JP2009042236A - Wireless system, its server, and its base station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a position with high precision without adding a GPS receiver at the terminal in a wireless LAN system. <P>SOLUTION: Respective base stations 110, 111, 112 detect the deviation among their own clocks by mutual radio communications. The respective base stations 110, 111, 112 measure the time of reception of a signal from a terminal 100. The location of the terminal 100 is detected by using the deviation among their own clocks of the respective stations and the time of reception. Accordingly, an additional GPS receiver or the like to the terminal is unnecessary for position detection. Since the measurement of the reception time of radio packets from the terminal and the acquirement of synchronization between the base stations are provided by a common function, the highly accurate position detection is provided at low cost with a small size. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to wireless position measurement, and more particularly to position measurement in a wireless LAN system.

Wireless LANs represented by the IEEE 802.11 standard are compatible with the Internet and realized high-speed data transfer using broadband wireless media (quasi-microwave, quasi-millimeter wave, infrared, etc.), not to mention offices, It has penetrated into public spaces called hot spots. In such a wireless LAN, various location information services such as “way guidance” and “neighbor guidance” based on location information of a terminal are disclosed in, for example, Japanese Patent Laid-Open No. 2001-264090. As a method for detecting the position of the terminal, for example, in Japanese Patent Application Laid-Open No. 2000-156882, GPS or base station C
A method based on S-ID (Cell Station ID) has been released. In the former, although the position of the terminal can be detected with a high accuracy of about 10 m, the terminal must be equipped with a GPS receiver. In the latter case, a GPS receiver is not required, but since the position of the terminal is obtained based on the CS-ID of the nearest base station that has the maximum reception power in the terminal, it is possible to obtain only the accuracy of the base station arrangement interval. I can't. As a result, inconvenience occurs in services that require accuracy, such as the above-mentioned “way guidance”.

Japanese Patent Laid-Open No. 2001-264090

JP 2000-156882 A

Therefore, in the wireless LAN system, it is a problem to detect the position with high accuracy without adding a GPS receiver to the terminal.

In the present invention, each base station detects a mutual clock deviation by mutual wireless communication, each base station measures a reception time of a signal from the terminal, The position of the terminal is detected from the reception time and the position of each base station.
More specifically, a first base station having a first clock and having known coordinates, a second base station having a second clock and having known coordinates, and a terminal are included. In the wireless system, the first and second base stations measure the reception time of the first signal transmitted from the terminal based on their own clocks, and the second base station transmits from the first base station The second signal reception time is measured based on the second clock, the coordinates of the first and second base stations, the transmission time of the second signal by the first clock, and the second clock The time difference between the first clock and the second clock is detected from the reception time of the signal by the second clock, the reception time of the first signal by the first clock, the second time of the first signal This is a wireless system that measures the position of a terminal based on a reception time by a clock and a time lag.

In another example, it further includes a third base station having a third clock and having known coordinates, and the third base station sets the reception time of the first signal transmitted from the terminal to the third time. From the coordinates of the first and third base stations, the transmission time of the second signal by the first clock, and the reception time of the second signal by the third clock, The time difference between the first clock and the third clock is detected, the reception time of the first signal by the first clock, the reception time of the first signal by the second clock, the first signal The position of the terminal is measured based on the reception time by the third clock and the time lag between the clocks.

  Preferably, control is performed so that the same communication channel is used prior to position measurement.

Another aspect of the present invention is a wireless system including a plurality of base stations, a plurality of communication channels, and a terminal, and has at least a first clock among the plurality of base stations and its coordinates are known. A first base station having a second clock and having a known coordinate, and a third base station having a third clock and having a known coordinate. Set up a common communication channel, first
In addition, the second and third base stations have a first measuring unit that measures the reception time of the first signal transmitted from the terminal based on their own clocks, and the second base station and the third base station The base station has a second measurement unit for measuring the reception time of the second signal transmitted from the first base station based on its own clock, and the first, second, and third base stations Coordinates, time of transmission of the second signal by the first clock,
The reception time of the second signal by the second clock, the reception time of the second signal by the third clock, the first
The reception time of the first signal by the first clock, the reception time of the first signal by the second clock, and
A wireless system that measures the position of a terminal using a reception time of a first signal by a third clock.

At this time, transmission power control may be performed on base stations using the same communication channel at base stations other than those set with a common communication channel.

In yet another embodiment, the apparatus includes a plurality of base stations, a plurality of communication channels, and a terminal. Among the plurality of base stations, the base station has a first clock and the coordinates thereof are known. A first base station, a second base station having a second clock and having known coordinates, and a third base station having a third clock and having known coordinates are The reception time of the first signal to be transmitted is measured based on its own clock, and the second base station and the third base station each determine the reception time of the second signal transmitted from the first base station. A server for use in a wireless system for measuring based on the clock of the server, wherein the server sets a common communication channel for the first to third base stations, and the server includes the first, second and second 3 base station coordinates, second signal transmission time by the first clock, second signal second clock Reception time, the reception time of the third clock of the second signal that,
The position of the terminal is measured using the reception time of the first signal by the first clock, the reception time of the first signal by the second clock, and the reception time of the first signal by the third clock. .

In the above, an example in which the transmission time is measured has been described. However, a configuration in which the transmission time of the signal is not measured is also possible. For example, a first base station whose coordinates are known, a second base station which has a second clock and whose coordinates are known, and a third clock whose coordinates are known. A wireless system including a certain third base station and a terminal, wherein the second and third base stations measure the reception time of the first signal transmitted from the terminal based on their own clocks, and The second and third base stations measure the reception time of the second signal transmitted from the first base station based on their own clocks,
And the second clock and the third base station from the coordinates of the second and third base stations, the reception time of the second signal by the second clock, and the reception time of the second signal by the third clock. The time difference of the first clock is detected, and the position of the terminal is measured based on the reception time of the first signal by the second clock, the reception time of the first signal by the third clock, and the time difference To do.

