JP2011078052A - Capture frequency-determining method and receiving apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel technique for more accurately obtaining a capture frequency. <P>SOLUTION: A GPS (global positioning system) satellite signal as a sort of CDMA (code division multiple access) signals and a replica code of the GPS satellite signal are used to perform correlative arithmetic operation of a reception signal receiving the GPS satellite signal. A plurality of model functions for calculation are then set by deviating, in a frequency direction, a correlative value model function obtained by modeling a change of a correlative value obtained by the correlative arithmetic operation in the frequency direction using a sinc function. A degree of conformity between the correlative value and each model function for calculation is calculated and based on the calculated degree of conformity, a conformed frequency conformed to the correlative value is determined. The conformed frequency determined is then determined as a capture frequency of the GPS satellite signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an acquisition frequency determination method and a reception apparatus.

  A GPS (Global Positioning System) is widely known as a positioning system using positioning signals, and is used in a GPS receiver built in a mobile phone or a car navigation device. The GPS receiver performs position calculation processing for obtaining a three-dimensional coordinate value indicating the position of the receiver and a clock error based on information such as the positions of a plurality of GPS satellites and pseudo distances from each GPS satellite to the receiver. .

  A GPS satellite signal is a type of communication signal that is spread-modulated by a CDMA (Code Division Multiple Access) method that has long been known as a spread spectrum modulation method. The frequency at which the GPS satellite transmits the GPS satellite signal (carrier frequency) is preliminarily defined as 1.57542 [GHz], but due to the influence of Doppler caused by the movement of the GPS satellite and the receiving device, The frequency at which the GPS receiver receives GPS satellite signals does not necessarily match the carrier frequency. Therefore, the GPS receiver performs a frequency search for capturing a GPS satellite signal from the received signals, and determines a capture frequency for capturing the GPS satellite signal.

  The acquisition frequency is generally determined by performing a correlation operation between the received signal and a spread code replica signal simulating the spread code of the GPS satellite signal while changing the frequency (so-called frequency direction correlation calculation). Used. For example, as disclosed in Patent Document 1, a method of determining a capture frequency by using triangular interpolation with respect to a correlation calculation result obtained for each frequency is used.

JP 2007-256111 A

  The technique disclosed in Patent Document 1 is a technique for approximating the correlation calculation result in the frequency direction to be an isosceles triangle shape and determining the acquisition frequency using triangular interpolation. Therefore, an isosceles triangle approximation may not be sufficient to obtain a more accurate capture frequency.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to propose a new technique for more accurately obtaining the capture frequency.

  A first form for solving the above problems is to perform correlation calculation of a received signal that has received the CDMA signal using a spread code replica of the CDMA signal, and to obtain an ideal curve of the correlation calculation result as a sinc function. Shifting the model function modeled by using a frequency direction, determining an adaptive frequency that matches the correlation calculation result, and determining an acquisition frequency of the CDMA signal based on the adaptive frequency This is a frequency determination method.

  As another invention, a correlation calculation unit that performs correlation calculation of a received signal that has received the CDMA signal using a spread code replica of the CDMA signal, and an ideal curve of the correlation calculation result are modeled using a sinc function. The model function is shifted in the frequency direction, an adaptive frequency determination unit that determines an adaptive frequency that matches the correlation calculation result, an acquisition frequency determination unit that determines an acquisition frequency of the CDMA signal based on the adaptive frequency, and the determination A receiving apparatus including an acquisition unit that acquires the CDMA signal using the acquired acquisition frequency may be configured.

  According to the first embodiment and the like, correlation calculation is performed on a received signal that has received a CDMA signal using a spreading code replica of the CDMA signal. Then, the model function obtained by modeling the ideal curve of the correlation calculation result using the sinc function is shifted in the frequency direction, and an appropriate frequency that matches the correlation calculation result is determined. Then, the acquisition frequency of the CDMA signal is determined based on the adaptive frequency.

  When a correlation calculation in the frequency direction is performed using a spread code replica on a signal modulated by CDMA, the ideal curve can be approximated using a sinc function. Therefore, the acquisition frequency of the CDMA signal is obtained more accurately by a method of searching for a frequency that matches the correlation calculation result between the received signal and the spread code replica while shifting the model function modeled using the sinc function in the frequency direction. It becomes possible.

  Further, as a second mode, the acquisition frequency determination method according to the first mode, wherein the matching frequency is determined by using a plurality of reference frequencies and a predetermined frequency selection pattern. A fitness calculation process for calculating a fitness between the model function and the correlation calculation result using the value of the model function and the value of the correlation calculation result at each of the fitness determination frequencies, and the model function as a frequency It is also possible to configure a capture frequency determination method in which the frequency having the maximum matching level is determined as the matching frequency by performing the shift in the direction.

