JP2006138732A - Radio position detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To resolve troubles wherein when a terminal position is detected by using reception timings measured at a plurality of base stations, detection accuracy degrades because some base station with imperfect synchronization are contained in the base stations used for measurement, or time can be taken long until position information is provided to a user because calculation of the signal measured at marginal stations can take long. <P>SOLUTION: A table correlating a base station emitting synchronizing signal and a base station where a wave emitted by the base station directly reach and a table having past position history of the terminal are hold. By referring to those tables, a proper base station is selected, position detection accuracy is improved and position detection time is shortened. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a position detection method for a wireless position measuring apparatus that receives a signal transmitted from a wireless radio wave source and measures the position of a terminal from the reception timing. In particular, a system position detection method for specifying the position of a terminal in a wireless LAN system is described.

  In wireless systems, for example, techniques for measuring the position of a terminal, such as GPS, have been proposed. On the other hand, IEEE 802.11a / b / g wireless LAN is a popular wireless system because it is inexpensive, easy to install, and requires no license. A system that detects the position of these wireless LANs without using GPS satellites has been considered. For example, as described in Japanese Patent Application Laid-Open No. 2004-101254 (Patent Document 1), the position detection method uses a time difference when a signal transmitted from a terminal is received by a base station installed at a known position. There is a method of calculating the difference in signal propagation distance from the terminal to each base station by calculating and multiplying the reception time difference by the speed of light and detecting the position of the terminal.

  A flow of position detection by a conventional wireless LAN will be described with reference to FIG. After starting position detection, base station selection 201 selects a base station that receives a radio signal for position detection. In the internal flow of the base station selection 201, for example, a base station within a predetermined distance r from the base station to which the terminal is connected is selected according to the process 206. Next, the base station occupation 102 occupies the selected base station. This is because the terminal communicates on one wireless channel among a plurality of wireless channels that can be used, and the base station that receives the terminal signal needs to switch to the same wireless channel as the terminal. If the selected base station has been occupied, the process waits until the occupation is released. With the radio channel setting 103, the selected base station and terminal are set to the same radio channel. The signal timing measurement 104 receives the terminal signal and the synchronization signal, respectively, performs signal processing, and obtains the reception timing of each signal. Here, the synchronization signal is a signal transmitted from a radio station whose coordinates are known. The position calculation 105 process calculates the terminal position from the reception timing.

  Base station occupancy 102, radio channel setting 103, and signal timing measurement 104 will be further described with reference to FIG. The terminal requests the server to detect its own position via the base station 1 that is connectable, usually closest to the terminal. For the base station occupation 102 and the radio channel setting 103, the server instructs the base station selected in the base station selection 201 to monitor the radio channel used for position detection. Each base station instructed to perform the monitoring returns a response to the server.

  Thereafter, signal timing measurement 104 is performed. The server requests the terminal to transmit the second radio packet on the radio channel via the base station 1 that has transferred the request. At that time, the base station 1 transmits a radio packet on the radio channel. In the drawing, only two peripheral base stations 2 and 3 are shown, but it is desirable to use three or more peripheral base stations in order to specify the position of the terminal based on the principle of triangulation. Here, three stations are secured by the base station connected to the terminal and the other two stations, but three stations (or more) other than the base station connected to the terminal are used as base stations for measuring the reception timing. It may be used. When the number of base stations that can be used for reception timing measurement is two or less, it is necessary to specify the position of the terminal using some kind of approximation.

  The base station 1 measures the transmission time of the first packet. Subsequently, the terminal transmits a second wireless packet on the wireless channel. Each base station instructed to monitor monitors the reception timing of the packet. Each base station transmits the result of measuring the reception timing or transmission timing of each wireless packet to the server. The server calculates the position of the terminal based on the time difference of the timing at which the signal transmitted from the terminal is received by the base station installed at a known position. The server communicates the calculated position to the terminal.

  A terminal position calculation method will be described. First, the error Eb0_bi (i = 1, 2) of the clocks of the base stations 2 and 3 with respect to the base station 1 is obtained from Equation 1, respectively. Next, the position error is obtained by substituting the obtained clock error into the simultaneous equations (i = 1, 2) shown in Equation 2 and solving for the terminal position (Xm, Ym). Here, Tp1_b0 and Rp2_b0 are the transmission time of the first radio packet and the reception timing of the second radio packet measured by the base station 1, respectively. Rp1_b1 and Rp2_b1 are the first and second radio packet reception timings measured by the base station 2. Rp1_b2 and Rp2_b2 are the first and second radio packet reception timings measured by the base station 3. (X0, Y0), (X1, Y1), and (X2, Y2) are the positions of the base stations 1, 2, and 3, respectively. c is the speed of light.

A more specific position calculation method is disclosed in Japanese Patent Application Laid-Open No. 2004-101254 (Patent Document 1).

