JP2012202814A - Gps timepiece with time correction function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GPS timepiece with a time correction function capable of securely acquiring time information from a GPS signal while suppressing power consumption.SOLUTION: When a reception environment of a GPS signal is bad and a reception level does not reach a predetermined threshold, reception operation is performed at intervals of one hour (first predetermined time), only acquisition operation is performed at this time, and a reception system concerned with the reception operation is in a halt state. In an environment in which a reception state is not so bad, but not good enough to obtain correct GPS time information, reception operation is performed at intervals of four hours (second predetermined time), and up to GPS time acquisition and comparison processing with an internal timer are performed in addition to the acquisition operation. Consequently, while the reception environment is bad, only a check on a correlation value by the acquisition operation is made and the reception operation is frequently repeated to keep a watch without missing a chance for recovery, and when the reception environment becomes better, up to the GPS time information is acquired to increase chances for time correction.

Description

  The present invention relates to a GPS timepiece that corrects time based on time information included in a received GPS signal.

  Global Positioning System (GPS), a global measurement system, is a satellite positioning system for examining the position of receivers on the earth. Positioning is based on the arrival time of transmission signals from each captured satellite, This is done by calculating on the receiver side the three-dimensional position of the receiver on the earth according to the distance from the satellite. Since the accuracy of positioning largely depends on the accuracy of arrival time, the satellite has an accurate time based on an atomic clock.

  The data sent from the GPS satellite includes various information used for positioning, and includes time data based on an atomic clock mounted on the satellite, satellite orbit information, and the like. In order to obtain the GPS satellite time information, the receiver side that receives the signal from the GPS satellite shows the TOW (Time of Week, GPS time, weekly from the beginning of the week among the signals from the GPS satellite. Need to receive a signal).

  In order to obtain this time information, it is necessary to receive radio waves from GPS satellites, correlate the received signals, and then calculate to obtain time data. That is, a GPS signal is received by an antenna of a receiver, the signal is converted into an intermediate frequency by RF means (Radio Frequency), and then a correlation is extracted by a baseband means to extract a GPS signal. The calculation means calculates the signal to extract time information.

Standard radio receivers and long wave radio timepieces use regular reception, which is received at a fixed time, but in the case of GPS receivers, reception sensitivity in buildings where the satellite cannot be seen, such as indoors. Therefore, there is a possibility that the GPS signal cannot be received on a regular basis and the time cannot be corrected in the middle of the night when there is a high possibility of being placed indoors. In addition, the operation of obtaining time information from the GPS signal is performed many times until the reception is successful, which increases power consumption.
On the other hand, in order to actually acquire time information after receiving a GPS signal, it is necessary to operate each unit such as an RF unit, a baseband unit, and a calculation unit, and power consumption becomes large. Therefore, in order to cover the required power, it is necessary to increase the battery size than usual.However, timepieces such as watches are required to be smaller and save power, so the battery size cannot be increased. However, it was necessary to change the battery frequently.

  Although it is a general watch problem, a special tool is usually required to open and close the wristwatch cover, and the user cannot easily change the battery. If the user can easily open and close the lid so that the user can easily replace the battery, it becomes difficult to design the structure to ensure airtightness and waterproofness. In addition, even when the battery is not replaced as a rechargeable type, it is necessary to ensure airtightness and waterproofing around the charging contact. As described above, in order to prepare for an increase in power consumption, it has been necessary to cope with such a large design change.

  In Patent Document 1, when the standard time signal reception timing including the time code is received at an unacceptable environment and the current time data of the time counting circuit cannot be corrected, the time data is as early as possible. A technique for correcting the current time data by shortening the predetermined interval for acquisition is disclosed.

  In Patent Document 2, when a plurality of partial correlation units are driven in a receiving terminal that performs communication in a code division multiple access communication system (CDMA), system synchronization cannot be performed from the correlation values during partial correlation. A technique of a synchronization acquisition circuit that realizes low power consumption by determining and stopping the operation of a corresponding partial correlation unit is disclosed.