  According to the second embodiment, the value of the model function at each of the plurality of fitness determination frequencies determined using the given reference frequency and the given frequency selection pattern, the received signal, and the spread code replica Using the value of the correlation calculation result, the fitness between the model function and the correlation calculation result is calculated. At this time, the fitness is calculated while shifting the model function in the frequency direction, and the frequency having the highest fitness is determined as the fitness frequency. Since the fitness determination frequency is determined using the reference frequency and the frequency selection pattern, it is possible to improve the efficiency of the process for determining the adaptation frequency.

  Further, as a third form, the acquisition frequency determination method of the second form, wherein the frequency selection pattern is a pattern of frequency intervals that defines characteristics of the model function with reference to a center frequency of the model function. You may comprise the acquisition frequency determination method.

  According to the third embodiment, by determining a frequency interval pattern that defines the characteristics of the model function as a frequency selection pattern with the center frequency of the model function as a reference, a frequency for determining fitness according to the characteristics of the model function. Is selected, and the reliability of the calculated fitness is improved.

  Further, as a fourth form, the acquisition frequency determination method according to the second or third form, wherein the goodness-of-fit calculation processing includes the goodness-of-fit according to a value change near the maximum value of the model function by the sinc function. The acquisition frequency determination method may be configured so as to include a process of performing a compensation calculation for suppressing the calculation error.

  According to the fourth aspect, the fitness calculation processing performs the compensation calculation processing for suppressing the fitness calculation error associated with the value change in the vicinity of the maximum value of the model function by the sinc function. As a result, the matching frequency is determined based on the matching degree in which the calculation error is suppressed, and the accuracy of the required acquisition frequency is further improved.

Explanatory drawing of the principle of acquisition frequency determination. The block diagram which shows the function structure of a portable telephone. The figure which shows the circuit structure of a baseband process circuit part. The figure which shows an example of the data structure of the data classified by model function for calculation. The flowchart which shows the flow of a baseband process. The flowchart which shows the flow of an acquisition frequency determination process. The figure which shows an example of an experimental result.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Below, the case where this invention is applied to the GPS receiver which receives the GPS satellite signal transmitted from a GPS (Global Positioning System) satellite is demonstrated. Of course, embodiments to which the present invention is applicable are not limited to the embodiments described below.

1. Principle First, the principle of acquisition frequency determination in this embodiment will be described.
GPS satellites are a kind of positioning satellites, and four or more satellites are arranged on each of the six orbiting surfaces of the earth. In principle, four or more satellites are always observed from anywhere on the earth in a geometrical arrangement. It is operated as possible.

  GPS satellites transmit navigation messages such as almanac and ephemeris in GPS satellite signals. The GPS satellite signal is a 1.57542 [GHz] communication modulated by a CDMA (Code Division Multiple Access) system known as a spread spectrum system by a PRN (Pseudo Random Noise) code which is a kind of spreading code different for each satellite. Signal. The PRN code is a pseudo-random noise code having a repetition period of 1 ms with a code length of 1023 chips as one PN frame.

  The GPS receiver performs a correlation calculation process that calculates and integrates the correlation between the PRN code and the replica code included in the received signal using, for example, an FFT (Fast Fourier Transform) operation, and outputs a GPS satellite signal from the received signal. To capture. The replica code is a signal that simulates a PRN code included in a GPS satellite signal to be captured that is generated in a pseudo manner. The GPS receiver performs this correlation calculation for each of the phase direction and the frequency direction.

  In the correlation calculation in the frequency direction, the correlation value is maximized when the frequency of the generated signal of the replica code matches the frequency of the received signal. More specifically, when the relationship between the frequency of the generated signal of the replica code and the correlation value obtained by the correlation calculation is plotted on a graph, the correlation value becomes maximum at a certain frequency, and the correlation value decreases as the distance from the frequency increases. The characteristic to do is seen. It is known that the frequency change of the correlation value can be ideally approximated using a “sinc function” obtained by dividing a sine function (sine function) by the variable.

  The inventor of the present application uses a model function (hereinafter referred to as a “correlation value model function”) in which the correlation value is modeled using a “sinc function” based on the frequency change characteristics of the correlation value. Thus, a method for determining an accurate acquisition frequency for acquiring a GPS satellite signal from a received signal has been devised. Note that the frequency in the following description means a frequency in an intermediate frequency band after down-converting a high-frequency received signal (RF (Radio Frequency) signal).

