JP2008002860A - Gps receiver and position detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce electric power consumption in the case of detecting positions by coin cells and other power supplies. <P>SOLUTION: A digital signal processing part 13 specifies satellites, of which the GPS signals can be received on the basis of the reception sensitivity of radio waves transmitted from a plurality of satellites, and n-pieces of channel decoders of a multi-channel decoder 15 can demodulate GPS signals and extract information. A GPS control circuit part 17 determines the channel decoders to which GPS signals of the specified satellites are to be allotted, controls the channel decoders to which GPS signals are allotted into an operating state, and controls the channel decoders to which GPS signals are not allotted to go into a stopped state of operation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a GPS receiver and a position detection method, and more particularly to a GPS receiver and a position detection method for detecting a current position by receiving radio waves from a satellite.

  A GPS (Global Positioning System) is a system that receives radio waves from a plurality of satellites and detects a current position. The satellites in this case are not geostationary satellites, but 32 satellites that orbit the altitude of 20,000 km and change their positions with respect to the earth. In order to detect the current position, it is necessary to receive GPS signals from at least three of the 32 satellites. Actually, in order to perform calculation in consideration of the altitude of the current position to be detected, the current position is detected by receiving GPS signals from four satellites. In general, in position detection using GPS, GPS signal data from each satellite is stored in each of 8 to 16 channels, and the position is detected based on the data of four channels with high reception sensitivity. To do. A 30-second mainframe is transmitted from each satellite. This main frame is composed of 5 subframes each having 6 seconds, and each subframe is composed of 300-bit data. Of the first to fifth subframes, the first subframe stores clock correction coefficient information specific to each satellite and the state of each satellite, and the second and third subframes store the clock correction coefficient information. “Ephemeris” which is orbit information unique to each satellite is stored, and “Almanac data” which is general orbit information common to all 32 satellites is stored in the fourth and fifth subframes. Stored.

Several proposals have been made regarding techniques for reducing power consumption in position detection using GPS.
For example, in a proposed RF receiver, a unit that receives and shapes an RF signal from an antenna and a 12-channel that receives an intermediate signal shaped by a reception and shaping stage are incorporated in a watch powered by a battery. A correlation stage, a microprocessor connected to the correlation stage and calculating X, Y, Z position, velocity, and time data as a function of data extracted from a GPS signal transmitted from a GPS satellite; Is equipped with a correlator and digital signal processing algorithm associated with the controller, allowing the GPS satellite to perform any synchronization task that should be automatically performed to acquire and track the GPS satellite when the channel is operational Auto-tracking. (See Patent Document 1)
In addition, in a proposed GPS receiver, when almanac data or ephemeris data has been acquired from a GPS satellite, a satellite with a high elevation angle is obtained from the approximate position or detailed position of the satellite obtained by the satellite position calculation unit. Set the priority of GPS satellites to be assigned to each reception channel of the receiving unit with the satellite at the highest position, the satellite with a low elevation angle at the middle, and the satellite that cannot be received at the lowest position, and positioning targets based on the priority Select a GPS satellite. The clock control unit supplies the clock signal only to the reception channel to which the selected GPS satellite is assigned, and stops the supply of the clock signal to the other reception channels to reduce power consumption. (See Patent Document 2)
JP 2002-122655 A JP 2004-191054 A

  However, in Patent Document 1 and Patent Document 2 described above, the GPS signal data from each satellite captured in channels 8 to 16 is stored, and three or four channels having high reception sensitivity are selected. When the reception environment is bad, it is difficult to acquire 3 or 4 satellites, and it takes a long time to acquire, or when 3 or 4 satellites cannot be acquired. Because of the power consumed in the 8th to 16th channels, not only the continuous measurement possible time is reduced due to the voltage drop of the battery, but also the device itself may stop functioning rather than the position detection.

For example, assuming that the specifications of a general coin-type battery are a voltage of 3 V, a standard current of 0.1 mA, and a standard capacity of 30 mAh, it can be used for 300 hours when 0.1 mA is passed at 3 V. In the GPS receiver, there is a current consumption of approximately 0.4 mA per channel. Therefore, the theoretical continuous measurable time H is expressed by the following equation.
H = 30 (mAh) /0.4 (mA) × number of channels In order to set the eight channels to the operating state,
H = 30 (mAh) /0.4 (mA) × 8 (ch) = 9.375 (h)
To bring 12 channels into operation,
H = 30 (mAh) /0.4 (mA) × 12 (ch) = 6.25 (h)
To bring 16 channels into operation,
H = 30 (mAh) /0.4 (mA) × 16 (ch) = 4.6875 (h)
It becomes.
For this reason, in the GPS receiver driven by a battery, there existed the subject of how to reduce the power consumption of a battery.

