Abstract:
An electronic timepiece includes a reception unit that receives satellite signals transmitted from positioning information satellites; a time information generating unit that generates an internal time; an automatic reception processing unit that activates the reception unit when predefined conditions are met to perform automatic reception processing, and performs simple time correction processing including acquiring time information from satellite signals received from one of the satellites, and, based thereon, correcting the internal time; and a manual reception processing unit that activates the reception unit via operation of an external member to perform manual reception processing, and performs simple time or high precision correction processing to correct the internal time, the high precision time correction processing including acquiring time and satellite orbit information from satellite signals received from two or more of the satellites, calculating a position of the timepiece, and correcting the internal time using the time information and the position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of, and claims priority under 35 U.S.C. §120 on, U.S. application Ser. No. 13/155,988, filed on Jun. 8, 2011, which is a continuation of, and claims priority under 35 U.S.C. §120 on, U.S. application Ser. No. 12/351,506, filed on Jan. 9, 2009, which claims priority under 35 U.S.C. §119 on Japanese Patent application No. 2008-007132, filed on Jan. 16, 2008. Each of the above-identified applications is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field of Invention 
     The present invention relates to an electronic timepiece and a control method for an electronic timepiece that adjusts the time based on signals received from positioning satellites such as GPS satellites. 
     2. Description of Related Art 
     The Global Positioning System (GPS) for determining the position of a GPS receiver uses GPS satellites that circle the Earth on known orbits, and each GPS satellite has an atomic clock on board. Each GPS satellite therefore keeps the time (referred to below as the GPS time or satellite time information) with extremely high precision. 
     An electronic device that has a timekeeping function for adjusting the time using time information (GPS time) from GPS satellites is taught, for example, in Japanese Unexamined Patent Appl. Pub. JP-A-H09-297191. 
     The electronic device taught in Japanese Unexamined Patent Appl. Pub. JP-A-H09-297191 receives signals from three or more GPS satellites to determine its position and the time zone at the determined position (current location). It then calculates and displays the current time at the current location using the time difference obtained for this time zone and the reference time from an internal clock. 
     When the electronic device taught in Japanese Unexamined Patent Appl. Pub. JP-A-H09-297191 moves to a different time zone, it can automatically adjust the change in the time difference resulting from such movement by regularly recalculating the time based on the positioning process, such as once a day. 
     However, the positioning process must acquire orbit information from three or more GPS satellites, the reception process is therefore time-consuming, and power consumption increases. This means that, particularly in small devices such as wristwatches where battery capacity is limited by the device size, the duration time is shortened by increased power consumption and user convenience is also impaired. 
     SUMMARY OF INVENTION 
     An electronic timepiece and a control method for an electronic timepiece according to the present invention can reduce power consumption while adjusting the time by receiving satellite signals from positioning information satellites. 
     A first aspect of the invention entails an electronic timepiece comprising a reception unit that receives satellite signals transmitted from positioning information satellites; a time information generating unit that generates an internal time; an automatic reception process unit that activates when predefined conditions are met, and performs simple time correction processing, which includes acquiring time information from satellite signals received from one of the positioning information satellites, and based thereon, correcting the internal time; and a manual reception processing unit that activates the reception unit via operation of an external operating member, and performs the simple time correction processing or high precision time correction processing, the latter of which includes acquiring time information and satellite orbit information from satellite signals received from more than one of the positioning information satellites, calculating a position of the electronic timepiece, and correcting the internal time using the time information and the position. 
     In another aspect of the invention, the simple time correction processing or the high precision time correction processing is selected and executed based on manual operation. 
     In another aspect of the invention, the electronic timepiece further comprises a memory that stores position information and the time difference information corresponding to the position measurement information. The high precision time correction processing further includes accessing the memory to acquire time difference information corresponding to the position. The correcting of the internal time information is then further based on the acquired time difference information and the time information. 
     This aspect of the invention makes the electronic timepiece more convenient when travelling across time zones because the time difference at the destination can be acquired and the time displayed by the timepiece automatically corrected to the current local time. More specifically, because the invention adjusts the time based on signals received from satellites, such as a GPS satellites, accessible all over the world, time difference information and time information can be acquired anywhere in the world, the time can be automatically adjusted in more geographical areas than is possible with a timepiece that uses standard time signals, and user convenience is thus improved. 
     In another aspect of the invention, the automatic reception processing unit starts the automatic reception processing when the internal time is equal to a predetermined time. 
     If reception starts automatically at a set time, the reception process can be executed at least once a day. As a result, the accuracy of the time displayed by the electronic timepiece can be improved, and a highly precise time display can be achieved. 
     In another aspect of the invention, the electronic timepiece further comprises an outdoor detection unit that detects whether or not the electronic timepiece is outdoors. The automatic reception processing unit starts the automatic reception processing when the outdoor detection unit detects that the electronic timepiece is outdoors. 
     If the automatic reception process runs when the timepiece is outdoors, the possibility that signals can be received from the positioning information satellites and that the time can be adjusted during automatic reception can be improved. 
     In another aspect of the invention, the electronic timepiece further comprises a memory that stores a record of whether reception succeeded or failed with a particular time period. The automatic reception processing unit controls the automatic reception processing based on the record stored in the memory. 
     The invention can therefore both reduce power consumption and automatically adjust the time difference without inconveniencing the user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a wristwatch with a GPS time adjustment device as an example of a timekeeping device with a time adjustment device according to the present invention. 
         FIG. 2  is a schematic section view of the wristwatch with a GPS time adjustment device shown in  FIG. 1 . 
         FIG. 3  is a block diagram showing the main internal hardware configuration of the wristwatch with a GPS time adjustment device shown in  FIG. 1  and  FIG. 2 . 
         FIG. 4  is a block diagram showing the configuration of the storage unit in a first embodiment of the invention. 
         FIG. 5  schematically describes the structure of the GPS satellite signal. 
         FIG. 6  schematically describes the structure of the GPS satellite signal. 
         FIG. 7  schematically describes subframe  1  of the GPS signal. 
         FIG. 8  is a block diagram showing the configuration of the control unit in a first embodiment of the invention. 
         FIG. 9  describes the automatic signal reception timing in the first embodiment of the invention. 
         FIG. 10  is a flow chart of the automatic reception process in the first embodiment of the invention. 
         FIG. 11  is a flow chart of the manual reception process in the first embodiment of the invention. 
