JP2015087343A - Satellite search method, time correction method, positioning device, and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accelerate satellite search.SOLUTION: A satellite search method includes the steps of: selecting a correlation data length when performing correlation operation between the input signal of a satellite signal for positioning and a replica code; and performing correlation operation with a selected correlation data length. A positioning device includes: a selection unit for selecting a correlation data length when performing correlation operation between the input signal of the satellite signal for positioning and the replica code; and a correlation operation unit for performing correlation operation with the selected correlation data length.

Description

  The present invention relates to a satellite search method and the like.

  A GPS (Global Positioning System) is widely known as a positioning system using positioning satellite signals. In GPS, a plurality of GPS satellite signals are captured, a position calculation is performed using navigation messages carried superimposed on each of the captured GPS satellite signals, and the position of the GPS receiver and clock error (clock bias) are calculated. Looking for. There are various demands for GPS receivers, and one of the typical demands is reduction of power consumption. For example, Patent Document 1 discloses a technique for reducing power consumption by changing the number of correlators used for capturing GPS satellite signals.

JP 2009-36749 A

  In addition, shortening TTFF (Time To First Fix) in GPS positioning is one of typical requests. Therefore, the present invention has been devised as an object to realize a technique that contributes to shortening of TTFF while reducing power consumption. Specifically, an object is to shorten the time required for capturing a GPS satellite (satellite search time). Note that the reduction in the satellite search time leads to a reduction in the time required for time correction using the time information (Z count) included in the navigation message, in addition to the reduction in TTFF.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  A first mode for solving the above-described problem is to select a correlation data length when performing a correlation operation between a received signal that has received a positioning satellite signal and a replica code, and a correlation selected by the selection. Performing a correlation calculation with a data length.

  Further, as another form, a selection unit that selects a correlation data length when performing a correlation operation between a received signal that has received a positioning satellite signal and a replica code, and a correlation that performs the correlation operation with the selected correlation data length You may comprise the positioning apparatus provided with the calculating part.

  Moreover, you may comprise the electronic device provided with the above-mentioned positioning apparatus as another form.

  According to the first embodiment and the like, the satellite search time can be shortened by performing the correlation calculation between the received signal of the positioning satellite signal and the replica code with a shorter correlation data length than usual. This is because when the correlation data length is short, the processing time of the correlation calculation is shortened. Therefore, the satellite search time can be shortened as much as possible by selecting a short correlation data length as much as possible.

  Further, as a second form, the correlation data length is a spreading code length or longer and a correlation calculation is performed with a length shorter than an interval of bit transition timings of a navigation message carried in the received signal. The correlation data length may be included, and the selection may constitute a satellite search method including selecting the first correlation data length at a cold start.

  According to the second embodiment, at the cold start, the correlation calculation is performed with a length that is equal to or longer than the spread code length and shorter than the bit transition timing interval of the navigation message carried in the received signal. Is done. For this reason, even if it is a cold start, a satellite search can be realized in a relatively short time.

  Further, as a third aspect, the satellite search method may further include setting a search frequency, and the selecting includes selecting the correlation data length based on the search frequency. good.

  According to the third embodiment, the search frequency is set, the correlation calculation is performed with the correlation data length selected based on the set search frequency, and the satellite search is executed.

  According to a fourth aspect, the selecting includes selecting a shorter correlation data length when the search frequency satisfies a predetermined range condition than when the search frequency does not satisfy the range condition. A search method may be configured.

  According to the fourth embodiment, when the search frequency is wide so as to satisfy the predetermined wide range condition, the satellite search is performed by performing the correlation calculation with a short correlation data length, compared with the narrow case where the wide range condition is not satisfied. Is executed. The wider the search frequency, the greater the number of correlation calculations. For this reason, when the search frequency is wide, the correlation calculation is performed with a short correlation data length compared with the narrow search frequency, thereby shortening the processing time required for one correlation calculation and the total time required for the satellite search. Can be shortened.

