Electronic timepiece and time difference correction method for an electronic timepiece

An electronic timepiece has a function for receiving satellite signals transmitted from positioning information satellites for capturable positioning information based on the received satellite signal and a positioning calculation unit that generates positioning information. A time information adjustment unit corrects the internal time information based on the time difference in the assumed positioning region when the time difference evaluation unit determines that the assumed positioning does not contain a time difference boundary. The positioning calculation unit reselects the specific number of positioning information satellites and continues the positioning calculation when the time difference evaluation unit determines that the assumed positioning region contains a time difference boundary. The reception unit terminates satellite signal reception when the time difference evaluation unit determines that the assumed positioning region does not contain a time difference boundary.

CROSS-REFERENCE TO RELATED APPLICATIONS

Japanese Patent Application No (s) 2008-227058 and 2008-249943 are hereby incorporated by reference in their entirety.

BACKGROUND

1. Field of Invention

The present invention relates to an electronic timepiece and to a time difference correction method for an electronic timepiece that corrects the time difference based on satellite signals received from positioning information satellites such as GPS satellites.

2. Description of Related Art

The Global Positioning System (GPS) in which satellites (GPS satellites) orbiting Earth on known orbits transmit signals carrying superposed time information and orbit information, and terrestrial receivers (GPS receivers) receive these signals to determine the location of the receiver, is widely known. Electronic timepieces that acquire accurate time information (“GPS time”) from GPS satellites and adjust the current internally kept time to the correct time have also been developed as one type of GPS receiver.

GPS time is the Coordinated Universal Time (UTC) delayed by the UTC offset (currently +14 seconds). Therefore, in order for an electronic timepiece that uses the GPS system to display the current local time, the acquired GPS time must be corrected to the current local time by adding this time difference to the UTC, and information about the time difference to UTC must be acquired.

This electronic timepiece determines its current position in order to acquire the time difference information. However, if the signal reception level is too low, the orbit information cannot be correctly demodulated and the position can therefore not be calculated. As a result, the position is generally calculated only when the signal reception level exceeds a specific threshold value. However, if the location of the GPS satellite used for the positioning calculation is poor, the positioning calculation error becomes too great and the correct position cannot be determined. As a result, the position is generally only calculated if an index denoting degradation of the precision of the positioning calculation based on the current GPS satellite location is less than a specific threshold value. Therefore, if these threshold values are fixed and the reception level is below the threshold value or the index to the positioning calculation precision is higher than the threshold value, the position will not be calculated even if the position can be calculated.

A method of increasing the precision of the positioning calculation as much as possible while also increasing the likelihood that the position will be calculated by setting these threshold values high for the initial positioning calculation and then gradually relaxing these threshold values if the positioning calculation is unsuccessful has therefore been proposed.

However, the method taught in Japanese Unexamined Patent Appl. Pub. JP-A-2006-138682 takes time for the positioning calculation to converge in order to maintain the highest possible precision in the positioning calculation. Because power consumption increases as the time required by the positioning calculation increases, applying this method in electronic timepieces such as battery-powered wristwatches is difficult.

SUMMARY OF INVENTION

An electronic timepiece according to a first aspect of the invention is an electronic timepiece having a function for receiving satellite signals transmitted from positioning information satellites, the electronic timepiece including a reception unit that receives the satellite signal and acquires satellite information from the received satellite signal, a satellite search unit that executes a process of searching for a capturable positioning information satellite based on the received satellite signal and capturing the found satellite signal, a positioning calculation unit that selects a specific number of positioning information satellites from among the positioning information satellites captured by the satellite search unit, executes a positioning calculation based on the satellite information contained in the satellite signals sent from the selected positioning information satellites, and generates positioning information, a time information adjustment unit that corrects internal time information based on the satellite information, a time information display unit that displays the internal time information, a storage unit that stores time difference information defining the time difference in each of a plurality of areas into which geographical information is divided, and a time difference evaluation unit that calculates an assumed positioning region based on the positioning information, and determines based on the time difference information if the assumed positioning region contains a time difference boundary. The time information adjustment unit correcting the internal time information based on the time difference in the assumed positioning region when the time difference evaluation unit determines that the assumed positioning region does not contain a time difference boundary, The positioning calculation unit reselecting the specific number of positioning information satellites and continuing the positioning calculation when the time difference evaluation unit determines that the assumed positioning region contains a time difference boundary. The reception unit terminating satellite signal reception when the time difference evaluation unit determines that the assumed positioning region does not contain a time difference boundary.

A time difference adjustment method for an electronic timepiece according to a second aspect of the invention is a time difference adjustment method for an electronic timepiece including a reception unit that receives satellite signals transmitted from positioning information satellites and acquires satellite information from the received satellite signal, a time information display unit that displays internal time information, and a storage unit that stores time difference information defining the time difference in each of a plurality of areas into which geographical information is divided. The time difference adjustment method has a step of acquiring the satellite information by means of the reception unit, a satellite search step of searching for a capturable positioning information satellite based on the received satellite signal and capturing the found satellite signal; a positioning calculation step of selecting a specific number of positioning information satellites from among the positioning information satellites captured by the satellite search step, executing a positioning calculation based on the satellite information contained in the satellite signals sent from the selected positioning information satellites, and generating positioning information; a step of calculating an assumed positioning region based on the positioning information; a time difference evaluation step of determining based on the time difference information if the assumed positioning region contains a time difference boundary; and a step of correcting the internal time information based on the time difference in the assumed positioning region and terminating satellite signal reception by the reception unit when the assumed positioning region is determined to not include a time difference boundary. The positioning calculation step selects the specific number of positioning information satellites again and continues the positioning calculation when the assumed positioning region is determined to contain a time difference boundary.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An electronic timepiece and a time difference adjustment process for an electronic timepiece according to the present invention optimize power consumption and adjust the time difference based on a satellite signal from a positioning information satellite using the least required power consumption.

(1) An electronic timepiece according to a first aspect of the invention is an electronic timepiece having a function for receiving satellite signals transmitted from positioning information satellites, the electronic timepiece including a reception unit that receives the satellite signal and acquires satellite information from the received satellite signal, a satellite search unit that executes a process of searching for a capturable positioning information satellite based on the received satellite signal and capturing the found satellite signal, a positioning calculation unit that selects a specific number of positioning information satellites from among the positioning information satellites captured by the satellite search unit, executes a positioning calculation based on the satellite information contained in the satellite signals sent from the selected positioning information satellites, and generates positioning information, a time information adjustment unit that corrects internal time information based on the satellite information, a time information display unit that displays the internal time information, a storage unit that stores time difference information defining the time difference in each of a plurality of areas into which geographical information is divided, and a time difference evaluation unit that calculates an assumed positioning region based on the positioning information, and determines based on the time difference information if the assumed positioning region contains a time difference boundary. The time information adjustment unit correcting the internal time information based on the time difference in the assumed positioning region when the time difference evaluation unit determines that the assumed positioning region does not contain a time difference boundary, The positioning calculation unit reselecting the specific number of positioning information satellites and continuing the positioning calculation when the time difference evaluation unit determines that the assumed positioning region contains a time difference boundary. The reception unit terminating satellite signal reception when the time difference evaluation unit determines that the assumed positioning region does not contain a time difference boundary.

The satellite information includes time information and orbit information for the positioning information satellite that is transmitted by the positioning information satellite.

The internal time information is information about the time kept internally by the electronic timepiece.

The assumed positioning region is a region in which the electronic timepiece is possibly located. For example, the assumed positioning region may be the area inside a circle of which the positioning calculation error is the radius and the center is the location indicated by the positioning information of the electronic timepiece (such as longitude and latitude) acquired by the positioning calculation.

If the calculated assumed positioning region does not contain a time difference boundary in the electronic timepiece according to the invention, the electronic timepiece is assured of being somewhere in the area with the same time difference. As a result, the standard for determining whether to end the time adjustment process (time difference adjustment process) can be whether or not the assumed positioning region contains a time difference boundary and not the precision of the positioning calculation.

For example, even if the assumed positioning region that is calculated is quite large (for example, the inside area of a circle with a radius of several hundred kilometers) because the precision of the positioning calculation is low, the time difference can be acquired and the time can be corrected if all of the assumed positioning region is within an extremely large single time zone area, such as China or over the ocean.

More specifically, even if the exact position cannot be determined because the precision of the positioning calculation is low, an electronic timepiece according to the invention can end the reception process and adjust the time depending upon the position of the electronic timepiece. The electronic timepiece according to the invention can therefore optimize the power consumption required for the positioning calculation and can finish adjusting the time (adjusting the time difference) with as little power consumption as possible.

When the assumed positioning region that is calculated contains a time difference boundary, the electronic timepiece according to the invention reselects the positioning information satellites and continues the positioning calculation. Because the precision of the positioning calculation can thus be improved, a small assumed positioning region not containing a time difference boundary can be easily calculated. The electronic timepiece can therefore easily identify the time difference even if located relatively near a time difference boundary, can optimize the power consumption required for the positioning calculation, and can finish adjusting the time (adjusting the time difference) with as little power consumption as possible.

