 2006.], the cluster header receives a transmission request message from cluster members and establishes a transmission / reception plan.

The plan is propagated to cluster members, and nodes send and receive data at fixed timings and channels. This protocol can increase the sleep time of the entire network, but has the disadvantage that the maximum bandwidth of the entire network depends on the number of transmit request messages that the cluster header can handle.

Since sensor nodes are usually located in a location that is not easily accessible to humans and are powered by a battery, it is very important to optimize the energy usage of the sensor nodes. To solve this problem, the existing media access control protocols for wireless sensor networks have focused on efficient energy use.

Recently, as the wireless sensor network is used in a wide range, the node density in the network is increasing, and some operating systems for the wireless sensor network enable several applications to operate within a sensor node.

This situation requires greater bandwidth than ever before in wireless sensor networks. Media access control protocols using only one channel do not guarantee smooth data transmission due to low bandwidth in high traffic situations.

The present invention was devised to solve the above-mentioned problems of the prior art, while transmitting / receiving nodes use multiple channels to increase the limited bandwidth of the wireless sensor network. Receiving a data message, the additional data message is sent to the additional channel, thereby providing a method for transmitting and receiving data over multiple channels in a wireless sensor network that does not interfere with the communication of other nodes proceeding data transmission and reception through the base channel. For that purpose.

In the wireless sensor network of the present invention proposed to solve the above problems and the constituent means for forming a data transmission and reception method through a multi-channel, in the wireless sensor network data transmission and reception method through a multi-channel, the sensor nodes for participating in the network Receiving a control message from peripheral sensor nodes within one hop distance and synchronizing time, Sensor nodes for participating in the network using the information contained in the received control message peripheral sensor node within two hop distance Identifying the time slots occupied by the mobile stations, selecting the available time slots and transmitting the available time slots to neighboring sensor nodes, and then entering a standby mode, the first time slot of the broadcast period in which the sensor nodes form a frame. Wake up at the beginning of this, the default Attempting to receive a broadcast message through a null; as a result of the attempt, sensor nodes that fail to receive the broadcast message enter a standby mode until their time slots present in a unicast interval begin; Sensor nodes that have received the broadcast message continue to broadcast on the base channel in the next time slots of the broadcast period until they fail to receive the broadcast message in the next time slots of the subsequent broadcast period. Sensor nodes attempting to receive a message and failing to receive a broadcast message enter a standby mode until their time slot existing in a unicast interval starts, and the sensor nodes are present in the unicast interval. Default in time slot of And receiving the data message transmitted by the transmitting nodes through the channel, and receiving the additional data message transmitted by the transmitting nodes through the additional channel.

The control message may include address information of a sensor node, time slot information occupied by itself, slot allocation vector information, sequence number originating from a sink node, and remaining time information of a frame for time synchronization. do.

In addition, the sensor nodes may be configured to perform time synchronization by setting their own timers as much as the remaining time of the frame by using the remaining time information of the frame for time synchronization included in the control message.

In addition, the sensor nodes perform an OR operation on the slot allocation vectors included in the control message received from the neighboring sensor nodes to form their slot allocation vector, and refer to the configured slot allocation vector thereof. This available time slot is selected.

In addition, the sensor nodes that have received the broadcast message may determine the remaining time of the frame calculated by their timer and the remaining time of the current frame included in the remaining time information of the current frame included in the broadcast message. The time synchronization is set by correcting the time synchronization by setting the averaged time to a timer.

In addition, after the sensor nodes receive the data message transmitted by the transmitting nodes through the base channel in their time slot in the unicast period, receiving the additional data message transmitted by the transmitting nodes through the additional channel After the sensor nodes receive the data message through the basic channel in their time slot, and then move to the additional channel in the next time slot of their time slot, the sensor nodes transmit their address information to the transmitting nodes. And transmitting, by the sensor node, the additional data message transmitted by the transmitting nodes through the additional channel.

According to the method for transmitting / receiving data through multiple channels in the wireless sensor network of the present invention having the above-mentioned problems and solutions, the transmitting / receiving nodes use multiple channels to increase the limited bandwidth of the wireless sensor network. Since the data message is received through the base channel in the time slot of and the additional data message is moved to and received from the additional channel, there is an advantage in that it does not interfere with the communication of other nodes performing data transmission and reception through the base channel.