  According to a fifth aspect of the present invention, there is provided a method for correcting a time measured by a clock unit, wherein the above-described satellite search method is executed, and the timepiece clock signal is acquired based on a positioning satellite signal captured by the satellite search method. A time correction method including correcting the time measured by the unit may be configured.

  As another form, the clock unit, a satellite capturing unit that captures a positioning satellite signal based on the result of the correlation calculation, and the clock unit based on the positioning satellite signal captured by the satellite capturing unit You may comprise the electronic device provided with the time correction part which corrects time-measurement time.

  According to the fifth embodiment and the like, the time required for correcting the time measured by the clock unit based on the acquired positioning satellite signal is shortened by shortening the time required for the satellite search.

An example of setting the search frequency according to the elapsed time from the last positioning. 1 is a configuration diagram of a portable electronic device. The block diagram of a baseband process circuit part. The flowchart of a positioning mode process. The flowchart of time mode processing. The flowchart of a satellite acquisition process. Experimental results of signal acquisition time when the correlation data length is different.

[Overview]
A GPS receiver that is a positioning device receives a GPS satellite signal that is a positioning satellite signal transmitted from a GPS satellite that is a positioning satellite, and superimposes the GPS satellite signal that is being carried on the received GPS satellite signal. Based on navigation messages such as orbit information (ephemeris and almanac), the GPS receiver position and clock error are obtained.

  The frequency (carrier frequency) at which a GPS satellite transmits a GPS satellite signal is previously defined as “1.57542 [GHz]”. However, due to the influence of Doppler caused by the movement of the GPS satellite and the GPS receiver, the GPS The frequency at which the receiver receives GPS satellite signals (reception frequency) deviates from this carrier frequency. For this reason, the GPS receiver performs correlation calculation between the received signal and a replica code, which is a pseudo C / A (Coarse and Acquisition) code generated inside the receiver, in each of the frequency direction and the phase direction. The GPS satellite signal is captured by, and measurement information such as the reception frequency and code phase of the captured GPS satellite signal is acquired based on the correlation calculation result.

  In the satellite search, the correlation calculation between the received signal and the replica code is repeatedly performed while shifting the phase and frequency by a predetermined amount. For this reason, as the range in which the correlation calculation in the frequency direction is performed (hereinafter referred to as “search frequency”) becomes wider, the number of correlation calculations increases, and as a result, the time required for the satellite search becomes longer. The search frequency is determined as a range centered on “1.57542 [GHz]”, which is the carrier frequency of the GPS satellite signal, and is expressed as “± 500 [Hz]”, for example.

  In addition, the correlation calculation is an operation in which a correlation value obtained by multiplying the reception signal at a certain moment and the replica code is integrated for a predetermined time (in other words, for a predetermined length). The time to be subjected to one correlation calculation, that is, the data length of the received signal is hereinafter referred to as “correlation data length”. If the correlation data length is constant, the longer the number of correlation calculations, the longer the time required for satellite search. If the search frequency is wide, the number of correlation calculations increases accordingly. In the present embodiment, the correlation data length is changed according to the search frequency to shorten the time required for capturing the GPS satellites. Specifically, when the search frequency is wide, the correlation data length is shortened, the time required for one correlation calculation (correlation processing time) is shortened, and the time required for capturing the GPS satellites is shortened.

  The search frequency is maximum in the case of so-called cold start. The cold start is a case where positioning is performed by starting a state in which a GPS satellite located in the sky of the portable electronic device 1 cannot be determined without having a navigation message such as ephemeris or almanac. Therefore, at the cold start, since the initial position, initial velocity, satellite orbit data, etc. of the GPS satellite are not included at all, the search frequency is maximized.