JP-A-7-198877 JP 2003-188767 A

As in the technique disclosed in Patent Document 1 described in the background art, in the regular reception (for example, 1 hour) with a constant interval, the reception interval is simply shortened due to a bad reception environment or an accidental factor. There is also a possibility that the reception fails continuously. In this case, the time of the internal clock gradually shifts. In this way, the normal reception operation is performed despite the poor environment, and the worse the environment, the higher the number of receptions. Therefore, simply shortening the reception interval and increasing the number of normal reception operations Only power consumption increases, and it cannot be said that it is an effective solution for acquiring time data at an early stage. That is, even in a situation where the environment is bad and reception is not possible, there is a processing process or circuit that consumes power wastefully because normal reception operation is performed to the end to determine reception information. In a time adjustment device that consumes a large amount of power such as receiving a GPS signal, when the number of reception operations increases, an increase in power consumption becomes noticeable when the time adjustment device operates at the same reception time as a normal reception operation.

  Further, in the technique disclosed in Patent Document 2, when a plurality of partial correlation units are driven in a terminal on the reception side, it is determined that system synchronization is not possible from the correlation value during calculation of partial correlation, and is applicable. Although it is described that the operation of the partial correlator is stopped, only the synchronization acquisition circuit that realizes low power consumption is disclosed, so that reception in a room such as a building is performed like the above-described time adjustment device. In situations where the sensitivity is low, power consumption can be reduced by stopping the operation of some of the correlation units, but the time when the GPS signal is scheduled to be received at night is likely to be placed indoors. Problems that cannot be fixed are not resolved.

  Therefore, in view of the above-described problems of the prior art, the object of the present invention is that in a time adjustment device equipped with a GPS receiver, the reception environment is bad or the scheduled reception fails continuously due to accidental factors. In this case, it is possible to avoid the unnecessary increase in the number of reception operations and the increase in power consumption when operating with the same reception time as the normal reception operation, and to ensure time information from GPS signals while suppressing power consumption. It is to provide a GPS clock with a time correction function that can be acquired.

  The GPS timepiece of the present invention basically employs the following configuration.

Corresponds to an internal clock that measures time, a GPS receiving unit that receives a GPS signal transmitted from a GPS satellite, acquires GPS time information based on the GPS signal, and the GPS time information acquired by the GPS receiving unit Then, in a GPS watch equipped with an arithmetic device that corrects the time counted by the internal watch, a receiving condition judging means for judging whether or not a receiving condition is satisfied, and a reception level of the GPS signal in the capturing operation Receiving level monitoring means for monitoring based on the calculated correlation value; and time difference determining means for calculating and determining a time difference between the GPS time information and the time counted by the internal clock, the reception level monitoring If it is determined by the means that the reception level does not reach a preset level, the GPS signal reception operation by the GPS reception unit is performed. And after the first predetermined time elapses, the reception condition determination unit determines whether the reception condition is satisfied, and the reception level monitoring unit determines that the reception level has reached a preset level. If the time difference is determined to be equal to or greater than the specified time by the time difference determination means, the reception system is paused, and after the second predetermined time has elapsed, the reception condition determination means determines whether or not the reception condition is satisfied. It is characterized by that. It is preferable that when the reception level exceeds a preset value, a Doppler shift of GPS radio waves is detected, and the GPS reception operation by the GPS receiving unit is suspended based on the Doppler shift.

  When the reception level monitoring means determines that the reception level has reached a preset level, the satellite number of the GPS satellite is stored, and the stored satellite number and the Doppler are stored in the next GPS satellite search. It is preferable to use the shift detection result and the correlation value calculation result.

According to the present invention, in a situation where normal reception is not possible, the number of useless reception operations increases, or the power consumption increases due to operation with the same reception time as the normal reception operation. It is possible to provide a GPS clock with a time correction function that can avoid time and reliably acquire time information from a GPS signal while suppressing power consumption.
In addition, the reception condition determining means can select and use various physical quantities to make the GPS clock with a time correction function configured according to the use environment of the user.
Further, the integration time of the correlation value can be varied to further reduce power consumption.

It is a functional block diagram explaining the GPS timepiece with a time correction function which is an embodiment of the present invention. It is a block diagram which shows the structure of a control part. It is a flowchart of a 1st embodiment. It is a flowchart of a 2nd embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, an outline of a radio wave including time information to be transmitted from a currently operated GPS satellite will be described. A plurality of GPS satellites transmitting positioning information and time information orbit about 20,000 kilometers above the earth's altitude. Each GPS satellite goes around the earth in about 12 hours. Due to the effects of general GPS antenna directivity and buildings, the elevation angle range where the received GPS signal is strong is 45 ° to 90 °. In the case of a satellite passing through the zenith, there are about 6 within the range. It's time.