         FIG. 12  is a continuation of the flow chart in  FIG. 11 . 
         FIG. 13  is a flow chart of the automatic reception process in a second embodiment of the invention. 
         FIG. 14  is a flow chart of the automatic reception process in a third embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention are described below with reference to the accompanying figures. 
     The embodiments described below are specific preferred embodiments of the present invention and certain technically preferred limitations are therefore also described, but the scope of the present invention is not limited to these embodiments or limitations unless specifically stated below. 
     Embodiment 1 
       FIG. 1  is a schematic diagram showing a wristwatch with a GPS time adjustment device (“GPS wristwatch  1 ” below) as an example of a timekeeping device with a time adjustment device according to the present invention, and  FIG. 2  is a schematic section view of the GPS wristwatch  1  in  FIG. 1 .  FIG. 3  is a block diagram showing the main hardware configuration of the GPS wristwatch  1  shown in  FIG. 1  and  FIG. 2 . 
     As shown in  FIG. 1 , the GPS wristwatch  1  has a time display unit including a dial  2  and hands  3 . A window is formed in a part of the dial  2 , and a display  4  such as an LCD panel is located in this window. 
     The hands  3  include a second hand, minute hand, and hour hand, and are driven through a wheel train by means of a stepping motor described below. 
     The display  4  is typically a LCD unit and is used for displaying the latitude and longitude, city name, or other location information, as well as messages. 
     The GPS wristwatch  1  receives satellite signals from a plurality of GPS satellites  5  orbiting the Earth on fixed orbits in space, acquires satellite time information, and can adjust the internally kept time based on the satellite time information. 
     The GPS satellite  5  is an example of a positioning information satellite used in the invention, and a plurality of GPS satellites  5  are orbiting the Earth in space. At present there are approximately 30 GPS satellites  5  in orbit. 
     The GPS wristwatch  1  has a crown  6  and buttons  7  and  8  as external operating members. 
     Internal Configuration of the GPS Wristwatch 
     The internal configuration of the GPS wristwatch  10  is described next. 
     As shown in  FIG. 2 , the GPS wristwatch  1  has an outside case  17  that is made of stainless steel, titanium, or other metal. 
     The outside case  17  is basically cylindrically shaped, and a crystal  160  is attached to the opening on the face side of the outside case  17  by an intervening bezel  16 . A back cover  26  is attached to the opening on the back side of the outside case  17 . The back cover  26  is annular and made of metal, and a back glass unit  23  is attached to the opening in the center. 
     Inside the outside case  17  are disposed a stepping motor for driving the hands  3 , a GPS antenna  11 , and a battery  24 . 
     The stepping motor is a device that is commonly used in timepieces, and has a motor coil  19  and a stator and rotor not shown. The stepping motor drives the hands  3  by means of an intervening wheel train. 
     This GPS antenna  11  is a patch antenna for receiving satellite signals from a plurality of GPS satellites  5  orbiting the Earth on fixed orbits in space. The GPS antenna  11  is located on the opposite side of the dial  2  as the side on which the time is displayed, and receives RF signals through the crystal  160  and the dial  2 . 
     The dial  2  and crystal  160  are therefore made from materials that pass RF signals, particularly the satellite signals transmitted from the GPS satellites  15 . The dial  2 , for example is plastic. The bezel  16  is ceramic in order to improve satellite signal reception. 
     A circuit board  25  is disposed on the back cover side of the GPS antenna  11 , and a battery  24  is disposed on the back cover side of the circuit board  25 . 
     The circuit board  25  is also populated with various circuit devices (such as IC devices) including a reception unit  18  that processes signals received by the GPS antenna  11  as described below, and a control unit  20  that controls, for example, the stepping motor that drives the hands  3 . The reception unit  18  and the control unit  20  operate using power supplied from the battery  24 . 
     The battery  24  is a lithium-ion battery or other type of storage battery. A magnetic sheet  21  is disposed below (on the back cover side of) the battery  24 , and a charging coil  22  is disposed with the magnetic sheet  21  between it and the battery  24 . The battery  24  can therefore be charged by the charging coil  22  by means of electromagnetic induction from an external charger. The magnetic sheet  21  can also divert the magnetic field. The magnetic sheet  21  therefore reduces the effect of the battery  24  and enables the efficient transmission of energy. The back glass unit  23  is disposed in the center part of the back cover  26  to facilitate power transmission. 
     The GPS wristwatch  1  is arranged as described above. 
     Circuit Design of the GPS Wristwatch 
     The circuit design of the GPS wristwatch  1  is described next. 
     As shown in  FIG. 3 , the GPS wristwatch  1  also has a GPS device  40 , and a time adjustment device  44 , and functions as a computer. As shown in  FIG. 3 , the time display device  45 , the GPS device  40 , and the time adjustment device  44  share some parts. 
     The configurations shown in  FIG. 3  are further described below. 
     GPS Device 
     As shown in  FIG. 3 , the GPS wristwatch  1  has a GPS device  40  that receives and processes satellite signals received from a GPS satellite  5 . 
     The GPS device  40  includes the GPS antenna  11 , a filter (SAW)  31 , and the reception unit  18 . The filter (SAW)  31  is a bandpass filter and in this embodiment of the invention extracts a 1.5-GHz satellite signal. The GPS device  40  thus renders the reception unit of the present invention. 
     The reception unit  18  processes the satellite signal extracted by the filter, and includes an RF (radio frequency) unit  27  and baseband unit  30 . 
     The RF unit  27  includes a PLL  34 , IF filter  35 , VCO (voltage controlled oscillator)  41 , A/D converter  42 , mixer  46 , low noise amplifier  47 , and IF amplifier  48 . 
     The satellite signal is extracted by the filter  31  and amplified by the low noise amplifier  47 , mixed by the mixer  46  with the signal from the VCO  41 , and down-converted to an IF (intermediate frequency) signal. 
     The IF signal mixed by the mixer  46  passes the IF amplifier  48  and IF filter  35 , and is converted to a digital signal by the A/D converter  42 . 
     The baseband unit  30  also includes a digital signal processor (DSP)  39 , a CPU (central processing unit)  36 , SRAM (static random access memory)  37 , and a real-time clock (RTC)  38 . A temperature-compensated crystal oscillator (TCXO)  32  and flash memory  33  are also connected to the baseband unit  30 . 