  On the other hand, if it is not a cold start, the search frequency is determined according to the elapsed time t from the final positioning. As described above, the reception frequency of the GPS satellite signal is shifted from the carrier frequency by Doppler or the like. That is, there is a possibility that the reception frequency of the current GPS satellite signal is fluctuating with respect to the reception frequency at the time of the final positioning, but the fluctuation range becomes larger as the elapsed time t from the final positioning becomes longer. For this reason, as shown in FIG. 1, the search frequency F is set to be wider as the elapsed time t from the last positioning is longer. In the example of FIG. 1, the gradient of the search frequency F with respect to the elapsed time t is increased until the elapsed time t reaches a predetermined time, and after the predetermined time is reached, the gradient is made gentle, but this is an example. . The search frequency F may be monotonously increased with respect to the elapsed time t.

  Several kinds of variable correlation data lengths are used. Among these, the minimum correlation data length value (first correlation data length) is equal to or longer than the length (spreading code length) of the C / A code that is the spreading code of the GPS satellite signal (1 ms or longer). The value is shorter than “20 milliseconds (that is, BTT (Bit Transition Time) interval)”, which is the bit length of one bit of the message.In the present embodiment, “half the bit length of the navigation message” The other types of correlation data lengths are “20 milliseconds”, “100 milliseconds”, and “1000 milliseconds” that match the bit length of the navigation message.

  If the correlation data length is short, the correlation power (correlation value peak magnitude) obtained as a result of the correlation calculation becomes small, and it becomes difficult to capture a GPS satellite having a weak signal strength. As a result of the experiment, the GPS receiver 10 of the present embodiment captures a GPS satellite signal having a signal intensity of “about −130 dBm or more” in the correlation calculation with the correlation data length of “10 milliseconds” as the minimum value. It was suitable.

[Constitution]
FIG. 2 is a configuration diagram of the portable electronic device 1 in the present embodiment. According to FIG. 2, the portable electronic device 1 includes a GPS antenna 12, a GPS receiver 10, a main processing unit 20, an operation unit 22, a display unit 24, a sound output unit 26, and a communication unit 28. The clock unit 30 and the main storage unit 32 are provided. The portable electronic device 1 of this embodiment is a runner's watch, for example.

  The GPS antenna 12 is an antenna that receives an RF (Radio Frequency) signal including a GPS satellite signal transmitted from a GPS satellite.

  The GPS receiver 10 includes an RF receiving circuit unit 14 and a baseband processing circuit unit 16.

  The RF receiving circuit unit 14 down-converts an RF signal received by the GPS antenna 12 into an intermediate frequency signal (IF (Intermediate Frequency) signal), amplifies the signal, converts the signal into a digital signal, and outputs the digital signal.

  The baseband processing circuit unit 16 captures and tracks a GPS satellite signal using the received signal data input from the RF receiving circuit unit 14, and uses time information, satellite orbit data, and the like extracted from the captured GPS satellite signal. Thus, the position and time of the GPS receiver 10 (portable electronic device 1) are calculated.

  FIG. 3 is a configuration diagram of the baseband processing circuit unit 16. 3, the baseband processing circuit unit 16 includes a memory unit 110, a replica code generation unit 120, a correlation calculation unit 130, a BB processing unit 200, and a BB storage unit 300.

  The memory unit 110 stores sample data obtained by sampling the received signal data input from the RF receiving circuit unit 14 at a predetermined sample time interval.

  The replica code generation unit 120 generates a C / A code replica code. Specifically, a replica code having a PRN (Pseudo Random Noise) number designated by the satellite acquisition unit 210 is generated with a designated phase shift amount.

  The correlation calculation unit 130 performs correlation calculation between the received signal data (sample data) stored in the memory unit 110 and the replica code generated by the replica code generation unit 120. At this time, the correlation integration with the replica code is performed on the data of the received signal in units of data having a length specified as the correlation data length by the satellite capturing unit 210.