Furthermore, it further includes a fourth base station having a fourth clock whose coordinates are known, and the fourth base station determines the reception time of the first signal transmitted from the terminal based on the fourth clock. Measuring, the coordinates of the first and second and fourth base stations, and the reception time of the second signal by the second clock;
The time difference between the second clock and the fourth clock is detected from the reception time of the second signal by the fourth clock, and the reception time of the first signal by the second clock is detected. The terminal position may be measured based on the reception time of the third clock, the reception time of the first signal by the fourth clock, and the time lag between the clocks.
Further, at least the first to fourth base stations may be controlled to use the same communication channel prior to position measurement.

Another aspect of the present invention is to detect the position of a terminal from the reception time of each base station in wireless communication with each other, the reception time of a signal from the terminal at each base station, and the position of each base station. It is a server characterized by. Alternatively, the position of the terminal is detected from the received signal in the wireless communication between each base station and the time when the signal is captured, the received signal from the terminal at each base station, the time when the signal is captured, and the position of each base station. It is a server characterized by doing.
Further, these servers may accumulate the delay amount in the reception processing of each base station, and use the delay amount for detecting the terminal position.
Furthermore, a base station used for position detection of the terminal and a server for determining the radio channel may be used based on the position of the base station that mediates the position detection request from the terminal. At this time, the transmission power in the radio channel may be controlled for the base station not used for position detection based on the base station used for position detection of the terminal and its radio channel.

The form of the base station of the present invention includes, as an example, a communication unit, a storage unit, a clock, a processing unit, a LAN I / F
The wireless packet reception time is derived from the baseband signal (I / Q) accumulated in the accumulation unit and the time related to the accumulation operation. At this time, the reception time of the radio packet may be derived from the cross-correlation between the reception baseband signal (I / Q) stored in the storage unit and a predetermined complex sequence and the time related to the storage operation. Good.

Another aspect of the present invention is an inter-base station synchronization method characterized in that in a wireless LAN system, base stations synchronize with each other by detecting a difference in clock between each other by mutual wireless communication. is there. At this time, in the wireless LAN system, the base stations may synchronize with each other by detecting the deviation rate per unit time of the respective clocks by repeating the mutual wireless communication a plurality of times.

Another aspect of the present invention is a wireless system including a plurality of base stations, a plurality of communication channels, and a terminal, and at least a first base station whose coordinates are known among the plurality of base stations. A second base station having a second clock and known coordinates, a third base station having a third clock and known coordinates, and a fourth clock having a fourth clock A common communication channel is set for the fourth base station whose coordinates are known, and each of the second, third, and fourth base stations determines the reception time of the first signal transmitted from the terminal. The first, second, and fourth base stations have a first measurement unit that measures the time based on the clock, and the second, third, and fourth base stations use the time of the second signal transmitted from the first base station based on their own clocks. A second measuring unit that measures the coordinates of the first, second, third, and fourth base stations, the second clock of the second signal Reception time, the reception time of the third clock of the second signal that,
The reception time of the second signal by the fourth clock, the reception time of the first signal by the second clock, the first
This is a wireless system that measures the position of the terminal using the reception time of the third signal by the third clock and the reception time of the first signal by the fourth clock. At this time, transmission power control may be performed on base stations using the same communication channel at base stations other than those set with a common communication channel.

Another aspect of the present invention includes a plurality of base stations, a plurality of communication channels, and a terminal,
Among the plurality of base stations, the first base station whose coordinates are known, the second base station having the second clock and the coordinates thereof are known, and the third clock having the coordinates thereof A third base station that is known;
The fourth base station having the fourth clock and having known coordinates measures the reception time of the first signal transmitted from the terminal based on its own clock, and the second base station and the third base station The base station and the fourth base station are servers used in a wireless system for measuring the reception time of the second signal transmitted from the first base station based on their own clocks. To set a common communication channel for the fourth base station, the server receives the coordinates of the first, second, third and fourth base stations, the second signal by the second clock Time, reception time of the second signal by the third clock, reception time of the second signal by the fourth clock, reception time of the first signal by the second clock, third clock of the first signal Using the reception time of the first signal and the reception time of the first clock by the fourth clock. It is a server for measuring.

In a wireless LAN system, the position of the terminal can be detected with high accuracy without adding a GPS receiver to the terminal.