     The baseband unit  30  then processes the digital signal input from the A/D converter  42  of the RF unit  27  based on a control signal, and processes (decodes) the satellite signal to acquire the satellite time information and positioning information. 
     The clock signal of the PLL  34  is generated by the TCXO  32 . 
     The RTC  38  generates time information on the receiver side for processing the satellite signals. The real-time clock 38 counts up at the reference clock output from the TCXO  32 . 
     Time Adjustment Device 
     The time adjustment device  44  includes the reception unit  18 , the control unit  20 , and a drive circuit  43 . This time adjustment device  44  renders the time information correction unit of the invention. 
     The control unit  20  includes a storage unit  20 A and controls driving the GPS device  40 , the hands  3 , and the display  4 . More specifically, the control unit  20  renders a reception control unit that sends control signals to the reception unit  18  and controls the reception operation of the GPS device  40 . 
     As shown in  FIG. 4 , the storage unit  20 A includes a time data storage unit  200  and a positioning information and time difference data storage unit  210 . 
     The received time data  201 , internal time data  202 , time data for timepiece display  203 , and time difference data  204  are stored in the time data storage unit  200 . 
     Three units of received time data can be stored as the received time data  201 . 
     The internal time data  202  stores the internal time information that is generated based on a reference signal from the crystal oscillator  20 B connected to the control unit  20 . As a result, updating the internal time and moving the hands  3  can continue even if the supply of power to the reception unit  18  is stopped. The control unit  20  and crystal oscillator  20 B thus render a time information generating unit that generates the internal time. 
     The time data for timepiece display  203  is used when the internal time data and the time displayed by the timepiece do not match, such as when the time is being adjusted and when the time difference is set. More specifically, when the internal time data  202  stores the UTC (Coordinated Universal Time) based on the time information acquired from a satellite signal, and the time difference data  204  is set, the time data for timepiece display  203  stores the time adjusted for this time difference. 
     The positioning information and time difference data storage unit  210  stores time difference data for each time zone, and stores the time difference data correlated to navigation information (positioning information). 
     The GPS wristwatch  1  thus comprised is driven by power supplied from a storage battery  24  through a regulator  29 . 
     A lithium ion battery or other rechargeable storage battery is used as the battery  24  in this embodiment of the invention, but a lithium battery or other type of primary battery may be used instead. The charging method when a secondary storage battery is used is not limited to using a charging coil  22  to charge by means of electromagnetic induction from an external charger as used in this embodiment of the invention, and the battery may be charged using a solar cell or other type of generating device disposed to the GPS wristwatch  1 . 
     A voltage detector (not shown in the figure) for detecting the voltage of the storage battery  24  is disposed to the control unit  20  to monitor the voltage of the storage battery  24 . This battery voltage monitor may operate continuously, but normally operates at a predetermined interval in order to reduce power consumption. 
     Description of the Navigation Message 
     The navigation message that is the signal (satellite signal) transmitted from each GPS satellite  5  is described below. Note that the data carried in the navigation message is modulated at 50 bps to the satellite signal. 
       FIG. 5  to  FIG. 7  schematically describe the GPS satellite signal. 
     As shown in  FIG. 5 , signals are transmitted from each of the GPS satellites  5  in units of one frame every 30 seconds. One frame contains five subframes. Each subframe is 6 seconds long, and contains 10 words (each word is 0.6 second). 
     The first word in each subframe is a telemetry (TLM) word storing the TLM data, and each TLM word starts with a preamble as shown in  FIG. 6 . 
     The TLM word is followed by a handover word HOW storing the HOW (handover) data, and each HOW starts with the time of week (TOW) (also called the Z count) indicating the GPS time information of the GPS satellite. 
     The GPS time is the number of seconds since 00:00:00 Sunday night, and is reset to zero at precisely 00:00:00 every Sunday night. The GPS time is thus information expressing the time since the start of the week in seconds, and the elapsed time is a number expressed in 1.5 second units. This GPS time is also called the Z count or the Z count data, and enables the GPS wristwatch  1  to know the current time. 
     As shown in  FIG. 7 , word hands  3  in subframe  1  contains words storing satellite correction data such as week number data (WN) and the satellite health information (SVhealth) 
     The same GPS week number identifies the week in which the current GPS time information is expressed. 
     More specifically, the starting point for the GPS time information is 00:00:00 of Jan. 6, 1980 referenced to the Coordinated Universal Time (UTC), and the week that started on this day is week 0. The GPS receiver can therefore get the precise GPS time from the week number and the elapsed time (number of seconds). 
     The week number is updated once a week. 
     Once the receiver gets the week number and counts the seconds passed since the week number was acquired, the current week number of the GPS satellite  5  can be known from the acquired week number and the elapsed time without getting the week number data again. As a result, the approximate current GPS time can be known once the Z count data is acquired. As a result, the GPS device  40  normally acquires only the Z count data when getting the time information. 
     The main frame of the navigation message contained in the signal from the GPS satellite  5  contains 1500 bits and is transmitted at 50 bps. 
     The main frame is divided into five subframes of 300 bits each. 
     One frame is equivalent to 30 seconds. One subframe is therefore equivalent to 6 seconds. As described above, the TLM word and the Z count data (TOW) in the HOW word are contained in the first two words of each subframe. The Z count data starts from subframe  1 , and six seconds of data is contained in each subframe. Subframe  1  to subframe  5  therefore contain the TLM word and the Z count (TOW) data in the HOW word. The Z count (TOW) data is therefore the time information for the next subframe. For example, the Z count data in subframe  1  is the time data for subframe  2 . 
     As shown in  FIG. 5  and  FIG. 6 , the navigation message carried in the satellite signal from the GPS satellite  5  includes the preamble data and the TOW in the HOW word, and subframe data, including satellite correction data such as the week number (WN) and satellite health data (SV HEALTH), the ephemeris (detailed orbit information for the transmitting GPS satellite  5 ), almanac (orbit information for all GPS satellites  5 ), and the UTC data. More specifically, the subframe data of the navigation message is carried in subframe  1  to subframe  5 , and the data in these five subframes render one frame data unit. The subframe data is divided into words  1  to  10 . 
     The HOW data or Z count data is therefore transmitted at 6-second intervals, and the week number, the ephemeris parameters and the almanac parameters are transmitted at 30-second intervals. 
