JP2007198984A - Signal acquisition device and signal acquisition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To acquire more surely a signal having a prescribed frequency, even when a clock signal whose frequency is fluctuated with elapse of time is used. <P>SOLUTION: A GPS signal reception part 104 acquires a GPS signal based on a GPS clock signal generated from a clock generation part 106 for GPS. A search frequency control part 109 controls a search object frequency of the GPS signal reception part 104 based on a frequency corresponding to reference correction information. A frequency comparison part 107 outputs a frequency difference with an ideal value of the frequency of the GPS clock signal. A clock frequency estimation part 122 discriminates a variation state of the frequency of the GPS clock signal based on a plurality of frequency differences at different times, estimates the frequency of the GPS clock signal at each time, and adjusts the reference correction information for correcting the search object frequency so that a search range of a GPS reception part 217 becomes an ideal frequency band. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a signal capturing device and a signal capturing method for capturing a signal having a predetermined frequency such as a signal transmitted from a GPS (Global Positioning System) satellite, and is particularly suitable for a mobile communication terminal such as a mobile phone. The present invention relates to a signal capturing apparatus and a signal capturing method.

  In recent years, mobile communication terminals capable of high-speed data transmission such as mobile phones and PDAs (Personal Digital Assistants) have become popular. In such a mobile communication terminal, in order to expand the convenience and application, it is attracting attention to add a position information acquisition function using a satellite positioning system.

  The satellite positioning system is a system that receives information transmitted from a plurality of artificial satellites orbiting the earth, measures the distance to each artificial satellite, and calculates the current position of the receiving device. . The GPS constructed by the US Department of Defense is a representative of such a satellite positioning system, and a plurality of artificial satellites called GPS satellites are arranged.

  The GPS satellite performs spread spectrum processing using a predetermined PRN (Pseudo Random Noise) code on a signal to be transmitted. That is, the mobile communication terminal obtains the original signal by performing despreading processing using a corresponding PRN code for a signal transmitted from the GPS satellite (hereinafter referred to as “GPS signal”). Is possible. Then, by performing processing such as message synchronization, ephemeris collection, and PVT (Position, Velocity, Time) calculation on the acquired signal, information about the current position and time of the self can be obtained.

  A mobile communication terminal equipped with such a positioning function is small and inexpensive as a device unit that generates a clock signal (hereinafter referred to as “GPS clock signal”) for use in GPS signal reception processing. For this reason, a crystal oscillator is widely applied (see, for example, Patent Document 1).

  However, since the oscillation frequency of the crystal oscillator varies depending on the ambient temperature and other use conditions, it is necessary to set a large search frequency range, and as a result, it may take time to capture a signal. Therefore, in this conventional proposal, a crystal oscillator inside the device is generated using a clock signal with high frequency accuracy obtained when the mobile communication terminal performs radio communication with the ground radio base station. It detects how much the frequency of the GPS clock signal deviates from its ideal value. And the signal processing regarding positioning is performed based on the frequency difference. Thereby, even if the frequency of the GPS clock signal generated by the crystal oscillator is different from the ideal value, it is possible to capture the signal at high speed by limiting the frequency search range.

  By the way, the PRN code used in the above-described spread spectrum processing of GPS signals has a code length of 1 ms (milliseconds), a chip rate of 1.023 MHz (megahertz), and the cycle of one chip is about 1 μs (microseconds). . This spread spectrum process is performed in synchronization with the time of the atomic clock mounted on each GPS satellite. Therefore, the mobile communication terminal cannot start the processing after the message synchronization described above unless it establishes time synchronization with the GPS satellite on the transmission side with an error accuracy of 0.5 μs or less, Unable to perform positioning.

  However, the mobile communication terminal normally operates independently from any GPS satellite in a state where reception of GPS signals has not started. Therefore, prior to positioning, first, a GPS signal is searched, and processing for establishing frequency synchronization or phase synchronization with the GPS signal and synchronization of a PRN code (hereinafter collectively referred to as “code synchronization”) is required.

FIG. 17 is an explanatory diagram showing an example of such a conventional GPS signal search. The horizontal axis represents the elapsed time since the search was started, and the vertical axis represents the frequency. Mobile communication terminal, the search target frequency 1 as a frequency to be searched, as a base point the search reference frequency f _b as frequencies of predetermined search criteria as a standard frequency of the GPS signal, with time Gradually move to the surrounding frequency band. This is because the frequency to be searched is precisely matched with the GPS signal frequency f ₀ as the frequency of the GPS signal reaching the mobile communication terminal due to the relative speed between the GPS satellite and the mobile communication terminal and other causes. This is because it is difficult to insert. In this example, a GPS signal is captured at time t. It is also possible to set the frequency accuracy higher than the standard frequency of the GPS signal by exchanging GPS satellite orbit information by communication with a server provided in the mobile phone network. In this case, the GPS signal can be captured at an earlier time.

On the other hand, if the search range is expanded, it takes time to search for the expanded range. Further, if the search speed is increased to shorten this time, there is a high possibility that the GPS signal will be erroneously missed if the signal level is low. Therefore, normally, as shown in the figure, a frequency upper limit value f _max and a frequency lower limit value f _min are determined for the search target frequency 1. Then, by expanding the search range at such a speed that the search target frequency 1 reaches the upper limit value and the lower limit value within a predetermined time, the set search range, that is, the frequency upper limit value f _max and the frequency are set. The search for the frequency band between the lower limit value f _min can be completed within a predetermined time. Here, when the GPS signal cannot be captured even after the search is completed, the series of search processes described above are re-executed.
Japanese Patent Laid-Open No. 2003-329761

  However, as described above, the crystal oscillator has a feature that the oscillation frequency changes due to a change in ambient temperature. The search for the GPS signal is performed using the GPS clock signal as an operation clock. Therefore, the oscillation frequency of the crystal oscillator fluctuates after the search is started, and the actual search range may deviate over time from the search range when the frequency of the GPS clock signal is an ideal value. is there. In this case, there is a possibility that a GPS signal that can be captured cannot be captured indefinitely.

  The present invention has been made in view of such a point, and even when a clock signal whose frequency fluctuates with the passage of time is used, a signal capturing device capable of capturing a signal having a predetermined frequency more reliably An object is to provide a signal acquisition method.

  In order to solve such a problem, a signal acquisition device of the present invention includes a frequency difference detection unit that detects a frequency difference as a difference from an ideal value of a frequency of a predetermined clock signal, and a plurality of times by the frequency difference detection unit. A clock frequency estimating means for estimating the frequency of a predetermined clock signal based on the detection result, and searching for a signal to be captured using the predetermined clock signal as an operation clock, and determining the frequency of the signal to be searched A signal receiving means for correcting based on the estimated value by the clock frequency estimating means is employed.

