JP2011220877A - Time indicating method and time indicating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a high sensitivity and low power consumption GPS chronometer which locates a positioning information satellite, even where the radio wave from the positioning information satellite is very weak as in a building, receives navigation message data regarding time and indicates an accurate time.SOLUTION: A time indicating method includes the steps of: accumulating correlation intensities in search while finely and frequently switching over an C/A code, storing and linearly extracting the same in and from correlation intensity storage means, preparing for received data a replica of each of fixed data, pattern data and increment data, and figuring out correlations with the accumulated data.

Description

  The present invention relates to a clock that corrects and displays the time of an internal clock based on time information included in radio waves from a satellite such as a position information satellite.

  The main purpose of the position information satellite is to obtain the position of the reception point from the position of a plurality of position information satellites and the delay time of radio waves from those position information satellites. However, position information satellites are equipped with extremely accurate clocks such as atomic clocks, and there are many clocks that display accurate time by correcting the time of the internal clock based on the time information from the position information satellite. (For example, refer to Patent Document 1).

  However, the clock is often installed in a place with relatively weak radio waves, such as a building, and one reception is not always sufficient, and the time of the internal clock is based on data obtained by intermittent reception multiple times. There is also disclosed a timepiece that corrects and displays (see, for example, Patent Document 2).

Such a conventional GPS timepiece will be described with reference to FIG.
In the conventional GPS timepiece shown in FIG. 25, radio waves from the position information satellite are converted into high-frequency signals by the antenna 2502. The RF means 2503 down-converts the frequency by mixing with local oscillation. The combination demodulating means 2504 increases the number of correlators that search for repeated radio waves from the position information satellite for each frequency to be searched and captures each position information satellite, and tracks each cycle of 1 ms of the C / A code. The correlation data superimposed on is extracted. In other words, the search was performed for each combination of frequency and satellite. The matching calculation means 2505 extracts the bit boundary of the correlation data for each 1 ms of the C / A code, aggregates the correlation data for 20 ms constituting each bit of the navigation message data, and repeats the subframe. The navigation message data is calculated from the navigation message data to the time information while ensuring the reliability of the received data by confirming that there is no inconsistency in the navigation message data received and extracted from. Specifically, when the first subframe of the navigation message data comes, time information data such as TLM and TOW and a subframe ID are received. Thereafter, the second subframe is received in the same manner, and the time of the internal clock is corrected and displayed only when the received data of the first subframe and the received data of the second subframe are matched, and the GPS signal is received. Exit. If there is no match, the process returns to the reception of the first subframe. Further, the TOW and the subframe ID are assumed to be consistent when they are incremented every time they are received. The RTC unit 2506 divides the internal reference clock to generate the internal time, and corrects the internal time based on the time information from the matching calculation unit 2505. The time display means 2507 displays the time based on the corrected internal time.

  However, in such a conventional GPS timepiece, when the radio wave from the position information satellite is weak, there is a problem that the circuit scale becomes large by increasing the number of steps of the correlation means in order to increase the sensitivity of the search. It was. Furthermore, by increasing the correlation means in order to increase the sensitivity of the search, not only the time for obtaining the correlation at one frequency is lengthened, but also the frequency range to be searched for becomes narrower because the range of frequencies that can be captured becomes narrower. Due to the synergistic effect due to the increase in the number of search, the search time is remarkably increased and the power consumption is significantly increased. In addition, when simultaneously searching a plurality of position information satellites in order to shorten the time for searching for position information satellites, the circuit scale is large because there are as many correlation means for searching as the number of satellites to be searched simultaneously. There was a problem to say.

  In addition, in such a conventional GPS watch, when the radio waves from the position information satellite are extremely weak, the received data of consecutive subframes often do not match, or even if they match, it is rarely a correct value. There was a problem that there was.

Japanese Patent Laid-Open No. 10-82875 JP 2007-263595 A

  Therefore, the present invention solves these problems of the GPS watch described above, and stably acquires time information with a relatively simple configuration, high speed and low power consumption even in a place where the radio wave is extremely weak such as the back of a building. It is to realize a GPS clock capable of displaying the correct time.

  For this purpose, it is necessary to improve all of the sensitivity when searching for a position information satellite, the sensitivity of tracking, and the sensitivity of data reception.

An aspect of the invention for solving the above-described problems will be described below.
As a first aspect, in a time display method for correcting time based on time information of radio waves coming from satellites, a satellite is searched by synthesizing correlation strengths for a plurality of cycles of pseudorandom codes included in radio waves from satellites. Navigation message data related to the time included in the radio wave from the satellite that is repeatedly updated as needed, and the tracking process that controls the radio wave from the satellite acquired in the synthetic search process to be received efficiently. A data composition receiving step for combining, a standard time calculating step for calculating standard time from navigation message data relating to the time received in the data combining receiving step, a reference clock generating step for generating a reference clock from which internal time is counted, and The internal clock is generated by counting the reference clock and It has a RTC step of modifying the internal time, and a time display step that displays the time by the internal time.

  As a second mode, in the first mode, the combined search step receives the radio wave from the satellite, down-converts the frequency, and then removes the carrier wave and the pseudo-random code to obtain the correlation strength obtained from the pseudo-random code. The satellite is searched and acquired by accumulating more than one cycle.

  As a third aspect, in the first aspect, the synthesis search step receives radio waves from the satellite and down-converts the frequency, and then removes the carrier wave from the low-frequency signal and supports one or more satellites. While switching the pseudo-random code replica within the time range of one chip of the pseudo-random code, the pseudo-random code is removed and the correlation strength is extracted, and the obtained correlation strength is equal to or more than one cycle of the pseudo-random code. By accumulating corresponding satellites, one or more position information satellites are searched and acquired substantially simultaneously.

  As a fourth aspect, in the first aspect, the synthesis search step receives the radio wave from the satellite, down-converts the frequency, and then calculates the correlation strength obtained by removing the carrier wave and the pseudo-random code for one cycle. After the above storage, the satellite is searched and captured by calculating the signal intensity, the phase of the pseudo random code, and the frequency deviation from the stored values.

  As a fifth aspect, in the first aspect, the data synthesis receiving step receives the radio wave from the satellite, down-converts the frequency, and then removes the carrier wave and the pseudo-random code from the correlation data obtained by removing the bit from the correlation data. Bit boundary detection step for detecting a boundary, bit data aggregation step for generating bit data by aggregating correlation data within the bit boundary detected in the bit boundary detection step, and bit data for synthesizing navigation message data from the bit data The bit boundary detection step includes a change extraction step for extracting changes in correlation data, a change accumulation step for accumulating changes in correlation data obtained in the change extraction step, and a change accumulated in the change accumulation step. A change point position calculating step for obtaining a boundary of bit data constituted by the correlation data;

  As a sixth aspect, in a time display device that corrects time based on time information of radio waves coming from a satellite, an antenna that receives radio waves from a position information satellite as a high frequency signal, and a low frequency by down-converting the high frequency signal from the antenna Synthetic demodulation that searches and captures position information satellites and extracts correlation data by synthesizing the correlation strength for multiple cycles of C / A code included in the low-frequency signal from the RF means for converting to a signal And means for repeatedly receiving and synthesizing the navigation message data relating to the time included in the correlation data from the synthesizing / demodulating means, and calculating the standard time, and generating the internal time by counting the internal reference clock RTC means for correcting the internal time according to the standard time, and the internal time from the RTC means It has a time display means for displaying the time, and control means for managing the entire and status and sequence.

  As a seventh aspect, in the sixth aspect, the synthesizing / demodulating means removes the carrier wave and the pseudo-random code from the low frequency signal to extract the correlation data and the correlation strength, and the obtained correlation strength is converted into the pseudo-random code. The position information satellite is searched and acquired by accumulating one cycle or more.

  As an eighth aspect, in the sixth aspect, the synthesizing / demodulating means removes the carrier wave from the low-frequency signal and, at the same time, replaces the pseudo-random code replica corresponding to one or more satellites with the time of one chip of the pseudo-random code. The pseudo-random code is removed while switching within the range to extract the correlation data and the correlation strength, and the obtained correlation strength is accumulated for one or more cycles of the pseudo-random code corresponding to one or more satellites. Search and capture almost simultaneously from two or more location information satellites.

  As a ninth aspect, in the sixth aspect, the synthesizing / demodulating means removes the carrier wave and the pseudo-random code from the low-frequency signal to extract the correlation data and the correlation strength, and the obtained correlation strength is converted into the pseudo-random code. Correlation strength storage means for storing at least one cycle, and a position information satellite is searched and captured by calculating a deviation between the signal strength, the phase of the pseudo random code and the frequency from the value stored in the correlation strength storage means.

