KR100897413B1 - Device and method for perceiving location of target - Google Patents

Abstract

The present invention relates to an apparatus and method for overcoming the difficulty of visual synchronization required in a wireless sensor network and recognizing the position of a tag provided on a target. The present invention comprises the steps of (a) receiving a signal transmitted from a tag provided in the target at the master node; (B) receiving the transmitted signal at the master node via at least one sensor node; And obtaining a time difference between steps (a) and (b) to obtain a position of the target. Therefore, according to the present invention, by detecting the position of the target without visual synchronization between the sensor and the tag in the wireless sensor network, the efficiency and practicality of the wireless sensor network are increased.

Tag, Master Node, Sensor Node, Latency

Description

DEVICE AND METHOD FOR PERCEIVING LOCATION OF TARGET}

1 is a diagram illustrating a delay of a signal inside a sensor.

2 is a view showing an embodiment of an apparatus for detecting a position of a target according to the present invention;

3 is a flowchart of an embodiment of a method for detecting a position of a target according to the present invention.

<Explanation of symbols for the main parts of the drawings>

100, 200: tag 210: master node

222: first sensor node 224: second sensor node

226: third sensor node

The present invention relates to an apparatus and method for detecting a position of a target, and more particularly, to an apparatus and method for recognizing the position of a tag provided on a target, overcoming the difficulty of visual synchronization required in a wireless sensor network.

The technical field to which the present invention belongs is a wireless sensor network, a visual synchronization technology, a location recognition system. Specifically, wireless network design technology, signal processing technology, synchronization technology, and the like may be related. The wireless communication technology used in the present invention is ultra wideband (UWB). BACKGROUND OF THE INVENTION A technology relating to a location recognition system based on a wireless sensor network has been reported in many patents. For example, U.S. Patent No. In 6119013 (enhanced time-difference localization system), the position of a moving node is determined using the arrival time of the radio wave and the reception angle of the radio wave. However, this method has the disadvantage of still requiring visual synchronization between the sensors.

As another method, there is a method of using a position recognition system through visual synchronization between sensors. However, this method has a disadvantage in that a lot of equipment is required for visual synchronization.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an apparatus and method for detecting a position of a target without visual synchronization between a sensor and a tag in a wireless sensor network.

Another object of the present invention is to increase the efficiency and practicality of a wireless sensor network by sensing the position of a target without visual synchronization.

In order to achieve the above object, the present invention provides a method comprising the steps of: (a) receiving a signal transmitted from a tag provided on a target at a master node; and (b) receiving the transmitted signal via at least one sensor node. It provides a method for detecting the position of the target comprising the step of receiving at the master node and obtaining the time difference between the steps (a) and (b).

Here, the method for detecting the position of the target further includes the step of obtaining a delay time of the signal at the sensor node in advance.

And, in step (a), it takes time for the signal transmitted from the tag to reach the master node and internal delay time of the master node, and in step (b), the signal transmitted from the tag includes The sum of the time to reach the sensor node and the internal delay time of each sensor node is taken.

In addition, the transmission or reception of the signal is performed in a wireless sensor network of any one of UWB, WLAN, Zigbee or RFID.

In addition, the step of obtaining the position of the target is performed based on the TODA.

According to another embodiment of the present invention, a tag provided in the target; A master node for receiving a signal transmitted from the tag; And at least one sensor node receiving the signal and transmitting the signal to the master node.

Here, at least one of the master node and the sensor node is delayed in the signal.

The apparatus for detecting a position of the target further includes a determination unit for obtaining a delay time of the signal at the master node and the sensor node to obtain a position of the target.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can specifically realize the above object will be described.

The same components as in the prior art are given the same names and the same reference numerals for convenience of description, and detailed description thereof will be omitted.

In the present invention, in the wireless network, by overcoming the difficulty of time synchronization by calculating the internal delay time of the sensor hardware equipment. To track the position of a moving object in a wireless sensor network, you need a tag attached to the moving object. The tag is attached to a person, robot or other object and transmits the tag's unique radio signal to sensors distributed in the surrounding space. Sensors distributed in the ubiquitous space calculate the position of the tag by measuring the strength of the signal from the tag or the direction of signal reception.

The method of determining the position of the tag using the signal strength is called received signal strength (RSS), and the method of tracking the location by measuring the direction in which the radio wave is received is called angle of arrival (AOA). The method of measuring position by calculating the time taken while arriving at the sensor is called time of arrival (TOA). In general, RSS or AOA is used for WLAN / RFID or ZigBee, which is a communication system based on modulation / demodulation method, and TOA is used for UWB system that transmits signals by an extremely short impulse method.

