JP2008151737A - Gps receiver and receiving method by the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GPS receiver having a reduced phase search amount in a synchronism retaining section. <P>SOLUTION: The GPS receiver contains a synchronously capturing section 104 that detects the code phase of a diffusion code of a reception signal from a GPS satellite to synchronously capture the reception signal, and detects the carrier frequency of a reception signal when the reception signal is synchronously captured. The synchronously capturing section 104 is caused to synchronously capture reception signals sequentially in the order of decreasing Doppler frequencies for each GPS satellite. The synchronous capturing section 104, when it detects carrier frequencies, is caused to sequentially feed the detected code phases and carrier frequencies to a synchronism retaining section, before the synchronously capturing for another GPS satellite is completed (S212, S300, S214, S216, S400, and S218). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a GPS receiver having a synchronization acquisition unit and a synchronization holding unit, and a reception method of the GPS receiver.

Conventionally, as a GPS receiver that measures the position of a moving object using an artificial satellite (GPS satellite), the code phase of the spread code of the received signal from the GPS satellite is detected and the received signal is synchronized and received. A synchronization acquisition unit that detects the carrier frequency of the received signal when the signal is acquired, and holds the synchronization of the code phase and carrier frequency of the spread code detected by the synchronization acquisition unit and a signal from a GPS satellite There is a GPS receiver provided with a synchronization holding unit that performs demodulation of (see, for example, Patent Document 1).
Japanese Patent No. 3726897

  In the GPS receiver described in Patent Document 1, a received signal from a GPS satellite is captured in a memory, and the synchronization acquisition unit sequentially converts the code phase of the spread code of the received signal for each GPS satellite. Detection and synchronization of the received signal are performed.

  In addition, after the received signal from the GPS satellite is buffered in the memory, a processing delay occurs until the code phase and carrier frequency of the spread code detected by the synchronization acquisition unit are sent to the synchronization holding unit. The unit re-searches the code phase in the vicinity of the initial value using the phase of the spread code and the carrier frequency of the received signal detected by the synchronization acquisition unit as the phase of the spread code and the initial value of the IF carrier in the synchronization holding unit. I am doing so. Then, after synchronization is established by this re-search, synchronization of the spreading code and carrier frequency is held for the signal from the GPS satellite, and data transmitted from the GPS satellite is demodulated (paragraph numbers 0307 to 0317). .

  For example, when receiving signals from four GPS satellites are captured and held in synchronization, the received signals from the four GPS satellites A to D are buffered in the memory as shown in FIG. Thus, the synchronization acquisition process is sequentially performed on the GPS satellites A to D. The synchronization holding unit, after completing all the synchronization acquisition for the GPS satellites A to D by the synchronization acquisition unit, in parallel with the GPS satellites A to D, the code of the spreading code of each received signal detected by the synchronization acquisition unit Using the phase and carrier frequency as the code phase of the spreading code and the initial value of the IF carrier in the synchronization holding unit, a process for re-searching the code phase within a predetermined range with the initial value as a reference is started. When the re-search of the code phase is completed and synchronization is established, the signals from the GPS satellites are held in sync with the spread code and carrier frequency and demodulated data transmitted from the GPS satellites.

  Here, if the data buffer time is T0, the synchronization acquisition times of GPS satellites A to D are TA, TB, TC, TD, the Doppler frequencies of GPS satellites A to D are Δfd, and the carrier frequency of the GPS satellite signals is frf. The phase change amount of the spread code due to the Doppler shift of the GPS satellite from the start of the buffering of the received signal to the memory is expressed as follows.

Phase change amount of spread code = (T0 + TA + TB + TC + TD) · Δfd / frf
In consideration of the worst value of the phase change amount of the spread code (for example, -5 Hz <Δfd <+5 Hz), the code phase search range of the synchronization holding unit is determined.

  However, the GPS receiver described in Patent Document 1 sends the code phase and carrier frequency of the spread code detected by the synchronization acquisition unit to the synchronization holding unit after the received signal from the GPS satellite is buffered in the memory. Since the time until the synchronization holding unit starts searching (T0 + TA + TB + TC + TD) is relatively long, it is necessary to widen the phase search range of the synchronization holding unit. As a result, there is a problem that it takes time until the first positioning is completed after the GPS receiver is activated.