(2) In an electronic timepiece according to another aspect of the invention, the satellite search unit continues a process searching for new capturable positioning information satellites until positioning information satellites equal to a maximum number of capturable satellites are captured, and executes a process of stopping the capture of at least one positioning information satellite and searching for a new capturable positioning information satellite when the maximum capturable number of positioning information satellites is captured and the time difference evaluation unit determines the assumed positioning region contains a time difference boundary.

Capturing a positioning information satellite may be stopped when the assumed positioning region is determined to include a time difference boundary as a result of calculating the position using at least combination of positioning information satellites.

In addition, when the positioning calculation is done using all satellite combinations and the assumed positioning regions that are calculated based on all of the calculations are determined to include a time difference boundary, capturing at least one positioning information satellite may be stopped.

In other words, when the time difference evaluation unit determines that the assumed positioning region does not contain a time difference boundary, the positioning calculation unit preferably performs the positioning calculation based on all positioning information satellite combinations, and when the time difference evaluation unit determines that the assumed positioning region contains a time difference boundary based on the results of all positioning calculations, the satellite search unit preferably executes a process to stop the capture of at least one positioning information satellite and search for a new positioning information satellite that can be captured. The positioning information satellite for which capturing is stopped is preferably the positioning information satellite that most degrades the positioning precision of the positioning calculation.

When the maximum number of capturable positioning information satellites are captured and the calculated assumed positioning region contains a time difference boundary, the electronic timepiece according to this aspect of the invention runs the positioning calculation using satellite information for a positioning information satellite newly captured as a substitute for at least one positioning information satellite. Because the precision of the positioning calculation can thus be improved, a small assumed positioning region not containing a time difference boundary can be easily calculated. The electronic timepiece can therefore easily identify the time difference even if located relatively near a time difference boundary, can optimize the power consumption required for the positioning calculation, and can finish adjusting the time (adjusting the time difference) with as little power consumption as possible.

(3) In an electronic timepiece according to another aspect of the invention the reception unit ends satellite signal reception when the time difference evaluation unit does not determine that the assumed positioning region does not contain a time difference boundary before a specified time limit passes.

(4) In an electronic timepiece according to another aspect of the invention the positioning calculation unit calculates the positioning information error based on a DOP value, and the time difference evaluation unit calculates the assumed positioning region based on said error.

For example, the positioning error may be calculated by multiplying a DOP value with the error in the distance between the positioning information satellite and the electronic timepiece computed by the positioning calculation, and the assumed positioning region may be the area inside a circle of which the center is the position identified by the positioning information and the radius is the positioning calculation error.

(5) Further preferably, the electronic timepiece also has a positioning information display unit that displays the positioning information, and updates the displayed positioning information when the time difference evaluation unit determines that the assumed positioning region does not contain a time difference boundary.

(6) In an electronic timepiece according to another aspect of the invention, the time difference information includes information identifying the position of a virtual region containing a plurality of areas defined with different time differences selected from the plurality of areas into which the geographical information is divided, and the time difference evaluation unit determines based on the time difference information if the assumed positioning region contains at least a part of the virtual region, and determines whether or not the assumed positioning region contains a time difference boundary based on the position of the area contained in the virtual region when the assumed positioning region contains the virtual region.

This aspect of the invention determines if the calculated assumed positioning region contains all or part of a virtual region, and if it does, references the position of an area inside the virtual region to determine if there is a time difference boundary. Therefore, if a region containing a dense grouping of multiple small time zones is defined as the virtual region, and the calculated assumed positioning region does not contain the virtual region, it is not necessary to separately determine if the assumed positioning region contains all or a part of these multiple small time zone regions. This aspect the invention can therefore optimize the time of the evaluation process that determines if the assumed positioning region contains a time difference boundary.

Furthermore, this aspect of the invention determines whether or not the assumed positioning region contains a time difference boundary based on the positions of the multiple areas contained in the virtual region when the assumed positioning region that is calculated contains a virtual region, high evaluation precision can be assured.

(7) In the electronic timepiece according to another aspect of the invention, the areas are grouped into first-level to N-level (where N≧2) areas; the time difference information includes first-level to N-level time difference information defining the time difference in each of the first-level to N-level areas; the virtual region in the k-level (where 1≦k<N) time difference information includes areas of levels k+1 and less; and the time difference evaluation unit determines based on the k level time difference information whether or not the assumed positioning region contains at least a part of the virtual region, and when the assumed positioning region contains at least a part of the virtual region, determines based on the k+1 level time difference information whether or not the assumed positioning region contains at least a part of the virtual region.

This aspect of the invention first references the first-level time difference information to determine if the assumed positioning region contains all or part of a first-level virtual region (a virtual region for which the information used to identify its position is defined in first-level time difference information). If the assumed positioning region contains all or part of a first-level virtual region, second-level time difference information is referenced next to determine if the assumed positioning region contains a second-level virtual region (a virtual region for which the information used to identify its position is defined in second-level time difference information). Likewise, if the assumed positioning region contains all or part of a k-level virtual region, k+1 level time difference information is referenced next to determine if the assumed positioning region contains a k+1 level virtual region (a virtual region for which the information used to identify its position is defined in k+1 level time difference information). If the assumed positioning region does not contain all or part of a k-level virtual region, whether or not the assumed positioning region contains a time difference boundary is determined based on the position of an area for which a k-level time difference is defined.

In other words, because this aspect of the invention executes the evaluation process while sequentially referencing time difference information suitably organized hierarchically according to the size of the region for which a time difference is defined, how much time is consumed by the evaluation process can be optimized.

(8) In an electronic timepiece according to another aspect of the invention the areas and the virtual region are drawn with a rectangular shape.

Because the shape of the areas for which a time difference is defined and the virtual regions is rectangular, this aspect of the invention only needs to store coordinate data for the two end points of the diagonals of the rectangles in order to determine the area. As a result, this aspect of the invention can greatly reduce the amount of time difference information that must be stored compared with a configuration that stores data for each of numerous short lines used to define a time difference boundary.

Yet further, if the size of the rectangular shapes of the time difference definition areas and virtual regions contained in the time difference information for each level is fixed, this aspect of the invention needs to store the coordinates of only one point for each area or region, and can thus further reduce the amount of time difference data.

In addition, because the time difference definition areas and virtual regions are rectangular, this aspect of the invention can very easily determine if the calculated assumed positioning region contains a time difference boundary.

(9) Another aspect of the invention is a time difference adjustment method for an electronic timepiece according to a second aspect of the invention is a time difference adjustment method for an electronic timepiece including a reception unit that receives satellite signals transmitted from positioning information satellites and acquires satellite information from the received satellite signal, a time information display unit that displays internal time information, and a storage unit that stores time difference information defining the time difference in each of a plurality of areas into which geographical information is divided. The time difference adjustment method has a step of acquiring the satellite information by means of the reception unit, a satellite search step of searching for a capturable positioning information satellite based on the received satellite signal and capturing the found satellite signal; a positioning calculation step of selecting a specific number of positioning information satellites from among the positioning information satellites captured by the satellite search step, executing a positioning calculation based on the satellite information contained in the satellite signals sent from the selected positioning information satellites, and generating positioning information; a step of calculating an assumed positioning region based on the positioning information; a time difference evaluation step of determining based on the time difference information if the assumed positioning region contains a time difference boundary; and a step of correcting the internal time information based on the time difference in the assumed positioning region and terminating satellite signal reception by the reception unit when the assumed positioning region is determined to not include a time difference boundary. The positioning calculation step selects the specific number of positioning information satellites again and continues the positioning calculation when the assumed positioning region is determined to contain a time difference boundary.

Preferred embodiments of the present invention are described below with reference to the accompanying figures. Note that the embodiments described below do not unduly limit the scope of the invention described in the accompanying claims. In addition, the invention does not necessary require all aspects of the configurations described below.

1. GPS System

GPS satellites10orbit the Earth on specific known orbits and transmit navigation messages superposed to a 1.57542 GHz carrier (L1 signal) to Earth. Note that a GPS satellite10is an example of a positioning information satellite in a preferred embodiment of the invention, and the 1.57542 GHz carrier signal with a superposed navigation message (referred to below as the “satellite signal”) is an example of a satellite signal in a preferred embodiment of the invention.

There are currently approximately 30 GPS satellites10in orbit, and in order to identify the GPS satellite10from which a satellite signal was transmitted, each GPS satellite10superposes a unique 1023 chip (1 ms period) pattern called a Coarse/Acquisition Code (CA code) to the satellite signal. The C/A code is an apparently random pattern in which each chip is either +1 or −1. The C/A code superposed to the satellite signal can therefore be detected by correlating the satellite signal with the pattern of each C/A code.

Each GPS satellite10has an atomic clock on board, and the satellite signal carries the extremely accurate time information (called the “GPS time information” below) kept by the atomic clock. The miniscule time difference of the atomic clock on board each GPS satellite10is measured by a terrestrial control segment, and a time correction parameter for correcting the time difference is also contained in the satellite signal. A GPS receiver1can therefore receive the satellite signal transmitted from one GPS satellite10and adjust the internally kept time to the correct time by using the GPS time information and time correction parameter contained in the received signal.

Orbit information describing the location of the GPS satellite10on its orbit is also contained in the satellite signal. The GPS receiver1can perform a positioning calculation using the GPS time information and the orbit information. This positioning calculation assumes that there is a certain amount of error in the internal time kept by the GPS receiver1. More specifically, in addition to the x, y, and z parameters for identifying the three-dimensional position of the GPS receiver1, the time difference is also an unknown value. As a result, a GPS receiver1generally receives satellite signals transmitted from four or more GPS satellites, and performs the positioning calculation using the GPS time information and orbit information contained in the received signals.

