KR20140126790A

KR20140126790A - Position estimating method based on wireless sensor network system

Info

Publication number: KR20140126790A
Application number: KR1020130044017A
Authority: KR
Inventors: 박용주; 임승옥; 문연국; 김영한
Original assignee: 전자부품연구원
Priority date: 2013-04-22
Filing date: 2013-04-22
Publication date: 2014-11-03

Abstract

The present invention relates to a method which can enhance the accuracy of the location estimate of each sensor node in a wireless sensor network. The sensor node location estimation method according to an embodiment of the present invention is used by the sensor nodes to locate self in the wireless sensor network including mobile anchor nodes aware of their own locations and at least one sensor which communicates with the anchor nodes wirelessly and includes an inertial sensor. The method includes the steps of: calculating the distance to the mobile anchor node by using at least one of the intensity and time delay of the reception signal received from the mobile anchor node; calculating a first location of the sensor node by using the distance to the mobile anchor node and the location information of the mobile anchor node; calculating the locational parameters of the sensor node by accumulated measurement values from the point at which the inertial sensor acquired the location information of the mobile anchor node; and calculating a second location by correcting the first location using the location parameters.

Description

[0001] The present invention relates to a position estimation method based on a wireless sensor network,

The present invention relates to a method for estimating the position of a sensor node in a wireless sensor network, and more particularly, to a method for improving the accuracy of position estimation.

The method of determining the node position in the wireless sensor network is largely divided into the method using the measured distance information and the method using no distance information. The method of using the distance is to obtain the distance from the node to know the position and the anchor node which knows the position, and then to perform the triangulation to find the position of the node.

The distance between the nodes is mainly measured by a Time of Arrival (ToA), a Time Difference of Arrival (TDoA), and a Received Signal Strength (RSS) method. ToA (Time of Arrival) is a method of measuring the distance by using the time when a signal that knows the propagation speed moves between nodes. TDoA (Time Difference of Arrival) is a method of measuring the distance using the time difference between signals arriving at two nodes simultaneously by transmitting two signals having different speeds.

The shorter the signal speed, the more accurate the measured value of the time difference between ToA (Time of Arrival) and TDoA (Time Difference of Arrival). However, the Time of Arrival (TOA) is difficult to find accurate distance measurements for fast signals such as RF (Radio Frequency), and the Time Difference of Arrival (TDoA) uses two signals. Do.

In addition, when a low-speed signal such as an ultrasonic wave or a sound wave is used, it is difficult to secure a loss of signal (LoS) in the case of a ToA (Time of Arrival) and a Time Difference of Arrival (TDoA) Therefore, it is difficult to obtain the accurate distance measurement value. RSS (Received Signal Strength) is a method of measuring distances using the strength of a signal arriving at a node. RF (Radio Frequency) signals used in RSS (Received Signal Strength) are more easily diffused than ultrasonic waves and sound waves, so it is easy to secure LoS (Loss of Signal) in the room and do not require additional hardware.

However, RSS (Received Signal Strength) is generally less accurate than other localization methods, and is particularly affected by obstacles such as walls and furniture indoors. The position of the node can be determined using the angle formed by the node and the node. AoA (Angle of Arrival) determines the position of a node by using the angle between two communicating nodes. To determine the angle, a node uses a multi-antenna to convert a Time of Arrival (ToA) or Received Signal Strength (RSS) value to an angle. However, it is difficult to construct a multi-antenna in a general node, and it is difficult to use the AoA (Angle of Arrival) generally because the size of a node increases.

There are Centroid and APIT (Approximate Point In Triangulation) methods, which do not use distance information. The location-based method, which does not use distance information, has been started in order to prevent the distance-based method in the multi-hop sensor network from the viewpoint of spreading the error to the network. The Centroid method is a method for regularly arranging anchor nodes to transmit their location information to neighboring nodes, and for comparing the strength of signals received from anchor nodes. The Centroid method allows accurate measurement as the number of anchor nodes that can communicate with a node increases, the RF propagation environment remains the same, the more the anchor nodes are arranged regularly. Therefore, the Centroid method is not suitable indoors.