  The present invention has been made in view of the above problems, and an object thereof is to reduce the amount of phase search of the synchronization holding unit.

  The first feature of the present invention is that the code phase of the spread code of the received signal from the GPS satellite is detected to acquire the synchronization of the received signal, and the carrier frequency of the received signal when the received signal is acquired. A GPS receiver comprising: a synchronization acquisition unit that performs detection; and a synchronization holding unit that maintains synchronization of a spread code of a received signal whose code phase and carrier frequency have been detected by the synchronization acquisition unit. On the other hand, for each GPS satellite, the reception signal is sequentially acquired, and when the code phase and the carrier frequency are detected by the synchronization acquisition unit, they are sequentially detected before the synchronization acquisition for other GPS satellites is completed. And a synchronization acquisition control means for sending the code phase and the carrier frequency to the synchronization holding unit.

  In such a configuration, the synchronization acquisition unit sequentially acquires the reception signal for each GPS satellite. When the code phase and the carrier frequency are detected by the synchronization acquisition unit, the synchronization acquisition unit acquires the synchronization acquisition for other GPS satellites. Since the detected code phase and carrier frequency are sequentially transmitted to the synchronization holding unit before the completion, the synchronization holding unit starts a search for the sequential code phase when receiving the code phase and the carrier frequency from the synchronization acquisition unit. Therefore, the amount of phase search of the synchronization holding unit can be reduced.

  The second feature of the present invention includes Doppler frequency calculation means for calculating a Doppler frequency of a received signal from a GPS satellite, and the transmission control means receives signals in descending order of Doppler frequency calculated by the Doppler frequency calculation means. It is to perform synchronous acquisition of signals.

  The phase search amount of the code phase of the synchronization holding unit needs to be increased as the start of synchronization acquisition is delayed and the Doppler frequency of the GPS satellite is increased, but according to the above configuration, in order of increasing Doppler frequency. Since the synchronization of the received signal is performed, the synchronization acquisition is performed so that the Doppler frequency of the satellite that is first synchronized and acquired is the largest, and the Doppler frequency becomes smaller for the satellite that is acquired later and synchronized. It is possible to minimize the amount of phase search.

  A third feature of the present invention is that the synchronization holding unit has a plurality of channels and performs synchronization holding for each channel. The total number of free channels in the synchronization holding unit is larger than 1, and the code phase The free channel determination means for determining whether or not the estimated value of the error is larger than the phase resolution that can be detected by the synchronization holding unit, and the synchronization acquisition control unit is configured such that the total number of free channels in the synchronization holding unit is greater than 1 by the free channel determination unit And when it is determined that the estimated value of the code phase error is larger than the phase resolution that can be detected by the synchronization holding unit, the synchronization holding unit is instructed to start synchronization holding using a plurality of empty channels. It is.

  In such a configuration, when the total number of free channels in the synchronization holding unit is larger than 1 and the estimated value of the code phase error is larger than the phase resolution that can be detected by the synchronization holding unit, a plurality of free channels are provided in the synchronization holding unit. Therefore, the synchronization holding unit can divide the search range by a plurality of designated empty channels and search for the time required for holding synchronization per channel. Can be shortened.

  The fourth feature of the present invention is that the synchronization acquisition control means causes the synchronization acquisition unit to perform synchronization acquisition in the first signal integration time, and then performs the second signal integration longer than the first signal integration time. This is to make the synchronization acquisition unit perform synchronization acquisition in time.

  In such a configuration, after the synchronization acquisition is performed in the first signal integration time, the synchronization acquisition is performed in the second signal integration time longer than the first signal integration time. It is possible to complete the synchronization acquisition earlier than in the case where the synchronization acquisition is performed with the signal integration time.

  In addition, the first to fourth features can be grasped as reception methods of the GPS receiver, respectively.

  A configuration of a GPS receiver according to an embodiment of the present invention is shown in FIG. The GPS receiver 100 includes a TCXO 101, an antenna 102, a frequency conversion unit 103, a synchronization acquisition unit 104, a synchronization holding unit 105, an RTC (Real Time Clock) 106, a RAM 107 as a volatile memory, a flash ROM 108 as a nonvolatile memory, and A CPU 109 is provided.