  The present invention is to solve such a conventional problem, and an object of the present invention is to reduce power consumption when position detection is performed using a coin-type battery or other small power source.

  The GPS receiver according to claim 1 is a receiving means for identifying a satellite capable of receiving a GPS signal based on reception sensitivity of radio waves transmitted from a plurality of satellites (in the embodiment, the digital signal processing unit of FIG. 1). 13), a predetermined number of information extracting means for demodulating the GPS signal and extracting information (in the embodiment, corresponding to n channel decoders 15 in FIG. 1), and receiving means An allocating unit (corresponding to the GPS control circuit unit 17 in FIG. 1 in the embodiment) that determines an information extracting unit that allocates the GPS signals of the satellites operated, and an information extracting unit to which the GPS signals are allocated by the allocating unit are operated. Control means for controlling the information extraction means to which the GPS signal is not assigned to the operation stopped state (in the embodiment, the GPS control circuit unit 17 in FIG. And those to), has a structure which includes a.

2. The GPS receiver according to claim 1, wherein, as described in claim 2, the assigning means includes the content of information extracted by the information extracting means to which the GPS signal is assigned according to the number of satellites capable of receiving the GPS signal. You may make it the structure which designates.
In the GPS receiving device according to claim 2, as described in claim 3, the assigning means, as the content of information extracted by the information extracting means when the number of satellites capable of receiving GPS signals is less than three, At least time information is specified, and when the number of satellites capable of receiving GPS signals is 3 or more, at least position information and time information are specified as the contents of information extracted by the information extraction means. Good.
In the GPS receiver according to claim 1, as described in claim 4, each of the predetermined number of information extracting means is operated by electric power supplied from the battery and a clock signal supplied by the control means. The information extraction means to which no GPS signal is assigned may be put into an operation stop state by stopping the clock signal.

According to a fifth aspect of the present invention, there is provided a position detection method for identifying a satellite capable of receiving a GPS signal based on reception sensitivity of radio waves transmitted from a plurality of satellites, and for extracting information by demodulating the GPS signal. Step B for determining information extraction means for assigning the GPS signals of the satellites identified in Step A from among a predetermined number of information extraction means (corresponding to n channel decoders 15 in FIG. 1 in the embodiment); The information extracting means to which the GPS signal is assigned in step B is controlled to be in the operating state, and the information extracting means to which the GPS signal is not assigned is controlled to be in the operation stopped state.
Step A to step C correspond to processing executed by the GPS control circuit unit 17 of FIG. 1 in the embodiment.

6. The position detection method according to claim 5, wherein, in the position detection method according to claim 6, the content of the information extracted by the information extracting means to which the GPS signal is assigned according to the number of satellites capable of receiving the GPS signal. You may make it the structure which designates.
In the position detection method according to claim 6, as described in claim 7, step B is performed as information contents extracted by the information extraction means when the number of satellites capable of receiving GPS signals is less than three. At least time information is specified, and when the number of satellites capable of receiving GPS signals is 3 or more, at least position information and time information are specified as the contents of information extracted by the information extraction means. Good.
In the position detection method according to claim 5, as described in claim 8, each of the predetermined number of information extraction means is operated by the power supplied from the battery and the clock signal supplied by step C. The information extraction means to which no GPS signal is assigned may be controlled to be in an operation stop state by stopping the clock signal.

  According to the present invention, when position detection is performed using a coin-type battery or other power source, an effect of reducing power consumption can be obtained.

Hereinafter, embodiments of a GPS receiver and a position detection method according to the present invention will be described in detail with reference to FIGS. 1 to 7.
FIG. 1 is a block diagram illustrating a configuration of a GPS receiving device 100 according to an embodiment of the present invention. As shown in FIG. 1, a GPS receiver 100 includes an antenna 10, an antenna preamplifier 11, a high-frequency receiving circuit 12, a digital signal processing unit 13, a clock unit 14, and a power supply unit (not shown) for supplying power thereto. It has.