  The frequency of the radio wave transmitted from the GPS satellite is basically 1575.42 MHz (name: L1 wave), and a signal called C / A is superimposed on this frequency. With this signal, data called a navigation message is transmitted. The navigation message includes time information.

One cycle of the navigation message is called a frame. One frame is 1500 bits, and it takes 30 seconds to transmit it. One frame is composed of five subframes (300 bits each). Transmission starts in order from subframe 1 and when transmission of subframe 5 is completed, transmission returns to transmission of subframe 1 again.
One subframe is divided into 10 words, and one word is 30 bits. At the head of each subframe, a TLM (telemetry) word is described, followed by a HOW (handover) word. The TLM word includes a synchronization pattern (printable), and the HOW word includes time information of a GPS signal indicating an elapsed time from 0 o'clock every Sunday.

FIG. 1 is a functional block diagram for explaining a GPS timepiece with a time correction function according to an embodiment of the present invention. A GPS clock 500 that receives radio waves transmitted from GPS satellites has the following configuration.
That is, the antenna 501 receives a signal from a GPS satellite (not shown). The analog signal processing circuit 502 converts the high frequency signal in the GHz band input from the antenna 501 to an intermediate frequency of several hundred MHz. A crystal oscillator 513 is used to convert to an intermediate frequency. The A / D converter 503 converts the intermediate frequency signal input from the analog signal processing circuit 502 into digital data.

In order to extract information from the received GPS signal, the phase must be synchronized with the C / A code of the GPS signal transmitted from each GPS satellite. That is, in order to acquire frame data transmitted from the GPS satellite, the baseband unit 511 synchronizes with the GPS satellite signal.
The signal processing circuit 504 inputs the digital data from the A / D converter 503 and, under the control of the CPU 507, the C / A code pattern data and C / A phase data of the GPS satellite to be captured are stored in the ROM 505. Read from the storage area. Then, C / A code pattern data is output at a phase based on the phase data to generate a C / A code for comparison, and a correlation value is obtained by taking a logical product (exclusive OR) with the input digital data. calculate. The code length of the C / A code is 1 ms. The calculated correlation value data is read by the CPU 507, and it is determined whether or not the GPS satellite has been captured based on the magnitude of the correlation value.

  The ROM 505 stores basic data for generating the C / A code for comparison, and an operation program for the GPS clock 500. The SRAM 506 is a memory for temporarily storing. Note that the signal processing circuit 504, the ROM 505, the SRAM 506, and the CPU 507 constitute the baseband unit 511, which can be formed into a one-chip IC.

When the GPS satellite is not captured, the operations necessary for the GPS reception processing in the analog signal processing circuit 502, the A / D converter 503, and the baseband unit 511 are stopped to prevent unnecessary consumption of operating power. To do.
Alternatively, after the analog signal processing circuit 502 and the A / D converter 503 are moved by, for example, about 5 ms and the digital data output from the A / D converter 503 is stored in the SRAM 506 during that time, the analog signal processing circuit 502 and the A / D converter 503 are moved. The baseband unit 511 may calculate the correlation value of the digital data stored in the SRAM 506 after the D converter 503 is stopped.

  In this way, by operating each circuit only when necessary, unnecessary power consumption is eliminated, and the operation of the analog signal processing circuit 502 and the A / D converter 503 and the correlation calculation in the baseband unit 511 are performed simultaneously. In this way, an increase in peak power consumption can be avoided.

  The calculation method for calculating the correlation value may be configured such that the integration time of the correlation value is variable, or the integration time may be changed depending on how the correlation value increases. Further, a correlation value may be calculated in order to obtain time information from the GPS signal, and the GPS signal reception interval may be changed according to the correlation value.

  If the GPS satellite can be acquired, the navigation message data is extracted by decoding the received GPS signal. The navigation message data includes data for obtaining GPS time information (Z count, GPS week number, etc.), and the CPU 507 can obtain GPS time information.