  As a tenth aspect, in the sixth aspect, the composition calculation means includes bit data generation means for collecting correlation data and generating bit data, data composition means for extracting navigation message data relating to time from the bit data, It has a standard time calculation means for calculating the standard time from the navigation message data from the data synthesis means, and the bit data generation means accumulates the change of the correlation data obtained by the change extraction means for extracting the change of the correlation data and the change extraction means. Change accumulating means, change point position calculating means for obtaining a boundary of bit data composed of correlation data from changes accumulated by the change accumulating means, and correlation data based on the change points from the change point position calculating means. Bit data aggregating means for outputting bit data.

  As an eleventh aspect, in the sixth aspect, the composition calculation means comprises a bit data generation means for collecting correlation data to generate bit data, a data composition means for extracting navigation message data relating to time from the bit data, Standard time calculation means for calculating the standard time from the navigation message data from the data synthesis means is provided, and the data synthesis means obtains the navigation message data from the bit data by accumulation or / and correlation with the replica.

  In the GPS timepiece according to the present invention, even when the radio wave from the position information satellite is weak, search, tracking and data reception can be performed with high sensitivity. For example, the navigation message data is stably included even in a place away from an indoor window. By receiving the time information, the accurate time can always be displayed.

Process flow chart showing a preferred embodiment of a GPS watch according to the present invention. Process flow diagram of synthetic search process according to the present invention Process flow diagram of synthetic search process according to the present invention Process flow diagram of synthetic search process according to the present invention Conceptual diagram showing the operation of the search calculation means according to the present invention. The flowchart which shows operation | movement of the search calculating means based on this invention. Process flow chart of data composition reception process according to the present invention Schematic diagram showing processing of bit boundary detection process according to the present invention 1 is a block diagram showing a preferred embodiment of a GPS watch according to the present invention. External view showing an embodiment of a time display means according to the present invention The block diagram which shows the structure of the synthetic | combination demodulation means based on this invention The block diagram which shows the structure of the signal strength accumulation means which concerns on this invention The block diagram which shows the structure of the synthetic | combination demodulation means based on this invention Timing diagram showing the operation of the timing means according to the present invention. The block diagram which shows the structure of the synthetic | combination demodulation means based on this invention The block diagram of the synthetic | combination calculating means based on this invention Block diagram of bit data generation means according to the present invention The block diagram which shows the structure of the synthetic | combination calculating means based on this invention The block diagram which shows the synthetic | combination method of the fixed data based on this invention The block diagram which shows the accumulation method of the repeating pattern data based on this invention The figure which shows an example of the replica of the repeating pattern data based on this invention Schematic diagram showing a method of synthesizing increment data according to the present invention. Timing diagram showing timing of navigation message data according to the present invention The figure which shows the timing of the navigation message data based on this invention Block diagram of a conventional GPS watch

  In the GPS timepiece according to the present invention, a combined search step of searching for and capturing a position information satellite by combining correlation strengths for a plurality of C / A code cycles that are pseudo-random codes included in radio waves from the position information satellite; Data that synthesizes navigation message data related to the time contained in the radio waves from the position information satellites that are repeatedly updated as needed, and the tracking process that controls the radio waves from the position information satellites captured in the synthesis search process. A combined reception step, a standard time calculation step for calculating standard time from navigation message data relating to the time received in the data combination reception step, a reference clock generation step for generating a reference clock from which internal time is counted, and a reference clock Generates internal time by counting and internal time by standard time Time display method characterized by comprising the RTC step of modifying, a time display step that displays the time by the internal time.

  Further, a GPS timepiece for realizing the above method includes an antenna that receives radio waves from a position information satellite as a high-frequency signal, RF means for down-converting the high-frequency signal from the antenna into a low-frequency signal, and RF A synthesizing / demodulating means for searching for and acquiring a position information satellite and extracting correlation data by synthesizing correlation strengths for a plurality of C / A code cycles included in the low-frequency signal from the means, and a correlation from the synthesizing / demodulating means Combining operation means for repeatedly receiving and synthesizing navigation message data relating to the time included in the data and calculating the standard time, and RTC means for generating an internal time by counting an internal reference clock and correcting the internal time by the standard time Time display means for displaying the time according to the internal time from the RTC means, It was constructed by the control means for managing the tasks and sequence.

  Before describing in detail the configuration and operation of the GPS timepiece according to the present invention, the navigation message data received by the GPS timepiece according to the present invention from the position information satellite will be described in advance. In the following description of the present embodiment, <> is used as a large heading, [] is used as a medium heading, and a small heading.

<Navigation message data>
[Timing of navigation message data]
The timing of the navigation message data from the position information satellite shown in FIG. 23 will be described.

  The entire navigation message data is composed of 25 frames including page numbers P1-25. Each frame is composed of five subframes having subframe numbers SF1 to SF5. The two subframes with subframe numbers SF4 and 5 have 25 pages with page numbers P1 to P25, and the page is switched for each frame. Each subframe is composed of 10 words having word numbers W1 to W10. Each word is composed of 30 bits of bit numbers b1-30. The first 24 bits of each word are sent in order from the MSB as data. The last 6 bits of each word are parity. Here, each bit is repeated for 20 cycles of the C / A code of 1023 chips of CA1-20.

  Since one C / A code is 1 ms, the time of each bit is 20 ms, the time of each word is 0.6 seconds, the time of each subframe is 6 seconds, and the time of each frame Is 30 seconds, and the total time of the navigation message data is 12.5 minutes. All of these are transmitted from the position information satellite in time series, and the entire navigation message data is repeated while its value is updated as needed.

[Navigation message data required for time acquisition]
FIG. 24 shows the time-series position of the navigation message data necessary for obtaining the time. In FIG. 23, for each item, the subframe number, page number, word number, and bit number indicate the time-series positions.

  Here, TLM indicates a position of the first word of each subframe including a predetermined preamble. TOW indicates the elapsed time from the beginning of the week. The subframe ID indicates a subframe number. WN indicates a week number. The health status indicates the reliability of the navigation message data sent from the position information satellite. UTC is a parameter necessary for obtaining Greenwich Mean Time from GPS time. Note that the 25th to 30th bits of each word are parity data.

<GPS watch method>
FIG. 1 shows an example of the process of the GPS timepiece according to the present invention. Hereafter, each process of the GPS timepiece according to the present invention will be described with reference to FIG. The entire process is performed using the control means.

  The GPS timepiece according to the present invention corrects the internal time based on time information from the position information satellite and displays the time based on the internal time. Acquisition of time information from the position information satellite and correction of the internal time are performed at the initial time, time adjustment operation from the user, or at a predetermined timing.

[Synthetic search process]
In order to obtain time-related information from the position information satellite, first, in the synthesis search step 101, the correlation strength for a plurality of C / A code cycles is synthesized while changing the phase of the C / A code and the C / A code for each frequency. Thus, the position information satellite is searched and captured. When a threshold is exceeded for a plurality of frequencies or phases of a plurality of C / A codes for a certain position information satellite, the frequency and the phase of the C / A code are detected with the signal having the maximum signal intensity as the acquisition result. In addition, when a plurality of position information satellites are captured, the satellite to be received is determined based on the signal strength. The synthesis search step 101 is performed using RF means and synthesis demodulation means.

[Tracking process]
When the position information satellite is acquired, tracking is performed in the tracking step 102. By the tracking process 102, the phase of the carrier wave and the phase of the C / A code are controlled to the optimum state by the respective PLLs. In the tracking step 102, tracking is started from the frequency of the radio wave from the position information satellite captured in the synthetic search step 101 and the phase of the C / A code. This tracking step 102 continues until data reception is completed. The tracking step 102 is performed using RF means and synthesis demodulation means.

[Data composition reception process]
In the data synthesis receiving step 103, the sensitivity is improved by repeatedly receiving and synthesizing the navigation message data relating to the time included in the radio wave from the position information satellite which is updated as necessary. The data composition reception step 103 is performed using RF means, composition demodulation means, and composition operation means.

[Standard time calculation process]
In the standard time calculation step 104, Greenwich Mean Time is obtained from the navigation message data relating to the time received in the data composition reception step 103.

[Reference clock generation process]
In the reference clock generation step 105, a clock signal having a fixed period which is a basis for ticking the time of the GPS clock is generated.

[RTC process]
In the RTC process 106, the internal clock is generated by counting the reference clock. Further, the internal time is corrected based on the Greenwich Mean Time obtained in the standard time calculation step 104. At this time, the internal time is the local time, and the time is corrected so that the time difference between Greenwich Mean Time 914 and Internal Time 915 is maintained. However, the internal time may be local time or Greenwich Mean Time, and may be converted according to a preset time difference.