  The antenna 10 is an omnidirectional antenna that receives a GPS signal transmitted from a GPS satellite. The GPS signal is a radio signal called an L1 wave having a fundamental frequency of 1575.42 MHz. The GPS signal includes a signal called a civilian C / A code (Coarse / Acquisition Code). The C / A code is encoded by a PRN code (Pseudo Random Noise Code) which is a pseudo noise code, and a different C / A code is assigned to each of up to 32 GPS satellites. Therefore, by despreading the received GPS signal with a C / A code unique to each GPS satellite, the GPS signal can be separated and received for each satellite.

  Further, the C / A code is transmitted repeatedly with a 1023 bit signal at a period of 1 ms. The navigation data is data in which the 20 cycles of the C / A code are taken as 1 bit. The navigation data includes data such as GPS satellite orbit information and time information. FIG. 2 is a diagram showing a format of navigation data. As shown in FIG. 2A, navigation data transmitted from a GPS satellite is composed of 25 pages of data with a 1500-bit, 30-second mainframe as one page. Therefore, it takes 12 minutes and 30 seconds to receive the 25-page mainframe. The main frame of each page is composed of five subframes of subframes 1 to 5. Each subframe is 300 bits and 6 seconds, and is composed of 10 words in which 1 word is 30 bits. In addition, the two synchronization words at the head of each subframe include 30-bit TLM (Telemetry) data and 30-bit HOW (Handover Word) data.

  The subframes 1 to 3 are composed of the same data through the main frame of 25 pages, but the subframe 4 and the subframe 5 are divided into 25 pages and transmitted because of the large amount of data. FIG. 2B is a diagram illustrating the contents of data in subframes 1 to 5. Subframe 1 includes a satellite clock correction coefficient of the GPS satellite itself that is transmitting, a data update time, and various flags. Subframe 2 and subframe 3 include orbit information (ephemeris data) of the transmitting GPS satellite itself. That is, subframes 1 to 3 are data unique to each GPS satellite. On the other hand, subframe 4 and subframe 5 include rough orbit information (almanac data), ionosphere correction factors, and satellite health data common to all GPS satellites on a maximum of 32 orbits. ing.

  In FIG. 1, the antenna preamplifier 11 amplifies a 1575.42 MHz high frequency signal received by the antenna 10 and supplies the amplified signal to the high frequency receiving circuit unit 12. The high frequency receiving circuit unit 12 detects and amplifies the high frequency signal, converts it to an intermediate frequency of 1.023 MHz, and supplies it to the digital signal processing unit 13.

  The digital signal processing unit 13 includes a multi-channel decoder 15, a memory 16, a GPS control circuit unit 17, a ROM 18, and a RAM 19. The multi-channel decoder 15 includes n (for example, 16) channel decoders including channel decoder (1) to channel decoder (n), and one GPS satellite is assigned to each reception channel. Independent reception processing, that is, processing for extracting the ephemeris and almanac information shown in FIG. 2 by demodulating the navigation data shown in FIG. 2 included in the GPS signal. The memory 16 stores GPS satellite information and reception sensitivity values extracted by the reception processing of the channel decoder (1) to channel decoder (n). The GPS control circuit unit 17 develops a necessary program such as a GPS reception control program from the system program and various application programs stored in the ROM 18 in the RAM 19, and based on the information stored in the memory 16. The multi-channel decoder 15 is controlled, and the power supply to the antenna preamplifier 11 and the high-frequency receiving circuit unit 12 is controlled.

The clock unit 14 includes a device control circuit unit 20, a clock circuit unit 21, an oscillation circuit unit 22, an input unit 23, a display output unit 24, a display unit 25, a ROM 26, and a RAM 27.
The device control circuit unit 20 develops necessary programs such as a time correction program and a position display program from the system program and various application programs stored in the ROM 26 in the RAM 27, and performs GPS control of the digital signal processing unit 13. While exchanging commands and data with the circuit unit 17, the operation of the clock unit 14 is controlled. The time measuring circuit unit 21 measures the time based on the clock signal output from the oscillation circuit unit 22 and supplies the device control circuit unit 20 with data of the current time that is recorded in units of 1 second, for example. The device control circuit unit 20 converts the data of the current time into display data and displays it on the display unit 25 via the display output unit 24. The input unit 23 inputs operation information from the user and information from another computer or storage medium to the device control circuit unit 20. When a mode signal for designating display content or a measurement instruction is input from the input unit 23, the device control circuit unit 20 performs processing according to the input content.

