KR100682450B1 - Method for reader collision avoidance using sensor nodes and apparatus thereof - Google Patents

Abstract

A method for preventing collision among readers by using a sensor node and a sensor reader node device applying the same are provided to reduce load of entire system with prevention of the collision among the readers by fusing the reader and the sensor node, and dividing the entire system according to a distance between the sensor nodes. A message transmitter(201) broadcasts a sensor information request message. A message receiver(202) receives a response signal of the request message from the sensor nodes(210) receiving the request message. A sensor information processor(203) sets the sensor nodes having response signal intensity over a predetermined level as neighboring nodes. The reader(204) reads a tag(230) in a non-collision state that the neighboring nodes do not read the tag, and the response signal includes an ID of the sensor nodes.

Description

Method for preventing collision between readers using sensor nodes and sensor reader node device to which the method is applied {Method for Reader Collision Avoidance using sensor nodes and Apparatus}

1A is a structural diagram of a collision avoidance system between readers using a sensor node.

1B illustrates an example of a combination of a sensor network and an RFID network.

2A is a block diagram of the present invention.

3 is a flowchart of the present invention.

4A is a detailed flowchart of a neighbor node configuration process of FIG. 3.

4B is a detailed flowchart of the reader collision checking process of FIG. 3.

4C is a detailed flowchart of the tag reading process of FIG. 3.

FIG. 4D is a flowchart of a process in which a management node of FIG. 3 manages collision of a leader using a sensor leader node information table.

5 illustrates an example of a signal flow diagram of FIG. 4A.

6 illustrates an example of the signal flow diagram of FIG. 4D.

7 is a graph showing the strength level of the RF signal according to the distance between neighboring nodes according to the present invention.

8 is a graph showing the throughput according to the number of sensor nodes for the present invention and the conventional anti-collision method.

9 is a graph showing the efficiency according to the number of sensor nodes for the present invention and the conventional anti-collision method.

10 is a graph showing throughput according to the range of neighboring nodes of the present invention.

The present invention relates to a system using a sensor node, and more particularly, to a collision avoidance method between readers using a sensor node and a sensor reader node device to which the method is applied.

Some RFID readers conventionally use the Aloha method to recognize tags and it does not take into account collisions between readers.

In addition, the conventional RFID reader anti-collision technologies include a colorwave algorithm and a Q learning algorithm. Colorwave has time slots to prevent collisions by dividing the time each reader reads. In addition, the Q learning algorithm prevents collision by assigning different frequencies used by the servers managing the readers.

All readers sharing time slots in the Colorwave algorithm must have time synchronization and have collision detection capabilities. In order to solve the time synchronization problem of the reader, a procedure and management for synchronization between the reader systems are required, which can bring a load on the entire system.

Also, the Q learning algorithm is applied only in a hierarchical environment consisting of a reader management server and a main server. The reader management server is a system for managing readers through the function of allocating the frequency of use of the reader, and the main server is a system for managing the reader management server. Therefore, the Q learning algorithm has a problem of frequency allocation, overhead of maintenance and management of the management system, and a problem of cost for building such a system.

Therefore, the conventional collision avoidance method between the leaders increases the load of the entire system, wastes a lot of resources in managing the system, and thus has a problem of lowering the throughput and efficiency of the system.

The first technical problem to be achieved by the present invention is to fuse the reader and the sensor node, and to divide the whole system according to the distance between the sensor nodes to prevent collision between the readers, thereby reducing the load of the entire system and resources to manage the system. The present invention provides a method for preventing collisions between readers using sensor nodes, which can prevent waste and detect collisions between readers, thereby improving throughput and efficiency of the system.

A second object of the present invention is to provide a sensor reader node device to which a collision avoidance method between readers using the sensor node is applied.

In order to solve the first technical problem, the present invention includes the steps of broadcasting a sensor information request message, receiving a response signal of the request message from the sensor nodes receiving the message, the strength of the response signal is It provides a method of preventing collision between readers using a sensor node comprising the step of setting the sensor nodes of a predetermined size or more as neighboring nodes, and if the neighboring nodes are in a non-colliding state.