An embodiment of a wireless LAN system according to the present invention will be described with reference to FIG. In the figure, 100 is a terminal, 110, 111, 112 are base stations, 120 is a server, and 130 is a local area network (LAN). Terminal 100 has a function of transmitting a first wireless packet to the base station.
Each of the base stations 110, 111, and 112 has a clock therein, and has a function of measuring the reception time of the first radio packet transmitted by the terminal 100.
The reception times measured with the clocks of the base stations are R _{p1_b0} , R _{p1_b1, and} R _{p1_b2} , respectively. The distance between the terminal and each base station is obtained from the time when the signal transmitted from the terminal 100 is received at each base station, and the coordinates of the terminal can be known based on the distance. However, the measured reception times R _{p1_b0} , R _{p1_b1,} R _{p1_b2} are measured based on the clocks specific to each base station, and the synchronization of the clocks of each base station is not guaranteed. Detect the deviation,
Calibration is required.
The base station 110 has a function of transmitting a second wireless packet to the base stations 111 and 112 and a function of measuring the transmission time of the packet. The transmission time measured with the clock of the base station 110 is _defined as T _{p2_b0} . The base station 110 transmits to the server 120 the reception time R _{p1_b0} of the first radio packet from the terminal 100 and the second radio packet transmission time T _{p2_b0} from the own station. The base stations 111 and 112 have a function of measuring the reception time of the second radio packet transmitted by the base station 110. The reception times measured with the clocks of the base stations are R _{p2_b1 and} R _{p2_b2} , respectively. In addition, base station 111
, 112, respectively, reception time R _{P1_b1} the first wireless packet from the terminal _100, and R _{P1_b2,} the second wireless packet reception time R _{P2_b1} from the base station 110 _transmits the R _{P2_b2} the server 120.
The server 120 accumulates the positions (X ₀ , Y ₀ ), (X ₁ , Y ₁ ), (X ₂ , Y ₂ ) of the base stations 110, 111, 112 in advance, The position (X _m , Y _m ) of the terminal 100 is calculated from each time R _{p1_b0} , R _{p1_b1,} R _{p1_b2} , T _{p2_b0} , R _{p2_b1,} R _{p2_b2 obtained} from the above.
Since the distance between the base station 110 and the base stations 111 and 112 is known in advance, the packet propagation time between the base stations can be obtained by dividing the distance by the speed of light. Therefore, if the propagation time is added to the transmission time from the base station 110 (based on the clock of the base station 110), the reception time at the base stations 111 and 112 (based on the clock of the base station 110) can be obtained. By detecting the difference between this reception time and the reception time measured by the base stations 111 and 112 using its own clock, the clock difference between the base stations can be calibrated.
Next, a method for calculating the position of the terminal 100 in the server will be described. Base station 110, 111, 112
Each have a clock. The position of the terminal (X _m , Y _m ) is the simultaneous equation (i = 1,
Obtained by solving 2). Here, c is the speed of light, and E _{b0 — bi} (i = 1, 2) is the clock error of the base stations 111 and 112 with respect to the base station 110, respectively.

Here, if the clock error E _{b0_bi} (i = 1, 2) of the base stations 111 and 112 with respect to the base station 110 is large, the position of the terminal cannot be calculated correctly. An error of 1 microsecond in time causes an error of 300 m in distance. However, these errors can be obtained by Equation 2 (i = 1, 2) from the measurement result of the transmission / reception time of the second wireless packet. In _Equation 2 (i = 1, 2), the right side (R _{p2_bi} -T _{p2_b0} ) is the base station 11i (i = 1 for the second radio packet transmission time in the base station 110)
, 2) shows the difference in the second radio packet reception time. The third term on the right side shows the propagation time between the base station 110 and the base station 11i (i = 1, 2).

From the above, the position (X _m , Y _m ) of the terminal 100 can be obtained by solving Equations 1 and 2.

A second embodiment of the wireless LAN system according to the present invention will be described with reference to FIG. In the embodiment of FIG. 1, it is possible to detect and calibrate a shift between clocks of each base station at a certain time.
However, when the clock period of each base station clock itself varies depending on conditions such as the characteristics of the apparatus and temperature, the amount of deviation between base stations changes with time. To calibrate this,
It is desirable to detect and calibrate the amount of change in clock deviation per unit time.
In FIG. 2, 100 indicates a terminal, 210, 211 and 212 indicate base stations, 220 indicates a server, and 130 indicates a local area network (LAN). Terminal 100 has a function of transmitting a first wireless packet to the base station. Each of the base stations 210, 211, and 212 has a clock therein, and has a function of measuring the reception time of the first radio packet transmitted by the terminal 100. The reception times measured with the clocks of the base stations are R _{p1_b0} , R _{p1_b1, and} R _{p1_b2} , respectively.
The base station 210 has a function of transmitting a second radio packet to the base stations 211 and 212 and a function of measuring the transmission time of the packet. The transmission time of the second wireless packet measured with the clock of the base station 210 is assumed to be _{Tp2_b0} . Further, the base station 210 has a function of transmitting a third wireless packet to the base stations 211 and 212 and a function of measuring the transmission time of the packet. Base station 210
_Let T _{p3_b0 be} the transmission time of the third wireless packet measured with the clock of. The base station 210 receives the first radio packet reception time R _{p1_b0} from the terminal 100, the second radio packet transmission time T _{p2_b0} from the own station, and the third radio packet transmission time T _{p3_b0} from the own station. Is transmitted to the server 220. The base station 210 may transmit the second wireless packet before the first wireless packet. Further, the base station 210 may transmit the second and third radio packets before the first radio packet, respectively.