  The BB processing unit 200 is realized by a processor such as a CPU (Central Processing Unit) or a DSP (Digital Signal Processor), and comprehensively controls each unit of the baseband processing circuit unit 16. The BB processing unit 200 includes a satellite capturing unit 210, a position calculating unit 220, and a time correcting unit 230, and positioning mode processing (see FIG. 4) in the positioning mode for calculating the position of the portable electronic device 1. In the time measurement mode in which the time of the clock unit 30 is corrected, time measurement mode processing (see FIG. 5) is performed. In the immediate mode, the position is not calculated. The positioning / time mode is switched and set in accordance with an instruction from the operation unit 22 by the user.

  The satellite capturing unit 210 captures a GPS satellite using the received signal data stored in the memory unit 110. Specifically, first, a search frequency is set for a GPS satellite to be captured. That is, if it is a cold start, the search frequency is set to a predetermined maximum value. If it is not a cold start, the search frequency is set according to the search frequency setting table 320 based on the elapsed time from the last positioning (previous positioning). The search frequency setting table 320 is a data table that defines the relationship between the elapsed time t from the final positioning and the search frequency F as shown in FIG. The satellite acquisition unit 210 of this embodiment corresponds to a selection unit that selects a correlation data length.

  Next, in accordance with the set search frequency, a correlation data length that is a data length of a reception signal for performing correlation calculation is set. That is, if the search frequency is set to the maximum value (corresponding to cold start), the correlation data length is set to a predetermined minimum value (first correlation data length, for example, 10 milliseconds). To do. If the search frequency is not the maximum value, the correlation data length is set according to the search frequency. That is, if the search frequency is equal to or higher than a predetermined threshold (the search frequency is “wide”), the correlation data length is set to a second correlation data length (for example, 20 milliseconds) that is longer than the first correlation data length. If it is less than the threshold (the search frequency is “narrow”), the correlation data length is set to a third correlation data length (for example, 100 milliseconds) longer than the second correlation data length. If the search frequency is narrow, the number of correlation calculations is small, so that the correlation data length is increased in order to capture the GPS satellite signal more reliably.

  Then, the correlation calculation unit 130 is caused to perform a correlation calculation of the set correlation data length for the set search frequency. This is a so-called frequency direction search (frequency search). In addition, the satellite acquisition unit 210 causes the replica code generation unit 120 to change the phase shift amount of the generated replica code, and causes the correlation calculation unit 130 to perform correlation calculation of the set correlation data length. This is a so-called phase direction search (phase search). As a result of the frequency direction search and the phase direction search, it is determined whether or not the GPS satellite signal has been acquired based on whether or not the peak of the correlation value is equal to or greater than a threshold value. The frequency at which the correlation value peak appears is the reception frequency, and the phase at which the correlation value peak appears is the code phase. For each captured GPS satellite, the reception frequency and code phase are acquired as measurement data 350 and stored in the BB storage unit 300.

  Data relating to GPS satellite acquisition by the satellite acquisition unit 210 is stored as satellite acquisition data 330. The satellite acquisition data 330 stores a satellite number, a search frequency, a high-speed search flag, a correlation data length, and acquisition success / failure for all GPS satellites. The high-speed search flag is a flag for storing either “1” or “0”, and “1” sets the correlation data length to the minimum value (first correlation data length), that is, the received signal This indicates that the time required for one correlation operation between the data and the replica code is the shortest, and is set to “1” at a cold start, for example.

  The position calculation unit 220 performs a position calculation process using the satellite orbit data 340 and the measurement data 350 acquired for each GPS satellite captured by the satellite capture unit 210, and the GPS receiver 10 (portable electronic device 1). Position and clock error (clock bias) are calculated. As the position calculation process, for example, a known method such as a least square method or a Kalman filter can be applied.

  The satellite orbit data 340 is data such as almanac and ephemeris of each GPS satellite, and is acquired by decoding the received GPS satellite signal. The measurement data 350 is data such as the reception frequency, code phase, and Doppler frequency of the received GPS satellite signal, and is acquired based on the correlation calculation result with the replica code. Further, the position and clock error data calculated by the position calculation unit 220 are accumulated and stored as positioning history data 360.