The precision of the positioning calculation differs according to the geometric positions of the GPS satellite10and the GPS receiver1. A DOP (dilution of precision) value representing the degree of precision loss in the positioning calculation resulting from the location of the GPS satellite10is therefore generally used. The precision of the positioning calculation is evaluated by multiplying the rangefinding precision (the precision measuring the distance between the GPS satellite10and the GPS receiver1) by a DOP value, and a lower DOP value represents higher precision in the positional measurement. Note that DOP can be expressed by a number of separate measurements, including GDOP (Geometric DOP) as a general indicator of the precision of the determined position and time; PDOP (Positional DOP) as an index to the precision of the determined position, HDOP (Horizontal DOP) as an index to the precision of the determined horizontal position, VDOP (Vertical DOP) as an index to the precision of the determined vertical position, and TDOP (Time DOP) as an index to the precision of the determined time.

1-2 Navigation Message

FIG. 2AtoFIG. 2Cdescribe the structure of the navigation message.

As shown inFIG. 2A, the navigation message is composed of data organized in a single main frame containing a total 1500 bits. The main frame is divided into five subframes of 300 bits each. The data in one subframe is transmitted in 6 seconds from each GPS satellite10. It therefore requires 30 seconds to transmit the data in one main frame from each GPS satellite10.

Subframe1contains satellite correction data such as the week number. The week number identifies the week to which the current GPS time information belongs. The GPS time starts at 00:00:00 on Jan. 6, 1980, and the number of the week that started that day is week number 0. The week number is updated every week.

Subframes2and3contain ephemeris data, that is, detailed orbit information for each GPS satellite10. Subframes4and5contain almanac data (general orbit information for all GPS satellites10in the constellation).

Each of subframes1to5starts with a telemetry (TLM) word containing 30 bits of telemetry (TLM) data, followed by a HOW word containing 30 bits of HOW (handover word) data.

Therefore, while the TLM words and HOW words are transmitted at 6-second intervals from the GPS satellite10, the week number data and other satellite correction data, ephemeris data, and almanac data are transmitted at 30-second intervals.

As shown inFIG. 2B, the TLM word contains preamble data, a TLM message, reserved bits, and parity data.

As shown inFIG. 2C, the HOW word contains time information called the TOW or Time of Week (also called the Z count). The Z count denotes in seconds the time passed since 00:00 of Sunday each week, and is reset to 0 at 00:00 of Sunday each week. More specifically, the Z count denotes the time passed from the beginning of each week in seconds, and the elapsed time is a value expressed in units of 1.5 seconds. Note, further, that the Z count denotes the time that the first bit of the next subframe data was transmitted. For example, the Z count transmitted in subframe1denotes the time that the first bit in subframe2is transmitted.

The HOW word also contains 3 bits of data denoting the subframe ID (also called the ID code). More specifically, the HOW words of subframes1to5shown inFIG. 2Acontain the ID codes 001, 010, 011, 100, and 101, respectively.

The GPS receiver1can get the GPS time information by acquiring the week number value contained in subframe1and the HOW words (Z count data) contained in subframes1to5. However, if the GPS receiver1has previously acquired the week number and internally counts the time passed from when the week number value was acquired, the current week number value of the GPS satellite can be obtained without acquiring the week number from the satellite signal. The GPS receiver1can therefore estimate the current GPS time information if the Z count is acquired. The GPS receiver1therefore normally acquires only the Z count as the time information.

Note that the TLM word, HOW word (Z count), satellite correction data, ephemeris, and almanac parameters are examples of satellite information in the invention.

The GPS receiver1may be rendered as a wristwatch with a GPS device (referred to herein as a GPS wristwatch). A GPS wristwatch is an example of an electronic timepiece according to one embodiment of the present invention, and a GPS wristwatch according to this embodiment of the invention is described next.

Configuration of a GPS Wristwatch

FIG. 3AandFIG. 3Bare figures describing the configuration of a GPS wristwatch according to a preferred embodiment of the invention.FIG. 3Ais a schematic plan view of a GPS wristwatch, andFIG. 3Bis a schematic section view of the GPS wristwatch inFIG. 3A.

As shown inFIG. 3A, the GPS wristwatch1has a dial11and hands12. A display13is disposed in a window formed in a part of the dial11. The display13may be an LCD (liquid crystal display) panel, and is used to display information such as the current latitude and longitude or the name of a city in the current time zone or location, or other message information. The hands12include a second hand, minute hand, and hour hand, and are driven through a wheel train by means of a stepping motor.

The dial11and hands12function as a time information display unit in the invention in a preferred embodiment of the invention. The display13functions as a positioning information display unit in a preferred embodiment of the invention.

By manually operating the crown14or buttons15and16, the GPS wristwatch1can be set to a mode (referred to below as the “time mode”) for receiving a satellite signal from at least one GPS satellite10and adjusting the internal time information, or a mode (referred to below as the “positioning mode”) for receiving satellite signals from a plurality of GPS satellites10, calculating the position, and correcting the time difference of the internal time information. The GPS wristwatch1can also regularly (automatically) execute the time mode or positioning mode.

As shown inFIG. 3B, the GPS wristwatch1has an outside case17that is made of stainless steel, titanium, or other metal.

The outside case17is basically cylindrically shaped, and a crystal19is attached to the opening on the face side of the outside case17by an intervening bezel18. A back cover26is attached to the opening on the back side of the outside case17. The back cover26is annular and made of metal, and a back glass unit23is attached to the opening in the center.

Inside the outside case17are disposed a stepping motor for driving the hands12, a GPS antenna27, and a battery24.

The stepping motor has a motor coil19, a stator and a rotor, and drives the hands12by means of an intervening wheel train.

The GPS antenna GPS antenna27is an antenna for receiving satellite signals from a plurality of GPS satellites10, and may be a patch antenna, helical antenna, or chip antenna, for example. The GPS antenna27is located on the opposite side of the dial11as the side on which the time is displayed (that is, on the back cover side), and receives RF signals through the crystal19and the dial11.

The dial11and crystal19are therefore made from a material, such as plastic, that passes RF signals in the 1.5 GHz band. To improve satellite signal reception performance, the bezel18is made from ceramic or other material.

A circuit board25is disposed on the back cover side of the GPS antenna27, and a battery24is disposed on the back cover side of the circuit board25.

Disposed to the circuit board25are a reception chip18including a reception circuit that processes satellite signals received by the GPS antenna27, and a control chip40that controls, for example, driving the stepping motor. The reception chip30and control chip40are driven by power supplied from the battery24.

The battery24is a lithium-ion battery or other type of rechargeable storage battery. A magnetic sheet21is disposed below (on the back cover side of) the battery24. A charging coil22is disposed with the magnetic sheet21between it and the battery24, and the battery24can be charged by the charging coil22by means of electromagnetic induction from an external charger.

The magnetic sheet21can also divert the magnetic field. The magnetic sheet21therefore reduces the effect of the battery24and enables the efficient transmission of energy. A back glass unit23is disposed in the center part of the back cover26to facilitate power transmission.

A lithium-ion battery or other storage battery is used as the battery24in this embodiment of the invention, but a lithium battery or other primary battery may be used instead. The charging method used when a storage battery is used is also not limited to charging by electromagnetic induction from an external charger through a charging coil22. For example, a solar cell may be disposed to the GPS wristwatch1to generate electricity for charging the battery.

GPS Wristwatch Circuit Configuration

FIG. 4describes the circuit configuration of a GPs wristwatch according to this embodiment of the invention.

The GPS wristwatch1includes a GPS device70and a time display device80.

The GPS device70includes the reception unit, satellite search unit, positioning calculation unit, time difference evaluation unit, and storage unit in a preferred embodiment of the invention, and executes the processes for receiving a satellite signal and acquiring satellite information, finding and capturing a GPS satellite10, calculating the position, calculating the assumed positioning region and determining time difference boundaries, and storing time difference information.

The time display device80includes the time information adjustment unit and time information display unit in a preferred embodiment of the invention, and executes the processes for adjusting the internal time information and displaying the internal time information.

The charging coil22charges the battery24with electricity through the charging control circuit28. The battery24supplies drive power through the regulator29to the GPS device70and time display device80.

GPS Device Configuration

The GPS device70has a GPS antenna27and a SAW (surface acoustic wave) filter31. As described inFIG. 3B, the GPS antenna27is an antenna for receiving satellite signals from a plurality of GPS satellites10. However, because the GPS antenna27also receives some extraneous signals other than satellite signals, the SAW filter31executes a process that extracts a satellite signal from the signal received by the GPS antenna27. More particularly, the SAW filter31is rendered as a bandpass filter that passes signals in the 1.5 GHz band.

The GPS device70includes a reception chip (reception circuit)30. The reception circuit30includes an RF (radio frequency) unit50and a baseband unit60. As described below, the reception circuit30executes a process that acquires satellite information including orbit information and GPS time information contained in the navigation message from the 1.5 GHz satellite signal extracted by the SAW filter31.