The base stations 211 and 212 have a function of measuring the reception time of the second wireless packet transmitted by the base station 210. The reception times of the second radio packet measured with the clock of each base station are R _{p2_b1 and} R _{p2_b2} , respectively. Further, the base stations 211 and 212 have a function of measuring the reception time of the third wireless packet transmitted by the base station 210. R _{p3_b1 and} R _{p3_b2} are the reception times of the third radio packet measured with the clock of each base station. In addition, the base stations 211 and 212 are respectively
First radio packet reception times R _{p1_b1 and} R _{p1_b2} from the terminal 100, second radio packet reception times R _{p2_b1 and} R _{p2_b2} from the base station 210, and third radio packet reception times from the base station 210 R
_{p3_b1 and Rp3_b2} are transmitted to the server 220.
The server 220 stores the positions (X ₀ , Y ₀ ), (X ₁ , Y ₁ ), (X ₂ , Y ₂ ) of the base stations 210, 211, 212 in advance, and stores each position and each base station The position (X _m , Y _m ) of the terminal 100 is calculated from each time R _{p1_b0} , R _{p1_b1,} R _{p1_b2} , T _{p2_b0} , R _{p2_b1,} R _{p2_b2} , T _{p3_b0} , R _{p3_b1,} R _{p3_b2 obtained} from.
Next, a method for calculating the position of the terminal 100 in the server will be described.
Each of the base stations 210, 211, and 212 has a clock. The position of the terminal (X _m , Y _m ) is obtained by solving the simultaneous equations (i = 1, 2) shown in Equation 1. However, here E _{b0_bi} (i = 1
, 2) are the clock errors of the base stations 211 and 212 with respect to the base station 210, respectively. Base station 210
, 211, 212, if the variation in clock speed is large, base station 211 to base station 210,
The clock error E _{b0_bi} (i = 1, 2) of 212 changes with time. Actually, IEEE802.11, which is a wireless LAN standard, allows the clock accuracy to be within ± 25 ppm, so that errors may increase by up to 50 microseconds per second between base stations. An error of 50 microseconds in time causes an error of 15000m in distance. However, such an error can be obtained from Equation 3 (i = 1, 2) from the measurement results of the transmission and reception times of the second and third wireless packets. In _Equation 3 (i = 1, 2), (T _{p3_b0} -T _{p2_b0} ) / (R _{p3_bi} -R _{p2_bi} ) in the right side brace is the clock of the base station 210 with respect to the clock of the base station 21 i (i = 1, 2) The ratio value of speed is shown. (R _{p2_bi} -R _{p1_bi} ) in the curly brackets indicates the difference between the second packet reception time and the first packet reception time of the base station 21i (i = 1, 2). (R _{p2_bi} -R _{p1_bi} ) to (T _{p3_b0-
Multiplying} T _{p2_b0} ) / (R _{p3_bi} -R _{p2_bi} ), the difference between the second packet reception time and the first packet reception time of the base station 21i (i = 1, 2) is _calculated as the clock speed of the base station 210. To obtain the value corrected by. Accordingly, the value in the curly brackets on the right side is a value obtained by correcting the second radio packet reception time at the base station 21i (i = 1, 2) with the clock speed of the base station 210. _Equation 3 is an extension of _Equation 2, and if there is no difference in clock speed between base stations, (T _{p3_b0} -T _{p2_b0} ) / (R _{p3_bi} -R _{p2_bi} ) is 1.
And agrees with the number 2.

From the above, the position (X _m , Y _m ) of the terminal 100 can be obtained by solving Equations 1 and 3.

A third embodiment of the wireless LAN system according to the present invention will be described with reference to FIG. 1 and 2
In this embodiment, at least one base station has a function of measuring a packet transmission time in order to know a clock shift between base stations. In this embodiment, a configuration in which this function is omitted is shown.
In FIG. 9, 100 is a terminal, 910, 911, 912, and 913 are base stations, 920 is a server, and 130 is a local area network (LAN). Terminal 100 has a function of transmitting a first wireless packet to the base station. Each of the base stations 911, 912, 913 has a clock inside, and the terminal 1
00 has a function of measuring the reception time of the first wireless packet transmitted. The reception times measured with the clocks of the base stations are R _{p1 (i) _b1} , R _{p1 (i) _b2, and} R _{p1 (i) _b3} , respectively.
The base station 910 has a function of transmitting a second wireless packet to the base stations 911, 912, and 913.
The base station 910 may further have a function of transmitting a third wireless packet to the base stations 911, 912, and 913. The base station 910 may transmit the second wireless packet before the first wireless packet. Further, the base station 910 may transmit the second and third radio packets before the first radio packet.

The base stations 911, 912, and 913 have a function of measuring the reception time of the second wireless packet transmitted by the base station 910. The reception times of the second radio packet measured with the clock of each base station are R _{p2 (j) _b1,} R _{p2 (j) _b2, and} R _{p2 (j) _b3} (j = 2), respectively. Further, the base stations 911, 912, and 913 may have a function of measuring the reception time of the third wireless packet transmitted by the base station 910.
The reception times of the third wireless packets measured with the clocks of the respective base stations are R _{p2 (j) _b1,} R _{p2 (j) _b2, and} R _{p2 (j) _b3} (j = 3), respectively.
In addition, each of the base stations 911, 912, and 913 receives the first radio packet from the terminal 100.
R _{p1 (i) _b1} , R _{p1 (i) _b2,} R _{p1 (i) _b3,} and second radio packet reception time R _{p2 (j) _b1,} R _{p2 (j) _b2,} R _p2 from the base station 910 _{(j) _b3} (j = 2) and, if necessary, the third radio packet reception time R _{p2 (j) _b1,} R _{p2 (j) _b2,} R _{p2 (j) _b3} (j = 3) to server 920.
The server 920 includes the positions (X ₀ , Y ₀ ), (X ₁ , Y ₁ ), (X
₂ , Y ₂ ), (X ₃ , Y ₃ ) are stored in advance, and each position and each time R _{p1 (i) _b1} , R _{p1 (i) _b2,} R _{p1 (i)} acquired from each base station _{_b3, R p2 (j) _b1} , R p2 (j) _b2, calculated from _{R p2 (j)} _b3 position of the terminal 100 (X _m, Y _m) of.
Next, a method for calculating the position of the terminal 100 in the server will be described.
Base stations 911, 912, and 913 each have a clock. The position of the terminal (X _m , Y _m ) can be obtained by solving the simultaneous equations (k = 2, 3) shown in Equation 4. However, here E _{b1_bk} (k = 2
, 3) are the clock errors of the base stations 912 and 913 with respect to the base station 911, respectively. These errors can be obtained from the measurement result of the reception time of the second wireless packet by Equation 5 (k = 2, 3, j = 2).

Base station 911, 912, 913 has a large variation in clock speed, base station for base station 911
When the error E _{b1_bk} (k = 2, 3) of the clocks 912 and 913 changes with time, the measurement result of the reception time of the third radio packet is further used to calculate the equation 6 (k = 2, 3, j = 2, h = 3).