  The time correction unit 230 decodes the Z count of the data carried in the GPS satellite signal captured by the satellite capturing unit 210 and acquires it as time information, and uses the acquired time information to Correct the time. The Z count is information included in a subframe of the navigation message. In the case of GPS, since the sub-frame period is 6 seconds, the Z count can be acquired if GPS satellite signals for 6 seconds at the latest can be received.

  The BB storage unit 300 is realized by a ROM (Read Only Memory), a RAM (Random Access Memory), or the like, and includes a system program and various functions for the BB processing unit 200 to comprehensively control the baseband processing circuit unit 16. In addition to storing programs, data, and the like for realization, it is used as a work area for the BB processing unit 200, and calculation results and the like of the BB processing unit 200 are temporarily stored. In the present embodiment, the BB storage unit 300 stores a baseband program 310, a search frequency setting table 320, satellite acquisition data 330, satellite orbit data 340, measurement data 350, and positioning history data 360. Is done.

  Returning to FIG. 2, the main processing unit 20 comprehensively controls each unit of the portable electronic device 1 according to various programs such as a system program stored in the main storage unit 32.

  The operation unit 22 is an input device configured with a touch panel, a button switch, and the like, and outputs an operation signal corresponding to a user operation to the main processing unit 20.

  The display unit 24 is a display device configured by an LCD (Liquid Crystal Display) or the like, and performs various displays based on display signals from the main processing unit 20.

  The sound output unit 26 is a sound output device composed of a speaker or the like, and performs various audio outputs based on the sound signal from the main processing unit 20.

  The communication unit 28 includes a communication device such as a wireless local area network (LAN) or Bluetooth (registered trademark), for example, and performs communication with an external device.

  The clock unit 30 is an internal clock and includes an oscillation circuit having a crystal oscillator, and measures the current time, the elapsed time from the designated timing, and the like.

  The main storage unit 32 is a storage device composed of a ROM, a RAM, and the like. The main processing unit 20 controls a system program for comprehensively controlling each unit of the portable electronic device 1 and various types of the portable electronic device 1. A program and data for realizing the functions are stored and used as a work area of the main processing unit 20 to temporarily store calculation results of the main processing unit 20, operation data from the operation unit 22, and the like.

[Process flow]
(A) Positioning Mode FIG. 4 is a flowchart for explaining the flow of positioning mode processing. This process is a process executed when the BB processing unit 200 is in the positioning mode. According to FIG. 4, the BB processing unit 200 first determines whether or not it is a so-called cold start based on the presence or absence of the satellite orbit data 340. If it is a cold start (step A1: YES), all the GPS satellites are determined. The high-speed search flag is set to “1” (step A3). If it is not a cold start (step A1: NO), step A3 is skipped.

  Next, a capture target satellite is selected (step A5). That is, with reference to the satellite orbit data 340, a GPS satellite located in the sky (at an elevation angle of 0 ° or more) at the current time measured by the clock unit 30 is determined and selected as a capture target satellite. However, if the satellite orbit data 340 such as a cold start is not provided, all GPS satellites are set as acquisition target satellites.

  Then, loop A processing is performed for each acquisition target satellite. In the loop A, first, the satellite orbit data 340 is referred to, the effective ephemeris of the capture target satellite is included, and the capture target satellite is the current position of the portable electronic device 1 (more precisely, the previous time) Positioning position) is determined within a visible range (for example, the entire sky with an elevation angle of 0 ° or more, or an elevation angle centered on the crown direction may be a range of a predetermined angle or more) (step A7). . In the case of a cold start, since it does not have the current position, it is determined that it is out of the visible range. If the capture target satellite does not have a valid ephemeris, or if the capture target satellite is outside the visible range (step A7: NO), the fast search flag of the capture target satellite is set to “1”. (Step A9) If the capture target satellite has a valid ephemeris and the capture target satellite is within the visible range (step A7: YES), step A9 is skipped.