[Time display process]
In the time display step 107, the time is displayed on the time display means by the internal time obtained in the RTC step 106. The display of the time based on the internal time may be updated every regular second, for example.

<First Example of Synthetic Search Process>
FIG. 2 shows a first example of the synthesis search process which is one of the features of the present invention. The first example of the synthesis search process will be described in detail with reference to FIG.

  The first example of the combined search step is that the correlation strength obtained by removing the carrier wave and the C / A code after receiving the radio wave from the satellite and down-converting the frequency is equal to or more than one cycle of the C / A code. Search and capture satellites by accumulating.

[Frequency setting process]
In the frequency setting step 201, the frequency to be demodulated is set inside the GPS timepiece so as to search within a range from -5 kHz to +5 kHz from the target value. This is because the frequency of the received radio wave may be shifted within a range of −5 kHz to +5 kHz due to the influence of the Doppler effect accompanying the movement of the position information satellite. The number of frequencies to be searched differs depending on how many correlation strengths of the C / A code are obtained. In the case of one cycle, the frequency is 21 for every 500 Hz. However, when the number of cycles is increased, it is necessary to make a small increment accordingly.

[CA code setting process]
In the CA code setting step 202, a C / A code replica corresponding to the position information satellite to be searched next is set in the GPS watch.

[Down conversion process]
In the down-conversion step 203, radio waves from the position information satellite are received by an antenna, and the frequency of the received high-frequency signal is down-converted to a low-frequency signal that can be easily processed by a heterodyne method.

[ADC process]
In the ADC step 204, the low-frequency signal obtained in the down-conversion step 203 is AD converted to a digital signal.

[Carrier elimination process]
In the carrier wave removing step 205, the carrier wave is removed from the digital signal obtained in the ADC step 204 by using a carrier wave replica, thereby obtaining the in-phase component I and the quadrature component Q of the chip data.

[Search correlation process]
In the search correlation step 206, the correlation strength is obtained by the correlation between the chip data obtained in the carrier wave removal step 205 and the C / A code replica set by the CA code setting means. Therefore, the sum of the squares of the correlation value of the in-phase component I and the correlation value of the quadrature component Q is used as the correlation strength. At this time, since the phase relationship between the chip data and the C / A code is unknown, the correlation strength is calculated while shifting the chip data with the shift register.

[Search result accumulation process]
The search result accumulation step 207 is one of the features of the present invention, and synthesizes the correlation strength obtained in the search correlation step by accumulating one more cycle of the C / A code. In order to perform cumulative addition for each correlation strength having the same C / A code phase, storage means for 1023 chips is used. For this reason, even if the number of cycles of the C / A code for performing the correlation calculation is increased, the circuit scale can be prevented from increasing.

[Cumulative number determination process]
In the accumulated number determination step 208, it is determined whether the number of C / A code cycles accumulated in the search result accumulation step has reached the number determined by the radio wave intensity or the like. If not, the process returns to the down conversion step. I did it.

[Capture judgment process]
In the acquisition determination step 209, it is determined whether the position information satellite has been acquired based on whether the value accumulated in the search result accumulation step exceeds a threshold value. At this time, the largest cumulative addition value for 1023 chips stored in the search result accumulation step is compared with a threshold value. If it is determined that it has been captured, the synthesis search process is terminated.

  Note that the capture determination may be performed in real time with a threshold value for one chip each time it is accumulated in the search result accumulation step.

[All CA code determination process]
In the all CA code determination step 210, it is determined whether or not the process up to the acquisition determination has been completed for C / A codes corresponding to all the position information satellites to be searched, and if not completed, the process returns to the CA code setting step.

[All frequency judgment]
In the all frequency determination process, it is determined whether or not the search for one frequency in the frequency determination process is completed, and if not completed, the process returns to the frequency setting process.

<Second Example of Synthetic Search Process>
FIG. 3 shows a second example of the synthesis search process.
In the second example of the combined search step, after receiving radio waves from the satellite and down-converting the frequency, the carrier wave is removed from the low-frequency signal and a C / A code replica corresponding to one or more satellites is created. While switching within the time range of one chip of C / A code, the C / A code is removed and the correlation strength is extracted, and the obtained correlation strength is transferred to one or more satellites for one or more cycles of C / A code. By accumulating correspondingly, search and capture from one or more position information satellites substantially simultaneously.

  In the second example of the combined search process, by inserting a C / A code loop inside the accumulated number of loops, a search for different C / A codes is time-divided within the time of one chip of the same circuit. And speeding up the overall search.

Each step of the second example of the synthesis search step is the same as that of the first example.
However, in the case of the first example, the accumulated number of loops is the same as the number of accumulated C / A code cycles. In the second example, the C / A code 1 is added to the accumulated number of C / A code cycles. The number of chips in the cycle was multiplied by 1023 chips.

<Third Example of Synthetic Search Process>
FIG. 4 shows a third example of the synthesis search process.
The third example of the combined search process is to store the correlation strength obtained by removing the carrier wave and the C / A code for one cycle or more after receiving the radio wave from the satellite and down-converting the frequency. The satellite is searched and captured by calculating the signal intensity, the phase of the C / A code, and the frequency deviation from the values obtained.

  In the third example of the combined search step, instead of accumulating in the search result accumulating step 206 of the first and second examples, the signal strength and frequency are stored as they are in the correlation strength storing step 401 and calculated from the stored values. Calculate.

  In the third example of the combined search process, the frequency setting process 201, the CA code setting process 202, the down conversion process 203, the ADC process 204, the carrier wave removal 205, the search correlation process 206, the cumulative number determination process 208, the acquisition determination process 209, All CA code determination step 210 and all frequency determination step 211 are substantially the same as in the first and second examples.

  However, in the cumulative number determination step, the determination is made not by the cumulative number but by the number of C / A code cycles stored in the correlation strength storage step 401.

  In the all frequency setting step, the correlation strength is set for 21 frequencies from the target value −5000 Hz to the target value +5000 Hz in steps of 500 Hz, regardless of the number of C / A code cycles stored in the correlation strength storage step 401. I did it.

[Correlation strength storage process]
In the correlation strength storage step 401, the correlation strength for each cycle of the C / A code and for each phase is temporarily stored as it is.

[Search calculation process]
In the search calculation step 402, the signal strength and the frequency are obtained by calculation from the values stored in the correlation strength storage step 401. The search calculation process 402 will be described based on an example shown in the conceptual diagram of FIG. 5 and the process flow diagram of FIG.

  In the conceptual diagram of FIG. 5, the horizontal axis is the phase of the C / A code, the unit is one chip, the vertical axis is the time, and the unit is one cycle of the C / A code. The rectangle indicates the area where the correlation strength is stored, and the width is 1023 chips. The stored values are usually multivalued and contain noise. A dotted line in the rectangular area indicates that there is a weak signal from the position information satellite.

  In order to extract this dotted line, the stored value on the line segment 512 by the combination of the upper end and the lower end is added.

  The upper end corresponds to the last one cycle of the C / A code, and the positions in the horizontal direction are 1023 with the phase of the C / A code being 1 to 1023. The lower end corresponds to the first cycle of the C / A code, and the horizontal position is derived from “the phase of the C / A code obtained by subtracting the number of C / A code cycles from the phase of the upper end C / A code”. From the phase of the C / A code at the upper end to the phase of the C / A code added by the number of C / A code cycles is moved at intervals of one chip. The reason for the lower end range is that the signal intensity output by the correlation means for search becomes weaker when the frequency shift is 1 chip or more per cycle of the C / A code. Therefore, the number of combinations of line segments is a value obtained by multiplying 1023 by 1 to twice the number of CA code cycles. The added value in all of these combinations indicates the signal strength, and if it is equal to or greater than the threshold value, it is determined that the position information satellite has been captured. As the threshold value, for example, a predetermined value corresponding to the number of C / A code cycles may be used so as not to be erroneously captured due to noise, or an addition value is statistically processed and obtained in advance. May be.

  An example of a process flow for line extraction is shown in FIG. In FIG. 6, while the upper end is moved from 1 to 1023, the lower end is moved from “upper end−the number of C / A code cycles” to “upper end + the number of C / A code cycles” to perform straight line extraction. Needless to say, the calculation may be performed with the upper and lower ends interchanged.

  In addition, the addition of the value of the data on a line segment calculates the phase of a corresponding C / A code for every cycle of a C / A code, and adds the memorize | stored value. At this time, if the phase of the C / A code does not become an integer, it may be rounded off or an interpolation process may be performed. If the line segment is out of the range of the area where the two-dimensional correlation strength is stored, 1023 is added to or subtracted from the phase of the C / A code to convert it into the area.