In _Equation 6 (k = 2, 3, j = 2, h = 3), the right brace (R _{p2 (h) _b1} -R _{p2 (j) _b1} ) / (R _{p2 (h) _bk} -R _{p2 ( j) _bk} ) indicates the value of the ratio of the clock speed of the base station 911 to the clock of the base station 91k (k = 2, 3). _Expression 6 is an extension of _Expression 5, and when the clock error E _{b1 — bk} (k = 2, 3) does not change with time, that is, when the clock speed ratio is 1, _Expression 6 _{matches Expression} 5. Note that the derivation of the clock error E _{b1_bk} (k = 2, 3) is not limited to using the measurement results of the reception times of the second and third radio packets, but the second, third _,. .. Measurement result of the reception time of the g-th (g ≧ 4) radio packet may be used. In that case, the number 6 (k = 2, 3, j = e, h = f, e
E _{b1 — bk} (k = 2, 3) may be determined based on, for example, an average value based on a plurality of clock errors obtained from ≠ f, e ≧ 2, f ≧ 3).
From the above, the position (X _m , Y _m ) of the terminal 100 can be obtained by solving the equations 4, 5 or 4, 6.

In this embodiment, the calculation example of the two-dimensional position of the terminal by three base stations is shown for the sake of simplicity of explanation, but the two-dimensional position of the terminal is calculated using N (N ≧ 4) base stations. Are also within the scope of the present invention. In this case, the equations may be established as (i = 1, 2,..., N−1) in the equations 1 to 3.
Alternatively, the equations may be established as (k = 1, 2,..., N) in Equations 4 to 6. What is necessary is just to obtain | require the solution of the simultaneous equations of several 1 or several 4 by the least squares method, for example. Or, Japanese Patent Application 2001-03
By applying the solution shown in 0859 “Position calculation method and position calculation device”, it is possible to calculate the position more accurately. Furthermore, calculating the three-dimensional position of the terminal is also within the scope of the present invention. In this case, z coordinates are added to Equations 1 to 3 for N (N ≧ 4) base stations (i = 1, 2
, ..., N-1). Alternatively, add the z-coordinate to Equations 4 to 6, and (k = 1
, 2, ..., N).

An embodiment of the system flow when detecting the position of the terminal will be described with reference to FIG.
The terminal requests the server to detect its own position via the connectable base station 310. Usually, it is the base station nearest to the terminal. If it is necessary to change the wireless channel used for position detection, the server instructs the terminal to change the wireless channel, and the terminal responds accordingly. Subsequently, the server instructs the base station 310 that has transferred the request and the base stations 311 to 312 in the vicinity thereof to monitor the wireless channel used for position detection.
Since the server stores the position of each base station in advance, it is easy to identify base stations in the vicinity of one base station. Each base station instructed to perform the monitoring returns a response to the server. Thereafter, the server requests the terminal to transmit the first wireless packet on the wireless channel via the base station 310 that has transferred the request. The terminal transmits a first wireless packet on the wireless channel. Each base station instructed to monitor monitors the reception time of the packet. After receiving the first radio packet, the base station 310 transmits the second radio packet on the radio channel to the neighboring base stations 311 to 312 after a certain time.
Base station 310 measures its transmission time. The neighboring base stations 311 to 312 each measure the reception time of the second wireless packet. Here, when the difference in clock speed between the base stations is large, the base station 310 further transmits the second radio packet to the neighboring base stations 311 to 312 after a certain period of time. A third wireless packet may be transmitted on the wireless channel. In this case, the base station 310 measures its transmission time, and the surrounding base stations 311 to 312
Each of them measures the reception time of the third wireless packet. Each base station transmits the result of measuring the reception time or transmission time of each wireless packet to the server. The server calculates the position of the terminal by the calculation method already described, and notifies the terminal of the position detection result.
If different codes are previously set and placed on the first, second, and third wireless packets, each base station can easily distinguish the packets when measuring the reception time.

Another embodiment of the system flow when detecting the position of the terminal will be described with reference to FIG. The terminal requests the server to detect its own position via the base station 310 that is connectable, usually closest to the terminal. The server instructs the base station 310 that transferred the request and the surrounding base stations 311 to 312 to monitor the wireless channel used for position detection. Since the server stores the position of each base station in advance, it is easy to identify base stations in the vicinity of one base station. Each base station instructed to perform the monitoring returns a response to the server. Thereafter, the server requests the terminal to transmit the first wireless packet on the wireless channel via the base station 310 that has transferred the request. At that time, the base station 310 transmits a radio packet on the radio channel. This is the second radio packet and the base station
310 measures the transmission time. The neighboring base stations 311 to 312 each measure the reception time of the second wireless packet. Subsequently, the terminal transmits a first wireless packet on the wireless channel. Each base station instructed to monitor monitors the reception time of the packet. When the difference in clock speed between the base stations is large, the base station 310 further, after receiving the first radio packet, with respect to the surrounding base stations 311 to 312 at a certain time or more,
A third wireless packet may be transmitted on the wireless channel. In this case, the base station 310 measures the transmission time, and the neighboring base stations 311 to 312 each measure the reception time of the third radio packet. Each base station transmits the result of measuring the reception time or transmission time of each wireless packet to the server. The server calculates the position of the terminal by the calculation method already described, and notifies the terminal of the position detection result.