  Next, the satellite capture unit 210 performs satellite capture processing (see FIG. 6) for the capture target satellite (step A11). The process of loop A is performed in this way.

  When the process of loop A for all the capture target satellites is completed, the position calculation unit 220 performs a position calculation process using the measurement data 350 acquired for each captured GPS satellite signal, and the GPS receiver 10 (mobile phone) The position and clock error of the mold electronic device 1) are calculated (step A13). When the above process is performed, the positioning mode process ends.

(B) Timekeeping Mode FIG. 5 is a flowchart for explaining the flow of timekeeping mode processing. This process is a process executed by the BB processing unit 200 in the time measurement mode. According to FIG. 5, the BB processing unit 200 first determines whether or not it is a so-called cold start based on the presence or absence of the satellite orbit data 340. If it is a cold start (step B1: YES), all the GPS satellites are determined. The high-speed search flag is set to “1” (step B3). If it is not a cold start (step B1: NO), step B3 is skipped.

  Next, a capture target satellite is selected (step B5). That is, with reference to the satellite orbit data 340, a GPS satellite located in the sky at the current time measured by the clock unit 30 is determined and selected as a capture target satellite. However, if the satellite orbit data 340 such as a cold start is not provided, all GPS satellites are set as acquisition target satellites.

  Then, loop B processing is performed for each of the capture target satellites. In the loop B, first, the satellite orbit data 340 is referred to, the effective ephemeris of the capture target satellite is included, and the capture target satellite is the current position of the portable electronic device 1 (more precisely, the previous time) It is determined whether it is located in the visible range (step B7). In the case of a cold start, since it does not have the current position, it is determined that it is out of the visible range. If the capture target satellite does not have a valid ephemeris, or if the capture target satellite is outside the visible range (step B7: NO), the fast search flag of the capture target satellite is set to “1”. (Step B9). If the capture target satellite has a valid ephemeris and the capture target satellite is within the visible range (step B7: YES), step B9 is skipped.

  Next, the satellite capture unit 210 performs a satellite capture process (see FIG. 6) for the capture target satellite (step B11). As a result of the satellite acquisition process, if acquisition of the acquisition target satellite is successful (step B13: YES), the process of loop B is terminated at that point. Then, the time correction unit 230 corrects the time measured by the clock unit 30 based on the time information acquired by decoding the captured GPS satellite signal (step B15). When the above processing is performed, the timekeeping mode ends.

(C) Satellite Capture Processing FIG. 6 is a flowchart for explaining the satellite capture processing executed in step A11 in FIG. 4 and step B11 in FIG. According to FIG. 6, the satellite acquisition unit 210 first determines the high-speed search flag of the acquisition target satellite. If the high-speed search flag is “1” (step C1: YES), the search frequency is set to the maximum value. The correlation data length is set to “10 milliseconds” that is the first correlation data length of the minimum value (step C3). Then, with the set search frequency and the set correlation data length, the correlation calculation unit 130 performs correlation calculation (frequency direction search and phase direction search) between the received signal and the replica code to acquire the acquisition target satellite. (Step C5).

  As a result, when a peak is detected such that the peak of the correlation value is equal to or greater than a certain value, it is determined that the capture target satellite has been successfully captured (step C7: YES), and the satellite capture process is terminated. On the other hand, if acquisition of the acquisition target satellite fails (step C7: NO), then the correlation data length is reset to “20 milliseconds”, which is the second correlation data length longer than the first correlation data length. Similarly (step C13), similarly, a correlation operation with the set correlation data length is performed to try to capture the capture target satellite (step C15). As a result, if acquisition of the acquisition target satellite fails (step C17: NO), similarly, the correlation data length is set to “100 milliseconds”, which is a third correlation data length longer than the second correlation data length, Then, “1000 milliseconds” is set in order, and a correlation calculation is performed with the set correlation data length to attempt acquisition of the acquisition target satellite (steps C19 to 27).