The internal clock 508 has a built-in reference oscillator such as a crystal oscillator (not shown), and measures the time by dividing the reference oscillation signal. The internal clock 508 is reset by GPS time information input from the CPU 507, and the time shift due to the oscillation frequency frequency error of the reference oscillator is compensated. The internal clock 508 is backed up by a battery (not shown) and always keeps time. A display 509 is means for displaying time information measured by an internal clock. The control device 512 is a control unit that controls the GPS clock 500 as a whole. When the internal clock 508 is in an active time zone or the like and is in a condition in which a reception operation is possible, a circuit necessary for GPS reception processing is used. And the time of the internal clock 508 is corrected. As an activity time zone, if you set a commuting time zone from 7 am to 9 am, or a time zone where you are likely to be outside depending on the person, for example, 8 am to 8 pm during the day, Since it can be assumed that the user wearing the GPS clock is outdoors, it becomes easier to receive GPS signals.
The counter 530 measures the waiting time until the next reception operation is performed, counts according to the set values of the first predetermined time and the second predetermined time, and notifies when the count is increased.

GPS watches are more resistant to reception while moving than radio timepieces, and have the characteristics that users can receive while they are active. On the other hand, in buildings where it is difficult to see satellites, the GPS watch has a weakness that reception is weak. The present invention utilizes these characteristics.
In general, during the daytime when the user is likely to be outdoors, for example, an internal clock is periodically used to determine the reception status from 7 am to 9 pm, and sufficient correlation values cannot be obtained. If it is determined that it is not suitable for reception, the operation is terminated. In addition, some conditions and operation patterns are considered and will be described later.

Next, control of the GPS timepiece of the present invention will be described. FIG. 2 is a functional block realized mainly by a program executed in the control device 512. The control device 512 includes a reception condition determination unit 521, a reception level monitoring unit 522, a time information correction unit 523, and a time difference determination unit 524.
The reception condition judgment means 521 controls to receive in the above-mentioned activity time zone, and performs automatic reception processing when the timekeeping content reaches a preset time with the internal clock 508. Thus, the start of reception processing using the GPS device is controlled. The reception level monitoring unit 522 performs processing for determining the reception level and monitoring whether the reception state is appropriate. The time information correcting means 523 performs processing for acquiring time information from the received satellite signal and correcting the time of the GPS wristwatch. The time difference determination means 524 performs a process of determining whether the difference between the acquired GPS time information and the internal clock is appropriate.

FIG. 3 is a flowchart showing an algorithm of processing performed by the GPS timepiece with a time correction function according to the first embodiment of the present invention. Hereinafter, it demonstrates according to each step.
First, in step SA01, it is determined whether or not the reception condition is satisfied by determining whether or not it is in the active time period from the timekeeping content of the internal clock. If the reception condition is not satisfied, the process returns to step SA01 again, and this is repeated until the reception condition is satisfied. This is a process corresponding to the function of the reception condition determination means 521 in the control device 512 shown in FIG.

If the reception condition is satisfied, the reception system is activated to start reception of GPS radio waves in step SA02, and then the process proceeds to step SA03 to perform a capturing operation for executing only the correlation calculation.
Here, the determination as to whether or not the reception condition is satisfied by the reception condition determination means 521 is made based on whether or not the GPS signal reception activation button is pressed, for example, in addition to determining whether or not the reception condition is in the activity time zone as described above. There is a way to detect. This is to obtain an optimum reception opportunity by having the user operate when a suitable reception environment is obtained. In addition, by using a physical quantity measured using an optical sensor and a physical quantity measured using a vibration sensor, it can be determined whether the environment is suitable for outdoor reception.

  After starting the receiving system in step SA02, the capturing operation is performed in step SA03. The correlation calculation at this time will be described. Roughly, the satellite number is sequentially changed from the first, the GPS satellite of each satellite number is searched, the signal level is detected, and the one having the maximum correlation value is specified. That is, the GPS satellite C / A code generation timing is adjusted to determine which GPS satellites can be synchronized. A signal is transmitted from the GPS satellite at the same frequency, but is determined by using a different C / A code for each GPS satellite. Therefore, by determining the C / A code included in the satellite signal of the received GPS satellite, it is possible to identify a GPS satellite that can be currently captured (synchronizable). The determination of the C / A code is based on the correlation between the received satellite signal and the C / A code generated internally. If the C / A code is the same, the peak value is output at a predetermined timing. In the case of different C / A codes, the output does not have a peak and is always zero, so that the C / A code of the GPS satellite can be specified.

  The satellite number of the GPS satellite specified by the capturing operation is stored in a storage unit such as the SRAM 506, and can be used for processing for acquiring next time information. As described above, since the C / A code length is 1 ms, the GPS satellite capture operation can be performed in a shorter time than the standard radio wave receiver even when the C / A code generation timing is adjusted. Receive processing can be performed.