An example of the system flow when detecting the position of the terminal of the wireless LAN system shown in FIG. 9 will be described with reference to FIG. The server instructs the base stations 911, 912, and 913 to monitor the wireless channel used for position detection. Each base station instructed to perform the monitoring returns a response to the server. Thereafter, the server requests the terminal to transmit the first wireless packet on the wireless channel via the base station 910. At that time, the base station 910 transmits a radio packet on the radio channel. This is the second wireless packet. Each of the base stations 911, 912, and 913 measures the reception time of the second wireless packet.
Subsequently, the terminal transmits a first wireless packet on the wireless channel. Each base station instructed to monitor monitors the reception time of the packet. If the difference in clock speed between the base stations is large, the server may request the terminal to transmit the first wireless packet again on the wireless channel via the base station 910. Good. That is, the figure
11, the flow in the broken line frame may be repeated. At that time, the base station 910 transmits a wireless packet again on the wireless channel. This is the third wireless packet. base station
911, 912, and 913 each measure the reception time of the third wireless packet. After measurement,
Each base station communicates the result to the server. The server calculates the position of the terminal by the calculation method already described.

As shown in the flow shown in FIGS. 3 and 8, the terminal first adds a flow for requesting the server to detect its own position via the base station 910, and finally the flow for the server to transmit the position detection result to the terminal. May be.

Next, an embodiment of a wireless channel control method in the wireless LAN system according to the present invention will be described with reference to FIGS. Wireless LAN systems usually use multiple wireless channels. As described above, in order to multicast the clock calibration packet, it is necessary to share the radio channel of the base station related to position measurement.