Next, a position detection method executed by the GPS receiving device 100 shown in FIG. 1 will be described based on a flowchart executed by cooperation of the GPS control circuit unit 17 and the device control circuit unit 20.
FIG. 3 is a flowchart of the main routine of the device control circuit unit 20. The device control circuit unit 20 first performs predetermined initialization (step SA1) to determine whether or not a mode signal is input from the input unit 23 (step SA2). When the mode signal is input, The mode signal is a time acquisition instruction for acquiring the current time, a three satellite acquisition (2D Fix) instruction for acquiring three GPS satellites and acquiring the current position, or acquiring four GPS satellites and acquiring the current position. It is determined whether it is a 4-satellite capture (3D Fix) instruction (step SA3).

  The device control circuit unit 20 sets the flag MODE to “0” when the mode signal is a time acquisition instruction (step SA4), and sets the MODE to “1” when the mode signal is a 2D Fix instruction (step SA5). ) When the mode signal indicates 3D Fix, MODE is set to “2” (step SA6). After setting MODE, or when the mode signal is not input and MODE is set to the previous value, device control circuit unit 20 determines whether or not a measurement instruction is input from input unit 23. (Step SA7) When the measurement instruction is input, the MODE value is sent to the GPS control circuit unit 17 and the execution of the measurement mode process is instructed (Step SA8).

  4 and 5 are flowcharts of the measurement mode process executed by the GPS control circuit unit 17. The GPS control circuit unit 17 activates an enable signal to the antenna preamplifier 11 and the high frequency reception circuit unit 12 to cause the antenna preamplifier 11 and the high frequency reception circuit unit 12 to transition from the operation stop state (sleep state) to the operation state. (Step SB1), satellite acquisition processing is executed (step SB2).

  FIG. 6 is a flowchart of the satellite acquisition process. The GPS control circuit unit 17 starts the multi-channel decoder 15 (step SC1), sets “1” to the variable CH designating the channel decoder (step SC2), and changes the value of CH to steps SC3 to SC The loop process of SC8 is executed. In this loop process, the GPS control circuit unit 17 starts satellite acquisition by the channel decoder (CH) (step SC3), determines whether or not acquisition is possible (step SC4), and when acquisition is not possible, It is determined whether or not a predetermined time has elapsed (step SC5). If a satellite can be acquired before the predetermined time has elapsed, the flag ON (CH) of the channel decoder is set to "1" (step SC). SC6), the value of CH is incremented by 1 (step SC7), and it is determined whether or not the value of CH exceeds the number of channel decoders (step SC8). Thereafter, the GPS control circuit unit 17 proceeds to step SC3 and repeats the loop processing.

  If the satellite cannot be captured in step SC4 and the predetermined time has elapsed in step SC5, the GPS control circuit unit 17 determines whether or not any satellite has been captured (step SC9). If there is none, the warning flag is turned on (step SC10). When the value of CH exceeds the number of channel decoders at step SC8, that is, when satellite acquisition processing is performed for all channel decoders, or when the warning flag is turned on at step SC10, the GPS control circuit unit 17 Returning to the measurement mode processing of FIG.

  In the measurement mode process of FIG. 4, after the satellite acquisition process, the GPS control circuit unit 17 determines whether or not the warning flag is off (step SB3). If the warning flag is off, that is, at least one When the satellite can be acquired, the acquisition number / reception sensitivity detection process is executed (step SB4). FIG. 7 is a flowchart of the acquisition number / reception sensitivity detection process.

  In FIG. 7, the GPS control circuit unit 17 sets the value of the variable CH designating the channel decoder to “1” (step SD1), and performs the loop processing from step SD2 to step SD6 while changing the value of CH. Execute. In this loop processing, the GPS control circuit unit 17 determines whether or not the value of the flag ON (CH) is “1” (step SD2), and when the value of ON (CH) is “1”. Determines whether the reception sensitivity value of the channel decoder (CH) is smaller than the threshold value A (step SD3). If the reception sensitivity value is smaller than A, the reception environment is bad and the GPS signal cannot be demodulated. Then, ON (CH) is reset to “0” (step SD4).