  The TCXO 101 is a temperature-compensated crystal oscillator, and generates a reference clock (for example, oscillation frequency = 16,368,000 Hz) of the GPS receiver 100.

  The antenna 101 receives radio waves transmitted from GPS satellites and converts them into electrical signals.

  The frequency conversion unit 103 includes a PLL circuit and an AD conversion circuit (not shown), and using this PLL circuit, a received signal received from a GPS satellite (for example, frequency = 1,575,420,000 Hz) is in the intermediate frequency band. An IF signal (for example, frequency = 4,092,000 Hz) is converted, and the IF signal is converted into digital data by an AD conversion circuit.

  The synchronization acquisition unit 104 detects the code phase of the spread code of the reception signal from the GPS satellite to acquire the synchronization of the reception signal, and also detects the carrier frequency of the reception signal when the synchronization acquisition of the reception signal is obtained. . The synchronization acquisition unit 104 has a DSP and a memory (not shown), stores the digital data AD-converted by the frequency conversion unit 103 in the memory, and performs correlation calculation processing on the data stored in the memory with a high-speed clock. By doing so, the code phase, carrier frequency, and satellite ID of the received signal from the GPS satellite are detected at high speed.

  The synchronization holding unit 105 has a not-shown DLL (Delay Locked Loop) circuit, and uses this DLL circuit to hold the synchronization of the spreading code and the carrier frequency detected by the synchronization acquisition unit 104 and to transmit signals from GPS satellites. Demodulate. The synchronization holding unit 105 has a function of detecting a signal level for each channel for which synchronization holding is continued.

  The RTC 106 has a counter (not shown) for measuring time, and counts the real time by this counter.

  The RAM 107 is used as a work memory for the CPU 109. The flash ROM 108 is used as a memory for storing various information such as positioning position information, satellite orbit information, and a search list described later.

  The CPU 109 has a ROM (not shown) and performs various processes according to programs stored in the ROM. The processing of the CPU 109 includes a positioning calculation process for calculating a positioning position (longitude, latitude, altitude) and the like based on information such as a code phase and a Doppler frequency included in a signal output from the synchronization holding unit 105.

  FIG. 2 shows a flowchart of the main process of the CPU 109. When the GPS receiver 100 is activated, the CPU 109 starts the process shown in FIG.

  First, the orbit information of the satellite and the previous positioning position (longitude, latitude, altitude) stored in the flash ROM 108 are read (S200). The flash ROM 108 stores satellite orbit information (almanac, ephemeris) and positioning position (longitude, latitude, altitude), which are periodically updated. Here, the orbit information of the satellite and the previous positioning position (longitude, latitude, altitude) are read from the flash ROM 108.

  Next, the real time (current time) is read from the RTC 106 (S202).

  Next, a satellite (visible satellite) estimated to be receivable at the current position is specified, and a Doppler frequency Fdopp (svid) of the satellite is calculated (S204). Note that svid is a satellite ID for identifying a GPS satellite. Further, the Doppler frequency Fdopp (svid) is the same as Δfd. The calculation of the Doppler frequency Fdopp (svid) is well known, and here, the approximate Doppler frequency Fdopp (svid) is calculated for each satellite from the current position of the GPS receiver 100, the current time, and the orbit information of the satellite.

  Next, information indicating the number of satellites for which synchronization holding has been completed is acquired from the synchronization holding unit 105, and it is determined whether the number of synchronization holding completed satellites is less than a threshold value Nsat (S206). If the number of satellites for which synchronization has been completed is greater than or equal to the threshold Nsat, the determination in S206 is NO and the process returns to S202. When a sufficient number of satellites (threshold value Nsat or more) are held in synchronization in this way, the processing of S202 to S206 is repeated without proceeding to the processing after S208.

  On the other hand, if a sufficient number of satellites (threshold value Nsat or more) are not synchronized, the determination in S206 is NO, and then a list of satellites that require synchronization acquisition (hereinafter referred to as a search list) is created. Then, rearrangement is performed in descending order of the absolute value of the Doppler frequency Fdopp (svid) (S208). Note that immediately after activation of the GPS receiver 100, the determination in S206 is NO, and the processing in S208 is performed.