In addition, since it listens only in its own time slot, there is an advantage of using energy efficiently.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of a method for transmitting and receiving data over a multi-channel in the wireless sensor network of the present invention having the above problems, means and effects.

1 is a flowchart illustrating a data transmission / reception method through multiple channels in a wireless sensor network according to an embodiment of the present invention. Referring to Figure 1 described in detail the procedure for transmitting and receiving data through a multi-channel in a wireless sensor network as follows.

First, after defining the important features and structure of the frame applied in the present invention, a method of transmitting and receiving data through multiple channels in a wireless sensor network will be described.

In the wireless sensor network proposed by the present invention, a data transmission / reception method through multiple channels is basically based on TDMA. Each sensor node owns a unique time slot within a 2-hop distance for data reception and powers up the radio transceiver for data reception only in that slot.

As a result, in order to access the receiving sensor nodes, several sensor nodes must use a carrier sense multiple access (CSMA) technique, but since each sensor node receives data only in its own time slot, it has a different destination node. Contention between transmitting nodes is eliminated. Thus, the energy consumption incurred during the competition is significantly reduced.

In addition, the frame structure used in the present invention is as shown in FIG. The time axis is divided into consecutive frames, and one frame consists of a broadcast period and a unicast period. In addition, there are several time slots in each section.

The length of the time slot is defined as the time at which one message can be received. Since each sensor node has a distributed time to turn on the radio transceiver, all nodes have to wait after turning on the radio transceiver in the first time slot of the broadcast interval to receive the broadcast message.

Since the present invention uses multiple channels simultaneously, the sender and receiver must agree on the timing as well as the radio channel over which data is to be exchanged. This requires in the present invention the presentation of a time synchronization technique between sensor nodes. The time synchronization scheme proposed by the present invention does not synchronize the system timer maintained by each sensor node, but synchronizes the sensor nodes by exchanging the remaining time of the current frame. This technique can be easily implemented by adjusting the expiration time of timer events maintained by each sensor node.

Referring to the data transmission and reception method through a multi-channel in the wireless sensor network of the present invention having the above important features and frame structure as follows.

First, sensor nodes to join the network must perform time synchronization after powering on. Each sensor node exchanges information for time synchronization with each other in order to perform time synchronization. The information for time synchronization is the remaining time of the current frame, and the remaining time information of the frame is transmitted and received by each sensor node through a control message described later.

Therefore, the sensor nodes for participating in the network receive a control message from the neighboring sensor nodes within one hop distance to perform time synchronization (S10). As shown in FIG. 4, the control message includes address information of a sensor node, time slot information occupied by itself, slot allocation vector information, order information originating from a sink node, and remaining time information of a frame for time synchronization. Include.

The control message is a broadcast message transmitted in a broadcast period of a frame. Therefore, the control message is transmitted and received only in the broadcast period, not in the unicast period.

The broadcast message including the control message transmits and receives each sensor node only during the broadcast period, and the sensor node to transmit the broadcast message competes with other sensor nodes through a back-off setting. .

As described above, each sensor node receives time remaining information of a frame included in a control message, which is a broadcast message, and performs time synchronization. Specifically, the sensor nodes perform time synchronization by setting their own timers by using the remaining time information of the frame for time synchronization included in the control message as the remaining time. When the remaining time of the frame set in the timer ends, each sensor node can know that a new frame is started, and the time synchronization is performed because the remaining time of the frame set in the timer of each sensor node is approximated. .

After each sensor node performs time synchronization as described above, the time slots occupied by neighboring sensor nodes within 2 hop distances are acquired by the sensor nodes for joining the network using the information included in the received control message. Identify and transmit their available time slots to neighboring sensor nodes (S20).

The control message received by the sensor nodes includes time slot allocation vectors maintained by each sensor node. Using these time slot allocation vectors, each sensor node can identify the time slots occupied by neighboring sensor nodes within a two hop distance.

Specifically, each sensor node collects a slot allocation vector from peripheral sensor nodes for a predetermined time. The slot allocation vector is maintained by each sensor node, and stores information on a time slot used within one hop distance from its sensor nodes.

Therefore, when a specific sensor node receives a time slot allocation vector from sensor nodes that are within one hop distance from it, the time that the sensor nodes that are within one hop distance are also used by the sensor nodes within one hop distance from itself Since the slot information is stored in the time slot vector, the specific sensor node can finally grasp all the time slots occupied by the sensor nodes that are two hops away from it.