  First, a frequency (hereinafter referred to as “reference frequency”) “fs” as a reference for determining the capture frequency is set. The reference frequency “fs” is 1.57542 [GHz], which is the carrier frequency of the GPS satellite signal (for example, after the carrier frequency is changed to the intermediate frequency in the initial position calculation after the GPS receiver is turned on). Frequency). If a GPS satellite signal has already been captured, the frequency (latest capture frequency) used as the capture frequency at that time can be set as the reference frequency.

  Next, using the set reference frequency “fs” and a predetermined frequency selection pattern, the fitness determination made up of a plurality of fitness determination frequencies (hereinafter referred to as “fitness determination frequencies”). Determine the frequency set. The adaptability determination frequency is a frequency used to determine the adaptability of the correlation value obtained by the correlation calculation in the frequency direction to the correlation value model function “M (f)”. The correlation value model function “M (f)” is a function that models a change in the frequency direction of the correlation value.

  The frequency selection pattern is a pattern determined in advance to select the fitness determination frequency using the reference frequency “fs”. The frequency selection pattern can be determined as an arbitrary pattern, but it is preferable that the frequency selection pattern be selected so that frequencies around the reference frequency “fs” are selected before and after the reference frequency “fs”. For example, five frequency patterns “fp−b”, “fp−a”, “fp”, “fp + a”, and “fp + b” are determined as frequency selection patterns with the pattern center frequency “fp” as the center. Can do.

  Here, the values of “a” and “b” are coefficients that determine the frequency interval of the fitness determination frequency (hereinafter referred to as “frequency interval coefficient”). For the frequency interval coefficients “a” and “b”, appropriate values are selected and set according to the spread in the frequency direction (width in the frequency direction) of the correlation value model function “M (f)”. More specifically, when the pattern center frequency “fp” is matched with the center frequency of the correlation value model function, the frequencies (the five frequencies described above) defined as the frequency selection pattern are correlated with the correlation value model function “M”. It is preferable to set a value included in the main lobe part of (f) ".

Next, the frequency selection pattern is applied to the reference frequency “fs” to select the fitness determination frequency. Specifically, the pattern frequency “fp” is replaced with the reference frequency “fs”, and the fitness determination frequency is selected according to the frequency selection pattern. For example, when the above-described frequency selection pattern including the five frequencies is applied, the five frequencies “fs−b”, “fs−a”, “fs”, “fs + a”, and “fs + b” are used for determining the fitness. Select as frequency “f _i ”. However, the suffix “i” indicates the frequency of the fitness determination frequency.

Next, for each fitness determination frequency “f _i ”, the correlation value “p _i ” is calculated by performing a correlation operation between the received signal and the replica code. For each fitness determination frequency “f _i ”, the correlation value model function “M (f)” is shifted in the frequency direction, and each fitness determination frequency “f _i ” is changed to each correlation value model function “M”. A function value “M (f _i )” obtained by substituting for “(f)” is obtained. Specifically, the correlation value model function “M (f)” is shifted in the frequency direction by a predetermined shift width, and the fitness value determination frequency “f _i ” is assigned to each obtained function to obtain the function value “M _j (f _i ) ”.

Here, each function obtained by shifting the correlation value model function by a predetermined shift width is referred to as “calculation model function” and is represented by “M _j (f)”. However, the subscript “j” indicates the number of the model function for calculation. Further, the amount of frequency shift from the correlation value model function “M (f)” of each calculation model function “M _j (f)” is represented by “Δf”.

The frequency shift width of the correlation value model function can be set as appropriate, but it is preferable to set a value shorter than the frequency interval of each fitness determination frequency “f _i ”. Further, the number of calculation model functions “M _j (f)” can be set as appropriate, but it is desirable that the number is sufficient to cover the frequency range. As the frequency shift width is shorter and the number of calculation model functions is larger, the acquisition frequency can be obtained more accurately.

但し、「ｐ_i」は、ｉ番目の適合度判定用周波数について得られた相関値を示している。また、「ｎ」は、適合度判定用周波数の総数を示している。 When the function value “M _j (f _i )” is calculated, the fitness “S _j ” is calculated for each calculation model function “M _j (f)” according to the following equation (1).

However, “p _i ” indicates the correlation value obtained for the i-th fitness determination frequency. In addition, “n” indicates the total number of fitness determination frequencies.