JP 2004-101254 A

  In the prior art, the selected base station is a base station in the vicinity of the base station to which the terminal is connected. In a real environment, when a neighboring base station is simply selected, a base station that is behind an obstacle such as a wall or a pillar may be included from the base station to which the terminal is connected. The synchronization signal transmitted from the base station does not reach the shaded base station linearly, but arrives after being reflected by a floor or a wall. Since the reflected wave has a longer path length than the direct wave, the reflected wave is synchronized at an incorrect timing delayed from the original synchronization timing. When calculating the position of a terminal using reception timings measured at a plurality of base stations, there is a problem that the detection accuracy deteriorates because the base station used for measurement includes a base station that is incompletely synchronized. there were.

Wireless LAN base stations are cheaper and easier to install than GPS satellites and cellular base stations, so they may be located relatively densely. For two-dimensional position calculation, the number of base stations to be received must be at least three. In the case of three-dimensional position calculation, the number of base stations to be received must be four or more. As described above, there are a plurality of wireless channels in a wireless LAN, but it is necessary to occupy a base station because it is necessary to match the wireless channels during a signal reception period. At this time, if an extra base station is selected, the waiting time increases. The signal processing for obtaining the reception timing related to the base station is processing with a large amount of calculation such as correlation calculation with the PN code. The time spent for these calculations increases in proportion to the number of base stations. Thus, when the number of base stations is larger than necessary, there is a problem that it takes time to provide location information to the user.
Here, this patent was made in view of the above-mentioned problems, and improves the positioning processing capability by eliminating the influence of shielding objects and improving the position detection accuracy and efficiently occupying the base station. With the goal.

  It has a base station information table that associates a base station that transmits a synchronization signal with a base station that a direct wave transmitted from the base station reaches, and a terminal information table that holds the past location history and acquisition time of the terminal. After selecting a base station to which the direct wave of the synchronization signal can reach by referring to the base station information table at the time of position detection, unnecessary base stations are reduced by the terminal information table. By selecting the optimal base station in this way, it is possible to prevent an increase in positioning error due to the influence of shielding objects, improve positioning accuracy, and shorten the detection time by making the base station occupied efficiently. Can do.

  As is apparent from the above description, according to the position detection method of the present invention, when the position of a terminal is detected using reception timings measured at a plurality of base stations, synchronization is incomplete with the base station used for measurement. It is possible to prevent deterioration in position detection accuracy due to the inclusion of various base stations. In addition, the waiting time and calculation time caused by selecting an extra base station can be reduced.

  An embodiment according to the present invention will be described with reference to FIG. In the flow of FIG. 1, the same processes as those of FIG. After starting position detection, base station selection 101 selects a base station that receives a radio signal for position detection. In the internal flow of base station selection 101, for example, according to processing 107, a base station to which a direct wave arrives from a base station to which a terminal is connected is selected. The base station to which the direct wave arrives is referred to from the base station information table described later. Next, an unnecessary base station is deleted from the terminal position detection history referred to from a terminal information table described later by processing 108. The base station determined to be unnecessary at this time is a base station that is separated from the past position of the terminal by a predetermined distance or more. This predetermined distance is, for example, the distance of the terminal's radio signal, the distance obtained by multiplying the difference between the terminal's previous positioning time and the current time by the average moving speed of the terminal of the system, and the error inherent to the position detection system. It is good also as a value which added the margin. However, the past position detection time is compared with the current time, and if a predetermined time has elapsed, the deletion is invalidated and the processing 108 is skipped. The same applies to the initial position detection of the terminal. In addition, even when the number of base stations after deletion falls below a predetermined number, the deletion is invalidated and the processing 108 is skipped. The predetermined number of stations is the number of stations equal to or more than the minimum number of base stations necessary for the position detection described above, and a value that takes into account the accuracy and detection time required by the system is set.

  Base station occupation 102 occupies the selected base station. If the selected base station has been occupied, the process waits until the occupation is released. With the radio channel setting 103, the selected base station and terminal are set to the same radio channel. The signal timing measurement 104 receives the terminal signal and the synchronization signal, respectively, performs signal processing, and obtains the timing of each received signal. The position calculation 105 process calculates the terminal position from the reception timing. The process of history update 106 updates a terminal position and an acquisition time in a terminal information table to be described later.

  FIG. 4 shows an example of the base station information table. In the table, a row corresponds to information of one base station. Information of one base station is composed of four fields: a base station identification number, installation coordinates, a direct wave arrival base station identification number, and an occupation flag. A direct wave reaching base station is a base station that can receive a signal transmitted by a base station represented by a base station identification number as a direct wave. The base station identification number is a number that can uniquely designate the base station. In the example of FIG. 4, the serial number is used, but the MAC address or IP address of the base station may be used. The direct wave arrival base station is a variable length field, and can record a plurality of base station identification numbers. The direct wave arrival base station can be visually determined from the surrounding environment such as a building or a reflection object at the time of installation. When the surrounding environment changes, it is necessary to modify the table, but in general, it is metal that shields or reflects radio waves, and in the indoor environment, it is a pillar or a shelf. Does not change. The occupation flag is a flag indicating that the base station is used for position detection. For example, 0 may be an available state, and 1 may be an occupied state.