As described above, when time slots occupied by neighboring sensor nodes within two hops of the sensor node are identified, they are stored in the time slot allocation vector maintained by the sensor node. Meanwhile, the sensor node may know the time slots that are not used by neighboring sensor nodes with reference to the time slot allocation vector, and thus, may determine and select the available time slots.

Each bit value of the slot allocation vector indicates whether a time slot is used. For example, if the bit value is "1", the corresponding time slot is used. If the bit value is "0", the corresponding time slot is not used.

As described above, the slot allocation vector is maintained by each sensor node, and is transmitted in a control message when transmitted to neighboring sensor nodes. That is, the slot allocation vector is included in a control message which is a broadcast message transmitted in a broadcast period and transmitted to neighboring sensor nodes.

Then, the sensor nodes perform an OR operation on the slot assignment vectors included in the control message received from the neighboring sensor nodes to form a slot assignment vector held by the sensor nodes. With reference to the slot allocation vector configured as described above, each sensor node can identify all the time slots occupied by the sensor nodes within two hops from the node, and can select the available time slot.

As described above, the slot allocation vector and the time slot information that can be occupied by collecting the remaining time information of the frame set in the time synchronization process and the slot allocation vector of the surrounding sensor nodes are broadcast in the broadcast period of the frame. It can be sent to surrounding sensor nodes in a cast message.

As above, the sensor nodes that configure their slot allocation vector and select their available time slots enter standby mode until the broadcast period of the next frame begins.

The sensor nodes entering the standby mode determine whether the first time slot of the broadcast period starts (s30). If it is determined that the first time slot of the broadcast period starts, the sensor nodes wake up.

When the first time slot of the broadcast period constituting the frame starts, and the time-synchronized sensor nodes wake up, attempts to receive a broadcast message using a basic channel among multiple channels (s40). The channel applied in the present invention is a multiple channel consisting of a basic channel and an additional channel.

As a result of attempting to receive the broadcast message through the basic channel as described above, the sensor nodes that do not receive the broadcast message in the first time slot of the broadcast interval no longer wait to receive the broadcast message and are not unicast. The standby mode is entered until their time slot existing in the interval starts (s50 and s70).

On the contrary, as a result of attempting to receive a broadcast message through the basic channel, the sensor nodes that receive the broadcast message in the first time slot of the broadcast interval wait for transmission and reception of the broadcast message in the next broadcast time slot. do.

That is, the sensor nodes that have received the broadcast message continue to broadcast through the base channel in the next time slots of the broadcast period until they fail to receive the broadcast message in the next time slot of the subsequent broadcast period. Attempt to receive the cast message (s60).

While attempting to receive a message in the next time slots of the broadcast interval, the sensor nodes that fail to receive the broadcast message enter a standby mode until their time slot existing in the unicast interval starts (s70). . In addition, when the broadcast message is received in all the time slots of the broadcast period, it enters the standby mode until its time slot existing in the unicast period starts.

Meanwhile, the sensor nodes that have received the broadcast message in the time slot of the broadcast period use the remaining time information of the frame included in the control message corresponding to the broadcast message to the remaining time of the frame held by the sensor node. To correct.

Specifically, the sensor nodes that have received the broadcast message average the remaining time of the frame calculated by their timer and the remaining time of the current frame included in the control message corresponding to the broadcast message. The time synchronization is corrected by setting the obtained time back to the timer.

Figure 3 is a schematic diagram for explaining the time synchronization correction technique proposed in the present invention. T1 and T2 represent the remaining time of the current frame of sensor node 1 and sensor node 2, respectively. After receiving the time synchronization message from the sensor node 1, the sensor node 2 calculates an average remaining time and matches its remaining time to that time. As a result, the starting points of the next frame periods of the two sensor nodes are close.

This periodic correction of time synchronization is due to the need for additional time synchronization error correction, since crystal oscillators used in sensor node platforms are generally cheap and inaccurate.

As described above in step S70, the sensor nodes that are in the standby mode until their time slots in the unicast period determine whether the current time slot is their time slot (s80). As a result of the determination, if it is not its time slot, it continues in the standby mode until its current time slot is its time slot.

On the contrary, when it is determined that the current time slot is a time slot of its own, the sensor nodes receive data messages transmitted by the transmitting nodes through the base channel in their time slots present in the unicast period. Subsequently, additional data messages transmitted by transmitting nodes are continuously received through the additional channel (s90). As a result, sensor nodes receive data messages over additional channels as well as the base channel. That is, continuous data messages are received through multiple channels.