FIG. 5 is a diagram for explaining a radio channel control method according to the present invention.
FIG. 6 is a diagram showing a flow of a radio channel control method according to the present invention.
In FIG. 5, 5000 indicates a server and 5900 indicates a terminal. Also, 501 * ~ 521 * (* is 1, 2, 3
, 4) indicates a base station. In the example of FIG. 5, four types of radio channels are allocated to the base station, and are distinguished by the last digit of each number indicating the base station. For example, the base station 5111 is assigned radio channel No. 1, and the base station 5164 is assigned radio channel No. 4.
Assume that the terminal 5900 requests the server 5000 for position detection via the base station 5111. The server 5000 includes, for example, four base stations 5063, 510 adjacent to the base station 5111 based on the position of the base station 5111.
2, 5122, 5164 are selected, and a total of five base stations obtained by adding the base station 5111 to these base stations are selected as base stations used for position detection of the terminal 5900 (FIG. 6, STEP 601).
Next, the server determines a wireless channel used for position detection (FIG. 6 STEP 602).
As a method for determining the radio channel, for example, the radio channel used by the terminal that requested the position detection (number 1 in the example of FIG. 5) may be selected as the radio channel for position detection as it is. Alternatively, the most frequently assigned radio channel (number 2 in the example of FIG. 5) may be selected from the selected base stations.
Server 5000 uses base stations 5063, 51 to use the determined radio channel for position detection.
02, 5122, 5164, 5111 and if necessary, the terminal 5900 is instructed (FIG. 6, STEP 603). In addition,
Base stations 5063, 5102, 5122, 51 used for position detection in order to suppress interference signals at the time of position detection
64 and 5111 neighboring base stations may be instructed to stop using the radio channel determined for position detection. Alternatively, control may be performed to reduce transmission power in the radio channel (FIG. 6, STEP 604). For example, in FIG. 5, when the radio channel No. 2 is selected, the base stations 5022 and 5202 are assigned the radio channel No. 2, so the server stops using the channel for these base stations. Instruct.
The server 5000 detects the position of the terminal 5900 and notifies the result (FIG. 6 STEP 605). Thereafter, the base station 5063, 5102, 5122, 5164, 5111 is instructed to restore the radio channel. Also, the base station 5022 and 5202 cancel the transmission power control instruction in the wireless channel (FIG. 6, STEP 606).
The configuration of the base station applied in this system will be described with reference to FIG. In the figure, a base station 400 includes a communication unit 410, a storage unit 420, a clock 430, a LAN I / F unit 440, and a control unit 450.
Communication unit 410 includes RF unit 411, DAC 412, ADC 413, BB unit 414, MAC unit 415, and I / F unit 416. The RF unit 411 converts the baseband signal input from the DAC 412 into a high frequency signal and transmits it from the antenna. The RF unit 411 converts the high frequency signal received from the antenna into a baseband signal and outputs the baseband signal to the ADC 413. The DAC 412 converts the digital baseband signal (I / Q) into an analog baseband signal (I / Q).
The ADC 413 converts the analog baseband signal (I / Q) into a digital baseband signal (I / Q). The BB unit 414 receives MPDU (MAC Protocol Data Units) from the MAC unit 415, generates a baseband signal, and outputs it to the DAC 412. Also, the BB unit 414 demodulates the baseband signal input from the ADC 413 to acquire MPDU (MAC Protocol Data Units), and outputs the MPDU to the MAC unit 415. The MAC unit 415 controls communication with other stations according to a MAC (Media Access Control) protocol. The I / F unit 416 mediates transmission / reception data with the outside of the communication unit 410 and accepts control of the communication unit from the outside.
The storage unit 420 includes a memory 421, a counter 422, and an I / F unit 423. Memory 421 is I /
In response to an instruction from the F unit 423, a transmission baseband signal (I / Q) is captured from the communication unit 410 in synchronization with the clock 430. Further, the memory 421 captures a reception baseband signal (I / Q) from the communication unit 410 in synchronization with the clock 430 in accordance with an instruction from the I / F unit 423. The counter 422 keeps time (counter value) in synchronization with the clock 430. In addition, the memory 4
21. Record the counter value at the start or end of each transmission / reception baseband signal (I / Q) at 21. The I / F unit 423 responds to reading of the memory and the counter value from the outside of the storage unit 420, and receives control of the storage unit from the outside.
The clock 430 supplies a common clock so that the communication unit 410 and the storage unit 420 are synchronized.
The LAN I / F 440 is an interface unit for a local area network.
The control unit 450 controls the communication unit 410 and the LAN I / F 440 and mediates communication between the terminal and the LAN. In addition, the control unit 450 controls the LAN I / F 440 and performs communication with the server. Furthermore, the control unit 450 controls the communication unit 410 and the storage unit 420 to calculate the transmission time or reception time of the wireless packet.
With reference to FIG. 10, an embodiment of a base station configuration applied in the third embodiment of the wireless LAN system shown in FIG. 9 will be described. However, since the characteristic part of the base station shown in FIG. 4 is the storage unit 1020, the difference will be described here.
The accumulation unit 1020 includes a memory 1021, a counter 1022, and an I / F unit 1023.
The memory 1021 takes in the reception baseband signal (I / Q) from the communication unit 410 in synchronization with the clock 430 according to an instruction from the I / F unit 1023. The counter 1022 keeps time (counter value) in synchronization with the clock 430. Further, in response to an instruction from the I / F unit 1023, the counter value at the start or end of capturing of the received baseband signal (I / Q) in the memory 1021 is recorded. I
The / F unit 1023 responds to reading of the memory and the counter value from the outside of the storage unit 1020 and receives control of the storage unit from the outside.
As described above, the configuration of the base station of the present embodiment has a form in which the function of measuring the packet transmission time is omitted as compared with the configuration of the base station shown in FIG. The reception time of the wireless packet is, for example, a reception baseband signal stored in the memory 421 or the memory 1021 and a known signal sequence (
For example, the peak position of the correlation value obtained by cross-correlation with the synchronization word included in the preamble of the received packet, and the time related to the reception processing of the received baseband signal recorded in the counter 422 or the counter 1022 (for example, , And the capture start time).
At this time, since the processing delay from the antenna end input to the ADC output is included, it is possible to obtain a more accurate reception time if this delay amount is measured in advance and corrected by the measured amount. Note that it is not essential to derive the reception time of the wireless packet at the base station. The reception baseband signal captured in the memory and the time related to the capturing process are transmitted to the server, and the server transmits the wireless packet reception time at the base station. The reception time may be derived.
The transmission time of the wireless packet is, for example, from the position of the level change of the transmission baseband signal stored in the memory 421 and the time (for example, the acquisition start time) related to the transmission baseband signal capture processing recorded in the counter 422 It can be easily derived. Alternatively, as in the case of the reception time, the correlation obtained by taking the cross-correlation between the transmission baseband signal stored in the memory 421 and a known signal sequence (for example, the synchronization word included in the preamble of the transmission packet) It is possible to derive from the peak position of the value and the time related to the acquisition process of the transmission baseband signal recorded in the counter 422. In either case, DA
Since the processing delay from the C input to the antenna end output is not included, it is possible to obtain a more accurate transmission time by measuring this delay amount in advance and correcting it by the measured amount. Note that it is not essential to derive the transmission time of the wireless packet in the base station, and the transmission baseband signal captured in the memory and the time related to the capturing process are transmitted to the server, and the server transmits the wireless packet transmission time in the base station. The transmission time may be derived.
For accurate derivation of the reception time or transmission time of the wireless packet, for example, Japanese Patent Laid-Open No. 2002-1
The “ranging and position measuring method using a spread spectrum signal and an apparatus for performing the method” disclosed in Japanese Patent No. 4152 can be applied.
In the base station 400, a wireless LAN card can be applied to 431 including the communication unit 410 and the clock 430. In addition, the control unit 450 and the LAN 440 including the LAN I / F 440 include those shown in FIG.
A PC with a built-in base station flow program can be applied.
As a server applied in this system, for example, a PC incorporating the server flow program shown in FIG. 3, FIG. 8, or FIG. 11, and FIG. 6 can be applied. Further, for example, a notebook PC or PDA incorporating the terminal flow program shown in FIG. 3, FIG. 8, or FIG.
FIG. 7 shows an example of a data format of information regarding each base station stored in the server. In the figure, base station information 1, 2,. . . , N is a unit of information about one base station. Which base station information is specified is specified by an identification number described in each base station information. In addition to this identification number, each base station information includes location, radio channel number,
Includes transmission delay and reception delay. The location position indicates the position of the base station specified by the identification number by a coordinate value.
The radio channel number indicates the number of the radio channel assigned to the base station specified by the identification number. The transmission delay amount and the reception delay amount indicate processing delay amounts at the time of transmission and reception of the base station specified by the identification number, respectively. These delay amounts are used to more accurately measure the transmission time and reception time of the base station.
As an application example of the present invention, there is a synchronization method between base stations in a wireless LAN system.
For example, in the embodiment of the wireless LAN system shown in FIG. 1, the server 120 _transmits the clock error E _{b0_bi} (i = 1, 2) obtained from _Equation 2 to the base stations 111 and 112, respectively. 111, 1
If 12 corrects the clock error, the base stations 111 and 112 can synchronize with the base station 110.
In addition, for example, in the embodiment of the wireless LAN system shown in FIG. 2, the clock error E _{b0_bi} (i = 1, 2) obtained by the server 220 from _Equation 3 and the base station for the clocks of the base stations 211 and 212 in _Equation 3 The value of the clock speed ratio of 210 (T _{p3_b0} -T _{p2_b0} ) / (R _{p3_bi} -R _{p2_bi} ) (i = 1, 2) is transmitted to the base stations 211 and 212, respectively. The clock error E _{b0_bi} (i = 1, 2) is corrected retroactively to the time R _{p1_bi} (i = 1, 2) when the first radio packet is received, and thereafter, the clock speed ratio value (T _{p3_b0} − The base stations 211 and 212 can be synchronized with the base station 210 by correcting the respective clocks by T _{p2 — b0} ) / (R _{p3 — bi} −R _{p2 — bi} ) (i = 1, 2).
Further, for example, in the embodiment of the wireless LAN system shown in FIG. 9, the base station for the clock error E _{b1_bk} (k = 2, 3) obtained by the server 920 from _Equation 6 and the clocks of the base stations 912 and 913 in _Equation 6. 911 clock speed ratio (R _{p2 (h) _b1} -R _{p2 (j) _b1} ) / (R _{p2 (h) _bk} -R _{p2 (j) _bk} ) (
k = 2, 3, j = 2, h = 3) to the base stations 912 and 913, respectively, and the time R _{p1 (i) _bk at} which each of the base stations 912 and 913 receives the first radio packet. The clock error E _{b1_bk} (k = 2, 3) is corrected retroactively to (k = 2, 3), and then the clock speed ratio value (R _{p2 (h) _b1} -R _{p2 (j) _b1} ) / If each clock is corrected by (R _{p2 (h) _bk} -R _{p2 (j) _bk} ) (k = 2, 3, j = 2, h = 3),
Base stations 912 and 913 can be synchronized with base station 911.
In the embodiment of the present invention, the signal used for ranging is a wireless LAN signal, which has a wider band than the GPS signal. For example, the bandwidth in IEEE 802.11b, one of the wireless LAN standards, is 22 MHz, and GP
Compared to the S bandwidth of 2 MHz, the bandwidth is wider. Since the time resolution of the signal is increased due to the broadband, the position can be detected with higher accuracy than GPS.
According to the embodiment of the present invention, since the terminal uses only a wireless packet transmission function that is originally provided for position detection, it is not necessary to add a GPS receiver or the like for position detection. And helps reduce size.
In the position detection method based on TDOA (Time Difference Of Arrival) adopted in the embodiment of the present invention, a function for measuring the reception time of a radio packet from a terminal and a function for synchronizing between base stations are required. . However, since the present invention is realized by the function of measuring the reception time or transmission time of the radio packet in the base station, it is useful for cost and size reduction by making the functions common. Furthermore, according to the method shown in the third embodiment of the present invention, the function of measuring the transmission time of the radio packet in the base station can be omitted, which is further useful for cost reduction. Further, since the base station is not actually synchronized, only the clock error is detected, and it is not necessary to stop the operation of the base station.
Even when there is a variation in the accuracy of the clock of the base station and the error of the clock changes with time, the method shown in the second embodiment of the present invention can suppress the deterioration of the positioning accuracy due to the clock error.
By measuring the transmission processing delay and the reception processing delay in the base station in advance, each of the transmission time and the reception time of the wireless packet is measured more accurately.
If the base station in the vicinity of the base station used for position detection is controlled so as to reduce the transmission power in the radio channel selected for position detection, the measurement accuracy of radio packet reception time is improved due to interference reduction. Detection accuracy is better.
Furthermore, according to the embodiment of the present invention, it is possible to synchronize base stations with time accuracy equivalent to position detection accuracy.