The correlation value obtained by the capturing operation in step SA03 is monitored by the reception level monitoring means 522 based on the magnitude of the correlation value. In step SA04, it is determined whether or not the correlation value is equal to or greater than a preset threshold value. If the specified correlation value is greater than or equal to the threshold value, the process proceeds to step SA05 to perform the GPS time information acquisition operation. However, if the correlation value is lower than the threshold value, the GPS time information is not acquired. In step SA10, the receiving system is paused.
After setting the receiving system to a dormant state in step SA10, the counter 1 starts counting in step SA11. When the counter 1 confirms that the first predetermined time has elapsed in step SA12, the process returns to step SA01 and waits until the reception condition is satisfied.

  The GPS time information is obtained by acquiring the time information of the GPS signal indicating the elapsed time from 0 o'clock every Sunday in the HOW word, and is implemented in step SA05. In step SA06, the time information of the internal clock is acquired, and it is determined whether or not the difference in time information from the previously acquired GPS time information is a time difference greater than or equal to the specified time (step SA07). In some cases, after stopping the receiving system in step SA13, the counter 2 starts counting in step SA14. When the counter 2 confirms that the second predetermined time has elapsed in step SA15, the process returns to step SA01 and waits until the reception condition is satisfied.

  Here, consider the case in which a time difference that exceeds the specified time occurs. For example, in an environment where the acquired GPS time information cannot be normally acquired in step SA05, a reception error may be confirmed by a parity check. Therefore, the time is different from the correct time information. Such erroneous GPS time information often has a time difference that is greater than or equal to the specified time when compared to the time information of the internal clock.

  If the time difference between the GPS time information and the time information of the internal clock in step SA07 is less than the specified time, it can be determined that the GPS time information has been normally acquired as the time difference caused by the accuracy error of the built-in crystal oscillator. In SA08, the time information of the internal clock is corrected based on the GPS time information acquired in the previous step SA05 and the time information of the internal clock acquired in step SA06. When the correction is completed, the receiving system is suspended in step SA09. Then, the process returns to step SA01 to wait for the next reception operation.

  In this way, the time difference determining means 524 determines the time difference in step SA07 and, depending on the result, temporarily sets the receiving system to a dormant state, or immediately proceeds to step SA08 and the time information correcting means 523 uses the internal clock. Correct the time.

  Here, as a specific example, consider a case where the first predetermined time is set to 1 hour and the second predetermined time is set to 4 hours. First, as a case where reception and time correction can be performed normally, a correlation value at the time of receiving a GPS signal is equal to or greater than a predetermined threshold, and a time difference between the acquired GPS time information and the internal clock is within a predetermined time. It is determined that the internal clock has entered the active time zone (SA01) and the reception environment has been prepared (SA01), and the GPS signal is received by the activation of the reception system (SA02) and the capture operation (SA03). The correlation value of the received signal is determined using the code (SA04). The obtained correlation value is equal to or greater than a predetermined threshold value, the GPS satellite is identified and GPS time information is acquired (SA05), the time information of the internal clock is read (SA06), and the time difference between both time information is determined. (SA07) Since the time difference is smaller than the predetermined time and the signal can be normally received, the time of the internal clock is corrected based on the acquired GPS time information (SA08), and the receiving system is in a sleep state after the time correction is completed. (SA09), it is in a standby state until the next scheduled reception time (SA16). In addition, there are various cases such as scheduled reception time that is the same reception time as the previous reception time, or after 24-hour counting, but it may be set to be approximately one day later. In this way, if normal reception can be performed, processing is performed at a stretch until the time is corrected, and the next reception standby state is entered.

  Next, there is a case where the reception is normal but the time cannot be corrected, that is, although the reception can be performed normally, the acquired GPS time information is abnormal, and the time difference between the GPS time information and the internal clock becomes a predetermined time or more. In steps SA01 to SA04, reception is started and a capturing operation is performed to confirm that the correlation value is equal to or greater than a predetermined threshold. Then, in steps SA05 and SA06, the GPS time information and the time information of the internal clock are acquired. As a result of taking the time difference (SA07), since it is equal to or longer than the predetermined time, the reception system is suspended (SA13), and the counter 2 starts counting for 4 hours (SA14). When 4 hours have passed (SA15), it waits until the reception condition is satisfied again (SA01) and repeats from the reception operation. In a state where this is repeated, a reception operation is performed every 4 hours to wait for a chance to acquire GPS time information normally.