In the process of receiving the additional data message transmitted by the transmitting nodes through the additional channel after receiving the data message transmitted by the transmitting nodes through the basic channel in the time slot of the sensor nodes in the unicast period, Move to receive a data message in the next time slot of its own time slot.

Specifically, after the sensor nodes receive the data message through the base channel in their time slot, they move to the additional channel in the next time slot of their time slot to receive the next consecutive data message. Then, the sensor nodes transmit a message containing their address information to the transmitting nodes to inform the transmitting nodes that they are waiting to receive data by moving to an additional channel in the next time slot of their time slot. . Then, the transmitting nodes transmit an additional data message through an additional channel, and the sensor nodes receive the additional data message transmitted by the transmitting nodes through the additional channel.

As described above, the exchange of the first message of the unicast message transmitted and received in the unicast period is performed in the basic channel. The sensor nodes change the frequency from their own unicast time slot to the base channel and wait for receiving a message.

Sensor nodes that have a unicast data message to send to the corresponding sensor node participate in competition through CSMA after changing the frequency to the same channel (base channel). If only one channel is used, the sensor node can receive only one unicast data message in one frame period.

In order to increase the reception bandwidth of the limited sensor node, the present invention proposes a channel shifting technique that can use multiple channels. A detailed description with reference to the accompanying FIG. 5 is as follows.

In FIG. 5, f1 is a basic channel, and the rest f2 to f4 are additional channels. In other words, assume that four multiple channels are available. If the sensor node receives a unicast data message on the base channel f1, it changes frequency to the next channel f2 in the next time slot for subsequent message reception.

Nodes with unicast data messages to be sent to the corresponding sensor node also participate in a race to move to the same channel f2 and send the message again. In this way, successive unicast data messages can be delivered up and down the channel.

One important thing to consider in this method is how to inform the transmitting sensor nodes that have lost their first contention that the receiving sensor node will remain in a waiting state after moving the channel in the next time slot. In the present invention, the receiving sensor node transmits a short message containing the address of its sensor node to the transmitting sensor node at the beginning of the time slot to inform that it is waiting for continuous message reception.

If the receiving sensor node once again summarizes the process of receiving data messages from a plurality of transmitting sensor nodes as follows.

In the unicast period, each node can receive unicast data messages only in its own unicast time slot. Transmitting sensor nodes that hold data messages to send to the receiving sensor node participate in competition through the setting of a back-off timer. The transmitting sensor node that has won the competition succeeds in transmitting the data message.

If only one channel is used, the transmission sensor nodes in contention have to retry in the next frame period, resulting in a large delay in data message transmission. Thus, in the present invention, transmitting sensor nodes that compete with the receiving sensor node move to a new additional channel in the next time slot.

This is because other sensor nodes may receive data messages on the base channel of the next time slot, moving the channel to avoid this. Transmitting sensor nodes that have moved to a new additional channel may once again compete, and the transmitting sensor nodes that have competed may transmit data messages by moving the channel again in the next time slot.

Hereinafter, the experimental results for the performance verification of the present invention.

In order to verify the performance of the present invention, the operating system for the sensor network in the TmoteSky sensor node platform is RETOS [H. Cha, S. Choi, I. Jung, H. Kim, H. Shin, J. Yoo, C. Yoon. RETOS: Resilient, Expandable, and Threaded Operating System for Wireless Sensor Networks. The Sixth International Conference on Information Processing in Sensor Networks (IPSN 2007).

As in the present invention, in implementing data transmission and reception through multiple channels in a wireless sensor network based on TDMA, since the most important is time synchronization, the error of the time synchronization scheme is first measured. The measurement results are shown in FIG.

A total of 20 sensor nodes were used, and the average number of nodes within 1-hop distance of each node was 4.5. Each node sends a message for time synchronization once every eight seconds, with an average time error of 1.65 ticks. Since we used a crystal oscillator with a period of 32.768 kHz, one tick equals 1/32 ms. This error value is sufficient to implement a TDMA based media access control protocol in a widely used sensor node platform.

The performance of the channel shift scheme required for using multiple channels in the present invention is shown in FIG. All nodes send a message to a receiving node once per second, and the number of transmitting nodes is changed from 1 to 9.