  In addition, the signal acquisition device of the present invention stores the information about the frequency difference as the difference from the ideal value of the frequency of the predetermined clock signal in association with the elapsed time from the start of the search for the signal to be acquired. A difference information storage means, a timer for measuring the elapsed time from the start of the search, and a clock for acquiring information corresponding to the elapsed time measured by the timer from the frequency difference information storage means and estimating the frequency of a predetermined clock signal A signal receiving unit that searches for a signal to be captured using a predetermined clock signal as an operation clock and corrects the frequency of the signal to be searched based on an estimated value by the clock frequency estimating unit. The structure which comprises a means is taken.

  The signal capturing device of the present invention also includes frequency difference detecting means for repeatedly detecting a frequency difference as a difference from an ideal value of the frequency of a predetermined clock signal at a predetermined cycle, and capturing the predetermined clock signal as an operation clock. And a signal receiving means for correcting the frequency of the signal to be searched based on the detection result each time the frequency difference detecting means performs a search. .

  The signal acquisition method of the present invention includes a frequency difference detection step for detecting a frequency difference as a difference from an ideal value of a frequency of a predetermined clock signal at a plurality of times, and a plurality of times at the plurality of times by the frequency difference detection step. A clock frequency estimating step for estimating the frequency of a predetermined clock signal based on the detection result, and a signal receiving means for searching for a signal to be captured using the predetermined clock signal as an operation clock, the signal to be searched And a search target frequency control step for correcting the frequency based on the estimated value by the clock frequency estimating means.

  According to the present invention, a frequency difference as a difference from an ideal value of the frequency of a predetermined clock signal is detected, and the frequency of the predetermined clock signal is estimated based on detection results at a plurality of times. Then, a signal to be captured is searched using a predetermined clock signal as an operation clock, and the frequency of the signal to be searched is corrected based on this estimated value. Alternatively, information regarding a frequency difference as a difference from an ideal value of the frequency of a predetermined clock signal is stored in association with an elapsed time after the search is started. Thereby, even when the frequency of the predetermined clock signal fluctuates with time, the fluctuation can be estimated, and the value of the frequency to be searched can be corrected in accordance with this. Further, the frequency difference is repeatedly detected at a predetermined cycle to correct the frequency to be searched. As a result, even when the frequency of the predetermined clock signal varies with time, the frequency value to be searched can be corrected to an appropriate value at a predetermined period. That is, a signal having a predetermined frequency can be captured more reliably. Furthermore, since resistance to frequency fluctuations of the clock signal is improved, a more flexible device design is possible.

  Hereinafter, a signal capturing device according to an embodiment of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a system configuration diagram showing a configuration of a communication system in which the signal acquisition device according to Embodiment 1 of the present invention is used. The communication system 20 includes a mobile phone 10, a mobile phone network 21, a radio base station 23 connected to the mobile phone network 21, and a GPS satellite disposed above the mobile phone 10 (for the sake of explanation here) 4 GPS satellites 24-1 to 24-4 are shown).

  The mobile phone 10 communicates with other mobile phones, fixed phones, or information servers (not shown) arranged in the mobile phone network 21 by transmitting and receiving radio signals to and from the radio base station 23. In addition, positioning is performed by capturing GPS signals transmitted from the four GPS satellites 24-1 to 24-4 and extracting information from the GPS signals. In this GPS signal, a PRN code such as a C / A code (Coarse / Acquisition Code) or a P code (Precise Code or Protected Code) that is different for each GPS signal is superimposed on a carrier wave having the same frequency of 1,57542 GHz (gigahertz). Is.

  FIG. 2 is a block diagram showing a configuration of the mobile phone 10 shown in FIG. The mobile phone 10 includes a radio antenna 101, a radio communication unit 102, a GPS antenna 103, a GPS signal receiving unit 104, a positioning calculation unit 105, a GPS clock generation unit 106, a frequency comparison unit 107, A reference frequency control unit 108, a search frequency control unit 109, a timer 110, a trigger output unit 111, a frequency difference information storage unit 112, and a positioning start instruction input unit 113 are mainly configured.

  The reference frequency control unit 108 includes a reference frequency setting unit 121 and a clock frequency estimation unit 122. The search frequency control unit 109 includes a reference correction information storage unit 123.

  Although not shown, the mobile phone 10 includes a CPU (Central Processing Unit), a storage medium such as a ROM (Read Only Memory) storing a control program, a working memory such as a RAM (Random Access Memory), and an existing memory. It is comprised by the communication circuit as hardware. That is, the function of each device unit described above is realized by the CPU executing the control program.

  The radio communication unit 102 transmits and receives radio signals to and from the radio base station 23 illustrated in FIG. Although not shown, the radio base station 23 includes a clock oscillator that generates a clock signal with high frequency accuracy. The clock signal is used as a carrier frequency to perform wireless communication with the wireless communication unit 102. The wireless communication unit 102 includes an AFC (Automatic Frequency Control) device having a PLL (Phase-Locked Loop) circuit (not shown), and a reference clock that is frequency-synchronized with the carrier frequency of the wireless signal transmitted from the wireless base station 23. Generate a signal.

  The GPS signal receiving unit 104 searches for and captures a GPS signal, and acquires information included in the GPS signal. And the positioning calculating part 105 performs the calculation for positioning based on this acquired information. That is, the mobile phone 10 is a mobile communication terminal having a function of connecting to the mobile phone network 21 and a positioning function by a GPS system.

  The positioning start instruction input unit 113 receives an instruction to start positioning by GPS. The GPS clock generation unit 106 generates a GPS clock signal used as an operation clock of the GPS signal reception unit 104 using a temperature compensated crystal oscillator (TCXO) (not shown). This GPS clock generation unit 106 is a self-running clock source that is not subjected to frequency synchronization like the AFC device of the wireless communication unit 102 of the mobile phone 10. Although it is a temperature compensation type, the oscillation frequency of the crystal oscillator varies due to the influence of the ambient temperature. Therefore, the frequency accuracy of the GPS clock signal is lower than the frequency accuracy of the reference clock signal output from the wireless communication unit 102.

  The trigger output unit 111 outputs a trigger for causing the frequency comparison unit 107 to perform frequency comparison using the timer 110.

  In response to this trigger, the frequency comparison unit 107 compares the frequency of the GPS clock signal with its ideal value, and outputs the frequency difference as frequency difference information. This frequency difference information is obtained by counting how many times the GPS clock signal rises in a section where the reference clock signal rises a predetermined number of times, for example, and the count value obtained when the frequency of the GPS clock signal is an ideal value and the actual count value Can be obtained by comparing.