  Further, in the search calculation step, an error of the searched frequency is obtained from the slope of the extracted line segment. By subtracting the phase of the C / A code at the lower end from the phase of the C / A code at the upper end and dividing the result by the number of cycles of the C / A code, the number of chips per C / A code cycle is obtained. Since one cycle of the C / A code is composed of 1023 chips, the frequency deviation ratio is obtained by further dividing this value by 1023. When this value is positive, the phase of the C / A code is delayed with time, so the frequency of the carrier replica generated internally may be lowered by the obtained ratio. Similarly, if it is negative, the frequency may be increased.

  Usually, since time has passed in a straight line extraction calculation or the like, the search may be performed again with a new frequency. However, the change in the phase of the C / A code during that time is detected as shown in FIG. You may make it obtain | require using the extension line 511. FIG.

  It should be noted that the fineness and range of the positions of the upper end and the lower end shown here are examples, and it goes without saying that this is not the case. Further, considering that the time has advanced even during one cycle of the C / A code, the two-dimensional storage area may be calculated more strictly as a parallelogram instead of a rectangle. The above is an example of the calculation, and any calculation may be used as long as it is a calculation for obtaining the signal strength and the frequency from the correlation strength corresponding to the C / A code of a plurality of cycles.

<Data composition reception process>
FIG. 7 shows an example of the flow of the data composition reception step 103. From now on, the data composition reception process which is another feature of the present invention will be described with reference to FIG.

  In the data synthesis reception process, after receiving radio waves from the satellite and down-converting the frequency, the bit boundary is detected from the correlation data obtained by removing the carrier wave and the pseudo-random code, and within the detected bit boundary. The correlation data is aggregated to generate bit data, and the navigation message data is synthesized from the bit data.

  In the data composition reception step 103, navigation message data relating to time is extracted. Here, a method for stably obtaining correct navigation message data with high reliability when radio waves from a position information satellite are weaker than noise will be mainly described.

  The down conversion process 203, the ADC process 204, and the carrier wave removal process 205 are almost the same as the synthesis search process.

[Data correlation process]
In the data correlation step 701, correlation data is obtained from the correlation between the chip data obtained in the carrier wave removal step 205 and the C / A code replica.

[Bit boundary detection process]
In a bit boundary detection step 702, a bit boundary every 20 ms is detected from the array of correlation data every 1 ms superimposed on each cycle of the CA code.

  The bit boundary detection step is composed of a change extraction step for extracting a change in correlation data, a change accumulation step for accumulating changes in correlation data obtained in the change extraction step, and correlation data from changes accumulated in the change accumulation step. This is performed by a change point position calculation step for obtaining a boundary of bit data.

  The bit boundary detection step 702 is performed by a change extraction step 721, a change accumulation step 722, and a change point position calculation step 723.

[Bit data aggregation process]
When the bit boundary is detected, the bit data is aggregated by adding the C / A code 20 cycles within the boundary in the bit data aggregating step 703 as in the conventional GPS clock to generate bit data.

[Bit data composition process]
When the bit data is aggregated, the bit data synthesis step 704 synthesizes the received values of different subframes for the navigation message data related to the time such as TLM, TOW, subframe ID, WN, UTC, etc. Improve the signal-to-noise ratio as a ratio.

[Reliability judgment process]
In the reliability determination step 705, generation of bit data and synthesis of bit data are repeated until a sufficient S / N ratio can be ensured. Note that the reliability determination step 705 is not necessarily required, and may be performed as necessary.
The bit boundary detection step 702 and the bit data synthesis step 704 characteristic of the present invention will be described in detail.

<Bit boundary detection process>
FIG. 8 shows an example of a method for searching for the boundary of each bit when the signal is weak.

[Signal buried in noise]
FIG. 8a is random noise. FIG. 8b is a signal that is weaker than noise and changes at bit boundaries. FIG. 8c is a sum of the noise of FIG. 8a and the signal of FIG. 8b, and represents the level of correlation data output from the synthesizing demodulation means. 8A, 8B, and 8C, the vertical axis represents each level, the horizontal axis is the time axis, and corresponds to 240 cycles of the full-range time-series C / A code, that is, 240 milliseconds.

  Since the signal shown in FIG. 8b is weaker than the noise shown in FIG. 8a, the bit boundary is not obvious from the correlation data output from the combined demodulating means obtained by adding the noise and the signal shown in FIG. 8c. Therefore, in order to clarify the bit boundaries, changes are extracted in consideration of the bit time being 20 ms, and the results are accumulated.

[Change extraction process]
Specifically, the change extraction is performed by calculating the square of the difference between the total value of the correlation data before 11 to 20 ms and the total value of the correlation data before 1 to 10 ms in consideration that the bit time is 20 ms. did. This is not a limitation as long as it is a method of removing the influence of polarity such as an absolute value instead of square. The total range of correlation data is also a preferred example, and is not limited to this. However, the change extraction results in FIG. 8d are shifted to the left by 10 milliseconds so as to correspond to the signal change points in FIG. 8b for convenience. As a result, the value of the change extraction result in FIG. 8d is often increased at the signal change point in FIG. 8b.

[Change accumulation process]
A specific method for accumulating changes is to divide the change extraction result of FIG. 8d every 20 ms in consideration of the bit time being 20 ms, and total the divided results. In other words, the change extraction results in which the remainder when the horizontal axis is divided by 20 are the same value are summed. The result is shown in FIG. 8e. However, the horizontal axis of FIG. 8e is a value obtained by adding 1 to the remainder. As a result of such accumulation, the position of the change point becomes clear.

[Change point position calculation process]
In order to calculate the position of the change point, the position of the peak of the change accumulation result in FIG. 8e may be obtained by detecting the maximum value or calculating the weighted average. However, when calculating the weighted average, it is necessary to assume that it is repeated cyclically when it is close to the end of the region. In the example of FIG. 8e, the change point is between the tenth and eleventh. Considering that the horizontal axis in FIG. 8d is shifted by 10 milliseconds, the output of the RF means in FIG. 8c is a bit boundary between the 20th and 21st, which is due to the change in the signal in FIG. 8b. Match. Thereafter, a bit boundary exists every 20 ms.

[Performance of bit boundary detection]
If the process of extracting and accumulating changes is performed in this way, no matter how weak the signal is theoretically, if the period for searching for the boundary of each bit, that is, the horizontal axis in FIGS. It is possible to detect the boundary.

<Configuration of GPS watch>
FIG. 9 shows a preferred example of the block configuration of the entire GPS watch 901 according to the present invention. Hereafter, each means which comprises a GPS timepiece is demonstrated in detail based on FIG.

[antenna]
In FIG. 9, an antenna 902 converts a gigahertz band radio wave from a position information satellite into a high frequency signal 911 and outputs it to the RF means 903.

[RF means]
The RF unit 903 down-converts the high frequency signal 911 from the antenna 902 into a low frequency signal 912 that can be easily processed by the synthesizing demodulation unit 904. For this reason, the RF means performs frequency down-conversion by extracting the difference component with a filter from the frequency component of the sum and difference generated by the product with the local oscillation. The local oscillation frequency is generated using a PLL based on the frequency oscillated by the temperature-compensated crystal oscillator (TCXO) because the higher the accuracy, the easier it is to capture the position information satellite. In the RF means, a low noise amplifier may be inserted and amplified as necessary.

[Synthetic demodulation means]
The synthesizing demodulator 904 demodulates the low frequency signal 912 from the RF unit 903. Therefore, the synthesizing / demodulating means 904 removes the carrier wave using the carrier wave replica, removes the CA code by the correlator, and obtains the correlation data including the correlation strength indicating the signal strength and the GPS navigation message data.

  Even when the radio wave from the position information satellite is weak, it is captured in a relatively simple configuration and in a short time by synthesizing the correlation results of repeated C / A codes. In addition, the circuit scale can be kept small by simultaneously using a plurality of position information satellites as one correlation means.

[Composite operation means]
Since the correlation data 904 output from the synthesizing / demodulating means 904 is a multivalued value obtained by the correlation of 1023 chips, noise is mixed in addition to the signal. If the signal is weaker than noise, determining the value of the received bit simply based on whether the correlation is positive or negative will reduce the data reliability. In order to solve this problem, the synthesizing arithmetic unit 905 realizes high sensitivity by synthesizing the correlation data from the synthesizing / demodulating unit 904 that receives intermittently repeatedly and obtains highly reliable data.

  In addition, the composite calculation means 905 converts the GPS time and UTC data based on the navigation message data included in the correlation data into a time corresponding to Greenwich Mean Time.