  The GPS control circuit unit 17 resets the ON (CH) at step SD4, or when ON (CH) is "0" at step SD2, or the value of the reception sensitivity of the channel decoder (CH) at step SD3. Is equal to or greater than A, the value of CH is incremented by 1 (step SD5), and it is determined whether the value of CH exceeds the number of channel decoders (step SD6). The value of CH is equal to or less than the number of channel decoders. In this case, the process proceeds to step SD2 to repeat the loop process.

  When the value of CH exceeds the number of channel decoders in step SD6, the GPS control circuit unit 17 sets the value of the flag MODE sent from the device control circuit unit 20 to “0”, “1”, or “2”. When the value of MODE is “0”, whether the number of channel decoders whose ON () is “1” satisfies the condition of “1” or more is satisfied. (Step SD8), when the MODE value is “1”, it is determined whether or not the number of channel decoders whose ON () is “1” satisfies the condition of “3” or more (step S8). SD9) If the MODE value is “2”, it is determined whether or not the number of channel decoders whose ON () is “1” satisfies the condition of “4” or more (step SD10). In step SD8, step SD9, or step SD10, the GPS control circuit unit 17 turns on the warning flag if none of the conditions is satisfied (step SD11). If any of the conditions is satisfied in step SD8, step SD9, or step SD10, or after the warning flag is turned on in step SD11, the process returns to the measurement mode process of FIG.

In FIG. 4, the GPS control circuit unit 17 determines whether or not the warning flag is off after executing the capture number / reception sensitivity detection process (step SB5). If the warning flag is off, It is determined whether or not MODE is “0” (step SB6). If MODE is “0”, the channel decoder 15 having ON () “1” and having the highest reception sensitivity is selected. Select (step SB7), stop the operation of other channel decoders (step SB8), extract time information from the selected channel decoder (step SB9), and send the time information to the clock unit 14 (Step SB10), the operations of the antenna preamplifier 11, the high frequency receiving circuit 12, and the channel decoder 15 are stopped (Step SB11).
If the warning flag is ON in step SB3 or SB5, the GPS control circuit unit 17 instructs the device control circuit unit 20 to display a warning for a predetermined time (step SB12), and the antenna preamplifier 11, high frequency The operations of the receiving circuit 12 and the channel decoder are stopped (step SB11).

  If the MODE is not “0” in step SB6, the GPS control circuit unit 17 determines whether the MODE is “1” or “2” (step SB13 in FIG. 5). In the case of “1”, the channel decoder having the first to third highest receiving sensitivity is selected from the channel decoders in which ON () is “1” (step SB14), and when the MODE is “2”, The channel decoder having the first to fourth highest receiving sensitivity is selected from the channel decoders whose ON () is “1” (step SB15).

  After selecting the channel decoder in step SB14 or step SB15, the GPS control circuit unit 17 stops the operation of the channel decoder other than the selected channel decoder (step SB16), and the position received from three or four GPS satellites. Information is extracted (step SB17), the current position is calculated based on the position information (step SB18), the calculation result is sent to the clock unit 14 (step SB19), the antenna preamplifier 11, and the high frequency receiving circuit 12 And the operation of the multi-channel decoder 15 is stopped (step SB11 in FIG. 4).

As described above, according to this embodiment, the digital signal processing unit 13 specifies satellites that can receive GPS signals based on the reception sensitivities of radio waves transmitted from a plurality of satellites. Each channel decoder can demodulate the GPS signal and extract information. The GPS control circuit unit 17 determines the channel decoder to which the GPS signal of the specified satellite is assigned, controls the channel decoder to which the GPS signal is assigned to the operating state, and sets the channel decoder to which the GPS signal is not assigned to the operation stopped state. Control.
Therefore, power consumption can be reduced when position detection is performed using a coin-type battery or other power source.

  In the above embodiment, the GPS control circuit unit 17 specifies the content of information extracted by the channel decoder to which the GPS signal is assigned according to the number of satellites that can receive the GPS signal. Furthermore, in this case, when the number of satellites that can receive GPS signals is less than 3, the GPS control circuit unit 17 designates at least time information as the contents of information extracted by the channel decoder and receives GPS signals. When the number of possible satellites is three or more, at least position information and time information are designated as the contents of information extracted by the channel decoder.