  On the other hand, if the high-speed search flag of the acquisition target satellite is “0” (step C1: NO), the search frequency is set according to the elapsed time t from the final positioning (step C9). If the set search frequency is equal to or greater than a predetermined threshold (step C11: YES), the correlation data length is set to “20 milliseconds” that is the second correlation data length (step C13), and the set search frequency is set. Then, a correlation operation with the set correlation data length is performed to try to acquire the acquisition target satellite (step C15). As a result, if the acquisition of the acquisition target satellite is successful (step C17: YES), the satellite acquisition process is terminated. On the other hand, if acquisition of the acquisition target satellite fails (step C17: NO), similarly, the correlation data length is the third correlation data length “100 milliseconds” and is longer than the third correlation data length. The fourth correlation data length is set to “1000 milliseconds” in order, and the acquisition of the capture target satellite is attempted by performing a correlation calculation with the set correlation data length (steps C19 to C27).

  If the set search frequency is less than the predetermined threshold (step C11: NO), the correlation data length is set to “100 milliseconds” that is the third correlation data length (step C19). A correlation calculation is performed with the correlation data length to attempt acquisition of the acquisition target satellite (step C21). As a result, if acquisition of the acquisition target satellite is successful (step C23: YES), the satellite acquisition processing is terminated. On the other hand, if acquisition of the acquisition target satellite fails (step C23: NO), similarly, the correlation data length is set to the fourth correlation data length “1000 milliseconds” (step C25), and the set correlation is set. An attempt is made to acquire the acquisition target satellite by performing a correlation operation with the data length (step C27). When the above processing is performed, the satellite acquisition processing is terminated.

[Experimental result]
The experimental result about the GPS receiver 10 in this embodiment is demonstrated. FIG. 7 is a diagram illustrating a measurement result of the signal acquisition time. In FIG. 7, the horizontal axis represents the number of measurements, and the vertical axis represents the signal acquisition time (unit: milliseconds).

  In this experiment, the correlation data length is set to “10 milliseconds” and “20 milliseconds”, and the time until the GPS satellite signal is acquired (signal acquisition time) is measured a plurality of times (30 times). And so on. The other conditions were the same in order to compare the difference in the signal acquisition time depending on the correlation data length. That is, for all GPS satellites, the search frequency was “± 6 kHz” and the Doppler frequency was “3 kHz”. In addition, in order to clarify the difference in signal acquisition time, satellite acquisition processing is performed in order from the first, and acquisition of 31 GPS satellites from the first to 31st fails, and the 32nd GPS satellite is acquired. When measured.

  According to the results of this experiment, the satellite acquisition time was on the order of “about 3600 milliseconds” on average when the correlation data length was “20 milliseconds”. On the other hand, when the correlation data length is “10 milliseconds”, the average is about “about 2600 milliseconds”. That is, it was confirmed that the satellite acquisition time can be shortened by shortening the correlation data length. According to the result of this experiment, it can be said that by reducing the correlation data length from “20 milliseconds” to “10 milliseconds”, a reduction of about “1000 milliseconds” can be realized.

[Function and effect]
Thus, according to this embodiment, the GPS satellite signal is captured by changing the correlation data length in the correlation calculation between the received signal of the GPS satellite signal and the replica code. Specifically, at the cold start, the correlation data length is set to a minimum value (for example, 10 milliseconds). If it is not during a cold start, the correlation data length is set according to the search frequency. That is, when the search frequency is “wide”, the correlation data length is shortened to shorten the processing time required for one correlation calculation. As a result, the time required for capturing the GPS satellite signal (satellite search) can be shortened.