[RTC means]
The RTC unit 906 generates an internal time 915 by counting an internal reference clock. In addition, the internal time 915 is corrected by Greenwich Mean Time 914 from the composition calculation means 905. At this time, the internal time is the local time, and the time is corrected so that the time difference between Greenwich Mean Time 914 and Internal Time 915 is maintained. However, the internal time may be local time or Greenwich Mean Time, and may be converted according to a preset time difference.

[Time display means]
FIG. 10 shows an example of the time display means 907. The time display unit 907 displays the time based on the internal time 915. The display time is updated, for example, every regular second. The display method of the time display means 907 may be, for example, a digital time display as shown in FIG. 10 (a) or an analog time display as shown in FIG. 10 (b). The GPS clock 901 according to the present invention may be a table clock, a wall clock, or a wristwatch.

[Control means]
The control unit 908 manages the overall status and sequence.
The synthesizing / demodulating means 904 which is one feature of the present invention will be described in detail with reference to the drawings.

<First Example of Synthetic Demodulation Unit>
FIG. 11 shows a first preferred example of the synthesizing / demodulating means 904 for performing a highly sensitive search without increasing the circuit scale. The first example of the synthesizing / demodulating means removes the carrier wave and the C / A code from the low frequency signal to extract the correlation data and the correlation strength, and accumulates the obtained correlation strength for one cycle or more of the C / A code. By doing so, the position information satellite is searched and captured.

[ADC means]
The ADC unit 1101 converts the low frequency signal output from the analog RF unit into a digital value.

[Carrier elimination means]
The carrier wave removing means 1102 obtains the in-phase component I and the quadrature component Q of the chip data 1111 by convolving a replica of the carrier wave from the NCO means 1105 with the signal from the ADC means 1101 for a period of about 1 chip (about 1 μs).

[CA correlation means]
The CA correlation unit 1104 calculates an inner product to obtain a correlation between the output of the carrier wave removal unit 1102 and the C / A code. The CA correlation unit 1104 is a general term for three correlation units: a correlation unit for search 1106, a correlation unit for CA code PLL 1107, and a correlation unit for carrier wave PLL 1108.

[search]
The correlation means for search 1106 captures in a short time when the phase of the C / A code is not known at all, so that a pair of in-phase component I and quadrature component Q of the chip data 1111 from the carrier wave removal means 1102 is obtained. And the correlation with the C / A code is calculated while shifting the in-phase component I and the quadrature component Q of the chip data 1111 with a shift register. Since the phase of the carrier wave is not locked at the time of the search, in order to obtain the strength of the signal from the position information satellite, the correlation result between each of the in-phase component I and the quadrature component Q of the chip data 1111 and the C / A code is obtained. The sum is squared and the sum is calculated and output as the correlation strength 1112.

[tracking]
Once the position information satellite is acquired, the frequency of the carrier wave and the phase of the C / A code can be roughly matched, but tracking is performed in order to lock them in an optimum state. In tracking, the phase of the CA code is matched with the CA code PLL, and the phase of the carrier is matched with the carrier PLL.

[CA code PLL]
The CA code PLL includes a carrier wave removing unit 1102, a CA code PLL correlating unit 1107, and a CA code PLL loop filter (not shown). The carrier removal means 1102 convolves with the advance component E and the 1/4 chip delayed by a period of 1/4 chip relative to the period of 1 chip convolved for the correlation means for search 1106 and the correlation means 1108 for the carrier PLL. A delay component L convoluted for a certain period is used. These E and L are initials of Early and Late, respectively. The CA code PLL correlator 1107 calculates the correlation with the C / A code for the leading component E and the lag component L, and shifts the chip period for convolution of the carrier wave removing unit 1102 back and forth so that each result is balanced. Let The time constant of the CA code PLL loop filter is adjusted by the strength of the radio wave from the position information satellite. Increasing the time constant of the loop filter for the CA code PLL increases the time to lock, but even if the radio wave from the position information satellite is weak, the sensitivity can be increased and the phase can be adjusted accurately. become.

[Carrier PLL]
The carrier PLL includes a carrier removal means 1102, a carrier PLL correlation means 1108, and a carrier PLL loop filter (not shown). A carrier wave replica generated by the NCO means so that the correlation means 1108 of the chip data 1111 calculates the correlation between the C / A code for the in-phase component I and the quadrature component Q of the chip data 1111 by the carrier PLL correlation means 1108 The received data can be extracted in synchronization with the in-phase component I by controlling the frequency of. Here, the NCO unit 1105 can control the frequency and phase with digital values by a numerically controlled oscillator. The time constant of a carrier PLL loop filter (not shown) of the carrier PLL 1108 is adjusted by the strength of the radio wave from the position information satellite. By increasing the time constant of the loop filter for the carrier PLL, the time to lock becomes longer, but even if the radio wave from the position information satellite is weak, the sensitivity can be increased and the phase can be adjusted accurately. Become.

[Signal strength accumulation means]
Here, the correlation strength 1112 output from the correlation means for search 1106 is accumulated by the signal strength accumulation means 1109 to obtain a signal strength 1113 obtained by accumulating the correlation strength 1112 with the C / A code of a plurality of cycles. When the signal intensity 1113 exceeds the threshold, it is determined that the position information satellite has been captured. In this case, the peak value indicates the intensity of the searched signal, and the timing of the peak value indicates the phase of the C / A code. As the threshold value, for example, a predetermined value corresponding to the cumulative number may be used, or the signal intensity 1113 may be obtained by statistical processing so as not to be erroneously captured due to noise.

The signal intensity accumulating means 1109 for this purpose will be described based on the example shown in FIG.
The signal strength accumulating means 1109 is provided with 1023 stages of shift registers equal to the number of chips for one cycle of the C / A code, and the sum of the output 1213 of the final stage and the correlation intensity 1112 is used as the input of the first stage. The correlation strength 1112 for each phase relationship with the A code is cumulatively added. Note that the shift timing of the shift register is synchronized with the carrier removal timing in the carrier removal means 1102. By configuring in this way, no matter how many cycles the C / A code is accumulated, it can be dealt with by increasing the number of bits so that the shift register is not saturated. When the number of C / A code cycles for calculating correlation is increased, the circuit scale can be made much smaller than when the number of stages of the correlation means itself is increased. Therefore, even when the radio wave from the position information satellite is weak, it is possible to perform a search with a reduced circuit scale.

  Needless to say, the value of the shift register is initialized before searching.

<Second Example of Synthetic Demodulation Unit>
FIG. 13 shows a second example of the synthesizing / demodulating means. In the first example of the synthesizing / demodulating means 904, when the radio wave from the position information satellite is weak, the signal strength can be obtained with a relatively simple configuration for the C / A code of a plurality of cycles. However, when the number of C / A code cycles is increased, there is a problem that the time for searching becomes longer and the power consumption increases. Therefore, in the second example of the synthesizing / demodulating means 904, the search correlation means 1106 is simultaneously used for searching a plurality of position information satellites, thereby shortening the total search time and suppressing an increase in power consumption.

  For this reason, the second example of the synthesizing / demodulating means removes the carrier wave from the low-frequency signal, and also makes a C / A code replica corresponding to one or more satellites within the time range of one chip of the C / A code. The correlation data and the correlation strength are extracted by removing the C / A code while switching to, and the obtained correlation strength is accumulated for one or more cycles of the pseudo-random code corresponding to one or more satellites. Search and capture from the above position information satellites substantially simultaneously. The synthesizing / demodulating means 904 will be described with reference to FIG.

  In FIG. 13, the ADC unit 1101, the carrier wave removal unit 1102, the CA correlation unit 1104, and the NCO unit 1105 are the same as those in the first example of the synthesis demodulation unit 904.

[CA code selection means]
In FIG. 13, CA code selecting means 1303 selects C / A codes corresponding to a plurality of position information satellites to be searched simultaneously by a selection signal from timing means 1302.

[First to n accumulating means]
The first to n accumulation means 1301 also accumulate the correlation strength 1112 of the position information satellites to be searched simultaneously. The first to n accumulating means 1301 are the same as the signal intensity accumulating means 1109 in the first example of the composite demodulating means 904, and are provided for each position information satellite to be searched simultaneously. First to n accumulation means 1301 correspond to first to nC / A codes, respectively.

[Timing means]
The timing unit 1302 selects the selections 1 to n for selection by the CA code selection unit 1303 and the accumulations Ck1 to n for capturing the signal strength by the first to n accumulation units 1301 in the shift register of the search correlator 1106. The clock is generated by counting a sufficiently fast clock in synchronization with the shift clock.