  Here, the search list will be described. FIG. 3 shows an example of the search list. As shown in the figure, the search list includes a satellite ID, an absolute value of the Doppler frequency Fdopp (svid), search flags 1 and 2, and a start position flag.

  Note that the search flag 1 is an identifier indicating whether or not synchronization acquisition has been completed when the synchronization acquisition process is performed at an integration time Tint1, which will be described later, and the search flag 2 is performed at an integration time Tint2, which will be described later. This is an identifier indicating whether or not synchronization acquisition at the time of completion is completed. The start position flag is an identifier indicating the satellite that is first started in the synchronization acquisition process.

  When no start position flag is specified (start position flag = 0), synchronization acquisition processing is performed in order from the top of the search list. When the start position flag is specified (start position flag = 1), the synchronization acquisition process is performed in order from the satellite with the start position flag specified, and the synchronization acquisition process is performed to the end of the search list. Returning to the top of the search list, synchronization acquisition processing is performed. In this way, the synchronization acquisition process is performed for all the satellites in the search list.

  The start position flag of the search list is reset to 0 when the synchronization acquisition process is started.

  In S208, processing for initializing search flags 1 and 2 in the search list to 0 indicating that processing has not been performed is also performed.

  In the next S210, the IF signal data is acquired and the time counter is reset. Specifically, the digital data converted into the IF signal of the intermediate frequency band by the frequency conversion unit 103 and AD-converted by the AD conversion circuit is stored in the memory of the synchronization acquisition unit 104, and the process from the time when the digital data is stored in the memory Reset the time counter that counts the time. The time counter starts counting elapsed time since reset.

  In S212, S300, and S214, according to the search list, the synchronization acquisition unit 104 sequentially performs synchronization acquisition of the received signal for each GPS satellite. When the carrier frequency is detected by the synchronization acquisition unit, another GPS satellite is detected. Before the acquisition of the synchronization with respect to is completed, a process of sequentially transmitting the detected code phase and carrier frequency to the synchronization holding unit is performed. In S216, S400, and S218, the synchronization acquisition unit 104 is sequentially acquired for each GPS satellite with a longer signal integration time according to the search list, and the synchronization acquisition unit performs code phase and carrier acquisition. When the frequency is detected, a process of sequentially transmitting the detected code phase and carrier frequency to the synchronization holding unit is performed before the synchronization acquisition for other GPS satellites is completed.

  In S212, it is determined whether or not there is a satellite whose search flag 1 is 0 in the search list. Specifically, referring to the search list, when the start position flag is not specified (start position flag = 0), there is a satellite in which the search flag 1 is 0 from the top (top) of the search list. If the start position flag is specified (start position flag = 1), it is determined whether there is a satellite with the search flag 1 set to 0 from the satellites with the start position flag specified. judge.

  If there is a satellite for which the search flag 1 is 0, the determination in S212 is YES, and then the satellite is subjected to synchronization acquisition processing at the integration time Tint1 (S300). This synchronization acquisition process will be described later in detail.

  When the synchronization acquisition process is completed, the search flag 1 of the satellite in the search list is set to 1 (S214), and the process returns to S212. As described above, the synchronization acquisition processing is performed on the satellites whose search flag 1 is 0 in the search list in the order shown in the search list.

  When there are no satellites whose search flag 1 is 0, the determination in S212 is NO, and it is next determined whether there is a satellite whose search flag 2 is 0 in the search list (S216). . Specifically, in the same manner as in S212, it is determined whether or not there is a satellite for which the search flag 2 is 0 according to the designation of the start position flag in the search list.

  If there is a satellite for which the search flag 2 is 0, the determination in S216 is YES, and then the satellite is subjected to synchronization acquisition processing with an integration time Tint2 longer than the integration time Tint1 (S400). The longer the integration time, the more sensitive the signal can be detected. This synchronization acquisition process will also be described later in detail.

  When the synchronization acquisition process is completed, the search flag 2 of the satellite in the search list is set to 1 (S218), and the process returns to S216. As described above, the synchronization acquisition process is performed on the satellites whose search flag 2 is 0 in the search list according to the order of the search list.

  When there is no satellite with the search flag 2 set to 0, the determination in S216 is NO and the process returns to S202.