  During this time, if the reception environment further deteriorates and it becomes difficult to receive normally, the correlation of the GPS signal obtained by the capturing operation in step SA03 becomes low, and the correlation value determination result (SA04) shows a predetermined value. When the value becomes smaller than the threshold, the receiving system is immediately stopped (SA10), and the counter 1 starts counting for one hour (SA11). After one hour has passed (SA12), it waits for the reception condition to be satisfied again (SA01) and repeats from the reception operation. In this state, a reception operation is performed every hour to wait for the reception environment to recover.

As described above, when the reception environment is considerably poor and the correlation value of the captured GPS signal is not equal to or greater than the predetermined threshold value, the reception operation is performed every hour. At that time, only the acquisition operation is performed and the other reception is performed. The system is in a dormant state.
In addition, the reception situation is not so bad, but in an environment where the correct GPS time information is not obtained, the reception operation is performed every 4 hours, and in addition to the capture operation, the GPS time acquisition and the comparison processing with the internal clock are performed. carry out. Therefore, although the power consumption is excessive compared with the case where only the capturing operation is performed, the time can be corrected immediately if reception is successful.

  When the reception environment is deteriorating, it is difficult to acquire GPS time information accurately, so only the correlation value is checked by the capture operation, and the reception operation is repeated frequently so as not to miss the opportunity for recovery. If the reception environment is improved, the GPS time information can be acquired after the capture operation to increase the time adjustment opportunity. Even if the reception environment is not good for a long time, While preventing the GPS time information from being acquired, the time cannot be corrected and the internal clock is prevented from shifting, and the power consumption for the reception operation during this time can be reduced.

Next, a case where the Doppler effect of the GPS signal is used will be described as a second embodiment.
The GPS signal reception frequency shift (Doppler shift) due to the Doppler effect is as follows.
It has been described that the frequency (transmission frequency) of a GPS signal transmitted from a GPS satellite is the same for all satellites. However, the reception frequency at the receiver varies depending on the elevation angle of the GPS satellite with respect to the receiver. This is because the Doppler effect affects the reception frequency. Specifically, when a signal is received from a GPS satellite located at the zenith with respect to the receiver, the Doppler shift (frequency shift) is 0, and the shift amount of the reception frequency with respect to the transmission frequency is also 0.

On the other hand, the Doppler shift increases as the elevation angle decreases, and the amount of deviation from the transmission frequency increases. In addition, the Doppler shift changes in the plus direction (+), that is, in the direction in which the frequency increases, when the GPS satellite moves toward the receiver, and the GPS satellite moves away from the receiver to the horizon. As it sinks, it changes in the negative direction (-), that is, in the direction in which the frequency decreases.
This is because the Doppler shift continuously changes from (+) → (0) → (−) until the GPS satellite passes through the zenith and the elevation angle reaches 0 °. , It is possible to grasp the approximate satellite position and predict the reception time of the next GPS signal in advance.

  FIG. 4 is a flowchart for explaining the present embodiment, showing an algorithm including a process for determining whether or not to continue acquisition of GPS time information based on whether or not the GPS satellite is moving in the zenith direction. Yes. The deviation of the Doppler frequency of the received radio wave when receiving the radio wave transmitted from the GPS satellite is measured, and the closer the value is to “0”, the easier the GPS satellite is to receive because it is located at the zenith. Further, it can be determined whether the GPS satellite is directed toward the zenith or deviated from the zenith depending on whether the frequency shift of the Doppler frequency is increased or decreased. In this way, by utilizing the fact that GPS signals of different frequencies are obtained depending on the position of the GPS satellite, the timing for acquiring GPS clock information is predicted, and an optimal reception operation is performed.

Hereinafter, description will be given according to each step of FIG.
In step SA01, it is determined whether or not the reception condition is satisfied by determining whether or not it is in the active time period from the timekeeping content of the internal clock. If the reception condition is not satisfied, the process returns to step SA01 again, and this is repeated until the reception condition is satisfied. If the reception condition is satisfied, the reception system is activated to start reception of GPS radio waves in step SA02, and then the process proceeds to step SA03 to perform a capturing operation for executing only the correlation calculation. The flow up to this point is the same as that in the flowchart of FIG. 3, and steps with the same number perform the same processing.