  Based on this frequency difference information, the reference frequency control unit 108 generates reference correction information that is information indicating a ratio of the ideal value of the frequency of the GPS clock signal to the frequency of the actual GPS clock signal. This reference correction information is used to correct a reference frequency (hereinafter referred to as “search reference frequency”) when the GPS signal receiving unit 104 captures a GPS signal. However, while the reference frequency setting unit 121 generates one reference correction information based on frequency difference information at a certain time, the clock frequency estimation unit 122 uses a GPS clock based on frequency difference information at a plurality of different times. It estimates how the frequency of the signal fluctuates, and sequentially generates reference correction information. Specifically, the clock frequency estimation unit 122 calculates the frequency fluctuation speed of the GPS clock signal based on frequency difference information at a plurality of times, and uses the calculation result to calculate the frequency of the GPS clock signal at each time. Estimate and generate reference correction information.

  When the frequency difference information is input from the reference frequency control unit 108, the frequency difference information storage unit 112 stores the frequency difference information and also stores time information indicating the input time in association with each other.

  The search frequency control unit 109 stores the latest reference correction information generated by the reference frequency setting unit 121 or the clock frequency estimation unit 122 in the reference correction information storage unit 123. Then, the search frequency control unit 109 determines a GPS signal search target frequency based on the search reference frequency, and sequentially instructs the GPS signal reception unit 104. At that time, the search frequency control unit 109 stores the GPS signal search unit in the reference correction information storage unit 123. The search target frequency is corrected based on the reference correction information.

  FIG. 3 shows a circuit configuration of the GPS signal receiving unit 104 shown in FIG. The GPS signal receiving unit 104 includes an amplifier circuit 131, a first mixer 132, a first band limiting filter 133, a second mixer and 134, a second band limiting filter 135, analog digital (A / D) It is mainly composed of a converter 136, a third mixer 137, an integrator 138, a frequency multiplier 139, a numerically controlled oscillator (NCO) 140, and a PRN code generation unit 141. The

The frequency multiplier 139 multiplies the GPS clock signal and converts it to a first local signal (frequency: f _Lo1 ) at the frequency level of the carrier wave of the GPS signal. The reception signal received by the GPS antenna 103 shown in FIG. 2 is amplified by the amplifier circuit 131, multiplied by the first local signal by the first mixer 132, and then unnecessary by the first band limiting filter 133. By removing such frequency components, the GPS signal is down-converted to a first IF (Intermediate Frequency) frequency (f _IF1 ). The numerically controlled oscillator 140 generates a second local signal (frequency: f _Lo2 ) having the same frequency as the input search target frequency using the GPS clock signal as an operation clock. The received signal converted to the first IF frequency output from the first band-limiting filter 133 is multiplied by the second local signal by the second mixer 134, and the second IF frequency (f _IF2 ) is multiplied. Converted. Here, the second IF frequency is a signal equivalent to a baseband, that is, near 0 Hz, but the second IF frequency _fLo2 may not be a baseband. From the received signal converted to the second IF frequency f _Lo2 , an unnecessary frequency component is removed by the second band limiting filter 135. Then, it is converted into a digital signal by the analog-digital converter 136.

  The PRN code generation unit 141 generates the PRN code in synchronization with the clock signal output from the numerical control oscillator 140. The received signal digitized by the analog / digital converter 136 is multiplied by the generated PRN code by the third mixer 137 and integrated by the integrator 138. That is, when the received signal is a GPS signal and the clock signal output from the numerically controlled oscillator 140 is frequency-synchronized with this, synchronization with the PRN code output from the PRN code generation unit 141 is established, and the integrator 138 The integrated value output by takes a peak. Therefore, the positioning calculation unit 105 shown in FIG. 2 determines whether code synchronization has been established by monitoring this integral value, and detects the capture of the GPS signal.

The set frequency of the numerically controlled oscillator 140 is based on the assumption that the frequency of the GPS clock signal matches the ideal value. Specifically, the first local signal described above is obtained by multiplying the GPS clock signal, and the numerically controlled oscillator 140 that outputs the second local signal operates on the assumption that the frequency of the GPS clock signal is correct. Then, the second local signal is output at the frequency set. Therefore, when the search target frequency is set to f _s , the frequency of the GPS clock signal is set to f _clk , and the multiplication rate of the frequency multiplier 139 is set to N _1, and the set frequency (f _nco ) of the numerically controlled oscillator 140 is _expressed by the following equation: By setting the content represented by (1), it becomes possible to search the search target frequency f _s .

_{f nco = f s -N 1 ×} f clk -f IF2 ...... (1)

When the frequency of the GPS clock signal is deviated from the ideal value, the first local signal and the second local signal are also deviated from the assumed frequency. For example, when the frequency of the GPS clock signal is m times the ideal value, the frequency of the first local signal and the frequency of the second local signal that are output are also m times the expected frequency. Therefore, the frequency of the signal that is down-converted by these signals, that is, the IF-converted received signal is also shifted from the IF frequency corresponding to the designated search target frequency f _s .

  Note that the GPS signal needs to be captured on different channels for all of the four GPS satellites 24-1 to 24-4 shown in FIG. Here, for simplification of explanation, it is assumed that the GPS signal receiving unit 104 is provided with only a configuration corresponding to the GPS satellite 24-1, but actually, the configuration shown in FIG. Provided.

  Hereinafter, the operation of each device unit of the mobile phone 10 having the above configuration will be described.

  The positioning start instruction input unit 113 includes a key switch (not shown). The user of the mobile phone 10 can input an instruction to start positioning by GPS at any timing by operating this key switch. In addition, an input of a positioning start instruction from the application software installed in the mobile phone 10 or the mobile phone network 21 side is also accepted. When this positioning start instruction is input, the positioning start instruction input unit 113 outputs positioning start instruction information indicating that to the GPS clock generation unit 106 and the trigger output unit 111.

  When the positioning start instruction information is input, the GPS clock generation unit 106 starts supplying power to the temperature compensated crystal oscillator and starts outputting the GPS clock signal. When the positioning start instruction information is input, the trigger output unit 111 first initializes the timer 110 to a value “0” and starts timing thereof, and further outputs a trigger to the frequency comparison unit 107.

  When a trigger is input from the trigger output unit 111, the frequency comparison unit 107 starts to input a reference clock signal output from the wireless communication unit 102 and a GPS clock signal output from the GPS clock generation unit 106. Then, the frequency of the GPS clock signal is compared with the ideal value, and the difference between the frequencies is output to the reference frequency setting unit 121 of the reference frequency control unit 108 as frequency difference information. This frequency difference information is obtained by counting how many times the GPS clock signal rises in a section where the reference clock signal rises a predetermined number of times, for example, and the count value obtained when the frequency of the GPS clock signal is an ideal value and the actual count value Can be obtained by comparing.