The RF unit50includes a low noise amplifier (LNA)51, a mixer52, a VCO (voltage controlled oscillator)53, a PLL (phase locked loop) circuit54, an IF (intermediate frequency) amplifier55, and IF filter56, and an A/D converter57.

The satellite signal extracted by the SAW filter31is amplified by the LNA51. The satellite signal amplified by the LNA51is mixed by the mixer52with a clock signal output from the VCO53, and is down-converted to a signal in the intermediate frequency band. The PLL circuit54phase compares a reference clock signal and a clock signal obtained by frequency dividing the output clock signal of the VCO53, and synchronizes the output clock signal of the VCO53to the reference clock signal. As a result, the VCO53can output a stable clock signal with the frequency precision of the reference clock signal. Note that a frequency of several megahertz can be selected as the intermediate frequency.

The signal mixed by the mixer52is then amplified by the IF amplifier55. This mixing step of the mixer52generates a signal in the IF band and a high frequency signal of several gigahertz. As a result, the IF amplifier55amplifies the IF band signal and the high frequency signal of several gigahertz. The IF filter56passes the IF band signal and removes this high frequency signal of several gigahertz (or more particularly attenuates the signal to a specific level or less). The IF band signal passed by the IF filter56is then converted to a digital signal by the A/D converter57.

The TXCO65generates a reference clock signal of a substantially constant frequency irrespective of temperature.

Time difference information is stored in the flash memory66. This time difference information is information that divides geographical information into a plurality of regions and defines the time difference for each region. The flash memory66thus functions as a storage unit in a preferred embodiment of the invention.

When the time mode or positioning mode is set, the baseband unit60demodulates the baseband signal from the digital signal (IF band signal) output by the A/D converter57of the RF unit50.

In addition, when the time mode or positioning mode is set, the baseband unit60executes a process to generate a local code of the same pattern as each C/A code, and correlate the local code with the C/A code contained in the baseband signal, in the satellite search process described below. The baseband unit60also adjusts the output timing of the local code to achieve the peak correlation value to each local code, and when the correlation value equals or exceeds a threshold value, determines successful synchronization with the GPS satellite10matching that local code (that is, determines that the GPS satellite10was captured). The baseband unit60(CPU62) thus functions as the satellite search unit in a preferred embodiment of the invention. Note that the GPS system uses a CDMA (code division multiple access) system enabling all GPS satellites10to transmit satellite signals at the same frequency using different C/A codes. Therefore, a GPS satellite10that can be captured can be found by evaluating the C/A code contained in the received satellite signal.

In order to acquire the satellite information from the captured GPS satellite10in the time mode and positioning mode, the baseband unit60executes a process to mix the local code having the same pattern as the C/A code of the GPS satellite10with the baseband signal. A navigation message containing the satellite information of the captured GPS satellite10is demodulated in the mixed signal. In the time mode or positioning mode, the baseband unit60then executes a process of detecting the TLM word in each subframe of the navigation message (the preamble data), and acquiring (and storing in SRAM63, for example) the satellite information including the orbit information and GPS time information contained in each subframe.

When the positioning mode is set, the baseband unit60calculates the position based on the GPS time information and orbit information, and acquires positioning information (more specifically, the longitude and latitude of the place where the GPS wristwatch1is located during reception) and positioning error (more specifically, the maximum distance between the place where the GPS wristwatch1is actually located and the location identified by the positioning information). The baseband unit60thus functions as the positioning calculation unit in a preferred embodiment of the invention.

In addition, when the positioning mode is set, the baseband unit60executes a process of calculating the region where the GPS wristwatch1could be positioned (the assumed positioning region) based on the positioning information and positioning error obtained in the positioning calculation. The baseband unit60then references the time difference information stored in flash memory66, and determines if the assumed positioning region includes a time difference boundary. If the baseband unit60determines that the assumed positioning region does not contain a time difference boundary, it acquires the time difference data for the assumed positioning region from the time difference information stored in flash memory66. More specifically, the baseband unit60functions as a time difference evaluation unit in a preferred embodiment of the invention.

Note that operation of the baseband unit60is synchronized to the reference clock signal output by the TXCO65. The RTC64generates the timing for processing the satellite signal. The RTC64counts up at the reference clock signal output from the TXCO65.

Note that the GPS device70functions as the reception unit in a preferred embodiment of the invention.

Time Display Device Configuration

The time display device80includes a control chip40(control unit), a drive circuit44, an LCD drive circuit45, and a crystal oscillator43.

The control unit40includes a storage unit41and oscillation circuit42and controls various operations.

The control unit40controls the GPS device70. More specifically, the control unit40sends a control signal to the reception circuit30and controls the reception operation of the GPS device70.

The control unit40also controls driving the hands12through the drive circuit44. The control unit40also controls driving the display13through the LCD drive circuit45. For example, in the positioning mode the control unit40controls the display13to display the current position.

The internal time information is stored in the storage unit41. The internal time information is information about the time kept internally by the GPS wristwatch1. This internal time information is updated by the reference clock signal generated by the crystal oscillator43and oscillation circuit42. The internal time information can therefore be updated and moving the hands12can continue even when power supply to the reception circuit30has stopped.

When the time mode is set, the control unit40controls operation of the GPS device70, corrects the internal time information based on the GPS time information and saves the corrected time in the storage unit41. More specifically, the internal time information is adjusted to the UTC (Coordinated Universal Time), which is acquired by adding the UTC offset (the current time+14 seconds) to the acquired GPS time information.

When the positioning mode is set, the control unit40controls operation of the GPS device70, corrects the time difference of the internal time information based on the GPS time information and the time difference data, and stores the corrected time in the storage unit41. The control unit40thus functions as a time information adjustment unit in a preferred embodiment of the invention.

The time difference adjustment process (positioning mode) in this first embodiment of the invention are described next.

Note that the control unit40and baseband unit60can be rendered as dedicated circuits for controlling these processes, or a CPU incorporated in the GPS wristwatch1can function as a computer by executing a control program stored in the storage unit41and SRAM63, for example, and control these processes. The control program can be installed through a communication network such as the Internet or from a recording medium such as CD-ROM or a memory card. Yet more specifically, as shown inFIG. 5, the time difference adjustment process can be executed by the control unit40functioning as a reception control component40-1, time information adjustment component40-2, and drive control component40-3, and the baseband unit60functioning as a satellite search component60-1, satellite information acquisition component60-2, positioning calculation component60-3, and time difference evaluation component60-4.

Time Difference Adjustment Process

FIG. 6is a flow chart showing an example of the time difference adjustment process of a GPS wristwatch according to the first embodiment of the invention.

When the positioning mode is set, the GPS wristwatch1executes the time difference adjustment process shown inFIG. 6.

When the time difference adjustment process starts, the GPS wristwatch1first controls the GPS device70by means of the control unit40(reception control component40-1) to execute the reception process. More specifically, the control unit40(reception control component40-1) activates the GPS device70, and the GPS device70starts receiving a satellite signal transmitted from a GPS satellite10(step S10).

The baseband unit60(satellite search component60-1) then starts the satellite search process (satellite search step) (step S12).

More specifically, if there are, for example, thirty GPS satellites10, the baseband unit60(satellite search component60-1) generates a local code with the same pattern as the C/A code of the satellite number SV while changing the satellite number SV sequentially from 1 to 30. The baseband unit60(satellite search component60-1) then calculates the correlation between the local code and the C/A code contained the baseband signal. If the C/A code contained in the baseband signal and the local code are the same, the correlation value will peak at a specific time, but if they are different codes, the correlation value will not have a peak and will always be substantially 0.

The baseband unit60(satellite search component60-1) adjusts the output timing of the local code so that the correlation value of the local code and the C/A code in the baseband signal goes to the peak, and determines that the GPS satellite10of the satellite number SV was captured if the correlation value is greater than or equal to the set threshold value. The baseband unit60(satellite search component60-1) then saves the information (such as the satellite number) of the captured GPS satellite10in SRAM63, for example.

The baseband unit60(satellite search component60-1) continues the satellite search process until the maximum number of capturable satellites (such as 12) is captured. Note that this maximum number of capturable satellites is the maximum number of GPS satellites10that can be captured at one time.

If the time-out period passes before the baseband unit60(satellite search component60-1) can capture at least one GPS satellite10(step S14returns Yes), the reception operation of the GPS device70is unconditionally aborted (step S42).

If the GPS wristwatch1is located in an environment where reception is not possible, such as certain indoor locations, there is no GPS satellite10that can be captured even after searching for all GPS satellites10in the constellation. By unconditionally terminating the GPS satellite10search when a GPS satellite10that can be captured cannot be detected even after the time-out period passes, the GPS wristwatch1can reduce wasteful power consumption. Note that the time-out period is the time limit from when reception starts until reception ends, and is set before reception starts.

If a GPS satellite10is captured before the time-out period passes (step S16returns Yes), the baseband unit60(satellite information acquisition component60-2) starts acquiring the satellite information (particularly the GPS time information and orbit information) from the captured GPS satellites10(step S18). More specifically, the baseband unit60(satellite information acquisition component60-2) executes a process of demodulating the navigation messages from each captured GPS satellite and acquiring the Z count data and ephemeris data. The baseband unit60(satellite information acquisition component60-2) then stores the acquired GPS time information and orbit information in SRAM63, for example.