In order to solve the second technical problem, the present invention provides a message transmitter for broadcasting a sensor information request message, a message receiver for receiving a response signal of the request message from the sensor nodes that receive the message, and the strength of the response signal. Provides a sensor reader node apparatus including a neighbor node setting unit configured to set sensor nodes having a predetermined size or more as neighbor nodes, and a reader unit reading the tag when the neighbor nodes are in a non-colliding state.

The present invention deals with a mechanism for RFID collision avoidance using a sensor network and specifically proposes a collision avoidance method and system structure. We propose an RFID sensor network by incorporating an RFID reader into a sensor node, and propose a mechanism to prevent the overload of the system using the strength of RF.

Hereinafter, with reference to the drawings will be described a preferred embodiment of the present invention.

1A is a structural diagram of a collision avoidance system between readers using a sensor node.

The system of FIG. 1A is composed of a sensor / reader (SR), a coordination node (CN), and a USN server (USR). SR is called sensor leader node and CN is called management node. Sensor reader node is a node that combines sensor node and RFID reader. It is a node that performs sensing function and tag recognition function and has reader collision prevention function.Managed node manages and maintains sensor reader node and connects with external network. A node that provides a node that performs synchronous operation for collision avoidance. USR can manage sensor reader nodes and management nodes and provide various functions to users. The communication between the sensor reader node and the management node can be made by IEEE 802.15.4.

1B illustrates an example of a combination of a sensor network and an RFID network.

FIG. 1B shows an example structure in which a sensor / RFID network is configured in a star topology around a management node, and a collision between readers is prevented by determining a collision range between readers using characteristics of RF of a sensor reader node. In FIG. 1B, the sensor / RFID network is configured in the form of a star topology, the communication distance between the sensor reader node and the management node is greater than 20 meters, and the distance that the reader can read the tags is less than 3 meters. The distance that a leader can affect other leaders is less than 6 meters.

2A is a block diagram of the present invention.

In FIG. 2A, the sensor nodes 210 are nodes existing outside the sensor reader node device 200 according to the present invention, and each of the sensor nodes 210 is a sensor reader node device 200 according to the present invention. It is configured to include. The management node 220 stores state information of the sensor nodes 200 and 210. The tag 230 stores information that each of the sensor nodes 210 wants to read.

The message transmitter 201 broadcasts a sensor information request message. Preferably, the message transmitter 201 includes an antenna for transmitting a radio signal such as an RF signal. Preferably, the message transmitter 201 converts the sensor information request message into an RF signal and transmits the RF signal.

The message receiver 202 receives the response signal of the request message from the sensor nodes 210 that have received the message. Preferably, the message receiver 202 may include an antenna for receiving a radio signal such as an RF signal.

Preferably, the response signal may include IDs of the sensor nodes 210.

The neighbor node setting unit 203 sets the sensor nodes whose strength of the received response signal is greater than or equal to a predetermined size as neighbor nodes. Preferably, the neighbor node setting unit 203 may include a memory device that stores information about the neighbor node. Preferably, the neighbor node setting unit 203 may include a nonvolatile memory device as a memory device.

Preferably, the neighbor node setting unit 203 may set IDs of the sensor nodes whose response signal strength is greater than or equal to a predetermined size as IDs of the neighbor nodes. Preferably, the neighbor node setting unit 203 measures the intensity of the response signal, and if the measured intensity is greater than or equal to a predetermined size, may store the ID included in the response signal in the neighbor node list.

Preferably, the neighbor node setting unit 203 uses the message transmitter 201 to read the tag 230 to the management node 220 that stores the state information of the neighbor node when the tag 230 is read. You can save the status information indicating that it is busy.

When the neighboring nodes are in a non-colliding state, the reader unit 204 reads the tag 230. Preferably, meaning that the neighboring nodes are in a non-colliding state may include a state in which the neighboring node does not read a tag. Preferably, the reader unit 204 may maintain a standby mode that does not lead the tag 230 for a predetermined time when the neighbor node leads the tag 230.

Preferably, if the reader unit 204 has a read request for the tag 230, the message transmitter 201 may transmit a reader conflict confirmation request message to the management node 220. Preferably, the message receiver 202 may determine that the neighboring node is in a non-collision state when the reader collision confirmation response message is received from the management node 220 in response to the reader collision confirmation request message.