For comparison, random access based low power listening (LPL) [A. El-Hoiydi, "Aloha with Preamble Sampling for Sporadic Traffic in Ad Hoc Wireless Sensor Networks.", IEEE International Conference on Communications (ICC), 2002.], and having a similar frame structure to the present invention, but using one channel. Crankshaft, a media access protocol [G. Halkes and K. Langendoen. Crankshaft: An Energy-Efficient MAC-Protocol For Dense Wireless Sensor Networks. EWSN07, 2007.].

As can be seen in Figure 7, due to the limited reception bandwidth of the receiver, the transmission success rate of the Crankshaft is sharply lowered when the number of transmitting nodes exceeds three. LPL also fails to achieve high transmission success rates due to the use of long preambles to wake up the receiver.

On the other hand, in the present invention, even if the number of transmitting nodes increases, there is no significant change in the transmission success rate. This is due to the fact that nodes in contention can move channels and attempt to retransmit in the next time slot.

1 is a flowchart illustrating a method for transmitting and receiving data through multiple channels in a wireless sensor network according to an embodiment of the present invention.

2 is a structure of a frame applied to the present invention.

3 is a schematic diagram for explaining correction of time synchronization according to an embodiment of the present invention.

4 is a structure of a control message applied to the present invention.

5 is a schematic diagram illustrating a channel movement method for multi-channel use according to an embodiment of the present invention.

6 is a result table of applying time synchronization according to an embodiment of the present invention.

7 is a graph illustrating the performance of a channel movement scheme for multi-channel use according to an embodiment of the present invention.

Claims (6)

In the method of transmitting and receiving data through multiple channels in a wireless sensor network, Sensor nodes for joining the network to receive a control message from peripheral sensor nodes within one hop distance to perform time synchronization; Sensor nodes for participating in the network use the information contained in the received control message to identify time slots occupied by neighboring sensor nodes within a 2-hop distance, and select the available time slots for the peripherals. After entering to the sensor nodes, entering a standby mode; Waking at the beginning of the first time slot of the broadcast period composing the frame, and attempting to receive a broadcast message through a basic channel; As a result of the attempt, the sensor nodes that failed to receive the broadcast message enter a standby mode until their time slots existing in the unicast period start, and the sensor nodes that receive the broadcast message receive subsequent broadcasts. Continue to receive the broadcast message on the base channel in the next time slots of the broadcast interval until the reception of the broadcast message in the next time slots of the cast period, and stop receiving the broadcast message. Sensor nodes that have failed to perform enter standby mode until their time slot existing in the unicast period starts; And receiving, by the sensor nodes, a data message transmitted by the transmitting nodes through a basic channel in a time slot of the sensor nodes, and receiving an additional data message transmitted by the transmitting nodes through an additional channel. Method of transmitting and receiving data through multiple channels in a wireless sensor network, characterized in that. The method according to claim 1, The control message may include address information of a sensor node, time slot information occupied by itself, slot allocation vector information, sequence number originating from a sink node, and remaining time information of a frame for time synchronization. Method of transmitting and receiving data through multiple channels in the sensor network. The method according to claim 2, In the wireless sensor network, the sensor nodes perform time synchronization by setting their own timers as the remaining time of the frame by using the remaining time information of the frame for time synchronization included in the control message. How to send and receive data through. The method according to claim 2, The sensor nodes perform OR operation on slot assignment vectors included in control messages received from neighboring sensor nodes to form their slot assignment vector, and refer to the configured slot assignment vector to enable them to be used. A method of transmitting and receiving data through multiple channels in a wireless sensor network, characterized in that the time slot is selected. The method according to claim 3, The sensor nodes that have received the broadcast message average the remaining time of the frame calculated by their timer and the remaining time of the current frame included in the remaining time information of the current frame included in the broadcast message. A method of transmitting and receiving data through multiple channels in a wireless sensor network, wherein the time synchronization is corrected by setting the obtained time to a timer. The method according to claim 1, After the sensor nodes receive the data message transmitted by the transmitting nodes through the basic channel in their time slot existing in the unicast period, receiving the additional data message transmitted by the transmitting nodes through the additional channel, After the sensor nodes receive the data message through the basic channel in their time slot, moving to the additional channel in the next time slot of their time slot, the sensor nodes are sent to the transmitting nodes their address information Transmitting the included message; receiving the additional data message transmitted by the transmitting nodes through the additional channel; and receiving the additional data message through the multiple channels in the wireless sensor network. .

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