However, in the case of RSS or AOA, since the positional accuracy is remarkably degraded, a TOA-based position tracking system using UWB has recently been researched and developed with much interest. However, in the case of TOA, the time synchronization between tags and sensors is absolutely necessary, and this time synchronization requires precision of several nanometers or up to hundreds of pico seconds. There are many difficulties. Therefore, as an alternative, a method of using a time difference of arrival (TDOA) using a difference in time of arrival of signals in two or more sensors has been studied.

In other words, when TDOA is used, the time synchronization between the tag and the sensor is not necessary, and only the time synchronization between the sensors is required, thereby increasing the practicality of the system design. However, this TDOA method also has many practical limitations because it must solve the difficult problem of visual synchronization between sensors. The present invention proposes a new TDOA-based location tracking system concept and method that does not require synchronization between sensors. In the present invention, in order to increase the clarity of the invention will be described with respect to the sensor network based location tracking system using UWB. However, if it is possible to grasp the transmission and reception time of the wireless signal with a high accuracy at a short distance indoors, the idea proposed in the present invention can be extended to other wireless sensor network system in addition to the UWB system.

1 is a diagram illustrating a delay of a signal inside a sensor. Referring to Figure 1 describes the delay of the signal inside the sensor as follows. The sensor cannot transmit the radio wave at the same time as it receives the signal. After receiving the signal, the sensor goes through a series of internal processing. In FIG. 1, a tag included in a sensor receives a radio signal at t ₁ , undergoes internal processing and a hardware delay, and then transmits a signal recognition signal to t ₂ .

In view of the internal delay time described above, the present invention proposes a method of determining the position of a moving object by calculating a unique internal processing and delay time of each sensor. Here, it is assumed that the internal delay time of each sensor is fixed with some accuracy. And even if a slight error exists, it is reasonable to assume that the internal delay time is fixed since it is an error that is acceptable in terms of practical operation.

2 is a view showing an embodiment of an apparatus for detecting a position of a target according to the present invention. Referring to Figure 2 describes an embodiment of the position sensing device of the target according to the present invention.

2 illustrates a structure of tracking a tag through initial time calibration of a wireless sensor network system. For example, in FIG. 2, a tag received from a master node 210, a first node Node-1, 222, a second node Node-2, 224, and a third node Node-3, 226. Using the transmission signal of 200, the position of the target equipped with the tag is determined by the TOA or TDOA method. In addition, although three sensor nodes are used in FIG. 2, at least one sensor node may be used, and as the number thereof increases, the position may be accurately determined, but the installation cost becomes complicated and the structure becomes complicated.

In the present embodiment, the signal of the tag 200 is transmitted to each sensor node and each sensor node notifies the master node 210 that the signal of the tag has been received, and records the time when these signals arrive at the master node. Determine your location. That is, in this embodiment, there is no need for visual synchronization between the sensors.

3 is a flowchart of an embodiment of a method for detecting a position of a target according to the present invention. Referring to Figure 3 describes an embodiment of the method for detecting the position of the target according to the present invention.

First, in this embodiment, an initial calibration method through four steps is required.

The first tag transmits a radio wave (impulse in the UWB system) (S310), the second master node receives a signal (referred to as a signal reception) (S320), and the third sensor node receives radio waves of the tag, After receiving the radio wave of the tag from the sensor nodes, and transmits a confirmation signal, the master node receives and records the confirmation signal of each sensor node (referred to as the reception of the b signal) (S330). Finally, the position of the target with the tag is obtained from the time difference between the a signal and the b signal (S340).

The apparatus and method for detecting a position of the target described above will be described in detail as follows. t0 is the time when the signal is sent from the tag, t ₁ ⁰ is the time required for the signal to travel from the tag to the master, t _m ⁰ is the delay time to process the signal arriving at the master from the tag inside the master. , t ₁ ⁱ is the time required for the signal to travel from the tag to node-i, t _d ⁱ is the time required to receive and transmit the tag's signal at node-i, i.e. the internal delay time, t ₂ ⁱ Is the time required for the signal to travel from node-i to the master, t _m ⁱ is the delay time for processing the signal from node-i internally in the master, and T ₀ is the signal arriving directly from the tag at the master. Received time, T _i is the time when the signal received via the node- _i from the tag to the master.