Preferably, the state information stored in the management node 220 includes information on whether the neighbor node is in operation of reading the tag 230, and the management node 220 according to the state information, the leader node acknowledgment response message. Alternatively, one of the reader collision check error messages may be generated. Preferably, when the reader collision check error message is received from the management node 220, the reader unit 204 may maintain a standby mode which does not read the tag for a predetermined time. Preferably, the message transmitter 201 may transmit a reader end message to the management node 220 when the read by the reader 204 is completed. Preferably, when the management node 220 receives the reader termination message, the management node 220 may delete the sensor node that transmitted the reader termination message from the list of sensor nodes leading the tag 230.

2B is a block diagram of the management node 220 of FIG. 1A.

The message receiver 221 receives the reader collision confirmation request message and transfers the message to the reader collision processing unit 222.

The leader collision processing unit 222 checks the neighbor node distance and the collision target node by using the information of the sensor readers of the received message to confirm the collision between the readers. Through this, if there is a collision, and if there is a collision, the message transmitter 223 transmits a reader collision confirmation error message to the sensor reader node, and if there is no collision, a reader collision confirmation response message is transmitted. In this case, the collision target node refers to a sensor reader node in which a tag lead is activated among neighboring nodes of the sensor reader node requesting a collision. In addition, the sensor reader node transmits the reader end message to the management node after the tag read is completed, and the management node 220 which receives the message through the message receiver 221 changes the state information of the sensor reader node information to inactive.

Preferably, the reader collision processing unit of the management node may include a sensor reader node information table to manage and maintain state information of the sensor leader node, and may record the state of the sensor leader node by being activated and deactivated.

3 is a flowchart of the present invention.

First, when entering a new system, a sensor information request message is broadcasted (step 300). In operation 310, a response signal of the sensor information request message is received from the sensor nodes that receive the message. When the response signal is received, sensor nodes having a strength of the response signal greater than or equal to a predetermined size are set as neighbor nodes (step 320). Next, it is determined whether neighboring nodes do not read a tag in a non-conflicting state (S330). At this time, if the neighbor nodes are in a collision state, the above process is repeated again (step 330). At this time, if the neighbor nodes are in a non-collision state, the tag is read (step 340).

4A is a detailed flowchart of a neighbor node configuration process (steps 300-320) of FIG. 3.

First, when a read request for an RFID tag is received, a sensor information request message is broadcasted (step 400). Next, the sensor reader node that has sent the sensor information request message receives a response message from the sensor node that has received the message (step 410). Next, the signal strength is measured for each received response message, and information about the neighbor sensor reader node is generated (step 415). Next, in step S420, the neighbor node is stored in the storage medium of the sensor reader node. Finally, the sensor reader node that has sent the sensor information request message receives the response message of the neighbor node for a predetermined time and ends when the predetermined time elapses (step 421).

4B is a detailed flowchart of the reader collision checking process 330 of FIG. 3.

First, the sensor reader node transmits a reader collision check request message to the management node in the state of completing the neighbor node setting process (step 300-320) (step 431). The reader collision check request message includes IDs of neighboring sensor readers and respective signal strengths. Next, after receiving the response signal from the management node, the message is analyzed to determine whether the message is the reader collision confirmation response message (steps 439-440). Finally, if the received message is a reader collision confirmation response message, the reader is activated (step 441). Activating a reader means that the reader leads the tag.

Preferably, when the received message is a reader collision error message, the reader collision confirmation request message may be retransmitted to the management node. Preferably, the retransmission of the leader collision confirmation message may be made after a certain time has elapsed to prevent the collision between the readers in advance.

4C is a detailed flowchart of the tag reading process 340 of FIG. 3.

When the sensor reader node receives the reader collision confirmation response message, the sensor reader node activates the reader to read the tag (step 445). For example, tag reads can be made for 50 ms. When the tag read is finished, the termination confirmation message is transmitted to the management node to update the sensor reader node information table, and the state information of the sensor reader node is changed to an inactive state (step 446). At this time, the termination confirmation message includes the reader termination message described above.

4D is a flowchart of a process of a management node managing a collision of a leader using a sensor leader node information table.