As can be seen from the equation (1), the fitness “S _j ” includes the correlation value “p _i ” at the fitness determination frequency and the fitness for each fitness determination frequency “f _i ”. The product of the function value “M _j (f _i )” at the determination frequency is obtained by summing up all the fitness determination frequencies “f _i ”. It means that the higher the matching degree, the higher the degree of matching of the correlation calculation result to the correlation value model function.

After calculating the "S _j" goodness-of-fit for each calculation model function "M _j (f)," goodness of fit "S _j" is to determine the model function for computation that resulted in maximum, shifting the frequency of the calculation model function The quantity “Δf” is specified. Then, the frequency “fs−Δf” obtained by subtracting the specified frequency shift amount “Δf” from the reference frequency “fs” is set as the appropriate frequency, and the capture frequency is determined based on the appropriate frequency. In the present embodiment, the matching frequency itself is determined as the capture frequency.

  A specific example of acquisition frequency determination will be described with reference to FIG. Here, the case where the correlation value model function is defined as “M (f) = sinc (f−fs)” using the sinc function will be illustrated and described. FIG. 1 shows the result of plotting the correlation value and the function value of the model function for calculation at each frequency with the reference frequency “fs” matched to the vertical axis. Further, the change in the frequency direction of the correlation value is indicated by a one-dot chain line, and the calculation model function is indicated by a solid line.

  The frequency selection pattern is set as a pattern in which the fitness determination frequencies are located in the main lobe portion of the sinc function. For example, assuming that the frequency interval coefficients “a” and “b” are “a = 15 [Hz]” and “b = 50 [Hz]”, respectively, “fs−50 [Hz]” and “fs−15 [Hz]”. , “Fs [Hz]”, “fs + 15 [Hz]”, and “fs + 50 [Hz]” are selected as the frequencies for determining the fitness.

  When the correlation calculation between the received signal and the replica code signal is performed for each of these five fitness determination frequencies, five correlation values as indicated by black circles in FIG. 1 are obtained. Although the correlation value is illustrated and described here as a value in the range of “−1” to “1”, the absolute value of the correlation value may be calculated to be a value in the range of “0” to “1”.

Next, assuming that the shift amount in the frequency direction of the correlation value model function is “Δf”, for example, the 0th calculation model function “M ₀ (f) = sinc (f−fs)” with “Δf = 0”, “ Delta] f = Delta] f ₁ "and the first calculation model function and" _{M 1 (f) = sinc (} f-fs + Δf 1) and "" Delta] f = second calculation model function was Delta] f ₂ "," M ₂ (f) = 3 (sinc (f−fs + Δf ₂ )) ”is set. In order to facilitate understanding, the number of model functions for calculation is illustrated and described here as three.

  Then, for each set calculation model function, when the function values are obtained by substituting the above-described five fitness determination frequencies, five function values indicated by white circles are obtained for the 0th calculation model function. For the first calculation model function, five function values indicated by triangles are obtained, and for the second calculation model function, five function values indicated by rectangles are obtained.

Then, using the correlation values indicated by the black circles and the function values indicated by the white circles, triangles, and squares, the fitness “S” is calculated for each calculation model function “M _j (f)” according to the following equation (2). _j "is calculated.

In this case, the fitness “S ₁ ” calculated for the first correlation value model function “M ₁ (f)” is maximized. This is because, in FIG. 1, among the three calculation model functions of the 0th to second calculation model functions, the most appropriate simulation / approximation of the frequency change of the correlation value indicated by the alternate long and short dash line is the first This is because the calculation model function is “M ₁ (f)”. Therefore, the frequency “fs−Δf ₁ ” obtained by subtracting the frequency shift amount “Δf ₁ ” of the first calculation model function “M ₁ (f)” from the reference frequency “fs” is set as the adaptive frequency, and this value is set as the capture frequency. decide.

2. Functional Configuration FIG. 2 is a block diagram showing a functional configuration of the mobile phone 1. The mobile phone 1 includes a GPS antenna 9, a GPS receiving unit 10, a host CPU (Central Processing Unit) 30, an operation unit 40, a display unit 50, a mobile phone antenna 60, and a mobile phone radio communication circuit. And a flash ROM (Read Only Memory) 80 and a RAM (Random Access Memory) 90.

  The GPS antenna 9 is an antenna that receives an RF (Radio Frequency) signal including a GPS satellite signal transmitted from a GPS satellite, and outputs the received signal to the GPS receiving unit 10.

  The GPS receiver 10 is a position calculation circuit that measures the position of the mobile phone 1 based on a signal output from the GPS antenna 9, and is a functional block corresponding to a so-called GPS receiver. The GPS receiving unit 10 includes an RF (Radio Frequency) receiving circuit unit 11 and a baseband processing circuit unit 20. The RF receiving circuit unit 11 and the baseband processing circuit unit 20 can be manufactured as separate LSIs (Large Scale Integration) or can be manufactured as one chip.