  The operation of the timing means 1302 will be described based on the timing chart shown in FIG. In the timing chart of FIG. 14, the correlator Ck which is a shift clock of the shift register of the search correlator 1106 and the selection clocks 1 to n generated by the timing means 1302 and the shift clock of the shift register of the first to n accumulation means. The timing relationship of accumulation Ck1-n is shown. The horizontal axis is a common time axis. The vertical axis represents the logical value of each signal, with the upper side being true and the lower side being false. A period indicated by an arrow in the figure indicates a period in which the shift register of the search correlator 1106 is shifted and a period in which the search correlator 1106 performs a correlation operation.

  The shift register of the correlator is shifted by the back of the correlator Ck of the search correlator 1106. When the shift is completed, the selection 1 signal is set to true, the first C / A code is selected, and the correlation between the value of the shift register of the search correlator and the first C / A code is performed. When the correlation calculation is completed, the first accumulating unit accumulates the correlation strength after the accumulation Ck1. When the accumulation of the first accumulation means is completed, selection 1 is set to false.

  When the accumulation of correlation outputs corresponding to the first C / A code is completed, the correlation outputs corresponding to the second to nC / A codes are sequentially accumulated in the same manner.

  The period of the correlation Ck is 978 ns, and the time corresponding to one C / A code phase of the correlation output corresponding to one C / A code is obtained by subtracting the shift time of the shift register of the correlation means for search of 10 ns or less. The accumulation needs to be completed. The time required for correlation and accumulation corresponding to one C / A code phase 1 chip is about 100 ns, and eight position information satellites are searched simultaneously.

<Third Example of Synthetic Demodulation Unit>
FIG. 15 shows a third example of the synthesizing / demodulating means. In the first and second examples of the synthesizing / demodulating means 904, when the radio wave from the position information satellite is weak, the signal intensity can be obtained with a relatively simple configuration for the C / A code of a plurality of cycles. However, if the number of C / A code cycles is increased, the frequency to be searched for must be made smaller, so that the problem of longer search time and higher power consumption remains. Therefore, in the third example of the synthesizing demodulation unit 904, a correlation strength storage unit 1501 for storing the correlation strengths for a plurality of cycles of the C / A code as it is is provided instead of the signal strength accumulating unit 1109, and the search calculation unit 1502 is used. By calculating, it becomes possible to detect the frequency in addition to the signal intensity at the same time, and even if the number of cycles of the C / A code to be searched is increased, the frequency to be searched does not need to be small.

  The third example of the synthesizing / demodulating means removes the carrier wave and the C / A code from the low frequency signal to extract the correlation data and the correlation strength, and stores the obtained correlation strength for one or more cycles of the C / A code. The position information satellite is searched and captured by calculating the signal intensity, the phase of the C / A code and the frequency deviation from the value stored in the correlation intensity storage means. A third example of the synthesizing / demodulating means 904 for this purpose will be described based on the example shown in FIG.

  In FIG. 15, the ADC unit 1101, the carrier wave removing unit 1102, the CA correlation unit 1104, and the NCO unit 1105 are the same as those in the first and second examples.

[Correlation strength storage means]
The correlation strength storage unit 1501 stores the correlation strength 1112 from the search correlation unit 1106 without being accumulated. One dimension of the correlation strength storage means 1501 is the phase of the C / A code and the unit is one chip, and the other dimension corresponds to the C / A code repetition cycle. The term “two dimensions” as used herein does not represent a physical position but a storage area that is distinguished by two variables.

[Search calculation means]
The search calculation means 1502 considers the value stored in the correlation strength storage means 1501 as image data and performs line extraction processing.

<Combining operation means>
FIG. 16 shows an example of the composition calculation means that is one of the features of the present invention. Combining calculation means is a bit data generating means for collecting correlation data to generate bit data, a data combining means for extracting navigation message data related to time from the bit data, and calculating a standard time from navigation message data from the data combining means. And a standard time calculation means.

[Bit data generation means]
In FIG. 16, the bit data generating means 1601 generates bit data 1611 constituting navigation message data from the correlation data 913 from the synthesizing / demodulating means. In the data synthesis reception step, bit boundaries for every 20 ms are detected from the correlation data obtained every 1 ms, which is the time for one cycle of the CA cycle, and 20 pieces of correlation data within the boundaries are aggregated to obtain bit data 1611. obtain. Accordingly, the bit data 1611 is generated every 20 ms.

[Data composition means]
The data synthesizing unit 1602 improves the sensitivity by synthesizing one or more bit data 1611 generated every 20 ms by the bit data generating unit 1601, and obtains navigation message data 1612 related to time.

[Standard time calculation means]
The standard time calculation means 1603 calculates Greenwich Mean Time 914 by calculation from the navigation message data 1612 related to time.

<Bit data generation means>
FIG. 17 shows an example of the configuration of the bit data generation means that is one of the features of the present invention. The bit data generation means detects the bit boundary using the method described in the bit boundary detection step, aggregates the correlation data within the boundary, and outputs the bit data. The bit data generating means is composed of correlation data from a change extracting means for extracting changes in correlation data, a change accumulating means for accumulating changes in correlation data obtained by the change extracting means, and a change accumulated by the change accumulating means. The change point position calculating means for obtaining the boundary of the bit data and the bit data collecting means for collecting the correlation data based on the change point from the change point position calculating means and outputting the bit data.

[Change Extraction Means]
The change extracting unit 1701 extracts the bit data boundary in order to detect the bit data boundary from the correlation data 913 output from the synthesis demodulating unit every 1 ms corresponding to each cycle of the C / A code. Since bit data is composed of 20 pieces of continuous correlation data, a change is extracted by convolving the correlation data with a replica composed of 20 numerical sequences that change in a step shape at the center. This convolution operation is performed every time one piece of correlation data is output. The change extraction means is used in the change extraction process.

[Change accumulation means]
The change accumulating means adds and accumulates the same surplus when the extraction result is divided by 20 by the change extracting means. The change accumulation means is used in the change accumulation process.

[Change point position calculation means]
The change point position calculation means obtains a representative value of the change point from the result accumulated by the change accumulation means by weighted average or peak value extraction. The boundary of the bit data of the correlation data is obtained from the representative point of the change point. The change point position calculation means is used in the change point position calculation step.

[Bit data aggregation means]
The bit data aggregating unit aggregates the correlation data within the boundary of the bit data output from the change point position calculating unit, and outputs the bit data.

<Bit data composition>
FIG. 18 shows an example of the configuration of the bit data synthesizing means 1602. If the radio waves from the position information satellite are weak, the reliability of each of the received bit data 1611 is not sufficient, and therefore the reliable navigation message data 1612 is accumulated from the bit data 1611 received multiple times or the bit data 1611 of multiple bits. And synthesized by correlation and reliability determination. Since noise is proportional to the square root of the number of accumulations and the signal is proportional to the number of accumulations, the signal-to-noise ratio can be improved and the reception sensitivity can be increased by accumulation.

  Also, navigation message data relating to time is extracted by correlation with a plurality of assumed bit data 1611 replicas. Here, the replica is an expected received value. Among navigation message data, a received value that is expected such as a preamble included in a TLM is expected, a received value that is repeated in a pattern with a received value such as a subframe ID, or a received value such as TOW. For data that is incremented each time it is received, a replica can be prepared. Since this replica makes a correlation determination from the bit data 1811 received a plurality of times or the bit data 1811 of a plurality of bits, a determination with high reliability is possible, and as a result, the reception sensitivity can be increased.

  For this reason, in the past, reliability was ensured by confirming that the received data of a plurality of times is consistent, but in the present invention, it is possible to stably receive even weaker radio waves. In addition, accumulation, correlation, and reliability determination are used.

[Detection of the frame position / preamble]
In order to obtain the navigation message data 1612, it is first necessary to know the position of the subframe. In order to know the position of the subframe, a preamble included in the TLM is searched. The preamble is a predetermined value and is the first 8 bits of the TLM shown in FIG. The subframe head 1821 is obtained by the cumulative P unit 1801, the correlation P unit 1802, and the reliability determination unit 1803 to determine the position of the subframe. FIG. 19 shows an example of a configuration and method for combining and receiving preambles.

(Cumulative P means)
The cumulative P means cumulatively adds all the data of the subframes so that it can be reliably detected even when the radio wave from the position information satellite is weaker than the noise. That is, since the subframe is composed of 300 bits, a 300-stage shift register is provided. The shift register is shifted to the right by one stage every time 1 bit of bit data is generated, and the sum of the output of the final stage and the bit data is input to the first stage of the shift register. Since the TLM value does not change, the TLM is added every time it is repeatedly received due to accumulation of subframe data. Needless to say, the value of the shift register is initialized before the cumulative addition.