Note that parallel to the satellite information acquisition process the baseband unit60(satellite search component60-1) continues the satellite search process described above until the maximum capturable number (such as 12) of GPS satellites10is captured. The baseband unit60(satellite information acquisition component60-2) also sequentially acquires the satellite information from each of the captured GPS satellites10.

If the time-out time passes before the baseband unit60(satellite information acquisition component60-2) acquires satellite information from N (where N is 3 or 4, for example) or more GPS satellites10(step S20returns Yes), the reception operation of the GPS device70ends unconditionally (step S42). The time-out time may pass without being able to correctly demodulate the satellite information for N (where N is 3 or 4, for example) or more GPS satellites10when, for example, the baseband unit60(satellite search component60-1) cannot capture N (where N is 3 or 4, for example) or the reception level of the satellite signal from a GPS satellite10is low.

However, if the satellite information for N (where N is 3 or 4, for example) or more GPS satellites10is successfully acquired before the time-out time passes (step S22returns Yes), the baseband unit60(positioning calculation component60-3) selects the group of N (where N is 3 or 4, for example) GPS satellites10from among the captured GPS satellites10(step S24).

In order to determine the three-dimensional position (x, y, z) of the GPS wristwatch1, three unknown values x, y, and z are needed. This means that in order to calculate the three-dimensional location (x, y, z) of the GPS wristwatch1, GPS time information and orbit information is required for three or more GPS satellites10. In addition, considering that the time difference between the GPS time information and the internal time information of the GPS wristwatch1is another unknown that is needed for even higher positioning precision, GPS time information and orbit information is needed for four or more GPS satellites10.

The flash memory baseband unit60(positioning calculation component60-3) reads the satellite information (GPS time information and orbit information) for the selected N (where N is 3 or 4, for example) GPS satellite10from SRAM63, for example, and generates the positioning information (the longitude and latitude of the location where the GPS wristwatch1is positioned) (step S26).

As described above, the GPS time information represents the time that the GPS satellite10transmitted the first bit of a subframe of the navigation message. Based on the difference between the GPS time information and the internal time information when the first bit of the subframe was received, and the time correction data, the baseband unit60(positioning calculation component60-3) can calculate the pseudorange between the GPS wristwatch1and each of the N (where N is 3 or 4, for example) GPS satellites10. The baseband unit60(positioning calculation component60-3) can also calculate the position of each of the N (where N is 3 or 4, for example) GPS satellites10based on the orbit information. Finally, based on the pseudorange to the GPS wristwatch1from each of the N (where N is 3 or 4, for example) GPS satellites10and the locations of the N (where N is 3 or 4, for example) GPS satellites10, the baseband unit60(positioning calculation component60-3) can generate the positioning information for the GPS wristwatch1.

The baseband unit60(positioning calculation component60-3) then calculates the positioning error (the maximum distance between the location where the GPS wristwatch1is positioned and the location identified by the positioning information). For example, the baseband unit60(positioning calculation component60-3) multiplies the rangefinding error (the measurement error of the distance between the GPS satellite10and the GPS wristwatch1) by the DOP value and uses the product as the positioning error. The PDOP value or HDOP value, for example, may be used as the DOP value.

Note that the satellite search process of the satellite search component60-1and the satellite information acquisition process of the satellite information acquisition component60-2continue parallel to the positioning calculation of the positioning calculation component60-3. More specifically, while the positioning calculation component60-3is calculating the position, the satellite information acquisition component60-2continues searching for GPS satellites10until the number of currently captured GPS satellites10reaches the maximum number of capturable satellites, and the satellite information acquisition component60-2sequentially acquires the satellite information of each newly acquired GPS satellite10. The positioning calculation component60-3can therefore continue calculating the position using satellite information from a newly captured GPS satellite10while sequentially selecting N (where N is 3 or 4, for example) GPS satellites10including a newly selected GPS satellite10.

The baseband unit60(time difference evaluation component60-4) then calculates the assumed positioning region (a region where the GPS wristwatch1is possibly located) based on the positioning information and positioning error (step S28). More specifically, the baseband unit60(time difference evaluation component60-4) calculates the region inside a circle of which the position identified from the positioning information is the center and the positioning error is the radius as the assumed positioning region.

The baseband unit60(time difference evaluation component60-4) then references the time difference information stored in flash memory66, and determines if the assumed positioning region contains a time difference boundary (step S30).

If the assumed positioning region contains a time difference boundary (step S32returns Yes), the baseband unit60(positioning calculation component60-3) determines if the position was calculated using all combinations of N (where N is 3 or 4, for example) GPS satellites10that can be selected from among the captured GPS satellites10(step S34).

If the position has not been calculated using any of the possible combinations of N (where N is 3 or 4, for example) GPS satellites10(step S34returns No), the GPS wristwatch1selects a combination of N (such as 3 or 4) GPS satellites10that has not been used for the positioning calculation (step S24), and repeats the positioning calculation sequence (steps S26to S32). By thus selecting another combination of N (such as 3 or 4) GPS satellites10and calculating the position, it may be possible to reduce the assumed positioning region to an area not containing a time difference boundary.

If the positioning calculation has been computed using all combinations of the N (such as 3 or 4) GPS satellites10(step S34returns Yes), the GPS wristwatch1repeats the process from the satellite search step (the sequence from step S12to S32). Alternatively, the GPS wristwatch1may repeat the process from the satellite information acquisition step (the sequence from step S18to S32).

However, if the assumed positioning region does not contain a time difference boundary (step S32returns No), the baseband unit60(time difference evaluation component60-4) references the flash memory66to acquire time difference data for the assumed positioning region from the time difference information, and the control unit40(time information adjustment component40-2) uses this time difference data to correct the internal time information stored in the storage unit41(step S36).

The reception operation of the GPS device70then ends (step S38).

Finally, the control unit40(drive control component40-3) controls the drive circuit44or LCD drive circuit45based on the corrected internal time information to adjust the displayed time (step S40).

Note that if the reception operation of the GPS device70is ended unconditionally (step S42), the control unit40(drive control component40-3) controls the drive circuit44or LCD drive circuit45to display an indication that reception failed (step S44).

FIG. 7describes a situation in which the first calculated assumed positioning region does not contain a time difference boundary in the time difference adjustment process shown inFIG. 6.

The geographical information100is map information including time zones, and includes a plurality of regions A, B, and C, for example, divided by borders denoted by solid lines in the figures. More specifically, the time difference varies in adjacent regions, and the borders between the regions are the time difference boundaries. For example, regions A, B, C are time zones with a time difference to UTC of +7, +8, and +9 hours, respectively. Data describing the borders between the regions (regions A, B, C in this example) and the time difference are stored as the time difference information corresponding to the geographical information100in flash memory66in the GPS wristwatch1according to this embodiment of the invention. The boundary data, for example, segments each border line into numerous short straight lines, and is stored as vector data (the coordinates of both ends of each line) for each line.

The GPS wristwatch1according to this embodiment of the invention starts the time difference adjustment process inFIG. 6, and in step S28the baseband unit60(time difference evaluation component60-4) calculates the assumed positioning region P1shown inFIG. 7. In step S30the baseband unit60(time difference evaluation component60-4) first reads the boundary data for the regions near the assumed positioning region P1from flash memory66, and determines if all of the assumed positioning region P1is contained within region B. The baseband unit60(time difference evaluation component60-4) then reads the time difference data for region B from flash memory66, and determines that the assumed positioning region P1does not contain a time difference boundary because only the time difference UTC+8 for region B is detected.

In step S36the baseband unit60(time difference evaluation component60-4) then acquires the time difference (UTC+8) in the assumed positioning region P1, and the control unit40(time information adjustment component40-2) adjusts the internal time information. The GPS device70then ends reception (step S38), the time displayed on the display unit is corrected, and the time difference adjustment process ends (step S40).

FIG. 8AandFIG. 8Bdescribe a situation in which the first calculated assumed positioning region contains a time difference boundary in the time difference adjustment process shown inFIG. 6.

Note that the geographical information100is identical to the geographical information100shown inFIG. 7, the same reference numerals are therefore used and further description thereof is omitted.

The GPS wristwatch1according to this embodiment of the invention starts the time difference adjustment process inFIG. 6, and in step S28the baseband unit60(time difference evaluation component60-4) calculates the assumed positioning region P1shown inFIG. 8A. In step S30the baseband unit60(time difference evaluation component60-4) first reads the boundary data for the regions near the assumed positioning region P1from flash memory66, and determines that parts of the assumed positioning region P1are contained within regions A, B, and C. The baseband unit60(time difference evaluation component60-4) then reads the time difference data for regions A, B, and C from flash memory66, and determines that the assumed positioning region P1contains a time difference boundary because the time differences in regions A, B, and C are different.

As a result, in step S24, the baseband unit60(positioning calculation component60-3) selects a new combination of N (such as 3 or 4) GPS satellites10and repeats the positioning calculation, and in step S28the baseband unit60(time difference evaluation component60-4) calculates the assumed positioning region P2shown inFIG. 8Bbased on the new positioning information.

In step S30the baseband unit60(time difference evaluation component60-4) then reads the time difference boundary data for the regions near the assumed positioning region P2from flash memory66, and because all parts of this assumed positioning region P2are contained within region B, determines that the assumed positioning region P2does not contain a time difference boundary.