In step 432, the management node receives a leader conflict confirmation request message. Upon receiving the reader collision check request message, the reader collision check request message is stored in the sensor reader node information table and the distance of the neighbor sensor reader node is checked using the signal strength included in the reader collision check request message (steps 433-434). Using the identified distance, a neighbor sensor reader node having a potential for collision of the reader is identified (step 435). If there is no target node that is active among neighboring sensor reader nodes that may be collided, a reader collision confirmation response message is sent to the sensor reader node (steps 436 and 437), and if there is an active node, a reader collision confirmation error message is transmitted. (Steps 436, 438).

5 illustrates an example of a signal flow diagram of FIG. 4A.

First, the sensor reader SR1 node retrieves information of a neighbor node. For this retrieval, the sensor information request message is broadcasted, and the neighboring nodes SR2 and SR3 that receive the message transmit the sensor information response message including the sensor ID. After receiving the response message, the sensor reader node SR1 analyzes the response message to check the RF strength and stores the sensor ID and the signal strength in the neighbor node information table. Similarly, the peripheral nodes SR2 and SR3 that have received the message of the sensor reader node SR1 also store the RF strength of the sensor reader node SR1 and the ID of SR1 in the neighbor node information table.

6 illustrates an example of the signal flow diagram of FIG. 4D.

The sensor reader (SR) node sends a reader collision check request message (RFID RC Check Request message) including information of the neighbor sensor reader node to the management node CN to request confirmation of whether the reader has collided. There are two cases, A) and B), depending on whether there is a collision.

Management node (CN) operates after checking the state of neighbor sensor reader node by using neighbor node information of sensor reader (SR) node included in reader collision check request message and sensor reader node information table of management node (CN). If there is no reader, a RFID RC Check Response message is transmitted and the state of the sensor reader node SR is activated.

The sensor reader node reads the tag when the sensor reader node that sent the reader collision check request message receives the RFID RC Check Response message. After reading the tag, the sensor reader (SR) node transmits an RFID end notification message to the management node CN to deactivate the state of the sensor reader node information table of the management node CN.

In addition, the management node CN compares the reader collision check request message with the activated sensor reader node list, and if there is an active node among neighboring nodes, the management node CN receives a reader collision error response message (RFID RC Erroe Response message). The acknowledgment message is sent to the sensor reader (SR) node. After receiving the reader collision error response message, the sensor reader node waits for a random time and retransmits the reader collision confirmation request message.

7 is a graph showing the strength level of the RF signal according to the distance between neighboring nodes according to the present invention.

7 is an experimental result of the RF signal strength used in the peripheral node discovery procedure. When discovering neighbor nodes, if all readers in the RF range of the sensor node are registered as neighbor nodes, only one reader can be read at a time in the whole system. To prevent this, reducing the range of neighboring nodes to a distance that would interfere with other readers can break a system into multiple zones. Assuming that the communication distance of the sensor node is more than 20m and the interference range of the reader is less than 6m, according to the above experiment result, if the limit of the neighbor node is limited to the node whose signal strength (LQI) is over 60, It can be utilized.

8 is a graph showing the throughput according to the number of sensor nodes for the present invention and the conventional anti-collision method.

If the reader decides to send a query once every 500 μsec while reading the tag, the result of Fig. 8 can be obtained. 8 is a comparison between the conventional anti-collision method Colorwave algorithm, Aloha algorithm without collision prevention and performance evaluation results according to the present invention.

As a measure for performance analysis, system throughput may be expressed as the number of successful queries of a reader generated in the entire system in unit time minutes. The query used here refers to the command the reader sends when reading the tag. The throughput is expressed by Equation 1 below.

In Fig. 8, the throughput of the present invention is the highest, and the throughput of the Colorwave algorithm, which is a conventional collision avoidance method, is shown next. Aloha algorithm that does not prevent collisions can be seen that throughput is not high due to collisions between readers and other causes.

9 is a graph showing the efficiency according to the number of sensor nodes for the present invention and the conventional anti-collision method.

The system efficiency is equal to the successful query divided by all the queries. The efficiency can be expressed by the equation (2).

In the present invention, the reader's query does not collide because other readers do not operate while the reader reads the tag. The efficiency is therefore almost 100%. In Figure 9, the efficiency of the present invention is shown to be near 100% similar to the theory. Although the efficiency of the conventional anti-collision method Colorwave algorithm is close to 1b00%, it is lower than the efficiency of the present invention. Aloha algorithm without collision avoidance is not efficient due to collisions between the readers and other causes.