Here, the time it takes for the signal to originate from the tag and arrive at the master is defined by the following equation.

t ₀ + t ₁ ⁰ + t _m ^o = T ₀

Here, the time taken for the signal to arrive at the master through the node-i from the tag is expressed by the following equation.

t ₀ + t ₁ ⁱ + t _d ⁱ + t ₂ ⁱ + t _m ⁱ = T _i , i = 1, ..., N

As described above, it is assumed that the time taken by the master node to process the signal (an internal delay occurs in the process of recording the received time after physically receiving the signal) is constant. Since t _m ⁰ is almost identical to t _m ⁱ , we can see that t ₂ ⁱ is constant because each node is fixed, and t ₂ ⁱ can be found in advance because the distance between each node is known. .

The time calibration initially required in the UWB system of this embodiment calculates an internal delay time processed in each node and uses it for future tag positioning. To do this, the tag is initially installed at a location where the tag is known, and this information is used to calculate the internal latency of the node. Therefore, for calibration, we fix the tag at a known location and calculate T ₁ ⁱ by measuring the distance between the tag and the nodes.

In addition, since T _o and T _i can be measured at the master, in mathematics t ₀ and t _m ⁰ are unknown values, and in equation (2) t ₀ , t _d ⁱ and t _m ⁱ are unknown. Value. The process of determining these unknown values is the initial calibration process. To find them, at node-1, i = 1, we get

T ₁ -T ₀ = t ₁ ¹ + t _d ¹ + t ₂ ^1- t ₁ ⁰

Therefore, since the position of the tag is known in the initial calibration process, the internal delay time of Node-1 we want is calculated as shown in the following equation.

t _d ¹ = T ₁ -T ₀ -t ₁ ¹ -t ₂ ^1- t ₁ ⁰

In addition, the internal delay time of other nodes can be calculated in the same way. After all, since UWB uses the TDOA method, T _i from Equation 3 Since T ₀ can be calculated, the time difference between the node-i and the master node can be calculated by the following equation.

t ₀ + t ₁ ^i- (t ₀ + t ₁ ⁰ ) = T _i- (t _d ⁱ + t ₂ ⁱ + t _m ⁱ ) -T ₀ + t _m ⁰

Therefore, the time difference of arrival according to the propagation movement distance of pure free space from Equation 5 is given by the following equation.

t ₁ ⁱ + t ₁ ⁰ = T _i -t _d ⁱ -t ₂ ⁱ -T ₀

Where T _i And T ₀ are the values observed at the master, and t _d ⁱ and t ₂ ⁱ are the known values through the distance between the calibration and the nodes. Thus, the position of the tag can be calculated by the TDOA. In order to reduce the effects of noise, a combination between nodes may be considered, which can be obtained from Equation 2 below.

t ₁ ⁱ -t ₁ ^j = T _i -t _d ⁱ -t ₂ ⁱ -T _j + t _d ^j + t ₂ ^j

T _i and T _j are the observed values, t _d ⁱ and t _d ^j are the values obtained by calibration, and t ₂ ⁱ and t ₂ ^j are the values calculated by the distance between the nodes. It can be seen from the above method that in order to calculate the position of the tag through TDOA calculation, the delay time of each node must be known, which can be obtained through an initial calibration process. Therefore, precisely positioning the initial tag is an important factor for overall system performance.

The present invention is not limited to the above-described embodiments, and such modifications are included in the scope of the present invention even if modifications are possible by those skilled in the art to which the present invention pertains.

The effects of the apparatus and method for detecting a position of a target according to the present invention described above are as follows.

First, it is possible to detect the position of a target in the wireless sensor network without visual synchronization between the sensor and the tag.

Second, by detecting the position of the target without visual synchronization, the efficiency and practicality of the wireless sensor network is increased.

Claims (9)

Transmitting a tag propagation signal in a tag provided at the target; Receiving the tag propagation signal at a master node and a plurality of sensor nodes; Transmitting an acknowledgment signal to the master node informing that the tag propagation signal has been received at each of the plurality of sensor nodes; Receiving the acknowledgment signal at the master node; And And obtaining a time difference between a reception time of the tag propagation signal and a reception time of the acknowledgment signal including an internal delay time for signal processing at each sensor node, and determining the position of the target. Position detection method of the target. delete delete delete The method of claim 1, wherein the transmission or reception, Position detection method of the target, characterized in that performed in the wireless sensor network of any one of UWB, WLAN, Zigbee or RFID. delete A tag provided at the target to transmit a tag propagation signal; A sensor node receiving the tag propagation signal and transmitting an acknowledgment signal through an internal delay time for signal processing; A master node which records the time at which the tag propagation signal is received, records an internal delay time for signal processing, and records the reception time of the acknowledgment signal; And And a determination unit for obtaining a position of the target by obtaining a time difference between a reception time of a tag propagation signal and a reception time of the acknowledgment signal at the master node. delete delete

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