  The RF receiving circuit unit 11 is an RF signal processing circuit block, and generates an oscillation signal for RF signal multiplication by dividing or multiplying a predetermined oscillation signal. Then, by multiplying the generated oscillation signal by the RF signal output from the GPS antenna 9, the RF signal is down-converted to an intermediate frequency signal (hereinafter referred to as an "IF (Intermediate Frequency) signal"), After the IF signal is amplified, it is converted into a digital signal by an A / D converter and output to the baseband processing circuit unit 20.

  The baseband processing circuit unit 20 performs correlation processing on the IF signal output from the RF receiving circuit unit 11 to capture and extract GPS satellite signals, decodes the data, and extracts navigation messages, time information, and the like. It is a circuit part.

  FIG. 3 is a diagram illustrating an example of a circuit configuration of the baseband processing circuit unit 20. The baseband processing circuit unit 20 includes a satellite capturing unit 21, a CPU 23, a ROM 25, and a RAM 27. The satellite capturing unit 21 is a circuit unit that captures a GPS satellite signal from the reception signal (IF signal) output from the RF receiving circuit unit 11, and includes a correlation calculation unit 211 and a replica code generation unit 213. ing.

  The correlation calculation unit 211 performs a correlation calculation process for calculating the correlation between the PRN code included in the received signal and the replica code generated by the replica code generation unit 213, and acquires the GPS satellite signal. If the GPS satellite signal to be captured is correct, the PRN code and replica code included in the GPS satellite signal match (capture success), and if they are incorrect, they do not match (capture failure). Therefore, by determining the peak of the calculated correlation value, it can be determined whether the acquisition of the GPS satellite signal was successful, by changing the replica code one after another, and performing the correlation operation with the same received signal, GPS satellite signals can be captured.

  The host CPU 30 is a processor that comprehensively controls each unit of the mobile phone 1 according to various programs such as a system program stored in the flash ROM 80. The host CPU 30 displays the position information input from the baseband processing circuit unit 20 on the display unit 50 or uses it for various applications.

  The operation unit 40 is an input device configured by, for example, a touch panel, a button switch, or the like, and outputs a pressed key or button signal to the host CPU 30. By operating the operation unit 40, various instructions such as a call request, a mail transmission / reception request, and a position calculation request are input.

  The display unit 50 is configured by an LCD (Liquid Crystal Display) or the like, and is a display device that performs various displays based on display signals input from the host CPU 30. The display unit 50 displays a position display screen, time information, and the like.

  The cellular phone antenna 60 is an antenna that transmits and receives cellular phone radio signals to and from a radio base station installed by a communication service provider of the cellular phone 1.

  The cellular phone wireless communication circuit unit 70 is a cellular phone communication circuit unit configured by an RF conversion circuit, a baseband processing circuit, and the like, and performs modulation and demodulation of the cellular phone radio signal, thereby enabling communication and mailing. Realize transmission / reception and so on.

  The flash ROM 80 is a readable / writable nonvolatile storage device, and stores a system program for the host CPU 30 to control the mobile phone 1 and various programs and data for realizing a position calculation function.

  The RAM 90 is a readable / writable volatile storage device, and forms a work area for temporarily storing a system program executed by the host CPU 30, various processing programs, data being processed in various processing, processing results, and the like. .

3. Data Configuration FIG. 3 shows an example of data stored in the ROM 25 of the baseband processing circuit unit 20. The ROM 25 stores a baseband processing program 251 that is read by the CPU 23 and executed as baseband processing (see FIG. 5), and a frequency selection pattern 253. Further, the baseband processing program 251 includes a capture frequency determination program 2511 executed as a capture frequency determination process (see FIG. 6) as a subroutine. These processes will be described later in detail using a flowchart.

  FIG. 3 shows an example of data stored in the RAM 27 of the baseband processing circuit unit 20. The RAM 27 stores a fitness determination frequency set 271, correlation value data 273, calculation model function-specific data 275, a capture frequency 277, and a GPS calculation position 279.

  FIG. 4 is a diagram illustrating an example of a data configuration of the calculation model function-specific data 275. The calculation model function-specific data 275 is data in which the result of the arithmetic processing for each of the plurality of calculation model functions is stored. Specifically, the number 2751 of the calculation model function, the frequency shift amount (Δf) 2753 from the correlation value model function of the calculation model function, and each fitness determination frequency are substituted into the calculation model function. The function value 2755 for matching frequency obtained by doing so and the fitness 2757 calculated using the calculation model function are stored.