  The reference frequency setting unit 121 outputs reference correction information to the search frequency control unit 109 in response to the input of the frequency difference information from the frequency comparison unit 107 by a reference frequency setting process described later. Further, frequency difference information is output to the clock frequency estimation unit 122 as appropriate.

  The clock frequency estimator 122 discriminates the state of fluctuation of the GPS clock signal in response to the input of the frequency difference information from the reference frequency setting unit 121 by frequency fluctuation discrimination processing described later, and estimates the frequency at each time Thus, appropriate reference correction information is generated.

  Each time the reference correction information is input, the search frequency control unit 109 updates the content stored in the reference correction information storage unit 123 with the reference correction information. The search frequency control unit 109 prepares a search frequency control algorithm for controlling the search target frequency in advance. Then, by using the reference correction information stored in the reference correction information storage unit 123 for the search frequency control algorithm, a GPS signal is sequentially scanned (sequential scan) for a predetermined search range.

  This search frequency control algorithm moves the search target frequency to both the high frequency side and the low frequency side as time elapses with reference to the search reference frequency in the same manner as described with reference to FIG. The GPS signal is searched for. The search frequency control unit 109 multiplies the search target frequency determined by this search frequency control algorithm by the stored value of the reference correction information storage unit 123 to the numerically controlled oscillator 140 shown in FIG. Output. That is, the search target frequency input to the GPS signal receiving unit 104 is corrected so as to compensate for the deviation from the ideal value of the frequency of the GPS clock signal.

  FIG. 4 shows a flow of trigger output processing by the trigger output unit 111. When receiving the positioning start instruction information from the positioning start instruction input unit 113 shown in FIG. 2 (step S201: YES), the trigger output unit 111 initializes the timer 110 and triggers at a predetermined cycle S. Is set to the parameter n used to output (step S202), and a trigger is output to the frequency comparison unit 107 (step S203). If the GPS signal search has not ended yet (step S204: NO), the trigger output unit 111 sets the time information output by the timer 110 to a value obtained by multiplying the period S by the parameter n at that time. It is determined whether or not it has been reached (step S205). If not reached yet (NO), the process returns to step S204.

  When the time information output from the timer 110 reaches the value obtained by multiplying the period S by the parameter n (step S205: YES), the trigger output unit 111 increases the parameter n by the value “1” (step S206). Returning to step S203, the trigger is output again. That is, a trigger is output at a period S, and frequency difference information is input to the repetitive reference frequency setting unit 121. The timer 110 may be synchronized with a GPS clock signal or a reference clock signal output from the wireless communication unit 102, or may be separately timed using a signal from another clock source (not shown). When the GPS signal search is completed (step S204: YES), the process returns to step S201 and waits for new positioning start instruction information to be input again (return).

  Note that the GPS signal search ends when, for example, code synchronization has been established with the number of GPS satellites 24 necessary for positioning, or a search is performed for a predetermined search range described later. This is when the code synchronization cannot be established with the number of GPS satellites 24 necessary for positioning. In this case, the trigger output unit 111 may return to step S202 and re-execute a series of search processes.

  FIG. 5 is a flowchart showing the flow of the reference frequency setting process by the reference frequency setting unit 121. When the frequency difference information is input from the frequency comparison unit 107 (step S221: YES), the reference frequency setting unit 121 generates reference correction information to be set in the search frequency control unit 109 corresponding to the content, The search frequency control unit 109 is instructed to initialize the search target frequency (step S222). The initialization of the reference correction information and the search target frequency will be described in detail later.

  The reference frequency setting unit 121 does not input the frequency difference information for the second and subsequent times after the start of positioning is instructed, that is, when the first frequency difference information is input at the start of the search (step S223). : NO), the reference correction information is output to the search frequency control unit 109, and the frequency difference information is stored in the frequency difference information storage unit 112 (step S224). Then, the reference frequency setting unit 121 waits for frequency difference information to be input again (return).

  When the frequency difference information is input for the second and subsequent times after the start of positioning is instructed, that is, when other frequency difference information has been input in the past since the search was started, the reference frequency setting unit 121 ( Step S223: YES), the latest frequency difference information and the reference correction information are output to the clock frequency estimation unit 122 to instruct the adjustment of the reference correction information (Step S225). Then, the reference frequency setting unit 121 waits for frequency difference information to be input again (return).

  FIG. 6 is a flowchart showing a flow of clock frequency estimation processing by the clock frequency estimation unit 122. When the latest frequency difference information is input from the reference frequency setting unit 121 and the adjustment of the reference correction information is instructed (step S241: YES), the clock frequency estimation unit 122 receives a reference frequency setting unit from the frequency difference information storage unit 112. 121 reads out the frequency difference information stored last and the time information associated therewith, and inputs the time information indicating the current time. And while specifying the frequency variation | change_quantity of the newest frequency difference information with respect to the frequency difference information stored at the end, the elapsed time corresponding to this frequency variation | change_quantity is specified (step S242). The specification of the elapsed time is determined by the cycle S set in the trigger output unit 111, and may be a default value.

  The clock frequency estimation unit 122 further calculates the rate of change in the frequency of the GPS clock signal based on the identified frequency fluctuation amount and elapsed time (step S243), and based on the calculation result and the latest frequency difference information. Then, a correction information adjustment algorithm for adjusting the reference correction information is determined (step S244). The correction information adjustment algorithm will be described later with reference to the drawings.

  Then, the clock frequency estimation unit 122 stores the latest frequency difference information in the frequency difference information storage unit 112 (step S245), and uses the determined correction information adjustment algorithm to determine reference correction information to be set at that time. Calculate and output to the search frequency control unit 109 (step S246). Thereafter, when a new instruction for adjusting the reference correction information is not given (step S247: NO) and the search of the GPS signal is not completed (step S248: NO), the process returns to step S246 to calculate and search the reference correction information. The output to the frequency control unit 109 is repeated.

  When the latest frequency difference information and the reference correction information are newly input from the reference frequency setting unit 121 and the clock frequency estimation unit 122 is instructed to adjust the reference correction information (step S247: YES), the clock frequency estimation unit 122 returns to step S242. Then, a new correction information adjustment algorithm is determined based on the frequency difference information stored in the frequency difference information storage unit 112 and the newly input reference correction information, and the adjustment of the reference correction information is continued. As described above, when the GPS signal search is completed while repeating steps S242 to S248 (step S248: YES), the clock frequency estimating unit 122 returns to step S241 again to give an instruction to adjust the first reference correction information. Wait (return).

  FIG. 7 is an explanatory diagram showing an example of how the search target frequency is changed by the GPS signal receiving unit 104. The horizontal axis represents the elapsed time since the search was started, and the vertical axis represents the frequency. In order to simplify the description, the ideal frequency of the GPS clock signal is the same as the chip rate of the PRN code, and the reference correction information storage unit 123 of the search frequency control unit 109 has an initial value “1”. "Is stored.