10 is a graph showing throughput according to the range of neighboring nodes of the present invention.

There are experimental results for cases with LQI greater than 60 and above 40.

FIG. 10 shows the results of experiments comparing a minimum signal strength (LQI) value registered in a neighbor node list in a neighbor node establishment procedure with more than 60 and more than 40. FIG. If the LQI value is 60 or more, the range of neighbor nodes is 4 meters or less in radius, and if it is 40 or more, 6 meters or less. According to the present invention, it can be seen that as the number of readers increases, the throughput of the entire system increases. In addition, it can be seen that the throughput of the entire system increases as the range of neighboring nodes is limited.

Preferably, the collision avoidance method between readers using the sensor node of the present invention may be provided in the form of a computer-readable recording medium for executing on a computer.

The invention can be implemented via software. When implemented in software, the constituent means of the present invention are code segments that perform the necessary work. The program or code segments may be stored on a processor readable medium or transmitted by a computer data signal coupled with a carrier on a transmission medium or network.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary and will be understood by those of ordinary skill in the art that various modifications and variations can be made therefrom. However, such modifications should be considered to be within the technical protection scope of the present invention. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, according to the present invention, it is possible to reduce the load of the entire system and to manage the system by fusing the reader and the sensor node and dividing the entire system according to the distance between the sensor nodes to prevent collision between the readers. There is an effect to prevent resource waste and improve the throughput and efficiency of the system.

Claims (16)

Broadcasting a sensor information request message; Receiving a response signal of the request message from the sensor nodes that have received the request message; Setting sensor nodes of which the intensity of the response signal is greater than or equal to a predetermined size as neighboring nodes; And And reading the tag if the neighboring nodes do not read the tag. The method of claim 1, Receiving the response signal is And the response signal includes IDs of the sensor nodes. The method of claim 2, Setting as the neighbor node And setting IDs of sensor nodes whose strength of the response signal is greater than or equal to a predetermined size as IDs of neighboring nodes. The method of claim 1, The setting to the neighbor nodes is Measuring the intensity of the response signal; And And storing the ID included in the response signal in a neighbor node list if the measured intensity is greater than or equal to a predetermined size. The method of claim 1, Leading the tag And storing the state information indicating that the tag is in operation in the management node storing the state information of the neighbor node when the tag is read. Way. The method of claim 1, And if the neighbor node is in the state of reading the tag, maintaining a standby mode in which the tag is not read for a predetermined time. The method of claim 1, Leading the tag Transmitting a reader conflict confirmation request message to a management node that stores state information of the neighbor node; And determining that the neighboring node is in a non-colliding state when a reader collision confirmation response message is received from the management node. The method of claim 7, wherein Leading the tag If a reader collision check error message is received from the management node, the method further includes maintaining a standby mode which does not read the tag for a predetermined time. A message transmitter for broadcasting a sensor information request message; A message receiver configured to receive a response signal of the request message from sensor nodes that receive the request message; A neighbor node setting unit configured to set sensor nodes having a magnitude greater than or equal to a predetermined magnitude as neighbor nodes; And And a reader unit configured to read the tag when the neighboring nodes do not lead a tag. The method of claim 9, The response signal is And sensor IDs of the sensor nodes. The method of claim 10, The neighbor node setting unit And sensor IDs of sensor nodes whose strength of the response signal is greater than or equal to a predetermined size as IDs of neighboring nodes. The method of claim 9, The neighbor node setting unit And measuring an intensity of the response signal and storing the ID included in the response signal in a neighbor node list if the measured intensity is greater than or equal to a predetermined magnitude. The method of claim 9, The neighbor node setting unit And sensor state node indicating that the tag is in operation of reading the tag to a management node storing the state information of the neighboring node when the tag is read. The method of claim 9, The reader unit And if the neighboring node is reading the tag, maintaining the standby mode in which the tag is not read for a predetermined time. The method of claim 9, The message transmitter Transmitting a reader conflict confirmation request message to a management node that stores state information of the neighbor node, The message receiving unit And when the reader collision confirmation response message is received from the management node, determines that the neighboring node is in a non-colliding state. The method of claim 15, The reader unit And a reader collision check error message is received from the management node to the message receiving unit, and maintains a standby mode in which the tag is not read for a predetermined time.

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