In step SA04, it is determined whether or not the correlation value obtained by the capturing operation is greater than or equal to a preset threshold value. If the correlation value is greater than or equal to a predetermined threshold value, the process proceeds to processing according to the Doppler shift amount, and the correlation value is preset. If it is not equal to or greater than the threshold value, the process proceeds to step SA10, and after the suspension of the receiving system (SA10), the start of counting by the counter 1 (SA11), and the determination of the elapse of the first predetermined time (SA12), the process returns to step SA01.

In step SA04.1, the Doppler shift amount is calculated from the frequency shift of the received GPS signal, and the behavior of the GPS satellite according to the frequency shift of (−), (0), (+) is detected, and the optimum Processing is performed.
In step SA04.1, if the Doppler shift amount is a minus (−) shift, it is assumed that the reception state deteriorates because the satellite moves far away, and the acquisition of GPS time information from the satellite is postponed. Then, the process proceeds to step SA10. After the suspension of the receiving system (SA10), the start of counting by the counter 1 (SA11), and the determination of the passage of the first predetermined time (SA12), the process returns to step SA01.

  If there is no Doppler shift and the shift is (0), it can be determined that the GPS satellite is in an orbit near the zenith that is most suitable for reception. Therefore, the process proceeds to step SA05, where GPS time information is acquired and an internal clock is acquired. Correct the time. Since the processing contents after step SA05 are the same as those in steps SA05 to SA09 and SA13 to SA16 in FIG. 3, they are omitted in FIG. 4. However, when the processing is completed, the processing returns to step SA01 and waits for the reception conditions to be satisfied. Repeat from the receiving operation.

  On the other hand, when the Doppler shift amount is (+), it is considered that the GPS satellite is approaching from a distance. Therefore, after temporarily suspending the reception system in Step SA04.2, the Doppler shift amount is determined in Step SA04.3. The time to the optimum reception time is calculated, and the counter 3 starts counting at step SA04.4 and waits until the optimum reception time is reached. When it is confirmed in step SA04.5 that the set time has elapsed, the process returns to step SA01 to perform the reception operation. At this time, the GPS satellite should have reached the optimum orbit for reception, that is, the top of the zenith, and the calculation result of the Doppler shift amount in step SA04.1 becomes (0) and proceeds to step SA05. After obtaining the time information and correcting the time of the internal clock, the process returns to step SA01.

  As described above, by obtaining the orbit information of the GPS satellite based on the Doppler shift amount and adding it to the determination condition of whether or not reception is possible, reception can be performed more efficiently and with low power consumption.

Next, as a third embodiment, a case will be described in which the GPS satellite number, the Doppler shift amount, and the correlation value calculation result are used when searching for the next GPS satellite.
The satellite number is stored in the SRAM 506 by the capturing operation of the satellite, and the acquisition of the time information is performed by the satellite of the number. For this reason, if this satellite number is used in the satellite search in the next reception operation, it is possible to perform highly accurate reception in a short time with low power consumption.
In addition, since the threshold value can be determined from the correlation value calculated by the reception level monitoring unit, the optimum threshold setting value can be set in the next reception operation, which can contribute to the improvement of reception accuracy.
By using the Doppler shift detection result described in the second embodiment in addition to these two pieces of stored information, the next reception operation can be performed at an optimal timing at which it is easy to receive a signal from the satellite. .

This will be described with reference to the flowchart of FIG. 4 used in the description of the second embodiment.
If it is determined in step SA01 that the reception condition is satisfied, the reception system is activated in step SA02, and the process proceeds to SA03 to perform a capture operation by correlation calculation. However, the satellite to be received is specified when the capture operation is completed. The satellite number is stored in the storage area of the SRAM 506.
In subsequent step SA04, it is determined whether or not the correlation value obtained by this capturing operation is greater than or equal to a preset threshold value. If the correlation value is greater than or equal to a predetermined threshold value, the process proceeds to a process corresponding to the Doppler shift amount, and in step SA03. The obtained correlation value and the threshold value used in step SA04 are temporarily held in the storage area of the SRAM 506.
If the correlation value is not greater than or equal to the preset threshold value, the process proceeds to step SA10, the reception system is suspended (SA10), the counter 1 starts counting (SA11), and the first predetermined time has elapsed (SA12). ), The process returns to step SA01.