  The base station information table in FIG. 4 is created / updated when the base station is installed or when the base station setting is changed. A method is conceivable in which an operator confirms whether the antenna position of another base station can be visually recognized from the antenna position of a certain base station, and when the operator can visually confirm the antenna position, the information is entered in the base station information table. Also, the propagation time from signal transmission to reception between each base station was measured, and whether the signal was received as a direct wave based on the linear distance obtained from the position of the transmitting base station and the position of the receiving base station The base station information table may be created by determining whether or not.

  FIG. 5 shows an example of the terminal information table. In the table, a line corresponds to information of one terminal. The information of one terminal is composed of five fields: a terminal identification number, a connection destination base station identification number, a position history, a position acquisition time history, and a used radio channel. The terminal identification number is a number that can uniquely specify the terminal. In the example of FIG. 5, the serial number is used, but the MAC address or IP address of the terminal may be used. The position history is a field for storing coordinates obtained by detecting the past position of the terminal. In order to determine the case where the terminal has never acquired the position, the position history may be determined using, for example, -99999. The position acquisition time history is a field for storing the position acquisition time. In the example of FIG. 5, the format of hour: minute: second.1 / 100 second is used, but a counter that circulates in a sufficiently longer time than the predetermined time used in the process 108 may be used. The used radio channel is a field that holds a radio channel used by the terminal.

  FIG. 3 is an example of a configuration of a position detection system using a wireless LAN. A base station 1 (304a), a base station 2 (304b), a base station 3 (304c), a server 300, and a terminal 306 are included. Base stations 1 to 3 and the server are connected to a wired network 303. The terminal is connected to a wired network by a wireless 305 via a base station. The server 300 is connected by a network 302 to a database (DB) 301 that holds a base station information table and a terminal information table. The server 300 reads the two tables from the DB (301) at the start of position detection, and performs base station selection. In addition, after the position calculation, the terminal information table is updated. In this description, the server 300 and the DB 301 have different configurations for easy explanation, but the DB may be included in the server.

  The above description is based on the premise of a system that performs position detection using the reception timing of a packet. However, other systems such as a system that uses received power of a signal from a terminal may be used. Even in such a system, since the reflected wave is not proportional to the linear distance from the transmitting position to the receiving position and the signal attenuation due to propagation including reflection, the reflected wave may not provide sufficient accuracy. This is because higher accuracy can be expected when positioning is performed using waves.

  As described above, according to the present invention, it is possible to improve position detection accuracy and shorten detection time in a position detection system using a wireless LAN. A position detection system using a wireless LAN can be used in an indoor environment where GPS radio waves do not reach, and can detect a position with higher accuracy than GPS. Therefore, it can be applied to goods management applications such as distribution warehouses.

The figure explaining an example of the position detection flow by this invention. The figure explaining the conventional position detection flow (1). The figure explaining an example of the position detection system by this invention. The figure explaining an example of the base station information table by this invention. The figure explaining an example of the terminal information table by this invention. FIG. 2 illustrates a conventional position detection flow (2).

Explanation of symbols

  101 Base station selection processing, 102 Base station occupation processing, 103 Radio channel setting, 104 Signal timing measurement, 105 Location calculation, 106 History update, 107 Direct wave arrival base station selection processing of terminal connection destination base station, 108 Based on terminal location history Base station selection, 201 Conventional base station selection processing example, 206 Base station selection processing within radius r of terminal connection destination base station, 300 server, 301 database (DB), 302 network, 303 wired network, 304 base station, 305 wireless Network, 306 terminals.

Claims (4)

A first radio signal transmitted from a radio station with known coordinates;
A second wireless signal transmitted from the terminal,
Receive at multiple radio stations, measure the reception timing of each,
In the wireless position detection method for performing the position detection calculation of the terminal,
Prior to the reception of the signal, in the selection process of the plurality of radio stations,
A process of selecting a radio station capable of receiving a direct wave of the first radio signal;
The process of narrowing down the wireless station based on the past location history of the terminal,
A wireless position detection method comprising: The wireless position detection method according to claim 1,
In the process of narrowing down wireless stations based on the past location history of the terminal,
If the time when the location was acquired in the past has passed a predetermined time,
And if you have not acquired a location in the past,
If the number of radio stations falls below the specified number due to narrowing down,
A wireless position detection method characterized by invalidating the narrowing-down process and skipping the process. In the radio | wireless position detection method of Claim 1 and Claim 2,
In the process of narrowing down the base station based on the past location history of the terminal,
To eliminate base stations that are more than a predetermined distance away from the terminal ’s past location,
A wireless position detection method characterized. The wireless position detection method according to claim 3.
The predetermined distance used in the process of narrowing down the base station based on the past location history of the terminal,
The reach of the second radio signal transmitted by the terminal,
The distance obtained by multiplying the elapsed time since the position was acquired in the past by the average moving speed of the terminal,
A wireless position detection method characterized in that an error margin is added.

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