  As described above, when the number of satellites that have completed synchronization holding becomes less than the threshold value Nsat, the synchronization acquisition unit 104 acquires synchronization of the received signal according to the search list.

  FIG. 4 shows a flowchart of the synchronization acquisition process performed in the previous S300 and S400. Note that only the integration time Tint differs between S300 and S400. In this synchronization acquisition process, first, the code phase error CPerr of the satellite is calculated (S302). Specifically, the elapsed time after data is stored in the memory of the synchronization acquisition unit 104 is read from the time counter and stored in the variable T. Here, assuming that the nominal frequency of TXCO 101 is Ftco, the deviation from the nominal frequency of TXCO 101 is ΔFtco, the carrier frequency of the received signal from the GPS satellite is Fcar, and the Doppler frequency of the GPS satellite is Fdopp, the estimation of the code phase error of the satellite The value CPerr (svid, T) can be calculated using Equation 1.

(Equation 1)
CPerr (svid, T) = 2T (| ΔFtxco | / Ftxco + | Fdopp (svid) | / Fcar)
Note that ΔFtxco can be as close to 0 as possible by using various estimation methods such as Japanese Patent No. 3115084. In this embodiment, ΔFtxco = 0, and an estimated value of the code phase error of the satellite. It is assumed that CPerr (svid, T) is calculated.

  Next, it is determined whether or not the estimated value CPerr (svid, T) of the satellite code phase error satisfies Expression 2 (S304).

(Equation 2)
CPerr (svid, T) / NChfree <CWthresh
However, NChfree is the total number of free channels in the synchronization holding unit 105, and CWthresh is a fixed threshold value.

  If the condition of Expression 2 is satisfied, the determination in S304 is YES, and then the synchronization acquisition process is performed with the designated integration time (S306). In the case of S300, the integration time is Tint1, and in the case of S400, the integration time is Tint2. However, the integration time Tint1 <the integration time Tint2.

  In S308, a determination process is performed to determine whether or not the received signal has been detected by the synchronization capturing unit 104. If a received signal is detected, the determination in S308 is YES, and then it is determined whether or not Expressions 3 and 4 are satisfied (S310). That is, it is determined whether or not the total number of free channels NChfree is greater than 1 and the estimated code phase error value CPerr (svid, T) is greater than the phase resolution that can be detected by the synchronization holding unit. In this embodiment, if the code phase error is less than 0.5 chips, synchronization is held using one empty channel, and if the code phase error is larger than 0.5 chips, a plurality of empty In order to perform synchronization holding using a channel, it is determined whether or not the estimated value CPerr (svid, T) of the code phase error is larger than 0.5 using Equation 4.

(Equation 3)
NChfee> 1
(Equation 4)
CPerr (svid, T)> 0.5
If Equations 3 and 4 are satisfied, the determination in S310 is YES, the detection result is notified to the synchronization holding unit 105, and synchronization holding processing is started using a plurality of channels (S312). Specifically, the synchronization acquisition unit 104 is caused to transmit a detection result including the detected code phase, carrier frequency, and satellite ID, and the synchronization holding unit 105 starts synchronization holding processing using a plurality of channels. Instruct. When receiving the detection result from the synchronization acquisition unit 104, the synchronization holding unit 105 starts the synchronization holding process using a plurality of channels.

  Further, when Expressions 3 and 4 are not satisfied, the determination in S310 is NO, the detection result is notified to the synchronization holding unit 105, and the synchronization holding process is started using one channel (S314). Specifically, the synchronization holding unit 105 is caused to send out the detected code phase and carrier frequency, and the synchronization holding unit 105 is instructed to start synchronization holding processing using one channel. When the synchronization holding unit 105 receives this detection result from the synchronization acquisition unit 104, the synchronization holding unit 105 starts the synchronization holding process using one channel.

  If the condition of Formula 2 is not satisfied in S304, the determination in S304 is NO, and then it is determined whether the next search start satellite has been determined (S316). Specifically, when the next search start satellite is determined with reference to the start position flag in the search list, the determination in S316 is YES, and this process ends.

  If the next search start satellite has not been determined, the determination in S316 is NO, and then the processing target satellite ID is set as the next search start satellite (S318). Specifically, the start position flag of the search list of the satellite ID to be processed is set to 1, and this process ends.

  If no signal is detected by the synchronization acquisition process in S306, the determination in S308 is NO, and the process ends without proceeding to the synchronization holding process in S312 and S314.

  FIG. 5 shows a flowchart of the synchronization holding process by the CPU 109. This synchronization holding process is performed independently of the main process shown in FIG.

  First, it is determined whether or not the synchronization holding unit 105 has received a capture result from the synchronization capturing unit 104 (S502).

  When the synchronization holding unit 105 receives the acquisition result from the synchronization acquisition unit 104, next, the satellite designated by the acquisition result is allocated to N empty channels (S504). Specifically, N satisfying Equations 5 and 6 is assigned as the number of empty channels.

(Equation 5)
N <2CPerr (svid, T)
(Equation 6)
N ≦ NChfree
For example, as shown in FIG. 6, when a designated satellite is assigned to four free channels # 1 to # 4, the code phase is shifted by CPerr (svid, T) / N and held synchronously. In this way, by using a plurality of empty channels to shift the code phase and maintain synchronization, the code phase search range per channel can be set to CPerr (svid, T) / N, as shown in FIG. As described above, the code phase search range is shortened to 1 / N as compared with the case where synchronization is maintained using one free channel # 1.

  Next, it is determined whether or not synchronization holding is completed in any one of the N channels (S506).

  Here, when the synchronization hold is completed in any one of the N channels, the determination in S506 is YES, and then another channel (N-1) to which the same satellite ID is assigned is released to be an empty channel. (S508). Specifically, the simultaneous holding unit 105 is instructed to open another channel (N-1) to which the same satellite ID is assigned to be an empty channel.

  Next, the satellite is deleted from the search list (S510), and the process proceeds to S516.

  Further, when the synchronization holding of one of the N channels has not been completed, the determination in S506 is NO, and then it is determined whether or not a certain time has passed without the synchronization holding being completed (S512).

  If the fixed time has not elapsed after the synchronization hold has not been completed, the determination in S512 is NO and the process returns to S506.

  If a certain period of time elapses while synchronization is not yet completed, the determination in S512 is YES, and then the N channel to which the designated satellite ID is assigned is released to be an empty channel (S514). Specifically, the simultaneous holding unit 105 is instructed to release the N channel to which the designated satellite ID is assigned and make it an empty channel.

  In the next step S516, the signal level of the channel holding the synchronization is investigated. Specifically, the signal level of the channel whose synchronization is being held is acquired from the synchronization holding unit 105.

  Next, it is determined whether or not the state in which the signal level is less than a predetermined threshold is continued for a certain time or more (S518).

  When the state where the signal level is lower than the predetermined threshold is continued for a certain time or more, the determination in S518 is YES, and then the channel is made an empty channel and the satellite is added to the search list (S520). ), The process returns to S502.

  If the state where the signal level is less than the predetermined threshold has not been continued for a certain period of time, the determination in S518 is NO, and the process returns to S502 without performing the process of S520.

  If the synchronization holding unit 105 has not received the acquisition result from the synchronization acquisition unit 104, the determination in S502 is NO, and the process proceeds to S516 without performing the processing of S506 to S514.

  As described above, the GPS receiver 100 in the present embodiment causes the synchronization acquisition unit 104 to sequentially acquire the reception signal for each GPS satellite, and when the carrier frequency is detected by the synchronization acquisition unit, Before completing acquisition of synchronization with other GPS satellites, a process of sequentially transmitting the detected code phase and carrier frequency to the synchronization holding unit is performed.

  In FIG. 8, taking as an example the case of performing synchronization acquisition of received signals from four GPS satellites A to D, the synchronization acquisition by the synchronization acquisition unit 104 and the code phase recovery by the synchronization holding unit 105 are performed from the data buffer to the memory. Indicates the search timing. Here, it is assumed that the Doppler frequency decreases in the order of GPS satellites A, B, C, and D. As shown in the figure, when the code phase and the carrier frequency are sequentially detected for each GPS satellite, the code phase and the carrier frequency are sequentially transmitted to the synchronization holding unit 105 when detected. That is, when synchronization acquisition is completed, the code phase and the carrier frequency are sequentially transmitted to the synchronization holding unit 105 without waiting for completion of synchronization acquisition for other GPS satellites.

  Here, the data buffer time is T0, the synchronization acquisition times of GPS satellites A to D are TA, TB, TC, TD, and the Doppler frequencies of GPS satellites A to D are Δfd (A), Δfd (B), Δfd ( C), Δfd (D), and assuming that the carrier frequency of the GPS satellite signal is frf, the phase change amount of the spread code due to the Doppler shift of each GPS satellite A to D from the start of buffering of the received signal to the memory is It is expressed as

Phase change amount of GPS satellite A = (T0 + TA) · Δfd (A) / frf
Phase change amount of GPS satellite B = (T0 + TA + TB) · Δfd (B) / frf
Phase change of GPS satellite C = (T0 + TA + TB + TC) · Δfd (C) / frf
Phase change amount of GPS satellite D = (T0 + TA + TB + TC + TD) · Δfd (D) / frf
Based on the phase change amount of the spread code, the phase search amount of the code phase of the synchronization holding unit is determined.

  Therefore, as shown in FIG. 9, the phase search amount of the code phase of the synchronization holding unit 105 is reduced as compared with the case where the synchronization holding is started after the acquisition of synchronization of the received signals from the four GPS satellites is completed. can do.

  According to the configuration described above, the synchronization acquisition unit sequentially acquires the reception signal for each GPS satellite. When the code phase and the carrier frequency are detected by the synchronization acquisition unit, the synchronization acquisition for the other GPS satellites is performed. Since the detected code phase and carrier frequency are sequentially sent to the synchronization holding unit before the completion of the operation, the synchronization holding unit starts the search for the sequential code phase when receiving the code phase and the carrier frequency from the synchronization acquisition unit. Therefore, the amount of phase search of the synchronization holding unit can be reduced.

  In addition, the phase search amount of the code phase of the synchronization holding unit needs to be increased as the start of synchronization acquisition is delayed and the Doppler frequency of the GPS satellite is increased, but according to the above configuration, the Doppler frequency Since the acquisition signal is acquired in descending order, the Doppler frequency of the satellite that is first acquired is the highest, and the Doppler frequency is reduced so that the satellite that is acquired later becomes lower. It is possible to minimize the amount of phase search by the unit.

  If the total number of free channels in the synchronization holding unit is larger than 1 and the estimated value of the code phase error is larger than the phase resolution that can be detected by the synchronization holding unit, the synchronization holding unit uses a plurality of free channels for synchronization holding. Therefore, the synchronization holding unit can search by dividing the search range by a plurality of designated empty channels, thereby reducing the time required for holding synchronization per channel. Is possible.

  In addition, since the synchronization acquisition is performed with the second signal integration time longer than the first signal integration time after the synchronization acquisition is performed with the first signal integration time, the second signal integration time from the beginning. It is possible to complete the synchronization acquisition earlier than in the case of performing the synchronization acquisition.

  In addition, this invention is not limited to the said embodiment, Based on the meaning of this invention, it can implement with a various form.

  For example, in the above embodiment, the synchronization acquisition process is performed at the integration time Tint1 at S300, and then the synchronization acquisition process is performed at the integration time Tint2 that is longer than the integration time Tint1 at S400. For example, after the synchronization acquisition process is performed at the integration time Tint2 in S400, the synchronization acquisition process may be further performed at the integration time Tint3 having an integration time longer than the integration time Tint2.

  The correspondence relationship between the configuration of the above embodiment and the configuration of the claims will be described. S212, S300, S214, S216, S400, and S218 in FIG. 2 correspond to synchronization acquisition control means, and S204 is Doppler frequency calculation. S310 corresponds to an empty channel determination unit.

It is a figure which shows the structure of the GPS receiver which concerns on one Embodiment of this invention. It is a flowchart of the main process by CPU. It is a figure which shows an example of a search list. It is a flowchart of the synchronous acquisition process by CPU. Flow chart of synchronization holding process by CPU It is a figure for demonstrating the search range of a code phase at the time of allocating a satellite to four vacant channels # 1- # 4. It is a figure for demonstrating the search range of a code phase at the time of allocating a satellite to one empty channel # 1. It is a figure which shows the timing of the code phase re-search by the synchronous acquisition by a synchronous acquisition part, and a synchronous holding | maintenance part from the data buffer to a memory. It is a figure for demonstrating a subject.

Explanation of symbols

100 ... GPS receiver, 101 ... TCXO, 102 ... antenna,
103 ... Frequency conversion unit, 104 ... Synchronization acquisition unit, 105 ... Synchronization holding unit, 106 ... RTC,
107 ... RAM, 108 ... flash ROM, 109 ... CPU.

Claims (8)

A synchronization acquisition unit that detects a code phase of a spread code of a reception signal from a GPS satellite and performs synchronization acquisition of the reception signal, and detects a carrier frequency of the reception signal when synchronization acquisition of the reception signal is obtained; ,
A synchronization holding unit that holds the synchronization of the spread code of the received signal in which the code phase and the carrier frequency are detected by the synchronization acquisition unit, and a GPS receiver comprising:
The synchronization acquisition unit sequentially acquires the received signal for each GPS satellite. When the code acquisition unit detects the code phase and the carrier frequency, the synchronization acquisition for other GPS satellites is terminated. A GPS receiver comprising a synchronization acquisition control means for sequentially transmitting the detected code phase and carrier frequency to the synchronization holding unit before performing. Comprising Doppler frequency calculating means for calculating a Doppler frequency of a received signal from the GPS satellite;
2. The GPS receiver according to claim 1, wherein the synchronization acquisition control unit performs synchronization acquisition of the received signals in descending order of the Doppler frequency calculated by the Doppler frequency calculation unit. The synchronization holding unit has a plurality of channels and performs synchronization holding for each channel.
Free channel determination means for determining whether the total number of free channels of the synchronization holding unit is greater than 1 and whether the estimated value of the code phase error is larger than the phase resolution that can be detected by the synchronization holding unit;
The synchronization acquisition control means determines that the number of empty channels in the synchronization holding unit is larger than 1 and the estimated value of the code phase error is larger than the phase resolution that can be detected by the synchronization holding unit. 3. The GPS receiver according to claim 1, wherein the GPS receiver instructs the synchronization holding unit to start synchronization holding using a plurality of empty channels. The synchronization acquisition control means causes the synchronization acquisition unit to perform synchronization acquisition in a first signal integration time, and then synchronizes with the synchronization acquisition unit in a second signal integration time longer than the first signal integration time. The GPS receiver according to claim 1, wherein acquisition is performed. A synchronization acquisition unit that detects a code phase of a spread code of a reception signal from a GPS satellite and performs synchronization acquisition of the reception signal, and detects a carrier frequency of the reception signal when synchronization acquisition of the reception signal is obtained; ,
A synchronization holding unit that holds the synchronization of the spread code of the received signal in which the code phase and the carrier frequency are detected by the synchronization acquisition unit, and a reception method of a GPS receiver comprising:
The synchronization acquisition unit sequentially acquires the received signal for each GPS satellite. When the code acquisition unit detects the code phase and the carrier frequency, the synchronization acquisition for other GPS satellites is terminated. A reception method for a GPS receiver, comprising: sequentially transmitting the detected code phase and carrier frequency to the synchronization holding unit before performing. 6. The reception method of a GPS receiver according to claim 5, wherein a Doppler frequency of a reception signal from the GPS satellite is calculated, and synchronization acquisition of the reception signal is performed in descending order of the calculated Doppler frequency. . The synchronization holding unit has a plurality of channels and performs synchronization holding for each channel.
It is determined whether the total number of empty channels in the synchronization holding unit is greater than 1 and the estimated value of the code phase error is larger than the phase resolution that can be detected by the synchronization holding unit, and the synchronization is performed by the empty channel determination unit. When it is determined that the total number of free channels in the holding unit is larger than 1 and the estimated value of the code phase error is larger than the phase resolution that can be detected by the synchronization holding unit, a plurality of free channels are used in the synchronization holding unit. 7. The reception method of the GPS receiver according to claim 5, wherein an instruction is given to start synchronization maintenance. After the synchronization acquisition unit performs synchronization acquisition in a first signal integration time, the synchronization acquisition unit performs synchronization acquisition in a second signal integration time longer than the first signal integration time. The reception method of the GPS receiver as described in any one of Claim 5 thru | or 7.

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