The flow from calculating the Doppler shift amount in step SA04.1 to detecting the behavior of the GPS satellite according to the frequency shift and performing the subsequent processing is as described in the second embodiment.
In this case, when the Doppler shift is in the positive direction (+), that is, when the GPS satellite is approaching, the reception system is paused in Step SA04.2, and then after Step SA04.3 and Step SA04.4, Step SA04. After waiting until the optimum reception time is reached in step 5, the process returns to step SA01.

When the reception operation is completed and the process returns to step SA01, the values obtained in the previous reception operation such as the satellite number, the correlation value, the threshold value set at that time, and the Doppler shift detection result are stored. . After returning to step SA01 and satisfying the reception conditions and starting the receiving system in step SA02, the satellite number acquired and stored last time is used when performing the capturing operation in step SA03.
In the capturing operation described in the first embodiment, the satellite number is sequentially changed from the first, the GPS satellite of each satellite number is searched, the signal level is detected, and the one having the maximum correlation value is specified. However, since the GPS satellite storing the satellite number should reach the optimum orbit for reception, that is, the top of the zenith at the present time, the capturing operation is performed using the satellite.

Thereby, the method of calculating the correlation value necessary for the capturing operation can be devised. For example, by reducing the number of correlators to be operated and operating at least one corresponding to the satellite number, power consumption can be reduced, while by assigning all correlators to the correlation value calculation of the satellite, Calculation time can be shortened. Moreover, it becomes possible to operate efficiently by using both together.
Alternatively, if the search is started from the satellite number instead of the first satellite as the change order of the satellite numbers during the capturing operation, even if the satellite cannot be detected, Searching can reduce the occurrence of problems.

  After obtaining the correlation value by the capturing operation in step SA03, it is determined whether or not the threshold value is preset in step SA04. The previously calculated correlation value, the threshold value set at that time, and the Doppler shift detection result Are stored in the storage area, and by creating a table associating them, it is possible to select and set the optimum threshold value from the mutual relationship. For example, from the relationship between the Doppler shift amount and the correlation value at the time of storing and holding, refer to the table to see how much the correlation value when the GPS satellite is positioned in the orbit optimal for reception is larger than the previous correlation value Then, if a predicted value is picked up and a threshold value is set in accordance with the predicted value, it is possible to make a highly accurate determination in monitoring the reception level.

  As described above, by storing various values obtained in the reception operation and using them in the next reception operation, further efficiency and low power consumption can be achieved.

500 GPS watch 501 Antenna 502 Analog signal processing circuit 503 A / D converter 504 Baseband circuit 505 ROM
506 SRAM
507 CPU
508 Internal clock 509 Display 510 Bus 511 Baseband unit 512 Controller 513 Crystal oscillator 521 Reception condition judgment means 522 Reception level monitoring means 523 Time information correction means 524 Time difference judgment means 530 Counter

Claims (3)

An internal clock that keeps time,
A GPS receiving unit that receives a GPS signal transmitted from a GPS satellite and acquires GPS time information based on the GPS signal;
An arithmetic unit that corrects the time counted by the internal clock in response to the GPS time information acquired by the GPS receiving unit;
GPS watch with
A reception condition judging means for judging whether or not the reception condition is satisfied;
Reception level monitoring means for monitoring the reception level of the GPS signal based on the correlation value calculated in the capturing operation;
Time difference determination means for calculating a time difference between the GPS time information and the time counted by the internal clock and making a determination;
When the reception level monitoring means determines that the reception level does not reach a preset level, the reception operation of the GPS signal by the GPS reception unit is suspended, and the reception condition determination is performed after a first predetermined time has elapsed. Determine whether or not the reception condition is satisfied by means,
If the reception level monitoring means determines that the reception level has reached a preset level, and the time difference determination means determines that the time difference is greater than or equal to the specified time, the reception system is suspended, A GPS timepiece with a time correction function, wherein the reception condition determination means determines whether or not a reception condition is satisfied after a second predetermined time has elapsed.   The GPS reception unit according to claim 1, wherein when the reception level exceeds a preset value, a Doppler shift of GPS radio waves is detected, and a GPS reception operation by the GPS reception unit is suspended based on the Doppler shift. GPS clock with time correction function described. When the reception level monitoring means determines that the reception level has reached a preset level, the satellite number of the GPS satellite is stored, and the stored satellite number and the Doppler are stored in the next GPS satellite search. The GPS timepiece with time correction function according to claim 2, wherein a shift detection result and a correlation value calculation result are used.

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