4). Processing Flow FIG. 5 is a flowchart showing the flow of baseband processing executed in the mobile phone 1 when the CPU 23 reads and executes the baseband processing program 251 stored in the ROM 25. Although not specifically described, during the execution of the following baseband processing, reception of the RF signal by the GPS antenna 9 and down-conversion of the RF signal to the IF signal by the RF reception circuit unit 11 are performed, and the IF signal is processed by the baseband processing. It is assumed that the circuit unit 20 is in an output state as needed.

  First, the CPU 23 performs capture target satellite determination processing (step A1). Specifically, a GPS satellite located in the sky at the latest GPS calculation position 279 at the current time measured by a clock unit (not shown) is determined by using satellite orbit data such as almanac and ephemeris, and is captured. Satellite.

  Next, the CPU 23 executes the process of loop A for each capture target satellite determined in step A1 (steps A3 to A9). In the process of loop A, the CPU 23 reads and executes the acquisition frequency determination program 2511 stored in the ROM 25, thereby performing acquisition frequency determination processing (step A5).

FIG. 6 is a flowchart showing the flow of acquisition frequency determination processing.
First, the CPU 23 determines whether or not the satellite capture unit 21 has captured the capture target satellite (step B1). If the CPU 23 determines that the capture is completed (step B1; Yes), it is stored in the RAM 27. The latest acquisition frequency 277 is set as a reference frequency (step B3).

  If it is determined in step B1 that the capture target satellite has not been captured yet (step B1; No), the CPU 23 converts the carrier frequency of the GPS satellite signal, more specifically, the carrier frequency into an intermediate frequency. The frequency after the setting is set as a reference frequency (step B4).

  Thereafter, the CPU 23 applies the frequency selection pattern 253 stored in the ROM 25 to determine a fitness determination frequency set (step B5). Specifically, for example, five frequencies centered on the reference frequency set in step B3 or B4 are selected according to the frequency selection pattern 253 to determine the fitness determination frequency set.

  Thereafter, the CPU 23 causes the correlation calculation unit 211 to perform a correlation operation between the received signal and the replica code for each fitness determination frequency included in the fitness determination frequency group determined in step B5, and correlates the correlation value. The value data 273 is stored in the RAM 27 (step B7).

  Next, the CPU 23 determines the number of correlation value model functions and the frequency shift width, and sets a plurality of calculation model functions. Then, the set number 2751 of each calculation model function and the frequency shift amount “Δf” 2753 are associated with each other and stored in the RAM 27 as calculation model function-specific data 275 (step B9).

  Next, the CPU 23 executes processing of loop B for each calculation model function (steps B11 to B17). In the process of loop B, the CPU 23 calculates a function value 2755 for each fitness determination frequency by substituting each fitness determination frequency into the calculation model function, and corresponds to the number 2751 of the calculation model function. In addition, the data is stored in the calculation model function-specific data 275 of the RAM 27 (step B13).

  Then, the CPU 23 uses the correlation value at each fitness determining frequency stored in the correlation value data 273 and the function value 2755 for matching determination frequency stored in the model function-specific data 275 for calculation. The fitness 2757 is calculated according to the equation (1). The calculated fitness 2757 is stored in the calculation model function-specific data 275 of the RAM 27 in association with the calculation model function number 2751 (step B15). Then, the CPU 23 shifts the processing to the next calculation model function.

  After performing the processing of steps B13 and B15 for all the calculation model functions, the CPU 23 ends the processing of loop B (step B17). Thereafter, the CPU 23 determines the calculation model function having the maximum fitness 2757 (step B19).

  Then, the CPU 23 determines the adaptive frequency based on the frequency shift amount “Δf” 2753 from the correlation value model function of the calculation model function determined in step B19 (step B21). Specifically, the frequency obtained by subtracting the frequency shift amount “Δf” 2753 from the currently set acquisition frequency 277 is determined as the adaptive frequency.

  Then, the CPU 23 determines the adaptive frequency determined in step B21 as the capture frequency 277, and updates and stores it in the RAM 27 (step B23). Then, the CPU 23 ends the capture frequency determination process.

  Returning to the baseband processing of FIG. 5, after performing the acquisition frequency determination process, the CPU 23 tries to acquire the GPS satellite signal from the acquisition target satellite at the acquisition frequency 277 determined in step B23. (Step A7). Then, the CPU 23 shifts the process to the next capture target satellite.