In step S36the baseband unit60(time difference evaluation component60-4) then acquires the time difference (UTC+8) in the assumed positioning region P1, and the control unit40(time information adjustment component40-2) adjusts the internal time information. The GPS device70then ends reception (step S38), and the time difference adjustment process ends with the time displayed on the display unit corrected (step S40).

As shown inFIG. 6, a GPS wristwatch according to a first embodiment of the invention calculates the position based on N GPS satellites10selected from among the captured GPS satellites10, and calculates the assumed positioning region based on the positioning information and positioning error obtained from the positioning calculation. Time difference information stored in flash memory66is then referenced, and the reception process ends and the displayed time is corrected if a time difference boundary is not contained in the calculated assumed positioning region. Note that if the calculated assumed positioning region does not contain a time difference boundary, the GPS wristwatch1is assured of being positioned somewhere in a region with a single time difference. Therefore, if the objective is to adjust the time (adjust the time difference), the standard for deciding whether to end the reception process can be whether or not the assumed positioning region contains a time difference boundary rather than the precision of the positioning calculation.

For example, in the situation shown inFIG. 7the assumed positioning region P1is a fairly large region (such as the inside of a circle with a radius of several hundred kilometers), but the GPS wristwatch1is necessarily positioned somewhere in a region with a time difference of UTC+8. More specifically, the time difference can be corrected even if the positioning precision is quite low. Situations in which the positioning precision is low include, for example, when the rangefinding precision is low because the GPS satellite10time and the internal time of the GPS wristwatch1are offset, and when the position of the GPS satellite10selected for the positioning calculation is poor and the DOP value is quite high. Because the related art continues the positioning calculation until the assumed positioning region is reduced to an area small enough to not contain a time difference boundary, the time adjustment process is time consuming and is unable to adjust the time in certain situations.

However, because the assumed positioning region can be quite large as long as it contains only one time zone, the GPS wristwatch according to a first embodiment of the invention can end the positioning calculation and adjust the time depending on the position even if the precision of the positioning calculation is low and the precise position cannot be determined.

In other words, because the GPS wristwatch according to the first embodiment of the invention ends the reception process and executes the time adjustment process without further reducing the assumed positioning region when the precision of the positioning calculation is low if the assumed positioning region that is calculated does not contain a time difference boundary, power consumption can be reduced.

In the situation shown inFIG. 8AandFIG. 8B, however, the assumed positioning region P1that is calculated first is quite large (such as the inside of a circle with a radius of several hundred kilometers), and the GPS wristwatch1may be located in a time zone with a time difference of UTC+7, UTC+8, or UTC+9. The GPS wristwatch1therefore does not adjust the time based on assumed positioning region P1. As a result, the GPS wristwatch according to the first embodiment of the invention can prevent incorrectly adjusting the time by not adjusting the time when a plurality of time zone candidates are present.

Furthermore, when the assumed positioning region that is calculated contains a time difference boundary, the GPS wristwatch according to the first embodiment of the invention repeatedly computes the positioning calculation until the assumed positioning region does not contain a time difference boundary unless the time limit is reached first, and immediately stops the reception operation and executes the time adjustment process when the assumed positioning region does not contain a time difference boundary. In other words, a GPS wristwatch according to the first embodiment of the invention can optimize the time of the high power consumption reception process and finish adjusting the time (correcting the time difference) with the lowest possible power consumption while allowing for repeating the time adjustment process as many times as required until the time limit is reached when the calculated assumed positioning region contains a time difference boundary.

Furthermore, if the time difference cannot be determined even though the time limit of the time adjustment process has passed, the GPS wristwatch according to the first embodiment of the invention ends the reception process and can therefore prevent wasteful power consumption.

As shown inFIG. 7,FIG. 8A, andFIG. 8B, each of the divided areas has a complicated shape in the foregoing first embodiment because the geographical information100is divided along time zone boundaries. A large amount of data is therefore needed to define the boundary lines in the first embodiment, thus requiring a large capacity storage device and possibly increasing the size of the wristwatch. Furthermore, because deciding whether or not the assumed positioning region includes a time difference boundary is complex, the decision is time consuming and power consumption can be expected to increase.

Therefore, in order to reduce the amount of time difference information (boundary line data), the geographical information100is divided into a plurality of regions of a constant size instead of along time zone boundaries, and the coordinates of each region and corresponding time difference data are stored as the time difference information in flash memory66.

Note that the basic configuration of a GPS wristwatch according to this second embodiment of the invention is identical to the configuration of the GPS wristwatch according to the first embodiment of the invention, and further description thereof is omitted.

FIG. 9shows an example of geographical information divided into a plurality of rectangular areas.

The geographical information100is divided into 16 rectangular areas contained in virtual region101, 16 rectangular areas contained in virtual region102, 16 rectangular areas contained in virtual region103, and rectangular area104, and the time difference to UTC is defined for each area. These areas for which the time difference is defined are called “time difference definition areas.” For example, a time difference of +8 is defined for time difference definition area104. A time difference of +7 is defined for time difference definition areas102A and102E in virtual region102, a time difference of +8 is defined for time difference definition areas1021,102J,102M,102N, and102P, and a time difference of +9 is defined for time difference definition areas102B,102C,102D,102F,102G,102H,102K,102L, and102O.

One time difference is thus defined for each time difference definition area. The GPS wristwatch according to the second embodiment of the invention then determines if the assumed positioning region contains a time difference boundary using the time difference definition areas as the smallest unit area as further described below. Therefore, because the precision of the time difference boundary evaluation can be improved if each time difference definition area is configured to not include an actual time difference boundary, the size of the time difference definition areas near a time difference boundary may be reduced according to the proximity to the boundary. However, when the time difference definition areas are rectangularly shaped, an actual time difference boundary may be contained no matter how small the time difference definition area. Furthermore, because the amount of time difference information increases if the number of small time difference definition areas increases and a storage device with a large storage capacity becomes necessary, the size of each time difference definition area is determined considering the tradeoff between the amount of time difference data and the precision of time difference boundary evaluation. As a result, a time difference definition area may include an actual time zone boundary.

When the time difference definition area includes an actual time difference boundary, the area of each region belonging to a different time zone in one time difference definition area may be compared and the time difference of the region that occupies the greatest area may be defined as the time difference of the time difference definition area, or if a large city is contained in one time difference definition area, the time difference of that city may be defined as the time difference of the time difference definition area. InFIG. 9, for example, time difference definition area102E includes a region with a time difference of UTC+7 and a region with a time difference of UTC+8, but because the area occupied by the UTC+7 region is greater than the area of the UTC+8 region, a time difference of +7 is defined for this time difference definition area102E.

Note that because virtual regions101,102, and103inFIG. 9each contain a plurality of time difference definition areas with different defined time differences, the time difference to UTC is not defined for these virtual regions. For example, because virtual region102covers time difference definition areas with time differences of +7, +8, and +9, a time difference value is not defined for virtual region102.

FIG. 10andFIG. 11show examples of the time difference information tables stored in flash memory66in a GPS wristwatch according to the second embodiment of the invention.

The region-time difference correlation table200shown inFIG. 10includes position data200-1and time difference data200-2for each of the virtual regions101,102, and103and time difference definition area104shown inFIG. 9.

The virtual regions101,102, and103and time difference definition area104shown inFIG. 9are, for example, rectangular areas approximately 1000-2000 km long in east-west and north-south directions. As a result, the position of each virtual region101,102, and103and the time difference definition area104can be identified using, for example, the coordinates (longitude and latitude) of the top left corner of the area and the coordinates (longitude and latitude) of the bottom right corner of the area. The coordinates for these two points are stored in flash memory66as the position data200-1in the region-time difference correlation table200.

Because a time difference of +8 is defined for time difference definition area104, “+8” is stored in flash memory66as the time difference data200-2of the time difference definition area104.

Because a time difference is not defined for virtual regions101,102, and103, a reference link Link1, Link2, and Link3to another region-time difference correlation table is stored in flash memory66as the time difference data200-2for virtual regions101,102, and103.

The region-time difference correlation table202shown inFIG. 11contains position data202-1and time difference data202-2for the time difference definition areas102A to102P contained in virtual region102shown inFIG. 9. The region-time difference correlation table202can be referenced using the reference link Link2stored as the time difference value for virtual region102in the region-time difference correlation table200shown inFIG. 10.

Because the time difference definition areas102A to102P are obtained by dividing the virtual region102into 16 parts as shown inFIG. 9in this embodiment of the invention, the time difference definition areas102A to102P are rectangular areas approximately 250-500 km square, for example. As a result, these areas can also be identified using, for example, the coordinates (longitude and latitude) of the top left corner of the area and the coordinates (longitude and latitude) of the bottom right corner of the area. The coordinates for these two points are stored in flash memory66as the position data202-1in the region-time difference correlation table202.

Furthermore, because a time difference is defined for each of the time difference definition areas102A to102P as shown inFIG. 9, the corresponding time difference is stored in flash memory66as the time difference data202-2for the time difference definition areas102A to102P.

Note that the time difference definition area104corresponds to a first-level area in a preferred embodiment of the invention, and time difference definition areas102A to102P correspond to second-level areas in a preferred embodiment of the invention. In addition, the region-time difference correlation table200corresponds to first-level time difference information in a preferred embodiment of the invention, and the region-time difference correlation table202corresponds to second-level time difference information in a preferred embodiment of the invention.