The APIT (Approximate Point In Triangulation) method predicts the position using whether the node exists in the triangle formed by the anchor nodes. The Approximate Point In Triangulation (APIT) method also uses the strength of the signal to predict the location of the node. In the conventional distance prediction method, since the error of the signal due to the obstacle is included in the triangulation in the room where many obstacles exist, it is difficult to recognize the accurate position of the node.

It is therefore an object of the present invention to provide a method for improving the accuracy of the magnetic location estimation of a sensor node.

According to an aspect of the present invention, there is provided a method for estimating a location of a sensor node, including: a mobile anchor node that knows its own location; at least one mobile node that performs wireless communication with the anchor node, A method for estimating a position of a sensor node in a wireless network system including sensor nodes,

Calculating a distance to the mobile anchor node using at least one of the strength and the time delay of the received signal received from the mobile anchor node, using the distance to the mobile anchor node and the location information of the mobile anchor node Calculating a first position of the sensor node, computing a position parameter of the sensor node using an accumulated measurement value from a moment when the inertia sensor acquires positional information of the movable anchor node, And computing a second position at which the first position is corrected using a position parameter.

As described above, according to the present invention, a method of estimating the position of another sensor node using an anchor node that knows its position information and wireless communication, and an inertial sensor (gyro, acceleration) It is possible to improve the accuracy of the position estimation by fusing the position estimation method.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a header structure of a frame RFRAME (ranging frame) used for self-localization in the embodiment of the present invention. FIG.
Figure 2 illustrates the structure of an IR-UWB PPDU in an embodiment of the present invention.
3 is a diagram illustrating an example of a self-location estimation method according to an embodiment of the present invention.
4 is a block diagram illustrating an internal configuration of a transmitter in a sensor node according to an embodiment of the present invention;
5 is a block diagram illustrating an internal configuration of a receiving node in a sensor node according to an embodiment of the present invention.
6 is a diagram illustrating an example of a method of estimating a magnetic position according to another embodiment of the present invention.
7 is a diagram illustrating an example of a method of estimating a magnetic location according to another embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements throughout. In the drawings, like reference numerals are used to denote like elements, and in the description of the present invention, In the following description, a detailed description of the present invention will be omitted.

1. Two Way Ranging (TWR) method for each sensor node using wireless sensor network

The frame used for ranging is called RFRAME (Ranging Frame). This RFRAME is not specifically defined, but is defined by setting the RNG bit located at the Hearer of a general IR-UWB frame to 1 as shown in FIG. Therefore, the Ranging process can be performed simultaneously with the transmission of the data.

Ranging in R-UWB is done by a special device between transmitting and receiving devices called Ranging counter.

This ranging counter controls the start and end of the frame at a particular location. The controlled timing is called RMARKER (Ranging Marker). This RMARKER refers to the time when the first pulse of the PHY header data is detected after the SFD of the PPDU (PHY Protocol Data Unit) ends as shown in FIG. However, in the actual distance detection, as shown in FIG. 3, since the distance between the antennas of the transmitting and receiving apparatus is measured to measure a precise distance, an error occurs from the point of time when the ranging counter operates. Therefore, it is necessary to correct this error to obtain a precise distance measurement. This error is called Ranging H / W offset or Device offset. In the transmitter, as shown in FIG. 4, since the distance to be measured at the time when the ranging counter is controlled is a reference time point of the antenna, a time error occurs between the two reference points, which is called the internal hardware time delay of the transmitter.

In the case of the receiver, the point at which the received signal enters the antenna is an accurate reference point of the distance measurement, but the point at which the actual ranging counter operates is after detecting the signal as shown in FIG. This error is called the internal hardware time delay of the receiver.