  After performing the processing of steps A5 and A7 for all the capture target satellites, the CPU 23 ends the processing of loop A (step A9). Thereafter, the CPU 23 calculates satellite information such as the satellite position, satellite moving speed, and satellite moving direction of the captured satellite based on the navigation message included in the captured GPS satellite signal (step A11).

  Based on the satellite information calculated in step A11, the CPU 23 performs a GPS position calculation process for calculating a position by using, for example, a position calculation calculation using a pseudo distance, and the calculated position is stored in the RAM 27 as a GPS calculation position 279. Store (step A13). The details of the position calculation calculation are well known in the art and will not be described in detail.

  Next, the CPU 23 outputs the GPS calculation position 279 to the host CPU 30 (step A15). Then, the CPU 23 determines whether or not to end the position calculation (step A17). When it is determined that the position calculation has not ended yet (step A17; No), the CPU 23 returns to step A1. If it is determined that the position calculation is to be terminated (step A17; Yes), the baseband process is terminated.

5). Effects According to the present embodiment, the correlation calculation of the received signal that received the GPS satellite signal is performed using a GPS satellite signal that is a kind of CDMA signal and a replica code of the GPS satellite signal. Then, a plurality of calculation model functions are set by shifting the correlation value model function obtained by modeling the change in the frequency direction of the correlation value obtained by the correlation calculation using the sinc function in the frequency direction. Then, a matching degree between the correlation value and each calculation model function is calculated, and a matching frequency matching the correlation value is determined based on the calculated matching degree. Then, the determined matching frequency is determined as the capture frequency of the GPS satellite signal.

  When a correlation calculation in the frequency direction is performed on a GPS satellite signal spread-modulated by the CDMA method using a replica code, an ideal curve can be approximated using a sinc function. For this reason, by shifting the correlation value model function modeled using the sinc function in the frequency direction and searching for a frequency that matches the correlation calculation result between the received signal and the replica code of the GPS satellite signal, The acquisition frequency can be obtained more accurately.

6). Modification 6-1. Application System In the above-described embodiment, a GPS satellite signal is taken as an example of a CDMA signal, and a method for determining a capture frequency in a GPS receiver that receives a GPS satellite signal has been described. However, a signal other than a GPS satellite signal is received. The present invention can be similarly applied to a receiving apparatus. In other words, any receiving apparatus that receives a signal that is spread-modulated by the CDMA method and that is configured to acquire a CDMA signal by performing a correlation operation using a spreading code replica may be used.

6-2. In the above-described embodiment, the case where the present invention is applied to a mobile phone that is a kind of electronic device has been described as an example. However, electronic devices to which the present invention can be applied are not limited thereto. Absent. For example, the present invention can be similarly applied to other electronic devices such as a car navigation device, a portable navigation device, a personal computer, a PDA (Personal Digital Assistants), and a wristwatch.

6-3. In the above-described embodiment, the GPS is described as an example of the satellite position calculation system, but WAAS (Wide Area Augmentation System), QZSS (Quasi Zenith Satellite System), GLONASS (GLObal NAvigation Satellite System), GALILEO Other satellite position calculation systems may be used.

6-4. Compensation calculation of suitability calculation error The sinc function used as the correlation value model function in the above-described embodiment has a characteristic that the function value becomes extremely small when slightly away from the center frequency. That is, the sinc function is a function having a large change in function value near the maximum value. For this reason, when the fitness value of the correlation value is calculated using the sinc function, the fitness value tends to be dragged in the direction of the maximum value, and there is a problem that a calculation error is easily included in the fitness value. Therefore, compensation calculation for suppressing the calculation error of the fitness may be performed.

式（３）から求められる適合度「Ｓ_j」は、式（１）から求められる適合度を、各適合度判定用周波数「ｆ_i」を計算用モデル関数「Ｍ_j（ｆ）」に代入することで得られる関数値「Ｍ_j（ｆ_i）」の合算値で割った値として表される。これは、式（１）から求められる適合度に対して平滑化処理を行ったことに相当する。 Specifically, the jth model function for calculation is “M _j (f)”, and the fitness “S _j ” is calculated according to the following equation (3).

For the fitness “S _j ” obtained from the equation (3), the fitness obtained from the equation (1) is substituted for each fitness determination frequency “f _i ” into the calculation model function “M _j (f)”. The function value “M _j (f _i )” obtained by doing this is expressed as a value divided by the sum. This is equivalent to performing the smoothing process on the fitness obtained from the equation (1).