     Because the signals described above are transmitted from the GPS satellites  5 , satellite signal reception as used herein means phase synchronization with the C/A code in the satellite signal transmitted from each GPS satellite  5 . 
     More specifically, the baseband unit  30  must synchronize with the signal from the GPS satellite  5  in order to get the frame data from a particular GPS satellite  5 . 
     The C/A code is used for synchronization with 1 ms precision, and is a 1023-chip pseudo random noise code that repeats every 1 ms. The C/A code (1023 chip (1 ms) code) is different for each of the plural GPS satellites  5 , and is unique to a particular satellite. 
     Therefore, to receive the satellite signal from a particular GPS satellite  5 , the GPS device  40  generates the unique C/A code for a particular GPS satellite  5  and phase synchronizes with the C/A code from the selected GPS satellite  5  to receive the satellite signal. 
     By synchronizing with the C/A code (1023 chips (1 ms)), the preamble of the TLM word and the HOW word of each subframe can be received, and the Z count data (time information) can be acquired from the HOW word. 
     The positioning information can be acquired by reading the ephemeris parameters in the satellite signals from three to four satellites. The ephemeris data can be acquired by receiving 600 bits or approximately 12 seconds from the preamble of subframe  2 , which is transmitted every 30 seconds. 
     The navigation message that is the satellite signal from the GPS satellites  5  is configured as described above. 
     System Configuration of the Time Adjustment Device (Time Information Adjustment Unit) 
     The configuration of the control system for the GPS wristwatch  1  according to the invention is described next with reference to  FIG. 8 .  FIG. 8  shows the function blocks rendered by primarily the control unit  20  executing a program. 
     More specifically, the control unit  20  includes a manual reception process unit  51 , a automatic reception process unit  52 , a simple time adjustment process unit  53 , and a high precision time adjustment process unit  54 . 
     The manual reception process unit  51  controls the reception unit  18  to execute a manual reception process when a predetermined operation is executed using the crown  6  or buttons  7  and  8  (external operating member) disposed to the GPS wristwatch  1 . 
     The automatic reception process unit  52  automatically operates the reception unit  18  to execute the automatic reception process when the status of the GPS wristwatch  1  meets predetermined conditions. In this embodiment of the invention a condition for executing the automatic reception process is that the time data for timepiece display  203 , which is updated by the control unit  20  based on a reference signal from the crystal oscillator  20 B, reaches a predetermined time. 
       FIG. 9  describes automatic reception process of the automatic reception process unit  52 . The automatic reception process tries to start the reception process at the timing of subframe  1 , which is transmitted every minute at the 0 and 30 seconds. The timing at which reception starts must allow for enough time to capture a satellite before the time data is received, and several seconds are required to complete satellite capture when offset of the internal time is considered. The automatic reception process unit  52  therefore starts driving the reception unit  18  to execute the reception operation several seconds before the 0 or 30 second of the minute. 
     The automatic reception process must also receive at least the data through word  3  of subframe  1  containing the week number and satellite health information. In the example shown in  FIG. 9 , the process ends after receiving to word  4 . 
     The simple time adjustment process unit  53  executes a simple time adjustment process to receive the satellite signal from one GPS satellite  5  by means of the reception unit  18 , acquire the time information (Z count) from the received satellite signal, and adjust the internal time. 
     The high precision time adjustment process unit  54  executes a high precision time adjustment process to receive satellite signals from a plurality of GPS satellites  5  by means of the reception unit  18 , acquire the time information and positioning information from the received satellite signal and determine the local position, and then adjust the internal time to the time acquired based on the positioning result. 
     This embodiment of the invention is configured so that the simple time adjustment process is executed by the simple time adjustment process unit  53  when the automatic reception process is executed by the automatic reception process unit  52 . 
     The high precision time adjustment process of the high precision time adjustment process unit  54  is executed only when the manual reception process is executed by the manual reception process unit  51 , and is not executed when the automatic reception process executes. 
     Automatic Reception Process 
     The automatic reception process of the GPS wristwatch  1  according to this embodiment of the invention is described next with reference to the flow chart in  FIG. 10 . 
     The automatic reception process unit  52  first determines if the reception conditions are satisfied (S 11 ). In this embodiment of the invention the automatic reception process unit  52  references the time data for timepiece display  203  and determines if it has reached the preset reception time (reception start timing) in step S 11 . 
     Note that the reception start timing is set with consideration for the RF unit  27  startup time and the satellite search time so that data acquisition can start at the 0 or 30 second mark of the minute. For example, if data acquisition is to start at 2:00:00 and it takes 3 seconds to activate the RF unit  27  and search for a satellite, the reception start time is set to 3 seconds before 2:00:00, that is, 1:59:57. 
     The reception start time may be set to a time when the likelihood is high that the user will not be wearing the GPS wristwatch  1 , such as sometime between 0:00 and 5:00. More particularly, the GPS wristwatch  1  is preferably stationary during the reception process in order for the GPS wristwatch  1  to execute the reception process in a stable condition. The automatic reception process is therefore preferably set for a time when the likelihood is high that the user is sleeping and the GPS wristwatch  1  is resting on a stand by a window, for example. 
     If the automatic reception process unit  52  determines in S 11  that the reception conditions are satisfied, it starts the automatic reception process using the simple time adjustment process unit  53  (S 12 ). 
     The simple time adjustment process unit  53  then drives the reception unit  18  and searches for a GPS satellite  5  (S 13 ). In the satellite search process the simple time adjustment process unit  53  sequentially changes the satellite number SV from 1 to 30 to find the GPS satellite  5  identified by each satellite number SV and detect the signal level (SNR) of the satellite. More specifically, the simple time adjustment process unit  53  adjusts the timing of the C/A code for each GPS satellite  5  to find a GPS satellite  5  with which it can synchronize. 
     Satellite signals from all of the GPS satellites  5  are transmitted on the same frequency, but are transmitted using code division multiple access (CDMA) by using a different C/A code for each GPS satellite  5 . The GPS satellites  5  that can currently be captured can therefore be determined by reading the C/A code contained in the received satellite signal. 
     As a result, the simple time adjustment process unit  53  adjusts the timing of the C/A code pattern for each GPS satellite  5  to find a GPS satellite  5  which it can synchronize. 
     The simple time adjustment process unit  53  then determines if one GPS satellite  5  was captured (S 14 ). 