[Modification]
The applicable embodiments of the present invention are not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention. Modifications will be described below. In the description of the modification, the same reference numerals are given to the same components as those in the embodiment, and the description thereof is omitted.

(A) Subject of processing In the above embodiment, the setting of the correlation data length has been described as being executed by the BB processing unit 200 of the baseband processing circuit unit 16, but this is the main processing unit 20 of the portable electronic device 1. May be executed.

(B) Electronic Device In the above-described embodiment, the case where the present invention is applied to a runners watch that is a kind of electronic device has been described as an example. However, the electronic device to which the present invention is applicable is not limited to this. Absent. For example, the present invention can be similarly applied to other electronic devices such as a car navigation device, a portable navigation device, a personal computer, a PDA (Personal Digital Assistant), a mobile phone, and a wristwatch.

  Among these electronic devices, the above-described setting of the correlation data length is particularly suitable for a GPS wristwatch having a time measurement mode. A GPS wristwatch is required to operate for a long time (for example, several months, one year, etc.) with a battery having a limited capacity, and thus there is a strong demand for suppressing power consumption. In the timekeeping mode, it is sufficient that the Z count can be acquired from one GPS satellite. In a general environment, there are several GPS satellites whose signal strength can be captured with the first correlation data length. This is because, by capturing such a satellite in a short time using the first correlation data length, the time required for time correction can be shortened, and as a result, power consumption can be suppressed.

(C) Satellite positioning system In the above-described embodiment, the GPS has been described as an example of the satellite positioning system, but WAAS (Wide Area Augmentation System), QZSS (Quasi Zenith Satellite System), GLONASS (GLObal NAvigation Satellite System), Other satellite positioning systems such as GALILEO and BeiDou (BeiDou Navigation Satellite System) may be used.

1 portable electronic device, 12 GPS antenna, 10 GPS receiver,
14 RF receiving circuit section, 16 baseband processing circuit section, 110 memory section,
120 replica code generation unit, 130 correlation calculation unit, 200 BB processing unit,
210 satellite acquisition unit, 220 position calculation unit, 230 time correction unit, 300 BB storage unit,
310 baseband program, 320 search frequency setting table,
330 satellite acquisition data, 340 satellite orbit data, 350 measurement data,
360 positioning history data, 20 main processing section, 22 operation section, 24 display section,
26 sound output unit, 28 communication unit, 30 clock unit, 32 main storage unit

Claims (8)

Selecting a correlation data length when performing a correlation operation between a received signal received a positioning satellite signal and a replica code;
Performing the correlation operation with the correlation data length selected by the selection;
Search method including satellite. The correlation data length includes a first correlation data length that is greater than or equal to a spreading code length and performs a correlation operation with a length shorter than an interval of bit transition timing of a navigation message carried in the received signal,
The selecting includes selecting the first correlation data length at a cold start;
The satellite search method according to claim 1. Further comprising setting a search frequency;
The selecting includes selecting the correlation data length based on the search frequency;
The satellite search method according to claim 1 or 2. The selecting includes selecting a short correlation data length when the search frequency satisfies a predetermined range condition as compared with a case where the search frequency does not satisfy the range condition.
The satellite search method according to claim 3. A method for correcting the clock time of a clock part,
Performing the satellite search method according to any one of claims 1 to 4,
Correcting the timekeeping time of the clock unit based on the positioning satellite signal captured by the satellite search method;
Time correction method including A selection unit that selects a correlation data length when performing a correlation operation between the received signal and the replica code received from the positioning satellite signal;
A correlation calculation unit for performing the correlation calculation with the selected correlation data length;
Positioning device equipped with.   An electronic apparatus comprising the positioning device according to claim 6. A clock part,
Based on the result of the correlation calculation, a satellite capturing unit that captures a positioning satellite signal;
Based on the positioning satellite signal captured by the satellite capturing unit, a time correcting unit that corrects the time measured by the clock unit;
The electronic device according to claim 7, comprising:

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