  Further, in the above embodiment, each of the n channel decoders of the multi-channel decoder 15 is operated by the power supplied from the battery and the clock signal supplied by the GPS control circuit unit 17, and the GPS control circuit unit 17 By stopping the clock signal, the channel decoder to which no GPS signal is assigned is put into an operation stop state.

In the GPS receiver of the above embodiment, power is supplied by a battery. However, power may be supplied by a power generation element that generates light by receiving light, vibration, or other energy. Even in such a configuration, the GPS control circuit 18 is brought into an operation state by applying a clock signal to each channel decoder of the multi-channel decoder 15, and is brought into an operation stop state by stopping the clock signal.
Therefore, power consumption can be reduced when position detection is performed by a power source that is limited in power supply, such as a coin-type battery or a power generation element that receives light, vibration, or other energy.

  In addition, the said embodiment is an example for implement | achieving this invention, and this invention is not limited to the following embodiment. That is, it is apparent that the present invention is capable of other embodiments and various modifications that are easily conceivable by those skilled in the art without departing from the scope of the claims appended to this specification.

The block diagram which shows the structure of the GPS receiver in embodiment of this invention. The figure which shows the frame structure in a GPS signal. The flowchart of the main routine which shows operation | movement of the GPS receiver in embodiment. The flowchart of the measurement mode process in FIG. The flowchart of the measurement mode process following FIG. The flowchart of the satellite acquisition process in FIG. The flowchart of the acquisition number / reception sensitivity detection process in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Antenna 11 Antenna preamplifier 12 High frequency receiving circuit part 13 Digital signal processing part 14 Clock part 15 Multichannel decoder 16 Memory 17 GPS control circuit part 18 ROM
19 RAM
20 Device Control Circuit Unit 21 Timekeeping Circuit Unit 22 Oscillation Circuit Unit 23 Input Unit 24 Display Output Unit 25 Display Unit 26 ROM
27 RAM

Claims (8)

Receiving means for identifying a satellite capable of receiving a GPS signal based on reception sensitivity of radio waves transmitted from a plurality of satellites;
A predetermined number of information extracting means for demodulating GPS signals and extracting information;
Allocating means for determining information extracting means for allocating the GPS signal of the satellite specified by the receiving means;
Control means for controlling the information extracting means to which the GPS signal is assigned by the assigning means to be in an operating state, and for controlling the information extracting means to which the GPS signal is not assigned to be in an operation stopped state;
A GPS receiver characterized by comprising:   2. The GPS receiving apparatus according to claim 1, wherein the assigning means designates the content of information extracted by the information extracting means to which the GPS signal is assigned according to the number of satellites that can receive the GPS signal. .   When the number of satellites capable of receiving GPS signals is less than three, the assigning means designates at least time information as the content of information extracted by the information extracting means, and the number of satellites capable of receiving GPS signals is 3. The GPS receiving apparatus according to claim 2, wherein in the case of three or more, at least position information and time information are designated as contents of information extracted by the information extracting means.   Each of the predetermined number of information extraction means is operated by power supplied from a battery and a clock signal supplied by the control means, and the control means is not assigned a GPS signal by stopping the clock signal. 2. The GPS receiver according to claim 1, wherein the information extracting means is in an operation stop state. Identifying a satellite capable of receiving GPS signals based on reception sensitivity of radio waves transmitted from a plurality of satellites; and
Step B for determining information extraction means for assigning the GPS signal of the satellite specified in Step A from among a predetermined number of information extraction means for demodulating the GPS signal and extracting information;
Step C for controlling the information extracting means to which the GPS signal is assigned in Step B to the operating state and the information extracting means to which the GPS signal is not assigned to the operating stop state;
Position detection method to execute.   6. The position detection method according to claim 5, wherein the step B specifies the content of information extracted by the information extraction means to which the GPS signal is assigned according to the number of satellites that can receive the GPS signal. .   In the step B, when the number of satellites capable of receiving GPS signals is less than three, at least time information is designated as the content of information extracted by the information extracting means, and the number of satellites capable of receiving GPS signals is 7. The position detecting method according to claim 6, wherein when there are three or more, at least position information and time information are designated as contents of information extracted by the information extracting means. Each of the predetermined number of information extraction means is operated by the power supplied from the battery and the clock signal supplied by the step C, and the GPS signal is not assigned to the step C by stopping the clock signal. 6. The position detecting method according to claim 5, wherein the information extracting means is controlled to be in an operation stop state.

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