For example, when the correlation value model function “M (f)” is defined as “M (f) = sinc (f−fs)”, the fitness “S _j ” is calculated according to the following equation (4). .

  FIG. 7 is a diagram illustrating an example of an experimental result when a simulation experiment for obtaining the adaptive frequency is performed. Here, the true value of the frequency shift amount “Δf” (the frequency shift amount from the correlation value model function of each calculation model function) is 2.5 [Hz] (Δf = 2.5 [Hz]), and the formula When the matching frequency is calculated using the matching degree calculated from (2) (hereinafter referred to as “no compensation calculation”), the matching frequency is calculated using the matching degree calculated from Equation (4). An experiment comparing the cases (hereinafter referred to as “compensation calculation”) was conducted.

  In FIG. 7, the horizontal axis indicates the frequency shift amount “Δf”, and the vertical axis indicates the correlation value and the fitness. Squares indicate the correlation values at the respective fitness determination frequencies. Further, the triangle indicates the fitness level when there is no compensation calculation, and the cross indicates the fitness level when there is a compensation calculation.

  From this experimental result, in the case of no compensation calculation, the degree of fitness is the maximum when Δf = 0 [Hz]. In this case, since the adaptive frequency is calculated as Δf = 0 [Hz] deviating from the true value, an accurate adaptive frequency cannot be obtained. On the other hand, in the case of compensation calculation, the fitness is the maximum at Δf = 2.5 [Hz]. In this case, since the matching frequency is calculated as Δf = 2.5 [Hz] which is a true value, an accurate matching frequency in which the calculation error of the matching degree is compensated is obtained.

6-5. Determination of acquisition frequency In the above-described embodiment, it has been described that the frequency with the highest degree of fitness is determined as the adaptive frequency and the adaptive frequency itself is determined as the acquisition frequency. However, the adaptive frequency itself is corrected or corrected. The acquisition frequency may be determined. For example, a history of matching frequencies obtained in the past is stored. Then, the current adaptive frequency is estimated based on the past frequency of the adaptive frequency, the average value of the estimated adaptive frequency and the adaptive frequency determined based on the fitness is calculated, and determined as the capture frequency.

6-6. Correlation Value Model Function In the above-described embodiment, a simple sinc function is described as an example of the correlation value model function. However, any function that models the frequency change of the correlation value using the sinc function may be used. The correlation value model function can be appropriately changed. For example, a function combining a sinc function and another function may be used.

  DESCRIPTION OF SYMBOLS 1 Portable telephone, 10 GPS receiving part, 11 RF receiving circuit part, 20 Baseband processing circuit part, 21 Satellite capture part, 23 CPU, 25 ROM, 27 RAM, 30 Host CPU, 40 Operation part, 50 Display part, 60 Mobile phone antenna, 70 Wireless communication circuit for mobile phone, 80 Flash ROM, 90 RAM

Claims (5)

Using a spreading code replica of a CDMA (Code Division Multiple Access) signal, performing a correlation operation on the received signal that has received the CDMA signal;
Shifting a model function obtained by modeling the ideal curve of the correlation calculation result using a sinc function in the frequency direction, and determining an adaptive frequency that matches the correlation calculation result;
Determining an acquisition frequency of the CDMA signal based on the adaptive frequency;
A method for determining an acquisition frequency including: Determining the adaptation frequency includes the value of the model function and the value of the correlation calculation result at each of a plurality of fitness determination frequencies determined using a given reference frequency and a given frequency selection pattern. And performing the fitness calculation process for calculating the fitness between the model function and the correlation calculation result by shifting the model function in the frequency direction, and the frequency having the highest fitness is used as the adaptation frequency. Is to judge,
The acquisition frequency determination method according to claim 1. The frequency selection pattern is a frequency interval pattern that defines characteristics of the model function with reference to a center frequency of the model function.
The acquisition frequency determination method according to claim 2. The fitness calculation process includes a process of performing a compensation operation for suppressing a calculation error of the fitness according to a value change in the vicinity of the maximum value of the model function by the sinc function.
The acquisition frequency determination method according to claim 2 or 3. A correlation calculation unit that performs a correlation calculation of the received signal that has received the CDMA signal using a spreading code replica of the CDMA signal;
An adaptive frequency determination unit that shifts a model function obtained by modeling the ideal curve of the correlation calculation result using a sinc function in the frequency direction, and determines an appropriate frequency that matches the correlation calculation result;
An acquisition frequency determination unit that determines an acquisition frequency of the CDMA signal based on the adaptive frequency;
An acquisition unit for acquiring the CDMA signal using the determined acquisition frequency;
A receiving device.

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