As described above there is no virtual region that includes the time difference definition area104, but time difference definition areas102A to102P are contained in virtual region102. Therefore, while the data for the time difference definition area104is contained in the region-time difference correlation table200, the data for time difference definition areas102A to102P is contained in a different region-time difference correlation table202that is referenced from region-time difference correlation table200using the reference link Link2. The time difference definition areas can therefore be thought of as being separated into levels by virtual regions. More specifically, the time difference definition area104corresponds to a first-level area in a preferred embodiment of the invention, and the time difference definition areas102A to102P correspond to second-level areas in a preferred embodiment of the invention. Furthermore, the region-time difference correlation table200corresponds to first-level time difference information in a preferred embodiment of the invention, and the region-time difference correlation table202corresponds to second-level time difference information in a preferred embodiment of the invention.

One virtual region may also contain another virtual region. For example, if a virtual region including time difference definition areas102A,102B,102E, and102F is defined, virtual region102will include another virtual region. In this situation time difference definition areas102A,102B,102E, and102F correspond to a third-level area, and the region-time difference correlation table containing the position data and time difference data for time difference definition areas102A,102B,102E, and102F corresponds to third-level time difference information in a preferred embodiment of the invention. The time difference definition areas can thus be divided into first-level to N-level areas, and time difference information including first-level to N-level region-time difference correlation tables may be stored in flash memory66.

FIG. 12is a flow chart of the process determining if the assumed positioning region contains a time difference boundary in a GPS wristwatch according to the second embodiment of the invention. Note, further, that the process shown inFIG. 12describes the specific operations executed in step S30in the time difference adjustment process shown inFIG. 6.

The baseband unit60(time difference evaluation component60-4) first detects any virtual regions and time difference definition areas (first areas) contained in the assumed positioning region from the first-level time difference information (first time difference information) (step S30-1). More specifically, the baseband unit60(time difference evaluation component60-4) references the position data (coordinate data) in the first time difference information and identifies the position of the first area, and then detects a first area of which at least part is contained in the area inside a circle corresponding to the assumed positioning region.

Next, the baseband unit60(time difference evaluation component60-4) acquires the time difference data (time difference values and reference links) of all detected first areas (step S30-2).

Next, the baseband unit60(time difference evaluation component60-4) then determines if the currently or previously acquired time difference values for all time difference definition areas match or not (step S30-3).

If at least a part of the current or previously acquired time difference values do not match (step S30-4returns No), the baseband unit60(time difference evaluation component60-4) determines that the assumed positioning region includes a time difference boundary (step S30-9).

However, if the time difference values for all of the current or previously acquired time difference definition areas match (step S30-4returns Yes), the baseband unit60(time difference evaluation component60-4) determines if processing the reference links for all of the currently or previously acquired virtual regions has been completed (step S30-5).

If there are any unprocessed links (step S30-6returns Yes), the baseband unit60(time difference evaluation component60-4) detects the k-th area contained in the assumed positioning region from the time difference information (k-th time difference information) retrieved by the reference link (step S30-7). The baseband unit60(time difference evaluation component60-4) then repeats steps S30-2to S30-7until there are no unprocessed reference links remaining or at least part of all currently or previously acquired time difference values do not match.

If there are no unprocessed reference links (step S30-6returns No), the baseband unit60(time difference evaluation component60-4) determines that the assumed positioning region does not contain a time difference boundary (step S30-8).

FIG. 13describes a situation in which the calculated assumed positioning region does not contain a time difference boundary in the process shown inFIG. 12. Note that in the situation shown inFIG. 13the data shown in the region-time difference correlation tables inFIG. 10andFIG. 11is stored in flash memory66, and the same assumed positioning region as in the situation described inFIG. 7is calculated.

The assumed positioning region P1shown inFIG. 13is determined to include only the time difference definition area104as a first area based on the position data of the region-time difference correlation table200shown inFIG. 10. The time difference for time difference definition area104in the region-time difference correlation table200shown inFIG. 10is +8. The assumed positioning region P1is therefore determined to not contain a time difference boundary, and +8 is acquired as the time difference in the assumed positioning region P1.

FIG. 14AandFIG. 14Bdescribe a situation in the process shown inFIG. 12in which the calculated assumed positioning region includes a time difference boundary. Note that in the situation shown inFIG. 14AandFIG. 14Bthe data shown in the region-time difference correlation tables inFIG. 10andFIG. 11is stored in flash memory66, and the same assumed positioning regions as in the situation described inFIG. 8AandFIG. 8Bare calculated.

The assumed positioning region P1shown inFIG. 14Ais determined to contain virtual regions101,102, and103and time difference definition area104as first areas based on the position data in the region-time difference correlation table200shown inFIG. 10. The time difference values for virtual regions101,102, and103in region-time difference correlation table200are the reference links Link1, Link2, and Link3, and the time difference in time difference definition area104is +8.

Based on the position data for the region-time difference correlation table202shown inFIG. 11referenced by Link2, the assumed positioning region P1is determined to include time difference definition areas102E,102F,1021,102J,102K,102M,102N, and102O. The time difference values for the time difference definition areas102E,102F,1021,102J,102K,102M,102N, and102O in the region-time difference correlation table202are, respectively, +7, +9, +8, +8, +9, +8, +8, and +9. The assumed positioning region P1is therefore determined to include a time difference boundary. The assumed positioning region P2shown inFIG. 14Bis therefore calculated next.

The assumed positioning region P2shown inFIG. 14Bis determined to include only the virtual region102as a first area based on the position data in the region-time difference correlation table200shown inFIG. 10. The time difference value for the virtual region102in the region-time difference correlation table200shown inFIG. 10is Link2.

Based on the position data in the region-time difference correlation table202shown inFIG. 11referenced by Link2, the P1is determined to contain time difference definition areas1021,102M, and102N as second areas. The time difference is +8 for each of the time difference definition areas102I,102M, and102N in region-time difference correlation table202. The assumed positioning region P2is therefore determined to not include a time difference boundary, and +8 is acquired as the time difference in assumed positioning region P2.

In addition to the effects of the GPS wristwatch according to the first embodiment of the invention, the GPS wristwatch according to the second embodiment of the invention has the following effect.

The GPS wristwatch according to the second embodiment of the invention determines if the assumed positioning region that is calculated covers all or part of a virtual region, and if it does references the position of the time difference definition areas inside that virtual region to determine if there is a time difference boundary therein. Therefore, if a region containing a dense grouping of multiple small time zones is defined as the virtual region, and the calculated assumed positioning region does not contain the virtual region, it is not necessary to separately determine if the assumed positioning region contains all or a part of these multiple small time zone regions. A GPS wristwatch according to the second embodiment of the invention can therefore optimize the time of the evaluation process that determines if the assumed positioning region contains a time difference boundary.

Furthermore, because the GPS wristwatch according to the second embodiment of the invention determines whether or not the assumed positioning region contains a time difference boundary based on the locations of the multiple time difference definition areas contained in the virtual region when the assumed positioning region that is calculated contains a virtual region, high evaluation precision can be assured.

The GPS wristwatch according to the second embodiment of the invention first references first-level time difference information and determines whether or not the assumed positioning region contains part or all of a first-level virtual region. If the assumed positioning region contains part or all of a first-level virtual region, second-level time difference information is referenced and whether or not the assumed positioning region contains part or all of a second-level virtual region is determined. Likewise, if the assumed positioning region contains part or all of a k-level virtual region, k+1 level time difference information is referenced and whether or not the assumed positioning region contains part or all of a k+1 level virtual region is determined. If the assumed positioning region does not contain part or all of a k-level virtual region, whether or not the assumed positioning region contains a time difference boundary is determined based on the location of the k-level time difference definition area.

In other words, because the GPS wristwatch according to the second embodiment of the invention executes the evaluation process while sequentially referencing time difference information organized suitably hierarchically according to the size of the region for which a time difference is defined, how much time is consumed by the evaluation process can be optimized.

Furthermore, because the shape of the time difference definition areas and virtual regions is rectangular, the GPS wristwatch according to the second embodiment of the invention only needs to store coordinate data for the two end points of the diagonals of the rectangles in order to determine the area. As a result, this aspect of the invention can greatly reduce the amount of time difference information that must be stored compared with a configuration that stores data for each of numerous short lines used to define a time difference boundary.

Yet further, if the size of the rectangular shapes of the time difference definition areas and virtual regions contained in the time difference information for each level is fixed, the GPS wristwatch according to the second embodiment of the invention needs to store the coordinates of only one point for each area or region, and can thus further reduce the amount of time difference data.

In addition, because the time difference definition areas and virtual regions are rectangular, the GPS wristwatch according to the second embodiment of the invention can very easily determine if the calculated assumed positioning region contains a time difference boundary.

FIG. 15is a flow chart of a time difference adjustment process in a GPS wristwatch according to the third embodiment of the invention.

The time difference adjustment process shown inFIG. 15is basically the same as the time difference adjustment process shown inFIG. 6. More specifically, steps S10to S44in the time difference adjustment process shown inFIG. 15are identical to steps S10to S44in the time difference adjustment process shown inFIG. 6, are therefore identified by the same reference numerals, and further description thereof is omitted.