Here, it is assumed that the trigger output unit 111 outputs a trigger at the first time t ₁ and the first frequency difference information Δf ₁ is input to the reference frequency setting unit 121 correspondingly. The reference correction information is information representing the ratio of the ideal value of the GPS clock signal frequency to the actual GPS clock signal frequency as described above. Accordingly, the reference frequency setting unit 121 sets the reference correction information as f _b / (f _b + Δf ₁ ), where the chip rate of the PRN code, that is, the ideal frequency of the GPS clock signal here is the search reference frequency f _b. Determine the value represented.

Then, as shown in the figure, immediately after the first time t ₁ , a frequency (hereinafter referred to as “actual search reference frequency”) f that is a reference when the GPS signal receiving unit 104 actually performs a search f. _s is approximately equal to the search reference frequency _{f b.}

However, since the first frequency difference information Δf ₁ is generated based on the radio clock signal, the frequency error Δd remains between the GPS signal frequency f ₀ as the chip rate of the PRN code of the GPS signal. However, compared with the case where the oscillation frequency of the GPS clock generation unit 106 is adjusted, the frequency accuracy is improved from several ppm (parts per million) to a value of 1 ppm or less. The frequency error Δd is determined by the frequency accuracy (frequency accuracy) of the wireless communication unit 102. Therefore, the ideal search range A, that is, the range between the frequency upper limit value f _max and the frequency lower limit value f _min of the search target frequency 301 is a size corresponding to the frequency accuracy of the wireless communication unit 102, and the search is performed. reference frequency f _b is set to be the center. In addition, the reference frequency setting unit 121 stores the first frequency difference information Δf ₁ in the frequency difference information storage unit 112.

  The search frequency control algorithm used by the search frequency control unit 109 changes the search target frequency 301 with time at a predetermined increase rate and increase / decrease rate. The increase rate and the increase / decrease rate are set such that the search for the search range A can be completed within a predetermined time when the frequency of the GPS clock signal maintains an ideal value.

Here, it is assumed that the frequency of the GPS clock signal fluctuates due to a change in ambient temperature during the search, and the actual search reference frequency f _s gradually decreases from the first time t _{1 as} shown in FIG. Then, the search target frequency 301 determined by the search frequency control algorithm described above also, since the reference is the search reference frequency f _s, so that gradually shifted to the lower side gradually from the ideal search target frequency. Then, take the time to frequency side search target frequency 301 ₁ as search target frequency 301 set in the search reference frequency f _b or more frequency bands reaches the upper frequency limit value f _max of the search range A. Then, if the GPS signal frequency f ₀ as shown in the figure has a frequency of higher side than search reference frequency f _b, the time to acquire the GPS signals such. On the other hand, the low-frequency side search target frequency 301 ₂ as the search target frequency 301 is set below the frequency band search reference frequency f _b is thus reached the lower frequency limit value f _min of the search range A at an earlier time.

Here, the trigger output unit 111 outputs a trigger at the second time t ₂ when the first time Δt ₁ has elapsed from the first time t _1, and the second frequency difference information Δf ₂ is correspondingly generated. Assume that the input is made to the reference frequency setting unit 121. Then, the clock frequency estimation unit 122 performs correction based on the second frequency difference information Δf ₂ and the first time Δt ₁ and the first frequency difference information Δf ₁ stored in the frequency difference information storage unit 112. Determine the information adjustment algorithm.

When the difference of the second frequency difference information Δf ₂ with respect to the _first frequency difference information Δf ₁ is expressed by a frequency fluctuation amount Δf, the fluctuation speed of the frequency of the GPS clock signal, that is, the fluctuation speed of the actual search reference frequency f _s is Δf / Δt ₁ . That is, assuming that the time information output from the timer 110 is the timer output time t, the frequency difference between the actual search reference frequency f _{s and} the search reference frequency f _{b in} the section from the _first time t ₁ to the second time t _2. Is represented by t × Δf / Δt ₁ . Therefore, the clock frequency estimation unit 122 determines the correction information adjustment algorithm for determining the reference correction information to the content represented by f _b / (f _b + Δf ₁ + t × Δf / Δt ₁ ).

Then, if the actual search reference frequency f _s changes in the same way after the second time t _{2, the} reference correction information determined by this correction information adjustment algorithm is sequentially designated, so that the second time t ₂ after the real search reference frequency f _s, as shown in the figure can be maintained almost the same state to search reference frequency f _b. Then, so that will change the ideal increase rate and decrease rate in the vertical search target frequency 301 also search the reference frequency f _b as shown in FIG. Therefore, it is possible to capture the GPS signal frequency f ₀ earlier than when the search reference frequency is set only at the first time t ₁ , and here, it is captured at the third time t _3. .

FIG. 8 is an explanatory diagram showing an example of a change in frequency to be searched by the GPS signal receiving unit 104 when the reference correction information is set only at the first time t ₁ for reference. It corresponds to. Actual search reference frequency f _s is descends gradually in the form of continued state until the second time t ₂ in FIG. Then, it is understood that the search target frequency 301 captures the GPS signal frequency f ₀ at a fourth time t ₄ after the _third time t _{3 in} FIG.

Note that search target frequency of the search frequency controller 109 to be initialized to the second time t _2, the re-start the search from the search reference frequency f _b. This, when only the correction of the actual search reference frequency f _s, the search target frequency 301 loses continuity, because the search frequency band is not performed may occur.

  In the GPS signal receiving unit 104 shown in FIG. 2, the original signal is extracted from the GPS signal captured by the GPS signal receiving unit 104, and the satellite capturing information such as the code phase, frequency, and signal level at the time of code synchronization is determined by the positioning calculation unit. To 105. Specifically, the integrator 138 shown in FIG. 3 has a peak output when code synchronization is established. Therefore, the positioning calculation unit 105 can acquire the satellite capture information described above by detecting this peak. The positioning calculation unit 105 performs a positioning calculation based on the acquired satellite acquisition information, and outputs a positioning result. Specifically, a pseudo distance between each of the four GPS satellites 24-1 to 24-4 shown in FIG. 1 is calculated from the phase shift amount of the PRN code, and the current position is calculated based on each calculated pseudo distance. Calculate and output the calculation result.

  As described above, according to the first embodiment of the present invention, the frequency of the GPS clock signal is compared with the frequency of the reference clock signal a plurality of times during the search period, and the GPS clock is based on the plurality of comparison results. The fluctuation speed of the signal is detected, and the fluctuation of the GPS clock signal thereafter is predicted. Then, the search reference frequency is corrected so as to compensate for the predicted fluctuation of the GPS clock signal. Thereby, even when the GPS clock signal fluctuates after the search starts, the actual search reference frequency can be adjusted to the ideal value, and the GPS signal search for the set search range can be performed more reliably.