(Correlation P means)
In the correlation P means, since the TLM is at the head of all subframes, the positive and negative signs of the 8-bit value at the head of the shift register are associated with 1 and 0, and compared with the inverted preamble in which the preamble and the preamble are inverted. To do. Conversely, 0 in the replica may be replaced with -1. The comparison is performed every time the shift register shifts to detect the preamble. The comparison means is not limited to the comparison with the preamble, and any configuration or method that can detect the preamble, such as calculating the correlation with the preamble or calculating the angle when viewed as a vector, may be used.

  Here, the inversion preamble is also used because the polarity of the input bit is unknown. In the following description, an example in which a preamble is detected will be described. However, when an inverted preamble is detected, received data is simply inverted.

(Reliability judgment means)
The reliability determination unit 1803 in FIG. 18 determines how much reliability the accumulation or correlation result from the bit data has. Therefore, navigation message data relating to time can be extracted while determining the reliability from the bit data.

  The number of receptions until the reliability obtained here becomes sufficient can be used in the subsequent reception of navigation message data.

  The reliability determination unit 1803 determines the reliability of the TLM when a preamble is detected. For this reason, the reliability determination means calculates the average and standard deviation of the absolute values of the bits constituting the TLM, and determines that the preamble detected by the comparison means is reliable when the average value is sufficiently larger than the standard deviation. To do. The reliability determination means does not necessarily have to be determined for the entire TLM, and it is sufficient to select bits that do not change in all subframes with a sufficient number of bits to obtain reliability. In addition, the determination of the reliability does not necessarily need to be the ratio between the average of the absolute values and the standard deviation, and any configuration or method can be used as long as it can be confirmed that the bipolarization is appropriately performed. good.

Needless to say, the reliability can be improved by using together the parity bit of the word number 1 including the preamble.
The reliability determination unit 1803 may be provided as necessary.

(When the radio wave is strong)
When the radio wave from the position information satellite is sufficiently strong, the bit data can be divided into two even in a small number of subframes, and a reliable preamble can be detected. However, in order to confirm whether or not the same value as the preamble or the inverted preamble is included other than the preamble, it is necessary to compare the entire subframes at a minimum.

  With this configuration, it is possible to detect the preamble by synthesizing a desired number of bit data according to the strength of the radio wave from the position information satellite.

[Detection of subframe ID]
The subframe ID is detected by the cumulative S means and the correlation S means.
20 and 21 show a method of combining and receiving repetitive pattern data in the case of a subframe ID. When the head position of the subframe is known, the subframe ID indicating the current subframe is detected. As described above, one frame is composed of five subframes and is in the order of subframe numbers 1 to 5. The subframe ID is a binary value of the subframe number.

(Cumulative S means)
If the radio wave is weak, it is difficult to specify the subframe ID by one reception. For this reason, the cumulative S means detects the subframe ID by cumulatively adding the received values of the subframe IDs a plurality of times. An example of the configuration for this is shown in FIG.

  In FIG. 20, since the subframe ID is repeated every 5 subframes, the received value of the subframe ID every 5 subframes is cumulatively added using the shift register for the 3 bits constituting the subframe ID. It was made the structure. Needless to say, the value of the shift register is initialized before the cumulative addition.

  Here, as shown in FIG. 24, the subframe ID is 3 bits of bit numbers 20 to 22 of the word number 2 of each subframe. The timing of accumulative addition by the accumulating S means is obtained by counting bit data from the subframe heads 18 to 21 obtained by the correlation P means.

(Correlation S means)
The correlation S means calculates the correlation between the received and accumulated subframe ID and the five replicas of the subframe ID, and detects the subframe ID from the replica having the strongest correlation.

  Five replicas for this purpose will be described with reference to FIG. The data arrangement of these replicas corresponds to the arrangement of the accumulated reception data of the accumulation circuit of FIG. The value in each vertical column of the replica is a value that matches the subframe ID when −1 is replaced with 0.

  The replica 1 in FIG. 21A has the largest correlation when the latest subframe ID is 1. This is because the binary value obtained by replacing -1 in the leftmost vertical column with 1 is 1. Since the subframe ID of the subframe immediately before the subframe with subframe ID 1 is 5, the second column from the left of replica 1 similarly replaces -1 with 1, and the binary value becomes 5. It is supposed to be. Similarly, all the vertical columns are configured such that when -1 is replaced with 1, binary values match the subframe ID.

  Similarly, the replica of FIG. 21B is for detecting that the latest subframe ID is 2, and the same applies to the replicas 3 to 5 of FIGS. 21C to 21E.

  Although an example of the configuration in which the subframe ID is detected from the received values of the subframe IDs of the five subframes having the subframe numbers 1 to 5 is shown, for example, when the radio wave is sufficiently strong, the subframe ID of the first subframe is It is also possible to make a determination based only on the received value, and it is sufficient to increase the number of received bits for detection as necessary.

  The method for detecting the subframe ID using a plurality of replicas at the same time has been described above. However, each time the 3 bits of the subframe ID are updated, it may be compared with one replica. For example, in order to detect that the latest subframe ID is 1, the correlation is calculated in the replica 1, and it is detected that the latest subframe ID is 1 when the correlation is high.

(Reliability of subframe ID)
As for the cumulative number of subframe IDs, it is usually sufficient to set the same number of times as when the preamble is detected, and the reliability determination means for the subframe ID can be omitted. That is, if 10 cycles of subframes are required to detect the preamble, the subframe ID may be detected in 10 subframes. Rather, in the method using the above-described replica, since the relationship between 3 bits is used, the cumulative number may be 1/3.

  However, it is also possible to determine the reliability of received data in the same manner as the preamble reliability determination means, assuming a sudden change in the noise environment.

  Further, the method of detecting the subframe ID by the replica having the strongest correlation has been described above. However, ideally, the value of the correlation with the five replicas is the front and rear replicas when the maximum value is 15. Is -1 and the correlation with other replicas is -5. These values are obtained, for example, when the inner products of the replicas 1 to 5 are -5, -1, 15, -1, and -5, respectively, assuming that the received data is the same as that of the replica 3. It is. Therefore, the reliability of subframe ID detection may be determined based on the fact that the correlation with each replica is close to these ratios.

[Detection of TOW]
TOW is bit numbers b1 to 17 of word number W2 of each page of each subframe. The TOW is detected by the cumulative T means, the storage T means, and the replica T means.

  FIG. 22 shows a case of TOW as an example of a method of combining and receiving increment data. The current time in one week is calculated from a 17-bit TOW that is incremented for each subframe. A configuration and method for receiving the TOW will be described with reference to FIG.

(Memory T means)
The increment data can be considered as a pattern data having a longer cycle. Therefore, with the increment data, the reception data is stored in the memory for the number of receptions in principle.

  In the case of the example shown in FIG. 22, the number of subframe receptions is five. Since 17 bits of TOW are received at the same time, 17 × 5 = 85 bits of memory are prepared to store the generated bit data. In FIG. 22, the data stored in the memory is assumed to be only 1 and −1 normalized without noise for convenience of explanation, but is usually multi-value data with superimposed noise. In FIG. 22, the value of the first to fifth received data is incremented by a binary value when -1 is replaced with 0. Note that values higher than the bit number b7 are not shown in the figure because of the same concept as the lower order.

(Replica T means and correlation T means)
In FIG. 22, the replica T means is used for calculating the correlation between the received data and the correlation T means for each bit of the vertical column of the received data. As the size of the replica T means, the value is dynamically changed for each bit, so that the number of receptions of 1 bit is sufficient.

  In the increment data, the correlation is calculated in order from the lower bit. Before calculating the correlation between the least significant bit replica and the least significant bit received data, the least significant bit replica is prepared in the replica T means. The replica of the least significant bit repeats 1 and −1 alternately corresponding to the increment data. If the increment data corresponding to the latest received data is set to 1, it is easy to understand because the correlation value can be used as the latest received value.

  That is, in the example of FIG. 22, the correlation between the bit number b1 of the storage T means and the replica T means is -5 by calculating the inner product. Saying that the inner product is negative indicates that the bit number b1 of the storage T means is in reverse phase with the replica. Therefore, the received value of the latest bit number b1 is a negative value.

  Next, the replica value of the next higher replica T means is determined. The period of the uppermost replica is twice the period of the least significant bit replica. Therefore, 1 and -1 are arranged alternately two by two in succession. The one-higher replica corresponding to the latest data is set to 1, and the timing of the change is determined from the polarity of the next-lower correlation result. That is, when the lower correlation is a positive value, the upper replica is changed as a carry is generated when the value of the lower replica changes from 1 to -1. Conversely, when the lower correlation is a negative value, the upper replica is changed when the lower replica is changed from −1 to 1. In the case of the replica of the bit number b2 in FIG. 22, since the correlation result of the bit number b1 is negative, the timing at which the replica of the bit number b1 changes from −1 to 1, that is, between the second and third from the top and the top To change between 4th and 5th.