     More specifically, if the received satellite signal is correlated to the C/A code generated by the automatic reception process unit  52 , the output will have an output peak at a predetermined time if the C/A codes are the same, but the output will not have a peak and be substantially flat at zero if the C/A codes differ. 
     Therefore, in S 14  the simple time adjustment process unit  53  determines if a GPS satellite  5  was captured by evaluating the result of the C/A code correlation process. 
     If a satellite has not been captured in S 14 , the simple time adjustment process unit  53  determines if the satellite search process has timed out (S 15 ). 
     More specifically, the code length of the C/A code is 1 ms, and the search for all GPS satellites  5  can be completed in approximately 2 seconds even if the C/A code output timing is adjusted and the Doppler frequency is also changed to search for all 30 GPS satellites  5 . Therefore, if synchronization with a GPS satellite  5  is not possible by the time a predetermined time, such as 2 seconds, passes after reception starts, the simple time adjustment process unit  53  determines that the satellite capture process has timed out. 
     If satellite capture has not timed out in S 15 , the simple time adjustment process unit  53  continues the satellite search process in S 13 . 
     If operation has timed out in S 15 , the simple time adjustment process unit  53  controls the reception unit  18  to end the reception process (S 16 ). 
     If the GPS wristwatch  1  is located where reception is not possible, such as indoors, operation will time out because there is no GPS satellite  5  with which it can synchronize even after searching for all GPS satellites  5 . Continuing to drive the reception unit  18  in this situation will simply waste power. 
     As a result, the GPS wristwatch  1  ends the GPS satellite  5  search (reception) process in S 16  if a GPS satellite  5  is not captured after a predetermined time has passed. This prevents wastefully consuming power. 
     If the simple time adjustment process unit  53  determines in S 14  that a satellite was captured, it starts the Z count acquisition process and then determines if the Z count of the satellite signal received from the GPS satellite  5  could be acquired (S 17 ). Because reception starts from subframe  1  in the automatic reception process, whether the Z count from subframe  1  could be acquired is determined first. 
     If the simple time adjustment process unit  53  determines in S 17  that the Z count could not be acquired, it determines if operation timed out (S 18 ). 
     If the simple time adjustment process unit  53  determines in S 18  that operation did not time out, it continues the Z count acquisition process and again determines in S 17  if the Z count was acquired. 
     If the simple time adjustment process unit  53  determines in S 18  that operation timed out, it ends the reception process (S 16 ). 
     More specifically, because the Z count is carried in each subframe, it is transmitted every 6 seconds. Furthermore, because this embodiment may at most receive the Z count carried in subframes  1  to  3 , operation times out and the reception process ends if the simple time adjustment process unit  53  cannot recognize the Z count data signal by the time 18 seconds pass after the Z count acquisition process starts. 
     If the Z count is acquired in S 17 , the simple time adjustment process unit  53  applies a parity check to the received Z count (time data) and matches it with the internal time (S 19 ). 
     In S 19  the simple time adjustment process unit  53  verifies the received Z count (time information) and the internal time data  202  stored in the time data storage unit  200 . Because as described above the simple time adjustment process unit  53  does not run the positioning process, it verifies the time by comparing the internal time data with the time information corrected by a preset transmission delay time. 
     If a match with the internal time data is not confirmed in S 19 , the simple time adjustment process unit  53  determines if operation timed out in S 18 , and continues the Z count acquisition process if operation did not time out. Because it takes 18 seconds for a timeout to occur, the simple time adjustment process unit  53  also processes subframes  2  and  3  in this embodiment of the invention. The simple time adjustment process unit  53  stores the data acquired from subframes  1  to  3  as the received time data  201  in the time data storage unit  200 . 
     The simple time adjustment process unit  53  determines a match with the internal time data using the Z count data from the acquired subframes  2  and  3 . 
     If a match is confirmed in S 19 , the simple time adjustment process unit  53  controls the reception unit  18  to stop reception (S 20 ). 
     The simple time adjustment process unit  53  then uses the acquired Z count (satellite time data) to adjust the internal time (S 21 ). The simple time adjustment process unit  53  determines the Coordinated Universal Time (UTC) by adding the UTC offset (currently +14 seconds) to the acquired Z count, and stores the result as the internal time data  202  in the time data storage unit  200 . The simple time adjustment process unit  53  then calculates the current local time by adding the time difference data  204  to the internal time data  202 , and updates the time data for timepiece display  203  to this current local time. 
     The control unit  20  then controls the drive circuit  43  to display the updated time data for timepiece display  203  using the hands  3 . 
     If shortening the reception time is desirable, the reception process may be ended without receiving subframe  3  if a match with the internal time data is confirmed when subframe  2  is received. This has the effect of reducing power consumption by shortening the reception time. 
     Manual Reception Process 
     The manual reception process of the GPS wristwatch  1  according to this embodiment of the invention is described next with reference to the flow chart in  FIG. 11 . 
     The manual reception process unit  51  decides if an external operating member such as the crown  6  or buttons  7  and  8  disposed to the GPS wristwatch  1  has been operated in a specific way (S 31 ). 
     If the manual reception process unit  51  detects in S 31  that the specific operation was asserted, it determines if the power supply voltage (the voltage of the storage battery  24 ) is greater than a predetermined voltage (S 32 ). 
     Because the manual reception process also determines the current location using the high precision time adjustment process unit  54 , the reception time is a relatively long 1 to 3 minutes, and power consumption therefore increases. The manual reception process unit  51  therefore first detects the power supply voltage to determine if there is sufficient voltage to enable reception for 1 to 3 minutes. 
     If the power supply voltage is less than or equal to the predetermined voltage in S 32 , the manual reception process unit  51  ends the manual reception process. 
     If the power supply voltage is greater than the predetermined voltage in S 32 , the manual reception process unit  51  uses the high precision time adjustment process unit  54  to start manual reception (S 33 ). 
     The high precision time adjustment process unit  54  drives the reception unit  18  to search for the GPS satellites  5  (S 34 ). This satellite search process is the same as the satellite search step S 13  in the automatic reception process, and looks for GPS satellites  5  with which synchronization is possible by adjusting the output timing of the C/A codes for the GPS satellites  5 . 
     The high precision time adjustment process unit  54  then determines if four GPS satellites  5  could be captured (S 35 ). While the number of GPS satellites  5  captured differs, the content of this satellite capture determination step S 35  is the same as the satellite capture determination step S 14  in the automatic reception process. More specifically, the simple time adjustment process unit  53  determines whether or not one GPS satellite  5  was captured because it is only necessary to acquire the Z count data, but the high precision time adjustment process unit  54  must capture four GPS satellites  5  for positioning. 
     The high precision time adjustment process unit  54  therefore determines if the GPS satellites  5  were captured by evaluating the results of the C/A code correlation process. 
     If S 35  determines that the satellites could not be captured, the high precision time adjustment process unit  54  determines if operation timed out in the same way as in step S 15  described above (S 36 ). 
     If operation did not time out (S 36  returns No), the high precision time adjustment process unit  54  continues the satellite search process in S 34 . 
     If operation did time out (S 36  returns Yes), the high precision time adjustment process unit  54  determines if one GPS satellite  5  was captured as shown in  FIG. 12  (S 37 ). More specifically, if four GPS satellites  5  cannot be captured, operation shifts from the high precision time adjustment process to the simple time adjustment process in order to capture one GPS satellite  5 , acquire the time data (Z count), and adjust the time. 
     If in S 37  one GPS satellite  5  has not been captured, the high precision time adjustment process unit  54  controls the reception unit  18  to end the reception process (S 38 ). 
     If S 37  determines that one GPS satellite  5  was captured, the high precision time adjustment process unit  54  operates the simple time adjustment process unit  53  to execute the simple time adjustment process. This simple time adjustment process is the same as shown in steps S 17  to S 21  in  FIG. 10 . 
     More particularly, the simple time adjustment process unit  53  determines if the Z count was acquired as described in S 17  (S 39 ). 
     If the Z count was acquired, the simple time adjustment process unit  53  applies a parity check to the received Z count (time data) and adjusts the internal time as described in S 19  (S 40 ). 
     If S 39  determines that the Z count was not acquired, and if a match with the internal time data is not confirmed in S 40 , the simple time adjustment process unit  53  determines if operation timed out as in S 18  (S 41 ). If the simple time adjustment process unit  53  determines that operation timed out in S 41 , the reception process ends (S 38 ). If operation did not time out, the Z count acquisition evaluation process continues (S 39 ). 
     If a match is confirmed in S 40 , the simple time adjustment process unit  53  controls the reception unit  18  to stop reception (S 42 ). 
     The simple time adjustment process unit  53  then uses the acquired Z count (satellite time data) to adjust the internal time as described in S 21  (S 43 ). 
     More specifically, the simple time adjustment process unit  53  determines the Coordinated Universal Time (UTC) by adding the UTC offset (currently +14 seconds) to the acquired Z count, and stores the result as the internal time data  202  in the time data storage unit  200 . Because the plural GPS satellites  5  required for positioning could not be captured, the positioning information could not be acquired, and the simple time adjustment process unit  53  also cannot acquire the time difference information for the current location based on the positioning information. The simple time adjustment process unit  53  therefore updates the time data for timepiece display  203  based on the previously set time difference data  204  and displays the updated time using the hands  3 . 
     Because the high precision time adjustment process unit  54  cannot update the time difference data  204  when the positioning information cannot be acquired, the time data for timepiece display  203  will match the current local time if the current location is in the same time zone as the previously set time difference data  204 , but will differ from the current local time if a different time zone has been entered. In this embodiment of the invention, therefore, the high precision time adjustment process unit  54  indicates on the display  4  that positioning was not possible so that if the user will not mistake the displayed time for the correct current local time if the user is crossing time zones. 
     In this situation the user may operate the buttons  7  and  8 , for example, to manually enter the time difference data  204  so that the current local time is displayed. 
     If it is determined in S 35  that four GPS satellites  5  were captured, the high precision time adjustment process unit  54  determines if orbit data (ephemeris) could be acquired for each of the GPS satellites  5  (S 44 ). 
     If the high precision time adjustment process unit  54  determines in S 44  that the orbit data was acquired, it determines if the positioning calculation based on the acquired orbit data has been completed (S 45 ). 
     If orbit data acquisition is not completed in S 44  or if the positioning calculation is not completed in S 45 , the high precision time adjustment process unit  54  determines if operation timed out and confirms if these processes ended in the predetermined time (S 46 ). Note that this timeout time is set according to the number of reception channels in the GPS wristwatch  1 . More specifically, if the GPS wristwatch  1  has a plurality of channels enabling simultaneously receiving satellite signals from a plurality of GPS satellites  5 , the timeout time may be set to approximately 1 minute, for example. However, if the GPS wristwatch  1  only has one reception channel, the GPS satellites  5  must be captured and data acquired one at a time, and the timeout time may be set to approximately 3 to 4 minutes, for example, because it takes approximately 3 to 4 minutes to complete the reception process. 
     If operation has not timed out in S 46 , steps S 44  and S 45  repeat. If operation has timed out in S 46 , operation shifts from the high precision time adjustment process to the simple time adjustment process, and steps S 39  to S 43  described above execute. 
     If the positioning calculation has ended in S 45 , the high precision time adjustment process unit  54  controls the reception unit  18  to end the reception process (S 47 ), and reads the time difference information from the positioning information and time difference data storage unit  210  based on the acquired navigation data (positioning information) (S 48 ). More specifically, a data table describing the relationship between the positioning information and time difference information (positioning information and time difference data storage unit  210 ) is stored in the time data storage unit  200 . The high precision time adjustment process unit  54  can therefore determine in which time zone the acquired positioning information is contained and can read the time difference information for that time zone. 
     This time difference information is stored as the time difference data  204  in the time data storage unit  200 . 
     Note that because the navigation process executed in a common car navigation system must continuously detect the current location, it must execute the navigation process continuously. However, the positioning process executed in this embodiment of the invention achieves its purpose once the current location has been determined when the high precision time adjustment process is triggered manually, and it is not necessary to execute the navigation (positioning) process continuously. Therefore, if the positioning calculation has completed and the current location has been determined in S 45 , the reception process can be ended. 
     The high precision time adjustment process unit  54  also uses the time difference data  204  and adjusts the hands  3  to display the current time at the current location (S 49 ). More specifically, the high precision time adjustment process unit  54  adds the UTC offset to the received satellite time information (Z count data and week number) to get the UTC, and updates the internal time data  202  to this value. The high precision time adjustment process unit  54  then determines the time at the current location using the internal time data  202  and time difference data  204 , and updates the time data for timepiece display  203 . 
     Note that the high precision time adjustment process unit  54  may also display the acquired positioning information and time zone information on the display  4 . 
     As described above, the GPS wristwatch  1  adjusts the time by means of the simple time adjustment process unit  53  when the automatic reception process is executed by the automatic reception process unit  52 . 
     However, when the manual reception process is executed by the manual reception process unit  51 , the positioning information and time difference information are acquired by the high precision time adjustment process unit  54 , and the time is adjusted to the local time based on the positioning information (time difference information) and the acquired time information if data acquisition is successful. If data acquisition failed, however, the time is adjusted based only on the acquisition of time information by the simple time adjustment process unit  53 . 
     The effect of this embodiment of the invention is described next. 
     (1) During the automatic reception process the GPS wristwatch  1  receives the Z count data from only one GPS satellite  5  and adjusts the internal time data by means of the simple time adjustment process unit  53 . During the automatic reception process the internal time can therefore be adjusted with a short reception process, and power consumption can be reduced in the automatic reception process. 
     More specifically, because the automatic reception process is executed without being invoked by the user, it is unclear whether the GPS wristwatch  1  is located where satellite signals from the GPS satellites  5  can be easily received. If the reception environment is poor and the positioning process that requires capturing four GPS satellites  5  executes, the likelihood that the required information can be acquired is low, reception is therefore time-consuming, and power consumption increases. 
     When the automatic reception process runs in this embodiment of the invention, however, only the Z count data is acquired and power consumption can be reduced because the positioning process does not execute. 
     (2) In this embodiment of the invention the high precision time adjustment process unit  54  that executes the positioning process operates only when the manual reception process is invoked, and does not operate when the automatic reception process runs, and the likelihood of the positioning process succeeding can be improved. 
     More specifically, the manual reception process is executed when the user operates an external operating member. In this situation the user generally invokes the manual reception process where satellite signals from the GPS satellites  5  can be easily received, such as outdoors. Therefore, if the positioning process that requires capturing four GPS satellites  5  is set to execute only in the manual reception process, the reception process executes where it is easy to capture a plurality of GPS satellites  5 , such as outdoors, and the probability of the positioning process succeeding can be improved. 
     (3) Because the automatic reception process executes when a predetermined time is reached, the Z count data can be received and the time adjusted once a day. As a result, the correct time can be automatically displayed on the GPS wristwatch  1 . 
     (4) Because the manual reception process executes the positioning process when reception is manually invoked by the user, the Coordinated Universal Time (UTC) and time difference at the current location can be automatically acquired if the user performs the operation to start manual reception after moving into a different time zone, such as when travelling abroad, for example. The current local time can therefore be automatically displayed, and the convenience of the GPS wristwatch  1  can be improved. 
     Furthermore, because the positioning process of the high precision time adjustment process unit acquires the time difference, it only needs to determine the time zone of the current location. It therefore does not need to continuously detect the current location, unlike a conventional car navigation system, the operating time of the reception unit  18  can be greatly reduced compared with the positioning process of a car navigation system even when the positioning process executes, and power consumption can also be reduced. 
     (5) Because the automatic reception process is set to run at 2:00 a.m., for example, the possibility that the GPS wristwatch  1  is stationary is high, and reception performance can be improved. 
     In addition, because the satellite health information is acquired in the manual reception process and the automatic reception process, whether the GPS satellite  5  from which signals are received is currently healthy can be determined. As a result, adjusting the time to the wrong time as a result of receiving signals from a GPS satellite  5  that is not healthy can be prevented even when adjusting the internal time based on the Z count data. 
     (6) Furthermore, because the manual reception process unit  51  and automatic reception process unit  52  control the reception unit  18  to stop the reception unit  18  when the reception process is not executing, current consumption can be further suppressed. 
     Embodiment 2 
     A second embodiment of the invention is described next. Note that in each of the embodiments described below parts that are the same or similar to like parts in another embodiment are identified by the same reference numerals, and further description thereof is omitted or simplified. 
     The first embodiment executes the automatic reception process once a day by determining if a predetermined time has arrived as the reception condition in S 11 . This second embodiment differs from the first embodiment in that a plurality of reception times are set in one day, and reception is controlled to execute once a day by determining if a prescribed amount of time has passed since the last successful reception. Other aspects of the automatic reception process and the manual reception process are the same as described in the first embodiment, and further description thereof is omitted below. 
     As shown in  FIG. 13 , the automatic reception process unit  52  in the second embodiment determines if the time data for timepiece display  203  has reached a time set as the automatic reception time, and more specifically determines if the time is 12:00 a.m., 2:00 a.m., 4:00 a.m., or 6:00 a.m. (S 111 ). 
     If the time is one of these set times in S 111 , whether the predetermined time since the last successful reception has passed is determined (S 112 ). Whether this time has passed is determined in S 112  so that reception does not occur more than once a day, that is, so that the reception process does not repeat at 2:00, 4:00, or 6:00 if reception is successful at midnight (0:00). This predetermined time may therefore be set to, for example, seven hours or more. 
     The reception process does not execute more than once a day because timepiece precision does not require receiving the satellite signal more than once a day, and power consumption increases accordingly if the signal is received more than once a day. 
     Therefore, if the predetermined time has not passed since the last successful reception in S 112 , steps S 111  and S 112  repeat. 
     However, if the predetermined time since the last successful reception has passed in S 112 , the automatic reception process unit  52  uses the simple time adjustment process unit  53  and starts the automatic reception process in the same way as described in the first embodiment (S 12 ). The steps executed by the simple time adjustment process unit  53  from S 12  to S 21  are the same as described in the first embodiment, and further description thereof is thus omitted. 
     This second embodiment of the invention has the same effect as the first embodiment. 
     In addition, because four automation reception times are set in S 111 , the possibility of successful reception can be improved compared with setting only one automatic reception time. 
     In addition, because the four automatic reception times are set at two hour intervals, reception is possible with the satellites at different positions, and if reception fails one at one automatic reception time due to the satellite locations, the probability of reception succeeding at the next automatic reception time can be improved. More specifically, because the GPS satellites  5  circle the Earth in approximately 12 hours, the satellite locations change and the reception conditions change if there is approximately two hours between the reception times. 
     Furthermore, because step S 112  checks if a predetermined time has passed since the last successful reception so that reception does not occur more than once a day, execution of the reception process can be minimized and power consumption can be reduced. 
     Embodiment 3 
     A third embodiment of the invention is described next. 
     The condition for running the automatic reception process in the first and second embodiments is whether the time has reached a preset time set, but in this third embodiment is set to whether or not the GPS wristwatch  1  is outdoors. 
     More specifically, the GPS wristwatch  1  according to this third embodiment of the invention has an outdoor detector for determining if the wristwatch  1  is outdoors or not. A solar power generating device or an ultraviolet sensor, for example, may be used as the outdoor detector. 
     If the wristwatch has a solar power generating device, the power output is greater when outdoors exposed to sunlight than when exposed to indoor lighting. Therefore, if the output power is detected to equal or exceed a predetermined level, the GPS wristwatch  1  is known to be outdoors. 
     Furthermore, sunlight contains ultraviolet light but indoor lighting contains substantially no ultraviolet light. Therefore, if the output of the ultraviolet sensor is equal to or exceeds a predetermined level, the GPS wristwatch  1  is known to be outdoors. 
     As shown in  FIG. 14  the automatic reception process unit  52  in the third embodiment first uses the outdoor detector to determine if the GPS wristwatch  1  is outdoors or not (S 113 ). 
     If the GPS wristwatch  1  is determined to be outdoors in S 113 , the automatic reception process unit  52  determines if a predetermined time since the last successful reception has passed (S 114 ). The automatic reception process unit  52  prevents executing the automatic reception process two or more times in one day even if the GPS wristwatch  1  is outdoors by determining if 22 hours, for example, have passed since the last successful reception. 
     If the predetermined time has passed in S 114 , the automatic reception process unit  52  determines if a predetermined time has passed since the last reception process (S 115 ). In this embodiment the automatic reception process unit  52  determines if 10 minutes, for example, have passed as the predetermined time since the last reception process. 
     Step S 115  is executed to prevent repeating the automatic reception process after a short time. More specifically, if in S 113  the GPS wristwatch  1  is detected to be outdoors, and in S 114  22 hours or more are determined to have passed since the last successful reception, the automatic reception process unit  52  executes the reception process. If reception fails this time, reception repeats until the conditions in S 113  and S 114  are satisfied. As a result, if the reception process executes and fails, step S 115  prevents the reception process from repeating until at least the predetermined time (10 minutes) has passed since the failed reception. 
     If S 115  determines that at least the predetermined time has passed, the automatic reception process unit  52  uses the simple time adjustment process unit  53  and starts the automatic reception process in the same way as described in the first embodiment (S 12 ). Thereafter, the simple time adjustment process unit  53  executes the same process as the automatic reception process described in the first embodiment. 
     This third embodiment of the invention has the same effect as the first embodiment. 
     Furthermore, because this embodiment executes the reception process after detecting outdoors in S 113 , the probability of capturing a GPS satellite  5  and reception succeeding can be improved. 
     In addition, because step S 114  checks if a predetermined time (such as 22 hours) since the last successful reception has passed so that reception does not occur more than once a day, the reception process can be minimized and power consumption can be reduced. 
     In addition, because S 115  checks if a predetermined time (such as 10 minutes) has passed since the last reception process, repeating the reception process after a short time can be prevented and depletion of the storage battery  24  can be prevented. 
     Variations 
     The invention is not limited to the embodiments described above. 
     More specifically, the conditions of the invention for executing the automatic reception process are not limited to those described above. For example, scheduled reception whereby reception occurs at a preset time as in the first and second embodiments can be combined with reception based on outdoor detection in the third embodiment. In this situation, if reception is successful at the scheduled time, operation can be controlled to not execute if a predetermined time has not passed since the successful reception even if an outdoor location is detected. Alternatively, if reception succeeds when an outdoor location is detected and the reception process runs, operation can be controlled to not execute the automatic reception process unless a predetermined time has passed since the successful reception, and if reception is successful once in a day, the reception process can be prevented from executing again the same day. 
     The reception condition can also be set so that the automatic reception process executes if the preset time has come and an outdoor location is detected. In this situation the probability of reception succeeding in the automatic reception process can be improved. 
     The timing of the automatic reception process in the first and second embodiments is not limited to the times described above, and other times may be used instead. A configuration enabling the user to set the automatic reception time is also conceivable. More particularly, if the user can set the automatic reception time, the time can be set to a time when reception is easiest based on the user&#39;s daily pattern, and the probability of successful reception can therefore be improved. 
     In the second and third embodiments operation is controlled to limit successful reception to once a day by determining if a predetermined time since the last successful reception has passed in S 112  and S 114 . However, a history of whether reception succeeded or failed can be stored, this history can be checked, and if reception succeeds once in a day, the reception process can be prevented from executing again the same day. 
     For example, the reception history may be reset at midnight (0:00), and if reception then succeeds, a record of successful reception can be stored. The reception process can then be controlled to check the reception history when the reception process is invoked to confirm if reception has already been successful that day. 
     Each of the foregoing embodiments controls the automatic reception process to execute at least once a day, but the interval between automatic reception processes may be increased so that the automatic reception process executes once every other day, for example. This automatic reception process interval may be set appropriately according to the accuracy of the internal time, for example. 
     In the embodiments described above the high precision time adjustment process unit  54  executes the positioning process during manual reception, but a configuration enabling the user to select whether the simple time adjustment process unit  53  or the high precision time adjustment process unit  54  operates during manual reception is also conceivable. If processing by the simple time adjustment process unit  53  is selected for manual reception, the reception process can be completed in a short time, and convenience can be improved. This can improve convenience when there has been no movement between time zones and the reception process is manually invoked. 
     Each of the foregoing embodiments executes the simple time adjustment process by means of the simple time adjustment process unit  53  if GPS satellite  5  capture fails, if acquisition of orbit data fails, or if the positioning calculation fails when the high precision time adjustment process unit  54  executes the high precision time adjustment process, but the reception process may be aborted without running the simple time adjustment process. 
     The foregoing embodiments are described with reference to a GPS satellite as an example of a positioning information satellite, but the positioning information satellite of the invention is not limited to GPS satellites and can be used with Global Navigation Satellite Systems (GNSS) such as Galileo (EU), GLONASS (Russia), and Beidou (China), and other positioning information satellites that transmit satellite signals containing time information, including the SBAS and other geostationary or quasi-zenith satellites. 
     Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.