  Note that the fluctuation speed of the GPS clock signal may be detected before the search is started. Further, frequency comparison may be performed at three or more different times to obtain a quadratic or higher order function that defines the fluctuation state of the GPS clock signal, and this may be used to predict fluctuations in the GPS clock signal. .

(Embodiment 2)
The actual search reference frequency is often changed in a pattern corresponding to specific information such as the ambient temperature of the temperature compensated crystal oscillator and the operating state of the apparatus. In such a case, the actual search reference frequency is corrected with higher accuracy if the pattern in which the actual search reference frequency fluctuates in what state is this specific information. GPS signals can be captured more reliably.

  FIG. 9 is a block diagram showing a configuration of a mobile phone as a mobile communication terminal device in which the signal capturing device according to Embodiment 2 of the present invention is used, and corresponds to FIG. 2 of Embodiment 1. . Therefore, the same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. The cellular phone 40 includes a reference frequency control unit 408 having a clock frequency estimation unit 422 that performs a clock frequency estimation process different in content from the clock frequency estimation unit 122 of FIG. In addition, the frequency difference information storage unit 112 is not provided, and the frequency variation information management unit 414 that manages frequency variation information as information regarding the frequency variation of the past GPS clock signal and the host that performs various host processes of the mobile phone 40. A processing unit 415 is provided. In addition, the frequency variation information management unit 414 includes a frequency difference information storage unit 424 that stores a plurality of frequency difference information.

  The host processing unit 415 grasps the operation state of the mobile phone 40, defines each operation state as device operation information, and outputs it. In addition, the temperature of the temperature compensated crystal oscillator detected by a temperature sensor (not shown) disposed in the vicinity of the temperature compensated crystal oscillator of the GPS clock generator 106 is input and output as oscillator temperature information.

FIG. 10 is an explanatory diagram illustrating an example of the contents of the frequency difference information storage unit 424. The horizontal axis represents the elapsed time since the search was started, and the vertical axis represents the frequency. Here, for three different device operation information, frequency difference information at each time when the oscillator temperature information is a certain value is stored as frequency variation information (profile). The first frequency variation information P ₁ is obtained when only the GPS signal receiving unit 104 is operating, and the second and third frequency variation information P ₂ and P ₃ are respectively the GPS signal receiving unit 104 and the wireless communication unit 102. Are both working. However, the second frequency variation information P ₂ is the case where the output level of the wireless communication unit 102 is low, a case where the output level of the third wireless communication unit 102 of the frequency variation information P ₃ is high.

  Such frequency variation information P is prepared for oscillator temperature information of each temperature section. Each frequency variation information P is time-series data composed of a plurality of frequency difference information. Therefore, by referring to the frequency difference information storage unit 424 and specifying a set of conditions of the oscillator temperature information and device operation information output from the host processing unit 415 and the time information output from the timer 110, the condition is determined. Matching or most similar frequency difference information can be acquired.

  FIG. 11 is a flowchart showing the flow of frequency fluctuation information management processing by the frequency fluctuation information management unit 414. When the latest frequency difference information is input from the clock frequency estimation unit 422 and the frequency variation information is requested (step S501: YES), the frequency variation information management unit 414 acquires time information output from the timer 110, and The host processing unit 415 is requested to acquire device operation information and oscillator temperature information (step S502). Then, the frequency variation information management unit 414 refers to the frequency difference information storage unit 424, and the frequency variation having contents that match or most similar to the combination of the acquired information and the frequency difference information input from the clock frequency estimation unit 422. Information is selected (step S503).

  The frequency variation information management unit 414 inputs time information again, reads out frequency difference information corresponding to the time information from the selected frequency variation information, and outputs it to the clock frequency estimation unit 422 (step S504). If the GPS signal search has not been completed yet (step S505: NO) and there is no new request for frequency variation information (step S506: NO), the frequency variation information management unit 414 returns to step S504. The time information is input again, and the corresponding frequency difference information is output to the clock frequency estimation unit 422. If there is a new request for frequency variation information (step S506: YES), the frequency variation information management unit 414 returns to step S502 and reselects the frequency variation information. When the GPS signal search is completed (step S505: YES), the process returns to step S501 again to wait for a request for new frequency variation information (return).

  FIG. 12 is a flowchart showing the flow of the clock frequency estimation process of the clock frequency estimation unit 422, and corresponds to FIG. 6 of the first embodiment. When the search is started and the latest frequency difference information is input and the adjustment of the reference correction information is instructed (step S521: YES), the clock frequency estimation unit 422 starts the search, and the latest frequency difference is input. Information is output to the frequency variation information management unit 414 (step S522). When the frequency difference information is not input from the frequency variation information management unit 414 (step S523: NO), the clock frequency estimation unit 422 returns to step S521 (return). If there is no new instruction to adjust the reference correction information (step S521: NO), the process proceeds directly to step S523.

  When the frequency difference information is input from the frequency variation information management unit 414 corresponding to step S522 (step S523: YES), the clock frequency estimation unit 422 generates reference correction information based on the frequency difference information. And output to the search frequency control unit (step S524). Then, the reference frequency control unit 408 returns to step S523 again and waits for the next frequency variation information to be input.

The reference correction information generated by the clock frequency estimation unit 422 is information representing the ratio of the ideal value of the GPS clock signal frequency to the actual GPS clock signal frequency as already described. Therefore, as in the first embodiment, assuming that the ideal frequency of the GPS clock signal is the same as the chip rate of the PRN code, that is, the search reference frequency f _b and the frequency difference information Δf is input, the clock frequency estimation unit 422 The reference correction information is determined to a value represented by f _b / (f _b + Δf).

  FIG. 13 is an explanatory diagram illustrating an example of a change in the search target frequency by the GPS signal receiving unit 104, and corresponds to FIG. 7 of the first embodiment. A search reference frequency when correction by the clock frequency estimation unit 422 is not performed is indicated by a one-dot chain line 531. Here, as a past search reference frequency measurement result, it is assumed that certain frequency variation information exists in the frequency difference information storage unit 424 and is represented by a dotted line 532 when the search start time is used as a reference.

  Frequency fluctuation information indicated by a dotted line 532 is input by the frequency fluctuation information management unit 414 from the device operation information, the oscillator temperature information, time information indicating the elapsed time since the search was started, and the clock frequency estimation unit 422. Is selected based on the frequency difference information. As already described, the GPS clock signal has substantially the same frequency when the operating state of the mobile phone 40 and the temperature of the temperature compensated crystal oscillator are the same. That is, it is predicted that the actual search reference frequency when the correction indicated by the alternate long and short dash line 531 is not performed fluctuates in substantially the same manner as the frequency fluctuation information indicated by the dotted line 532 as shown in FIG.