The time difference adjustment process shown inFIG. 15adds a step of displaying the assumed positioning region (the process in step S46) to the time difference adjustment process shown inFIG. 6. Note that this step of displaying the assumed positioning region (the process in step S46) may be executed before the step of adjusting the displayed time (the process of step S40).

FIG. 16describes an example of displaying the assumed positioning region in step S46in the time difference adjustment process shown inFIG. 15, and schematically describes the face of a GPS wristwatch according to the third embodiment of the invention.

Note that the basic configuration of a GPS wristwatch according to this second embodiment of the invention is identical to the configuration of the GPS wristwatch according to the first embodiment of the invention, and further description thereof is omitted.

A map300is formed on the surface of the GPS wristwatch3, and rotating hands301and302are disposed along along the top edge of the map300. The map300is a world map, and the current location is displayed by the hands301and302anywhere in the world the GPS wristwatch3is located. The world map may be rendered using any existing mapping method, is not limited to a Japan-centric world map, and may be rendered using other projection methods.

The map300is formed at a fixed position by engraving, printing, or other suitable means on the surface of the dial11. The dial11may be made using a transparent material, and a pattern of the map may be engraved or printed facing the back. Alternatively, the map300may be printed on film, and this film may be affixed to the back of a transparent dial11. In other words, the dial11or display face can be rendered in any way enabling the map300to be viewed normally from the front.

The hands301and302have rotary shafts303and304, and can move rotationally on these shafts over the surface of the dial11. Driving the hands301and302is controlled by the control unit40(drive control component40-3) through the drive circuit44.

The paths305and306traced by the hands301and302when the hands rotate are indicated by the double-dot lines in the figure. The map300is formed to be contained inside the area covered by the paths305and306of the hands301and302. The two hands301and302can intersect at any desired point within this area. A specific point on the map300can thus be indicated by the intersection of the two hands301and302.

The rotary shafts303and304are disposed on opposite sides of the map300with the top edge part of the map300therebetween. A line joining the centers of the rotary shafts303and304is an escape line307. The escape line307is denoted by a dot-dash line and is located outside the top edge of the map300. More precisely, part of the map300image is above the escape line307, but parts that are not used to indicate the current position by the hands301and302are allowed to be outside the escape line307.

The hands301and302can be removed to a position off the map300when they are positioned on the escape line307, that is, when the distal end of each points to the other rotary shaft303,304.

When the positioning mode is set and the time difference adjustment process ends, the control unit40(drive control component40-3) controls driving the hands301and302so that the position on the map300corresponding to the positioning information is indicated by the intersection of the hands301and302. Because the GPS wristwatch3thus displays the positioning information by means of the intersection of the hands301and302instead of using a digital display, high precision positioning information is not required. More specifically, the GPS wristwatch3in this embodiment of the invention can indicate the approximate position even when a relatively large assumed positioning region is calculated by the time difference adjustment process. Note that when a particularly large assumed positioning region (such as an area with a radius of several hundred kilometers) is calculated, the hands301and302may be caused to oscillate over the area of the assumed positioning region as a way of indicating the size of the assumed positioning region.

In addition to the effects of the GPS wristwatch according to the first embodiment of the invention, the GPS wristwatch according to the third embodiment of the invention has the following effects.

The GPS wristwatch according to the third embodiment of the invention can clearly indicate a single point on the map300using the intersection of two hands301and302. Because the intersecting hands301and302extend to the periphery, the intersection of the hands can easily track the current position and the hands are suitable to sensorially determining the current position.

In addition, by rendering a map300on the dial11or display surface, the GPS wristwatch according to the third embodiment of the invention does not need to use a liquid crystal display panel, for example, and can maintain a desirable appearance for a wristwatch1.

FIG. 17is a flow chart of a time difference adjustment process in a GPS wristwatch according to the fourth embodiment of the invention. Note that the basic configuration of a GPS wristwatch according to this fourth embodiment of the invention is identical to the configuration of the GPS wristwatch according to the first embodiment of the invention, and further description thereof is omitted.

The time difference adjustment process shown inFIG. 17is basically the same as the time difference adjustment process shown inFIG. 6. More specifically, steps S10to S44in the time difference adjustment process shown inFIG. 17are identical to steps S10to S44in the time difference adjustment process shown inFIG. 6, are therefore identified by the same reference numerals, and further description thereof is omitted.

The time difference adjustment process shown inFIG. 16differs from the time difference adjustment process shown inFIG. 6in that when the assumed positioning regions calculated from all combinations of the N (such as 3 or 4) GPS satellites10contain a time difference boundary (when step S32returns Yes), the satellite search process repeats. In addition, before starting the satellite search step the baseband unit60(satellite search component60-1) determines if the number of currently captured GPS satellites10has reached the maximum number of capturable satellites (such as 12) (step S48).

If the number of captured GPS satellites10equals the maximum number of capturable satellites (such as 12) (step S48returns Yes), the baseband unit60(satellite search component60-1) stops the capture of the M (such as 1) GPS satellites10that are the cause of the greatest degradation of positioning precision, and removes those satellites from the group of searched satellites (step S50). Because the baseband unit60(positioning calculation component60-3) has calculated the position using all combinations of N (such as 3 or 4) GPS satellites10, the baseband unit60(satellite search component60-1) knows which GPS satellites10are included when the positioning precision drops.

The GPS wristwatch1then repeats the satellite search and following steps (steps S12to S34). Because this enables calculating the position by selecting a newly captured GPS satellite10instead of the GPS satellite10that degrades the positioning precision, it may be possible to reduce the assumed positioning region to a size not including a time difference boundary.

However, if the maximum capturable number (such as 12) of GPS satellites10has not been captured (step S48returns No), the GPS wristwatch1repeats the satellite search and following steps (steps S12to S34).

Note that when the assumed positioning region contains a time difference boundary (step S32returns Yes) in the time difference adjustment process shown inFIG. 17, and all combinations of the N GPS satellites10have been selected from among the captured GPS satellites10and used for the positioning calculation (step S34returns Yes), the satellite search step repeats.

In addition to the effects of the GPS wristwatch according to the first embodiment of the invention, the GPS wristwatch according to the fourth embodiment of the invention has the following effects.

If the assumed positioning region contains a time difference boundary regardless of which combination of N GPS satellites10is selected from the captured GPS satellites10, the GPS wristwatch according to the fourth embodiment of the invention captures a new GPS satellite10and uses the satellite information from that satellite for the positioning calculation. In addition, if the number of currently captured GPS satellites10equals the maximum number of capturable satellites, the positioning calculation is done using the satellite information from a newly captured GPS satellite10instead of the M (such as 1) GPS satellites10that most degrade the positioning precision. Because the positioning precision can thus be improved, calculating a small assumed positioning region that does not contain a time difference boundary is easy. Therefore, the GPS wristwatch according to the fourth embodiment of the invention can easily determine the time difference even when in a location that is relatively near a time difference boundary, optimize the power consumption required by the positioning calculation, and complete the time adjustment process (time difference adjustment process) while consuming as little power as possible.

FIG. 18is a flow chart of a time difference adjustment process in a GPS wristwatch according to a fifth embodiment of the invention.

The time difference adjustment process shown inFIG. 18is basically the same as the time difference adjustment process shown inFIG. 17. More specifically, steps S10to S44in the time difference adjustment process shown inFIG. 18are identical to steps S10to S44in the time difference adjustment process shown inFIG. 17, are therefore identified by the same reference numerals, and further description thereof is omitted.

The time difference adjustment process shown inFIG. 18adds a step of displaying the assumed positioning region (the process in step S46) to the time difference adjustment process shown inFIG. 17. Note that this step of displaying the assumed positioning region (the process in step S46) may be executed before the step of adjusting the displayed time (the process of step S40).

The assumed positioning region can be displayed in step S46in the time difference adjustment process shown inFIG. 18using the GPS wristwatch shown inFIG. 16, for example.

In addition to the effects of the GPS wristwatch according to the fourth embodiment of the invention, the GPS wristwatch according to the fifth embodiment of the invention has the following effects.

The GPS wristwatch according to the fifth embodiment of the invention can clearly indicate a single point on the map300using the intersection of two hands301and302. Because the intersecting hands301and302extend to the periphery, the intersection of the hands can easily track the current position and the hands are suitable to sensorially determining the current position.

In addition, by rendering a map300on the dial11or display surface, the GPS wristwatch according to the fifth embodiment of the invention does not need to use a liquid crystal display panel, for example, and can maintain a desirable appearance for a wristwatch1.

It will be obvious to one with ordinary skill in the related art that the invention is not limited to the embodiments described above and can be varied in many ways without departing from the scope of the accompanying claims.

The invention includes configurations that are effectively the same as the configurations of the preferred embodiments described above, including configurations with the same function, method, and effect, and configurations with the same object and effect. The invention also includes configurations that replace parts that are not fundamental to the configurations of the preferred embodiments described above. The invention also includes configurations achieving the same operational effect as the configurations of the preferred embodiments described above, as well as configurations that can achieve the same object. The invention also includes configurations that add technology known from the literature to the configurations of the preferred embodiments described above.

Preferred embodiments of the invention are described in detail above, and, based on this disclosure, one skilled in the related art will recognize that many variations that do not actually depart from the novel innovations and effects of the invention are possible. Such variations are included in the scope of the present invention to the extent embodied in any claims.