  Thereafter, the correlation calculation and the replica determination are repeated in the same manner until the correlation calculation of the most significant bit is executed. Thus, the latest TOW value can be obtained by synthesizing the increment data a plurality of times from the correlation of every 17 bits of the TOW obtained.

(Utilization of parity data)
Although not described in detail, the parity bit of the word number W2 including the TOW and the subframe ID is stored in the memory at the same time as the received data in units of words, and the latest TOW value or subframe ID value is stored. The received data at each receiving timing is decremented by calculating the parity data based on the obtained back-calculated data, and the received parity data is used as a parity replica to receive the received data based on the correlation between the received data and the parity replica. Data reliability can be improved.

[BD position calculation means]
When the TOW and the subframe ID are combined, the reception timing of other navigation messages such as WN related to time, health information, and UTC can be known. In the BD position calculation means, the reception timing 1803 of the navigation message data relating to the time is generated from the subframe head 1821 from the correlation P means, the subframe ID 1822 from the correlation S means, and the TOW 1823 from the correlation T means.

[Cumulative F means]
The cumulative F means repeats other navigation messages such as WN related to time, health information, UTC, etc., and repeatedly adds bit data data 1611 at the reception timing 1803 from the BD position calculating means 1809, so that even when the radio wave is weak, it is stable. Received data can be obtained. Since these navigation messages have a low frequency of change, the values repeatedly received as fixed values may be accumulated bit by bit. The same applies to these parity bits.

<Other implementation methods>
Although different flows are shown in FIGS. 2 to 4 for the synthesis search process, these may be used alone or in combination. Similarly, FIGS. 11, 13 and 15 show different configurations for the synthesizing / demodulating means, but these may be used alone or in combination.

  In the data synthesis reception process, the flow of processing in the order of the ADC process, the carrier wave removal process, the search correlation process, or the data correlation process has been described, but the order may be changed, and is not limited thereto. Similarly, in the synthesizing / demodulating means, an example in which the ADC means, the carrier wave removing means, and the CA correlation means are configured in this order is shown, but these may be interchanged, and this is not restrictive.

  Furthermore, the synthesis operation means, the RTC means, and the control means may be realized by a dedicated logic circuit, but may be realized by using a programmable device such as a general-purpose CPU.

  Further, the signal strength accumulating means shown in FIG. 12, the TLM accumulating means shown in FIG. 19, and the subframe ID accumulating means shown in FIG. 20 are realized by configuring a shift register. There is no limitation on the above, and any device may be used as long as it has a similar function such as using a storage means such as a random access memory.

  Further, the cumulative number may be determined by determining the reliability for each, but may be determined by the cumulative number in other accumulating means.

  In the above, an example in the case of the heterodyne system has been described, but demodulation may be performed by a direct conversion system or the like.

<Summary>
As described above, the GPS watch according to the present invention can perform search, tracking, and data reception with high sensitivity even when the radio wave from the position information satellite is weak. For example, it is stable even in a place away from an indoor window. By receiving the time information included in the navigation message data, it is possible to always display the accurate time.

101 Synthetic search process 102 Tracking process 103 Data synthesis receiving process 104 Standard time calculation process 105 Reference clock generation process 106 RTC process 107 Time display process 902 Antenna 903 RF means 904 Synthetic demodulation means 905 Composite calculation means 906 RTC means 907 Time display means 908 Control means

Claims (11)

  In a time display method for correcting time based on time information of radio waves coming from satellites, a synthetic search step for searching and capturing satellites by synthesizing multiple correlation strengths of pseudo random codes included in radio waves from satellites; , A tracking step for controlling so as to efficiently receive radio waves from the satellite captured in the synthetic search step, and data synthesis reception for synthesizing navigation message data relating to the time contained in the radio wave from the satellite repeated while updating A standard time calculation step for calculating a standard time from navigation message data relating to the time received in the data synthesis reception step, a reference clock generation step for generating a reference clock from which internal time is counted, and the reference clock Count to generate internal time and internal by standard time Time display method comprising the RTC step of modifying the time, and a time display step that displays the time by the internal time.   In the synthetic search step, after receiving radio waves from the satellite and down-converting the frequency, the correlation strength obtained by removing the carrier wave and the pseudo-random code is accumulated for one or more cycles of the pseudo-random code. The time display method according to claim 1, wherein the time display is performed by searching.   The synthetic search step receives a radio wave from a satellite and down-converts the frequency, and then removes a carrier wave from the low-frequency signal, and also creates a pseudo-random code replica corresponding to one or more satellites. The pseudo-random code is removed while switching within the time range of one chip, and the correlation strength is extracted, and the obtained correlation strength is accumulated for one or more cycles of the pseudo-random code corresponding to the one or more satellites. The time display apparatus according to claim 1, wherein the time display device acquires and searches from one or more position information satellites substantially simultaneously.   The composite search step receives the radio wave from the satellite, down-converts the frequency, stores the correlation strength obtained by removing the carrier wave and the pseudo random code for one cycle or more, and then stores the correlation strength from the stored value. The time display method according to claim 1, wherein the satellite is searched and acquired by calculating a difference between the signal strength and the phase and frequency of the pseudo-random code. The data synthesis reception step includes a bit boundary detection step of detecting a bit boundary from correlation data obtained by removing a carrier wave and a pseudo random code after receiving radio waves from a satellite and down-converting the frequency; A bit data aggregation step of generating bit data by aggregating the correlation data within the bit boundary detected in the bit boundary detection step, and a bit data synthesis step of synthesizing navigation message data from the bit data,
The bit boundary detection step includes a change extraction step for extracting a change in the correlation data, a change accumulation step for accumulating changes in the correlation data obtained in the change extraction step, and the correlation from the change accumulated in the change accumulation step. The time display method according to claim 1, further comprising a change point position calculation step for obtaining a boundary of bit data constituted by data.   In a time display device for correcting time based on time information of radio waves coming from a satellite, an antenna for receiving radio waves from a position information satellite as a high-frequency signal, and RF means for down-converting the high-frequency signal from the antenna into a low-frequency signal Synthesizing and demodulating means for searching and capturing a position information satellite and extracting correlation data by synthesizing correlation strengths for a plurality of C / A code cycles included in a low-frequency signal from the RF means; And means for repeatedly receiving and synthesizing navigation message data relating to the time included in the correlation data from the means and calculating the standard time, and generating an internal time by counting an internal reference clock and generating the internal time according to the standard time. RTC means to correct the time and the time is displayed by the internal time from the RTC means A time display means that, time display device and a control unit for managing the entire and status and sequence.   The synthesizing / demodulating means removes a carrier wave and a pseudo-random code from the low-frequency signal to extract correlation data and correlation strength, and accumulates the obtained correlation strength for one cycle or more of the pseudo-random code to obtain position information. The time display device according to claim 6, wherein a satellite is searched and captured.   The synthesizing / demodulating means removes a carrier wave from the low-frequency signal and switches a pseudo-random code replica corresponding to one or more satellites within a time range of one chip of the pseudo-random code while changing a pseudo-random code. The correlation data and the correlation strength are extracted by the removal, and the obtained correlation strength is accumulated from one or more position information satellites by accumulating the correlation strength corresponding to the one or more satellites for one or more cycles of the pseudo-random code. The time display device according to claim 6, wherein the time display device is searched and captured simultaneously.   The composite demodulating means removes the carrier wave and the pseudo random code from the low frequency signal to extract the correlation data and the correlation strength, and stores the obtained correlation strength for one cycle or more of the pseudo random code. The time display device according to claim 6, wherein the position information satellite is searched and captured by calculating a signal intensity, a phase difference between the pseudo random code and a frequency from a value stored in the correlation intensity storage means. The synthesis calculation means includes bit data generation means for collecting the correlation data to generate bit data, data synthesis means for extracting navigation message data relating to time from the bit data, and navigation message data from the data synthesis means. Has standard time calculation means to calculate standard time,
The bit data generating means includes a change extracting means for extracting a change in the correlation data, a change accumulating means for accumulating changes in the correlation data obtained by the change extracting means, and the correlation from the changes accumulated by the change accumulating means. A change point position calculating means for obtaining a boundary of bit data constituted by data, and a bit data aggregating means for collecting the correlation data based on the change point from the change point position calculating means and outputting bit data. Item 7. A time display device according to Item 6. The synthesis calculation means includes bit data generation means for collecting the correlation data to generate bit data, data synthesis means for extracting navigation message data relating to time from the bit data, and navigation message data from the data synthesis means. Has standard time calculation means to calculate standard time,
The time display device according to claim 6, wherein the data synthesizing means obtains the navigation message data from the bit data by accumulation or / and correlation with a replica.

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