It is a block diagram which shows the Example of the wireless LAN system by this invention. It is a block diagram which shows the 2nd Example of the wireless LAN system by this invention. It is a flowchart which shows the Example of the system flow of the position detection by this invention. It is a block diagram which shows the structural example of the base station in this invention. FIG. 5 is a plan view for explaining a radio channel control method according to the present invention. It is a flowchart which shows the flow of the control method of the radio channel by this invention. It is a format figure which shows the Example of the data format of the base station information which a server accumulate | stores in this invention. It is a flowchart which shows another Example of the system flow of the position detection by this invention. It is a block diagram which shows the 3rd Example of the wireless LAN system by this invention. It is a block diagram which shows another structural example of the base station in this invention. It is a flowchart which shows another Example of the system flow of the position detection by this invention.

Explanation of symbols

100, 5900: terminal, 110, 111, 112, 210, 211, 212, 310, 311, 312, 400, 5022, 5063, 5
102, 5111, 5122, 5164, 5202: Base station, 120, 220, 5000: Server, 130: LAN, 410: Communication unit, 420, 1020: Storage unit, Clock: 430, LAN I / F unit: 440, Control Part 450, 411: RF part, 41
2: DAC, 413: ADC, 414: BB section, 415: MAC section, 416: I / F section, 421, 1021: Memory, 422, 102
2: Counter, 423, 1023: I / F section.

Claims (3)

A first base station having a first clock and whose coordinates are known;
A second base station having a second clock and whose coordinates are known;
A wireless system including a terminal,
The first and second base stations measure the reception time of the first signal transmitted from the terminal based on their own clocks,
The second base station measures the reception times of the second and third signals transmitted from the first base station based on the second clock,
The coordinates of the first and second base stations, and
The time of transmission of the second and third signals by the first clock;
From the reception time of the second and third signals by the second clock,
Estimating a time change relationship between the first timepiece and the second timepiece;
Based on the reception time of the first signal by the first timepiece, the reception time of the first signal by the second timepiece, and the time variation of the timepiece,
A wireless system for measuring the position of the terminal. A third base station having a third clock and whose coordinates are known;
The third base station measures the reception time of the first signal transmitted from the terminal based on the third clock,
From the coordinates of the first and third base stations, the transmission time of the second and third signals by the first clock, and the reception time of the second and third signals by the third clock , Estimating the time change relationship between the first clock and the third clock,
The reception time of the first signal by the first clock, the reception time of the first signal by the second clock, the reception time of the first signal by the third clock, and the interval between the clocks The wireless system according to claim 1, wherein the position of the terminal is measured based on a relationship of time changes.   The radio system according to claim 2, wherein at least the first to third base stations are controlled to use the same communication channel prior to position measurement.

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