Therefore, when the correction using the frequency variation information indicated by this dotted line 532 at time t ₅ of the fifth is started, fifth after time t ₅ of the as shown in the figure the actual search reference frequency f _s can be maintained almost the same state to the reference frequency f _b it is. Then, at time _{t 6} of the sixth high frequency side search target frequency 301 ₁ arrives at the GPS signal frequency _{f 0.}

  As described above, according to the second embodiment of the present invention, the frequency variation information indicating how the GPS clock signal varies with time corresponding to the contents of the oscillator temperature information and the device operation information is stored. Keep it. When searching for a GPS signal, the corresponding frequency variation information is read based on the oscillator temperature information, device operation information, and time information at that time, and the search reference frequency is sequentially corrected using this information. Thereby, even when the GPS clock signal fluctuates after the search starts, the actual search reference frequency can be adjusted to the ideal value, and the GPS signal search for the set search region can be performed more reliably. Further, the processing is simplified and the addition to the apparatus can be reduced as compared with the case where the fluctuation of the GPS clock signal is estimated by calculation.

  Note that the clock frequency estimation unit 422 calculates the rate of change in the frequency of the GPS signal based on the plurality of frequency difference information input from the frequency variation information management unit 414, and calculates the calculation result. Based on this, reference correction information may be generated. Alternatively, information indicating the rate of change of the frequency difference information may be stored in the frequency difference information storage unit 424 as the frequency variation information. Further, the clock frequency estimation unit 422 passes information indicating the rate of change of the frequency of the GPS signal to the frequency variation information management unit 414, and the frequency variation corresponding to the rate of change is transmitted on the frequency variation information management unit 414 side. Information may be selected. In addition, the information stored in the frequency difference information storage unit 424 may be a past measurement value of the device itself. In this case, a function unit that measures frequency difference information, time information, and other information in association with the start of the search and records the information may be provided. Needless to say, the measurement results of other apparatuses having the same configuration may be stored.

(Embodiment 3)
If the process for correcting the actual search reference frequency is performed in a sufficiently short cycle, it is possible to realize a GPS signal search without the correction of the fluctuation speed of the actual search reference frequency.

  FIG. 14 is a block diagram showing a configuration of a mobile phone as a mobile communication terminal device in which the signal capturing device according to Embodiment 3 of the present invention is used, and corresponds to FIG. 2 of Embodiment 1. . Therefore, the same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. The reference frequency control unit 608 of the cellular phone 60 does not include the clock frequency estimation unit 122 of FIG. 2, and instead of the reference frequency setting unit 121 of FIG. 2, a reference frequency setting unit 621 that performs processing different from this is provided. I have. The cellular phone 60 includes a trigger output unit 611 in which a cycle S having a value different from the trigger output unit 111 in FIG. 2 is set, and the frequency difference information storage unit 112 in FIG. Not.

  The search target frequency instructed by the search frequency control unit 109 to the GPS signal receiving unit 104 has a certain frequency width. Even if the frequency of the GPS signal deviates from this search target frequency, if the frequency difference is small, the GPS signal can be captured. Therefore, even when the search target frequency shifts discontinuously, the discontinuity can be ignored if the shift amount is sufficiently small. Therefore, the trigger output unit 611 is set with a period S corresponding to a short time of 500 ms or less. Thus, frequency difference information is input to the reference frequency control unit 608 in a shorter cycle than the reference frequency control unit 108 of FIG.

  FIG. 15 is a flowchart showing the flow of the reference frequency setting process by the reference frequency setting unit 621, and corresponds to FIG. 5 of the first embodiment. When frequency difference information is input from the frequency comparison unit 107 (step S701: YES), the reference frequency setting unit 621 does not input frequency difference information for the second and subsequent times after the start of positioning is instructed, that is, a search. In the case of the start time (step S702: NO), the search frequency control unit 109 is instructed to initialize the search target frequency (step S703). Then, the reference frequency setting unit 621 generates reference correction information corresponding to the content of the frequency difference information input in step S701, and outputs this to the search frequency control unit 109 (step S704). Then, it waits for the frequency difference information to be input again (return). On the other hand, when the frequency difference information is input for the second and subsequent times (step S702: YES), the reference frequency setting unit 621 proceeds to step S704 without issuing an instruction to initialize the search target frequency.

FIG. 16 is an explanatory diagram illustrating an example of a change in the search target frequency by the GPS signal receiving unit 104, and corresponds to FIG. 7 of the first embodiment. If the period S set in the trigger output unit 611 is a value corresponding to the third time Delta] t _3, the actual search reference frequency f _S every third time Delta] t ₃ as shown in the figure the reference frequency f It will be corrected to _b . On the other hand, since the search target frequency is not initialized as in the first and second embodiments, the search target frequency 301 is discontinuous. In particular, in a state of omission of the frequency band occurs in the search target frequency 301 ₁ higher frequency side than the actual search reference frequency f _S.

However, since the third time Δt ₃ is short, its frequency band is very narrow and has little influence on the actual search. In addition, the search frequency control unit 109 widens the frequency band designated as the search target frequency 301 at a time, or the search has a small change rate of the search target frequency 301 when the actual search reference frequency f _S is used as a reference. By applying a frequency control algorithm, it is possible to search for continuous frequency bands. Thus, here will be GPS signal is captured at time t ₇ of the seventh. Searched if the rate of change of frequency 301 is similar to FIG. 7, the time required from the time t ₁ the rate of change the first search target frequency 301 to the seventh time t ₇ when based on the search reference frequency f _S is substantially the same as the time required for the second time t ₂ in FIG. 7 to a third time t _3. Therefore, the GPS signal can be captured earlier by the first time Δt ₁ for detecting the fluctuation speed of the actual search reference frequency f _S.

  As described above, according to the third embodiment of the present invention, the correction of the actual search reference frequency is performed in small increments so that the fluctuation speed of the GPS clock signal can be ignored. As a result, the correction of the fluctuation speed of the actual search reference frequency can be omitted, and the process is simplified, so that the cost of the apparatus can be reduced and the load can be reduced. As in the first embodiment, the rate of change of the frequency of the GPS clock signal may be obtained, and the period for outputting the trigger may be set to an appropriate value according to the rate of change.