The internal hardware time delay of the transmitter and the receiver is stored in the PHYTx_RMARKER_offset and phyRx_RMARLER_offset values of the PHY, respectively, and the value is transmitted in the ranging report at the end of the ranging process.

Generally, the clocks of the transmitter and the receiver are not synchronized with each other. Therefore, when TWR (Two Way Ranging) as shown in FIG. 6 is used, a clock offset occurs between the two devices. As a result, a visual error is generated as shown in Table 1. The horizontal axis of the table represents the tolerance of the clock and the vertical axis represents the response time at the receiving device.

2 ppm 20 ppm 40 ppm 80ppm 100us 0.1 ns 1 ns 2 ns 4 ns 5ms 5 ns 50ns 100 ns 200ns

If the clock error of the transmitter and receiver is more than 20ppm, an error of more than 30cm will occur. Since the device is configured to have a clock tolerance of 20ppm, the clock error of the transmitter and receiver is 40ppm. In this case, the distance error due to the colock offset becomes 60cm.

SDS-TWR (Symmetric Double-Sided Two-Way Ranging) is a method that can be used to reduce the distance measurement error by clock offset. SDS-TWR is performed as shown in Fig.

The SDS-TWR transmits once again after the TWR is performed, and corrects the clock offset using the response time difference between the two devices. Therefore, distance error does not occur due to the length of the response time in the receiving apparatus like TWR, but error occurs due to the response time difference. The values are shown in Table 2 below.

As shown in Table 2, when compared with Table 1, it can be seen that the distance error caused by the clock offset is greatly reduced. Therefore, it is reasonable to use SDS-TWR instead of TWR for UWB-based distance measuring devices.

2 ppm 20 ppm 40 ppm 80ppm 1us 0.0005 ns 0.005 ns 0.01 ns 0.02 ns 10us 0.005 ns 0.05 ns 0.1 ns 0.2 ns 100us 0.05 ns 0.5 ns 1 ns 2 ns

2. Self-localization method of each sensor node using inertial sensor

The inertial navigation system measures the inertia of the moving object and performs inertial navigation calculation. The inertial navigation system uses the distance and the first-order position information calculated in the TWR distance measuring apparatus for calculation. The inertial navigation system outputs the position, speed and attitude of the moving object obtained as a result of the above calculation.

The inertial navigation system can be configured as described below.

The inertial navigation system may include an inertial sensor unit, an inertial sensor error compensator, and an inertial navigation equation calculator.

The inertial sensor unit outputs the velocity increment and each increment of the moving object.

The inertial sensor unit may include three orthogonal gyroscopes and three orthogonal accelerometers. The gyroscope outputs each increment for an inertial frame, and the accelerometer outputs the velocity increment for the inertial coordinate system. Each of the increments and the rate increments includes various types of errors due to their characteristics.

The inertia sensor error compensator receives the velocity increment and the increment, and compensates the error for the value to output a velocity increment (acceleration) compensated for the error and an increment (angular acceleration) for each increment.

The operator of the moving object identifies an error which the sensor has by itself through a test measurement when the sensor such as the gyroscope and the accelerometer is constructed. The error compensator compensates the error based on the identified error.

The inertial navigation equation calculator receives the error-compensated velocity increment and each increment from the inertial sensor error compensator. The inertial navigation equation calculator outputs the position, velocity, and posture of the moving object based on the inputs.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It is to be understood that the invention may be embodied in other specific forms. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims

A method of estimating a position of a sensor node in a wireless network system including a mobile anchor node that knows its own position and at least one sensor node that performs wireless communication with the anchor node and includes an inertia sensor,
Calculating a distance to the mobile anchor node using at least one of the strength and the time delay of the received signal received from the mobile anchor node;
Calculating a first position of the sensor node using a distance between the first sensor node and the movable anchor node;
Calculating a position parameter of the sensor node using the accumulated measurement value from the time when the inertia sensor acquires the position information of the mobile anchor node; And
Computing a second position at which the first position is corrected using the position parameter;
The method comprising the steps of: