Abstract:
A positioning device has a reception unit for receiving navigation messages transmitted continuously in a time series from positioning information satellites orbiting the Earth and determines the location of the positioning device based on the navigation messages received by the transmission unit. Each navigation message is segmented into a plurality of data transmission blocks that are transmitted sequentially, a portion of the data transmission blocks carry almanac data containing orbital information for all positioning information satellites including the positioning information satellite transmitting the received navigation message, and the data transmission blocks carrying the almanac data are transmitted non-contiguously. The positioning device also has signal discrimination unit for identifying the start of receiving a data transmission block containing the non-contiguously transmitted almanac data, and identifying the end of receiving the data transmission block containing the almanac data. The reception unit intermittently receives the signals of the data transmission blocks containing the almanac data by receiving the navigation messages in the reception time of the data transmission blocks containing the almanac data identified by the signal discrimination unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Japanese Patent application No. 2006-208594 is hereby incorporated by reference in its entirety.  
       BACKGROUND  
       [0002]     1. Field of Invention  
         [0003]     The present invention relates to a positioning device that determines its own position, to a positioning method, and to a timepiece having the positioning device.  
         [0004]     2. Description of the Related Art  
         [0005]     GPS (global positioning system) receivers are positioning devices that use signals from orbiting satellites to determine the position of the GPS receiver (device).  
         [0006]     GPS devices receive signals from four or more GPS satellites to determine the position of the GPS device. More specifically, the GPS device selects four or more GPS satellites from among the constellation of GPS satellites orbiting the Earth and receives signals from the selected GPS satellites to determine the position of the GPS device.  
         [0007]     The signals from the GPS satellites include orbital information describing the precise orbit of and information about the status of the GPS satellite that is transmitting the signal (called “ephemeris”), and information about the orbits of all GPS satellites in the constellation (called the “almanac”). The ephemeris and almanac are transmitted in a “navigation message.” 
         [0008]     The same almanac is transmitted by all of the GPS satellites and is transmitted in segments due to the large amount of transmitted data. More specifically, as shown in  FIG. 12 , the navigation message is transmitted in one frame containing five subframes. The first three subframes contain clock correction data and high accuracy ephemeris, that is, the detailed orbital information describing the precise orbit and status of the GPS satellite transmitting the signal, and subframes  4  and  5  contain the almanac, that is, the information about the orbits of all GPS satellites. The almanac is further divided into pages 1 to 25. The almanac pages are sequentially transmitted in subframe  4  and subframe  5  until all of the information for one navigation message has been transmitted.  
         [0009]     A Coarse/Acquisition (C/A) code composed of 1023 chips with a value of 1 or 0 is transmitted every 1 ms on a 1574.2 Hz carrier wave from the GPS satellite, and is transmitted superimposed with the navigation message. A unique C/A code is assigned to each GPS satellite, and the C/A code enables the GPS receiver to identify which GPS satellite transmitted the data.  
         [0010]     The GPS receiver generates a signal of the same content as the C/A code assigned to each GPS satellite to synchronize with the signal from the GPS satellite and measure the transmission time from each GPS satellite while demodulating the navigation message from each GPS satellite to acquire the data from the GPS satellites.  
         [0011]     It takes 30 seconds to transmit one complete frame of the navigation message, and it therefore takes 12.5 minutes to acquire all 25 pages of the almanac. A problem with this is that continuously receiving the GPS signals increases power consumption by the GPS receiver and the power supply of the GPS receiver therefore does not last long.  
         [0012]     To solve this problem, Japanese Patent 3744180 (JP11-237462) (paragraph [0011]) teaches a GPS receiver that reduces power consumption by setting a time once a day to receive a certain subset of non-consecutive almanac pages at a 30 second delay and rewrite the internally stored data with the data transmitted from the GPS satellite over a number of reception cycles spanning plural days.  
         [0013]     As shown in  FIG. 13 , however, if the GPS receiver taught in Japanese Patent 3744180 receives one set of almanac pages one day and the user travels a significant distance to a different location before the GPS receiver receives the rest of the almanac pages the next day, the almanac data received before traveling may be rendered invalid. This makes it difficult to use this GPS receiver in devices, such as timepieces, that may travel great distances in a short period of time.  
       SUMMARY OF THE INVENTION  
       [0014]     Instead of receiving the almanac pages in parcels over plural days, the positioning device, positioning method, and timepiece having the positioning device of the present invention enable continuously receiving all pages of the almanac containing orbital information for all positioning satellites in the constellation while still reducing power consumption.  
         [0015]     A first aspect of the invention is a positioning device that has a reception unit for receiving navigation messages transmitted continuously in a time series from positioning information satellites orbiting the Earth and determines the location of the positioning device based on the navigation messages received by the transmission unit. Each navigation message is segmented into a plurality of data transmission blocks that are transmitted sequentially, a portion of the data transmission blocks carry almanac data containing orbital information for all positioning information satellites including the positioning information satellite transmitting the received navigation message, and the data transmission blocks carrying the almanac data are transmitted non-contiguously. The positioning device has a signal discrimination unit for identifying the start of receiving a data transmission block containing the non-contiguously transmitted almanac data, and identifying the end of receiving the data transmission block containing the almanac data. The reception unit intermittently receives the signals of the data transmission blocks containing the almanac data by receiving the navigation messages in the reception time of the data transmission blocks containing the almanac data identified by the signal discrimination unit.  
         [0016]     The navigation messages transmitted continuously in a time series from positioning information satellites are segmented into a plurality of data transmission blocks that are transmitted sequentially, and the data transmission blocks carrying the almanac data are transmitted non-contiguously. A signal discrimination unit identifies the start of receiving a data transmission block containing the non-contiguously transmitted almanac data, and identifies the end of receiving the data transmission block containing the almanac data. The reception unit intermittently receives the signals of the data transmission blocks containing the almanac data by receiving the navigation messages during the reception time of the data transmission blocks containing the almanac data identified by the signal discrimination unit.  
         [0017]     Because the reception unit selectively receives the signals of the data transmission blocks containing the almanac data, the reception unit does not need to remain constantly in the reception state when receiving the navigation message, and thereby reduces power consumption by the positioning device. In addition, the positioning device can also sequentially receive all of the plural data transmission blocks in the navigation messages transmitted in a time series from the positioning information satellites.  
         [0018]     Preferably, the signal discrimination unit detects the transmission time of the data transmission block based on a sign signal generated synchronized to the C/A code that is unique to the positioning information satellite, and identifies the reception start time of a data transmission block containing the almanac data and the reception end time of the data transmission block containing the almanac data based on the sign signal timed to the transmission time.  
         [0019]     This aspect of the invention detects the transmission time of the data transmission block based on a sign signal generated synchronized to the C/A code that is unique to the positioning information satellite, and identifies the reception start time of a data transmission block containing the almanac data and the reception end time of the data transmission block containing the almanac data based on the sign signal timed to the transmission time.  
         [0020]     In other words, this aspect of the invention can accurately identify when reception of a data transmission block containing the almanac data starts and when reception of the data transmission block containing the almanac data ends, and can get highly precise information, by means of a sign signal that is synchronized to the C/A code that is unique to the positioning information satellite.  
         [0021]     In another aspect of the invention the plurality of data transmission blocks is five subframes; and the signal discrimination unit has a control signal unit that outputs a control signal for getting a synchronization signal synchronized to preamble data and TOW data contained in each subframe, and asynchronously acquiring two subframes containing the almanac data based on the sign signal.  
         [0022]     In this aspect of the invention the signal discrimination unit has a control signal unit that outputs a control signal for getting a synchronization signal synchronized to preamble data and TOW data contained in the five subframes asynchronously to the two subframes containing the almanac data that are acquired based on the sign signal.  
         [0023]     This aspect of the invention efficiently captures the two subframes containing the almanac data carried in the navigation messages that are consecutively transmitted in a time series from the positioning satellites.  
         [0024]     In another aspect of the invention the five subframes constitute one frame; and the signal discrimination unit has a counter that, based on the sign signal and the synchronization signal, detects the end of the fifth subframe, which contains almanac data, in a frame, detects the timing of three subframes and two subframes using the sign signal, and outputs a counter signal at this timing; and a signal generating unit that inverts the control signal output from the control signal unit and outputs the inverted control signal, and generates a signal acquired by comparing the inverted control signal and the counter signal.  
         [0025]     In this aspect of the invention the signal discrimination unit has a counter that detects the end of the fifth subframe, which contains almanac data, of a frame, detects the timing of three subframes and two subframes based on the sign signal and the synchronization signal, and outputs a counter signal at this timing; and a signal generating unit that inverts the control signal output from the control signal unit and outputs the inverted control signal, and generates a signal acquired by comparing the inverted control signal and the counter signal.  
         [0026]     The signal generating unit in this aspect of the invention generates a signal by comparing the inverted control signal and the counter signal, thereby more precisely acquiring the timing for intermittent reception by the reception unit, and efficiently reducing power consumption.  
         [0027]     Another aspect of the invention is a positioning method that has a reception unit for receiving navigation messages transmitted continuously in a time series from positioning information satellites orbiting the Earth and determines the location of the positioning device based on the navigation messages received by the transmission unit. Each navigation message is segmented into a plurality of data transmission blocks that are transmitted sequentially, a portion of the data transmission blocks carry almanac data containing orbital information for all positioning information satellites including the positioning information satellite transmitting the received navigation message, and the data transmission blocks carrying the almanac data are transmitted non-contiguously. The positioning method has a signal discrimination unit for identifying the start of receiving a data transmission block containing the non-contiguously transmitted almanac data, and identifying the end of receiving the data transmission block containing the almanac data; and the reception unit intermittently receives the signals of the data transmission blocks containing the almanac data by receiving the navigation messages in the reception time of the data transmission blocks containing the almanac data identified by the signal discrimination unit.  
         [0028]     Another aspect of the invention is a timepiece having a positioning device that has a reception unit for receiving navigation messages transmitted continuously in a time series from positioning information satellites orbiting the Earth and determines the location of the positioning device based on the navigation messages received by the transmission unit. Each navigation message is segmented into a plurality of data transmission blocks that are transmitted sequentially, a portion of the data transmission blocks carry almanac data containing orbital information for all positioning information satellites including the positioning information satellite transmitting the received navigation message, and the data transmission blocks carrying the almanac data are transmitted non-contiguously. The timepiece positioning device has a signal discrimination unit for identifying the start of receiving a data transmission block containing the non-contiguously transmitted almanac data, and identifying the end of receiving the data transmission block containing the almanac data. The reception unit intermittently receives the signals of the data transmission blocks containing the almanac data by receiving the navigation messages in the reception time of the data transmission blocks containing the almanac data identified by the signal discrimination unit.  
         [0029]     The invention can reduce power consumption in a small device such as a timepiece that requires low power consumption and could move long distances in a short period of time, and enables receiving almanac data containing orbital information about all of the positioning information satellites continuously after first receiving the navigation message.  
         [0030]     Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]      FIG. 1  shows a wristwatch with a GPS receiver as an example of a timepiece having a GPS receiver according to the present invention.  
         [0032]      FIG. 2  is a block diagram showing the internal hardware configuration of the GPS wristwatch shown in  FIG. 1 .  
         [0033]      FIG. 3  is a block diagram showing the basic software arrangement of the GPS wristwatch of the invention.  
         [0034]      FIG. 4  is a block diagram of the first storage unit shown in  FIG. 3 .  
         [0035]      FIG. 5  is a block diagram of the second storage unit shown in  FIG. 3 .  
         [0036]      FIG. 6  is a block diagram of the third storage unit shown in  FIG. 3 .  
         [0037]      FIG. 7  is a flow chart describing the operation of the GPS wristwatch according to a preferred embodiment of the invention.  
         [0038]      FIG. 8  is a flow chart of the initialization mode executed in step ST 2  in  FIG. 7 .  
         [0039]      FIG. 9  is a flow chart of the normal processing mode executed in step ST 7  in  FIG. 7 .  
         [0040]      FIG. 10  is a flow chart of the intermittent reception timing program executed in step ST 15  in  FIG. 8 .  
         [0041]      FIG. 11  is a timing chart of the intermittent reception timing program shown in  FIG. 10 .  
         [0042]      FIGS. 12A and 12B  illustrate the structure of the GPS satellite signal.  
         [0043]      FIG. 13  describes the use of a GPS wristwatch in one scenario. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0044]     Preferred embodiments of the present invention are described below with reference to the accompanying figures.  
         [0045]     The embodiments described below are specific desirable examples of the invention and technically desirable limitations are described, but the scope of the invention is not limited to these embodiments except as may be specifically described below.  
         [0046]      FIG. 1  shows a timepiece having a positioning device according to the invention.  FIG. 1  schematically describes a wristwatch  10  with a GPS receiver (referred to below as a GPS wristwatch  10 ), and  FIG. 2  is a block diagram showing the internal hardware configuration of the GPS wristwatch  10  shown in  FIG. 1 .  
         [0047]     As shown in  FIG. 1  this GPS wristwatch  10  has a dial  12  with long and short hands  13  on the front, a display  14  such as an LCD module for displaying information, and an operating unit  27  used for manual operations by the user.  
         [0048]     As shown in  FIG. 1  the GPS wristwatch  10  has an antenna  11 , and the antenna  11  is used to receive signals from GPS satellites  15   a  to  15   d  orbiting the Earth on specific orbits.  
         [0049]     These GPS satellites  15   a  to  15   d  are simply one example of positioning system satellites.  
         [0050]     As shown in  FIG. 2  the GPS wristwatch  10  has an internal timekeeping unit and a GPS unit, and is arranged to function as a computer.  
         [0051]     More specifically, the timekeeping unit in this embodiment of the invention renders an electronic timepiece.  
         [0052]     The arrangement shown in  FIG. 2  is further described below.  
         [0053]     As shown in  FIG. 2  the GPS wristwatch  10  has a bus  16  to which are connected a CPU  17 , RAM  18 , ROM  19 , and other devices.  
         [0054]     Also connected to the bus  16  is a positioning unit, which in this aspect of the invention is a GPS receiver by way of example. More specifically, the antenna  11 , a filter (SAW)  20 , RF unit  21 , and baseband unit  22  are connected to the bus  16 .  
         [0055]     Signals received from the GPS satellites  15   a  to  15   d  shown in  FIG. 1  are thus passed from the antenna  11  through the filter (SAW)  20  and RF unit  21  and extracted by the baseband unit  22  as the GPS signal.  
         [0056]     The signals received from the GPS satellites  15   a  to  15   d  are described in further detail below.  
         [0057]     A timekeeping unit is also connected to the bus  16 . More specifically, a real-time clock (RTC)  23  and temperature-compensated crystal oscillator (TCXO)  24  are connected as the timekeeping unit.  
         [0058]     The display  14  shown in  FIG. 1  is also connected to the bus  16 .  
         [0059]     The bus  16  is thus an internal bus with the addresses and data paths needed to connect all of the other requisite devices.  
         [0060]     The RAM  18  is working memory used by the CPU  17  to execute programs and control the ROM  19  and other devices connected to the bus  16 . The ROM  19  stores the programs and other data.  
         [0061]     The GPS unit is an example of a receiver for receiving navigation messages transmitted from positioning satellites such as the GPS satellites  15   a  to  15   d.    
         [0062]     The operating unit  27  is also connected to the bus  16  for accepting input from the user.  
         [0063]      FIG. 3  to  FIG. 6  are block diagrams showing the basic software structure of the GPS wristwatch  10 ,  FIG. 3  being an overview.  
         [0064]     As shown in  FIG. 3  the GPS wristwatch  10  has a control unit  26  that controls overall operation. Connected to the control unit  26  are a power supply  25 , the antenna  11 , the display  14 , the operating unit  27 , the real-time clock (RTC)  23 , and the other devices shown in  FIG. 2 . While not shown in  FIG. 2 , a signal discriminator  28  for generating a signal controlling the power output of the power supply  25  is also connected to the control unit  26 . This signal discriminator  28  is a PLL circuit or counter, for example, disposed to the baseband unit  22  shown in  FIG. 2 . The control unit  26  runs the programs and processes the data stored in the first storage unit  30 , the second storage unit  40 , and the third storage unit  50 .  
         [0065]      FIG. 3  to  FIG. 6  show the programs, data storage units storing preset data, and data storage units storing data after processing by the programs as being respectively stored in the first storage unit  30 , the second storage unit  40 , and the third storage unit  50 . However, these programs and data are not necessarily stored separately as shown in the figures, and the programs, data storage units storing preset data, and data storage units storing data after processing by the programs are not necessarily rendered separately but are shown this way for simplicity.  
         [0066]      FIG. 4  is a block diagram showing the internal arrangement of the first storage unit  30  shown in  FIG. 3 . As shown in  FIG. 3 , the first storage unit  30  has a initialization mode program storage unit  31  and a initialization mode positioning data storage unit  32 . As shown in  FIG. 4 , a initialization mode selection program  311 , a initialization mode execution program  312 , and an intermittent reception program  313  are stored in the initialization mode program storage unit  31 , and the first frame data  322  and the almanac data  323  that are acquired by the initialization mode execution program  312  and the intermittent reception program  313  are stored in the initialization mode positioning data storage unit  32 . The subframe data in the first frame data  322  is stored to areas a to e.  
         [0067]     The almanac data  323  shown in  FIG. 4  includes all of the almanac data contained in the navigation message except for the almanac data in the first data frame  322  of the navigation message. The data  322 ,  323  stored in the initialization mode positioning data storage unit  32  is overwritten by the positioning data acquired in the initialization mode the next time the programs in the initialization mode program storage unit  31  run. The data  322 ,  323  in the initialization mode positioning data storage unit  32  is therefore kept until the positioning data is acquired in the initialization mode the next time the programs in the initialization mode program storage unit  31  run. The programs in the initialization mode program storage unit  31  are run, for example, the first time the power is turned on after the GPS wristwatch  10  is purchased or when the power is turned on again after being turned and left off for several months after the positioning data is first acquired.  
         [0068]      FIG. 5  is a block diagram showing the internal arrangement of the second storage unit  40  shown in  FIG. 3 . As shown in  FIG. 3  the second storage unit  40  has a normal mode program storage unit  41  and a normal mode positioning data storage unit  42 . As shown in  FIG. 5 , a normal mode selection program  411  and a normal mode execution program  412  are stored in the normal mode program storage unit  41 , and non-almanac data  422  is stored in the normal mode positioning data storage unit  42 . The non-almanac data  422  includes the data in the subframes other than the subframes containing the almanac data in the navigation messages transmitted from the GPS satellites. More specifically, the navigation message carries information about the health and status of the GPS satellite that is transmitting the navigation message (called “satellite correction data” below) and ephemeris describing the precise orbit of the transmitting satellite in subframes  1  to  3 , and the data in the non-almanac data  422  is the data from subframes  1  to  3  as shown in  FIG. 12A .  
         [0069]     The subframe data in the non-almanac data  422  is unique to a particular GPS satellite. The programs stored in the normal mode program storage unit  41  are therefore run at a regular interval to acquire the subframes containing the satellite correction data and emphemeris, and this subframe data overwrites the non-almanac data  422  stored in the normal mode positioning data storage unit  42 .  
         [0070]      FIG. 6  is a block diagram showing the internal arrangement of the third storage unit  50  shown in  FIG. 3 . As shown in  FIG. 3  the third storage unit  50  has another program storage unit  51 , another data storage unit  52 , and an other data storage unit  53 .  
         [0071]     The other program storage unit  51  stores satellite signal capture programs that are run when executing the programs stored in the initialization mode program storage unit  31  and the normal mode program storage unit  41 , and programs for correcting the internal clock of the GPS wristwatch  10  based on time information carried in the navigation message transmitted from the GPS satellite.  
         [0072]     The other data storage unit  52  stores data that is required when running the programs stored in the initialization mode program storage unit  31  and the normal mode program storage unit  41 . The data stored in the other data storage unit  52  includes preset data stored in a C/A code storage unit  521  and initialization mode selection conditions storage unit  522 , and data that can be overwritten by the user in a threshold time settings storage unit  523 .  
         [0073]     The other data storage unit  53  stores data resulting from running the programs stored in the initialization mode program storage unit  31 , the normal mode program storage unit  41 , and the other program storage unit  51 .  
         [0074]      FIG. 7  to  FIG. 10  are flow charts describing the main steps in the operation of the GPS wristwatch  10 .  
         [0075]     The programs and data shown in  FIG. 3  to  FIG. 6  are described in further detail below while describing the operation of the GPS wristwatch  10  according to this embodiment of the invention with reference to the flow charts in  FIG. 7  to  FIG. 10 .  
         [0076]     In order to set the time kept by the real-time clock (RTC)  23  (timekeeping unit) of the GPS wristwatch  10 , the user first turns the GPS wristwatch  10  power on. This causes the GPS wristwatch  10  to run the initialization step ST 1  shown in  FIG. 7  so that the initialization mode selection program  311  in the initialization mode program storage unit  31  shown in  FIG. 4  executes to select the initialization mode selection conditions  522   a  in the initialization mode selection conditions storage unit  522  in the other data storage unit  52  shown in  FIG. 6 .  
         [0077]     The initialization mode selection conditions  522   a  in this aspect of the invention are: when data has not yet been stored in the initialization mode positioning data storage unit  32  of the GPS wristwatch  10 , such as when the power is turned on the first time after the GPS wristwatch  10  is purchased; when data is stored in the initialization mode positioning data storage unit  32  but the normal processing mode in step ST 7  does not end and the time cannot be corrected because, for example, several months have passed since the initialization mode positioning data was acquired or the power has been off for several months; or the user asserts a command for manual initialization in step ST 9 .  
         [0078]     Step ST 2  in  FIG. 7  executes next.  
         [0079]      FIG. 8  is a flow chart of the initialization mode execution step ST 2  shown in  FIG. 7 .  
         [0080]      FIG. 10  is a flow chart of the intermittent reception program executed in step ST 15  in  FIG. 8 .  
         [0081]      FIG. 11  describes the operation of the intermittent reception program in  FIG. 10 .  FIG. 11  (a) represents the C/A code, (b) shows the subframes of the navigation message transmitted from the GPS satellite, (c) shows the output signal after controlling the telemetry word TLM and handover word HOW (preamble and time of week TOW synchronization pulse) output from the PLL circuit with a phase comparator and locking (synchronizing) subframes  1  to  3 , (d) shows the output pulse of the counter, (e) is the inversion of the output signal shown in (c), and (f) shows the power supply signal waveform output from a signal discriminator linked to the power supply  25  shown in  FIG. 3 . These signals (a) to (f) are referenced to the same time base in  FIG. 11 .  
         [0082]     The almanac data containing orbital information for all satellites is intermittently received primarily in the initialization mode as described below with reference to  FIG. 8 ,  FIG. 10 , and  FIG. 11 .  
         [0083]     The initialization mode starts by scanning for a GPS satellite  15   a  in step ST 11  in  FIG. 8 . More specifically, the GPS unit shown in  FIG. 2  operates to receive transmissions from the GPS satellites  15   a  through the antenna  11  and search for the GPS satellites  15   a  from which signals can be captured.  
         [0084]     If signals from at least four GPS satellites  15   a  can be captured (step ST 12  returns Yes), control goes to step ST 15 . If signals from at least four GPS satellites  15   a  cannot be captured (step ST 12  returns No), control goes to step ST 13 . Step ST 13  determines that reception is not possible because the GPS satellite signals cannot be detected. A message instructing the user to proceed with manual operation is then presented on the display  14  shown in  FIG. 1  and  FIG. 2  (step ST 14 ), and the GPS signal reception mode is turned off.  
         [0085]     Step ST 15  runs the intermittent reception program  313  shown in  FIG. 4  to receive signals from the captured GPS satellites  15   a.  The intermittent reception program  313  shown in  FIG. 4  proceeds as shown in the flow chart in  FIG. 10 . The intermittent reception program  313  is run by the control unit  26  in conjunction with the signal discriminator  28  shown in  FIG. 3 .  
         [0086]     The structure of the GPS signals transmitted from each of the GPS satellite  15   a  is shown in  FIG. 12A  and described below.  
         [0087]     As shown in  FIG. 12A , each GPS satellite  15   a  transmits signals in data frame units and transmits one frame every 30 seconds. Each frame consists of five subframes, and one subframe is transmitted every 6 seconds. Each subframe contains 10 words (1 word is 0.6 second).  
         [0088]     The first word in each subframe is a telemetry (TLM) word, and each TLM word starts with a preamble as shown in  FIG. 12B .  
         [0089]     The TLM word is followed by a handover word HOW, and each HOW starts with the time of week TOW indicating the GPS time information of the GPS satellite.  
         [0090]     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 same GPS week number is added to the GPS time throughout the week, and the GPS receiver can therefore get the precise GPS time by reading the week number and the elapsed time (number of seconds). The GPS time is referenced to the Coordinated Universal Time (UTC).  
         [0091]     The receiver must synchronize with the signal from the GPS satellite  15   a  in order to receive the frame data from a particular GPS satellite  15   a,  and the C/A code is used for synchronization with 1 ms precision. The C/A code is a 1023-chip pseudo random noise code that repeats every  1  ms.  
         [0092]     Signals from the GPS satellites  15   a  are transmitted as described above. As a result, this embodiment of the invention is phase synchronized with the C/A code from each selected GPS satellite  15   a  and generates a clock signal (sign signal) in step ST 71  in  FIG. 10 . The GPS receiver uses the data in the C/A code storage unit  521  shown in  FIG. 6  for phase synchronization with the C/A code from each GPS satellite  15   a  and thereby synchronize with the GPS satellite  15   a  signal.  
         [0093]     Control then goes to step ST 72  to synchronize with the preamble of the TLM word and the TOW in the HOW word shown in  FIG. 12B . As shown in  FIG. 12A , the data in each subframe, including the ephemeris (precise orbital information for a particular GPS satellite  15   a ) and the almanac (orbital information for all GPS satellites  15   a ) and the UTC, is received to acquire the data for the first frame. Receiving the first frame takes 30 seconds.  
         [0094]     The frame and subframes shown in  FIG. 12  show an example of a specific unit of a satellite signal in which the TOW is an example of the time information of a positioning information satellite (such as a GPS satellite  15   a ) and the TLM and HOW words are examples of time-related information units, and the names of the parts where the ephemeris and almanac data are stored are examples of the time and other transmission information units.  
         [0095]     In step ST 73  the data acquired in step ST 72  is stored sequentially by subframe unit to the first frame data  322  storage areas a to e in the initialization mode positioning data storage unit  32  shown in  FIG. 4 .  
         [0096]     Control then goes to step ST 74 . As shown in  FIG. 12B , the subframe data includes the preamble of the TLM word and the TOW in the HOW word, and this data is common to each subframe. By using this common data to compare each subframe, the end of the subframe  5  containing the almanac data portion of the frame data can be detected from the subframe data stored in areas a to e of the first data frame  322  acquired in step ST 73 . A counter N is initialized to 0 when the first data frame is received, is then incremented to N=N+1 whenever the end of subframe  5  is detected, and reception continues until N≧power supply  25  when control then goes to step ST 83 .  
         [0097]     Control goes from step ST 74  to ST 75  and a counter pulse is output from a counter (not shown in the figure) set in the baseband unit  22  shown in  FIG. 2  at alternating 18 second and 12 second intervals. These 18 second and 12 second intervals are equal to the transmission time required to receive subframes  1  to  3  and subframes  4  and  5 , respectively, of the navigation message transmitted form the GPS satellite  15   a.  As shown in  FIG. 11 ( d ), the counter pulse is a rectangular wave that alternates between 0 and 1 where 0 is the base, outputs 0 for 18 seconds from the end of subframe  5 , then outputs 1 for 12 seconds, and then repeats.  
         [0098]     Step ST 76  synchronizes the preamble and then the TOW word based on the subframe data acquired in step ST 72 , and outputs the synchronization pulses.  
         [0099]     As indicated by the solid line in  FIG. 11 ( c ), the synchronization pulses are rectangular wave pulses that alternate between 1 and 0 during the 6 second period required to transmit the data for each subframe. More specifically, the synchronization pulses are rectangular wave pulses that go to 1 for the time required to transmit the TLM and HOW words containing the preamble and TOW data (that is, for 1.2 second from the beginning of the subframe) and then go to 0 for the time required to transmit the remaining subframe data (that is, for 4.8 seconds).  
         [0100]     In step ST 77 , the signals output in step ST 76  are input to the phase comparator of the PLL circuit in the baseband unit  22  shown in  FIG. 2 . This phase comparator controls the locked (synchronous) and unlocked (asynchronous) phases, and the signals are output from the PLL circuit after locking/unlocking control. The resulting synchronization signal is shown in  FIG. 11 ( c ) where the solid line denotes the unlocked phase corresponding to the subframe  4  and subframe  5  transmission time, and the dotted line denotes the locked phase corresponding to the subframe  1  to subframe  3  transmission time. This locked/unlocked control time is based on the clock signal (sign signal) acquired by synchronization with the C/A code.  
         [0101]     In step ST 78  the sign of the output signal acquired from the PLL circuit in step ST 77  is inverted. As shown schematically in  FIG. 11 ( e ), inverting the sign changes the signal levels of 1 and 0 described in  FIG. 11 ( c ) to −1 and 0, and produces a replica of the signal (rectangular wave pulse) shown in  FIG. 11 ( c ).  
         [0102]     Step ST 79  compares the counter pulse signal output in step ST 75  and the inverted signal output from the PLL circuit in step ST 78  to acquire the reception mode/pause mode power signal shown in  FIG. 11 ( f ) controlling the intermittent reception timing. The power supply sequence in  FIG. 11 ( f ) shows enabling the reception mode during the transmission of the data other than the TLM and HOW words in subframe  4  and subframe  5 , and entering the pause mode during transmission of subframes  1  to  3  and during transmission of the TLM and HOW words in subframe  4  and subframe  5 . This power supply wave controls the power supply  25  shown in  FIG. 2  and  FIG. 3  to receive only the required portions of the navigation message from the GPS satellite  15   a  through the antenna  11 . While data spread across 25 pages must be received in order to receive the entire almanac transmitted in the navigation message, the invention can accurately receive the almanac without receiving the TLM and HOW words in subframe  4  and subframe  5  and can also reduce power consumption by controlling switching between the reception mode and the pause mode, that is, turning the reception mode on and off.  
         [0103]     The almanac can also be accurately acquired because a clock signal (sign signal) is created synchronized to the C/A code in the received navigation message and the signals shown in  FIG. 11 ( a ) to ( f ) are controlled by this clock signal.  
         [0104]     Furthermore, because power consumption is reduced without dividing almanac reception over different days, the positioning device of the invention can be easily incorporated into small devices such as a wristwatch.  
         [0105]     At the intermittent reception timing of the power supply signal shown in  FIG. 11 ( f ) and acquired in step ST 79 , steps ST 80 , ST 81 , and ST 82  get the subframe  4  and subframe  5  data other than the TLM and HOW word portions and store the acquired data as the almanac data  323  shown in  FIG. 4 . Steps ST 80  to ST 82  repeat until all almanac data in the navigation message transmitted from the GPS satellite  15   a  is acquired. When all almanac data has been received, step ST 83  ends the intermittent reception program.  
         [0106]     Control then goes to step ST 16  in  FIG. 8  to get the UTC data by intermittent reception. In step ST 17  the GPS wristwatch  10  then measures the pseudo-satellite-distance from each satellite based on the data acquired from each satellite. More specifically, the pseudo-satellite-distance calculation program  513  shown in  FIG. 6  measures the signal transmission time from each of the GPS satellites  15   a  (the time it took the signals to travel from the GPS satellite to the GPS wristwatch  10 ) using the internal real-time clock (RTC)  23 , and based on this transmission time and the speed of light (the speed of electromagnetic wave transmission: c) calculates the distance between the GPS wristwatch  10  and each of the four GPS satellites  15   a  from which the emphemeris was received. The calculated data is then stored in the calculated pseudo-satellite-distance storage unit  531  shown in  FIG. 6 . This data is rewritable and the satellite distance is also calculated in the normal processing mode. The data calculated at this time is stored in the calculated pseudo-satellite-distance storage unit  531  shown in  FIG. 6  and is overwritten after a specific period of time.  
         [0107]     The receiver data measurement program  514  shown in  FIG. 6  is then executed in step ST 18  to calculate the position and altitude of the GPS wristwatch  10  and the true signal transmission delay time in four simultaneous equations based on the pseudo-satellite-distance calculated for each of the four GPS satellites, and thereby calculate the position and altitude of the GPS wristwatch  10  and the true signal transmission delay time. This provides the true transmission delay time and the transmission delay time measured by the real-time clock (RTC)  23 . This data is then stored in the receiver data measurement storage unit  532  shown in  FIG. 6 . The data stored in the receiver data measurement storage unit  532  is also measured when the normal processing mode described below executes, and is overwritten after a prescribed amount of time.  
         [0108]     The receiver data measurement program  514  shown in  FIG. 6  then generates and stores in the receiver data measurement storage unit  532  the time required to receive the signals transmitted from the four GPS satellites  15   a  referenced to the actually measured transmission delay time, the calculated true transmission delay time and the position of the GPS wristwatch  10 , and the transmission delay time as measured by the real-time clock (RTC)  23 .  
         [0109]     The determined position is then stored as the positioning data in the receiver data measurement storage unit  532  shown in  FIG. 6 . The difference (the offset time) between the true transmission delay time calculated in step ST 18  and the transmission delay time measured by the real-time clock (RTC)  23  is also stored in the receiver data measurement storage unit  532 .  
         [0110]     The time correction program  515  shown in  FIG. 6  then runs in step ST 19  to offset (adjust) the RTC time data stored in the RTC time data storage unit  533  based on the offset time stored in the receiver data measurement storage unit  532 . As described above, the offset time is the difference between the true transmission delay time and the transmission delay time measured by the real-time clock (RTC)  23 .  
         [0111]     Based on the current position of the GPS wristwatch  10  and the offset time determined using the pseudo-satellite-distances calculated from the navigation messages received from each of the GPS satellite  15   a,  the time correction program  515  thus adjusts the RTC time data of the internal clock based on the offset time. UTC data is also stored in the RTC time data storage unit  533  shown in  FIG. 6  in addition to the RTC time data.  
         [0112]     Next, as shown in step ST 20 , the display on the dial  12  is adjusted based on the RTC time data storage unit  533  shown in  FIG. 6 , which includes the UTC reference data acquired from the GPS satellites  15   a.  The time at the current location, such as Japanese Standard Time, is thus displayed on the dial  12  to reflect the time difference.  
         [0113]     Referring again to the flow chart in  FIG. 7 , step ST 3  determines if the initialization mode ended normally. If it did not end normally (step ST 3  returns No), control goes to step ST 4  and the manual display program  512  shown in  FIG. 6  is run to display a prompt asking the user to manually select the operating mode.  
         [0114]     If the user selected the initialization mode in step ST 9 , control loops back to step ST 2  in  FIG. 7 . If the initialization mode is not selected, control goes to step ST 7  and the normal processing mode executes. This initialization mode selection condition is one of the initialization mode selection conditions  522   a  stored in the initialization mode selection conditions storage unit  522  shown in  FIG. 6 .  
         [0115]     If the initialization mode terminates normally (step ST 3  returns Yes), control goes to step ST 5 . In step ST 5  the threshold time setting, which is the normal mode selection threshold time (such as 24 hours), stored in the threshold time settings storage unit  523  shown in  FIG. 6  is read and then counted by the threshold time timer execution program  511 . Step ST 6  then determines if 24 hours have passed. If 24 hours have passed, control goes to step ST 7  and the normal processing mode executes. If 24 hours have not passed, the threshold time timer execution program  511  continues counting and counts until 24 hours have passed. The normal mode selection program  411  shown in  FIG. 5  runs when the time counted by the threshold time timer execution program  511  reaches 24 hours, and the normal mode execution program  412  then executes.  
         [0116]      FIG. 9  is a flow chart showing the steps of the normal processing mode executed in step ST 7  in  FIG. 7 . Steps ST 21  to ST 24  in  FIG. 9  are the same as steps ST 11  to ST 14  in  FIG. 8 , and further description thereof is omitted here. More specifically, the process corresponding to step ST 11  in  FIG. 8  is step ST 21  in  FIG. 9 , the process corresponding to step ST 12  in  FIG. 8  is step ST 22  in  FIG. 9 , the process corresponding to step ST 13  in  FIG. 8  is step ST 23  in  FIG. 9 , and the process corresponding to step ST 14  in  FIG. 8  is step ST 24  in  FIG. 9 .  
         [0117]     If signals from four or more GPS satellites  15   a  are captured in step ST 22 , control goes to step ST 25 . Step ST 25  gets the data in the navigation message other than the data acquired in the initialization mode executed in step ST 2 . In this case the GPS wristwatch  10  first uses the data in the internal C/A code storage unit  521  shown in  FIG. 6  to synchronize with the C/A code from a specific GPS satellite  15   a.  The GPS wristwatch  10  then synchronizes with the preamble of the TLM word and the TOW of the HOW word that are contained in the navigation messages from the GPS satellite  15   a.  Referring to  FIG. 12A , the data other than the almanac data carried in subframe  4  and subframe  5 , that is, the ephemeris, UTC code, and clock correction data, are thus read and written to the non-almanac data  422  in the normal mode positioning data storage unit  42  shown in  FIG. 5 . It is not necessary to read the almanac data at this time because the almanac data was already read in the initialization mode in step ST 2  and stored to the initialization mode positioning data storage unit  32 . As a result, the normal processing mode only needs to read the data in subframes  1  to  3  in the navigation message from each GPS satellite  15   a  as shown in  FIG. 12A .  
         [0118]     More specifically, after synchronizing with the C/A code, the GPS wristwatch  10  operates in the reception mode for only the time needed to synchronize to the preamble of each TLM word and the TOW of each HOW word and capture subframes  1  to  3  (that is, 18 seconds). Power consumption is thereby reduced.  
         [0119]     In step ST 26  the pseudo-satellite-distance calculation program  513  shown in  FIG. 6  calculates the pseudo-satellite-distance for each satellite based on the data stored in the non-almanac data  422  and the data acquired in the initialization mode in step ST 2  and stored to the initialization mode positioning data storage unit  32 , and writes the calculated distances to the calculated pseudo-satellite-distance storage unit  531 .  
         [0120]     The pseudo-satellite-distance calculation program  513  calculates the pseudo-satellite-distances using the same method described in step ST 17  in  FIG. 8 .  
         [0121]     Control then goes to step ST 27  and the receiver data measurement program  514  shown in  FIG. 6  runs to calculate the position and altitude of the GPS wristwatch  10  and the true transmission delay time using the method described in step ST 18  in  FIG. 8 . The true transmission delay time and the transmission delay time measured by the real-time clock (RTC)  23  are stored in the receiver data measurement storage unit  532  shown in  FIG. 6 , overwriting and updating the data acquired in the initialization mode in step ST 2 .  
         [0122]     The receiver data measurement program  514  shown in  FIG. 6  then generates and stores in the receiver data measurement storage unit  532  the time required to receive the signals transmitted from the four GPS satellites  15   a  referenced to the actually measured transmission delay time, the calculated true transmission delay time and the position of the GPS wristwatch  10 , and the transmission delay time as measured by the real-time clock (RTC)  23 . These values overwrite and update the values acquired in the initialization mode in step ST 2 .  
         [0123]     The determined position is then stored as the positioning data in the receiver data measurement storage unit  532  shown in  FIG. 6 , overwriting and updating the value acquired in the initialization mode in step ST 2 . The difference (the offset time) between the true transmission delay time calculated in step ST 18  and the transmission delay time measured by the real-time clock (RTC)  23  is also stored in the receiver data measurement storage unit  532 , overwriting and updating the value acquired in the initialization mode in step ST 2 .  
         [0124]     The time correction program  515  shown in  FIG. 6  then runs in step ST 19  to offset (adjust) the RTC time data stored in the RTC time data storage unit  533  based on the offset time stored in the receiver data measurement storage unit  532 . As described above, the offset time is the difference between the true transmission delay time and the transmission delay time measured by the real-time clock (RTC)  23 .  
         [0125]     Based on the current position of the GPS wristwatch  10  and the offset time determined using the pseudo-satellite-distances calculated from the navigation messages received from each of the GPS satellite  15   a,  the time correction program  515  thus adjusts the RTC time data of the internal clock based on the offset time. UTC data is also stored in the RTC time data storage unit  533  shown in  FIG. 6  in addition to the RTC time data.  
         [0126]     Next, as shown in step ST 20 , the display on the dial  12  is adjusted based on the RTC time data storage unit  533  shown in  FIG. 6 , which includes the UTC reference data acquired from the GPS satellites  15   a.  The time at the current location, such as Japanese Standard Time, is thus displayed on the dial  12  to reflect the time difference.  
         [0127]     If the normal processing mode ends normally, step ST 8  in  FIG. 7  returns to step ST 5  to resume counting the normal mode selection threshold time so that the data is updated every 24 hours.  
         [0128]     If the normal processing mode does not end normally, control returns to step ST 2 , the initialization mode runs, and the new almanac is received.  
         [0129]     The invention is described using a GPS wristwatch  10  by way of example, but the method of acquiring the almanac data in the initialization mode according to the present invention can obviously be used in other small devices.  
         [0130]     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.