  In each of the embodiments described above, a clock signal obtained by communication with a radio base station is used as a reference clock signal as a target for comparison of GPS clock signals. However, other clock signals are used. May be. For example, when a GPS signal can be acquired on a certain channel, a clock signal obtained in synchronization with the carrier frequency of the GPS signal may be used as a reference clock signal for a search on another channel. Further, although the description has been made assuming that the ideal frequency of the GPS clock signal is the same as the chip rate of the PRN code, it is naturally not limited to this. The frequency difference information output from the frequency comparison unit can be similarly applied by multiplying the value obtained by dividing the chip rate of the PRN code by the ideal value of the GPS clock signal. Furthermore, the case where the present invention is applied to a mobile phone having a GPS function has been described. However, the present invention is not limited to this, and an attempt is made to capture a signal having a predetermined frequency using a clock signal whose frequency may vary. Of course, the present invention can be applied to other various apparatuses.

  The present invention is suitable for use in a mobile communication terminal having a function of capturing a signal transmitted from a GPS (Global Positioning System) satellite.

The system block diagram which shows the structure of the communication system in which the signal acquisition apparatus which concerns on Embodiment 1 of this invention is used. 1 is a block diagram showing a configuration of a mobile phone according to Embodiment 1 of the present invention. 1 is a circuit configuration diagram showing a circuit configuration of a GPS signal receiving unit according to Embodiment 1 of the present invention. The flowchart which shows the flow of the trigger output process by the trigger output part which concerns on Embodiment 1 of this invention. The flowchart which shows the flow of the reference frequency setting process by the reference frequency setting part which concerns on Embodiment 1 of this invention. The flowchart which shows the flow of the clock frequency estimation process by the clock frequency estimation part which concerns on Embodiment 1 of this invention. Explanatory drawing which shows an example of the mode of the change of the search object frequency by the GPS signal receiving part which concerns on Embodiment 1 of this invention. Explanatory drawing which shows an example of the mode of a change of the search object frequency by the GPS signal receiving part when the search reference frequency is set only at the first time for reference. The block diagram which shows the structure of the mobile telephone as a mobile communication terminal device in which the signal acquisition apparatus which concerns on Embodiment 2 of this invention is used. Explanatory drawing which shows an example of the content of the frequency difference information storage part which concerns on Embodiment 2 of this invention. The flowchart which shows the flow of the frequency variation information management process by the frequency variation information management part which concerns on Embodiment 2 of this invention. The flowchart which shows the flow of the clock frequency estimation process of the clock frequency estimation part which concerns on Embodiment 2 of this invention. Explanatory drawing which shows an example of the mode of the change of the search object frequency by the GPS signal receiving part which concerns on Embodiment 2 of this invention. A block diagram showing a configuration of a mobile phone as a mobile communication terminal device in which a signal capturing device according to Embodiment 3 of the present invention is used The flowchart which shows the flow of the reference frequency setting process by the reference frequency setting part which concerns on Embodiment 3 of this invention. Explanatory drawing which shows an example of the mode of the change of the search object frequency by the GPS signal receiving part which concerns on Embodiment 3 of this invention. Explanatory drawing which shows an example of the state of the search of the conventional GPS signal by the conventional proposal

Explanation of symbols

10, 40, 60 Mobile phone 20 Communication system 21 Mobile phone network 23 Radio base station 24 GPS satellite 101 Radio antenna 102 Radio communication unit 103 GPS antenna 104 GPS signal reception unit 105 Positioning calculation unit 106 GPS clock generation unit 107 Frequency Comparison unit 108, 408, 608 Reference frequency control unit 109 Search frequency control unit 110 Timer 111, 611 Trigger output unit 112 Frequency difference information storage unit 113 Positioning start instruction input unit 121, 621 Reference frequency setting unit 122, 422 Clock frequency estimation unit 123 Reference Correction Information Storage Unit 131 Amplifier Circuit 132 First Mixer 133 First Band Limiting Filter 134 Second Mixer 135 Second Band Limiting Filter 136 Analog-to-Digital Converter 137 Third Mixer 138 Integrator 1 39 Frequency Multiplier 140 Numerically Controlled Oscillator 141 PRN Code Generation Unit 414 Frequency Fluctuation Information Management Unit 415 Host Processing Unit 424 Frequency Difference Information Storage Unit

Claims (7)

A frequency difference detecting means for detecting a frequency difference as a difference from an ideal value of the frequency of a predetermined clock signal;
Clock frequency estimating means for estimating the frequency of the predetermined clock signal based on detection results at a plurality of times by the frequency difference detecting means;
A signal receiving means for searching for a signal to be captured using the predetermined clock signal as an operation clock, and correcting the frequency of the signal to be searched based on an estimated value by the clock frequency estimating means;
A signal capturing device comprising: A frequency difference information storage means for storing information relating to a frequency difference as a difference from an ideal value of the frequency of a predetermined clock signal in association with an elapsed time from the start of a search for a signal to be captured;
A timer for measuring an elapsed time from the start of the search;
Clock frequency estimation means for acquiring information corresponding to the elapsed time measured by the timer from the frequency difference information storage means and estimating the frequency of the predetermined clock signal;
A signal receiving means for searching for a signal to be captured using the predetermined clock signal as an operation clock, and correcting the frequency of the signal to be searched based on an estimated value by the clock frequency estimating means;
A signal capturing device comprising: A frequency difference detecting means for repeatedly detecting a frequency difference as a difference from an ideal value of a frequency of a predetermined clock signal at a predetermined period;
The signal to be captured is searched using the predetermined clock signal as an operation clock, and the frequency of the signal to be searched is corrected based on the detection result each time the frequency difference detection unit performs the detection. Signal receiving means for
A signal capturing device comprising:   4. The signal acquisition according to claim 1, wherein the frequency difference detection unit detects the frequency difference by comparing a clock signal having a known frequency with the predetermined clock signal. 5. apparatus. Search frequency control means for calculating a value obtained by multiplying the frequency of the signal to be searched by the ratio of the ideal value of the frequency of the predetermined clock signal to the estimated value by the clock frequency estimation means,
3. The signal capturing apparatus according to claim 1, wherein the signal receiving unit corrects the frequency of a signal to be searched based on a calculation result by the search frequency control unit.   The clock frequency estimation means calculates a change rate of the frequency of the predetermined clock signal based on the latest detection result obtained by the frequency difference detection means and a detection result before this, and the calculated change 2. The signal capturing apparatus according to claim 1, wherein the frequency of the predetermined clock signal is estimated based on a rate and the latest detection result. A frequency difference detection step of detecting a frequency difference as a difference from an ideal value of the frequency of a predetermined clock signal at each of a plurality of times; and
A clock frequency estimating step for estimating a frequency of the predetermined clock signal based on detection results at the plurality of times by the frequency difference detecting step;
A search target frequency for correcting a frequency of a signal to be searched based on an estimated value by the clock frequency estimating means for a signal receiving means for searching for a signal to be acquired using the predetermined clock signal as an operation clock Control steps;
A signal acquisition method comprising:

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